| 1. |
- 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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| 2. |
- 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
-
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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Acharya, S, et al.
(författare)
-
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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| 6. |
- Acharya, S, et al.
(författare)
-
Elliptic and triangular flow of (anti)deuterons in Pb-Pb collisions at sNN =5.02 TeV
- 2020
-
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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| 7. |
- Acharya, S, et al.
(författare)
-
Evidence of rescattering effect in Pb–Pb collisions at the LHC through production of K(892)0⁎ and ϕ(1020) mesons
- 2020
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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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| 8. |
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| 9. |
- Acharya, S, et al.
(författare)
-
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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| 10. |
- Acharya, S, et al.
(författare)
-
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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| 11. |
- Acharya, S, et al.
(författare)
-
J/ψ elliptic and triangular flow in Pb-Pb collisions at √sNN = 5.02 TeV
- 2020
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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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| 12. |
- Acharya, S, et al.
(författare)
-
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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| 13. |
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| 14. |
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| 15. |
- Acharya, S, et al.
(författare)
-
Measurement of nuclear effects on ψ(2S) production in p-Pb collisions at √sNN = 8.16 TeV
- 2020
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:7
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive ψ(2S) production is measured in p-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair sNN = 8.16 TeV, using the ALICE detector at the CERN LHC. The production of ψ(2S) is studied at forward (2.03 < ycms< 3.53) and backward (−4.46 < ycms< −2.96) centre-of-mass rapidity and for transverse momentum pT< 12 GeV/c via the decay to muon pairs. In this paper, we report the integrated as well as the ycms- and pT-differential inclusive production cross sections. Nuclear effects on ψ(2S) production are studied via the determination of the nuclear modification factor that shows a strong suppression at both forward and backward centre-of-mass rapidities. Comparisons with corresponding results for inclusive J/ψ show a similar suppression for the two states at forward rapidity (p-going direction), but a stronger suppression for ψ(2S) at backward rapidity (Pb-going direction). As a function of pT, no clear dependence of the nuclear modification factor is found. The relative size of nuclear effects on ψ(2S) production compared to J/ψ is also studied via the double ratio of production cross sections [σψ(2S)/σJ/ψ]pPb/[σψ(2S)/σJ/ψ]pp between p-Pb and pp collisions. The results are compared with theoretical models that include various effects related to the initial and final state of the collision system and also with previous measurements at sNN = 5.02 TeV. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 16. |
- Acharya, S, et al.
(författare)
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Measurement of the Low-Energy Antideuteron Inelastic Cross Section
- 2020
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Ingår i: Physical Review Letters. - 1079-7114. ; 125:16
-
Tidskriftsartikel (refereegranskat)abstract
- In this Letter, we report the first measurement of the inelastic cross section for antideuteron-nucleus interactions at low particle momenta, covering a range of 0.3≤p
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| 17. |
- Acharya, S, et al.
(författare)
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Measurements of inclusive jet spectra in pp and central Pb-Pb collisions at sNN =5.02 TeV
- 2020
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Ingår i: Physical Review C. - 2469-9985. ; 101:3
-
Tidskriftsartikel (refereegranskat)abstract
- This article reports measurements of the pT-differential inclusive jet cross section in pp collisions at s=5.02TeV and the pT-differential inclusive jet yield in Pb-Pb 0-10% central collisions at sNN=5.02TeV. Jets were reconstructed at midrapidity with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm. For pp collisions, we report jet cross sections for jet resolution parameters R=0.1-0.6 over the range 20
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| 18. |
- Acharya, S, et al.
(författare)
-
Multiplicity dependence of inclusive J/ψ production at midrapidity in pp collisions at s=13 TeV
- 2020
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 810
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the inclusive J/ψ yield as a function of charged-particle pseudorapidity density dNch/dη in pp collisions at s=13 TeV with ALICE at the LHC are reported. The J/ψ meson yield is measured at midrapidity (|y|<0.9) in the dielectron channel, for events selected based on the charged-particle multiplicity at midrapidity (|η|<1) and at forward rapidity (−3.7<η<−1.7 and 2.8<η<5.1); both observables are normalized to their corresponding averages in minimum bias events. The increase of the normalized J/ψ yield with normalized dNch/dη is significantly stronger than linear and dependent on the transverse momentum. The data are compared to theoretical predictions, which describe the observed trends well, albeit not always quantitatively. © 2020 European Organization for Nuclear Research
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| 19. |
- Acharya, S, et al.
(författare)
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Multiplicity dependence of K*(892)0 and ϕ(1020) production in pp collisions at s=13 TeV
- 2020
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 807
-
Tidskriftsartikel (refereegranskat)abstract
- The striking similarities that have been observed between high-multiplicity proton-proton (pp) collisions and heavy-ion collisions can be explored through multiplicity-differential measurements of identified hadrons in pp collisions. With these measurements, it is possible to study mechanisms such as collective flow that determine the shapes of hadron transverse momentum (pT) spectra, to search for possible modifications of the yields of short-lived hadronic resonances due to scattering effects in an extended hadron-gas phase, and to investigate different explanations provided by phenomenological models for enhancement of strangeness production with increasing multiplicity. In this paper, these topics are addressed through measurements of the K⁎(892)0 and ϕ(1020) mesons at midrapidity in pp collisions at s= 13 TeV as a function of the charged-particle multiplicity. The results include the pT spectra, pT-integrated yields, mean transverse momenta, and the ratios of the yields of these resonances to those of longer-lived hadrons. Comparisons with results from other collision systems and energies, as well as predictions from phenomenological models, are also discussed. © 2020 European Organization for Nuclear Research
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| 20. |
- Acharya, S, et al.
(författare)
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Multiplicity dependence of π , K, and p production in pp collisions at √s=13 TeV
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:8
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the measurements of π±, K ±, p and p ¯ transverse momentum (pT) spectra as a function of charged-particle multiplicity density in proton–proton (pp) collisions at s=13TeV with the ALICE detector at the LHC. Such study allows us to isolate the center-of-mass energy dependence of light-flavour particle production. The measurements reported here cover a pT range from 0.1 to 20 GeV / c and are done in the rapidity interval | y| < 0.5. The pT-differential particle ratios exhibit an evolution with multiplicity, similar to that observed in pp collisions at s=7TeV, which is qualitatively described by some of the hydrodynamical and pQCD-inspired models discussed in this paper. Furthermore, the pT-integrated hadron-to-pion yield ratios measured in pp collisions at two different center-of-mass energies are consistent when compared at similar multiplicities. This also extends to strange and multi-strange hadrons, suggesting that, at LHC energies, particle hadrochemistry scales with particle multiplicity the same way under different collision energies and colliding systems. © 2020, CERN for the benefit of the ALICE collaboration.
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| 21. |
- Acharya, S, et al.
(författare)
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Non-linear flow modes of identified particles in Pb-Pb collisions at √sNN = 5.02 TeV
- 2020
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:6
-
Tidskriftsartikel (refereegranskat)abstract
- The pT-differential non-linear flow modes, v4,22, v5,32, v6,33 and v6,222 for π±, K±, KS0 , p + p ¯ , Λ + Λ ¯ and ϕ-meson have been measured for the first time at sNN = 5.02 TeV in Pb-Pb collisions with the ALICE detector at the Large Hadron Collider. The results were obtained with a multi-particle technique, correlating the identified hadrons with reference charged particles from a different pseudorapidity region. These non-linear observables probe the contribution from the second and third order initial spatial anisotropy coefficients to higher flow harmonics. All the characteristic features observed in previous pT-differential anisotropic flow measurements for various particle species are also present in the non-linear flow modes, i.e. increase of magnitude with increasing centrality percentile, mass ordering at low pT and particle type grouping in the intermediate pT range. Hydrodynamical calculations (iEBE-VISHNU) that use different initial conditions and values of shear and bulk viscosity to entropy density ratios are confronted with the data at low transverse momenta. These calculations exhibit a better agreement with the anisotropic flow coefficients than the non-linear flow modes. These observations indicate that non-linear flow modes can provide additional discriminatory power in the study of initial conditions as well as new stringent constraints to hydrodynamical calculations. [Figure not available: see fulltext.]. © 2020, The Author(s).
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| 22. |
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| 23. |
- Acharya, S, et al.
(författare)
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Production of ω mesons in pp collisions at √s=7TeV
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:12
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Tidskriftsartikel (refereegranskat)abstract
- The invariant differential cross section of inclusive ω(782) meson production at midrapidity (| y| < 0.5) in pp collisions at s=7TeV was measured with the ALICE detector at the LHC over a transverse momentum range of 2
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| 24. |
- Acharya, S, et al.
(författare)
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Search for a common baryon source in high-multiplicity pp collisions at the LHC
- 2020
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 811
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the measurement of the size of the particle-emitting source from two-baryon correlations with ALICE in high-multiplicity pp collisions at s=13 TeV. The source radius is studied with low relative momentum p–p, p‾–p‾, p–Λ, and p‾–Λ‾ pairs as a function of the pair transverse mass mT considering for the first time in a quantitative way the effect of strong resonance decays. After correcting for this effect, the radii extracted for pairs of different particle species agree. This indicates that protons, antiprotons, Λ s, and Λ‾ s originate from the same source. Within the measured mT range (1.1–2.2) GeV/c2the invariant radius of this common source varies between 1.3 and 0.85 fm. These results provide a precise reference for studies of the strong hadron–hadron interactions and for the investigation of collective properties in small colliding systems. © 2020 CERN for the benefit of the ALICE Collaboration
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| 25. |
- Acharya, S, et al.
(författare)
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Underlying event properties in pp collisions at √s = 13 TeV
- 2020
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2020:4
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Tidskriftsartikel (refereegranskat)abstract
- This article reports measurements characterizing the Underlying Event (UE) associated with hard scatterings at midrapidity (|η| < 0.8) in pp collisions at s = 13 TeV. The hard scatterings are identified by the leading particle, the charged particle with the highest transverse momentum (pTleading) in the event. Charged-particle number-densities and summed transverse-momentum densities are measured in different azimuthal regions defined with respect to the leading particle direction: Toward, Transverse, and Away. The Toward and Away regions contain the fragmentation products of the hard scatterings in addition to the UE contribution, whereas particles in the Transverse region are expected to originate predominantly from the UE. The study is performed as a function of pTleading with three different pT thresholds for the associated particles, pTtrack > 0.15, 0.5, and 1.0 GeV/c. The charged-particle density in the Transverse region rises steeply for low values of pTleading and reaches a plateau. The results confirm the trend that the charged-particle density in the Transverse region shows a stronger increase with s than the inclusive charged-particle density at midrapidity. The UE activity is increased by approximately 20% when going from 7 TeV to 13 TeV pp collisions. The plateau in the Transverse region (5
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