arXiv subjects

Rupa Chatterjee

Publications and source records attributed to Rupa Chatterjee.

49 records · Page 3Linked to original sources

arXiv2010

Equation of state of strongly interacting matter: spectra for thermal particles and intensity correlation of thermal photons

We find that an equation of state for hot hadronic matter consisting of all baryons having $M < 2$ GeV and all mesons having $M < 1.5$ GeV, along with Hagedorn resonances in thermal and chemical equilibrium, matches rather smoothly with lattice equation of state (p4 action, ${N_τ}=8$) for T up to $\approx 200$ MeV, when corrected for the finite volume of hadrons. Next we construct two equations of state for strongly interacting matter; one, HHL, in which the above is matched to the lattice equation of state at $T=165$ MeV and the other, HHB, where we match it to a bag model equation of state with critical temperature $T_c=165$ MeV. We compare particle spectra, thermal photon spectra and histories of evolution of the quark-gluon plasma produced in the central collision of gold (lead) nuclei at RHIC (LHC) energies, considering ideal hydrodynamical expansion of the system. The particle and thermal photon spectra are seen to differ only marginally, for the two equations of state. The history of evolution shows differences in the evolution of temperature and radial velocity, as one might expect. We calculate intensity interferometry of thermal photons and find it to be quite distinct for the two equations of state, especially for the outward correlation. The longitudinal correlation also shows a dependence on the equation of state, though, to a smaller extent.

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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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arXiv2009

Formation Time of QGP from Thermal Photon Elliptic Flow

We show that the transverse momentum dependent elliptic flow $v_2(p_T)$ of thermal photons is quite sensitive to the initial formation time ($τ_0$) of Quark Gluon Plasma (QGP) for semi-central collision of gold nuclei at RHIC \cite{tau}. A smaller value of the formation time or a larger initial temperature leads to a significant increase in the thermal photon radiation from QGP phase, which has a smaller $v_2$. The elliptic flow of thermal photon is dominated by the contribution from the quark matter at intermediate and high $p_T$ range and as a result sum $v_2$ decreases with smaller $τ_0$ for $p_T \ge 1.5$ GeV. On the other hand we find that the elliptic flow parameter for hadrons depends only marginally on the value of $τ_0$.

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arXiv2009

A Reanalysis of Single Photon Data at CERN SPS

We reanalyze the WA98 single photon data at CERN SPS by incorporating several recent developments in the study of prompt and thermal photon production from relativistic heavy ion collisions. Isospin and shadowing corrected NLO pQCD, along with an optimized scale for factorization, fragmentation and renormalization are considered for prompt photon production. Photons from thermal medium are estimated by considering a boost invariant azimuthally anisotropic hydrodynamic expansion of the plasma along with a well tested equation of state and initial conditions. A quantitative explanation of the data is obtained by combining $κ\times$ prompt with thermal photons, where $κ$ is an overall scaling factor. We show that, elliptic flow of thermal photons can play a crucial role to distinguish between the `with' and `without' phase transition scenarios at SPS energy.

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arXiv2009

Single photons from relativistic collision of lead nuclei at CERN SPS: A reanalysis

We present a reanalysis of single photon production from relativistic collision of lead nuclei at CERN SPS measured by the WA98 experiment. The refinements include use of iso-spin and shadowing corrected NLO pQCD treatment for prompt photon production using an optimized scale for factorization, renormalization, and fragmentation and use of hydrodynamics suited for non-central collisions along with a well tested equation of state admitting a quark-hadron phase transition. A quantitative explanation of the data requires a large initial temperature (at a small formation time of about 0.2 fm/$c$) and a moderate increase in the prompt yield which could perhaps be attributed to the Cronin effect in nuclei. The data can also be explained using a moderate initial temperature (at a formation time of about 1 fm/$c$) with a very large $K$-factor multiplying the prompt yield. We show that different initial times give rise to different values for the elliptic flow parameter $v_2$ for thermal photons. We also show that a measurement of $v_2$ for thermal photons could also distinguish between the scenarios with or without a phase transition.

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arXiv2009

Electromagnetic probes

We introduce the seminal developments in the theory and experiments of electromagnetic probes for the study of the dynamics of relativistic heavy ion collisions and quark gluon plasma.

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arXiv2009

Elliptic flow of thermal photons and formation time of quark gluon plasma at RHIC

We calculate the elliptic flow of thermal photons from Au+Au collisions at RHIC energies for a range of values for the formation time $τ_0$ but fixed entropy (or particle rapidity density). The results are found to be quite sensitive to $τ_0$. The $v_2$ for photons decreases as $τ_0$ decreases and admits a larger contribution from the QGP phase which has a smaller $v_2$. The elliptic flow coefficient for hadrons, on the other hand, is only marginally dependent on $τ_0$.

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arXiv2009

Time Evolution of Thermal Photon Elliptic Flow

Elliptic flow of thermal photons has a great potential to explore the early time dynamics and evolution of Quark Gluon Plasma. $p_T$ dependent temporal contours for photon spectra and elliptic flow from quark matter and hadronic phases, as well as the $p_T$ integrated results show gradual build-up of flow with time and relative contributions from different phases to that very clearly. Unlike hadrons, photon flow is quite sensitive to the initial thermalization time $τ_0$, and its value can be estimated with the experimental determination of $v_2$.

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arXiv2007

Evolution of pion HBT radii from RHIC to LHC -- Predictions from ideal hydrodynamics

We present hydrodynamic predictions for the charged pion HBT radii for a range of initial conditions covering those presumably reached in Pb+Pb collisions at the LHC. We study central (b=0) and semi-central (b=7fm) collisions and show the expected increase of the HBT radii and their azimuthal oscillations. The predicted trends in the oscillation amplitudes reflect a change of the final source shape from out-of-plane to in-plane deformation as the initial entropy density is increased.

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arXiv2007

Elliptic flow of thermal dileptons in relativistic nuclear collisions

We calculate the transverse momentum and invariant mass dependence of elliptic flow of thermal dileptons for Au+Au collisions at the Relativistic Heavy Ion Collider. The system is described using hydrodynamics, with the assumption of formation of a thermalized quark-gluon plasma at some early time, followed by cooling through expansion, hadronization and decoupling. Dileptons are emitted throughout the expansion history: by annihilation of quarks and anti-quarks inthe early quark-gluon plasma stage and through a set of hadronic reactions during the late hadronic stage. The resulting differential elliptic flow exhibits a rich structure, with different dilepton mass windows providing access to different stages of the expansion history. Elliptic flow measurements for dileptons,combined with those of hadrons and direct photons, are a powerful tool for mapping the time-evolution of heavy-ion collisions.

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arXiv2006

Elliptic flow of thermal photons and dileptons

In this talk we describe the recently discovered rich phenomenology of elliptic flow of electromagnetic probes of the hot matter created in relativistic heavy-ion collisions. Using a hydrodynamic model for the space-time dynamics of the collision fireball created in Au+Au collisions at RHIC, we compute the transverse momentum spectra and elliptic flow of thermal photons and dileptons. These observables are shown to provide differential windows into various stages of the fireball expansion.

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arXiv2006

Azimuthal flow of decay photons in relativistic nuclear collisions

An overwhelming fraction of photons from relativistic heavy ion collisions has its origin in the decay of $π^0$ and $η$ mesons. We calculate the azimuthal asymmetry of the decay photons for several azimuthally asymmetric pion distributions. We find that the $k_T$ dependence of the elliptic flow parameter$v_2$ for the decay photons closely follows the elliptic flow parameter $v_2^{π^0}$ evaluated at $p_T \approx k_T+δ$, where $δ\approx$ 0.1 -- 0.2 GeV, for typical pion distributions measured in nucleus-nucleus collisions at relativistic energies. Similar results are obtained for photons from the 2-$γ$ decay of $η$ mesons. Assuming that the flow of $π^0$ is similar to those for $π^+$ and $π^-$ for which independent measurements would be generally available, this ansatz can help in identifying additional sources for photons. Taken along with quark number scaling suggested by the recombination model, it may help to estimate $v_2$ of the parton distributions in terms of azimuthal asymmetry of the decay photons at large $k_T$.

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arXiv2006

Elliptic flow of thermal photons in relativistic nuclear collisions

We predict the transverse momentum (pT) dependence of elliptic flow of thermal photons for Au+Au collisions at the Relativistic Heavy Ion Collider. We model the system hydrodynamically, assuming formation of a thermalized quark-gluon plasma at some early time, followed by cooling through expansion, hadronization and decoupling. Photons are emitted throughout the expansion history. Contrary to hadron elliptic flow, which hydrodynamics predicts to increase monotonically with pT, the elliptic flow of thermal photons is predicted to first rise and then fall again as pT increases. Photon elliptic flow at high pT is shown to reflect the quark momentum anisotropy at early times when it is small, whereas at low pT it is controlled by the much larger pion momentum anisotropy during the late hadronic emission stage. An interesting structure is predicted at intermediate pT ~ 0.4 GeV/c where photon elliptic flow reflects the momenta and the (compared to pions) reduced v2 of heavy vector mesons in the late hadronic phase.

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