arXiv subjects

Jorg Ruppert

Publications and source records attributed to Jorg Ruppert.

16 recordsLinked to original sources

arXiv2009

Jet energy loss, photon production, and photon-hadron correlations at RHIC

Jet energy loss, photon production and photon-hadron correlations are studied together at high transverse momentum in relativistic heavy-ion collisions at RHIC energies. The modification of hard jets traversing a hot and dense nuclear medium is evaluated by consistently taking into account induced gluon radiation and elastic collisions. The production of high transverse momentum photons in Au+Au collisions at RHIC is calculated by incorporating a complete set of photon-production channels. Comparison with experimental photon production and photon-hadron correlation data is performed, using a (3+1)-dimensional relativistic hydrodynamic description of the thermalized medium created in these collisions. Our results demonstrate that the interaction between the hard jets and the soft medium is important for the study of photon production and of photon-hadron correlation at RHIC.

hep-ph↗

arXiv2007

Mach cone shock waves at RHIC

Energy and momentum lost by hard jets propagating through hot and dense nuclear matter have to be redistributed in the medium. It has been conjectured that collective sound modes are excited. Those lead to Mach cone nuclear shock waves in the nuclear medium that are shown to account for three and four particle angular correlation structures of hadrons with a (semi-)hard trigger hadron in heavy-ion collisions at RHIC.

hep-ph↗

arXiv2007

Low Mass Dimuons Produced in Relativistic Nuclear Collisions

The NA60 experiment has measured low-mass muon pair production in In-In collisions at 158 A GeV with unprecedented precision. We show that this data is reproduced very well by a dynamical model with parameters scaled from fits to measurements of hadronic transverse mass spectra and Hanbury-Brown and Twiss correlations in Pb-Pb and Pb-Au collisions at the same energy. The data is consistent with in-medium properties of $ρ$ and $ω$-mesons at finite temperature and density as deduced from empirical forward-scattering amplitudes. Inclusion of the vacuum decay of the $ρ$-meson after freeze-out is necessary for an understanding of the mass and transverse momentum spectrum of dimuons with $M \apprle 0.9 {\rm GeV}/c^2$.

hep-ph↗

arXiv2007

Radiative and Collisional Jet Energy Loss in the Quark-Gluon Plasma at RHIC

We calculate and compare bremsstrahlung and collisional energy loss of hard partons traversing a quark-gluon plasma. Our treatment of both processes is complete at leading order in the coupling and accounts for the probabilistic nature of the jet energy loss. We find that the nuclear modification factor $R_{AA}$ for neutral $π^0$ production in heavy ion collisions is sensitive to the inclusion of collisional and radiative energy loss contributions while the averaged energy loss only slightly increases if collisional energy loss is included for parent parton energies $E\gg T$. These results are important for the understanding of jet quenching in Au+Au collisions at $200 {\rm AGeV}$ at RHIC. Comparison with data is performed applying the energy loss calculation to a relativistic ideal (3+1)-dimensional hydrodynamic description of the thermalized medium formed at RHIC.

hep-ph↗

arXiv2007

Three-particle azimuthal correlations and Mach shocks

Measurements of angular correlations of hadrons with a (semi-)hard trigger hadron in heavy-ion collisions at RHIC show large angular structures opposite to the trigger which were a priori unexpected. These away side large angle correlations were first observed in two-particle correlations and have recently also been investigated in three-particle correlation measurements by the PHENIX and STAR collaborations. We show that the correlation signal can be understood in terms of sonic shockwaves ('Mach cones') excited by hard partons supersonically traversing the medium. The propagation of such shocks through the medium evolution is treated in a Monte Carlo (MC) framework. We demonstrate that two- and especially three-particle correlations offer non-trivial insight into the medium-averaged speed of sound and the evolution of flow. Our findings imply that the assumption of "deflected jets" is not necessary to account for the observed correlations.

hep-ph↗

arXiv2007

What to learn from dilepton transverse momentum spectra in heavy-ion collisions?

Recently the NA60 collaboration has presented high precision measurements of dimuon spectra double differential in invariant mass $M$ and transverse pair momentum $p_T$ in In-In collisions at $158 {\rm AGeV}$. While the $M$-dependence is important for an understanding of in-medium changes of light vector mesons and is $p_T$ integrated insensitive to collective expansion, the $p_T$-dependence arises from an interplay between emission temperature and collective transverse flow. This fact can be exploited to derive constraints on the evolution model and in particular on the contributions of different phases of the evolution to dimuon radiation into a given $M$ window. We present arguments that a thermalized evolution phase with $T > 170 {\rm MeV}$ leaves its imprint on the spectra.

hep-ph↗

arXiv2007

The rapidity structure of Mach cones and other large angle correlations in heavy-ion collisions

The pattern of angular correlations of hadrons with a (semi-)hard trigger hadron in heavy-ion collisions has attracted considerable interest. In particular, unexpected large angle structures on the away side (opposite to the trigger) have been found. Several explanations have been brought forward, among them Mach shockwaves and Cherenkov radiation. Most of these scenarios are characterized by radial symmetry around the parton axis, thus angular correlations also determine the rapidity dependence of the correlation. If the observed correlations are remnants of an away side parton after interaction with the medium created in the collision, pQCD allows to calculate the distribution $P(y)$ of the away side partons in rapidity. The measured correlation then arises as a folding of $P(y)$ and the rapidity structure of the correlation taking into account the detector acceptance. This places non-trivial and rather stringent constraints on the underlying scenario. We investigate these dependences and demonstrate that Mach shockwaves survive this folding procedure well whereas Cherenkov radiation scenarios face new challenges.

hep-ph↗

arXiv2007

Prospects of Medium Tomography using 2-,3- and 4-Particle Correlations for a (semi-)hard Trigger

Hard partons propagating through hot and dense matter lose energy, leading to the observed depletion of hard hadron spectra in nucleus nucleus collision as compared to scaled proton proton collisions. This lost energy has to be redistributed in the medium due to the conservation of energy, which is manifest in the p_T dependence of the angular correlation pattern of hadrons associate with a (semi-) hard trigger. While at low p_T a splitting of a broad peak is observed, at high p_T the structure shows vacuum width, albeit with reduced yield. This sugests a transfer of energy from hard partons to a collectively recoiling medium. We present a systematic study of these phenomena using a realistic medium evolution and a Monte-Carlo simulation of the experimental trigger and show what information about the medium can be derived from multiparticle correlations.

hep-ph↗

arXiv2006

Dimuon transverse momentum spectra as a tool to characterize the emission region in heavy-ion collisions

Previous dilepton measurements in heavy-ion collisions have mainly focused on invariant mass spectra to clarify in-medium changes of vector meson properties. However, a dimuon is characterized by two scales -- invariant mass $M$ and transverse momentum $p_T$. Like transverse momentum spectra of hadrons, $p_T$ spectra of dileptons arise from an interplay between emission temperature and collective transverse flow, whereas the invariant mass is insensitive to flow. Having two control parameters of which only one is sensitive to flow allows at given $M$ to characterize the emission region in terms of average temperature and flow. Thus, one is able to study what phases of the fireball evolution radiate into a given mass window. We demonstrate this technique using the dimuon transverse momentum spectra measured by the NA60 collaboration and present strong arguments that a thermalized evolution phase with $T > 170$ MeV leaves an imprint in the spectra.

hep-ph↗

arXiv2006

Reply to 'Comment on: 'Non-perturbative finite T broadening of the rho meson and dilepton emission in heavy ion-collisions''

Nota bene: the numerical calculation underlying Version 1 of this reply and the original work Phys.Rev. C71:064903,2005 contains a basic numerical error (wrong factor in the self-energy formulas of Phys. Rev.C71:064903,2005). This renders the numerical results presented there and in Version 1 of the reply invalid and enforces a careful reinvestigation of Phys. Rev.C71:064903,2005 and the reply. Calculations for an erratum of Phys. Rev. C71:064903,2005 are in progress.

nucl-th↗

arXiv2006

What does the rho-meson do? In-medium mass shift scenarios versus hadronic model calculations

The NA60 experiment has studied low-mass muon pair production in In-In collisions at $158 {\rm AGeV}$ with unprecedented precision. With these results there is hope that the in-medium modifications of the vector meson spectral function can be constrained more thoroughly than before. We investigate in particular what can be learned about collisional broadening by a hot and dense medium and what constrains the experimental results put on in-medium mass shift scenarios. The data show a clear indication of considerable in-medium broadening effects but disfavor mass shift scenarios where the $ρ$-meson mass scales with the square root of the chiral condensate. Scaling scenarios which predict at finite density a dropping of the $ρ$-meson mass that is stronger than that of the quark condensate are clearly ruled out since they are also accompanied by a sharpening of the spectral function.

nucl-th↗

arXiv2006

What the NA60 dilepton data can tell

The NA60 experiment has studied low-mass muon pair production in In-In collisions at 158 AGeV with unprecedented precision. Thus, there is hope that the in-medium modifications of the vector meson spectral function can be constrained more thoroughly than from previous experiments. Towards this goal, we present a study comparing different models for the in-medium modification of vector mesons. In particular, we investigate what can be learned about collisional broadening by a medium at finite temperature and baryon density and what model independent constraints can be obtained from the data. Of special relevance is a comparison to $p_T$-cuts of the dilepton spectra. Those not only provide independent tests of the evolution model and $p_T$-dependence of the spectral function but also unambiguously decide if the observed yield in the higher mass spectrum $M > 1 {\rm GeV}$ is mainly due to the hot phase of the evolution or four pion annihilation processes.

hep-ph↗

arXiv2005

Mach cones in an evolving medium

The energy and momentum lost by a hard parton propagating through hot and dense matter has to be redistributed in the nuclear medium. Apart from heating the medium, there is the possibility that collective modes are excited. We outline a formalism that can be used to track the propagation of such a mode through the evolving medium if its dispersion relation is known. Under the assumption that a sound wave is created, we track the jet energy loss as a function of spacetime and follow the resulting mach cone throughout the fireball evolution.We compare with the angular correlation pattern of hard hadrons as obtained by the PHENIX collaboration and find good agreement with the data provided that a substantial fraction of jet energy ($\sim$ 90%) is deposited into a propagating mode and that the hot matter can be characterized by an EOS with a soft point (not necessarily a mixed phase).

hep-ph↗

arXiv2005

Jet-medium interactions: wakes in the QCD medium

We calculate the wake induced in a hot, dense QCD medium by a fast parton in the framework of linear response theory. We discuss two different scenarios: (i) a weakly coupled quark gluon plasma (pQGP) described by hard-thermal loop (HTL) perturbation theory and (ii) a scenario where the plasma has the properties of a quantum liquid. We show that Mach cones can appear in the second scenario, but not in the first one.

hep-ph↗

arXiv2005

Flow dependence of high $p_T$ parton energy loss in heavy-ion collisions

The measured transverse momentum spectra and HBT correlations of bulk (i.e. low $p_T$) matter can be well explained by assuming that the soft sector of particles produced in ultrarelativistic heavy-ion collisions is (approximately) thermalized and undergoes collective accelerated expansion in both longitudinal and transverse direction. However, this implies that bulk matter will have a non-vanishing flow component transverse to the trajectory of a high $p_T$ partonic jets. In general, this will increase the energy loss experienced by the jet parton and modify the shape of the jet cone. In this paper, we present a systematic study of the magnitude of the additional energy loss induced by flow under realistic assumptions for the medium evolution. We argue that a perturbative QGP description may be sufficient for the measured $R_{AA}$ if flow during the medium evolution is taken into account properly.

hep-ph↗

arXiv2005

Waking the Colored Plasma

We calculate the wake induced in a hot, dense QCD medium by a fast parton in the framework of linear response theory. We discuss two different scenarios: a weakly coupled quark gluon plasma (pQGP) described by hard-thermal loop (HTL) perturbation theory and a strongly coupled QGP (sQGP), which had the properties of a quantum liquid.

hep-ph↗