arXiv subjects

Subhasis Chattopadhyay

Publications and source records attributed to Subhasis Chattopadhyay.

48 records · Page 3Linked to original sources

arXiv2014

Parton shadowing and $J/ψ$-to-Drell-Yan ratio in nuclear collisions at SPS and FAIR

We have analyzed the data on $J/ψ$-to-Drell-Yan production cross section ratio in proton-nucleus ($p+A$) and nucleus-nucleus ($A+A$) collisions, measured by the NA50 collaboration in the SPS energy domain. Two component QVZ model has been employed to calculate $J/ψ$ production cross sections. For both $J/ψ$ and Drell-Yan production, nuclear modifications to the free nucleon structure functions are taken into account. In heavy-ion collisions, such modifications are assumed to be proportional to the local nuclear density resulting in centrality dependent initial state effects. Differences in quark and gluon shadowing leads to a new source of impact parameter dependence of the $J/ψ$ to Drell-Yan production ratio. For $J/ψ$, final state interaction of the produced $c\bar{c}$ pairs with the nuclear medium is also taken into account. A satisfactory description of the data in both $p+A$ and $A+A$ collisions is obtained. Role of the shadowing corrections are investigated in detail. Model calculations are extrapolated to predict the centrality dependence of $J/ψ$-to-Drell-Yan ratio in the FAIR energy regime.

hep-ph↗

arXiv2013

Charmonium suppression in a baryon rich quark-gluon plasma

We have investigated the charmonium survival probability, in a high baryon density parton plasma, expected to be produced in nuclear collisions at FAIR. Charmonia are assumed to undergo complete dissociation by color screening, if the in-medium Debye radius becomes comparable to the spatial size of the corresponding bound state. Results indicate a non-trivial dependence of the suppression pattern on the plasma evolution dynamics. A much larger magnitude of suppression is foreseen induced by cold nuclear matter compared to that due to plasma screening.

hep-ph↗

arXiv2012

J/$ψ$ suppression in a dense baryonic medium

We have examined the available latest SPS data on $J/ψ$ suppression in Pb+Pb and In+In collisions at 158 A GeV. Our employed model, with parameters fixed by $p$-$p$ and $p$-nucleus collisions, gives excellent description of NA50 and NA60 data on centrality dependence of $J/ψ$ suppression. The model is then applied to predict the centrality dependence of $J/ψ$ production in Au+Au collisions at FAIR energy domain. A much larger suppression of $J/ψ$ is predicted. In addition the possible effects of a baryon rich medium on $J/ψ$ production is also investigated.

hep-ph↗

arXiv2011

J/Psi production in proton induced collisions at FAIR

We have examined the production of J/$ψ$ mesons in high energy proton-proton and proton-nucleus collisions at beam energies in the range from 158 GeV to 920 GeV, available from different fixed target experiments. In the employed model J/$ψ$ production in hadronic collisions is assumed to be a factorisable two step process: (i) production of a $c\bar{c}$ pair which can be reliably described by perturbative QCD, and (ii) formation of J/$ψ$ resonance from the $c\bar{c}$ pair, which can be conveniently parameterized incorporating different existing physical mechanisms of color neutralization. We show that, for lower collision energies, J/$ψ$ production through quark-anti-quark annihilation gives larger contribution at higher $x_F$, while gluon-gluon fusion dominates the production at smaller $x_F$. For proton-nucleus collisions the model takes into account both the initial state modification of parton distributions in nuclei and the final state interaction of the produced $c\bar{c}$ pairs with the target nucleons. The model is found to give reasonable description of data on J/$ψ$ production in protonic and proton-nucleus collisions, for different existing fixed target experiments. In case of proton-nucleus collisions, our calculations show a non-negligible dependence of the final state nuclear dissociation of J/$ψ$ mesons on the energy of the incident proton beam. The model has been applied to predict the J/$ψ$ production and suppression expected in proton-nucleus collisions at energies relevant to FAIR, the upcoming accelerator facility at Darmstadt, Germany. The amount of suppressions, for different mechanisms of J/$ψ$ hadronization has been found to be distinguishably different which might help an experimental settlement of the much controversial issue of color neutralization.

hep-ph↗

arXiv2011

Study of γ-charge correlation in heavy ion collisions, various approaches

Event-by-event γ-charge correlation is used in studying systems going through QCD chiral phase transition. In this paper various methods for measuring γ-charge correlation in heavy ion collisions have been discussed. Dynamical fluctuation due to formation of domains of DCC that can affect γ-charge correlation has been discussed. We study known detector and statistical effects involved in these measurements and suggest suitable robust observables Δν_{dyn} and r_{m,1} sensitive to small γ-charge correlation signal. These variables are constructed based on moments of multiplicity distributions of photon and charged particles. Estimations of expected measurable signals of γ-charge correlation from various available models such as for ideal Boltzmann gas of pions, monte-carlo models based on transport and mini-jets have been discussed. Collision centrality dependence of the observables have been estimated from Central Limit Theorem and found to be consistent with the model predictions. We find that observables show high sensitivity to fraction of DCC events and have nonlinear dependence on fraction of pions carrying DCC signals. Variation of r_{m,1} with orders of its higher moments m is an observable to extract the nature and strength of γ-charge correlation.

nucl-ex↗

arXiv2010

Differential elliptic flow of identified hadrons and constituent quark number scaling at FAIR

Differential elliptic flow $v_2(p_{T})$ for identified hadrons has been investigated in the FAIR energy regime, employing a hadronic-string transport model (UrQMD) as well as a partonic transport model (AMPT). It has been observed that both the models show a mass ordering of $v_2$ at low $p_{T}$ and a switch over resulting a baryon-meson crossing at intermediate $p_{T}$. AMPT generates higher $v_2$ values compared to UrQMD. In addition, constituent quark number scaling behavior of elliptic flow has also been addressed. Scaling behavior in terms of the transverse momentum $p_T$ is found to absent for both the partonic as well as the hadronic model. However UrQMD and AMPT with string melting scenario do exhibit a NCQ scaling of $v_2$ at varying degree, with respect to transverse kinetic energy $KE_T$. But default AMPT, where partonic scatterings are not included, does not show any considerable scaling behavior. A variable $α$ is defined to quantify the degree of $KE_T$ scaling. We found that UrQMD gives better scaling than AMPT at FAIR.

hep-ph↗

arXiv2009

Track fitting by Kalman Filter method for a prototype cosmic ray muon detector

We have developed a track fitting procedure based on Kalman Filter technique for an Iron Calorimeter (ICAL) prototype detector when the detector is flushed with single muon tracks. The relevant track parameters i.e., momentum, direction and charge are reconstructed and analyzed. This paper discusses the design of the prototype detector, its geometry simulation by Geant4, and the detector response with the cosmic ray muons. Finally we show the resolution of reconstructed momenta and also the charge identification efficiency of $μ^+$ and $μ^-$ events in the magnetized ICAL.

nucl-ex↗

arXiv2009

A method based on transverse energy balance of jets for selection of direct photons and fragmentation photons in high energy pp collisions

Direct photons are important probes in high energy collisions. They play an important role in determining the parton distribution function directly inside a proton as well as the nature of the matter formed in heavy ion collisions. However fragmentation photons play the role of prominent background in identifying the direct photons. In the present work we developed a new method based on the transverse energy balance of jets for enrichment of direct photon candidates in pp collisions. This method can reject 35% of the background photons (fragmentation) which can not be suppressed by isolation. Efficiency of detection of direct photon decrease by 10% in the method.

nucl-ex↗

arXiv2005

Preliminary Results on Direct Photon-Photon HBT Measurements in $\sqrt{s_{\rm{NN}}}$ = 62.4 GeV and 200 GeV Au+Au Collisions at RHIC

We present the preliminary results on direct photon interferometry measurements in Au+Au collisions at $\sqrt{s_{\rm{NN}}}$ = 62.4 and 200 GeV using the STAR (Solenoidal Tracker at RHIC) detector. Photons are reconstructed via $e^+/e^-$ conversions in STAR Time Projection Chamber(TPC) and energy deposited by photons in STAR Barrel Electromagnetic Calorimeter(BEMC). The two-photon correlations are measured using (1) both photons measured using BEMC; (2) one photon from conversions and the other measured with BEMC. Both the methodologies and the possible constraints in the correlation function measurements are discussed.

nucl-ex↗

arXiv2005

Determination of $γ^{direct}/π^0$ using photon-charge particle correlation measurement in high energy heavy ion and pp collisions

A method has been proposed for the determination of $γ$ to $π^0$ ratio in high energy pp and nucleus-nucleus collisions at large transverse momentum ($p_T$). In photon measuring device, it is proposed that shower shape analysis is made to select only cases with wide showers. These candidates come mostly from $π^0$. Correlation is measured between those photon candidates as trigger particles and associated charged particles above selected $p_T$. The ratio of yields of near and far angle correlation peaks for $π^0$ events is compared with correlation peaks from other set of events where trigger particle contains photons for direct-photon jets alongwith $π^0$. The comparative study in reduction of yield of near angle peak is used to extract photon fraction.

nucl-ex↗

arXiv2004

Correlation of high energy photons and charged particles in p+p and d+Au collisions at $\sqrt{s}=200$ GeV

Azimuthal correlations between high energy photons from $π^0$ decay ($p_T^γ < 10.5$ GeV) and charged hadrons ($p_T^{hadron}$ above a threshold of 2, 3 or 4 GeV/c) have been measured in p+p and d+Au collisions at $\sqrt{s}=200$ GeV. Clear jet-like correlations are observed at $Δϕ=0$ and 180 degrees, with peak widths decreasing with increasing $p_T^{hadron}$. Jet $ $ and $\sqrt{< k_T^2 >}$ in d+Au collisions are deduced from the distributions. {\it These results are presented in Quark Matter 2004 poster session.

nucl-ex↗

arXiv1997

Large Mass Diphotons From Relativistic Heavy Ion Collisions

We evaluate the production of large mass diphotons from quark annihilation at BNL RHIC and CERN LHC energies from central collisions of gold nuclei. The collision is assumed to lead to either a thermally and chemically equilibrated quark gluon plasma, or a free-streaming quark gluon gas having an identical initial entropy, or a chemically equilibrating quark gluon system, with the same entropy at $T=T_c$. We also obtain an estimate of hard photon pairs from initial state quark annihilation and find that the thermal production dominates the yield up to $M \approx$ 4 GeV at RHIC, and up to 6 GeV at LHC. A simulation study of decay versus thermal diphotons is presented.

nucl-th↗