Relativistic Heavy Ion Collider Experiments Research Articles

Experimental overview: Quarkonium production in relativistic particle collisions

Quarkonium provides a golden probe of the formation of the Quark Gluon Plasma (QGP). Its production in heavy-ion collisions can be affected by an interplay of different phenomena such as medium-induced dissociation and heavy-quark (re)combination in the QGP, and cold nuclear matter effects due to the presence of the nucleus. The measurement of quarkonium states in different collision systems and beam energies allows to gain further insights on these effects and probe the properties of the QGP. In these proceedings, an overview of the main experimental quarkonium measurements in proton-proton, protonnucleus and nucleus-nucleus collisions is presented, giving emphasis on the most recent results from the Large Hadron Collider and Relativistic Heavy Ion Collider experiments shown at the 2023 Quark Matter conference.

Rivet and the analysis preservation in heavy-ion collisions experiments

The comparison of experimental data and theoretical predictions is important for our understanding of the mechanisms for interactions and particle production in hadron collisions, both at the Large Hadron Collider and at the Relativistic Heavy-Ion Collider experiments. Several tools were ideated to help with that. Rivet (Robust Independent Validation of Experiment and Theory) is a framework that facilitates the comparison between measurements from high-energy physics experiments and Monte Carlo event generators able to produce outputs using the HepMC package. Rivet contains a repository with analysis algorithms developed by experiments, providing analysis documentation and preservation. The recent developments for the implementation of centrality and multiplicity classes in Rivet are presented in this contribution.

A topological realization of spin polarization through vortex formation in collisions of Bose–Einstein condensates

The global spin polarization of hadrons in heavy ion collisions has been measured in the solenoidal tracker at relativistic heavy ion collider experiments, which opens up a new window in the study of the hottest, least viscous, and most vortical fluid that has ever been produced in the laboratory. We present a different approach to spin polarization from conventional ones: a topological realization of spin polarization through quantum vortex formation in collisions of Bose–Einstein condensates. This approach is based on the observation that the vortex is a topological excitation in a superfluid in the presence of local orbital angular momentum and is an analog of spin degrees of freedom. The formation processes of vortices and vortex–antivortex pairs are investigated by solving the Gross–Pitaevskii equation with a large-scale parallel algorithm on a graphics processing unit to very high precision. In a rotating environment, the primary vortex with winding number one is stable against perturbation, which has minimal energy and fixed orbital angular momentum (OAM), but the vortices with larger winding numbers are unstable and will decay into primary vortices through a redistribution of the energy and vorticity. The injection of OAM can also be realized in non-central collisions of self-interacting condensates, part of the OAM of the initial state will induce the formation of vortices through concentration of energy and vorticity density around topological defects. Different from a hydrodynamical description, the interference of the wave function plays an important role in the transport of energy and vorticity, reflecting the quantum nature of the vortex formation process. The study of the vortex formation may shed light on the nature of particle spin and spin–orbit couplings in strong interaction matter produced in heavy-ion collisions.

Pythia8 underlying event tune for RHIC energies

We report an underlying event tune for the pythia8 Monte Carlo event generator that is applicable for hadron collisions primarily at $\sqrt{s}$ ranges available at the Relativistic Heavy-Ion Collider (RHIC). We compare our new pythia8 tuned predictions to midrapidity inclusive ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$ spectra, jet substructure, Drell-Yan production, and underlying event measurements from RHIC and the Tevatron, as well as underlying event data from the Large Hadron Collider. With respect to the default pythia8 Monash Tune, the new ``Detroit'' tune shows significant improvements in the description of the experimental data. Additionally, we explore the validity of pythia8 predictions for forward rapidity $\ensuremath{\pi}$ in $\sqrt{s}=200\text{ }\text{ }\mathrm{GeV}$ collisions, where neither tune is able to sufficiently describe the data. We advocate for the new tune to be used for pythia8 studies at current and future RHIC experiments, and discuss future tuning exercises at lower center-of-mass energies, where forward/backward kinematics are essential at the upcoming Electron-Ion Collider.

Realistic implementation of chiral magnetic wave in heavy ion collisions

A chiral magnetic wave (CMW) is a gapless collective excitation of chiral charges along the direction of magnetic field in the quark-gluon plasma that arises from the triangle anomaly of QCD. We perform a reliable study of the CMW in a realistic simulation of heavy ion collisions, and find that the CMW contributions to the charge-dependent elliptic flow of pions, $\ensuremath{\Delta}{v}_{2}\ensuremath{\equiv}{v}_{2}({\ensuremath{\pi}}^{\ensuremath{-}})\ensuremath{-}{v}_{2}({\ensuremath{\pi}}^{+})$, linearly depending on the net charge asymmetry ${A}_{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\equiv}({N}_{+}\ensuremath{-}{N}_{\ensuremath{-}})/({N}_{+}+{N}_{\ensuremath{-}})$ with a positive slope $r$, is comparable to the recent experimental results from the Relativistic Heavy Ion Collider (RHIC). We identify a ``freeze-out hole effect,'' which is a direct consequence of the propagation of the CMW during the realistic evolution of the fireball, as the dominant physics effect responsible for a sizable contribution from the CMW to the slope parameter $r$, and emphasize that a proper treatment of the freeze-out condition is crucial in any reliable computation of the CMW contribution to the slope parameter $r$. We also implement a chiral phase transition effect in our study, which illustrates the sensitivity of the results to chiral phase transition temperature, and suggest that the CMW can be an important probe of the QCD chiral phase transition. Our results on the impact parameter dependence compare well with the RHIC experiments. We also give predictions for the Large Hadron Collider (LHC) energy.

Heavy-quark-state production inA-Acollisions atspp=200GeV

We estimate differential rapidity cross sections for $J/\ensuremath{\Psi}$ and $\ensuremath{\Upsilon}(1S)$ production via Cu-Cu and Au-Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC), and the relative probabilities of ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ to $J/\ensuremath{\Psi}$ production via $p$-$p$ collisions using our recent theory of mixed heavy-quark hybrids, in which the ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ mesons have approximately equal normal $q\overline{q}$ and hybrid $q\overline{q}g$ components. We also estimate the relative probabilities of ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ to $J/\ensuremath{\Psi}$ production via Cu-Cu and Au-Au collisions, which will be measured in future RHIC experiments. We also review production ratios of $\ensuremath{\Upsilon}(2S)$ and $\ensuremath{\Upsilon}(3S)$ to $\ensuremath{\Upsilon}(1S)$ in comparison to recent experimental results.This is an extension of our recent work on $p$-$p$ collisions for possible tests of the production of quark-gluon plasma via $A$-$A$ collisions at RHIC.

Wounded quarks and multiplicity at relativistic ion colliders

In this paper, we propose a parameterization which is based on a phenomenological model involving the wounded quarks interactions for explaining the average charged particle multiplicity $\ < n_{ch}\ >$, the central pseudo-rapidity density $\ < (dn/d\eta)_{\eta=0}\ >$ and complete rapidity dependence of $dn/d{\eta}$ in relativistic heavy-ion collider experiments. The model also interrelates nucleus-nucleus (A-A) collisions with p-A and p-p interactions. Our parameterization rests on simple assumptions regarding mean number of participating quarks and their average number of collisions. The results for $\ < n_{ch}\ >$ and their variations with the mass number of colliding nuclei, center-of-mass energy ($\sqrt{s_{NN}}$) and collision centrality are well supported by the available experimental data. Finally we give the predictions from our model for A-A collisions at the Large Hadron Collider (LHC) and Compressed Baryonic Matter (CBM) experiments. Our results indicate the existence of a possible universal production mechanism for p-p, p-A and A-A collisions.

Laboratory Portrait of the Relativistic Heavy Ion Collider

The Relativistic Heavy Ion Collider (RHIC), located at Brookhaven National Laboratory (BNL) on Long Island, is the largest facility for basic nuclear physics research in the United States. Operated by the U.S. Department of Energy (DOE), it serves well over 1,000 international users. The collider itself, and its two major detectors, PHENIX and STAR, began operations in 2000 and have been steadily improved and upgraded each year since. Two smaller detectors, PHOBOS and BRAHMS, completed their missions in 2005 and 2006, respectively. To date, RHIC experiments have produced over 300 refereed papers with more than 20,000 citations, over 200 Ph.D.s, and a number of major scientific awards and accelerator technology innovations.

η/sRatio in Finite Nuclei

Experiments at the Relativistic Heavy Ion Collider (RHIC) suggest that the state of matter produced in the experiments has a low shear-viscosity to entropy-density ratio $\ensuremath{\eta}/s$. We ask here the following question: what is this ratio in the usual finite nuclei at low temperature? We use the experimental and theoretical results for the widths of giant vibrational states in nuclei in order to calculate the above ratio. We find that the values of $\ensuremath{\eta}/s$ are not very different from the ones found in the RHIC experiments.

Long range correlations and the soft ridge in relativistic nuclear collisions

Relativistic Heavy Ion Collider experiments exhibit correlations peaked in relative azimuthal angle and extended in rapidity. Called the ridge, this peak occurs both with and without a jet trigger. We argue that the untriggered ridge arises when particles formed by flux tubes in an early Glasma stage later manifest transverse flow. Combining a blast wave model of flow fixed by single-particle spectra with a simple description of the Glasma, we find excellent agreement with current data.

The strongly coupled quark–gluon plasma created at RHIC**Work supported by US Department of Energy, grant DE-FG02-01ER41190.

The relativistic heavy-ion collider (RHIC) was built to re-create and study in the laboratory the extremely hot and dense matter that filled our entire universe during its first few microseconds. Its operation since June 2000 has been extremely successful, and the four large RHIC experiments have produced an impressive body of data which indeed provide compelling evidence for the formation of thermally equilibrated matter at unprecedented temperatures and energy densities—a ‘quark–gluon plasma (QGP)’. A surprise has been the discovery that this plasma behaves like an almost perfect fluid, with extremely low viscosity. Theorists had expected a weakly interacting gas of quarks and gluons, but instead we seem to have created a strongly coupled plasma liquid. The experimental evidence strongly relies on a feature called ‘elliptic flow’ in off-central collisions, with additional support from other observations. This paper explains how we probe the strongly coupled QGP, describes the ideas and measurements which led to the conclusion that the QGP is an almost perfect liquid, and shows how they tie relativistic heavy-ion physics into other burgeoning fields of modern physics, such as strongly coupled Coulomb plasmas, ultracold systems of trapped atoms and superstring theory.

Long range untriggered two particle correlations

Relativistic Heavy Ion Collider experiments exhibit correlations peaked in relative azimuthal angle and extended in rapidity. Called the ridge, this peak occurs both with and without a jet trigger. We argue that the untriggered ridge arises when particles formed by flux tubes in an early glasma stage later manifest transverse flow. Combining a blast wave model of flow fixed by single-particle spectra with a simple description of the glasma, we find excellent agreement with current data.

The Magnetic Component of Quark-Gluon Plasma is also a Liquid

The magnetic scenario for strongly coupled quark-gluon plasma (sQGP) emphasizes the role of monopoles near or above the deconfinement temperature, and specifically predicts that they help reduce its viscosity by the "magnetic bottle" effect. Here we present results for monopole-(anti)monopole correlation functions from our classical molecular dynamics simulations, which are in good agreement with the lattice results. By analysis of the correlation functions, we show that the magnetic Coulomb coupling runs in the direction opposite to the electric one. However, as T decreases to T_(c), the magnetic coupling never gets too weak, with the plasma parameter always large enough (Gamma>1). This nicely agrees with empirical evidence from the BNL Relativistic Heavy Ion Collider experiments, implying that magnetic objects should also form a good liquid with low viscosity.

Toward an understanding of the single electron data measured at the BNL Relativistic Heavy Ion Collider (RHIC)

High transverse momentum (${p}_{T}$) single nonphotonic electrons which have been measured in the RHIC experiments come dominantly from heavy meson decay. The ratio of their ${p}_{T}$ spectra in $\mathit{pp}$ and $\mathit{AA}$ collisions [${R}_{\mathit{AA}}({p}_{T})$] reveals the energy loss of heavy quarks in the environment created by $\mathit{AA}$ collisions. Using a fixed coupling constant and the Debye mass (${m}_{D}\ensuremath{\approx}\mathit{gT}$) as the infrared regulator, perturbative QCD (pQCD) calculations are not able to reproduce the data, neither the energy loss nor the azimuthal $({v}_{2})$ distribution. Employing a running coupling constant and replacing the Debye mass by a more realistic hard thermal loop (HTL) calculation, we find a substantial increase in the collisional energy loss, which brings the ${v}_{2}({p}_{T})$ distribution as well as ${R}_{\mathit{AA}}({p}_{T})$ to values close to the experimental ones without excluding a contribution from radiative energy loss.

Extracting Boer-Mulders functions fromp+DDrell-Yan processes

We extract the Boer-Mulders functions of valence and sea quarks in the proton from unpolarized $p+D$ Drell-Yan data measured by the FNAL E866 Collaboration. Using these Boer-Mulders functions, we calculate the $\mathrm{cos}2\ensuremath{\phi}$ asymmetries in unpolarized $pp$ Drell-Yan processes, both for the FNAL E866/NuSea and the BNL Relativistic Heavy Ion Collider experiments. We also estimate the $\mathrm{cos}2\ensuremath{\phi}$ asymmetries in the unpolarized $p\overline{p}$ Drell-Yan processes at GSI.

Systematic studies of the centrality andsNNdependence of thedET/dηanddNch/dηin heavy ion collisions at midrapidity

The PHENIX experiment at the relativistic heavy ion collider (RHIC) has measured transverse energy and charged particle multiplicity at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at center-of-mass energies $\sqrt{{s}_{\mathrm{NN}}}=19.6,130$, and $200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ as a function of centrality. The presented results are compared to measurements from other RHIC experiments and experiments at lower energies. The $\sqrt{{s}_{\mathrm{NN}}}$ dependence of $dE{}_{T}/d\ensuremath{\eta}$ and $dN{}_{\mathrm{ch}}/d\ensuremath{\eta}$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE{}_{T}/d\ensuremath{\eta}$ and $dN{}_{\mathrm{ch}}/d\ensuremath{\eta}$ is similar at all measured incident energies. At RHIC energies, the ratio of transverse energy per charged particle was found to be independent of centrality and growing slowly with $\sqrt{{s}_{\mathrm{NN}}}$. A survey of comparisons between the data and available theoretical models is also presented.

Recent Results from the RHIC Experiments Searching for QGP

The relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory (BNL) have provided Au+Au, d+Au and p+p collisions at s N N = 200 GeV. The prime purpose of the heavy ion collisions is to produce and to study the property of a new state of matter: Quark Gluon Plasma (QGP) at an extreme conditions; high temperature and density. The several experiments (STAR, PHENIX, BRAHMS and PHOBOS) at RHIC are trying to find signals of the QGP. Small collision systems (d+Au and p+p) were also examined to establish the bases for the comparison with the heavy ion collisions with Au+Au. The jet suppression at high p T found in Au+Au collision was an unique feature of the heavy ion collisions, where jets were even slightly enhanced in the light system with d+Au collisions. This might be explained by the energy loss of high energy partons traveling through the QGP matter. Another striking evidence found in the heavy ion collisions was the quark number scaling of the elliptic flow parameter: v 2 , which might reflect the existence of the QGP phase in the earlier time when v 2 is generated. The chemical and thermal freeze-out parameters give the later history of the collision, having in mind that the trend of the chemical freeze-out temperature is approaching to the expected phase boundary as a function of the beam energy, the system might have already been in the QGP phase in earlier time before the hadronization.

Observability of neutron stars with quarks

Recent Chandra observations have raised expectations that the objects RX J185635-3754 and 3C58 are either bare strange quark stars or stars with extended quark cores. However, these observations can also be interpreted in terms of normal neutron stars. Essential requirements for either explanation are that they simultaneously account for the observed (i) spectral features (i.e., thermal or nonthermal, possible lines), (ii) bounds on the inferred mass (M) and radius (R), and (iii) the cooling curves (effective temperatures T and luminosities L vs. age). Compact stars offer the promise of delineating QCD at finite baryon density (Lattimer and Prakash, 2001) in a fashion complementary to relativistic heavy ion collider experiments, which largely address the finite temperature, but baryon poor regime.

Development of large linear silicon drift detectors for the STAR experiment at RHIC

Large area linear Silicon Drift Detectors (SDD) are being developed for high energy and relativistic heavy ion collider experiments. SDDs have been proposed for the inner tracking detector in the STAR experiment at the BNL relativistic heavy ion collider to become operational in 1999. The Silicon Vertex Tracker (SVT) will consist of a three layer barrel structure composed of 216 individual detectors, each 6.3 × 6.3 cm 2. Prototypes, including one-way drift detectors (4.5 × 4.5 cm 2) and bi-directional drift detectors (6 × 6 cm 2) have been manufactured,and their properties have been studied. Design considerations, as well as test results, are presented in this article. Recent work has focused on minimizing the inactive guard structure area in order to optimize tracking efficiency. Particular attention is given to discussion of parameters that are sensitive to the reduced guard structure area, such as leakage current, maximum voltage and drift non-linearities.

Signals of quark-gluon plasma

Production and observation of a quark-gluon plasma (QGP) is one of the most ambitious goals of the ultrarelativistic heavy ion experiments being carried out at CERN's super proton synchrotron (SPS) and at Brookhaven's Alternating Gradient Synchrotron (AGS). Future experiments at Brookhaven's Relativistic Heavy Ion Collider (RHIC) and at CERN's Large Hadron Collider (LHC) will give a new dimension to this search. In this review, the physics of QGP is presented with particular emphasis on its promising signatures existing in the literature. We hope that the present survey will lead us to identify some unambiguous signatures of QGP before the advent of RHIC and LHC experiments.