arXiv subjects

Sabyasachi Ghosh

Publications and source records attributed to Sabyasachi Ghosh.

103 records · Page 6Linked to original sources

arXiv2013

Analysis of $ω$ self-energy at finite temperature and density in the real-time formalism

Using the real time formalism of field theory at finite temperature and density we have evaluated the in-medium $ω$ self-energy from baryon and meson loops. We have analyzed in detail the discontinuities across the branch cuts of the self-energy function and obtained the imaginary part from the non-vanishing contributions in the cut regions. An extensive set of resonances have been considered in the baryon loops. Adding the meson loop contribution we obtain the full modified spectral function of $ω$ in a thermal gas of mesons, baryons and anti-baryons in equilibrium for several values of temperature and baryon chemical potential.

nucl-th↗

arXiv2013

Heavy flavor suppression: role of hadronic matter

The role of hadronic matter in the suppression of open heavy flavored mesons has been studied. The heavy-quarks (HQs) suppression factors have been calculated and contrasted with the experimental data obtained from nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadronic Collider (LHC) experiments. It is found that the suppression in the hadronic phase at RHIC energy is around $20%-25%$ whereas at the LHC it is around $10%-12%$ for the D meson. In case of B meson the hadronic suppression is around $10%-12%$ and $5%-6%$ at RHIC and LHC energies respectively. Present study suggests that the suppression of heavy flavor in the hadronic phase is significant at RHIC. However, the effect of hadronic suppression at LHC is marginal, this makes the characterization of QGP at LHC less complicated.

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arXiv2013

Characterizing quark gluon plasma by thermal photons and lepton pairs

The photon spectra measured by the ALICE collaboration in Pb+Pb collisions at Large Hadron Collider (LHC) energies has been analyzed with a view of extracting the properties of thermal system formed in these collisions. The results of the analysis are compared with the previously studied spectra measured at Super Proton Synchrotron (SPS) and Relativistic Heavy Ion Collider (RHIC) energies. The thermal dilepton spectra from the Pb+Pb collision at LHC energy has been predicted for the initial conditions constrained by the thermal photon spectra at the same collision conditions. The slope of the photon has been used to estimate the rise in the effective degeneracy with the charged particle multiplicity of the system. The slopes of the lepton pair spectra for different invariant mass windows have been used to conjecture the average radial flow velocity of the high temperature phase.

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arXiv2012

Effect of spectral modification of $ρ$ on shear viscosity of a pion gas

We evaluate the shear viscosity of a pion gas in the relativistic kinetic theory approach. The in-medium propagator of the $ρ$ meson at finite temperature is used to evaluate the $π-π$ scattering amplitude in the medium. The real and imaginary parts of the self-energy calculated from one-loop diagrams are seen to have noticeable effects on the scattering cross-section. The consequences on temperature dependence of the shear viscosity evaluated in the Chapman-Enskog and relaxation time approximations are studied.

nucl-th↗

arXiv2012

Drag and diffusion coefficients of $B$ mesons in hot hadronic matter

The drag and diffusion coefficients of a hot hadronic medium consisting of pions, kaons and eta using open beauty mesons as a probe have been evaluated. The interaction of the probe with the hadronic matter has been treated in the framework of chiral perturbation theory. It is observed that the magnitude of both the transport coefficients are significant, indicating substantial amount of interaction of the heavy mesons with the thermal bath. The results may have significant impact on the experimental observables like the suppression of single electron spectra originating from the decays of heavy mesons produced in nuclear collisions at RHIC and LHC energies

hep-ph↗

arXiv2012

In-medium vector mesons and low mass lepton pairs from heavy ion collisions

The rho and omega meson self-energy at finite temperature and baryon density have been analysed for an exhaustive set of mesonic and baryonic loops in the real time formulation of thermal field theory. The large enhancement of spectral strength below the nominal rho mass is seen to cause a substantial enhancement in dilepton pair yield in this mass region. The integrated yield after space-time evolution using relativistic hydrodynamics with quark gluon plasma in the initial state leads to a very good agreement with the experimental data from In-In collisions obtained by the NA60 collaboration.

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arXiv2012

Elliptic flow of thermal dileptons as a probe of QCD matter

We study the variation of elliptic flow of thermal dileptons with transverse momentum and invariant mass of the pairs for Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The dilepton productions from quark gluon plasma (QGP) and hot hadrons have been considered including the spectral change of light vector mesons in the thermal bath. The space time evolution has been carried out within the frame work of 2+1 dimensional ideal hydrodynamics with lattice+hadron resonance gas equation of state. We find that a judicious selection of invariant mass(M) and transverse momentum (p_T) windows can be used to extract the collective properties of quark matter, hadronic matter and also get a distinct signature of medium effects on vector mesons. Our results indicate a reduction of elliptic flow (v_2) for M beyond phi mass, which if observed experimentally would give the measure of v_2 of the partonic phase.

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arXiv2011

Observing many body effects on lepton pair production from low mass enhancement and flow at RHIC and LHC energies

The $ρ$ spectral function at finite temperature calculated using the real-time formalism of thermal field theory is used to evaluate the low mass dilepton spectra. The analytic structure of the $ρ$ propagator is studied and contributions to the dilepton yield in the region below the bare $ρ$ peak from the different cuts in the spectral function are discussed. The space-time integrated yield shows significant enhancement in the region below the bare $ρ$ peak in the invariant mass spectra. It is argued that the variation of the inverse slope of the transverse mass ($M_T$) distribution can be used as an efficient tool to predict the presence of two different phases of the matter during the evolution of the system. Sensitivity of the effective temperature obtained from the slopes of the $M_T$ spectra to the medium effects are studied.

nucl-th↗

arXiv2011

$ρ$ self energy at finite temperature and density in the real-time formalism

The $ρ$ meson self-energy in nuclear matter from baryonic loops is analysed in the real time formulation of field theory at finite temperature and density. The discontinuities across the branch cuts of the self-energy function are evaluated for an exhaustive set of resonances in the loops considering the fully relativistic thermal baryon propagator including anti-baryons. Numerical calculations show a significant broadening of the $ρ$ spectral function coming from the Landau cut. Adding the contribution from mesonic loops, the full spectral function of the $ρ$ in a thermal gas of mesons, baryons and antibaryons in equilibrium is evaluated at various values of temperature and baryonic chemical potential.

nucl-th↗

arXiv2011

Dragging $D$ mesons by hot hadrons

We evaluate the drag and diffusion coefficients of a hot hadronic medium consisting of pions, nucleons, kaons and eta using open charm mesons as a probe. The interaction of the probe with the hadronic matter has been treated in the framework of effective field theory. It is observed that the magnitude of both the transport coefficients are significant, indicating substantial amount of interaction of the heavy mesons with the thermal hadronic system. The results may have noticeable impact on the experimental observable like the suppression of single electron spectra originating form the decays of heavy mesons in nuclear collisions at relativistic energies.

nucl-th↗

arXiv2011

The $ρ$ meson in hot hadron matter and low mass dilepton spectra

The structure of the one loop self-energy graphs of the $ρ$ meson is analyzed in the real time formulation of thermal field theory. The modified spectral function of the $ρ$ meson in hot hadronic matter leads to a large enhancement of lepton pair production below the bare peak of the $ρ$. It has been shown that the effective temperature extracted from the inverse slope of the transverse momentum distributions for various invariant mass ($M$) windows of the pair can be used as an efficient tool to characterize different phases of the evolving matter.

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arXiv2010

Relativistic spectral function of nucleon in hot nuclear matter

We present a simple calculation of the nucleon self-energy in nuclear matter at finite temperature in a relativistic framework, using the real time thermal field theory. The imaginary parts of one-loop graphs are identified with discontinuities across the unitary and the Landau cuts. We find that in general both the cuts contribute significantly to the spectral function in the region of (virtual) nucleon mass usually considered, even though the unitary cut is ignored in the literature. Also our relativistic spectral function differs from the one in non-relativistic approximation, used in some earlier calculations.

hep-ph↗

arXiv2010

Analytic structure of rho meson propagator at finite temperature

We analyse the structure of one-loop self-energy graphs for the rho meson in real time formulation of finite temperature field theory. We find the discontinuities of these graphs across the unitary and the Landau cuts. These contributions are identified with different sources of medium modification discussed in the literature. We also calculate numerically the imaginary and the real parts of the self-energies and construct the spectral function of the rho meson, which are compared with an earlier determination. A significant contribution arises from the unitary cut of the pi-omega loop, that was ignored so far in the literature.

hep-ph↗