Induced photon emission from quark jets in ultrarelativistic heavy-ion collisions

We study the induced photon bremsstrahlung from a fast quark produced in AA collisions due to multiple scattering in quark-gluon plasma. For RHIC and LHC conditions, the induced photon spectrum is sharply peaked at a photon energy close to the initial quark energy. In this region, the contribution of the induced radiation to the photon fragmentation function exceeds the ordinary vacuum radiation. Contrary to previous analyses [4–7], our results show that, at RHIC and LHC energies, the final-state interaction effects in quark-gluon plasma do not suppress the direct photon production and may even enhance it at p _T ～5–15 GeV.     

Direct hadron production in ultrarelativistic heavy-ion collisions

Hadrons emitted by the pre-surface layer of a quark-gluon plasma (QGP) before the phase transition into a hadronic gas are considered as possible sources of direct information about QGP. It is shown that if QGP is created in ultrarelativistic heavy-ion collisions, then these hadrons strongly contribute at soft p_t at SpS energy and dominate up to an order of magnitude at LHC energy.     

Low mass dielectrons at LHC energy

We study the thermal production of low mass dielectrons in central nucleus-nucleus collisions at LHC energy. We assume initial quark-gluon plasma production, followed by a first order quark-hadron phase transition and subsequent hadronization; the expansion of the system is described by Bjorken's hydrodynamical model. In the quark-gluon plasma, we include both the basisq annihilation process and lowest order QED and QCD corrections. In the hadronic phase, we consider pion annihilation as well as pion scattering with virtual bremsstrahlung leading to dielectron production. Our results are then compared to dielectron rates from ⁰ and Dalitz decays. We conclude that it will be rather difficult to disentangle the quark-gluon plasma contributions from competing dielectron production processes.     

Photons from jet–plasma interaction in relativistic heavy ion collisions

We expose the role of collisional energy loss on high p _T photon data measured by PHENIX collaboration by calculating photon yield in jet–plasma interaction. The phase-space distribution of the participating jet is dynamically evolved by solving Fokker–Planck equation. It is shown that the data are reasonably well reproduced when contributions from all the relevant sources are taken into account. Predictions at higher beam energies relevant for LHC experiment have been made.     

Fixed target project AFTER at the LHC beams for heavy ion and hadron physics

High intensity proton and lead ion beams at the LHC collider allow one to use the beam halo by placing a fixed target or a bent crystal for beam extraction. The particle energy in this case is just half that at the RHIC collider, but the luminosity exceeds the collider luminosity many times. It is also possible to install a polarized target in the extracted beam. The project AFTER is aimed at investigation of rare processes, polarization phenomena, determination of the parameters required for analysis of cosmic rays and neutrino astrophysics, detailed investigation of quarkonia production and suppression depending on the phase transition of matter to the quark-gluon phase.     

Two-photon correlations as the signal of a sharp transition in quark-gluon plasma

The photon production arising due to time variation of a medium has been considered. The Hamilton formalism for photons in a time-variable medium (plasma) has been developed with application to inclusive photon production. The results have been used for calculation of the photon production in the course of the transition from a quark-gluon phase to a hadronic phase in relativistic heavy-ion collisions. The relative strength of the effect and the specific two-photon correlations have been evaluated. It is demonstrated that the opposite-side two-photon correlations are indicative of a sharp transition from the quark-gluon phase to hadrons.     

Dilepton from Passage of Jets Through Spherical Expanding QGP

We calculate the large mass dileptons production from the jet-dilepton conversion in spherical expanding quark-gluon plasma at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. The jet-dilepton production exceeds the thermal and Drell-Yan dilepton production in the large mass region of 4.5 GeV< M< 5.5 GeV and 7 GeV< M< 9 GeV in central Pb+Pb collisions at √s_NN=2.76 TeV and 5.5 TeV, respectively. We present the solution of (1+3)-dimensional fluid hydrodynamics with spherical symmetry. We find that the transverse flow of the QGP leads to a rapid cooling of the fire ball and suppression of the jet-dilepton conversion. The suppression is also evident at intermediate and large mass at LHC energies. The energy loss of the jet-dilepton conversion is concerned.     

Hard thermal photon production in relativistic heavy ion collisions

The recent status of hard thermal photon production in relativistic heavy ion collisions is reviewed and the current rates are presented with emphasis on corrected bremsstrahlung processes in the quark–gluon plasma (QGP) and quark–hadron duality. Employing Bjorken hydrodynamics with an EOS supporting the phase transition from QGP to hot hadron gas (HHG), thermal photon spectra are computed. For SPS 158 GeV Pb + Pb collisions, comparison with other theoretical results and the WA98 direct photon data indicates significant contributions due to prompt photons. Extrapolating the presented approach to RHIC and LHC experiments, predictions of the thermal photon spectrum show a QGP outshining the HHG in the high-p_T-region.     

Radion production at LHC via the process of vector-boson fusion

The possibility of observing the radion in the process of vector-boson fusion at the Large Hadron Collider (LHC) in proton-proton collisions at the c.m. energy of √s = 14 TeV is studied. A region of kinematical variables where background processes can be suppressed substantially and where the process in which the production of a radion is followed by its decay to two Z bosons can be separated is found. It is shown that the radion could be discovered in the process under study at an energy scale of up to 0.75 TeV at the LHC luminosity of L = 300 fb^?1.     

Properties of hot and dense nuclear matter in a mixed phase

The QCD phase transition is treated within a statistical model taking into account the coexistence of interacting quark-gluon and hadron phases. Being in agreement with the recent lattice QCD data, this statistical mixed phase model predicts that the “softest point” of the equation of state, resulting in the longest-lived fireball effect, is atε _{sp ≈ 0.35}GeV/fm³. It is shown that this “softest point” is washed out at the baryon densities higher than the normal nuclear density. The approach is extended to include strangeness. Attention is drawn to the study of signatures for forming the mixed quark-hadron phase of nuclear matter in the collision energy rangeE _lab ≈ 2–10 GeV/A.     

Variation of jet quenching from RHIC to LHC and thermal suppression of the QCD coupling constant

We perform a joint jet tomographic analysis of the data on the nuclear modification factor R _AA from PHENIX at RHIC and ALICE at LHC. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the observed slow variation of R _AA from RHIC to LHC indicates that the QCD coupling constant is suppressed in the quark-gluon plasma produced at LHC.     

Proof of factorization of fragmentation function in non-equilibrium QCD

In this paper, we prove factorization of fragmentation function in non-equilibrium QCD by using Schwinger-Keldysh closed-time path integral formalism. We use the background field method of QCD in a pure gauge in path integral approach to prove factorization of fragmentation function in non-equilibrium QCD. Our proof is valid in any arbitrary gauge fixing parameter α. This may be relevant to study hadron production from quark-gluon plasma at high energy heavy-ion colliders at RHIC and LHC.     

Dilepton from Passage of Jets Through Spherical Expanding QGP

We calculate the large mass dileptons production from the jet-dilepton conversion in spherical expanding quark-gluon plasma at Relativistic Heavy Ion Collider(RHIC) and Large Hadron Collider(LHC) energies.The jetdilepton production exceeds the thermal and Drell Yan dilepton production in the large mass region of 4.5 GeVM 5.5 GeV and 7 GeV M 9 GeV in central Pb+Pb collisions at SNNS~(1/2)=2.76 TeV and 5.5 TeV,respectively.We present the solution of(1+3)-dimensional fluid hydrodynamics with spherical symmetry.We find that the transverse flow of the QGP leads to a rapid cooling of the fire ball and suppression of the jet-dilepton conversion.The suppression is also evident at intermediate and large mass at LHC energies.The energy loss of the jet-dilepton conversion is concerned.     

Dilepton production from ρ-mesons in a quark-gluon plasma

Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π⁺-π⁻ annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma. Received: 8 September 1999 / Revised version: 22 October 1999     

Anomalous mass dependence of radiative quark energy loss in a finite-size quark-gluon plasma

We demonstrate that for a finite-size quark-gluon plasma the induced gluon radiation from heavy quarks is stronger than that for light quarks when the gluon formation length becomes comparable with (or exceeds) the size of the plasma. The effect is due to oscillations of the light-cone wave function for the in-medium q→gq transition. The dead cone model by Dokshitzer and Kharzeev neglecting quantum finite-size effects is not valid in this regime. The finite-size effects also enhance the photon emission from heavy quarks.     

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and¹⁶O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and ⁰ spectra have been measured in the pseudorapidity range 1.52.1 for the transverse momentum region 0.4 GeV/cp _T 2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of ⁰ and mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.     

Direct soft photon production inK + p andπ + p interactions at 250 GeV/c

Inclusive production of direct soft photons is studied inK ⁺ p andK ⁺ π interactions at 250 GeV/c. Total cross sections, Feynman-x and transverse momentum distributions of direct γ's are presented. The measured cross sections are several times larger than expected from QED inner bremsstrahlung, indicating the presence of an anomalous soft photon source. The model of Lichard and Van Hove, based on the “cold quark-gluon plasma” picture, agrees with the data.     

Heavy ion collisions at CMS and quark-gluon plasma

One of the most actual goals in high energy physics is reaching the state of deconfinement of hadronic matter and studying the properties of resultant quark-gluon plasma (QGP). Jet production, as well as other hard processes, is considered to be an efficient probe for formation of QGP in future experiments on heavy ion collisions at LHC.The Compact Muon Solenoid (CMS) is the general purpose detector designed to run at the LHC and optimized mainly for the search of the Higgs boson in proton-proton collisions. However, a good muon system and electromagnetic and hadron calorimeters with fine granularity gives the possibility to cover several important aspects of the heavy ion physics. The production of heavy quarkonia Γ, Γ′, Γ″ through their muon decay channel and the energy loss of hard jets, are valuable processes for studying the phase transition from the hadronic matter to the plasma of deconfined quarks and gluons.     

Λc enhancement from strongly coupled QGP

We propose the enhancement of Λ _c yield in heavy ion collisions at RHIC and LHC as a novel signal for the existence of diquarks in the strongly coupled quark-gluon plasma produced in these collisions as well as in the Λ _c . Assuming that stable bound diquarks can exist in the quark-gluon plasma, we argue that the yield of Λ _c would be increased by two-body collisions between [ud] diquarks and c quarks, in addition to normal three-body collisions among u, d and c quarks. A quantitative study of this effect based on the coalescence model shows that including the contribution of diquarks to Λ _c production indeed leads to a substantial enhancement of the Λ _c /D ratio in heavy ion collisions.     

Effect of curvature on a statistical model of quark-gluon-plasma fireball in the hadronic medium

The free energy of a quark-gluon plasma fireball in the hadronic medium is calculated in the Ramanathan et al statistical model after incorporating the effect of curvature. The result with the inclusion of curvature is found to produce significant improvements in all the parameters we calculated with respect to the earlier results. The surface tension with this curvature effect is found to be 0.17T _c³, which is two times the earlier value of surface tension which is 0.078T _c³, and this new result is nearly close to the lattice value 0.24T _c³. As far as transition is concerned, a thermodynamic variable like entropy shows weakly first-order phase transition and it shows continuity in the behaviour of specific heat.