arXiv subjects

Jörg Ruppert

Publications and source records attributed to Jörg Ruppert.

8 recordsLinked to original sources

arXiv2009

Systematic Comparison of Jet Energy-Loss Schemes in a realistic hydrodynamic medium

We perform a systematic comparison of three different jet energy-loss approaches. These include the Armesto-Salgado-Wiedemann scheme based on the approach of Baier-Dokshitzer-Mueller-Peigne-Schiff and Zakharov (BDMPS-Z/ASW), the Higher Twist approach (HT) and a scheme based on the approach of Arnold-Moore-Yaffe (AMY). In this comparison, an identical medium evolution will be utilized for all three approaches: not only does this entail the use of the same realistic three-dimensional relativistic fluid dynamics (RFD) simulation, but also includes the use of identical initial parton-distribution functions and final fragmentation functions. We are, thus, in a unique position, not only to isolate fundamental differences between the various approaches, but also to make rigorous calculations for different experimental measurements using "state of the art" components. All three approaches are reduced to a version which contains only one free tunable parameter, this is then related to the well known transport parameter $\hat{q}$. We find that the parameters of all three calculations can be adjusted to provide a good description of inclusive data on $R_{AA}$ versus transverse momentum. However, we do observe slight differences in their predictions for the centrality and azimuthal angular dependence of $R_{AA}$ vs. $p_T$. We also note that the value of the transport coefficient $\hat{q}$ in the three approaches to describe the data differs significantly.

nucl-th↗

arXiv2008

Radiative jet energy loss in a three-dimensional hydrodynamical medium and high $p_T$ azimuthal asymmetry of $π_0$ suppression at mid and forward rapidity at RHIC

The nuclear modification factor $R_{AA}$ for $π_0$ production in Au+Au collisions at $\sqrt{s}=200$ AGeV is calculated, and studied at high transverse momenta $p_T$. The soft thermalized nuclear medium is described within the framework of relativistic ideal three-dimensional hydrodynamics. The energy loss of partonic jets is evaluated in the context of gluon bremsstrahlung in the thermalized partonic matter. We provide a systematic analysis of the azimuthal asymmetry of $π_0$ suppression at high $p_T$ in central and non-central collisions, at mid and forward rapidity. The determination of $R_{AA}$ as a function of $p_T$, at different azimuthal angles, and different rapidities makes for a stringent test of our theoretical understanding of jet energy loss over a variety of in-medium path lengths, temperatures and initial partonic jet energies. This lays the groundwork for a precise tomography of the nuclear medium.

hep-ph↗

arXiv2005

Mass and Width of the Rho Meson in a Nuclear Medium from Brown-Rho Scaling and QCD Sum Rules

We explore the range of values of the in-medium width of a $ρ$-meson at rest which is compatibale with the QCD sum rule approach in a nuclear medium assuming vector meson dominance and a Brown-Rho scaling law of the $ρ$-meson mass with the chiral condensate. The lower and upper bounds for the in-medium width are found to be strongly increasing with the decreasing mass of the $ρ$-meson (increasing nuclear density). We also study the bounds for the in-medium width in models not satisfying the Brown-Rho scaling law. It is shown that the in-medium width depends on how rapidly the mass decreases in comparison to the change of the quark condensate. The bounds for the in-medium width increase with density only if the relative change of the quark condensate is stronger than the relative decrease in mass. This is important for experimental tests of the Brown-Rho scaling paradigm and other dropping $ρ$-mass scenarios.

hep-ph↗

arXiv2005

Focus talk on interactions between jets and medium

The energy and momentum lost by a hard parton propagating through hot and dense matter has to be redistributed during the nuclear medium evolution. Apart from heating the medium, there is the possibility that collective modes are excited leading to the emergence of Mach cones or Cherenkov radiation. Recent two-particle correlation measurements by STAR \cite{Wang:2004kf} and PHENIX \cite{Adler:2005ee} at RHIC indicate that such phenomena may play an important role in understanding the jet-medium interactions. Possible collective modes are discussed and it is demonstrated that Mach cones as created by colorless or colored sound are a possible explanation of the hardronic two-particle correlation data.

hep-ph↗

arXiv2005

A Colorful Wake for Gerhard Soff

We calculate the wake induced in a hot QCD plasma by a fast parton in the framework of linear response theory. We discuss two scenarios: ($i$) a weakly coupled quark-gluon plasma described by hard-thermal loop perturbation theory and ($ii$) a strongly coupled quark-gluon plasma which resembles a quantum liquid. We show that a Mach cone can appear in the second scenario, but not in the first one

nucl-th↗

arXiv2005

Probing Color Response - Wakes in a Color Plasma

The wake induced in a hot QCD medium by a high momentum parton (jet precursor) is calculated in the framework of linear response theory. Two different scenarios are discussed: a weakly coupled quark gluon plasma (pQGP) as described by hard-thermal loop (HTL) perturbation theory and a strongly cupled QGP (sQGP) with the properties of a quantum liquid. In the latter case the wake could exhibit a pronounced Mach cone structure. This physical mechanism could be important for the understanding of preliminary data from the PHENIX and STAR experiments at RHIC on the angular distribution of low-pt secondaries stemming from the away-side jet which indicate maxima at $Δϕ=π\pm 1.1$.

hep-ph↗

arXiv2005

Non-perturbative finite $T$ broadening of the $ρ$ meson and dilepton emission in heavy ion-collisions

We study self-consistently the finite $T$ broadening of the $ρ$-meson and its implications for dilepton emission in heavy ion-collisions. For this purpose finite width effects at finite temperature due to the $ρ$-$π$ interaction are investigated in a self-consistent $Φ$-functional approach. The temperature dependence of the $ρ$-meson and pion spectral functions and self-energies is discussed. The spectral functions show considerable broadening in comparison with a perturbative calculation on the one-loop level. Using these spectral functions, we make a comparison to dilepton emission data from the CERES NA49 collaboration employing a parametrized fireball evolution model of collision. We demonstrate that these non-perturbative finite width effects are in-medium modifications relevant to the understanding of the enhancement of the low invariant mass spectrum of dileptons emitted in A-A collisions.

nucl-th↗

arXiv2004

The Quark-Mass Dependence of T_C in QCD: Working up from m=0 or down from m=infinity ?

We analyze the dependence of the QCD transition temperature on the quark (or pion) mass. We find that a linear sigma model, which links the transition to chiral symmetry restoration, predicts a much stronger dependence of T_c on m_pi than seen in present lattice data for m_pi >~ 0.4 GeV. On the other hand, working down from m_pi=infinity, an effective Lagrangian for the Polyakov loop requires only small explicit symmetry breaking, b_1 ~ exp(-m_pi), to describe T_c(m_pi) in the above mass range. Physically, this is a consequence of the flat potential (large correlation length) for the Polyakov loop in the three-color pure gauge theory at T_c. We quantitatively estimate the end point of the line of first order deconfining phase transitions: m_pi = 1.8 GeV and Tc = 240 MeV for three flavors and three colors.

hep-ph↗