arXiv subjects

Dinesh Kumar Srivastava

Publications and source records attributed to Dinesh Kumar Srivastava.

At least 19 recordsLinked to original sources

arXiv2009

Interference of thermal photons from quark and hadronic phases in relativistic collisions of heavy nuclei

We explore the intensity correlations for thermal photons having $K_T\leq$ 2 GeV/$c$, for central collisions of heavy nuclei at RHIC and LHC energies. These photons get competing contributions from the quark and the hadronic phases. This competition gives rise to a unique structure, especially in the outward correlation function, due to the interference between the photons from the two sources. The temporal separation of the two sources provides the life time of the system and their strengths provide the relative contribution of the two phases. The results are found to be quite sensitive to the quark-hadron phase transition temperature and the formation time of the plasma.

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arXiv2005

Intensity interferometry of thermal photons from relativistic heavy ion collisions

Intensity interferometry of thermal photons, having transverse momenta $k_T \approx $ 0.1 -- 2.0 GeV, produced in relativistic collision of heavy nuclei is studied. It is seen to provide an accurate information about the temporal and spatial structure of the interacting system. The source dimensions and their $k_T$ dependence revealed by the photon interferometry, display a richness not seen in pion interferometry. We attribute this to difference in the source functions, the fact that photons come out from every stage of the collision and from every point in the system, and the fact that the rate of production of photons is different for the quark-gluon plasma, which dominates the early hot stage, and the hadronic matter which populates the last phase of the collision dynamics. The usefulness of this procedure is demonstrated by an application to collision of lead nuclei at the CERN SPS. Prediction for the transverse momentum dependence of the sizes for SPS, RHIC, and LHC energies are given.

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arXiv2002

Production of intermediate-mass dileptons in relativistic heavy ion collisions

The production of intermediate mass dileptons in ultrarelativistic nuclear collisions at SPS energies is studied. The acceptance and detector resolution inherent to measurements by the NA50 experimental collaboration are accurately modeled. The measured centrality dependence of the intermediate mass lepton pair excess is also addressed.

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arXiv2002

The extent of strangeness in equilibration in quark-gluon plasma

The evolution and production of strangeness from chemically equilibrating and transversely expanding quark gluon plasma which may be formed in the wake of relativistic heavy ion collisions is studied with initial conditions obtained from the Self Screened Parton Cascade (SSPC) model. The extent of partonic equilibration increases almost linearly with the square of the initial energy density, which can then be scaled with number of participants.

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arXiv2001

Scaling of hadronic transverse momenta in a hydrodynamic treatment of relativistic heavy ion collisions

The transverse momenta of hadrons in central nucleus-nucleus collisions are evaluated in a boost invariant hydrodynamics with transverse expansion. Quark gluon plasma is assumed to be formed in the initial state which expands and cools via a first order phase transition to a rich hadronic matter and ultimately undergoes a freeze-out. The average transverse momentum of pions, kaons, and protons is estimated for a wide range of multiplicity densities and transverse sizes of the system. For a given system it is found to scale with the square-root of the particle rapidity density per unit transverse area, and consistent with the corresponding values seen in $p\overline{p}$ experiments at 1800 GeV, suggesting a universal behaviour. The average transverse momentum shows only an approximate scaling with multiplicity density per nucleon which is at variance with the $p\overline{p}$ data.

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arXiv2001

Scaling of single photon production in hadronic collisions

Scaling of single photon production in $pp$ and $p\overline{p}$ collisions is studied. It is empirically observed the available data scales $\sim \sqrt{s}/p_T^5$ for $x_T=2p_T/\sqrt{s} \leq 0.1$ and $\sim (\sqrt{s})^{3.3}/p_T^9$ for larger $x_T$. The NLO pQCD predictions for $pp$ collisions at $\sqrt{s}$ of 200 and 5500 GeV, relevant for RHIC and LHC energies are seen to closely follow this scaling behaviour. Implications for single photon production in heavy ion collisions are discussed.

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arXiv2001

Radiation of single photons from $Pb+Pb$ collisions at the CERN SPS and quark hadron phase transition

The production of single photons in $Pb+Pb$ collisions at the CERN SPS as measured by the WA98 experiment is analysed. A quark gluon plasma is assumed to be formed initially, which expands, cools, hadronizes, and undergoes freeze-out. A rich hadronic equation of state is used and the transverse expansion of the interacting system is taken into account. The recent estimates of photon production in quark-matter (at two loop level) along with the dominant reactions in the hadronic matter leading to photons are used. About 50% of the single photons are seen to have a thermal origin. An addition of the thermal and prompt photons is seen to provide a very good description of the data. Most of the thermal photons having large transverse momenta arise from the quark-matter, which contributes dominantly through the mechanism of annihilation of quarks with scattering, and which in turn is possible only in a hot and dense plasma of quarks and gluons. The results thus confirm the formation of quark gluon plasma and the existence of this mechanism of the production of single photons.

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arXiv2001

Emission of single photons, hadrons, and dileptons in $Pb+Pb$ collisions at CERN SPS and quark hadron phase transition

The production of single photons in $Pb+Pb$ collisions at the CERN SPS as measured by the WA98 experiment is analysed. A quark gluon plasma is assumed to be formed initially, which expands, cools, hadronizes, and undergoes freeze-out. A rich hadronic equation of state is used and the transverse expansion of the interacting system is taken into account. The recent estimates of photon production in quark-matter (at two loop level) along with the dominant reactions in the hadronic matter leading to photons are used. About half of the radiated photons are seen to have a thermal origin. The same treatment and the initial conditions provide a very good description to hadronic spectra measured by several groups and the intermediate mass dileptons measured by the NA50 experiment, lending a strong support to the conclusion that quark gluon plasma has been formed in these collisions.

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arXiv2001

Erratum: Eur. Phy. J. C 12 (2000) 109 (A Second Look at Single Photon Production in $S+Au$ Collisions at 200 A$\cdot$GeV and Implications for Quark Hadron Phase Transition)

It has been shown recently that the values of $J_T$ and $J_L$ which appear in Eqs.(2) and (5) of the above paper and which are taken from the work of Aurenche et al are too large by a factor of 4. Correcting for this changes the Fig.~2. More-over, now the emissions from the quark matter dominate only for $p_T <$ 1 GeV/$c$. The basic result of the paper, that the upper limit of the single-photon production in the WA80 experiment is consistent with the rates for photon production at two-loop level remains valid.

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arXiv2001

Erratum: Eur. Phy. J. C 10 (1999) 487 (Photon production in relativistic heavy-ion collisions using rates with two-loop calculations from quark matter)

It has been shown recently shown that the values of $J_T$ and $J_L$ which appear in Eq.(2) and (5) of the above paper and which are taken from the work of Aurenche et al are too large by a factor of 4. Correcting for this changes the Fig.~1--4. The basic result of the paper, that the emissions from the quark matter can outshine those from the hadronic matter when the photon rates upto two-loop level are used, remains valid though the range of $p_T$ over which it happens is reduced to $p_T <$ 0.5, 1, and 2 GeV/$c$ respecitively at SPS, RHIC, and LHC energies.

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arXiv2001

$J/ψ$ suppression: gluonic dissociation {\em vs.} colour screening

We evaluate the suppression of $J/ψ$ production in an equilibrating quark gluon plasma for two competing mechanisms: Debye screening of colour interaction and dissociation due to energetic gluons. Results are obtained for $S+S$ and $Au+Au$ collisions at RHIC and LHC energies. At RHIC energies the gluonic dissociation of the charmonium is found to be equally important for both the systems while the screening of the interaction plays a significant role only for the larger systems. At LHC energies the Debye mechanism is found to dominate for both the systems. While considering the suppression of directly produced $Υ$ at LHC energies, we find that only the gluonic dissociation mechanism comes into play for the initial conditions taken from the self screened parton cascade model in these studies. Thus we find that a systematic study of quarkonium suppression for systems of varying dimensions can help identify the source and the extent of the suppression.

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arXiv2000

Determination of equation of state of quark matter from $J/ψ$ and $Υ$ suppression at RHIC and LHC

The long life-time of the quark-gluon plasma likely to be created in the relativistic heavy ion collisions at RHIC and LHC energies renders it sensitive to the details of the equation of state of the quark-matter. We show that the $p_T$ dependence of the survival probability of the directly produced $J/ψ$ at RHIC energies and that of the directly produced $Υ$ at LHC energies is quite sensitive to the speed of sound in the quark matter, which relates the pressure and the energy density of the plasma. The transverse expansion of the plasma is shown to strongly affect the $J/ψ$ suppression at LHC energies.

hep-ph↗

arXiv1999

Single Photon Production in Relativisitic Heavy Ion Collisions and Quark Hadron Phase Transition

We discuss the recent developments in the study of single photon production in relativistic heavy ion collisions. In particular their production at SPS, RHIC, and LHC energies is re-examined in view of the results of Aurenche et al which show that the rate of photon production from quark gluon plasma, evaluated at the order of two loops far exceeds the rates evaluated at one-loop level which have formed the basis of all the estimates of photons so far. We find that the production of photons from quark matter could easily out-shine those from the hadronic matter in certain ideal conditions. We further show that the earlier results lending support to the possibility of quark-hadron phase transition from the measured yield of single photons in $S+Au$ collisions at CERN SPS remain valid when an account is made for these developments, though they leave a scope for the formation of (chemically) non-equilibrated plasma.

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arXiv1999

The Evolution of Dynamical Screening in the Parton Cacade Model

We determine the time evolution of the colour screening mass in high energy nuclear collisions, as provided by the parton cascade model. Using our result, we discuss the onset of deconfinement and the onset of quarkonium suppression in a general, not necessarily equilibrated environment of strongly interacting constituents.

hep-ph↗

arXiv1999

Scaling of particle production with number of participants in high-energy A+A collisions in the parton-cascade model

In view of the recent WA98 data of $π^0$ spectra from central Pb+Pb collisions at the CERN SPS, we analyze the production of neutral pions for A+A collisions across the periodic table at $\sqrt{s}=17$ AGeV and 200 AGeV within the framework of the parton-cascade model for relativistic heavy ion collisions. The multiplicity of the pions (having $p_T > 0.5$ GeV) in the central rapidity region, is seen to scale as $\sim (N_{part})^α$, where $N_{part}$ is the number of participating nucleons, which we have approximated as 2A for central collisions of identical nuclei. We argue that the deviation of $α$ ($\simeq 1.2$) from unity may have its origin in the multiple scattering suffered by the partons. We also find that the constant of proportionality in the above scaling relation increases substantially in going from SPS to RHIC energies. This would imply that the (semi)hard partonic activity becomes a much cleaner signal above the soft particle production at the higher energy of RHIC, and thus much less dependent on the (lack of) understanding of the underlying soft physics background.

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arXiv1999

A Second Look at Single Photon Production in S+Au Collisions at 200 A$\cdot$GeV and Implications for Quark Hadron Phase Transition

We reanalyze the production of single photons in S+Au collisions at CERN SPS to investigate: i) the consequences of using a much richer equation of state for hadrons than the one used in an earlier study by us; and, ii) to see if the recent estimates of photon production in quark-matter (at two loop level) by Aurenche et al. are consistent with the upper limit of the photon production measured by the WA80 experiment. We find that the measured upper limit is consistent with a quark hadron phase transition. The measured upper limit is also consistent with a scenario where no phase transition takes place, but where the hadronic matter reaches a density of several hadrons per unit volume; which is rather unphysical.

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arXiv1999

Photon production in relativistic heavy ion collisions

The production of single photons in relativistic heavy ion collisions at CERN SPS, BNL RHIC and CERN LHC energies is re-examined in view of the recent studies of Aurenche et al which show that the rate of photon production from quark gluon plasma, evaluated at the order of two loops far exceeds the rates evaluated at one-loop level which have formed the basis of all the estimates of photons so far. We find that the production of photons from quark matter could easily out-shine those from the hadronic matter in certain ideal conditions.

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arXiv1999

Production and Thermal Equilibration of Partons in Relativistic Heavy Ion Collisions: $\sqrt{s}= 20 vs. 200 A GeV$

The production and thermalization of partons liberated in relativistic heavy ioncollisions is investigated within the parton cascade model. The momentum distribution of the partons near z=0 is found to become isotropic beyond about 1 fm/c after the overlap for the collision of lead nuclei at $\sqrt{s}=20 A GeV$ indicating a thermalization. At $\sqrt{s}=200 A GeV$ this is attained by about 0.5 fm/c after the complete overlap.

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