arXiv subjects

P. Garg

Publications and source records attributed to P. Garg.

87 records · Page 5Linked to original sources

arXiv2016

Forward $J/ψ$ production in U$+$U collisions at $\sqrt{s_{NN}}$=193 GeV

The invariant yields for $J/ψ$ production at forward rapidity $(1.2<|y|<2.2)$ in U$+$U collisions at $\sqrt{s_{_{NN}}}$=193 GeV have been measured as a function of collision centrality. The invariant yields and nuclear-modification factor $R_{AA}$ are presented and compared with those from Au$+$Au collisions in the same rapidity range. Additionally, the direct ratio of the invariant yields from U$+$U and Au$+$Au collisions within the same centrality class is presented, and used to investigate the role of $c\bar{c}$ coalescence. Two different parameterizations of the deformed Woods-Saxon distribution were used in Glauber calculations to determine the values of the number of nucleon-nucleon collisions in each centrality class, $N_{\rm coll}$, and these were found to give significantly different $N_{\rm coll}$ values. Results using $N_{\rm coll}$ values from both deformed Woods-Saxon distributions are presented. The measured ratios show that the $J/ψ$ suppression, relative to binary collision scaling, is similar in U$+$U and Au$+$Au for peripheral and midcentral collisions, but that $J/ψ$ show less suppression for the most central U$+$U collisions. The results are consistent with a picture in which, for central collisions, increase in the $J/ψ$ yield due to $c\bar{c}$ coalescence becomes more important than the decrease in yield due to increased energy density. For midcentral collisions, the conclusions about the balance between $c\bar{c}$ coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine $N_{\rm coll}$.

nucl-ex↗

arXiv2016

Indication of Differential Kinetic Freeze-out at RHIC and LHC Energies

The transverse momentum spectra at RHIC and LHC for A+A and p+p collisions are studied with Tsallis distributions in different approaches i.e. with and without radial flow. The information on the freeze-out surface in terms of freeze-out volume, temperature, chemical potential and radial flow velocities for different particle species are obtained. These parameters are found to show a systematic behavior with mass dependence. It is observed that the heavier particles freeze-out early as compared to lighter particles and freeze-out surfaces are different for different particles, which is a direct signature of mass dependent differential freeze-out. Further, we observe that the radial flow velocity decreases with increasing mass. This confirms the mass ordering behavior in collectivity observed in heavy-ion collisions. It is also observed that the systems created in peripheral heavy-ion collisions and in proton-proton collisions are of similar thermodynamic nature.

hep-ph↗

arXiv2016

Effect of correlations on cumulants in heavy-ion collisions

We study the effects of correlations on cumulants and their ratios of net-proton multiplicity distributions which have been measured for central (0\%-5\%) Au + Au collisions at the Relativistic Heavy Ion Collider (RHIC). This effect has been studied assuming individual proton and anti-proton distributions as a Poisson or Negative Binomial Distribution (NBD). In-spite of significantly correlated production due to baryon number, electric charge conservation and kinematical correlations of protons and anti-protons, the measured cumulants of the net-proton distribution follow the independent production model. In the present work we demonstrate how the introduction of the correlations will affect the cumulants and their ratios for the difference distributions. We have also demonstrated this study using the proton and anti-proton distributions obtained from the HIJING event generator.

nucl-th↗

arXiv2016

Multiplicity fluctuations in heavy-ion collisions using canonical and grand-canonical ensemble

We report the higher order cumulants and their ratios for baryon, charge and strangeness multiplicity in canonical and grand-canonical ensembles in ideal thermal model including all the resonances. When the number of conserved quanta is small, an explicit treatment of these conserved charges is required, which leads to a canonical description of the system and the fluctuations are significantly different from the grand canonical ensemble. Cumulant ratios of total charge and net-charge multiplicity as a function of collision energies are also compared in grand canonical ensemble.

nucl-th↗

arXiv2015

Inclusive cross section and double-helicity asymmetry for $π^{0}$ production at midrapidity in $p$$+$$p$ collisions at $\sqrt{s}=510$ GeV

PHENIX measurements are presented for the cross section and double-helicity asymmetry ($A_{LL}$) in inclusive $π^0$ production at midrapidity from $p$$+$$p$ collisions at $\sqrt{s}=510$~GeV from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The $π^{0}A_{LL}$ results follow an increasingly positive asymmetry trend with $p_T$ and $\sqrt{s}$ with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on $π^0$ and jet $A_{LL}$, and suggested a positive contribution of gluon polarization to the spin of the proton $ΔG$ for the gluon momentum fraction range $x>0.05$. The data presented here extend to a currently unexplored region, down to $x\sim0.01$, and thus provide additional constraints on the value of $ΔG$. The results confirm the evidence for nonzero $ΔG$ using a different production channel in a complementary kinematic region.

hep-ex↗

arXiv2015

Net-baryon number fluctuations with the hadron resonance gas model using Tsallis distribution

We explore a hadron resonance gas model using Tsallis non-extensive distribution to study the energy dependence of the product of the moments, $Sσ$ and $κσ^2$ of net-proton multiplicity distributions of published STAR data in \auau collisions at relativistic heavy-ion collider (RHIC) energies. While excellent agreements are found between model predictions and measurements of $Sσ$ and $κσ^2$ of most peripheral collisions and $Sσ$ of most central collisions, the $κσ^2$ for most central collisions deviates significantly from the predictions particularly at \sqsn = 19.6 GeV and $27$ GeV. This could be an indication of the presence of dynamical fluctuations, which are not contained in the HRG-Tsallis model.

nucl-th↗

arXiv2014

Chaotic mixing in a planar, curved channel using periodic slip

We propose a novel strategy for designing chaotic micromixers using curved channels confined between two flat planes. The location of the separatrix between the Dean vortices, induced by centrifugal force, is dependent on the location of the maxima of axial velocity. An asymmetry in the axial velocity profile can change the location of the separatrix. This is achieved physically by introducing slip alternatingly at the top and bottom walls. This leads to streamline crossing and Lagrangian chaos. An approximate analytical solution of the velocity field is obtained using perturbation theory. This is used to find the Lagrangian trajectories of fluid particles. Poincare sections taken at periodic locations in the axial direction are used to study the extent of chaos. The extent of mixing, for low slip and low Reynolds numbers, is shown to be greater when Dean vortices in adjacent half cells are counter-rotating. Wide channels are observed to have much better mixing than tall channels; an important observation not made for separatrix flows till now. Eulerian indicators are used to gauge the extent of mixing with varying slip length and it is shown that an optimum slip length exists which maximizes the mixing in a particular geometry.

nlin.CD↗

arXiv2014

Nuclear matter effects on $J/ψ$ production in asymmetric Cu+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

We report on $J/ψ$ production from asymmetric Cu+Au heavy-ion collisions at $\sqrt{s_{_{NN}}}$=200 GeV at the Relativistic Heavy Ion Collider at both forward (Cu-going direction) and backward (Au-going direction) rapidities. The nuclear modification of $J/ψ$ yields in Cu$+$Au collisions in the Au-going direction is found to be comparable to that in Au$+$Au collisions when plotted as a function of the number of participating nucleons. In the Cu-going direction, $J/ψ$ production shows a stronger suppression. This difference is comparable in magnitude and has the same sign as the difference expected from shadowing effects due to stronger low-$x$ gluon suppression in the larger Au nucleus. The relative suppression is opposite to that expected from hot nuclear matter dissociation, since a higher energy density is expected in the Au-going direction.

nucl-ex↗

arXiv2014

Concept for an Electron Ion Collider (EIC) detector built around the BaBar solenoid

The PHENIX collaboration presents here a concept for a detector at a future Electron Ion Collider (EIC). The EIC detector proposed here, referred to as ePHENIX, will have excellent performance for a broad range of exciting EIC physics measurements, providing powerful investigations not currently available that will dramatically advance our understanding of how quantum chromodynamics binds the proton and forms nuclear matter.

nucl-ex↗

arXiv2013

Structural characterization of as-deposited cesium iodide films studied by X-ray diffraction and transmission electron microscopy techniques

In the present work, cesium iodide (CsI) thin films of different thickness have been prepared by thermal evaporation technique. The crystallite size and grain size of these films are compared by using X-ray diffraction (XRD) profile analysis as well as by transmission electron microscopy (TEM) counting, respectively. These two methods provide less deviation between crystallite size and grain size in the case of thin CsI films of 4 nm, but there is comparatively large difference in case of thicker CsI films (20 nm, 100 nm and 500 nm). It indicates that dislocations are arranged in a configuration which causes small orientational difference between two adjacent coherent regions. The size obtained from XRD corresponds to two separate regions, whereas in the TEM micrograph the two regions may seem to correspond one region particularly in case of thicker films. Other physical parameters such as strain, stress and deformation energy density are also estimated precisely for the prominent XRD peaks of thicker CsI films in the range $2θ= 20^{0}-80^{0}$ by using a modified Williamson-Hall (W-H) analysis assuming uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM).

cond-mat.mtrl-sci↗

arXiv2013

Conserved number fluctuations in a hadron resonance gas model

Net-baryon, net-charge and net-strangeness number fluctuations in high energy heavy-ion collisions are discussed within the framework of a hadron resonance gas (HRG) model. Ratios of the conserved number susceptibilities calculated in HRG are being compared to the corresponding experimental measurements to extract information about the freeze-out condition and the phase structure of systems with strong interactions. We emphasize the importance of considering the actual experimental acceptances in terms of kinematics (pseudorapidity ($η$) and transverse momentum ($p_{T}$)), the detected charge state, effect of collective motion of particles in the system and the resonance decay contributions before comparisons are made to the theoretical calculations. In this work, based on HRG model, we report that the net-baryon number fluctuations are least affected by experimental acceptances compared to the net-charge and net-strangeness number fluctuations.

nucl-ex↗

arXiv2013

Unfolding of event-by-event net-charge distributions in heavy-ion collisions

An unfolding method, based on Bayes theorem is presented to obtain true event-by-event net-charge multiplicity distribution from a corresponding measured distribution, which is subjected to detector artifacts. The unfolding is demonstrated to work for widely varying particle production mechanism, beam energy and collision centrality. Further the necessity of taking into account the detector effects is emphasized before comparing the experimental measurements to the theoretical calculations, particularly in case of higher moments. The advantage of this approach being that one need not construct new observable to cancel out detector effects which loose their ability to be connected to physical quantities calculable in standard theories.

hep-ph↗

arXiv2013

Moments of net-charge multiplicity distribution in Au+Au collisions measured by the PHENIX experiment at RHIC

Beam Energy Scan (BES) program at RHIC is important to search for the existence of the critical point in the QCD phase diagram. Lattice QCD have shown that the predictions of the susceptibility of the medium formed in heavy-ion collisions can be sensitive to the various moments (mean ($μ$) =${ }$, variance ($σ^2$) = ${<(x-μ)^2>}$, skewness (S) = $\frac{<(x-μ)^3>}{σ^3}$ and kurtosis ($κ$) =$\frac{<(x-μ)^4>}{σ^4} -3$) of conserved quantities like net-baryon number ($Δ$B), net-electric charge ($Δ$Q) and net-strangeness ($Δ$S). Any non-monotonic behavior of the higher moments would confirm the existence of the QCD critical point. The recent results of the higher moments of net-charge multiplicity distributions for Au+Au collisions at $\sqrt{s}_{NN}$ varying from 7.7 GeV to 200 GeV from the PHENIX experiment at RHIC are presented. The energy and centrality dependence of the higher moments and their products (S$σ$ and $κσ^{2}$) are shown for the net-charge multiplicity distributions. Furthermore, the results are compared with the values obtained from the heavy-ion collision models, where there is no QCD phase transition and critical point.

nucl-ex↗

arXiv2013

Unfolding of event-by-event net-charge distributions in heavy-ion collision

We discuss a method to obtain the true event-by-event net-charge multiplicity distributions from a corresponding measured distribution which is subjected to detector effects such as finite particle counting efficiency. The approach is based on the Bayes method for unfolding of distributions. We are able to faithfully unfold back the measured distributions to match with their corresponding true distributions obtained for a widely varying underlying particle production mechanism, beam energy and collision centrality. Particularly the mean, variance, skewness, kurtosis, their products and ratios of net-charge distributions from the event generators are shown to be successfully unfolded from the measured distributions constructed to mimic a real experimental distribution. We demonstrate the necessity to account for detector effects before associating the higher moments of net-charge distributions with physical quantities or phenomena. The advantage of this approach being that one need not construct new observable to cancel out detector effects which loose their ability to be connected to physical quantities calculable in standard theories.

nucl-ex↗

arXiv2012

Performance studies of the PHENIX Hadron Blind Detector at RHIC

Electron pairs or di-leptons in general are unique probes to study the hot and dense matter formed in relativistic heavy ion collisions at RHIC. Particularly, low mass di-leptons are sensitive to chiral symmetry restoration effects and to thermal radiation emitted by the plasma via virtual photons, providing a direct measurement of the quark gluon plasma temperature. But the experimental challenge is the huge combinatorial background created by $e^+e^-$ pairs from copiously produced $π^0$ Dalitz decay and $γ$ conversions. In order to reduce this background, a Hadron Blind Detector was proposed in PHENIX for electron identification in high-density hadron environment. In the present paper some of the performance studies of the HBD carried with data from 2009 Run are discussed.

physics.ins-det↗