arXiv subjects

Kapil Saraswat

Publications and source records attributed to Kapil Saraswat.

15 recordsLinked to original sources

arXiv2026

Final-state effects on the transverse-momentum spectra of charged hadrons in $p+Pb$ and $Pb+Pb$ collisions at $\sqrt {s_{\rm{NN}}}~=~5.02$~TeV using the modified Tsallis distribution

The ATLAS Collaboration has reported measurements of the transverse momentum ($p_{\rm{T}}$) spectra of charged hadrons in proton-proton ($p+p$), proton-lead ($p+Pb$), and lead-lead ($Pb+Pb$) collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{\rm{NN}}}~=$~5.02~TeV within the rapidity interval $-2.5<y<2.0$. In the present work, we investigate medium effects on charged-hadron production in $p+Pb$ and $Pb+Pb$ collisions using a phenomenological modified Tsallis parametrization that accounts for transverse collective flow in the low-to-intermediate $p_{\rm{T}}$ region and medium-induced parton energy loss at high $p_{\rm{T}}$. The modified parametrization provides a consistent description of the measured spectra over the full investigated $p_{\rm{T}}$ range across different centrality classes. The extracted energy-loss exponent $α$, which characterizes the energy dependence of parton energy loss, is found to lie in the range 0.59$-$0.73 for $p+Pb$ collisions and 0.32$-$0.59 for $Pb+Pb$ collisions. In addition, the extracted parameters exhibit a clear centrality dependence, reflecting enhanced collective effects in central collisions. These results provide quantitative insight into the interplay between transverse collective flow and medium-induced parton energy loss in charged-hadron production at LHC energies.

hep-ph↗

arXiv2024

Phenomenological study of the charged particles production in pPb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV

We have studied transverse momentum ($p_{\rm{T}}$) spectra of charged hadrons in various pseudo-rapidity ranges for p-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. The medium effects such as collective flow and energy loss resulting from heavy-ion collisions have also been investigated using modified Tsallis distribution function over a wide range of $p_{\rm{T}}$ that indicates the transverse collective flow at low and intermediate $p_{\rm{T}}$ range and in-medium energy loss in high $p_{\rm{T}}$ range.

hep-ph↗

arXiv2024

Medium effects of charged-hadron production in $p+Pb$ and $Pb+Pb$ collisions at LHC energies using modified Tsallis distribution

The transverse momentum ($p_T$) spectra of charged hadrons in $p+p$, $p+Pb$ and $Pb+Pb$ collisions at $\sqrt {s_{NN}} = 5.02$ TeV are presented here within the rapidity range of $-2.5<y<2.0$. We study the medium effects, which is produced by heavy ion collisions, on the behaviour of charged hadrons, by using a phenomenological fit function. These effects are attributed to two main factors: the transverse collective flow and the the energy loss of charged hadrons due to multiple scatterings. We observe the transverse collective flow at low and intermediate $p_T$ region and the energy loss at high $p_T$ region. Here we take all the published data from the ATLAS collaboration.

hep-ph↗

arXiv2021

Understanding partonic energy loss from measured light charged particles and jets in PbPb collisions at LHC energies

We perform a comprehensive study of partonic energy loss reflected in the nuclear modification factors of charged particles and jets measured in PbPb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 and 5.02 TeV in wide transverse momentum ($p_{\rm T}$) and centrality range. The $p_{\rm T}$ distributions in pp collisions are fitted with a modified power law and the nuclear modification factor in PbPb collisions can be obtained using effective shift ($Δp_{\rm T}$) in the spectrum measured at different centralities. Driven by physics consideration, the functional form of energy loss given by $Δp_{\rm T}$ can be assumed as power law with different power indices in three different $p_{\rm T}$ regions. The power indices and the boundaries of three $p_{\rm T}$ regions are obtained by fitting the measured nuclear modification factor as a function of $p_{\rm T}$ in all collision centralities simultaneously. The energy loss in different collisions centralities are described in terms of fractional power of number of participants. It is demanded that the power law functions in three $p_T$ regions and their derivatives are continuous at the $p_{\rm T}$ boundaries. The $Δp_{\rm T}$ for light charged particles is found to increase linearly with $p_{\rm T}$ in low $p_{\rm T}$ region below $\sim 5-6$ GeV/$c$ and approaches a constant value in high $p_{\rm T}$ region above $\sim 22-29$ GeV/$c$ with an intermediate power law connecting the two regions. The method is also used for jets and it is found that for jets, the $Δp_{\rm T}$ increases approximately linearly even at very high $p_{\rm T}$.

hep-ph↗

arXiv2018

Charged current deep inelastic scattering of muon neutrinos off ^{56}Fe

In this paper, we study charged current deep inelastic scattering of muon neutrinos off ^{56}Fe nuclei using Hirai, Kumano and Saito model. The LHA Parton Distribution Functions (PDFs) - CT10 are used to describe the partonic content of hadrons. Modification of PDFs inside the nuclei is done using EPPS16 parameterization at next-to-leading order. Target mass correction has also been incorporated in the calculations. We calculate the structure functions (F_{2}(x,Q^{2}) and xF_{3}(x,Q^{2})), the ratios (R_{2}(x,Q^{2}) = \frac{F^{^{56}Fe}_{2}}{F^{Nucleon}_{2}} and R_{3}(x,Q^{2}) = \frac{F^{^{56}Fe}_{3}}{F^{Nucleon}_{3}}) and the differential cross sections of muon neutrino deep inelastic scattering off a nucleon and ^{56}Fe nuclei. We compare the obtained results with measured experimental data. The present theoretical approach gives a good description of data.

hep-ph↗

arXiv2018

Charged current quasi elastic scattering of muon anti-neutrino off ^{12}C

In this work, we study charged current quasi elastic scattering of muon anti-neutrino off nucleon and nucleus using a formalism based on Llewellyn Smith (LS) model. Parameterizations by Galster et al. are used for electric and magnetic Sach's form factors of nucleons. We use Fermi gas model along with Pauli suppression condition to take into account the nuclear effects in anti-neutrino - nucleus QES. We calculate muon anti-neutrino-p and muon anti-neutrino-^{12}C charged current quasi elastic scattering differential and total cross sections for different values of axial mass M_{A} and compare the results with data from GGM, SKAT, BNL, NOMAD, MINERvA and MiniBooNE experiments. The present theoretical approach gives an excellent description of differential cross section data. The calculations with axial mass M_{A} = 0.979 and 1.05 GeV are compatible with data from most of the experiments.

hep-ph↗

arXiv2018

Charged and Neutral Current Pion Production in Neutrino-Nucleus Scattering

In this article, we present the charged and neutral current coherent pion production in the neutrino-nucleus interaction in the resonance region using the formalism based on the partially conserved axial current (PCAC) theorem which relates the neutrino-nucleus cross section to the pion-nucleus elastic cross section. The pion nucleus elastic cross section is calculated using the Glauber model approach. We calculate the integrated cross sections for neutrino-carbon, neutrino-iron and neutrino-oxygen scattering. The results of integrated cross-section calculations are compared with the measured data

hep-ph↗

arXiv2018

Freeze-out of Strange Hadron in pp, pPb and PbPb Collisions at LHC Energies

In this article, we will present a systematic analysis of transverse momentum spectra of the strange hadron in different multiplicity events produced in pp collision at $\sqrt{s}$ = 7 TeV, pPb collision at $\sqrt{s_{NN}}$ = 5.02 TeV and PbPb collision at $\sqrt{s_{NN}}$ = 2.76 TeV. The differential freeze out scenario of strange hadron $K^{0}_{s}$ assumed while analyzing the data using a Tsallis distribution which is modified to include transverse flow. The $p_{T}$ distributions of strange hadron in different systems are characterized in terms of the parameters namely, Tsallis temperature ($T$), power ($n$) and average transverse flow velocity ($β$).

hep-ph↗

arXiv2018

Transverse momentum spectra of hadrons in high energy pp and heavy ion collisions

We present a study of transverse momentum ($p_{T}$) spectra of unidentified charged particles in pp collisions at RHIC and LHC energies from $\sqrt{s}$ = 62.4 GeV to 13 TeV using Tsallis/Hagedorn function. The power law of Tsallis/Hagedorn form gives excellent description of the hadron spectra in $p_{T}$ range from 0.2 to 300 GeV/$c$. The power index $n$ of the $p_T$ distributions is found to follow a function of the type $a+b/\sqrt {s}$ with asymptotic value $a = 5.72$. The parameter $T$ governing the soft bulk contribution to the spectra remains almost same over wide range of collision energies. We also provide a Tsallis/Hagedorn fit to the $p_{T}$ spectra of hadrons in pPb and different centralities of PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV. The data/fit shows deviations from the Tsallis distribution which become more pronounced as the system size increases. We suggest simple modifications in the Tsallis/Hagedorn power law function and show that the above deviations can be attributed to the transverse flow in low $p_T$ region and to the in-medium energy loss in high $p_T$ region.

hep-ph↗

arXiv2017

Charged current quasi elastic scattering of muon neutrino with nuclei

We present a study on the charge current quasi elastic scattering of $ν_μ$ from nucleon and nuclei which gives a charged muon in the final state. To describe nuclei, the Fermi Gas model has been used with proposed Pauli suppression factor. The diffuseness parameter of the Fermi distribution has been obtained using experimental data. We also investigate different parametrizations for electric and magnetic Sach's form factors of nucleons. Calculations have been made for CCQES total and differential cross sections for the cases of $ν_μ-N$, $ν_μ-^{12}C$ and $ν_μ-^{56}Fe$ scatterings and are compared with the data for different values of the axial mass. The present model gives excellent description of measured differential cross section for all the systems.

hep-ph↗

arXiv2017

Strange hadron production in pp, pPb and PbPb collisions at LHC energies

We present a systematic analysis of transverse momentum $(p_{T})$ spectra of the strange hadrons in different multiplicity events produced in pp collision at $\sqrt{s}$ = 7 TeV, pPb collision at $\sqrt{s_{NN}}$ = 5.02 TeV and PbPb collision at $\sqrt{s_{NN}}$ = 2.76 TeV. Both the single and differential freeze out scenarios of strange hadrons $K^0_s$, $Λ$ and $Ξ^-$ are considered while fitting using a Tsallis distribution which is modified to include transverse flow. The $p_{T}$ distributions of these hadrons in different systems are characterized in terms of the parameters namely, Tsallis temperature $(T)$, power $(n)$ and average transverse flow velocity $(β)$. It is found that for all the systems, transverse flow increases as we move from lower to higher multiplicity events. In the case of the differential freeze-out scenario, the degree of thermalization remains similar for events of different multiplicity classes in all the three systems. The Tsallis temperature increases with the mass of the hadrons and also increases with the event multiplicity in pp and pPb system but shows little variation with the multiplicity in PbPb system. In the case of the single freeze-out scenario, the difference between small systems (pp, pPb) and PbPb system becomes more evident. The high multiplicity PbPb events show higher degree of thermalization as compared to the events of pp and pPb systems. The trend of variation of the temperature in PbPb system with event multiplicity is opposite to what is found in the pp and pPb systems.

nucl-th↗

arXiv2017

Energy loss of heavy quarks and $B$ and $D$ meson spectra in PbPb collisions at LHC energies

We study the production and evolution of charm and bottom quarks in hot partonic medium produced in heavy ion collisions. The heavy quarks loose energy in the medium which is reflected in the transverse momentum spectra of heavy mesons. The collisional energy loss of heavy quarks has been calculated using QCD calculations. The radiative energy loss is obtained using two models namely reaction operator formalism and generalized dead cone approach. The nuclear modification factors, $R_{AA}$ as a function of transverse momentum by including shadowing and energy loss are calculated for $D^{0}$ and $B^{+}$ mesons in PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV and for $D^{0}$ mesons at $\sqrt{s_{NN}}$ = 2.76 TeV and are compared with the recent measurements. The radiative energy loss from generalized dead cone approach alone is sufficient to produce measured $D^{0}$ meson $R_{AA}$ at both the LHC energies. The radiative energy loss from reaction operator formalism plus collisional energy loss gives good description of $D^{0}$ meson $R_{AA}$. For the case of $B^{+}$ meson, the radiative energy loss from generalized dead cone approach plus collisional energy loss gives good description of the CMS data. The radiative process is dominant for charm quarks while for the bottom, both the radiative process and the elastic collisions are important.

hep-ph↗

arXiv2016

Coherent Pion Production in Neutrino Nucleus Scattering

In this article, we study the coherent pion production in neutrino-nucleus interaction in the resonance region using the formalism based on partially conserved axial current (PCAC) theorem which relates the neutrino-nucleus cross section to the pion-nucleus elastic cross section. The pion nucleus elastic cross section is calculated using the Glauber model in terms of pion-nucleon cross sections obtained by parameterizing the experimental data. We calculate the differential and integrated cross sections for charged current coherent pion production in neutrino carbon scattering. The results of integrated cross section calculations are compared with the measured data. Predictions for the differential and integrated cross sections for coherent pion productions in neutrino iron scattering using above formalism are also made.

hep-ph↗

arXiv2015

Energy loss of $B$ and $D$ mesons in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV

We present the calculations of collisional and radiative energy loss of $B$ and $D$ mesons in the medium produced in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The nuclear modification factor $R_{AA}$ of $B$ and $D$ mesons including shadowing and energy loss are calculated and compared with the measured data. While the $D$ meson $R_{AA}$ can be described in terms of the radiative energy loss alone, both the collisional as well as radiative energy loss are required to explain the $B$ meson measurements.

hep-ph↗

arXiv2015

Constraining heavy quark energy loss using $B$ and $D$ meson measurements in heavy ion collision at RHIC and LHC energies

In this work, we calculate energy loss of heavy quark (charm and bottom) due to elastic collisions and gluon radiation in hot/dense medium. The collisional energy loss has been obtained using QCD calculations. The radiative energy loss is calculated using reaction operator formalism and generalized dead cone approach. We rederive the energy loss expression using same assumptions as generalized dead cone approach but obtain slightly different results. We also improve the model employed to calculate path length and the system evolution. The nuclear modification factors $R_{AA}$ including shadowing and energy loss are evaluated for $B$ and $D$ mesons and are compared with the measurements in PbPb collision at $\sqrt{s_{NN}}$ = 2.76 TeV and with the D meson and Heavy flavour (HF) electrons measurements in AuAu collision at $\sqrt{s_{NN}}$ = 200 GeV. The radiative energy loss calculated by reaction operator formalism added with collisional energy loss describes the RHIC HF electron suppression in high $p_{T}$ range. It also describes the LHC measurement of $B$ meson suppression but overestimates the suppression of $D$ meson. The radiative energy loss from generalized dead cone approach describes the charm suppression at both RHIC as well as LHC energies and requires energy loss due to collisions to be added in order to describe the bottom suppression at LHC.

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