arXiv subjects

Bedangadas Mohanty

Publications and source records attributed to Bedangadas Mohanty.

At least 37 records · Page 2Linked to original sources

arXiv2019

Effect of color reconnection on forward-backward multiplicity and mean transverse momentum correlation

Color reconnection (CR) mechanism in PYTHIA model has been reported to be essential to describe the flow-like collective effect observed in high multiplicity $p$+$p$ and $p$+Pb collisions. In this work, we test this mechanism towards explaining the Forward-Backward multiplicity correlation (b$_{\mathrm {cor}}$) measurements in $p$+$p$ collisions at the LHC energies. Out of the three different CR schemes implemented in PYTHIA, (a) MPI based CR (default mechanism), (b) QCD based CR and (c) Gluon moved CR, we found that the QCD based CR scheme describes relatively better the ALICE measurements of b$_{\mathrm {cor}}$ in $p$+$p$ collisions at $\sqrt{\mathrm s}$ = 0.9 and 7 TeV. In addition, we have tuned the parameters of the default CR mechanism in PYTHIA to describe simultaneously the measured charged particle multiplicity pseudo-rapidity ($η$) distribution and b$_{\mathrm {cor}}$. We found that an average number of multipartonic interactions ($\langle N_{\mathrm {MPI}} \rangle$) between 2.5 to 3 and CR range between 0.9 to 2.5 best describes the experimental data. Finally, we have presented a study using PYTHIA events for $p$+$p$ collisions at $\sqrt{\mathrm s}$ = 7 TeV which shows that the strength of Forward-Backward mean transverse momentum correlation (b$^{\langle p_{\mathrm{T}}\rangle \langle p_{\mathrm{T}} \rangle}_{\rm {cor}}$) is found to increase with CR in contrast to decrease of b$_{\rm {cor}}$ values with CR effect. Hence, simultaneously studying the b$^{\langle p_{\mathrm{T}}\rangle \langle p_{\mathrm{T}} \rangle}_{\rm {cor}}$ and b$_{\mathrm {\rm {cor}}}$ in the experiments will help in establishing the arguments either in favour or in disfavour of CR effect in the measurements.

hep-ph↗

arXiv2019

Estimation of attractive and repulsive interactions from the fluctuation observables at RHIC using van der Waals hadron resonance gas Model

Experimental data on the moments of net-proton distribution in central Au-Au collisions for various center of mass energies ($\sqrt{\mathrm {s_{NN}}}$) measured by the STAR collaboration at the Relativistic Heavy-Ion Collider (RHIC) are compared to the corresponding results from a van der Waals type interacting hadron resonance gas (VDWHRG) model. The parameters representing the attractive and repulsive interactions in the VDWHRG model have been extracted by fitting the $σ^{2}$/$M$, $\it{S}σ$ and $κσ^{2}$, where $M$ is the mean, $σ$ is the standard deviation, $\it{S}$ is the skewness and $κ$ the kurtosis of the net-proton distribution. Considering all the three moment products we observe that the strength of the repulsive interactions increases with decrease in $\sqrt{\mathrm {s_{NN}}}$ = 200 to 19.6 GeV while the strength of the attractive interaction is of the similar magnitude. For $\sqrt{\mathrm {s_{NN}}}$ = 11.5 and 7.7 GeV there is drop in the strength of both attractive and repulsive interactions relative to $\sqrt{\mathrm {s_{NN}}}$ = 19.6 GeV. On the other hand, if we consider only the higher order moment products, $\it{S}σ$ and $κσ^{2}$, which are more sensitive to critical point physics, a segregation with respect to the strength of the attractive parameter is observed. The data for $\sqrt{\mathrm {s_{NN}}}$ = 19.6 and 27 GeV supports a larger attractive strength compared to other energies. For this latter case, the repulsive interaction values are of similar order for most of the beam energies studied, except for 7.7 GeV where the parameter value is not well constrained due to large uncertainties.

hep-ph↗

arXiv2019

Transport coefficients for multi-component gas of hadrons using Chapman Enskog method

The transport coefficients of a multi-component hadronic gas at zero and non-zero baryon chemical potential are calculated using the Chapman-Enskog method. The calculations are done within the framework of an $S$-matrix based interacting hadron resonance gas model. In this model, the phase-shifts and cross-sections are calculated using $K$-matrix formalism and where required, by parameterizing the experimental phase-shifts. Using the energy dependence of cross-section, we find the temperature dependence of various transport coefficients such as shear viscosity, bulk viscosity, heat conductivity and diffusion coefficient. We finally compare our results regarding various transport coefficients with previous results in the literature.

nucl-th↗

arXiv2019

Thermodynamics of a gas of hadrons with attractive and repulsive interaction within S-matrix formalism

We report the effect of including repulsive interactions on various thermodynamic observables calculated using a S-matrix based Hadron Resonance Gas (HRG) model to already available corresponding results with only attractive interactions [A. Dash, S. Samanta, and B. Mohanty, Phys. Rev. C 97, 055208 (2018)]. The attractive part of the interaction is calculated by parameterizing the two body phase shifts using K-matrix formalism while the repulsive part is included by fitting to the experimental phase shifts which carry the information about the nature of the interaction. We find that the bulk thermodynamic variables for a gas of hadrons such as energy density, pressure, entropy density, speed of sound and specific heat are suppressed by the inclusion of repulsive interactions and are more pronounced for second and higher order correlations and fluctuations, particularly for the observables $χ^2_Q$, $χ^2_B-χ^4_B$ and $C_{BS}$ in the present model. We find a good agreement between lattice QCD simulations and the present model for $C_{BS}$. We have also computed two leading order Fourier coefficients of the imaginary part of the first order baryonic susceptibility at imaginary baryon chemical potential within this model and compared them with the corresponding results from lattice. Additionally, assuming that the value of interacting pressure versus temperature for a gas of hadrons calculated in S-matrix formalism is same as that from a van der Waals HRG (VDWHRG) model, we have quantified the attractive and repulsive interactions in our model in terms of attractive and repulsive parameters used in the VDWHRG model. The values of parameters thus obtained are $a=1.54\pm 0.064$ GeV $\text{fm}^{3}$ and $r=0.81\pm 0.014$ fm.

hep-ph↗

arXiv2019

Exploring the hadron resonance gas phase on the QCD phase diagram

Lattice computations of strongly interacting matter at finite temperature $T$ and baryon chemical potential $μ_B$ suggest that the QCD thermodynamics deep in the hadronic phase can be adequately modeled by an ideal hadron resonance gas (I-HRG). However, it is not clear where on the $(μ_B, T)$ plane this description breaks down, making it essential to account for hadronic interactions and change in the nature of the degrees of freedom. We have studied several thermodynamic functions within the I-HRG model and try to identify the region of the QCD phase diagram where it becomes essential to include non-ideal effects into the I-HRG model. We work with only those thermodynamic quantities that show a monotonic rise with $T$ and $μ_B$ in I-HRG. Their high temperature limiting values where QCD becomes simply a Stefan-Boltzmann (SB) gas of massless quarks and gluons is known. The rise of these quantities in I-HRG beyond the corresponding SB limit values indicate the need to include interactions into I-HRG to study QCD thermodynamics. This works as a guiding principle on the QCD phase diagram where interacting HRG can take over from I-HRG. For $μ_B/T\leq2$, $χ^Q_2$ shoots the SB limit at the smallest $T$, while for higher values of $μ_B/T$,$C_{BS}=-3χ^{BS}_{11}/χ^S_2$ takes over. We further comment on the relative positions between the freezeout curve obtained by thermal fits to the measured hadron yields and the obtained line where I-HRG overshoots SB limit.

hep-ph↗

arXiv2019

Energy Loss Due to Defect Formation from $^{206}$Pb Recoils in SuperCDMS Germanium Detectors

The Super Cryogenic Dark Matter Search experiment (SuperCDMS) at the Soudan Underground Laboratory studied energy loss associated with Frenkel defect formation in germanium crystals at mK temperatures using in situ $^{210}$Pb sources. We examine the spectrum of $^{206}$Pb nuclear recoils near its expected 103 keV endpoint energy and determine an energy loss of $\left(6.08\pm0.18\right)$ %, which we attribute to defect formation. From this result and using TRIM simulations, we extract the first experimentally determined average displacement threshold energy of $\left(19.7^{+0.6}_{-0.5}\right)$ eV for germanium. This has implications for the analysis thresholds of future germanium-based dark matter searches.

physics.ins-det↗

arXiv2018

Effect of limited statistics on higher order cumulants measurement in heavy-ion collision experiments

We have studied the effect of limited statistics of data on measurement of the different order of cumulants of net-proton distribution assuming that the proton and antiproton distributions follow Possionian and Binomial distributions with initial parameters determined from experimental results for two top center of mass energies ($\sqrt{s_{\mathrm{NN}}}=200$ and $62.4$ GeV) in most central ($0-5$%) Au$+$Au collisions at Relativistic Heavy Ion Collider (RHIC). In this simulation, we observe that the central values for higher order cumulants have a strong dependence on event sample size and due to statistical randomness the central values of higher order cumulants could become negative. We also present a study on the determination of the statistical error on cumulants using delta theorem, bootstrap and sub-group methods and verified their suitability by employing a Monte Carlo procedure. Based on our study we find that the bootstrap method provides a robust way for statistical error estimation on high order cumulants. We also present the exclusion limits on the minimum event statistics needed for determination of cumulants if the signal strength (phase transition or critical point) is at a level of $5$% and $10$% above the statistical level. This study will help the experiments to arrive at the minimum required event statistics and choice of proper method for statistical error estimation for high order cumulant measurements.

nucl-ex↗

arXiv2018

Study of charged particle multiplicity, average transverse momentum and azimuthal anisotropy in Xe+Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV using AMPT model

We have studied the average charged particle density ($<$dN$_{ch}$/d$η$$>$), transverse momentum ($p_{\mathrm{T}}$) spectra, $<$$p_{\mathrm{T}}$$>$ and azimuthal anisotropies of inclusive charged particles produced in Xe+Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV using A Multiphase Transport Model (AMPT), which includes the deformation of Xe$^{129}$ nucleus. Calculations have been performed with the string melting version of AMPT model and compared with the recent measurements from the ALICE experiment. The model results over predict the measured $<$dN$_{ch}$/d$η$$>$ for central collisions, agree with the data for mid-central collisions and under predict the measurements for peripheral collisions. The centrality dependence of $<$$p_{\mathrm{T}}$$>$ of charged particles measured in ALICE is not reproduced by the model results. The calculated elliptic flow ($v_{2}$) from AMPT model overpredicts the ALICE measurements in central collisions but are consistent with the data in mid central collisions. We find that the model shows a mild centrality dependence of triangular flow and overestimates the ALICE measurements. Within the model framework, we have also studied various collision configurations of Xe nuclei such as body-body, tip-tip, side-side and random. We find a strong dependence of the above observable on the collision configurations.

nucl-ex↗

arXiv2018

Role of system size on freezeout conditions extracted from transverse momentum spectra of hadrons

The data on hadron transverse momentum spectra in different centrality classes of p+Pb collisions at $\sqrt{s}_{NN} = 5.02$ TeV has been analysed to extract the freezeout hypersurface within a simultaneous chemical and kinetic freezeout scenario. The freezeout hypersurface has been extracted for three different freezeout schemes that differ in the way strangeness is treated: i. unified freezeout for all hadrons in complete thermal equilibrium (1FO), ii. unified freezeout for all hadrons with an additional parameter $γ_S$ which accounts for possible out-of-equilibrium production of strangeness (1FO$+γ_S$), and iii. separate freezeout for hadrons with and without strangeness content (2FO). Unlike in heavy ion collisions where 2FO performs best in describing the mean hadron yields as well as the transverse momentum spectra, in p+Pb we find that 1FO$+γ_S$ with one less parameter than 2FO performs better. This confirms expectations from previous analysis on the system size dependence in the freezeout scheme with mean hadron yields: while heavy ion collisions that are dominated by constituent interactions prefer 2FO, smaller collision systems like proton + nucleus and proton + proton collisions with lesser constituent interaction prefer a unified freezeout scheme with varying degree of strangeness equilibration.

hep-ph↗

arXiv2018

Finite size effect of hadronic matter on its transport coefficients

We have theoretically investigated the finite system size effect of hadronic matter on its transport coefficients like shear viscosity, bulk viscosity, and electrical conductivity. We have used a Hadron Resonance Gas (HRG) model to calculate the thermodynamical quantities like entropy density, speed of sound and also the above transport coefficients. All these quantities are found to be sensitive to finite system size effects of hadronic matter. The effect of finite system size is found to be more when the system is at low temperatures and gets reduced at high temperatures. Owing to the intimate linking between system size and centrality, we have presented the centrality dependence of transport coefficients. We have also explored to link of our results with the macroscopic picture of hydrodynamical evolution.

hep-ph↗

arXiv2018

Bulk viscosity coefficient of hadronic matter

The bulk viscosity coefficient of hadronic matter has been estimated in this present work, where the thermodynamical equilibrium quantity like speed of sound in the medium has been obtained by using standard hadron resonance gas model. Whereas, the non-equilibrium quantity like thermal widths of medium constituents have been calculated in the framework field theory at finite temperature. Our values of bulk viscosity coefficient are in agreement with some earlier estimations.

nucl-th↗

arXiv2018

Interacting hadron resonance gas model in K-matrix formalism

An extension of Hadron Resonance Gas (HRG) model is constructed to include interactions using relativistic virial expansion of partition function. The non-interacting part of the expansion contains all the stable baryons and mesons and the interacting part contains all the higher mass resonances which decay into two stable hadrons. The virial coefficients are related to the phase shifts which are calculated using K-matrix formalism in the present work. We have calculated various thermodynamics quantities like pressure, energy density, and entropy density of the system. A comparison of thermodynamic quantities with non interacting HRG model, calculated using the same number of hadrons, shows that the results of above formalism are larger. A good agreement between equation of state calculated in K-matrix formalism and lattice QCD simulations is observed. Specifically the lattice QCD calculated interaction measure is well described in our formalism. We have also calculated second order fluctuations and correlations of conserved charges in K-matrix formalism. We observe a good agreement of second order fluctuations and baryon-strangeness correlation with lattice data below the cross-over temperature.

nucl-th↗

arXiv2018

Criticality in a Hadron Resonance Gas model with the van der Waals interaction

The van der Waals interaction is implemented in a Hadron Resonance Gas model. It is shown that this model can describe Lattice QCD data of different thermodynamical quantities satisfactorily with the van der Waals parameters $a = 1250 \pm 150$ MeV fm$^3$ and $r = 0.7 \pm 0.05$ fm. Further, a phase transition is observed in this model with the critical point at temperature, $T = 62.1$ MeV and baryon chemical potential, $μ_B = 708$ MeV.

hep-ph↗

arXiv2017

Freezeout systematics due to the hadron spectrum

We investigate systematics of the freezeout surface in heavy ion collisions due to the hadron spectrum. The role of suspected resonance states that are yet to be confirmed experimentally in identifying the freezeout surface has been investigated. We have studied two different freezeout schemes - unified freezeout scheme where all hadrons are assumed to freezeout at the same thermal state and a flavor dependent sequential freezeout scheme with different freezeout thermal states for hadrons with or without valence strange quarks. The data of mean hadron yields as well as scaled variance of net proton and net charge distributions have been analysed. We find the freezeout temperature $T$ to drop by $\sim5\%$ while the dimensionless freezeout parameters $μ_B/T$ and $VT^3$ ($μ_B$ and $V$ are the baryon chemical potential and the volume at freezeout respectively) are insensitive to the systematics of the input hadron spectrum. The observed hint of flavor hierarchy in $T$ and $VT^3$ with only confirmed resonances survives the systematics of the hadron spectrum. It is more prominent between $\sqrt{s_{NN}}\sim10 - 100$ GeV where the maximum hierarchy in $T\sim10\%$ and $VT^3\sim40\%$. However, the uncertainties in the thermal parameters due to the systematics of the hadron spectrum and their decay properties do not allow us to make a quantitative estimate of the flavor hierarchy yet.

nucl-th↗

arXiv2017

Measurements of spin alignment of vector mesons and global polarization of hyperons with ALICE at the LHC

We present the measurements related to global polarization of $Λ$ hyperons and spin alignment of $\mathrm{K^{*0}}~$ vector mesons at mid-rapidity for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~$= 2.76 TeV using the ALICE detector at the LHC. The global polarization measurements are carried out with respect to the first order event plane while the spin alignment measurements are carried out with respect to the production plane. No global polarization signal for $Λ$ is observed for 5-15\% and 15-50\% central Pb-Pb collisions. The spin density matrix element $ρ_{00}$ is found to have values slightly below 1/3 at low transverse momentum ($p_{\mathrm{T}}$) for $\mathrm{K^{*0}}~$ mesons, while it is consistent with 1/3 (no spin alignment) at higher $p_{\mathrm{T}}$. No spin alignment is observed for $\mathrm{K^{*0}}~$ in pp collisions at $\sqrt{s}$ = 13 TeV and for the spin zero hadron $\mathrm{K^{0}_{S}}~$ in 20-40\% Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~$ = 2.76 TeV.

nucl-ex↗

arXiv2017

3D Simulation of Electron and Ion Transmission of GEM-based Detectors

Time Projection Chamber (TPC) has been chosen as the main tracking system in several high-flux and high repetition rate experiments. These include on-going experiments such as ALICE and future experiments such as PANDA at FAIR and ILC. Different $\mathrm{R}\&\mathrm{D}$ activities were carried out on the adoption of Gas Electron Multiplier (GEM) as the gas amplification stage of the ALICE-TPC upgrade version. The requirement of low ion feedback has been established through these activities. Low ion feedback minimizes distortions due to space charge and maintains the necessary values of detector gain and energy resolution. In the present work, Garfield simulation framework has been used to study the related physical processes occurring within single, triple and quadruple GEM detectors. Ion backflow and electron transmission of quadruple GEMs, made up of foils with different hole pitch under different electromagnetic field configurations (the projected solutions for the ALICE TPC) have been studied. Finally a new triple GEM detector configuration with low ion backflow fraction and good electron transmission properties has been proposed as a simpler GEM-based alternative suitable for TPCs for future collider experiments.

physics.ins-det↗

arXiv2017

Contrasting Freezeouts in Large Versus Small Systems

We study the data on mean hadron yields and contrast the chemical freezeout conditions in p+p, p+Pb and Pb+Pb at the Large Hadron Collider (LHC) energies. We study several schemes for freezeout that mainly differ in the way strangeness is treated: i. strangeness freezes out along with the non-strange hadrons in complete equilibrium (1CFO), ii. strangeness freezes out along with non-strange hadrons with an additional parameter $γ_S$ accounting for non-equilibrium production of strangeness (1CFO+$γ_S$), and iii. strangeness freezes out earlier than non-strange hadrons and in thermal equilibrium (2CFO). A comparison of the chisquares of the fits indicate a dependence of the freezeout scheme on the system size. The minimum bias p+p and different centralities of p+Pb and peripheral Pb+Pb data prefer 1CFO$+γ_S$ with $γ_S$ approaching unity as we go from p+p to central p+Pb and peripheral Pb+Pb. On the other hand, the mid-central to central Pb+Pb data prefer 2CFO over 1CFO+$γ_S$. Such system size dependence of freezeout scheme could be an indication of the additional interaction in Pb+Pb over p+Pb and p+p.

nucl-th↗

arXiv2017

A Review of Elliptic Flow of Light Nuclei in Heavy-Ion Collisions at RHIC and LHC Energies

We present a review of the measurements of elliptic flow ($v_{2}$) of light nuclei ($d$,$\bar{d}$, $t$, $^{3}\rm He$, and $^{3}\overline{\rm He}$) from the RHIC and LHC experiments. Light (anti)nuclei $v_{2}$ have been compared with that of (anti)proton. We observed a similar trend in light nuclei $v_{2}$ to that in identified hadron $v_{2}$ with respect to the general observations such as ($p_{\rm T}$) dependence, low $p_{\rm T}$ mass ordering, and centrality dependence. We also compared the difference of nuclei and antinuclei $v_{2}$ with the corresponding difference of $v_{2}$ of proton and antiproton at various collision energies. Qualitatively they depict similar behavior. We also compare the data on light nuclei $v_{2}$ to various theoretical models such as blast-wave and coalescence. We then present a prediction of $v_{2}$ for $^{3}\rm He$ and $^{4}\rm He$ using coalescence and blast-wave models.

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