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Register a new userTowards a qualitative hadron-parton correspondence in the nuclear modification factor
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In this work, we propose a method to show the correspondence between hadron and its quark component nuclear modification factors. A parton and hadron cascade model PACIAE based on the PYTHIA6.4 is employed to calculate the hadron and its quark component nuclear modification factors in the 0-5% most central $Pb+Pb$ collisions at $sqrt{s_{NN}}$=2.76 TeV. It turns out that the hadron nuclear modification factor is usually smaller than that of its quark component. On the other hand, it is shown in our study that the dead cone effect is more likely to be identified with the quarks and mesons but not with the baryon states obviously.
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The nuclear modification factor is derived using Tsallis non-extensive statistics in relaxation time approximation. The variation of nuclear modification factor with transverse momentum for different values of non-extensive parameter, $q$, is also observed. The experimental data from RHIC and LHC are analysed in the framework of Tsallis non-extensive statistics in a relaxation time approximation. It is shown that the proposed approach explains the $R_{AA}$ of all particles over a wide range of transverse momenta but doesnt seem to describe the rise in $R_{AA}$ at very high transverse momenta.
The event generator based on the higher-twist energy loss formalism -- Modular All Twist Transverse-scattering Elastic-drag and Radiation (MATTER) -- is further developed and coupled to a hydrodynamic model for studying jet modification in relativistic nuclear collisions. The probability of parton splitting is calculated using the Sudakov form factor that is constructed by a combination of vacuum and medium-induced splitting functions; and the full parton showers are simulated, including both energy-momentum and space-time evolutions of all jet partons. With the assumption that partons below a virtual scale of 1 GeV is absorbed by the medium, this framework is able to provide a reasonable description of the nuclear modification of both leading hadrons and jets at high transverse momentum at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.
The suppression of the nuclear modification factor for heavy flavor hadrons is usually attributed to the energy loss of heavy quarks propagating in a QCD plasma. Nevertheless it is puzzling that the suppression is as strong as for light flavors. We show that when accounting for the quark momentum shift associated to the opening of the recombination/coalescence channel for hadron production in the plasma, it is not necessary to invoke such strong energy loss. This shift is expressed in terms of an increase of the heavy baryon to meson ratio in nuclear with respect to proton collisions. When this mechanism is included along with a moderate energy loss, data from RHIC and LHC for the nuclear modification factor of electrons coming from heavy flavor decays as well as of charm mesons, can be reasonably described.
Relativistic heavy ion collisions, which are performed at large experimental programs such as Relativistic Heavy Ion Colliders (RHIC) STAR experiment and the Large Hadron Colliders (LHC) experiments, can create an extremely hot and dense state of the matter known as the quark gluon plasma (QGP). A huge amount of sub-nucleonic particles are created in the collision processes and their interaction and subsequent evolution after the collision takes place is at the core of the understanding of the matter that builds up the Universe. It has recently been shown that event-by-event fluctuations in the spatial distribution between different collision events have great impact on the particle distributions that are measured after the evolution of the created system. Specifically, these distributions are greatly responsible for generating the observed azimuthal anisotropy in measurements. Furthermore, the eventual cooling and expansion of the fluctuating system can become very complex due to lumps of energy density and temperature, which affects the interaction of the particles that traverse the medium. In this configuration, heavy flavor particles play a special role, as they are generally created at the initial stages of the process and have properties that allow them to retain memory from the interactions within the whole evolution of the system. However, the comparison between experimental data and theoretical or phenomenological predictions on the heavy flavor sector cannot fully explain the heavy quarks coupling with the medium and their subsequent hadronization process. [Full abstract in file]
We have updated the parton and hadron cascade model PACIAE for the relativistic nuclear collisions, from based on JETSET 6.4 and PYTHIA 5.7 to based on PYTHIA 6.4, and renamed as PACIAE 2.0. The main physics concerning the stages of the parton initiation, parton rescattering, hadronization, and hadron rescattering were discussed. The structures of the programs were briefly explained. In addition, some calculated examples were compared with the experimental data. It turns out that this model (program) works well.
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