Function Of Transverse Momentum Research Articles

Contribution of coherent electron production to measurements of heavy-flavor decayed electrons in heavy-ion collisions

Heavy quarks, produced at early stages of heavy-ion collisions, are an excellent probe of the Quark-Gluon Plasma (QGP) also created in these collisions. Electrons from open heavy-flavor hadron decays (HFE) are good proxies for heavy quarks, and have been measured extensively in the last two decades to study QGP properties. These measurements are traditionally carried out by subtracting all known background sources from the inclusive electron sample. More recently, a significant enhancement of e+e-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$e^+e^-$$\\end{document} pair production at very low transverse momenta was observed in peripheral heavy-ion collisions. The production characteristics is consistent with coherent photon–photon interactions, which should also constitute a background source to the HFE measurements. In this article, we provide theoretical predictions for the contribution of coherent electron production to HFEs as a function of transverse momentum, centrality and collision energy in Au+Au and Pb+Pb collisions.

Measurement of forward charged hadron flow harmonics in peripheral PbPb collisions at sNN=5.02TeV with the LHCb detector

Flow harmonic coefficients, vn, which are the key to studying the hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions, have been measured in various collision systems and kinematic regions and using various particle species. The study of flow harmonics in a wide pseudorapidity range is particularly valuable to understand the temperature dependence of the shear viscosity to entropy density ratio of the QGP. This paper presents the first LHCb results of the second- and the third-order flow harmonic coefficients of charged hadrons as a function of transverse momentum in the forward region, corresponding to pseudorapidities between 2.0 and 4.9, using the data collected from PbPb collisions in 2018 at a center-of-mass energy of 5.02 TeV. The coefficients measured using the two-particle angular correlation analysis method are smaller than the central-pseudorapidity measurements at ALICE and ATLAS from the same collision system but share similar features. ©2024 CERN, for the LHCb Collaboration 2024 CERN

Exploring Global Polarization Splitting in Au+Au Collisions at sNN=19.6 GeV Using Viscous Hydrodynamic Model CLVisc

We present a systematic study of the global polarization of Λ and Λ¯ hyperons in Au+Au collisions at sNN=19.6 GeV using the viscous hydrodynamic model CCNU-LBNL-Viscous hydrodynamic model (CLVisc) with a modified 3D optical Glauber model initial condition. The global polarization splitting as a function of transverse momentum and rapidity is investigated. It is shown that the magnitude of the net baryon density and its longitudinal titled geometry at the initial stage both have significant effects on the global polarization splitting of Λ and Λ¯ hyperons. Specifically, an increase in the magnitude of the net baryon density leads to a corresponding minor increase in the global polarization splitting. Similarly, alterations in the tilted geometry of net baryon density results in significant changes in the splitting of the global polarization.

Charm production and fragmentation fractions at midrapidity in pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{\ extrm{s}} $$\\end{document} = 13 TeV

Measurements of the production cross sections of prompt D0, D+, D*+, Ds+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\ extrm{D}}_{\ extrm{s}}^{+} $$\\end{document}, Λc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Lambda}_{\ extrm{c}}^{+} $$\\end{document}, and Ξc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Xi}_{\ extrm{c}}^{+} $$\\end{document} charm hadrons at midrapidity in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ALICE detector are presented. The D-meson cross sections as a function of transverse momentum (pT) are provided with improved precision and granularity. The ratios of pT-differential meson production cross sections based on this publication and on measurements at different rapidity and collision energy provide a constraint on gluon parton distribution functions at low values of Bjorken-x (10−5–10−4). The measurements of Λc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Lambda}_{\ extrm{c}}^{+} $$\\end{document} (Ξc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Xi}_{\ extrm{c}}^{+} $$\\end{document}) baryon production extend the measured pT intervals down to pT = 0(3) GeV/c. These measurements are used to determine the charm-quark fragmentation fractions and the cc¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{c}\\overline{\ extrm{c}} $$\\end{document} production cross section at midrapidity (|y| < 0.5) based on the sum of the cross sections of the weakly-decaying ground-state charm hadrons D0, D+, Ds+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\ extrm{D}}_{\ extrm{s}}^{+} $$\\end{document}, Λc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Lambda}_{\ extrm{c}}^{+} $$\\end{document}, Ξc0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Xi}_{\ extrm{c}}^0 $$\\end{document} and, for the first time, Ξc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Xi}_{\ extrm{c}}^{+} $$\\end{document}, and of the strongly-decaying J/ψ mesons. The first measurements of Ξc+\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Xi}_{\ extrm{c}}^{+} $$\\end{document} and Σc0,++\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Sigma}_{\ extrm{c}}^{0,++} $$\\end{document} fragmentation fractions at midrapidity are also reported. A significantly larger fraction of charm quarks hadronising to baryons is found compared to e+e− and ep collisions. The cc¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \ extrm{c}\\overline{\ extrm{c}} $$\\end{document} production cross section at midrapidity is found to be at the upper bound of state-of-the-art perturbative QCD calculations.

First measurement of prompt and non-prompt D⁎+ vector meson spin alignment in pp collisions at [formula omitted] TeV

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|<0.8) as a function of transverse momentum (pT) in proton–proton (pp) collisions collected by ALICE at the centre-of-mass energy s=13TeV. The diagonal spin density matrix element ρ00 of D⁎+ mesons was measured from the angular distribution of the D⁎+→D0(→K−π+)π+ decay products, in the D⁎+ rest frame, with respect to the D⁎+ momentum direction in the pp centre of mass frame. The ρ00 value for prompt D⁎+ mesons is consistent with 1/3, which implies no spin alignment. However, for non-prompt D⁎+ mesons an evidence of ρ00 larger than 1/3 is found. The measured value of the spin density element is ρ00=0.455±0.022(stat.)±0.035(syst.) in the 5<pT<20GeV/c interval, which is consistent with a Pythia 8 Monte Carlo simulation coupled with the EvtGen package, which implements the helicity conservation in the decay of D⁎+ meson from beauty mesons. In non-central heavy-ion collisions, the spin of the D⁎+ mesons may be globally aligned with the direction of the initial angular momentum and magnetic field. Based on the results for pp collisions reported in this letter it is shown that alignment of non-prompt D⁎+ mesons due to the helicity conservation coupled to the collective anisotropic expansion may mimic the signal of global spin alignment in heavy-ion collisions.

Production of muons from heavy-flavour hadron decays in heavy-ion collisions with ALICE at the LHC

Measurements of the production of muons from heavy-flavour hadron decays at forward rapidity (2.5 < y < 4.0) in Pb–Pb collisions at and 5.02 TeV with the ALICE detector are presented along with the R AA measurements in different centrality intervals as a function of transverse momentum, p T. Results of the measured R AA at both energies are shown and are compared to the different model predictions.

Study of exclusive photoproduction of charmonium in ultra-peripheral lead-lead collisions

The cross-sections of exclusive (coherent) photoproduction J/ψ and ψ(2S) mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV are measured using a data sample corresponding to an integrated luminosity of 228 ± 10 μb−1, collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for J/ψ and ψ(2S) mesons. The integrated cross-sections are measured to be {sigma}_{J/psi}^{textrm{coh}} = 5.965 ± 0.059 ± 0.232 ± 0.262 mb and {sigma}_{psi (2S)}^{textrm{coh}} = 0.923 ± 0.086 ± 0.028 ± 0.040 mb, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be {sigma}_{psi (2S)}^{textrm{coh}}/{sigma}_{J/psi}^{textrm{coh}} = 0.155 ± 0.014 ± 0.003, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.

Measurements of the Elliptic and Triangular Azimuthal Anisotropies in Central ^{3}He+Au, d+Au and p+Au Collisions at sqrt[s_{NN}]=200 GeV.

The elliptic (v_{2}) and triangular (v_{3}) azimuthal anisotropy coefficients in central ^{3}He+Au, d+Au, and p+Au collisions at sqrt[s_{NN}]=200 GeV are measured as a function of transverse momentum (p_{T}) at midrapidity (|η|<0.9), via the azimuthal angular correlation between two particles both at |η|<0.9. While the v_{2}(p_{T}) values depend on the colliding systems, the v_{3}(p_{T}) values are system independent within the uncertainties, suggesting an influence on eccentricity from subnucleonic fluctuations in these small-sized systems. These results also provide stringent constraints for the hydrodynamic modeling of these systems.

Anisotropic flow and flow fluctuations of identified hadrons in Pb–Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV

The first measurements of elliptic flow of π±, K±, textrm{p}+overline{textrm{p}} , {textrm{K}}_{textrm{S}}^0 , Lambda +overline{Lambda} , ϕ, {Xi}^{-}+{overline{Xi}}^{+} , and {varOmega}^{-}+{overline{varOmega}}^{+} using multiparticle cumulants in Pb–Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV are resented. Results obtained with two- (v2{2}) and four-particle cumulants (v2{4}) are shown as a function of transverse momentum, pT, for various collision centrality intervals. Combining the data for both v2{2} and v2{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 pT-differential anisotropic flow measurements for identified hadrons with two-particle correlations, namely the mass ordering at low pT and the approximate scaling with the number of constituent quarks at intermediate pT, are similarly present in the four-particle correlations and the combinations of v2{2} and v2{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 pT range.

Proton, deuteron and triton flow measurements in Au+Au collisions at sqrt{s_{_{{text {NN}}}}}= 2.4 GeV

High-precision measurements of flow coefficients v_{n} (n = 1 - 4) for protons, deuterons and tritons relative to the first-order spectator plane have been performed in Au+Au collisions at sqrt{s_{_{{text {NN}}}}}= 2.4 GeV with the High-Acceptance Di-Electron Spectrometer (HADES) at the SIS18/GSI. Flow coefficients are studied as a function of transverse momentum p_{{text {t}}} and rapidity y_{{text {cm}}} over a large region of phase-space and for several classes of collision centrality. A clear mass hierarchy, as expected by relativistic hydrodynamics, is found for the slope of v_{1}, d v_{1}/d y^{prime }|_{y^{prime } = 0} where y^{prime } is the scaled rapidity, and for v_{2} at mid-rapidity. Scaling with the number of nucleons is observed for the p_{{text {t}}} dependence of v_{2} and v_{4} at mid-rapidity, which is indicative for nuclear coalescence as the main process responsible for light nuclei formation. v_{2} is found to scale with the initial eccentricity langle epsilon _{2} rangle , while v_{4} scales with langle epsilon _{2} rangle ^{2} and langle epsilon _{4} rangle . The multi-differential high-precision data on v_{1}, v_{2}, v_{3}, and v_{4} provides important constraints on the equation-of-state of compressed baryonic matter.

Azimuthal anisotropy measurement of (multi)strange hadrons in Au+Au collisions at sNN=54.4 GeV

Azimuthal anisotropy of produced particles is one of the most important observables used to access the collective properties of the expanding medium created in relativistic heavy-ion collisions. In this paper, we present second ($v_{2}$) and third ($v_{3}$) order azimuthal anisotropies of $K_{S}^{0}$, $\phi$, $\Lambda$, $\Xi$ and $\Omega$ at mid-rapidity ($|y|<$1) in Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 54.4 GeV measured by the STAR detector. The $v_{2}$ and $v_{3}$ are measured as a function of transverse momentum and centrality. Their energy dependence is also studied. $v_{3}$ is found to be more sensitive to the change in the center-of-mass energy than $v_{2}$. Scaling by constituent quark number is found to hold for $v_{2}$ within 10%. This observation could be evidence for the development of partonic collectivity in 54.4 GeV Au+Au collisions. Differences in $v_{2}$ and $v_{3}$ between baryons and anti-baryons are presented, and ratios of $v_{3}$/$v_{2}^{3/2}$ are studied and motivated by hydrodynamical calculations. The ratio of $v_{2}$ of $\phi$ mesons to that of anti-protons ($v_{2}(\phi)/v_{2}(\bar{p})$) shows centrality dependence at low transverse momentum, presumably resulting from the larger effects from hadronic interactions on anti-proton $v_{2}$.

Drell-Yan transverse momentum dependence over a wide mass range

The measurement of the differential cross section for opposite-charge electron or muon pairs as a function of transverse momentum is presented in this report. The measurement is performed in several invariant mass bins, from 50 GeV to 1 TeV. The results are presented for inclusive production as well as for the production in association with one jet. The results are obtained from proton-proton interactions recorded with the CMS detector at the LHC at a centre-of-mass energy of 13 TeV during 2016. The integrated luminosity of the data is 36.3fb−1. The measurements are compared with several theoretical predictions.

Measurements of second-harmonic Fourier coefficients from azimuthal anisotropies in p+p, p+Au, d+Au, and He3+Au collisions at sNN=200 GeV

Recently, the PHENIX Collaboration has published second- and third-harmonic Fourier coefficients $v_2$ and $v_3$ for midrapidity ($|\eta|<0.35$) charged hadrons in 0\%--5\% central $p$$+$Au, $d$$+$Au, and $^3$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV utilizing three sets of two-particle correlations for two detector combinations with different pseudorapidity acceptance [Phys. Rev. C {\bf 105}, 024901 (2022)]. This paper extends these measurements of $v_2$ to all centralities in $p$$+$Au, $d$$+$Au, and $^3$He$+$Au collisions, as well as $p$$+$$p$ collisions, as a function of transverse momentum ($p_T$) and event multiplicity. The kinematic dependence of $v_2$ is quantified as the ratio $R$ of $v_2$ between the two detector combinations as a function of event multiplicity for $0.5$$<$$p_T$$<$$1$ and $2$$<$$p_T$$<$$2.5$ GeV/$c$. A multiphase-transport (AMPT) model can reproduce the observed $v_2$ in most-central to midcentral $d$$+$Au and $^3$He$+$Au collisions. However, the AMPT model systematically overestimates the measurements in $p$$+$$p$, $p$$+$Au, and peripheral $d$$+$Au and $^3$He$+$Au collisions, indicating a higher nonflow contribution in AMPT than in the experimental data. The AMPT model fails to describe the observed $R$ for $0.5$$<$$p_T$$<$$1$ GeV/$c$, but there is qualitative agreement with the measurements for $2$$<$$p_T$$<$$2.5$ GeV/$c$.

Transverse momentum spectra and suppression of charged hadrons in deformed Xe–Xe collisions at $$\sqrt{s_{NN}}$$ = 5.44 TeV using HYDJET++ model

In this study, we systematically investigate deformed Xe-Xe collisions at 5.44 TeV center of mass energy. We exploit the Monte Carlo HYDJET++ model to compute transverse momentum ($p_{T}$) distribution, nuclear modification factor $R_{AA}$ and relative suppression in terms of $R_{CP}$ as a function of transverse momentum and centrality of collision of charged hadrons in body-body and tip-tip geometrical configurations, respectively. We have compared HYDJET++ model results to those from ALICE experimental data and AMPT model (String-Melting version) results. Minimum bias Xe-Xe collisions show a suitable match with ALICE experimental data at midrapidity. Average transverse momentum ($\langle p_{T} \rangle$) show strong centrality dependence. The contribution of hard parton scatterings to the total charged hadron yield is discussed. Both nuclear modification factor $R_{AA}$ and relative suppression $R_{CP}$ show a clear dependence on centrality as well as transverse momentum. The charged hadron observables show a clear dependence on the geometrical configuration of the collisions. HYDJET++ model justifies experimental data more closely than the AMPT model.

Measurement of exclusive vector meson photoproduction in pPb collisions with the CMS experiment

The exclusive photoproduction of vector mesons provides a unique opportunity to constrain the gluon distribution function within protons and nuclei. Measuring vector mesons of various masses over a wide range of rapidity and as a function of transverse momentum provides important information on the evolution of the gluon distribution within nuclei. A variety of measurements, including the exclusive J/ψ, ρ, and Υ meson production in pPb (at nucleonnucleon center of mass energies of 5.02 and 8.16 TeV) and PbPb (5.02 TeV) collisions, are presented as a function of squared transverse momentum and the photon-proton center of mass energy. Finally, compilations of these data and previous measurements are compared to various theoretical predictions.

Factorization breaking for higher moments of harmonic flow

We study correlations between harmonic flow vectors squared measured at different transverse momenta. One of the flow harmonics squared is taken at a fixed transverse momentum and correlated to the momentum averaged harmonic flow squared of the same order. Such four particle correlators, dependent on transverse momentum, have been recently measured experimentally. Factorization coefficients based on the ratio of such four-particle correlators allow the independent measurement of the flow vector and flow magnitude factorization breaking coefficient. Moreover, the correlation of the angles of flow harmonics as a function of transverse momentum can be extracted. Results are compared to preliminary data of the ALICE Collaboration. We also present predictions for the momentum dependent factorization breaking coefficient between mixed flow harmonics. The correlators with squares of mixed harmonics can serve as a way to independently measure the flow vector, flow magnitude, and flow angle correlations, and could be used to gain additional information on the fluctuating initial state and the dynamics in heavy-ion collisions.

Measurement of prompt [formula omitted]-meson production and azimuthal anisotropy in Pb–Pb collisions at [formula omitted

The production yield and angular anisotropy of prompt Ds+ mesons were measured as a function of transverse momentum (pT) in Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV collected with the ALICE detector at the LHC. Ds+ mesons and their charge conjugates were reconstructed at midrapidity (|y|<0.5) from their hadronic decay channel Ds+→ϕπ+, with ϕ→K−K+, in the pT intervals 2<pT<50GeV/c and 2<pT<36GeV/c for the 0–10% and 30–50% centrality intervals. For pT>10GeV/c, the measured Ds+-meson nuclear modification factor RAA is consistent with the one of non-strange D mesons within uncertainties, while at lower pT a hint for a Ds+-meson RAA larger than that of non-strange D mesons is seen. The enhanced production of Ds+ relative to non-strange D mesons is also studied by comparing the pT-dependent Ds+/D0 production yield ratios in Pb–Pb and in pp collisions. The ratio measured in Pb–Pb collisions is found to be on average higher than that in pp collisions in the interval 2<pT<8GeV/c with a significance of 2.3σ and 2.4σ for the 0–10% and 30–50% centrality intervals. The azimuthal anisotropy coefficient v2 of prompt Ds+ mesons was measured in Pb–Pb collisions in the 30–50% centrality interval and is found to be compatible with that of non-strange D mesons. The main features of the measured RAA, Ds+/D0 ratio, and v2 as a function of pT are described by theoretical calculations of charm-quark transport in a hydrodynamically expanding quark–gluon plasma including hadronisation via charm-quark recombination with light quarks from the medium. The pT-integrated production yield of Ds+ mesons is compatible with the prediction of the statistical hadronisation model.

Measurement of inclusive electrons from open heavy-flavor hadron decays in p+p collisions at s=200 GeV with the STAR detector

We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum ($p_{\rm T}$) at mid-rapidity ($|y|<$ 0.7) in $p$+$p$ collisions at $\sqrt{s} = 200$ GeV. The result is presented for 2.5 $<p_{\rm T}<$ 10 GeV/$c$ with an improved precision above 6 GeV/$c$ with respect to the previous measurements, providing more constraints on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.

Checking nonflow assumptions and results via PHENIX published correlations in p+p , p+Au , d+Au , and He3+Au at sNN=200 GeV

Recently the PHENIX Collaboration has made available two-particle correlation Fourier coefficients for multiple detector combinations in minimum bias p+p and 0-5% central p+Au, d+Au, 3He+Au collisions at 200 GeV [1]. Using these coefficients for three sets of two-particle correlations, azimuthal anisotropy coefficients $v_2$ and $v_3$ are extracted for midrapidity charged hadrons as a function of transverse momentum. In this paper, we use the available coefficients to explore various non-flow hypotheses as well as compare the results with theoretical model calculations. The non-flow methods fail basic closure tests with AMPT and PYTHIA/ANGANTYR, particularly when including correlations with particles in the low multiplicity light-projectile going direction. In data, the non-flow adjusted $v_2$ results are modestly lower in p+Au and the adjusted $v_3$ results are more significantly higher in p+Au and d+Au. However, the resulting higher values for the ratio $v_3/v_2$ in p+Au at RHIC compared to p+Pb at the LHC is additional evidence for a significant over-correction. Incorporating these additional checks, the conclusion that these flow coefficients are dominated by initial geometry coupled with final-state interactions (e.g.~hydrodynamic expansion of quark-gluon plasma) remains true, and explanations based on initial-state glasma are ruled out. The detailed balance between intrinsic and fluctuation-driven geometry and the exact role of weakly versus strongly-coupled pre-hydrodynamic evolution remains an open question for triangular flow, requiring further theoretical and experimental investigation.

Global and local polarization of Λ (Λ) hyperons in Pb–Pb collisions in ALICE at the LHC

The global polarization of the Λ and Λ¯ hyperons (PH) has been measured in Pb–Pb collisions at √SNN = 2.76 TeV and 5.02 TeV in ALICE at the Large Hadron Collider (LHC). The hyperon global polarization is found to be consistent with zero at both collision energies. The local polarization of the Λ and Λ¯ hyperons along the beam (z) direction, Pz, has also been measured in Pb–Pb collisions at √SNN = 5.02 TeV. The Pz, measured as a function of the hyperon emission angle relative to the second harmonic symmetry plane, exhibits a second harmonic sine modulation, as expected due to elliptic flow. The measurements of global and local hyperon polarization are reported for different collision centralities and as a function of transverse momentum in semicentral collisions. These results show the first experimental evidence of a non-zero hyperon Pz in Pb–Pb collisions at the LHC.