| 1. |
- Acharya, S, et al.
(författare)
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ALICE Collaboration
- 2019
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Ingår i: XXVIIth International Conference on Ultrarelativistic Nucleus–Nucleus Collisions (Quark Matter 2018). - 0375-9474. ; 982, s. 975-984
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Konferensbidrag (refereegranskat)
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| 2. |
- Acharya, S, et al.
(författare)
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Analysis of the apparent nuclear modification in peripheral Pb–Pb collisions at 5.02 TeV
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 793, s. 420-432
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Tidskriftsartikel (refereegranskat)abstract
- Charged-particle spectra at midrapidity are measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair s NN =5.02 TeV and presented in centrality classes ranging from most central (0–5%) to most peripheral (95–100%) collisions. Possible medium effects are quantified using the nuclear modification factor (R AA ) by comparing the measured spectra with those from proton–proton collisions, scaled by the number of independent nucleon–nucleon collisions obtained from a Glauber model. At large transverse momenta (8
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| 3. |
- Acharya, S, et al.
(författare)
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Anisotropic flow in Xe–Xe collisions at sNN=5.44 TeV
- 2018
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 784, s. 82-95
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Tidskriftsartikel (refereegranskat)abstract
- The first measurements of anisotropic flow coefficients vn for mid-rapidity charged particles in Xe–Xe collisions at sNN=5.44 TeV are presented. Comparing these measurements to those from Pb–Pb collisions at sNN=5.02 TeV, v2 is found to be suppressed for mid-central collisions at the same centrality, and enhanced for central collisions. The values of v3 are generally larger in Xe–Xe than in Pb–Pb at a given centrality. These observations are consistent with expectations from hydrodynamic predictions. When both v2 and v3 are divided by their corresponding eccentricities for a variety of initial state models, they generally scale with transverse density when comparing Xe–Xe and Pb–Pb, with some deviations observed in central Xe–Xe and Pb–Pb collisions. These results assist in placing strong constraints on both the initial state geometry and medium response for relativistic heavy-ion collisions. © 2018 European Organization for Nuclear Research
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| 4. |
- Acharya, S, et al.
(författare)
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Anisotropic flow of identified hadrons in Xe-Xe collisions at √sNN = 5.44 TeV
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021:10
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of elliptic (v2) and triangular (v3) flow coefficients of π±, K±, p+p ¯ , KS0, and Λ+Λ ¯ obtained with the scalar product method in Xe-Xe collisions at sNN = 5.44 TeV are presented. The results are obtained in the rapidity range |y| < 0.5 and reported as a function of transverse momentum, pT, for several collision centrality classes. The flow coefficients exhibit a particle mass dependence for pT< 3 GeV/c, while a grouping according to particle type (i.e., meson and baryon) is found at intermediate transverse momenta (3 < pT< 8 GeV/c). The magnitude of the baryon v2 is larger than that of mesons up to pT = 6 GeV/c. The centrality dependence of the shape evolution of the pT-differential v2 is studied for the various hadron species. The v2 coefficients of π±, K±, and p+p ¯ are reproduced by MUSIC hydrodynamic calculations coupled to a hadronic cascade model (UrQMD) for pT< 1 GeV/c. A comparison with vn measurements in the corresponding centrality intervals in Pb-Pb collisions at sNN = 5.02 TeV yields an enhanced v2 in central collisions and diminished value in semicentral collisions. [Figure not available: see fulltext.] © 2021, The Author(s).
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| 5. |
- Acharya, S, et al.
(författare)
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Anisotropic flow of identified particles in Pb-Pb collisions at √sNN=5.02 TeV
- 2018
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:9
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Tidskriftsartikel (refereegranskat)abstract
- The elliptic (v2), triangular (v3), and quadrangular (v4) flow coefficients of π±, K±, p+p¯,Λ+Λ¯,KS0, and the ϕ-meson are measured in Pb-Pb collisions at sNN=5.02 TeV. Results obtained with the scalar product method are reported for the rapidity range |y| < 0.5 as a function of transverse momentum, pT, at different collision centrality intervals between 0–70%, including ultra-central (0–1%) collisions for π±, K±, and p + p ¯. For pT< 3 GeV/c, the flow coefficients exhibit a particle mass dependence. At intermediate transverse momenta (3 < pT < 8–10 GeV/c), particles show an approximate grouping according to their type (i.e., mesons and baryons). The ϕ-meson v2, which tests both particle mass dependence and type scaling, follows p + p ¯ v2 at low pT and π±v2 at intermediate pT. The evolution of the shape of vn(pT) as a function of centrality and harmonic number n is studied for the various particle species. Flow coefficients of π±, K±, and p + p ¯ for pT < 3 GeV/c are compared to iEBE-VISHNU and MUSIC hydrodynamical calculations coupled to a hadronic cascade model (UrQMD). The iEBE-VISHNU calculations describe the results fairly well for pT < 2.5 GeV/c, while MUSIC calculations reproduce the measurements for pT < 1 GeV/c. A comparison to vn coefficients measured in Pb-Pb collisions at sNN=2.76 TeV is also provided.[Figure not available: see fulltext.]. © 2018, The Author(s).
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| 6. |
- Acharya, S, et al.
(författare)
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(Anti-)deuteron production in pp collisions at √s=13TeV
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:9
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Tidskriftsartikel (refereegranskat)abstract
- The study of (anti-)deuteron production in pp collisions has proven to be a powerful tool to investigate the formation mechanism of loosely bound states in high-energy hadronic collisions. In this paper the production of (anti-)deuterons is studied as a function of the charged particle multiplicity in inelastic pp collisions at s=13 TeV using the ALICE experiment. Thanks to the large number of accumulated minimum bias events, it has been possible to measure (anti-)deuteron production in pp collisions up to the same charged particle multiplicity (d Nch/ d η∼ 26) as measured in p–Pb collisions at similar centre-of-mass energies. Within the uncertainties, the deuteron yield in pp collisions resembles the one in p–Pb interactions, suggesting a common formation mechanism behind the production of light nuclei in hadronic interactions. In this context the measurements are compared with the expectations of coalescence and statistical hadronisation models (SHM). © 2020, The Author(s).
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| 7. |
- Acharya, S, et al.
(författare)
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Azimuthal Anisotropy of Heavy-Flavor Decay Electrons in p -Pb Collisions at sNN =5.02 TeV
- 2019
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Ingår i: Physical Review Letters. - 1079-7114. ; 122:7
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Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between heavy-flavor decay electrons and charged particles at midrapidity (|η|<0.8) are measured in p-Pb collisions at √sNN=5.02 TeV. The analysis is carried out for the 0%–20% (high) and 60%–100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavor hadrons. A Fourier decomposition of the modulation results in a positive second-order coefficient (v2) for heavy-flavor decay electrons in the transverse momentum interval 1.5
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| 8. |
- Acharya, S, et al.
(författare)
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Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at √sNN=5.02TeV
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:10
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at s=5.02TeV and p–Pb collisions at sNN=5.02TeV with the ALICE detector at the LHC is reported. The D , D +, and D ∗ + mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 30.3GeV/c and pseudorapidity | η| < 0.8. The properties of the correlation peaks appearing in the near- and away-side regions (for Δ φ≈ 0 and Δ φ≈ π, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators. © 2020, The Author(s).
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| 9. |
- Acharya, S, et al.
(författare)
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Calibration of the photon spectrometer PHOS of the ALICE experiment
- 2019
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 14:May 2019
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Tidskriftsartikel (refereegranskat)abstract
- The procedure for the energy calibration of the high granularity electromagnetic calorimeter PHOS of the ALICE experiment is presented. The methods used to perform the relative gain calibration, to evaluate the geometrical alignment and the corresponding correction of the absolute energy scale, to obtain the nonlinearity correction coefficients and finally, to calculate the time-dependent calibration corrections, are discussed and illustrated by the PHOS performance in proton-proton (pp) collisions at s=13 TeV. After applying all corrections, the achieved mass resolutions for π0 and η mesons for pT > 1.7 GeV/c are σm π0 = 4.56 ± 0.03 MeV/c2 and σm η = 15.3 ± 1.0 MeV/c2, respectively.
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| 10. |
- Acharya, S, et al.
(författare)
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Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe–Xe collisions at sNN=5.44TeV
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 790, s. 35-48
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, dNch/dη and total charged-particle multiplicity, Nch tot, in Xe–Xe collisions at a centre-of-mass energy per nucleon–nucleon pair of sNN=5.44TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of −3.5<η<5. The values of dNch/dη at mid-rapidity and Nch tot for central collisions, normalised to the number of nucleons participating in the collision (Npart) as a function of sNN follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of Npart, and up to the 5% most central collisions the trends are the same as the ones observed in Pb–Pb at a similar energy. For more central collisions, the Xe–Xe scaled multiplicities exceed those in Pb–Pb for a similar Npart. The results are compared to phenomenological models and theoretical calculations based on different mechanisms for particle production in nuclear collisions. All considered models describe the data reasonably well within 15%. © 2018
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| 11. |
- Acharya, S, et al.
(författare)
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Centrality dependence of J/ψ and ψ(2S) production and nuclear modification in p-Pb collisions at √sNN = 8.16 TeV
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021
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Tidskriftsartikel (refereegranskat)abstract
- The inclusive production of the J/ψ and ψ(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair sNN = 8.16 TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals −4.46 < ycms< −2.96 (Pb-going direction) and 2.03 < ycms< 3.53 (p-going direction), down to zero transverse momentum (pT). The J/ψ and ψ(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The pT-differential J/ψ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average 〈pT〉 and 〈pT2〉 values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/ψ increases from below unity in peripheral collisions to above unity in central collisions, while for the ψ(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at sNN = 5.02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects. [Figure not available: see fulltext.] © 2021, The Author(s).
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| 12. |
- Acharya, S, et al.
(författare)
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Charged jet cross section and fragmentation in proton-proton collisions at s =7 TeV
- 2019
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Ingår i: Physical Review D. - 2470-0010. ; 99:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the differential charged jet cross section and jet fragmentation distributions measured with the ALICE detector in proton-proton collisions at a center-of-mass energy s=7 TeV. Jets with pseudorapidity |η|40 GeV/c, the pythia calculations also agree with the measured charged jet cross section. pythia6 simulations describe the fragmentation distributions to 15%. Larger discrepancies are observed for pythia8. © 2019 CERN, for the ALICE Collaboration. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
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| 13. |
- Acharya, S, et al.
(författare)
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Charged-particle multiplicity fluctuations in Pb–Pb collisions at √sNN = 2.76 TeV
- 2021
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6052. ; 81:11
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb–Pb collisions at sNN = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range | η| < 0.8 and transverse momentum 0.2 < pT< 2.0 GeV/c. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The η and pT dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb–Pb collisions. © 2021, The Author(s).
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| 14. |
- Acharya, S, et al.
(författare)
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Charged-particle production as a function of multiplicity and transverse spherocity in pp collisions at √s=5.02 and 13 TeV
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the inclusive charged-particle transverse momentum (pT) spectra as a function of charged-particle multiplicity density at mid-pseudorapidity, d Nch/ d η, in pp collisions at s=5.02 and 13 TeV covering the kinematic range | η| < 0.8 and 0.15 < pT< 20 GeV/c. The results are presented for events with at least one charged particle in | η| < 1 (INEL>0). The pT spectra are reported for two multiplicity estimators covering different pseudorapidity regions. The pT spectra normalized to that for INEL>0 show little energy dependence. Moreover, the high-pT yields of charged particles increase faster than the charged-particle multiplicity density. The average pT as a function of multiplicity and transverse spherocity is reported for pp collisions at s=13 TeV. For low- (high-) spherocity events, corresponding to jet-like (isotropic) events, the average pT is higher (smaller) than that measured in INEL>0 pp collisions. Within uncertainties, the functional form of ⟨ pT⟩ (Nch) is not affected by the spherocity selection. While EPOS LHC gives a good description of many features of data, PYTHIA overestimates the average pT in jet-like events. © 2019, CERN for the benefit of the ALICE collaboration.
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| 15. |
- Acharya, S, et al.
(författare)
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Charged-particle pseudorapidity density at mid-rapidity in p–Pb collisions at √sNN = 8.16 TeV
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:4
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Tidskriftsartikel (refereegranskat)abstract
- The pseudorapidity density of charged particles, d N ch / d η, in p–Pb collisions has been measured at a centre-of-mass energy per nucleon–nucleon pair of sNN = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, | η| < 1.8. The d N ch / d η value is 19.1 ± 0.7 at | η| < 0.5. This quantity divided by ⟨ N part ⟩ / 2 is 4.73 ± 0.20 , where ⟨ N part ⟩ is the average number of participating nucleons, is 9.5% higher than the corresponding value for p–Pb collisions at sNN = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agree within uncertainties with data in the Pb-going side, while HIJING overestimates, showing a symmetric behaviour, and EPOS underestimates the p-going side of the d N ch / d η distribution. Saturation-based models reproduce the distributions well for η> - 1.3. The d N ch / d η is also measured for different centrality estimators, based both on the charged-particle multiplicity and on the energy deposited in the Zero-Degree Calorimeters. A study of the implications of the large multiplicity fluctuations due to the small number of participants for systems like p–Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity. © 2019, CERN for the benefit of the ALICE collaboration.
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| 16. |
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| 17. |
- Acharya, S, et al.
(författare)
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Coherent J / ψ and ψ ′ photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at √sNN=5.02 TeV
- 2021
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:8
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Tidskriftsartikel (refereegranskat)abstract
- The coherent photoproduction of J/ψ and ψ′ mesons was measured in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN−−−√ = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J/ψ is reconstructed using the dilepton (l+l−) and proton–antiproton decay channels, while for the ψ′ the dilepton and the l+l−π+π− decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 μb−1. The results are compared with theoretical models for coherent J/ψ and ψ′ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6×10−4, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J/ψ cross section including ALICE measurements at forward rapidity. The ratio of ψ′ to J/ψ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.
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| 18. |
- Acharya, S, et al.
(författare)
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Coherent J/ψ photoproduction at forward rapidity in ultra-peripheral Pb–Pb collisions at sNN=5.02 TeV
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 798
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE collaboration performed the first rapidity-differential measurement of coherent J/ψ photoproduction in ultra-peripheral Pb–Pb collisions at a center-of-mass energy sNN=5.02 TeV. The J/ψ is detected via its dimuon decay in the forward rapidity region (−4.0
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| 19. |
- Acharya, S, et al.
(författare)
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Coherent photoproduction of ρ 0 vector mesons in ultra-peripheral Pb-Pb collisions at √sNN = 5.02 TeV
- 2020
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:6
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Tidskriftsartikel (refereegranskat)abstract
- Cross sections for the coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at sNN = 5.02 TeV are reported. The measurements, which rely on the π+π− decay channel, are presented in three regions of rapidity covering the range |y| < 0.8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/c2 and a width of about 140 MeV/c2 is reported and compared with similar observations from other experiments. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 20. |
- Acharya, S, et al.
(författare)
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Constraining the Chiral Magnetic Effect with charge-dependent azimuthal correlations in Pb-Pb collisions at √sNN = 2.76 and 5.02 TeV
- 2020
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:9
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Tidskriftsartikel (refereegranskat)abstract
- Systematic studies of charge-dependent two- and three-particle correlations in Pb-Pb collisions at sNN = 2.76 and 5.02 TeV used to probe the Chiral Magnetic Effect (CME) are presented. These measurements are performed for charged particles in the pseudorapidity (η) and transverse momentum (pT) ranges |η| < 0.8 and 0.2 < pT< 5 GeV/c. A significant charge-dependent signal that becomes more pronounced for peripheral collisions is reported for the CME-sensitive correlators γ1, 1 = 〈cos(φα + φβ − 2Ψ2)〉 and γ1, − 3 = 〈cos(φα − 3φβ + 2Ψ2)〉. The results are used to estimate the contribution of background effects, associated with local charge conservation coupled to anisotropic flow modulations, to measurements of the CME. A blast-wave parametrisation that incorporates local charge conservation tuned to reproduce the centrality dependent background effects is not able to fully describe the measured γ1,1. Finally, the charge and centrality dependence of mixed-harmonics three-particle correlations, of the form γ1, 2 = 〈cos(φα + 2φβ − 3Ψ3)〉, which are insensitive to the CME signal, verify again that background contributions dominate the measurement of γ1,1.
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| 21. |
- Acharya, S, et al.
(författare)
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Dielectron and heavy-quark production in inelastic and high-multiplicity proton–proton collisions at s=13TeV
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 788, s. 505-518
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of dielectron production is presented as a function of invariant mass and transverse momentum (pT) at midrapidity (|ye|<0.8) in proton–proton (pp) collisions at a centre-of-mass energy of s=13 TeV. The contributions from light-hadron decays are calculated from their measured cross sections in pp collisions at s=7 TeV or 13 TeV. The remaining continuum stems from correlated semileptonic decays of heavy-flavour hadrons. Fitting the data with templates from two different MC event generators, PYTHIA and POWHEG, the charm and beauty cross sections at midrapidity are extracted for the first time at this collision energy: dσcc¯/dy|y=0=974±138(stat.)±140(syst.)±214(BR)μb and dσbb¯/dy|y=0=79±14(stat.)±11(syst.)±5(BR)μb using PYTHIA simulations and dσcc¯/dy|y=0=1417±184(stat.)±204(syst.)±312(BR)μb and dσbb¯/dy|y=0=48±14(stat.)±7(syst.)±3(BR)μb for POWHEG. These values, whose uncertainties are fully correlated between the two generators, are consistent with extrapolations from lower energies. The different results obtained with POWHEG and PYTHIA imply different kinematic correlations of the heavy-quark pairs in these two generators. Furthermore, comparisons of dielectron spectra in inelastic events and in events collected with a trigger on high charged-particle multiplicities are presented in various pT intervals. The differences are consistent with the already measured scaling of light-hadron and open-charm production at high charged-particle multiplicity as a function of pT. Upper limits for the contribution of virtual direct photons are extracted at 90% confidence level and found to be in agreement with pQCD calculations. © 2018 The Author
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| 22. |
- Acharya, S, et al.
(författare)
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Dielectron production in proton-proton and proton-lead collisions at sNN =5.02 TeV
- 2020
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Ingår i: Physical Review C. - 2469-9985. ; 102:5
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Tidskriftsartikel (refereegranskat)abstract
- The first measurements of dielectron production at midrapidity (|ηe|<0.8) in proton–proton and proton–lead collisions at √sNN=5.02TeV at the LHC are presented. The dielectron cross section is measured with the ALICE detector as a function of the invariant mass mee and the pair transverse momentum pT,ee in the ranges mee<3.5 GeV/c2 and pT,ee<8 GeV/c, in both collision systems. In proton–proton collisions, the charm and beauty cross sections are determined at midrapidity from a fit to the data with two different event generators. This complements the existing dielectron measurements performed at √s=7 and 13 TeV. The slope of the √s dependence of the three measurements is described by FONLL calculations. The dielectron cross section measured in proton–lead collisions is in agreement, within the current precision, with the expected dielectron production without any nuclear matter effects for e+e− pairs from open heavy-flavor hadron decays. For the first time at LHC energies, the dielectron production in proton–lead and proton–proton collisions are directly compared at the same √sNN via the dielectron nuclear modification factor RpPb. The measurements are compared to model calculations including cold nuclear matter effects, or additional sources of dielectrons from thermal radiation.
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| 23. |
- Acharya, S, et al.
(författare)
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Dielectron production in proton-proton collisions at √s=7 TeV
- 2018
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:9
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Tidskriftsartikel (refereegranskat)abstract
- The first measurement of e+e− pair production at mid-rapidity (|ηe| < 0.8) in pp collisions at s=7 TeV with ALICE at the LHC is presented. The dielectron production is studied as a function of the invariant mass (mee < 3.3 GeV/c2), the pair transverse momentum (pT,ee < 8 GeV/c), and the pair transverse impact parameter (DCAee), i.e., the average distance of closest approach of the reconstructed electron and positron tracks to the collision vertex, normalised to its resolution. The results are compared with the expectations from a cocktail of known hadronic sources and are well described when PYTHIA is used to generate the heavy-flavour contributions. In the low-mass region (0.14 < mee < 1.1 GeV/c2), prompt and non-prompt e+e− sources can be separated via the DCAee. In the intermediate-mass region (1.1 < mee < 2.7 GeV/c2), a double-differential fit to the data in mee and pT,ee and a fit of the DCAee distribution allow the total c c ¯ and b b ¯ cross sections to be extracted. Two different event generators, PYTHIA and POWHEG, can reproduce the shape of the two-dimensional mee and pT,ee spectra, as well as the shape of the DCAee distribution, reasonably well. However, differences in the c c ¯ and b b ¯ cross sections are observed when using the generators to extrapolate to full phase space. Finally, the ratio of inclusive to decay photons is studied via the measurement of virtual direct photons in the transverse-momentum range 1 < pT < 8 GeV/c. This is found to be unity within the statistical and systematic uncertainties and consistent with expectations from next-to-leading order perturbative quantum chromodynamic calculations.[Figure not available: see fulltext.]. © 2018, The Author(s).
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| 24. |
- Acharya, S, et al.
(författare)
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Direct photon elliptic flow in Pb–Pb collisions at sNN=2.76 TeV
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 789, s. 308-322
-
Tidskriftsartikel (refereegranskat)abstract
- The elliptic flow of inclusive and direct photons was measured at mid-rapidity in two centrality classes 0–20% and 20–40% in Pb–Pb collisions at sNN=2.76 TeV by ALICE. Photons were detected with the highly segmented electromagnetic calorimeter PHOS and via conversions in the detector material with the e+e− pairs reconstructed in the central tracking system. The results of the two methods were combined and the direct-photon elliptic flow was extracted in the transverse momentum range 0.9
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| 25. |
- Acharya, S, et al.
(författare)
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Elliptic and triangular flow of (anti)deuterons in Pb-Pb collisions at sNN =5.02 TeV
- 2020
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Ingår i: Physical Review C. - 2469-9985. ; 102:5
-
Tidskriftsartikel (refereegranskat)abstract
- The measurements of the (anti)deuteron elliptic flow (v2) and the first measurements of triangular flow (v3) in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision sNN = 5.02 TeV are presented. A mass ordering at low transverse momentum (pT) is observed when comparing these measurements with those of other identified hadrons, as expected from relativistic hydrodynamics. The measured (anti)deuteron v2 lies between the predictions from the simple coalescence and blast-wave models, which provide a good description of the data only for more peripheral and for more central collisions, respectively. The mass number scaling, which is violated for v2, is approximately valid for the (anti)deuterons v3. The measured v2 and v3 are also compared with the predictions from a coalescence approach with phase-space distributions of nucleons generated by iebe-vishnu with ampt initial conditions coupled with urqmd, and from a dynamical model based on relativistic hydrodynamics coupled to the hadronic afterburner smash. The model predictions are consistent with the data within the uncertainties in midcentral collisions, while a deviation is observed in the most central collisions. © 2020 CERN.
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| 26. |
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| 27. |
- Acharya, S, et al.
(författare)
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Energy dependence of exclusive J / ψ photoproduction off protons in ultra-peripheral p–Pb collisions at √sNN=5.02 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:5
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration has measured the energy dependence of exclusive photoproduction of J / ψ vector mesons off proton targets in ultra–peripheral p–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02 TeV. The e + e - and μ + μ - decay channels are used to measure the cross section as a function of the rapidity of the J / ψ in the range - 2.5 < y< 2.7 , corresponding to an energy in the γp centre-of-mass in the interval 40 < W γ p < 550 GeV. The measurements, which are consistent with a power law dependence of the exclusive J / ψ photoproduction cross section, are compared to previous results from HERA and the LHC and to several theoretical models. They are found to be compatible with previous measurements. © 2019, CERN for the benefit of the ALICE collaboration.
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| 28. |
- Acharya, S, et al.
(författare)
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Energy dependence of ϕ meson production at forward rapidity in pp collisions at the LHC
- 2021
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:8
-
Tidskriftsartikel (refereegranskat)abstract
- The production of ϕ mesons has been studied in pp collisions at LHC energies with the ALICE detector via the dimuon decay channel in the rapidity region 2.5 < y< 4. Measurements of the differential cross section d 2σ/ d yd pT are presented as a function of the transverse momentum (pT) at the center-of-mass energies s=5.02, 8 and 13 TeV and compared with the ALICE results at midrapidity. The differential cross sections at s=5.02 and 13 TeV are also studied in several rapidity intervals as a function of pT, and as a function of rapidity in three pT intervals. A hardening of the pT-differential cross section with the collision energy is observed, while, for a given energy, pT spectra soften with increasing rapidity and, conversely, rapidity distributions get slightly narrower at increasing pT. The new results, complementing the published measurements at s=2.76 and 7 TeV, allow one to establish the energy dependence of ϕ meson production and to compare the measured cross sections with phenomenological models. None of the considered models manages to describe the evolution of the cross section with pT and rapidity at all the energies. © 2021, The Author(s).
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| 29. |
- Acharya, S, et al.
(författare)
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Event-shape and multiplicity dependence of freeze-out radii in pp collisions at √s = 7 TeV
- 2019
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:9
-
Tidskriftsartikel (refereegranskat)abstract
- Two-particle correlations in high-energy collision experiments enable the extraction of particle source radii by using the Bose-Einstein enhancement of pion production at low relative momentum q ∝ 1/R. It was previously observed that in pp collisions at s = 7TeV the average pair transverse momentum kT range of such analyses is limited due to large background correlations which were attributed to mini-jet phenomena. To investigate this further, an event-shape dependent analysis of Bose-Einstein correlations for pion pairs is performed in this work. By categorizing the events by their transverse sphericity ST into spherical (ST > 0:7) and jet-like (ST < 0:3) events a method was developed that allows for the determination of source radii for much larger values of kT for the first time. Spherical events demonstrate little or no background correlations while jet-like events are dominated by them. This observation agrees with the hypothesis of a mini-jet origin of the non-femtoscopic background correlations and gives new insight into the physics interpretation of the kT dependence of the radii. The emission source size in spherical events shows a substantially diminished kT dependence, while jet-like events show indications of a negative trend with respect to kT in the highest multiplicity events. Regarding the emission source shape, the correlation functions for both event sphericity classes show good agreement with an exponential shape, rather than a Gaussian one. [Figure not available: see fulltext.]. © 2019, The Author(s).
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| 30. |
- Acharya, S, et al.
(författare)
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Event-Shape Engineering for the D-meson elliptic flow in mid-central Pb-Pb collisions at √sNN=5.02 TeV
- 2019
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:2
-
Tidskriftsartikel (refereegranskat)abstract
- The production yield of prompt D mesons and their elliptic flow coefficient v 2 were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10–30% and 30–50% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair sNN=5.02 TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the azimuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks in the Quark-Gluon Plasma and provide information on their participation in the collective expansion of the medium. D mesons were reconstructed via their hadronic decays at mid-rapidity, |η| < 0.8, in the transverse momentum interval 1 < p T < 24 GeV/c. The v 2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-meson azimuthal anisotropy and the collective expansion of the bulk matter, while the per-event D-meson yields do not show any significant modification within the current uncertainties. © 2019, The Author(s).
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| 31. |
- Acharya, S, et al.
(författare)
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Evidence of rescattering effect in Pb–Pb collisions at the LHC through production of K(892)0⁎ and ϕ(1020) mesons
- 2020
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 802
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of K(892)0⁎ and ϕ(1020) resonance production in Pb–Pb and pp collisions at sNN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (|y| < 0.5) via their hadronic decay channels and the transverse momentum (pT) distributions are obtained for various collision centrality classes up to pT = 20 GeV/c. The pT-integrated yield ratio K(892)0⁎/K in Pb–Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the ϕ(1020)/K ratio does not show any suppression. Furthermore, the measured K(892)0⁎/K ratio in central Pb–Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the ϕ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K(892)0⁎ decay products in the hadronic phase of the collisions. The K(892)0⁎/K yield ratios in Pb–Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4–7 fm/c for central collisions. The pT-differential ratios of K(892)0⁎/K, ϕ(1020)/K, K(892)0⁎/π, ϕ(1020)/π, p/K(892)0⁎ and p/ϕ(1020) are also presented for Pb–Pb and pp collisions at sNN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-pT phenomenon.
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| 32. |
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| 33. |
- Acharya, S, et al.
(författare)
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Experimental Evidence for an Attractive p-φ Interaction
- 2021
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Ingår i: Physical Review Letters. - 1079-7114. ; 127:17
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter presents the first experimental evidence of the attractive strong interaction between a proton and a φ meson. The result is obtained from two-particle correlations of combined p-φ p¯-φ pairs measured in high-multiplicity pp collisions at s=13 TeV by the ALICE Collaboration. The spin-averaged scattering length and effective range of the p-φ interaction are extracted from the fully corrected correlation function employing the Lednický-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the p-φ interaction. These data demonstrate that the interaction is dominated by elastic p-φ scattering. Furthermore, an analysis employing phenomenological Gaussian- and Yukawa-type potentials is conducted. Under the assumption of the latter, the N-φ coupling constant is found to be gN-φ=0.14±0.03(stat)±0.02(syst). This work provides valuable experimental input to accomplish a self-consistent description of the N-φ interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium. © 2021 CERN.
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| 34. |
- Acharya, S, et al.
(författare)
-
Exploration of jet substructure using iterative declustering in pp and Pb–Pb collisions at LHC energies
- 2020
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 802
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at s=7 TeV and central Pb–Pb collisions at sNN=2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the zg, and its dependence on the opening angle, in both pp and Pb–Pb collisions. We also present the measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb–Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as colour coherence. © 2020 The Author(s)
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| 35. |
- Acharya, S, et al.
(författare)
-
First measurement of the |t|-dependence of coherent J/ψ photonuclear production
- 2021
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 817
-
Tidskriftsartikel (refereegranskat)abstract
- The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV with the J/ψ produced in the central rapidity region |y|<0.8, which corresponds to the small Bjorken-x range (0.3−1.4)×10−3. The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x. © 2021 The Author(s)
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| 36. |
- Acharya, S, et al.
(författare)
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First measurements of N-subjettiness in central Pb-Pb collisions at √sNN = 2.76 TeV
- 2021
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021:9
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration reports the first fully-corrected measurements of the N-subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of s = 7 TeV and sNN = 2.76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, τ2/τ1, which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate of two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of R = 0.4 and charged jet transverse momentum of 40 ≤ pT,jet ≤ 60 GeV/c, which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the τ2/τ1 observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of τ2/τ1, together with the splitting aperture angle ∆R, are also performed in pp collisions at s = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at s = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for τ2/τ1 are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions. [Figure not available: see fulltext.] © 2021, The Author(s).
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| 37. |
- Acharya, S., et al.
(författare)
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First study of the two-body scattering involving charm hadrons
- 2022
-
Ingår i: Physical Review D. - 2470-0010. ; 106:5
-
Tidskriftsartikel (refereegranskat)abstract
- This article presents the first measurement of the interaction between charm hadrons and nucleons. The two-particle momentum correlations of pD- and p¯D+ pairs are measured by the ALICE Collaboration in high-multiplicity pp collisions at s=13 TeV. The data are compatible with the Coulomb-only interaction hypothesis within (1.1-1.5)σ. The level of agreement slightly improves if an attractive nucleon (N)D¯ strong interaction is considered, in contrast to most model predictions which suggest an overall repulsive interaction. This measurement allows for the first time an estimation of the 68% confidence level interval for the isospin I=0 inverse scattering length of the ND¯ state f0,I=0-1 [-0.4,0.9] fm-1, assuming negligible interaction for the isospin I=1 channel. © 2022 CERN.
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| 38. |
- Acharya, S, et al.
(författare)
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Global polarization of Λ Λ hyperons in Pb-Pb collisions at sNN = 2.76 and 5.02 TeV
- 2020
-
Ingår i: Physical Review C. - 2469-9985. ; 101:4
-
Tidskriftsartikel (refereegranskat)abstract
- The global polarization of the Λ and Λ hyperons is measured for Pb-Pb collisions at sNN=2.76 and 5.02 TeV recorded with the ALICE at the Large Hadron Collider (LHC). The results are reported differentially as a function of collision centrality and hyperon's transverse momentum (pT) for the range of centrality 5-50%, 0.5
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| 39. |
- Acharya, S, et al.
(författare)
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Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at √sNN = 5.02 TeV
- 2020
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:5
-
Tidskriftsartikel (refereegranskat)abstract
- Anisotropic flow coefficients, vn, non-linear flow mode coefficients, χn,mk, and correlations among different symmetry planes, ρn,mk are measured in Pb-Pb collisions at sNN = 5.02 TeV. Results obtained with multi-particle correlations are reported for the transverse momentum interval 0.2 < pT< 5.0 GeV/c within the pseudorapidity interval 0.4 < |η| < 0.8 as a function of collision centrality. The vn coefficients and χn,mk and ρn,mk are presented up to the ninth and seventh harmonic order, respectively. Calculations suggest that the correlations measured in different symmetry planes and the non-linear flow mode coefficients are dependent on the shear and bulk viscosity to entropy ratios of the medium created in heavy-ion collisions. The comparison between these measurements and those at lower energies and calculations from hydrodynamic models places strong constraints on the initial conditions and transport properties of the system.
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| 40. |
- Acharya, S, et al.
(författare)
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HΛ3 and H‾Λ‾3 lifetime measurement in Pb–Pb collisions at sNN=5.02 TeV via two-body decay
- 2019
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 797
-
Tidskriftsartikel (refereegranskat)abstract
- An improved value for the lifetime of the (anti-)hypertriton has been obtained using the data sample of Pb–Pb collisions at sNN=5.02 TeV collected by the ALICE experiment at the LHC. The (anti-)hypertriton has been reconstructed via its charged two-body mesonic decay channel and the lifetime has been determined from an exponential fit to the dN/d(ct) spectrum. The measured value, τ=242−38 +34 (stat.) ± 17 (syst.) ps, is compatible with representative theoretical predictions, thus contributing to the solution of the longstanding hypertriton lifetime puzzle. © 2019 The Author
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| 41. |
- Acharya, S, et al.
(författare)
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Inclusive heavy-flavour production at central and forward rapidity in Xe–Xe collisions at sNN=5.44 TeV
- 2021
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 819
-
Tidskriftsartikel (refereegranskat)abstract
- The first measurements of the production of muons and electrons from heavy-flavour hadron decays in Xe–Xe collisions at sNN=5.44 TeV, using the ALICE detector at the LHC, are reported. The measurement of the nuclear modification factor RAA is performed as a function of transverse momentum pT in several centrality classes at forward rapidity (2.5
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| 42. |
- Acharya, S, et al.
(författare)
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Inclusive J/ψ production at forward and backward rapidity in p-Pb collisions at √sNN=8.16 TeV
- 2018
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2018:7
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/ψ production is studied in p-Pb interactions at a centre-of-mass energy per nucleon-nucleon collision sNN=8.16 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed, via its decay to a muon pair, in the centre-of-mass rapidity intervals 2.03 < ycms < 3.53 and −4.46 < ycms < −2.96, where positive and negative ycms refer to the p-going and Pb-going direction, respectively. The transverse momentum coverage is pT < 20 GeV/c. In this paper, ycms- and pT-differential cross sections for inclusive J/ψ production are presented, and the corresponding nuclear modification factors RpPb are shown. Forward results show a suppression of the J/ψ yield with respect to pp collisions, concentrated in the region pT ≲ 5 GeV/c. At backward rapidity no significant suppression is observed. The results are compared to previous measurements by ALICE in p-Pb collisions at sNN=5.02 TeV and to theoretical calculations. Finally, the ratios RFB between forward- and backward-ycmsRpPb values are shown and discussed.[Figure not available: see fulltext.]. © 2018, The Author(s).
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| 43. |
- Acharya, S, et al.
(författare)
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Inclusive J/ψ production at mid-rapidity in pp collisions at √s = 5.02 TeV
- 2019
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2019:10
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/ψ production is studied in minimum-bias proton-proton collisions at a centre-of-mass energy of s = 5.02 TeV by ALICE at the CERN LHC. The measurement is performed at mid-rapidity (|y| < 0.9) in the dielectron decay channel down to zero transverse momentum pT, using a data sample corresponding to an integrated luminosity of Lint = 19.4 ± 0.4 nb−1. The measured pT-integrated inclusive J/ψ production cross sec- tion is dσ/dy = 5.64 ± 0.22(stat.) ± 0.33(syst.) ± 0.12(lumi.) μb. The pT-differential cross section d2σ/dpTdy is measured in the pT range 0–10 GeV/c and compared with state-of- the-art QCD calculations. The J/ψ 〈pT〉 and 〈pT2〉 are extracted and compared with results obtained at other collision energies. [Figure not available: see fulltext.]. © 2019, The Author(s).
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| 44. |
- Acharya, S, et al.
(författare)
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Inclusive J / ψ production at midrapidity in pp collisions at √s=13 TeV
- 2021
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 81:12
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the inclusive J / ψ production cross section measured at the CERN Large Hadron Collider in proton–proton collisions at a center-of-mass energy s=13 TeV. The J / ψ mesons are reconstructed in the e +e - decay channel and the measurements are performed at midrapidity (| y| < 0.9) in the transverse-momentum interval 0 < pT< 40 GeV/c, using a minimum-bias data sample corresponding to an integrated luminosity Lint=32.2nb-1 and an Electromagnetic Calorimeter triggered data sample with Lint=8.3pb-1. The pT-integrated J / ψ production cross section at midrapidity, computed using the minimum-bias data sample, is dσ/dy|y=0=8.97±0.24(stat)±0.48(syst)±0.15(lumi)μb. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and pT-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models. © 2021, The Author(s).
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| 45. |
- Acharya, S, et al.
(författare)
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Inclusive J/ψ production in Xe–Xe collisions at sNN=5.44 TeV
- 2018
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 785, s. 419-428
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/ψ production is studied in Xe–Xe interactions at a centre-of-mass energy per nucleon pair of sNN=5.44 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed via its decay into a muon pair, in the centre-of-mass rapidity interval 2.5
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| 46. |
- Acharya, S, et al.
(författare)
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Investigation of the p–Σ0 interaction via femtoscopy in pp collisions
- 2020
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 805
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter presents the first direct investigation of the p–Σ0 interaction, using the femtoscopy technique in high-multiplicity pp collisions at s=13 TeV measured by the ALICE detector. The Σ0 is reconstructed via the decay channel to Λγ, and the subsequent decay of Λ to pπ−. The photon is detected via the conversion in material to e+e− pairs exploiting the capability of the ALICE detector to measure electrons at low transverse momenta. The measured p–Σ0 correlation indicates a shallow strong interaction. The comparison of the data to several theoretical predictions obtained employing the Correlation Analysis Tool using the Schrödinger Equation (CATS) and the Lednický–Lyuboshits approach shows that the current experimental precision does not yet allow to discriminate between different models, as it is the case for the available scattering and hypernuclei data. Nevertheless, the p–Σ0 correlation function is found to be sensitive to the strong interaction, and driven by the interplay of the different spin and isospin channels. This pioneering study demonstrates the feasibility of a femtoscopic measurement in the p–Σ0 channel and with the expected larger data samples in LHC Run 3 and Run 4, the p–Σ0 interaction will be constrained with high precision. © 2020 European Organization for Nuclear Research
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| 47. |
- Acharya, S, et al.
(författare)
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J/ψ elliptic and triangular flow in Pb-Pb collisions at √sNN = 5.02 TeV
- 2020
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:10
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusive J/ψ elliptic (v2) and triangular (v3) flow coefficients measured at forward rapidity (2.5 < y < 4) and the v2 measured at midrapidity (|y| < 0.9) in Pb-Pb collisions at sNN = 5.02 TeV using the ALICE detector at the LHC are reported. The entire Pb-Pb data sample collected during Run 2 is employed, amounting to an integrated luminosity of 750 μb−1 at forward rapidity and 93 μb−1 at midrapidity. The results are obtained using the scalar product method and are reported as a function of transverse momentum pT and collision centrality. At midrapidity, the J/ψ v2 is in agreement with the forward rapidity measurement. The centrality averaged results indicate a positive J/ψ v3 with a significance of more than 5σ at forward rapidity in the pT range 2 < pT< 5 GeV/c. The forward rapidity v2, v3, and v3/v2 results at low and intermediate pT (pT ≲ 8 GeV/c) exhibit a mass hierarchy when compared to pions and D mesons, while converging into a species-independent curve at higher pT. At low and intermediate pT, the results could be interpreted in terms of a later thermalization of charm quarks compared to light quarks, while at high pT, path-length dependent effects seem to dominate. The J/ψ v2 measurements are further compared to a microscopic transport model calculation. Using a simplified extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson vn measurements can be described based on those for charged pions and J/ψ flow. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 48. |
- Acharya, S, et al.
(författare)
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J/ψ production as a function of charged-particle multiplicity in p-Pb collisions at √sNN = 8.16 TeV
- 2020
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:9
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive J/ψ yields and average transverse momenta in p-Pb collisions at a center-of-mass energy per nucleon pair sNN = 8.16 TeV are measured as a function of the charged-particle pseudorapidity density with ALICE. The J/ψ mesons are reconstructed at forward (2.03 < ycms< 3.53) and backward (−4.46 < ycms< −2.96) center-of-mass rapidity in their dimuon decay channel while the charged-particle pseudorapidity density is measured around midrapidity. The J/ψ yields at forward and backward rapidity normalized to their respective average values increase with the normalized charged-particle pseudorapidity density, the former showing a weaker increase than the latter. The normalized average transverse momenta at forward and backward rapidity manifest a steady increase from low to high charged-particle pseudorapidity density with a saturation beyond the average value. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 49. |
- Acharya, S, et al.
(författare)
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Jet-associated deuteron production in pp collisions at s=13 TeV
- 2021
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 819
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Tidskriftsartikel (refereegranskat)abstract
- Deuteron production in high-energy collisions is sensitive to the space–time evolution of the collision system, and is typically described by a coalescence mechanism. For the first time, we present results on jet-associated deuteron production in pp collisions at s=13 TeV, providing an opportunity to test the established picture for deuteron production in events with a hard scattering. Using a trigger particle with high transverse-momentum (pT>5 GeV/c) as a proxy for the presence of a jet at midrapidity, we observe a measurable population of deuterons being produced around the jet proxy. The associated deuteron yield measured in a narrow angular range around the trigger particle differs by 2.4–4.8 standard deviations from the uncorrelated background. The data are described by PYTHIA model calculations featuring baryon coalescence. © 2021 The Author
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- Acharya, S, et al.
(författare)
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Jet fragmentation transverse momentum distributions in pp and p-Pb collisions at √s , √sNN = 5.02 TeV
- 2021
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2021:9
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Tidskriftsartikel (refereegranskat)abstract
- Jet fragmentation transverse momentum (jT) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at sNN = 5.02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm with resolution parameter R = 0.4 in the pseudorapidity range |η| < 0.25. The jT values are calculated for charged particles inside a fixed cone with a radius R = 0.4 around the reconstructed jet axis. The measured jT distributions are compared with a variety of parton-shower models. Herwig and Pythia 8 based models describe the data well for the higher jT region, while they underestimate the lower jT region. The jT distributions are further characterised by fitting them with a function composed of an inverse gamma function for higher jT values (called the “wide component”), related to the perturbative component of the fragmentation process, and with a Gaussian for lower jT values (called the “narrow component”), predominantly connected to the hadronisation process. The width of the Gaussian has only a weak dependence on jet transverse momentum, while that of the inverse gamma function increases with increasing jet transverse momentum. For the narrow component, the measured trends are successfully described by all models except for Herwig. For the wide component, Herwig and PYTHIA 8 based models slightly underestimate the data for the higher jet transverse momentum region. These measurements set constraints on models of jet fragmentation and hadronisation. [Figure not available: see fulltext.] © 2021, The Author(s).
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