| 1. |
- Acharya, S., et al.
(författare)
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Anisotropic flow and flow fluctuations of identified hadrons in Pb–Pb collisions at √sNN = 5.02 TeV
- 2023
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2023:5
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Tidskriftsartikel (refereegranskat)abstract
- The first measurements of elliptic flow of π ±, K ±, p + p ¯ , KS0 , Λ + Λ ¯ , ϕ, Ξ −+ Ξ ¯ + , and Ω −+ Ω ¯ + using multiparticle cumulants in Pb–Pb collisions at sNN = 5.02 TeV are resented. Results obtained with two- (v 2{2}) and four-particle cumulants (v 2{4}) are shown as a function of transverse momentum, p T, for various collision centrality intervals. Combining the data for both v 2{2} and v 2{4} also allows us to report the first measurements of the mean elliptic flow, elliptic flow fluctuations, and relative elliptic flow fluctuations for various hadron species. These observables probe the event-by-event eccentricity fluctuations in the initial state and the contributions from the dynamic evolution of the expanding quark–gluon plasma. The characteristic features observed in previous p T-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low p T and the approximate scaling with the number of constituent quarks at intermediate p T, are similarly present in the four-particle correlations and the combinations of v 2{2} and v 2{4}. In addition, a particle species dependence of flow fluctuations is observed that could indicate a significant contribution from final state hadronic interactions. The comparison between experimental measurements and CoLBT model calculations, which combine the various physics processes of hydrodynamics, quark coalescence, and jet fragmentation, illustrates their importance over a wide p T range. [Figure not available: see fulltext.]. © 2023, The Author(s).
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| 2. |
- Acharya, S., et al.
(författare)
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Closing in on critical net-baryon fluctuations at LHC energies: Cumulants up to third order in Pb–Pb collisions
- 2023
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 844
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Tidskriftsartikel (refereegranskat)abstract
- Fluctuation measurements are important sources of information on the mechanism of particle production at LHC energies. This article reports the first experimental results on third-order cumulants of the net-proton distributions in Pb–Pb collisions at a center-of-mass energy sNN=5.02 TeV recorded by the ALICE detector. The results on the second-order cumulants of net-proton distributions at sNN=2.76 and 5.02 TeV are also discussed in view of effects due to the global and local baryon number conservation. The results demonstrate the presence of long-range rapidity correlations between protons and antiprotons. Such correlations originate from the early phase of the collision. The experimental results are compared with HIJING and EPOS model calculations, and the dependence of the fluctuation measurements on the phase-space coverage is examined in the context of lattice quantum chromodynamics (LQCD) and hadron resonance gas (HRG) model estimations. The measured third-order cumulants are consistent with zero within experimental uncertainties of about 4% and are described well by LQCD and HRG predictions. © 2022 The Author
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| 3. |
- Acharya, S., et al.
(författare)
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Constraining hadronization mechanisms with Λc+/D0 production ratios in Pb–Pb collisions at sNN=5.02 TeV
- 2023
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 839
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Tidskriftsartikel (refereegranskat)abstract
- The production of prompt Λc+ baryons at midrapidity (|y|<0.5) was measured in central (0–10%) and mid-central (30–50%) Pb–Pb collisions at the center-of-mass energy per nucleon–nucleon pair sNN=5.02 TeV with the ALICE detector. The results are more precise, more differential in centrality, and reach much lower transverse momentum (pT=1 GeV/c) with respect to previous measurements performed by the ALICE, STAR, and CMS Collaborations in nucleus–nucleus collisions, allowing for an extrapolation down to pT=0. The pT-differential Λc+/D0 ratio is enhanced with respect to the pp measurement for 4
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| 4. |
- Acharya, S., et al.
(författare)
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Constraining the K ¯ N coupled channel dynamics using femtoscopic correlations at the LHC
- 2023
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Ingår i: European Physical Journal C. - 1434-6044. ; 83:4
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of K - with protons is characterised by the presence of several coupled channels, systems like K ¯ n and π Σ with a similar mass and the same quantum numbers as the K - p state. The strengths of these couplings to the K - p system are of crucial importance for the understanding of the nature of the Λ (1405) resonance and of the attractive K - p strong interaction. In this article, we present measurements of the K - p correlation functions in relative momentum space obtained in pp collisions at s=13 Te, in p–Pb collisions at sNN=5.02 Te, and (semi)peripheral Pb–Pb collisions at sNN=5.02 Te. The emitting source size, composed of a core radius anchored to the K + p correlation and of a resonance halo specific to each particle pair, varies between 1 and 2 fm in these collision systems. The strength and the effects of the K ¯ n and π Σ inelastic channels on the measured K - p correlation function are investigated in the different colliding systems by comparing the data with state-of-the-art models of chiral potentials. A novel approach to determine the conversion weights ω , necessary to quantify the amount of produced inelastic channels in the correlation function, is presented. In this method, particle yields are estimated from thermal model predictions, and their kinematic distribution from blast-wave fits to measured data. The comparison of chiral potentials to the measured K - p interaction indicates that, while the π Σ – K - p dynamics is well reproduced by the model, the coupling to the K ¯ n channel in the model is currently underestimated. © 2023, The Author(s).
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| 5. |
- Acharya, S., et al.
(författare)
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Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb–Pb collisions at √sNN = 5.02 TeV
- 2023
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2023:6
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Tidskriftsartikel (refereegranskat)abstract
- The first measurement of the e+e− pair production at low lepton pair transverse momentum (p T,ee) and low invariant mass (m ee) in non-central Pb–Pb collisions at sNN = 5.02 TeV at the LHC is presented. The dielectron production is studied with the ALICE detector at midrapidity (|η e | < 0.8) as a function of invariant mass (0.4 ≤ m ee < 2.7 GeV/c 2) in the 50–70% and 70–90% centrality classes for p T,ee < 0.1 GeV/c, and as a function of p T,ee in three m ee intervals in the most peripheral Pb–Pb collisions. Below a p T,ee of 0.1 GeV/c, a clear excess of e+e− pairs is found compared to the expectations from known hadronic sources and predictions of thermal radiation from the medium. The m ee excess spectra are reproduced, within uncertainties, by different predictions of the photon–photon production of dielectrons, where the photons originate from the extremely strong electromagnetic fields generated by the highly Lorentz-contracted Pb nuclei. Lowest-order quantum electrodynamic (QED) calculations, as well as a model that takes into account the impact-parameter dependence of the average transverse momentum of the photons, also provide a good description of the p T,ee spectra. The measured 〈pT,ee2〉 of the excess p T,ee spectrum in peripheral Pb–Pb collisions is found to be comparable to the values observed previously at RHIC in a similar phase-space region. [Figure not available: see fulltext.]. © 2023, The Author(s).
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| 6. |
- Acharya, S., et al.
(författare)
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Elliptic flow of charged particles at midrapidity relative to the spectator plane in Pb–Pb and Xe–Xe collisions
- 2023
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 846
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the elliptic flow coefficient relative to the collision plane defined by the spectator neutrons v2{ΨSP} in collisions of Pb ions at center-of-mass energy per nucleon–nucleon pair sNN=2.76 TeV and Xe ions at sNN=5.44 TeV are reported. The results are presented for charged particles produced at midrapidity as a function of centrality and transverse momentum for the 5–70% and 0.2–6 GeV/c ranges, respectively. The ratio between v2{ΨSP} and the elliptic flow coefficient relative to the participant plane v2{4}, estimated using four-particle correlations, deviates by up to 20% from unity depending on centrality. This observation differs strongly from the magnitude of the corresponding eccentricity ratios predicted by the TRENTo and the elliptic power models of initial state fluctuations that are tuned to describe the participant plane anisotropies. The differences can be interpreted as a decorrelation of the neutron spectator plane and the reaction plane because of fragmentation of the remnants from the colliding nuclei, which points to an incompleteness of current models describing the initial state fluctuations. A significant transverse momentum dependence of the ratio v2{ΨSP}/v2{4} is observed in all but the most central collisions, which may help to understand whether momentum anisotropies at low and intermediate transverse momentum have a common origin in initial state fluctuations. The ratios of v2{ΨSP} and v2{4} to the corresponding initial state eccentricities for Xe–Xe and Pb–Pb collisions at similar initial entropy density show a difference of (7.0±0.9)% with an additional variation of +1.8% when including RHIC data in the TRENTo parameter extraction. These observations provide new experimental constraints for viscous effects in the hydrodynamic modeling of the expanding quark–gluon plasma produced in heavy-ion collisions at the LHC. © 2022 The Author(s)
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| 7. |
- Acharya, S., et al.
(författare)
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Enhanced Deuteron Coalescence Probability in Jets
- 2023
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Ingår i: Physical Review Letters. - 0031-9007. ; 131:4
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Tidskriftsartikel (refereegranskat)abstract
- The transverse-momentum (pT) spectra and coalescence parameters B2 of (anti)deuterons are measured in p-p collisions at s=13 TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest pT in the event (pTlead>5 GeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase-space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using pythia8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in pythia8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the B2Jet is not reproduced by the models, which instead give a decreasing trend. © 2023 CERN.
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| 8. |
- Acharya, S., et al.
(författare)
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f0(980) production in inelastic pp collisions at s = 5.02 TeV
- 2023
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 846
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Tidskriftsartikel (refereegranskat)abstract
- The measurement of the production of f0(980) in inelastic pp collisions at s=5.02 TeV is presented. This is the first reported measurement of inclusive f0(980) yield at LHC energies. The production is measured at midrapidity, |y|
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| 9. |
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| 10. |
- Acharya, S., et al.
(författare)
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First measurement of prompt and non-prompt D⁎+ vector meson spin alignment in pp collisions at s=13 TeV
- 2023
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 846
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Tidskriftsartikel (refereegranskat)abstract
- This letter reports the first measurement of spin alignment, with respect to the helicity axis, for D⁎+ vector mesons and their charge conjugates from charm-quark hadronisation (prompt) and from beauty-meson decays (non-prompt) in hadron collisions. The measurements were performed at midrapidity (|y|
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