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Pradip Roy

Publications and source records attributed to Pradip Roy.

At least 73 records · Page 4Linked to original sources
arXiv2008

$ρ$-$ω$ mixing and spin dependent CSV potential

We construct the charge symmetry violating (CSV) nucleon-nucleon potential induced by the $ρ^0$-$ø$ mixing due to the neutron-proton mass difference driven by the $NN$ loop. Analytical expression for for the two-body CSV potential is presented containing both the central and non- central $NN$ interaction. We show that the $ρ$$NN$ tensor interaction can significantly enhance the charge symmetry violating $NN$ interaction even if momentum dependent off-shell $ρ^0$-$ω$ mixing amplitude is considered. It is also shown that the inclusion of form factors removes the divergence arising out of the contact interaction. Consequently, we see that the precise size of the computed scattering length difference depends on how the short range aspects of the CSV potential are treated.

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arXiv2008

Matter induced charge symmetry breaking and pion form factor in nuclear medium

Medium modification of pion form factor has been evaluated in asymmetric nuclear matter. It is shown that both the shape and the pole position of the pion form factor in dense asymmetric nuclear matter is different from its vacuum counterpart with $ρ$-$ω$ mixing. This is due to the density and asymmetry dependent $ρ$-$ω$ mixing which could even dominate over its vacuum counterpart in matter. Effect of the in-medium pion factor on experimental observables {\it e.g.}, invariant mass distribution of lepton pairs has been demonstrated.

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arXiv2007

Thermal Radiation from Au + Au Collisions at \sqrt{s} = 200 GEV/A Energy

The transverse momentum distribution of the direct photons measured by the PHENIX collaboration in $Au + Au$ collisions at $\sqrt{s}=200$ GeV/A has been analyzed. It has been shown that the data can be reproduced reasonably well assuming a deconfined state of thermalized quarks and gluons with initial temperature more than the transition temperature for deconfinement inferred from lattice QCD. The value of the initial temperature depends on the equation of state of the evolving matter. The sensitivities of the results on various input parameters have been studied. The effects of the modifications of hadronic properties at non-zero temperature have been discussed.

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arXiv2006

Collisional energy loss and the suppression of high $p_T$ hadrons

We calculate nuclear suppression factor ($R_{AA}$) for light hadrons by taking only the elastic processes and argue that in the measured $p_T$ domain of RHIC, collisional rather than the radiative processes is the dominant mechanism for partonic energy loss.

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arXiv2006

Energy loss and dynamical evolution of quark $p_T$ spectra

Average energy loss of light quarks has been calculated in a two stage equilibrium scenario where the quarks are executing Brownian motion in a gluonic heat bath. The evolution of the quark $p_T$ spectra is studied by solving Fokker-Planck equation in an expanding plasma. Results are finally compared with experimentally measured pion $p_T$ spectrum at RHIC.

hep-ph↗
arXiv2006

Can collisional energy loss explain nuclear suppression factor for light hadrons ?

We argue that in the measured $p_T$ domain of RHIC, collisional rather than the radiative energy loss is the dominant mechanism for jet quenching. Accordingly we calculate nuclear suppression factor for light hadrons by taking only the elastic energy loss in sharp contrast with the previous calculations where only the radiative loss are considered.

hep-ph↗
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

Charmonium Productions: Nucleon-Nucleon versus Nucleus-Nucleus Collisions

Charmonium productions in $p-p$ and $A-B$ collisions have been estimated within the ambit of colour evaporation model (CEM). The model parameters have been fixed by fitting the theoretical results with CDF data. The method is then applied to RHIC and LHC energies to obtain the transverse momentum distributions of $J/ψ$, $ψ^{\prime}$ and $χ_c$. Suppression due to Debye screening in a quark gluon plasma (QGP) is estimated at various centrality cuts. The final $p_T$ distributions of various resonances are then predicted convoluting with the survival probability.

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arXiv2005

Stopping power of hot QCD plasma

The partonic energy loss has been calculated taking both the hard and soft contributions for all the $2 \to 2$ processes, revealing the importance of the individual channels. Cancellation of the intermediate separation scale has been exhibited. Subtleties related to the identical final state partons have properly been taken into account. The estimated collisional loss is compared with its radiative counter part. We show that there exists a critical energy ($E_c$) below which the collisional loss is more than its radiative counterpart. In addition, we present closed form formulas for both the collision probabilities and the stopping power ($dE/dx$)

hep-ph↗
arXiv2004

Charmonium at LHC: Production, Propagation and Decay

The productions of muon pairs from the decay of heavy quarkonia have been evaluated for different centrality of the nuclear collisions at LHC energies. The effects of the various comover scenarios on the survival probability of the heavy quarkonia have been considered. The effects of shadowing and comover suppressions on the dilepton spectra originating from the decays of J/ψis found to be substantial. The dilepton yield from the thermal J/ψhas also been estimated and found to be small.

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arXiv2003

Thermal photons from $πρ\ra πγ$ revisited

We evaluate the photon spectra from the reaction $πρ\ra πγ$ for the exchange of $π$, $ρ$, $ω$, $ϕ$ and $a_1$ as intermediary mesons. It is found that the contributions from the intermediary $a_1$ is more than any other meson exchange processes up to photon energies 2.5 GeV.

hep-ph↗
arXiv2003

Role of in-medium hadrons in photon-nucleus reactions : shadowing and dilepton spectrum

We study the effect of in-medium hadronic properties in photon nucleus interactions in the context of shadowing as well as the dilepton spectrum for incident photon energies in the range 1.1- 3 GeV. A reasonable agreement with the experimental data for shadowing is obtained in a scenario of downward spectral shift of the hadrons. We show that distinguishable features for in-medium changes of the hadronic properties can be observed experimentally through the dilepton spectrum by judicious choice of target nuclei and incident energy of photons.

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arXiv2003

Thermal Radiation from Nucleons and Mesons

Thermal photon emission rates due to meson-nucleon interactions have been evaluated. An exhaustive set of reactions involving p(\bar p), n(\bar n), rho, omega, a_1, pi and eta is seen to provide a sizeable contribution to the emission rate from hot hadronic matter. Contributions from baryonic resonances are found to be negligibly small.

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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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arXiv2003

Spectral Red-Shift Versus Broadening from Photon and Dilepton Spectra

We estimate the photon and dilepton emission rates from hot hadronic matter with in-medium spectral shift and broadening of vector mesons. It is observed that both the WA98 photon data and CERES/NA45 dilepton data can be well reproduced with similar initial conditions. The freeze-out condition has been constrained by the transverse mass spectra of pions and protons measured by the NA49 collaboration. We argue that simultaneous measurement of the $p_T$ spectra of single photons as well as invariant mass distribution of dileptons is crucial to understand the in-medium spectral function of the vector mesons.

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arXiv2002

Shadowing in photo-production : role of in-medium hadrons

We study the effects of in-medium hadronic properties on shadowing in photon-nucleus interactions in Glauber model as well as in the multiple scattering approach. A reasonable agreement with the experimental data is obtained in a scenario of downward spectral shift of the hadrons. Shadowing is found to be insensitive to the broadening of the spectral functions. An impact parameter dependent analysis of shadowing might shed more light on the role of in-medium properties of hadrons.

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