arXiv subjects

Abhi Modak

Publications and source records attributed to Abhi Modak.

7 recordsLinked to original sources

arXiv2026

Recent ALICE results from light-ion collision systems

This article presents recent measurements by the ALICE Collaboration in proton--oxygen (pO), oxygen--oxygen (OO), and neon--neon (Ne--Ne) collisions delivered by the LHC in July 2025. Measurements of the primary charged-particle pseudorapidity density and the elliptic and triangular flow coefficients of charged particles are reported. Experimental evidence of the suppression of neutral pion yields in OO collisions relative to the proton--proton baseline is also discussed. Comparisons of these new data with theoretical models provide key input to understand particle production, collective phenomena, and parton energy loss in small collision systems.

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arXiv2024

Charged-particle production in pp collisions at $\sqrt{s}$ = 13.6 TeV and Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeV with ALICE

This article presents the measurement of charged-particle pseudorapidity ($\eta$) density, $\mathrm{d}N_{\rm ch}/\mathrm{d}\eta$, in proton$-$proton (pp) collisions at a centre-of-mass energy $\sqrt{s}$ = 13.6 TeV, and in lead$-$lead (Pb$-$Pb) collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}$ = 5.36 TeV. The analysis is performed using the Run 3 data recorded during 2022 and 2023 by the upgraded ALICE detector. The charged-particle multiplicity is measured at midrapidity ($|\eta|<1$) using the new monolithic active pixel sensors-based Inner Tracking System and the Time Projection Chamber upgraded with Gas Electron Multiplier-based readout system. The measurements in pp collisions are reported for inelastic events with at least one charged particle having $|\eta|<1$ whereas for Pb$-$Pb collisions, the $\mathrm{d}N_{\rm ch}/\mathrm{d}\eta$ is obtained for different centrality classes, ranging from 0$-$5\% (most central) to 70$-$80\% (most peripheral). The energy dependence of average charged-particle pseudorapidity density ($\langle \mathrm{d}N_{\rm ch}/\mathrm{d}\eta \rangle$) measured in $|\eta|<0.5$ is studied and compared to earlier measurements at lower collision energies. In Pb$-$Pb collisions, the evolution of $\langle \mathrm{d}N_{\rm ch}/\mathrm{d}\eta \rangle$ as a function of the average number of participating nucleons, $\langle N_{\mathrm{part}} \rangle$, determined with a Glauber model, is also studied and compared with predictions from theoretical models.

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arXiv2023

Inclusive photon multiplicity at forward pseudorapidities in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV with ALICE

Global observables such as the pseudorapidity distributions of particle multiplicities in the final state are crucial to shed light into the physics processes involved in hadronic collisions. In proton$-$lead (p$-$Pb) collisions at Large Hadron Collider (LHC) energies, such measurements provide an important baseline to understand lead$-$lead (Pb$-$Pb) results by disentangling hot nuclear matter effects from the ones due to the cold nuclear matter. Multiplicity measurements can also put constraints on theoretical models describing the initial stages of the collision, e.g., to what degree the nucleon and the nuclei interact as dilute (partons) or dense (CGC-like) fields. The study of inclusive photon multiplicity aims to provide complementary measurements to those obtained with charged particles. In these proceedings, the pseudorapidity distributions of inclusive photons at forward pseudorapidity ($2.3 < \eta_{\rm lab} < 3.9$) in pp and p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV are presented. The data samples were collected using the Photon Multiplicity Detector (PMD) of ALICE. The multiplicity dependence of photon production in p$-$Pb collisions is presented and a comparison with charged-particle distributions measured at mid-pseudorapidity is shown. The results are also compared with predictions from Monte Carlo event generators.

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arXiv2022

System-size dependence of particle production at mid- and forward rapidity with ALICE

The pseudorapidity densities of charged particles and inclusive photons produced in high energy nuclear collisions are essential observables to characterise the global properties of the collisions, such as the achieved energy density, and to provide important constraints for Monte Carlo model calculations. In the LHC Run 1 and Run 2 configurations, ALICE had large coverage to measure charged particles over a pseudorapidity range ($-3.4~<~\eta~<~5.0$), combining the data from the Silicon Pixel Detector (SPD) and the Forward Multiplicity Detector (FMD). The inclusive photons are measured at forward rapidity using the Photon Multiplicity Detector (PMD), covering the pseudorapidity range $2.3~<~\eta~<~3.9$. New results on charged-particle pseudorapidity densities measured in pp, p$-$Pb, and Pb$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV using Run 1 and Run 2 data are presented. Inclusive photon production is reported for p$-$Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV. The charged-particle rapidity densities are derived from the measured charged-particle pseudorapidity densities, and then parameterized by a normal distribution. This allows us to study the evolution of the width of the rapidity distributions as a function of the number of participants in all three collision systems. The performance of the new Inner Tracking System (ITS) designed for ALICE Run 3 configuration is also discussed for pilot beam pp collisions at $\sqrt{s}$ = 0.9 TeV.

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arXiv2022

Jet modification in absence of QGP-medium: the role of multiparton interactions and color reconnection

Recent studies of high-multiplicity events in small collision systems (proton-proton and proton-lead) have drawn research interest towards the possibility of the formation of partonic medium in such systems. One of the important consequences of the formation of dense partonic medium is quenching of high-momentum final-state particles resulting in several experimental observations such as suppression in nuclear modification factor $R_{\rm AA}$, modification of jet shape observable $\rho(r)$ and jet fragmentation ($z^{\rm ch}$) distributions, etc. In this work, we study $\rho(r)$ and $z^{\rm ch}$ for inclusive charged-particle jets in proton-proton (pp) collisions at $\sqrt{s}$~=~13~TeV using PYTHIA~8 Monash~2013 Monte Carlo simulation. We show that the color reconnection (CR) and multiparton interaction (MPI) mechanisms in PYTHIA~8 can lead to an increased rate of jet production. We also find that the mechanisms of MPI and CR and change in the gluonic contribution in high-multiplicity events result in significant modification of $\rho(r)$ and $z^{\rm ch}$ compared to those in minimum bias events for 10~$<p_{\rm T,\,jet}^{\rm ch}<$~20~GeV/$c$. We notice a direct connection of $\langle N_{\rm MPI}\rangle$ and gluonic contribution with the amount of modification in $\rho(r)$ -- the larger the number of MPIs and/or gluonic contribution, the larger the amount of modification of $\rho(r)$.

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arXiv2021

Measurements of inclusive photons at forward rapidities in p-Pb collisions at $\sqrt{s\rm_{NN}}$ = 5.02 TeV with ALICE

We present multiplicity and pseudorapidity distributions of inclusive photons at forward rapidity in proton-lead (p-Pb) collisions at $\sqrt{s\rm_{NN}}$ = 5.02 TeV using the data obtained from Photon Multiplicity Detector (PMD) of ALICE. The centrality dependence of pseudorapidity distributions of inclusive photons is also studied. Results are compared with the previous ALICE measurements of charged-particle production and with theoretical predictions from Monte Carlo models, DPMJET and HIJING.

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arXiv2021

Effect of magnetic field on jet transport coefficient $\hat{q}$

We report the estimation of jet transport coefficient, $\hat{q}$ for quark- and gluon-initiated jets using a simple quasi-particle model in absence and presence of magnetic field. This model introduces a temperature and magnetic field-dependent degeneracy factor of partons, which is tuned by fitting the entropy density of lattice quantum chromodynamics data. At a finite magnetic field, $\hat{q}$ for quark jets splits into parallel and perpendicular components whose magnetic field dependence comes from two sources: the field-dependent degeneracy factor and the phase space part guided from the shear viscosity to entropy density ratio. Due to the electrically neutral nature of gluons, the estimation of $\hat{q}$ for gluon jets is affected only by the field-dependent degeneracy factor. In presence of a finite magnetic field, we find a significant enhancement in $\hat{q}$ for both quark- and gluon-initiated jets at low temperature, which gradually decreases towards high temperature. We compare the obtained results with the earlier calculations based on the anti-de Sitter/conformal field theory correspondence, and a qualitatively similar trend is observed. The change in $\hat{q}$ in presence of magnetic field is, however, quantitatively different for quark- and gluon-initiated jets. This is an interesting observation which can be explored experimentally to verify the effect of magnetic field on $\hat{q}$.

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