Thoughts on opportunities from high-energy nuclear collisions
This document summarizes thoughts on opportunities from high-energy nuclear collisions.
hep-ph↗
arXiv subjects
Rene Bellwied
Publications and source records attributed to Rene Bellwied.
Determination of freeze-out conditions from fluctuation observables measured at RHIC
We extract chemical freeze-out conditions via a thermal model approach from fluctuation observables measured at RHIC and compare with results from lattice QCD and statistical hadronization model fits. The possible influence of additional critical and non-critical fluctuation sources not accounted for in our analysis is discussed.
hep-ph↗
Freeze-out conditions from net-proton and net-charge fluctuations at RHIC
We calculate ratios of higher-order susceptibilities quantifying fluctuations in the number of net protons and in the net-electric charge using the Hadron Resonance Gas (HRG) model. We take into account the effect of resonance decays, the kinematic acceptance cuts in rapidity, pseudo-rapidity and transverse momentum used in the experimental analysis, as well as a randomization of the isospin of nucleons in the hadronic phase. By comparing these results to the latest experimental data from the STAR collaboration, we determine the freeze-out conditions from net-electric charge and net-proton distributions and discuss their consistency.
hep-ph↗
Is there a flavor hierarchy in the deconfinement transition of QCD?
We present possible indications for flavor separation during the QCD crossover transition based on continuum extrapolated lattice QCD calculations of higher order susceptibilities. We base our findings on flavor specific quantities in the light and strange quark sector. We propose a possible experimental verification of our prediction, based on the measurement of higher order moments of identified particle multiplicities. Since all our calculations are performed at zero baryochemical potential, these results are of particular relevance for the heavy ion program at the LHC.
hep-lat↗
Hadron formation in the deconfined matter at RHIC and LHC
We have studied the probability of two succinct particle production mechanisms, likely to occur in the transition from the deconfined medium produced in RHIC and LHC heavy ion collisions back to the hadron gas, which is abundant at lower temperatures. Evidence has been found for in-medium fragmentation of non-equilibrated partons in the deconfined medium as well as bound state formation in the quark-gluon phase itself, as described by lattice QCD . Through the comparison to PNJL model calculations we attempt to quantify an extended phase of mixed degrees of freedom in a temperature range just above the QCD transition temperature. The extracted hadron formation probabilities exhibit flavor and baryon number dependencies, which are experimentally verifiable. We confront the calculations of the non-equilibrium and equilibrium particle production in heavy ion collisions with measurements from RHIC and LHC.
hep-ph↗
Statistical hadronization phenomenology in $K/π$ fluctuations at ultra-relativistic energies
We discuss the information that can be obtained from an analysis of fluctuations in heavy ion collisions within the context of the statistical model of particle production. We then examine the recently published experimental data on ratio fluctuations, and use it to obtain constraints on the statistical properties (physically relevant ensemble, degree of chemical equilibration, scaling across energies and system sizes) and freeze-out dynamics (amount of reinteraction between chemical and thermal freeze-out) of the system.
nucl-th↗
Are there hadronic bound states above the QCD transition temperature?
Recent lattice QCD calculations, at physical pion masses and small lattice spacings that approach the continuum limit, have revealed that non-diagonal quark correlators above the critical temperature are finite up to about 2 $T_c$. Since the transition from hadronic to free partonic degrees of freedom is merely an analytic cross-over, it is likely that, in the temperature regime between 1-2 $T_c$, quark and gluon quasiparticles and pre-hadronic bound states can coexist. The correlator values, in comparison to PNJL model calculations beyond mean-field, indicate that at least part of the mixed phase resides in color-neutral bound states. A similar effect was postulated for the in-medium fragmentation process, i.e. for partons which do not thermalize with the system and thus constitute the non-equilibrium component of the particle emission spectrum from a deconfined plasma phase. Here, for the first time we investigate the likelihood of forming bound states also in the equilibrated, parton dominated phase above $T_c$ which is described by lattice QCD.
hep-ph↗
ALICE EMCal Physics Performance Report
The ALICE detector at the LHC (A Large Ion Collider Experiment) will carry out comprehensive measurements of high energy nucleus-nucleus collisions, in order to study QCD matter under extreme conditions and the phase transtion between conïned matter and the Quark-Gluon Plasma (QGP). This report presents our current state of understanding of the Physics Performance of the large acceptance Electromagnetic Calorimeter (EMCal) in the ALICE central detector. The EMCal enhances ALICE's capabilities for jet measurements. The EMCal enables triggering and full reconstruction of high energy jets in ALICE, and augments existing ALICE capabilities to measure high momentum photons and electrons. Combined with ALICE's excellent capabilities to track and identify particles from very low pT to high pT, the EMCal enables a comprehensive study of jet interactions in the medium produced in heavy ion collisions at the LHC.
physics.ins-det↗
Physics with the ALICE Electromagnetic Calorimeter
I will present physics measurements which are achievable in the ALICE experiment at the LHC through the inclusion of a new electromagnetic calorimeter. I will focus on jet measurements in proton proton and heavy ion collisions. Detailed simulations have been performed on jet reconstruction, jet triggering, heavy flavor jet reconstruction through electron identification, gamma-jet reconstruction and the measurements of identified hadrons and resonances in jets. I will show the physics capabilities which are made possible through the combination of calorimeter information with the other detector components in ALICE.
nucl-ex↗
Future Experiments in Relativistic Heavy Ion Collisions
The measurements at RHIC have revealed a new state of matter, which needs to be further characterized in order to better understand its implications for the early evolution of the universe and QCD. I will show that, in the near future, complementary key measurements can be performed at RHIC, LHC, and FAIR. I will focus on results than can be obtained using identified particles, a probe which has been the basis for this conference over the past three decades. The sophisticated detectors, built and planned, for all three accelerator facilities enable us to measure leptons, photons, muons as well as hadrons and resonances of all flavors almost equally well, which makes these experiments unprecedented precision tools for the comprehensive understanding of the physics of the early universe.
nucl-ex↗
What are the degrees of freedom in the partonic fluid at RHIC ?
Recent RHIC data show evidence of multiple hadron production mechanisms in heavy ion collisions compared to simple fragmentation in vacuum. I will review the measurements of collective flow, high momentum quenching, and two particle angular correlations to show that neither thermal production nor string fragmentation can describe the abundances, the angular distributions or the kinematic properties of all hadrons produced at RHIC. The proposed new hadronization mechanisms not only serve as evidence for a deconfined partonic phase of matter, but also for strong coupling of the degrees of freedom in the deconfined phase. I will point out a surprising lack of flavor dependence in these properties at RHIC, though, which might have to lead to further revisions of our understanding of the relevant degrees of freedom in the partonic phase and during the hadronization process.
nucl-ex↗
Particle production mechanisms from RHIC to LHC
I will review RHIC data with respect to the intriguing possibility that the hadron production mechanism in the produced partonic medium might be different than in vacuum. I will use the measurements of collective features, such as flow and quenching of identified particles, to show that different regions of the particle momentum spectrum are likely populated through different mechanisms, and that the medium seems to play an important role in hadronization. Finally I will address the question whether the different initial conditions achievable in heavy ion collisions at LHC energies, compared to RHIC, might affect the properties of the deconfined quark-gluon phase and its hadronization to baryonic matter.
nucl-ex↗
STAR results from the first RHIC year
An overview is presented of the results of the STAR experiment from the analysis of Au+Au collisions at $\sqrt{s_{_{NN}}} = 130$ GeV acquired during the first year of RHIC operation. The transverse momentum distribution of negative hadrons has been studied out to 6 GeV/$c$ in central Au+Au collisions and elliptic flow measurements out to 4.5 GeV/$c$ in non-central collisions. This allows us to study hard processes and potentially effects of nuclear matter on parton propagation. Soft processes, which dominate particle production below around 2 GeV/$c$, have also been studied through the identified spectra of kaons, $\bar{p}$, and strange baryons.
hep-ph↗
Is Strangeness still interesting at RHIC ?
With the advent of the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL), Heavy Ion Physics will enter a new energy regime. The question is whether the signatures proposed for the discovery of a phase transition from hadronic matter to a Quark Gluon Plasma (QGP), that were established on the basis of collisions at the BEVALAC, the AGS, and the SPS, respectively, are still useful and detectable at these high incident energies. In the past two decades, measurements related to strangeness formation in the collision were advocated as potential signatures and were tested in numerous fixed target experiments at the AGS and the SPS. In this article I will review the capabilities of the RHIC detectors to measure various aspects of strangeness, and I will try to answer the question whether the information content of those measurements is comparable to the one at lower energies.
nucl-ex↗