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Bedangadas Mohanty

Publications and source records attributed to Bedangadas Mohanty.

At least 91 records · Page 5Linked to original sources
arXiv2010

Energy dependence of pbar/p ratio in p+p collisions

We have compiled the experimentally measured pbar/p ratio at midrapidity in p+p collisions from \sqrt{s} = 23 to 7000 GeV and compared it to various mechanisms of baryon production as implemented in PYTHIA, PHOJET and HIJING/B-Bbar models. For the models studied with default settings, PHOJET has the best agreement with the measurements, PYTHIA gives a higher value for \sqrt{s} < 200 GeV and the ratios from HIJING/B-Bbar are consistently lower for all the \sqrt{s} studied. Comparison of the data to different mechanisms of baryon production as implemented in PYTHIA shows that through a suitable tuning of the suppression of diquark-antidiquark pair production in the color field relative to quark-antiquark production and allowing the diquarks to split according to the popcorn scheme gives a fairly reasonable description of the measured pbar/p ratio for \sqrt{s} < 200 GeV. Comparison of the beam energy dependence of the pbar/p ratio in p+p and nucleus-nucleus (A+A) collisions at midrapidity shows that the baryon production is significantly more for A+A collisions relative to p+p collisions for \sqrt{s} < 200 GeV. We also carry out a phenomenological fit to the y_beam dependence of the pbar/p ratio.

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arXiv2009

Extrapolation of Multiplicity distribution in p+p(\bar(p)) collisions to LHC energies

The multiplicity (N_ch) and pseudorapidity distribution (dN_ch/dη) of primary charged particles in p+p collisions at Large Hadron Collider (LHC) energies of \sqrt(s) = 10 and 14 TeV are obtained from extrapolation of existing measurements at lower \sqrt(s). These distributions are then compared to calculations from PYTHIA and PHOJET models. The existing \sqrt(s) measurements are unable to distinguish between a logarithmic and power law dependence of the average charged particle multiplicity ( ) on \sqrt(s), and their extrapolation to energies accessible at LHC give very different values. Assuming a reasonably good description of inclusive charged particle multiplicity distributions by Negative Binomial Distributions (NBD) at lower \sqrt(s) to hold for LHC energies, we observe that the logarithmic \sqrt(s) dependence of are favored by the models at midrapidity. The dN_ch/dηversus ηfor the existing measurements are found to be reasonably well described by a function with three parameters which accounts for the basic features of the distribution, height at midrapidity, central rapidity plateau and the higher rapidity fall-off. Extrapolation of these parameters as a function of \sqrt(s) is used to predict the pseudorapidity distributions of charged particles at LHC energies. dN_ch/dηcalculations from PYTHIA and PHOJET models are found to be lower compared to those obtained from the extrapolated dN_ch/dηversus ηdistributions for a broad ηrange.

hep-ex↗
arXiv2009

Predictions of elliptic flow and nuclear modification factor from 200 GeV U + U collisions at RHIC

Predictions of elliptic flow ($v_2$) and nuclear modification factor ($R_{AA}$) are provided as a function of centrality in U + U collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. Since the $^{238}$U nucleus is naturally deformed, one could adjust the properties of the fireball, density and duration of the hot and dense system, for example, in high energy nuclear collisions by carefully selecting the colliding geometry. Within our Monte Carlo Glauber based approach, the $v_2$ with respect to the reaction plane $v_2^{RP}$ in U + U collisions is consistent with that in Au + Au collisions, while the $v_2$ with respect to the participant plane $v_2^{PP}$ increases $\sim$30-60% at top 10% centrality which is attributed to the larger participant eccentricity at most central U + U collisions. The suppression of $R_{AA}$ increases and reaches $\sim$0.1 at most central U + U collisions that is by a factor of 2 more suppression compared to the central Au + Au collisions due to large size and deformation of Uranium nucleus.

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arXiv2008

STAR results on medium properties and response of the medium to energetic partons

We report new STAR results on the consequences of highly energetic partons propagating through the medium formed in heavy ion collisions using correlations as an experimental probe. The recent results providing insights about color factor effects and path length dependence of parton energy loss, system size dependence of di-hadron fragmentation functions, conical emission and ridge formation in heavy ion collisions are presented.

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arXiv2007

Search for color charge dependence of energy loss at RHIC

The non-Abelian feature of quantum chromodynamics (QCD) results in the gluons losing more energy than quarks in the medium formed in high energy heavy-ion collisions. Experimental results in p+p collisions when compared to NLO pQCD calculations show that at high transverse momentum (pT) the produced protons+anti-protons are dominantly from gluon jets and charged pions have substantial contribution from quark jets. If such a scenario is applied to heavy-ion collisions at RHIC, one would expect the difference in quark and gluon energy loss to have an effect on measured observables, such as high pT pbar(p)/pi ratios and the nuclear modification factor for various particles species. We discuss the experimental results and some possible future measurements.

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arXiv2007

Properties of particle production at large transverse momentum in Au+Au and Cu+Cu collisions at RHIC

We present the incident energy and system size dependence of the pT spectra for charged pions, protons, and anti-protons using Au+Au and Cu+Cu collisions at Sqrt(sNN) = 62.4 and 200 GeV in STAR experiment at RHIC. Through these measurements in the pT range of 0.2 < pT < 10 GeV/c we conduct a systematic study of the beam energy, system size and particle species dependence of nuclear modification factors and address specific predictions from the quark coalescence models regarding the beam energy dependence of baryon enhancement in the intermediate pT (2 < pT < 6 GeV/c) region.

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arXiv2005

Kaon to Pion ratio in Heavy Ion Collisions

The momentum integrated Boltzmann equation has been used to study the evolution of strangeness of the strongly interacting system formed after the heavy ion collisions at relativistic energies.We argue that the experimentally observed non-monotonic, horn-like structure in the variation of the $K^+/π^+$ with colliding energy appears due to the release of large number of colour degrees of freedom.

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arXiv2005

phi production at RHIC: characterization of co-existence phase

We extract the effective degrees of freedom that characterize the co-existing phase of quark gluon plasma and hadrons. Experimental data on phi at mid-rapidity is used to set a lower bound to the critical temperature of quark hadron phase transition. The production and evolution of strangeness have been studied by using Boltzmann equation. The results have been contrasted with the experimental data obtained by STAR collaboration at RHIC for Au + Au collisions at sqrt{s_{NN}}=200 GeV. Our study reveals that the phi mesons freeze out at a temperature ~ 160 MeV, a value close to the transition temperature for quark-hadron phase transition.

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arXiv2005

Particle production at forward rapidity in d+Au and Au+Au collisions in STAR experiment at RHIC

We present the recent results from the STAR experiment on charged and neutral particle measurements at the forward rapidity in d+Au collisions at sqrt{s_{NN}} = 200 GeV and Au+Au collisions at sqrt{s_{NN}} = 62.4 GeV. The nuclear modification factor for charged and neutral hadrons in d+Au collisions are presented. Measurements of Lambda and anti-Lambda production at forward rapidity and the variation of net baryon density as a function of collision centrality are discussed. We have also studied the limiting fragmentation of photons and charged particles in Au+Au collisions. The photons and charged particles separately follow the energy independent limiting fragmentation behaviour. However they have been observed to follow a different centrality dependence of limiting fragmentation.

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arXiv2005

First Results from Photon Multiplicity Detector at RHIC

We present the first measurement of multiplicity and pseudorapidity distributions of photons in the pseudorapidity region 2.3 < eta < 3.7 for different centralities in Au + Au collisions at sqrt{s_NN} = 62.4 GeV. The pseudorapidity distribution of photons, dominated by neutral pion decays, has been compared to those of identified charged pions, photons, and inclusive charged particles from heavy ion and nucleon-nucleon collisions at various energies. Scaling of photon yield with number of participating nucleons and limiting fragmentation scenario for inclusive photon production has been studied.

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arXiv2005

The width of the rapidity distribution in heavy ion collisions

We have studied the widths of the rapidity distributions of particles produced in nucleus-nucleus collisions at various center of mass energies and as a function of centrality at SPS energies. We show that the width of the rapidity distribution is sensitive to longitudinal flow, velocity of sound in the medium, and rescattering of particles. We explore the possibility of distinguishing the initial hard scattering regime from final state effects by studying the variation in the width of the rapidity distribution of the particles with centrality for various pT values.

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arXiv2004

Lepton interferometry in relativistic heavy ion collisions - a case study

We propose intensity interferometry with identical lepton pairs as an efficient tool for the estimation of the source size of the expanding hot zone produced in relativistic heavy ion collisions. This can act as a complementary method to two photon interferometry. The correlation function of two electrons with the same helicity has been evaluated for RHIC energies. The thermal shift of the rho meson mass has negligible effects on the HBT radii.

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arXiv2004

Quark participants and global observables

We show that the centrality dependence of charged particle and photon pseudorapidity density at midrapidity along with the transverse energy pseudorapidity density at SPS and RHIC energies scales with the number of participating constituent quarks. The number of charged particles and transverse energy per participant constituent quark is found to increase with increase in beam energy.

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arXiv2003

Velocity of sound in relativistic heavy-ion collisions

We have studied the rapidity distribution of secondary hadrons produced in nucleus-nucleus collisions at ultra-relativistic energies within the ambit of the Landau's hydrodynamical model. A reasonable description of the data can also be obtained by using the Bjorken's hydrodynamical model if the boost invariance is restricted to a finite rapidity range. The sensitivity of the hadronic spectra on the equation of state vis- a -vis the velocity of sound has been discussed. The correlation between the velocity of sound and the freeze-out temperature has been indicated. The effects of the non-zero widths of various mesonic and baryonic degrees of freedom up to the mass value ~ 2.5 GeV is seen to be small.

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arXiv2003

Transverse momentum spectra of hadrons in pp, pA and AA collisions

The transverse momentum spectra of the produced hadrons have been compared to a model which is based on the assumption that a nucleus-nucleus collision is a superposition of isotropically decaying thermal sources at a given freeze out temperature. The freeze-out temperature in nucleus-nucleus collisions is fixed from the inverse slope of the transverse momentum spectra of hadrons in nucleon-nucleon collision. The successive collisions in the nuclear reaction leads to gain in transverse momentum, as the nucleons propagate in the nucleus following a random walk pattern. The average transverse rapidity shift per collision is determined from the nucleon-nucleus collision data. Using these information we obtain parameter free result for the transverse momentum distribution of produced hadrons in nucleus-nucleus collisions. It is observed that such a model is able to explain the transverse mass spectra of produced pions at SPS energies. However it fails to satisfactorily explain the transverse mass spectra of kaons and protons. This indicates the presence of collective effect which cannot be accounted for by the initial state collision broadening of transverse momentum of produced hadrons, the basis of random walk model.

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arXiv2003

Indication of a Co-Existing Phase of Quarks and Hadrons in Nucleus - Nucleus Collisions

The variation of average transverse mass of identified hadrons with charge multiplicity have been studied for AGS, SPS and RHIC energies. The observation of a plateau in the average transverse mass for multiplicities corresponding to SPS energies is attributed to the formation of a co-existence phase of quark gluon plasma and hadrons. A subsequent rise for RHIC energies may indicate a deconfined phase in the initial state. Several possibilities which can affect the average transverse mass are discussed. Constraints on the initial temperature and thermalization time have been put from the various experimental data available at SPS energies.

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arXiv2003

Photon interferometry and size of the hot zone in relativistic heavy ion collisions

The parameters obtained from the theoretical analysis of the single photon spectra observed by the WA98 collaboration at SPS energies have been used to evaluate the two photon correlation functions. The single photon spectra and the two photon correlations at RHIC energies have also been evaluated, taking into account the effects of the possible spectral change of hadrons in a thermal bath. We find that the ratio $R_{side}/R_{out} \sim 1$ for SPS and $R_{side}/R_{out} <1$ for RHIC energy.

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