arXiv subjects

B. K. Singh

Publications and source records attributed to B. K. Singh.

At least 37 records · Page 2Linked to original sources

arXiv2022

Pseudorapidity Window Size Dependence of Multiplicity Fluctuations in High-Energy Collisions with System Size and Beam Energies

An investigation of the critical behavior of strongly interacting QCD matter has been performed by analyzing fluctuation observables on event-by-event (ebe) basis measured in high-energy collision experiments. The fluctuation analysis is performed using nuclear interactions at different target sizes and at different colliding beam energies as a function of varying width of pseudorapidity interval. For the sake of comparison, event-by-event multiplicity fluctuations in hadronic and heavy-ion collisions (p-H, p-A and A-B) are studied within the framework of the Lund Monte Carlo based FRITIOF model. Charged particle multiplicity and the variance of the multiplicity distribution are estimated for the interactions involving different target sizes and beam momenta i.e., p-H, p-CNO, p-AgBr at 200A GeV/c and $^{16}$O-AgBr collisions at 14.6, 60 and 200A GeV/c. Further, multiplicity fluctuations are quantified in terms of intensive quantity, the scaled variances $ω$ and the strongly intensive quantity $Σ_{FB}$ derived from the charged particle multiplicity and the width of the multiplicity distribution. Strongly intensive quantity $Σ_{FB}$ is a quantity of great significance to extract information about short and long-range multiplicity correlations. Furthermore, the collision centrality and centrality bin width dependent behavior of the multiplicity fluctuation have been examined in the framework of Lund Monte Carlo based FRITIOF model. Results based on the fluctuation analysis carried out in the present study are interpreted in terms of dynamics of collision process and the possibility of related QCD phase transition.

nucl-ex↗

arXiv2021

Anisotropic flow and correlations between azimuthal anisotropy Fourier harmonics in Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV under HYDJET++ framework

The study of anisotropic harmonic flow coefficients $ v_{n}$(n=2,3,4) is performed in Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV under Monte Carlo HYDJET++ model (HYDrodynamics plus JETs) framework. Anisotropic flow of identified particles and correlation between the azimuthal harmonic flow amplitudes is presented. Here, we have considered body-body and tip-tip type of geometrical configurations for Xe-Xe collision systems. The kinematic ranges $|η|<0.8$, $0 2$ are considered. The results have been shown for seven classes of centrality and compared with the ALICE experimental data. The anisotropic flow of identified charged particles show a strong centrality dependence. Mass ordering is observed for $v_{2},v_{3}$ and $v_{4}$. Mass ordering is different for different ranges of transverse momentum $p_{T}$. Strong correlation is observed between $v_{3}-v_{2}$, $v_{4}-v_{2}$, and $v_{4}-v_{3}$. Such correlation is centrality dependent and is different in different centrality windows. The anisotropic flow coefficients show a clear dependence on the total charged particle multiplicity. HYDJET++ model justifies experimental data well enough.

hep-ph↗

arXiv2020

Power-law solution for homogeneous and isotropic universe in $f(R,T)$ gravity

In the present work, we search the simplest cosmological model in $f(R,T)$ gravity by considering its functional form $f(R,T) = R + ξR T$ with $ξ$ being positive constant. We have constructed the Einstein's field equation in $f(R,T)$ gravity for homogeneous and isotropic space time. The explicit solution of the constructed model is obtained by considering the scale factor as $a = αt^β$ with $α$ and $β$ being free parameters. The values of $α$ and $β$ are obtained by using Markov Chain Monte Carlo (MCMC) method to constraining the model under consideration with observational $H(z)$ data. Some physical and kinematic properties of the model are also discussed.

physics.gen-ph↗

arXiv2020

Existence of bulk viscous universe in $f(R,T)$ gravity and confrontation with observational data

In this paper we have investigated a bulk viscous universe in $f(R,T)$ gravity where $R$ and $T$ are the Ricci scalar and trace of energy momentum tensor respectively. We have obtained explicit solutions of field equations in modified gravity by considering the power law form of scale factor. The Hubble parameter and deceleration parameter are derived in terms of cosmic time and redshift both. We have estimated the present values of these parameters with observational Hubble data and SN Ia data sets. At 1$σ$ level, the estimated values of $q_{0}$ and $m$ are obtained as $q_{0}=-0.30 \pm 0.05$ \& $ m = 0.70 \pm 0.02 $ where $q_{0}$ is the present value of deceleration parameter and $m$ is the model parameter. The energy conditions and Om(z) analysis for the anisotropic LRS Bianchi type I model are also discussed.

physics.gen-ph↗

arXiv2018

Humidity effects on evolution of CsI thin Films: Fractal studies of rough surfaces

The present work investigates the morphological, micro-structural, compositional and fractal analysis for CsI thin films in case of "as-deposited" and "1 hour humid air aged". The variation of grain sizes obtained from transmission electron microscopy (TEM) technique are found to be in the range of ~ 313 nm to ~ 1058 nm. The average grain size is found to increase after exposing to humidity. The experimental values of interplanner spacing are found to be less than the standard value which signifies that a compressive stress is acting in the film. The elemental compositions of CsI film has been investigated by the means of energy dispersive X-ray spectroscopy (EDAX) technique. The atomic percentage of Cs:I (1:1) is found to be increased by a factor of two after exposing to humidity. The surface morphology of CsI thin films is analyzed by the atomic force microscopy (AFM) for both cases. The fractal analysis is performed on the AFM micrographs. The autocorrelation function and height-height correlation function is used to study the correlation properties of surface and roughness exponent. It is found that the fractal dimension is affected after exposing to humidity.

physics.ins-det↗

arXiv2018

Structural and optical properties of CsI thin films: Influence of film thickness and humidity

Structural and optical studies have been performed on the thermally-evaporated "as-deposited" and "humid air aged" CsI thin films. The structural analysis for both "as-deposited" and "humid air aged" films shows a well-oriented peaks position of (110) and (220) lattice planes with a compressive stress in the films. The crystal quality has been investigated through the structural parameters. The increase in peak intensity as well as sharpness with film thickness implies the improvement of crystallinity. The optical absorbance of CsI films has been analyzed in the wavelength range of 190 nm - 900 nm in order to estimate the band gap energy of the films. Slater's model has also been used to explain the degradation of band gap energy with the increase in crystallite size.

physics.ins-det↗

arXiv2018

Growth evolution of self-affine thermally evaporated KBr thin films: A fractal assessment

In this article, fractal concepts were used to explore the thermally evaporated potassium bromide thin films of different thicknesses 200, 300, and 500 nm respectively; grown on aluminium substrates at room temperature. The self-affine or self similar nature of growing surfaces was investigated by autocorrelation function and obtained results are compared with the morphological envelope method. Theoretical estimations revealed that the global surface parameters such as, interface width and lateral correlation length are monotonically decreased with increasing film thickness. Also, from height profile and A-F plots, it has been perceived that irregularity/ complexity of growing layers was significantly influenced by thickness. On the other hand, the fractal dimension and local roughness exponent, estimated by height-height correlation function, do not suggest such dependency.

cond-mat.mtrl-sci↗

arXiv2018

Transverse Momentum Distribution and Elliptic Flow of Charged Hadrons in $U$+$U$ collisions at $\sqrt{s_{NN}}=193$ GeV using HYDJET++

Recent experimental observations of the charged hadron properties in $U+U$ collisions at $193$ GeV contradict many of the theoretical models of particle production including two-component Monte Carlo Glauber model. The experimental results show a small correlation between the charged hadron properties and the initial geometrical configurations (e.g. body-body, tip-tip etc.) of $U+U$ collisions. In this article, we have modified the Monte Carlo HYDJET++ model to study the charged hadron production in $U+U$ collisions at $193$ GeV center-of-mass energy in tip-tip and body-body initial configurations. We have modified the hard as well as soft production processes to make this model suitable for $U+U$ collisions. We have calculated the pseudorapidity distribution, transverse momentum distribution and elliptic flow distribution of charged hadrons with different control parameters in various geometrical configurations possible for $U+U$ collision. We find that HYDJET++ model supports a small correlation between the various properties of charged hadrons and the initial geometrical configurations of $U+U$ collision. Further, the results obtained in modified HYDJET++ model regarding $dn_{ch}/dη$ and elliptic flow ($v_{2}$) suitably matches with the experimental data of $U+U$ collisions in minimum bias configuration.

nucl-th↗

arXiv2018

Correlations and Event-by-Event Fluctuations in High Multiplicity Events Produced in $^{208}$Pb-$^{208}$Pb Collisions

Analysis of high multiplicity events produced in 158A GeV/c $^{208}$Pb-$^{208}$Pb collisions is carried out to study the event-by-event fluctuations. The findings reveal that the method of scaled factorial moments can be used to identify the events having densely populated narrow phase space bins. A few events sorted out adopting this approach are individually analyzed. It is observed that these events do exhibit large fluctuations in their pseudorapidity, $η$ and azimuthal angle, $ϕ$ distributions arising out due to some dynamical reasons. Two particle $Δη$-$Δϕ$ correlation study applied to these events too indicates that some complex two-dimensional structure of significantly high magnitude are present in these events which might have some dynamical origin. The findings reveal that the method of scaled factorial moments may be used as an effective triggering for events with large dynamical fluctuations.

hep-ex↗

arXiv2018

Universal Freezeout Condition for Charged Hadrons in a Hybrid Approach

Hadronic freezeout during the evolution of the medium created in heavy-ion collisions is an important phenomena. It is quite useful to find a universal freezeout condition for each and every nuclear collisions. In this article, we have constructed a hybrid model to calculate the ratio of transverse energy to total mean multiplicity $E_{T} /N_{ch}$, since this ratio can possibly act as a freezeout condition in heavy-ion collision experiments. Present hybrid model blends two approaches : Tsallis statistics and wounded quark approach. Recently, Tsallis statistics has been reliably used to obtain the transverse momentum distribution of charged hadrons produced in relativistic ion collisions. On the other side it has been shown that the pseudorapidity distribution of charged hadrons can be calculated satisfactorily using the wounded quark model (WQM). We have used this hybrid model to calculate the transverse energy density distributions, $dE_{T}/dη$ at midrapidity using charged particle pseudorapidity distributions, $dN_{ch}/dη$ and mean transverse momentum $\langle p_{T} \rangle$ in various type of nuclear collisions. We found that present hybrid model satisfactorily explains the experimental data whether other models fail to reproduce the data at central and at peripheral collisions simultaneously. Finally, ratio of transverse energy to total mean multiplicity, $E_{T} /N_{ch}$ has been computed within hybrid model and compared with the available experimental data at RHIC and LHC energies. We observed no explicit dependence of $E_{T} /N_{ch}$ on energy as well as centrality and thus it can definitely act as a freezeout criteria.

hep-ph↗

arXiv2017

X-ray diffraction line profile analysis of KBr thin films

In the present work, the microcrystalline characteristics of KBr thin films have been investigated by evaluating the breadth of diffraction peak. The Williamson-Hall, the Size-Strain Plot and the single line Voigt methods are employed to deconvolute the finite crystallite size and microstrain contribution from the broaden X-ray profile. The texture coefficient and dislocation density have been determined along each diffraction peak. Other relevant physical parameters such as stress, Young's modulus and energy density are also estimated using Uniform Stress-Deformation and Uniform Deformation Energy Density approximation of Williamson-Hall method.

cond-mat.mtrl-sci↗

arXiv2017

Correlation between photoemissive and morphological properties of KBr thin film photocathodes

In the present work, the morphological properties of KBr photocathodes are correlated with their photoemissive behaviour using a combination of analyzing techniques including SEM, TEM and AFM. From morphological studies, it is observed that KBr films have granular characteristics with varied average grain size and grain density. Structure and orientation of individual grains have been investigated by selected area electron diffraction technique and found to be the crystalline in nature with a face centered cubic structure. It is evident from the AFM analysis that the root mean square roughness and maximum area peak height have been decreased with the deposition of more KBr layers. The photoemission studies reveal that the resultant photocurrent is enhanced with increasing film thickness and it is directly related to the surface area coverage and grain density.

physics.ins-det↗

arXiv2017

Study of charged particle production in $U$-$U$ collisions in a Wounded Quark Model

Recently, there has been a growing interest in the study of deformed uranium-uranium ($U$-$U$) collisions in its various geometrical configurations due to their usefulness in understanding the different aspects of quantum chromodynamics (QCD). In this paper we have studied the particle production in deformed $U$-$U$ collisions at $\sqrt{s_{NN}}$ = $193$ GeV using modified wounded quark model (WQM). At first, we have shown the variation of quark-nucleus inelastic scattering cross-section ($σ_{qA}^{in}$) with respect to centralities for various geometrical orientations of $U$-$U$ collisions in WQM. After that we have calculated the pseudorapidity density ($dn_{ch}/dη$) within WQM using two-component prescription. Further we have calculated the transverse energy density distribution ($dE_{T}/dη$) along with the ratio of transverse energy to charged hadron multiplicity ($E_{T}/N_{ch}$) for $U$-$U$ collisions and compared them with the corresponding experimental data. We have shown the scaling behavior of $dn_{ch}/dη$ and $dE_{T}/dη$ for different initial geometry of $U$-$U$ collision with respect to $p$-$p$ data at $\sqrt{s_{NN}}=200$ GeV. Furthermore we have shown the Bjorken energy density achieved in $U$-$U$ collisions for various configurations and compared them with experimental data of $Au$-$Au$ at 200 GeV. We observe that the present model suitably describes the experimental data for minimum bias geometrical configuration of $U$-$U$ collisions. An estimate for various observables in different initial geometries of $U$-$U$ collisions is also presented which will be tested in future by experimental data.

nucl-th↗

arXiv2016

Multiplicity and Pseudorapidity distributions of charged particles in asymmetric and deformed nuclear collisions in a Wounded Quark Model

The charged particle multiplicity ($n_{ch}$) and pseudorapidity density $(dn_{ch}/dη)$ are key observables to characterize the properties of matter created in heavy ion collisions. The dependence of these observables on collision energy and the collision geometry are a key tool to understand the underlying particle production mechanism. Recently a lot of focus has been made on asymmetric and deformed nuclei collisions since these collisions can provide a deeper understanding about the nature of quantum chromodynamics (QCD). On phenomenological perspective a unified model which describes the experimental data coming from various kind of collision experiments, is much needed to provide the physical insights about the production mechanism. In this paper, we have calculated the charged hadron multiplicities for nucleon-nucleus (such as proton-lead $(p-Pb)$ and asymmetric nuclei collisions like deutron-gold $(d-Au)$, and copper-gold $(Cu-Au)$ within a new version of wounded quark model (WQM) and shown their variation with respect to centrality. Further we have used a suitable density function within our WQM to calculate pseudorapidity density of charged hadrons at mid-rapidity in the collisions of deformed uranium nuclei. We found that our model with suitable density functions describes the experimental data for symmetric, asymmetric and deformed nuclei collisions simultaneously over a wide range of collision energy.

hep-ph↗

arXiv2015

Event by Event Analysis of High Multiplicity Events Produced in 158 A GeV/c 208 Pb- 208 Pb Collisions

An extensive analysis of individual high multiplicity events produced in 158 A GeV /c 208Pb- 208Pb collisions is carried by adopting different methods to examine the anomalous behavior of these rare events. A method of selecting the events with densely populated narrow regions or spikes out of a given sample of collision events is discussed.Employing this approach two events with large spikes in their eta- and phi- distributions are selected for further analysis. For the sake of comparison, another two events which do not exhibit such spikes are simultaneously analyzed. The findings suggest that the systematic studies of particle density fluctuations in one- and two-dimensional phase-spaces and comparison with those obtained from the studies of correlation free Monte Carlo events, would be useful for identifying the events with large dynamical fluctuations. Formation of clusters or jet like phenomena in multihadronic final states in individual events is also discussed and the experimental findings are compared with the independent particle emission hypothesis by carrying out Monte Carlo simulations.

nucl-ex↗

arXiv2015

Optical and structural properties of CsI thin film photocathode

In the present work performance of cesium iodide thin film photocathode is studied in detail. The optical absorbance of cesium iodide thin films have been analyzed in the spectral range of 190 nm to 900 nm. The optical band gap energy of 500 nm thick cesium iodide film is calculated using Tauc plot from absorbance data. Refractive index is estimated from envelope plot of transmittance data using Swanepoel's method. Absolute quantum efficiency measurement has been carried out in the wavelength range of 150 nm to 200 nm. Crystallographic nature and surface morphology are investigated by X-ray diffraction, transmission electron microscopy and atomic force microscopy techniques. In addition, elemental composition result gained by energy dispersive X-ray analysis is also reported in the present work.

cond-mat.mtrl-sci↗

arXiv2015

Effect of humid air exposure on photoemissive and structural properties of KBr thin film photocathode

We have investigated the influence of water molecule absorption on photoemissive and structural properties of potassium bromide (KBr) thin film photocathode under humid air exposure at relative humidity (RH) 65%. It is evident from photoemission measurement that the photoelectron yield of KBr photocathode is degraded exponentially with humid air exposed time. Structural studies of the "as-deposited" and "humid air aged" films reveal that there is no effect of RH on film's crystalline face centered cubic (fcc) structure. However, the average crystallite size of "humid air exposed film" KBr film has been increased as compared to "as-deposited". In addition, topographical properties of KBr film are also examined by means of scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) and it is observed that granular characteristic of film has been altered, even for short exposure to humid air.

physics.ins-det↗

arXiv2015

Photoemission and optical constant measurements of Cesium Iodide thin film photocathode

The performance of cesium iodide as a reflective photocathode is presented. The absolute quantum efficiency of a 500 nm thick film of cesium iodide has been measured in the wavelength range 150 nm to 200 nm. The optical absorbance has been analyzed in the wavelength range 190 nm to 900 nm and the optical band gap energy has been calculated. The dispersion properties were determined from the refractive index using an envelope plot of the transmittance data. The morphological and elemental film composition have been investigated by atomic force microscopy and X-ray photo-electron spectroscopy techniques.

physics.ins-det↗