arXiv subjects
Publications and source records attributed to Robert Vertesi.
A selection of recent ALICE results from pp, p--Pb, Pb--Pb and Xe--Xe collisions taken during the Run 1 and Run 2 phases are summarized in this contribution, and the prospects for the upcoming Run 3 phase are outlined.
Heavy quarks (charm and beauty) are produced early in the nucleus-nucleus collisions, and heavy flavor survives throughout the later stages. Measurements of heavy-flavor quarks thus provide us with means to understand the properties of the Quark-Gluon Plasma, a hot and dense state of matter created in heavy-ion collisions. Production of heavy-flavor in small collision systems, on the other hand, can be used to test Quantum-chromodynamics models. After a successful completion of the Run-I data taking period, the increased luminosity from the LHC and an upgraded ALICE detector system in the Run-II data taking period allows for an unprecedented precision in the study of heavy quarks. In this article we give an overview of selected recent results on heavy-flavor measurements with ALICE experiment at the LHC.
The ALICE experiment at the Large Hadron Collider (LHC) ring is designed to study the strongly interacting matter at extreme energy densities created in high-energy heavy-ion collisions. In this paper we investigate correlations of heavy and light flavours in simulations at LHC energies at mid-rapidity, with the primary purpose of proposing experimental application of these methods. Our studies have shown that investigating the correlation images can aid the experimental separation of heavy quarks and help understanding the physics that create them. The shape of the correlation peaks can be used to separate the electrons stemming from b quarks. This could be a method of identification that, combined with identification in silicon vertex detectors, may provide much better sample purity for examining the secondary vertex shift. Based on a correlation picture it is also possible to distinguish between prompt and late contributions to D meson yields.
Measurements of the heavy-flavour hadron production are a powerful tool to study the nature of strong interaction and to understand the properties of nuclear matter that is created in ultra-relativistic hadron-hadron collisions. The excellent tracking and vertexing capabilities of the ALICE experiment, together with its particle identification systems, allow for an efficient identification and reconstruction of decays of hadrons that contain heavy quarks. A selection of recent measurements on open heavy-flavour production from pp collisions at $\sqrt{s}=7$ TeV and p--Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV, collected with the ALICE detector during the LHC Run-1 phase, are discussed in this paper.
We report on the latest measurements of the production of $Υ$ mesons in heavy-ion collisions from the STAR experiment at RHIC. New measurements of the nuclear modification factors of the $Υ$(1S+2S+3S) and $Υ$(1S) states in U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV are presented as a function of the number of participants ($N_{part}$) in the collisions. In addition, the suppression of $Υ$(1S) and $Υ$(2S+2S) is presented versus the quark-antiquark binding energy. Preliminary results on Upsilon suppression in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, reconstructed via the dimuon channel, are also reported.
Bottomonium measurements provide unique insight into hot and cold nuclear matter effects present in the medium that is formed in high-energy heavy-ion collisions. Recent STAR results show that in $\sqrt{s_{NN}}$ = 200 GeV central Au+Au collisions the $Υ$(1S) state is suppressed more than if only cold nuclear matter effects were present, and the excited state yields are consistent with a complete suppression. In 2012, STAR also collected 263.4 $μ$b$^{-1}$ high-energy-electron triggered data in U+U collisions at $\sqrt{s_{NN}}$= 193 GeV. Central U+U collisions, with an estimated 20% higher energy density than in central Au+Au data, extend the $Υ$(1S+2S+3S) and Upsilon(1S) nuclear modification trends observed in Au+Au towards higher number of participant nucleons, and confirm the suppression of the $Υ$(1S) state. We see a hint with 1.8 sigma significance that the $Υ$(2S+3S) excited states are not completely suppressed in U+U collisions. These data support the sequential in-medium quarkonium dissociation picture and favor models with a strong $q\bar{q}$ binding.
The production of different quarkonium states provides unique insight to the hot and cold nuclear matter effects in the strongly interacting medium that is formed in high energy heavy ion collisions. While LHC explores the energy frontier, RHIC has a broad physics program to explore the nuclear modification at different energies in a wide range of systems. Some of the most interesting recent results on $J/ψ$ and $Υ$ production in p+p, d+Au and A+A collisions from PHENIX and STAR are summarized in this work.
We present a selection of recent heavy flavor results from the STAR experiment. Measurements of $D^0$ and $D^*$ meson production in $\sqrt{s}$=200 and 500 GeV p+p, as well as in $\sqrt{s_{NN}}$=200 GeV d+Au, Au+Au and 193 \GeV U+U collisions are presented and implications on the production mechanism are discussed. We report on the production and elliptic flow of electrons from semi-leptonic decays of heavy flavor hadrons in \snn{}=39, 62.4 and 200 GeV Au+Au collisions. Nuclear modification of $J/ψ$ production in $\sqrt{s_{NN}}$=39, 62.4 and 200 GeV Au+Au, and 193 GeV U+U, and of $Υ$ in 200 GeV d+Au, Au+Au, and 193 GeV U+U collisions are compared to theoretical models. Finally we discuss the prospects of heavy flavor measurements with the recent detector upgrades.
We report recent Upsilon measurements in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV, and detail the analysis in U+U collisions at $\sqrt{s_{NN}}$=193 GeV. Results on Upsilon production versus rapidity are consistent with pQCD predictions in p+p collisions. However, Upsilon production in mid-rapidity (|y|<0.5) d+Au collisions is suppressed with respect to p+p collisions beyond model predictions that take into account modification of parton distribution functions and initial parton energy loss inside nuclei. The nuclear modification factor R_AA shows a significant suppression in central Au+Au and U+U collisions, consistent with model calculations including color screening effects in a deconfined medium.
Three-dimensional analyses of the pion source revealed a heavy, non-Gaussian tail in the direction of the pair transverse momentum. The interpretation of these pion sources in terms of pure hydrodynamical evolution is, however, complicated by the strong contribution of feed-down from long-lived resonances to the source. On the other hand, kaons provide a much cleaner probe of the expanding fireball. Here we present a recent three-dimensional kaon correlation analysis using Cartesian harmonics decomposition technique. In contrary to pions, the three-dimensional source function of kaons is largely Gaussian. Comparison with thermal simulations and a hydrokinetic model show that resonance decays, as well as non-zero emission duration and/or rescattering in the hadronic phase play an important role. The analysis of the three dimensional extent of the kaon source w.r.t. the pair transverse momentum favors the hydrokinetic model over the exact mT-scaling featured by perfect hydrodynamical models.
In sqrt(sNN) = 200 GeV Au+Au collisions PHENIX reported a significant enhancement in the low-mass region (0.1 < m_ee < 0.7 GeV) of the dielectron spectrum, which is still not fully understood. Several theoretical works and an indirect measurement suggest that, due to the possible restoration of the U_A(1) part of the chiral symmetry in a hot and dense medium, the mass of the eta' meson may substantially decrease. This work reports on a statistically acceptable description of the PHENIX low-mass dilepton enhancement using a radial flow dominated meson spectra, chain decays of long-lived resonances and an in-medium eta' mass modification.
New results from the 2010 RHIC low energy program show a substantial suppression of neutral pions in central Au+Au collisions at both sqrt{s_NN}=39 and 62.4 GeV c.m.s. energies. At high pT the 62.4 GeV and 200 GeV data follow the same suppression pattern. On the other hand, otherwise successful pQCD predictions do not describe the 39 GeV data. These observations indicate that initial state effects may play a dominant role at smaller c.m.s. energies and at lower pT . The azimuthal dependence of the nuclear modification factor R_AA is strongly correlated with the (approximately elliptical) geometry of the overlap region. The dependence of R_AA on the reaction plane, determined up to pT=20 GeV/c from 2007 high-luminosity sqrt{s_NN}=200 GeV Au+Au data provides great selectivity among theories, and favours the ASW scenario with AdS/CFT correspondence over the pQCD-based models.
A particle called η' meson is found to reduce its mass in less than 10^-22 second in high energy heavy ion collisions at RHIC. Apparently this is the fastest mass reduction ever observed. This indicates the restoration of a lost symmetry of strong interactions in a hot and dense, hadronic matter.
A reduction of the mass of the η'(958) meson may indicate the restoration of the UA(1) symmetry in a hot and dense hadronic matter, corresponding to the return of the 9th, "prodigal" Goldstone boson. We report on an analysis of a combined PHENIX and STAR data set on the intercept parameter of the two-pion Bose-Einstein correlation functions, as measuremed in \sqrt{s_NN} = 200 GeV Au+Au collisions at RHIC. To describe this combined PHENIX and STAR dataset, an in-medium η' mass reduction of at least 200 MeV is needed, at the 99.9 % confidence level in a broad model class of resonance multiplicities. Energy, system size and centrality dependence of the observed effect is also discussed.