arXiv subjects

P. K. Sahu

Publications and source records attributed to P. K. Sahu.

At least 19 recordsLinked to original sources

arXiv2026

Bjorken Initial Energy Density and Viscous Longitudinal Hydrodynamic Evolution in Xe-Xe Collisions

We present a systematic study of the Bjorken initial energy density in Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44$ TeV, estimated using charged-particle multiplicity data and a generalized transverse overlap geometry applicable beyond the most central collisions. The dependence of the extracted energy density is examined by adopting both a constant formation time and a centrality-dependent formation time derived from Pb-Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV. Corresponding Bjorken energy density estimates for Pb-Pb collisions are also presented for comparison. Taking the Bjorken energy density and formation time as initial conditions, the subsequent longitudinal evolution of the quark-gluon plasma (QGP) formed in these collisions is studied. Both ideal and first-order viscous boost-invariant hydrodynamics are employed to assess the influence of dissipation. We observe that viscous effects slow the longitudinal expansion and lead to entropy production dominated by early-time dynamics. The lifetime of the QGP is observed to increase with centrality and is substantially enhanced by viscous effects. These effects are highly sensitive to the choice of formation time, particularly in peripheral collisions. A comparative analysis of Xe-Xe and Pb-Pb collisions demonstrates that the longitudinal evolution is primarily controlled by the initial energy density scale set by the Bjorken prescription. Consequently, when this scale is comparable, both systems exhibit nearly identical evolution patterns, while appreciable distinctions emerge in peripheral collisions due to system-size and geometric effects.

hep-ph↗

arXiv2025

Bjorken initial energy density estimation in Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44$ TeV using ALICE

The Bjorken initial energy density ($ε_{B}$) has been estimated in different centrality classes in Xe-Xe collisions using Bjorken formula. Three different cases have been considered. In Case I, we have fixed the formation time ($τ_{0}$) and varied the area of overlap region ($A_{overlap}$). In Case II, we have fixed both $τ_{0}$ and $A_{overlap}$ and we have varied both $τ_{0}$ and $A_{overlap}$ in Case III. We observed that the $ε_{B}$ is first increasing and then decreasing while going from central to peripheral collisions in Case I whereas it is decreasing in Case II and III, as expected. The $ε_{B}$ value for top central and mid central collisions in Case II and for all centrality classes in Case III are greater than 1 $GeV/(fm)^{3}$, indicating the possibility of QGP medium formation respectively. The $ε_{B}$ results of the Pb-Pb at $\sqrt{s_{NN}} = 2.76$ and 5.02 TeV are compared. In Case II, it is observed that in the centrality class (0-5)%, the $ε_{B}$ value in Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44$ TeV is 34.66% less than in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV and 57.12% less than at 5.02 TeV. This may be interpreted as, the system size in Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44$ TeV is 34.66% smaller than in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV and 57.12% smaller than at 5.02 TeV. Similarly in Case III in the centrality class (0-5)%, the $ε_{B}$ value in Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44$ TeV is 3.22% more than in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV and 32.18% less than at 5.02 TeV. This may be interpreted as, the system size in Xe-Xe collisions at $\sqrt{s_{NN}} = 5.44$ TeV is 3.22% bigger than in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV and 32.18% smaller than at 5.02 TeV. The results obtained in the Case III seems more suitable than Case II.

hep-ph↗

arXiv2023

Higher order dynamical charge fluctuations in heavy-ion collisions

The event-by-event charge fluctuation measurements are proposed to provide the signature of quark-gluon plasma (QGP) in heavy-ion collisions. Measure of dynamical charge fluctuations is expected to carry information of initial fractional charge of the QGP phase at the final state. We propose the higher order charge fluctuation measurement to study the QGP signal in heavy-ion collisions. This higher order charge fluctuation observable can amplify the signature of QGP. Also, the SMASH model is used to study the behavior of these observable in heavy-ion collisions at center of mass energies accessible in the STAR beam energy scan program.

nucl-th↗

arXiv2021

Thermal properties of hot and dense medium in interacting hadron resonance gas model

The meson exchange interaction based on relativistic mean-field (RMF) theory has been introduced in the hadron resonance gas (HRG) model, called interacting HRG (iHRG) model. This model can be used to explain the experimental data both at finite temperature ($T$) with finite chemical potential ($μ_B$) and finite temperature at vanishing chemical potential. The nuclear matter equation of state also can be explained at zero temperature with finite baryon density (finite chemical potential) due to the presence of attractive and repulsive interactions between the hadrons in the iHRG model. Similarly, the lattice equation of state is well described at $μ_B$ = 0 and finite temperature by the iHRG model. In the present study, we have calculated the thermodynamical quantities as a function of temperature and chemical potential using both HRG and iHRG models. Also, we have presented the isothermal compressibility ($k_T$), specific heat ($C_V$), and speed of sound ($c_s^2$) as a function of $μ_B$, $T$, and center of mass energies. The effect of kinematic acceptance on these quantities are also presented as a function of $μ$ and $T$. Results from this study on $k_T$ are compared with results from other heavy-ion transport models and experimental data up to LHC energies.

nucl-th↗

arXiv2019

Hadron production in pp and p-Pb collisions: A mass dependent phenomenon

The mass dependence plays a significant role in the yield enhancement or suppression of hadrons in pp and p-Pb collisions at the LHC energies. This has been observed by parameterizing the variation of yield ratios between any two hadrons with event charged-particle multiplicity using a single empirical function. We notice that this variation is independent of all quantum numbers and solely depends on masses of hadrons and masses of their valence quarks. The function shows that the amount of quark deconfinement increases with event multiplicity, and the quark coalescence favours more the production of heavier hadrons compared to lighter ones.

nucl-ex↗

arXiv2018

Calculating charged particle observables using modified Wood Saxon model in HIJING for U+U collisions at $\sqrt{s_{NN}}$ = 193 GeV

We have implemented spherical harmonics in default Wood Saxon distribution of the HIJING model and calculated various physical observables such as transverse momentum, charged particle multiplicity, nuclear modification factor and particle ratios for charged particles at top RHIC energy with collisions of Uranium (U) nuclei. Results have been compared with available experimental data. We observe that, a particular type of collision configuration can produce significant magnitude change in observables. We have noticed that the tip-tip configuration shows higher magnitude of particle yield in central collisions, while the body-body configuration shows higher value in the cases of peripheral collisions, with the flip in the trend occurring for the mid-central U+U collisions. We observe that particle ratios are independent of configuration type.

nucl-th↗

arXiv2018

Application of Nilsson model for deformed nucleus in relativistic heavy ion collisions

Electron scattering methods, involving nucleus which have little or no intrinsic deformation suggest nucleon distribution to be of Fermi type. This distribution is further parameterised as Wood Saxon (WS) distribution, where an uniform charge density with smoothed-out surface have been implemented. Incorporating shape modification in WS, earlier attempts were made to explain observables in deformed nuclear collisions, such as charged particle multiplicity. In this work, we use an alternate approach known as Nilsson model or Modified Harmonic Oscillator (MHO), to explain charged particle multiplicity in U+U collisions at top RHIC energy. We have implemented the formalism in HIJING model and we found that the model describes the experimental data to an extent.

nucl-th↗

arXiv2018

Ethernet based Data logger for Gaseous Detectors

A data logger is designed to monitor and record ambient parameters such as temperature, pressure and relative humidity along with gas flow rate as a function of time. These parameters are required for understanding the characteristics of gas-filled detectors such as Gas Electron Multiplier (GEM) and Multi-Wire Proportional Counter (MWPC). The data logger has different microcontrollers and has been interfaced to an ethernet port with a local LCD unit for displaying all measured parameters. In this article, the explanation of the data logger design, hardware, and software description of the master microcontroller and the DAQ system along with LabVIEW interface client program have been presented. We have implemented this device with GEM detector and displayed few preliminary results as a function of above parameters.

physics.ins-det↗

arXiv2017

Azimuthal correlations of D-mesons in $p$+$p$ and $p$+Pb collisions at LHC energies

We study the correlations of D mesons produced in $p$+$p$ and $p$+Pb collisions. These are found to be sensitive to the effects of the cold nuclear medium and the transverse momentum ($p_T$) regions we are looking into. In order to put this on a quantitative footing, as a first step we analyse the azimuthal correlations of D meson-charged hadron(Dh), and then predict the same for D meson -anti D meson ($D\overline{D}$) pairs in $p$+$p$ and $p$+Pb collisions with strong coupling at leading order $\cal{O}$($α_{s}^{2}$) and next to leading order $\cal{O}$($α_{s}^{3}$) which includes space-time evolution (in both systems), as well cold nuclear matter effects (in $p$+Pb). This also sets the stage and baseline for the identification and study of medium modification of azimuthal correlations in relativistic collision of heavy nuclei at the Large Hadron Collider.

hep-ph↗

arXiv2016

Production of D-mesons in $p$+$p$ and $p$+Pb collisions at LHC energies

We present theoretical model comparison with published ALICE results for D-mesons (D$^0$, D$^+$ and D$^{*+}$) in $p$+$p$ collisions at $\sqrt{s}$ = 7 TeV and $p$+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. Event generator HIJING, transport calculation of AMPT and calculations from NLO(MNR) and FONLL have been used for this study. We found that HIJING and AMPT model predictions are matching with published D-meson cross-sections in $p$+$p$ collisions, while both under-predict the same in $p$+Pb collisions. Attempts were made to explain the $R_{pPb}$ data using NLO-pQCD(MNR), FONLL and other above mentioned models.

hep-ph↗

arXiv2016

Building of a 4-channel TTL scaler for counting detector signals

A scaler has been fabricated to count the signals from any radiation de- tector. It can count signals of frequency up to 140 kHz. Transistor Transistor Logic (TTL) is used in this scaler. In this article the details of the design, fabrication and operation processes of the scaler is presented.

physics.ins-det↗

arXiv2016

Long-term stability test of a triple GEM detector

The main aim of the study is to perform the long-term stability test of gain of the single mask triple GEM detector. A simple method is used for this long- term stability test using a radioactive X-ray source with high activity. The test is continued till accumulation of charge per unit area > 12.0 mC/mm2. The details of the chamber fabrication, the test set-up, the method of measurement and the test results are presented in this paper.

physics.ins-det↗

arXiv2015

Design and fabrication of a data logger for atmospheric pressure, temperature and relative humidity for gas-filled detector development

A novel instrument has been developed to monitor and record the ambient pa- rameters such as temperature, atmospheric pressure and relative humidity. These parameters are very essential for understanding the characteristics such as gain of gas filled detectors like Gas Electron Multiplier (GEM) and Multi Wire Propor- tional Counter (MWPC). In this article the details of the design, fabrication and operation processes of the device has been presented.

physics.ins-det↗

arXiv2015

Characterizations of GEM detector prototype

At NISER-IoP detector laboratory an initiative is taken to build and test Gas Electron Multiplier (GEM) detectors for ALICE experiment. The optimisation of the gas flow rate and the long-term stability test of the GEM detector are performed. The method and test results are presented.

physics.ins-det↗

arXiv2014

Experimental reconstruction of primary hot isotopes and characteristic properties of the fragmenting source in the heavy ion reactions near the Fermi energy

The characteristic properties of the hot nuclear matter existing at the time of fragment formation in the multifragmentation events produced in the reaction $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon are studied. A kinematical focusing method is employed to determine the multiplicities of evaporated light particles, associated with isotopically identified detected fragments. From these data the primary isotopic yield distributions are reconstructed using a Monte Carlo method. The reconstructed yield distributions are in good agreement with the primary isotope distributions obtained from AMD transport model simulations. Utilizing the reconstructed yields, power distribution, Landau free energy, characteristic properties of the emitting source are examined. The primary mass distributions exhibit a power law distribution with the critical exponent, $A^{-2.3}$, for $A \geq 15$ isotopes, but significantly deviates from that for the lighter isotopes. Landau free energy plots show no strong signature of the first order phase transition. Based on the Modified Fisher Model, the ratios of the Coulomb and symmetry energy coefficients relative to the temperature, $a_{c}/T$ and $a_{sym}/T$, are extracted as a function of A. The extracted $a_{sym}/T$ values are compared with results of the AMD simulations using Gogny interactions with different density dependencies of the symmetry energy term. The calculated $a_{sym}/T$ values show a close relation to the symmetry energy at the density at the time of the fragment formation. From this relation the density of the fragmenting source is determined to be $ρ/ρ_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature of fragmenting source are determined in a self-consistent manner as $a_{sym} = (24.7 \pm 3.4) MeV$ and $T=(4.9 \pm 0.2)$ MeV.

nucl-ex↗

arXiv2014

A novel determination of density, temperature and symmetry energy for nuclear multi-fragmentation through primary fragment yield reconstruction

For the first time primary hot isotope distributions are experimentally reconstructed in intermediate heavy ion collisions and used with antisymmetrized molecular dynamics (AMD) calculations to determine density, temperature and symmetry energy coefficient in a self-consistent manner. A kinematical focusing method is employed to reconstruct the primary hot fragment yield distributions for multifragmentation events observed in the reaction system $^{64}$Zn + $^{112}$Sn at 40 MeV/nucleon. The reconstructed yield distributions are in good agreement with the primary isotope distributions of AMD simulations. The experimentally extracted values of the symmetry energy coefficient relative to the temperature, $a_{sym}/T$, are compared with those of the AMD simulations with different density dependence of the symmetry energy term. The calculated $a_{sym}/T$ values changes according to the different interactions. By comparison of the experimental values of $a_{sym}/T$ with those of calculations, the density of the source at fragment formation was determined to be $ρ/ρ_{0} = (0.63 \pm 0.03 )$. Using this density, the symmetry energy coefficient and the temperature are determined in a self-consistent manner as $a_{sym} = (24.7 \pm 1.9) MeV$ and $T=(4.9 \pm 0.2)$ MeV

nucl-ex↗

arXiv2014

Proton decay and new contribution to neutrino-less double beta decay in SO(10) with low-mass Z-prime boson, observable n-nbar oscillation, lepton flavor violation, and rare kaon decay

Conventionally for observable $n-{\bar n}$ oscillation through Pati-Salam intermediate gauge symmetry in $SO(10)$, the canonical seesaw mechanism is also constrained by $M_R \sim M_C \le 10^6$ GeV which yields light neutrino masses much larger than the neutrino oscillation data. Recently, this difficulty has been evaded via inverse seesaw mechanism, but with proton lifetime far beyond the experimentally accessible limits. In the present work, adopting the view that we may have only a TeV scale $Z^{\prime}$ gauge boson, we show how a class of non-SUSY $SO(10)$ models allow experimentally verifiable proton lifetime and the new contributions to neutrinoless double beta decay in the $W_L-W_L$ channel, lepton flavor violating branching ratios, observable $n-{\bar n}$ oscillation, and lepto-quark gauge boson mediated rare kaon decays. The occurrence of Pati-Salam gauge symmetry with unbroken D-parity and two gauge couplings at the highest intermediate scale guarantees precision unification in such models. This symmetry also ensures vanishing GUT threshold uncertainy on $\sin^2θ_W$ or on the highest intermediate scale. Although the proton lifetime prediction is brought closer to the ongoing search limits with GUT threshold effects in the minimal model, no such effects are needed in a non-minimal model. We derive a new analytic expression for the $0νββ$ decay half-life and show how the existing experimental limits impose the lower bound on the lightest of the three heavy sterile neutrino masses, $M_{S_1}\ge 14\pm 4$ GeV. We also derive a new lower bound on the lepto-quark gauge boson mass mediating rare kaon decay, $M_{\rm lepto} \ge (1.53{\pm 0.06})\times 10^6$ GeV. The $n-{\bar n}$ mixing times are predicted in the range$τ_{n-{\bar n}}\simeq 10^8-10^{13}$ sec.

hep-ph↗

arXiv2013

Phase transitions in neutron star and magnetars and their connection with high energetic bursts in astrophysics

The phase transition from normal hadronic matter to quark matter in neutron stars (NS) could give rise to several interesting phenomena. Compact stars can have such exotic states up to their surface (called strange stars (SS)) or they can have quark core surrounded by hadronic matter, known as hybrid stars (HS). As the state of matter of the resultant SS/HS is different from the initial hadronic matter, their masses also differ. Therefore, such conversion leads to huge energy release, sometimes of the order of $10^{53}$ ergs. In the present work we study the qualitative energy released by such conversion. Recent observations reveal huge surface magnetic field in certain stars, termed magnetars. Such huge magnetic fields can modify the equations of state (EOS) of the matter describing the star. Therefore, the mass of magnetars are different from normal NS. The energy released during the conversion process from neutron magnetar (NM) to strange magnetar/hybrid magnetar (SS/HS) is different from normal NS to SS/HS conversion. In this work we calculate the energy release during the phase transition in magnetars. The energy released during NS to SS/HS conversion exceeds the energy released during NM to SM/HM conversion. The energy released during the conversion of NS to SS is always of the order of $10^{53}$ ergs. The amount of energy released during such conversion can only be compared to the energy observed during the gamma ray bursts (GRB). The energy liberated during NM to HM conversion is few times lesser, and is not likely to power GRB at cosmological distances. However, the magnetars are more likely to lose their energy from the magnetic poles and can produce giant flares, which are usually associated with magnetars.

astro-ph.HE↗