arXiv subjects

Zubayer Ahammed

Publications and source records attributed to Zubayer Ahammed.

18 recordsLinked to original sources

arXiv2026

Exploring the Effects of Color Reconnection on Net-Charge Fluctuations in $pp$ Collisions at $\sqrt{s}=2.76 \text{ TeV}$ using PYTHIA Monash

This work explores the effects of various color reconnection (CR) configurations on the net charge fluctuations of charged particles generated in $pp$ collisions at a center-of-mass energy of $\sqrt{s}$ = 2.76 TeV, simulated with the PYTHIA Monash using the variable $ν_{(+,-,\text{dyn})}$. The results are compared with experimental data from ALICE, revealing that the current PYTHIA simulation settings overestimate the net charge fluctuations relative to the experimental observations. Furthermore, $ν_{(+,-,\text{dyn})}$ exhibits a clear dependence on the MPICR range parameter, where increasing the range leads to more negative $ν_{(+,-,\text{dyn})}$ values, suggesting the geometric extent of CR directly modulates the strength of local charge correlation. To ensure these effects are not a trivial consequence of particle density, a comparison with a retuned NoCR baseline at fixed multiplicity was performed. This analysis confirms that CR induces a genuine dynamical shift in fluctuations that persists independently of the average charged-particle density. The study also shows that the net charge and net pion channels display the strongest suppression in $\langle N_{\text{ch}} \rangle ν_{(+-,\text{dyn})}$ compared to the net kaon and net proton channels. Overall, the study offers a useful benchmark against experimental results and sheds light on the underlying dynamics of the PYTHIA Monash.

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arXiv2026

Radiation Tolerance Characterisation of an Indigenously Developed p-type Silicon Pad Sensor for Forward Calorimetry Applications

We report on the radiation tolerance characterisation of a p-type silicon pad sensor indigenously designed by BARC-VECC and fabricated at Bharat Electronics Limited (BEL), India -- representing a significant step toward establishing a domestic silicon sensor manufacturing capability for high-energy physics applications. Single-pad test structures were irradiated with neutrons over a range of fluences from $\sim10^{7}$ to $\sim2.5\times10^{14}$~1~MeV~$n_{\mathrm{eq}}$/cm$^{2}$, spanning the operational regime relevant to forward calorimetry in high-luminosity heavy-ion collider experiments. Post-irradiation performance was characterised through systematic measurement of leakage current evolution and calorimetric response as functions of accumulated neutron fluence. A single-exponential annealing model is introduced to describe the time dependence of leakage current within the observation window, and the current-related damage constant $α$ is extracted and compared with the RD48 reference value. The results demonstrate that the sensors survive the target fluence with measurable but recoverable degradation, validating the fabrication process and providing a baseline for future qualification of this indigenous sensor production chain.

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arXiv2026

Machine Learning-Based Cluster Classification to Suppress Background in a Prototype RPC Detector

Resistive Plate Chambers (RPCs) are widely used as tracking detectors in many high-energy physics experiments. It has been observed that low-resistive bakelite RPC prototypes frequently exhibit a secondary hit component, appearing as a long tail or an additional peak in the time-correlation spectra relative to the trigger detector. These secondary hits, which affect both the time and spatial resolution, are difficult to distinguish from genuine signals in high-rate environments without an external trigger. As a result, they can significantly degrade track reconstruction efficiency and increase processing time. We present a machine-learning-based strategy to separate signal and background hit clusters using fifteen cluster-level descriptors that encode both statistical properties (histogram mean, width, cluster size) and fit-based parameters (Gaussian-fit mean, width, amplitude, chi^2, NDF) of the time and ADC distributions. Using laboratory data collected from a single-gap low resistive RPC with a three-scintillator master trigger, we trained and evaluated three classifiers-DNN, 1D-CNN, and XGBoost-on balanced signal/background samples. All models demonstrate strong discrimination capability, with XGBoost showing the most robust generalization performance. Feature-importance analysis indicates that cluster size and temporal-shape descriptors are the dominant discriminants. These results highlight that compact, interpretable cluster-level features combined with machine-learning classifiers offer a practical and effective approach to suppress background in self-triggering low resistive RPC detectors.

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arXiv2025

Effect of Isolation Criteria on Prompt Photon Production in Relativistic Nuclear Collisions

Prompt photon measurements in relativistic nuclear collisions serve as an essential comparative basis for heavy ion studies enabling the separation of medium induced effects. However, the identification of prompt photons is experimentally challenging due to substantial backgrounds from photons produced in hadron decays and jet fragmentation. Appropriate isolation criteria are applied to suppress these background contributions. We analyze prompt photon spectra using the JETPHOX framework to quantify the relative contributions of fragmentation and direct production mechanisms to the total photon yield. We perform a systematic study of the impact of isolation criteria on prompt photon production in relativistic nuclear collisions with emphasis on their dependence on beam energy and photon transverse momentum. The fragmentation contribution is found to be substantially large particularly for $p_T < 15$ GeV and the isolation criterion plays a crucial role in the analysis of prompt photons in that $p_T$ region. A dynamical isolation criterion suppresses the fragmentation component more effectively than a fixed one in this region. Furthermore, the isolation criterion shows a stronger dependence on beam energy and photon $p_T$ than on system size. These observations emphasize the importance of employing carefully selected and consistent isolation criteria when comparing experimental data with theoretical calculations especially for observables sensitive to fragmentation.

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arXiv2022

Performance of a prototype bakelite RPC at GIF++ using self-triggered electronics for the CBM Experiment at FAIR

The Muon Chamber (MuCh) is a sub-system of the Compressed Baryonic Matter (CBM) experiment for the detection of low-mass-vector mesons produced in high energy heavy-ion collisions at beam energies ranging from 2 AGeV to 11 AGeV and decaying in the di-muon channel. MuCh consists of a segmented absorber and four detector triplet stations sandwiched between the absorber segments. At the 3rd and 4th stations of MuCh, Resistive Plate Chambers (RPCs) have been conceived for muon tracking. We have tested the performance of a low resistivity bakelite RPC prototype equipped with self-triggered front end electronics (MuCh-XYTER) for the CBM Muon Chamber. A systematic study on the muon detection efficiency and time resolution has been carried out in a high-rate photon background at the Gamma Irradiation Facility (GIF++) at CERN. The details of the measurement setup and the results are presented here.

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arXiv2020

Study of diffusion coefficients of identified particles at energies available at BNL Relativistic Heavy Ion Collider

Using event-by-event fluctuations, we study the diffusion parameters of net-charge, net-pion, net-kaon, and net-proton in the heavy-ion jet interaction generator (HIJING), and ultra-relativistic quantum molecular dynamics (UrQMD) models at different collision energies \sqsn available at BNL Relativistic Heavy Ion Collider (RHIC). The diffusion parameter ($σ$) of net-charge and identified particles are estimated in rapidity space at various \sqsn. It is observed that, the $σ$ values are independent of collision energies but emphasises the particle-species dependence of diffusion coefficient in the QGP medium. The present work on particle-species dependence of diffusion coefficient provides a baseline for comparison with the experimental data.

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arXiv2020

Fluctuations of identified particle yields using the ν dyn variable at energies available at the BNL Relativistic Heavy Ion Collider

We study the fluctuations of net-charge, net-pion, net-kaon and net-proton using $D$-measure and $ν_{dyn}$ variables in heavy-ion jet interaction generator (HIJING), ultra-relativistic quantum molecular dynamics (UrQMD), and hadron resonance gas (HRG) model at different collision energies \sqsn. It has been observed that, the values of $D$ strongly dependent on $Δη$ in HIJING and UrQMD models and independent in HRG model. The diffusion coefficients ($σ$) of identified particles are estimated at various \sqsn. It is observed that, the $σ$ values are independent of collision energies but emphasizes the particle species dependence of diffusion coefficient in the QGP medium. This study provides a realistic baseline for comparison with the experimental data.

hep-ph↗

arXiv2019

Impact of the chromo-electromagnetic field fluctuations on transport coefficients of heavy quarks and shear viscosity to entropy density ratio of quark-gluon plasma

The chromo-electromagnetic field fluctuations in the quark-gluon plasma (QGP) play an important role as these field fluctuations result energy gain of heavy quarks. We consider these fluctuations and evaluate the transport coefficients, e.g., drag and diffusion coefficients of charm quarks and shear viscosity to entropy density ratio ($η/s$) of the QGP. We find a significant effect of such fluctuations on the transport coefficients. These fluctuations cause a reduction of the drag and diffusion coefficients. We also observe that the shear viscosity to entropy density ratio of the QGP is closer to the value obtained in Lattice QCD (LQCD) and functional renormalization group calculations when the effects of such fluctuations are included.

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arXiv2019

The role of the stochastic color field fluctuations on $J/ψ$ suppression in ultra-relativistic heavy-ion collisions

We consider the effect of the stochastic color field fluctuations in addition to the collisional as well as the radiative energy losses in the propagation of charm quarks in the hot and dense deconfined medium of quarks and gluons created in ultra-relativistic heavy-ion collisions. These fluctuations lead to energy gain of the propagating charm quarks. We construct and solve Langevin transport equations for charm quarks under the evolving background matter described by the ($3+1$)-D relativistic viscous hydrodynamics. Considering the energy gain of charm quarks, the nuclear modification factor $R_{AA}$ of $J/ψ$ is calculated. Interestingly, the experimental measurements for $J/ψ$ suppression in $Au-Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV by PHENIX Collaboration and $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 2.76$ TeV by ALICE and CMS Collaborations, can be nicely described with the effect of these field fluctuations without invoking the regeneration phenomena.

hep-ph↗

arXiv2019

Heavy flavour Langevin diffusion with the chromo-electromagnetic field fluctuations in the quark-gluon plasma

The chromo-electromagnetic field is produced due to the motion of partons in a quark-gluon plasma created by relativistic heavy-ion collisions. The fluctuations in the produced chromo-electromagnetic field are important, since they cause heavy quarks to gain energy in the low velocity limit. We study the effect of such fluctuations on heavy quark diffusion in quark-gluon plasma within the framework of Langevin dynamics under the background matter described by the ($3+1$)-dimensional relativistic viscous hydrodynamics. Theoretical calculations of the nuclear modification factor ($R_{AA}$) of heavy mesons ($D$ and $B$ mesons), with the effect of these fluctuations, are compared with experimental measurements in $Au-Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and $Pb-Pb$ collisions at $\sqrt{s_{NN}} = 2.76$ and $5.02$ TeV by the ALICE and CMS experiments at the CERN Large Hadron Collider (LHC). We find a significant effect of these fluctuations in describing the the measured $R_{AA}$ of $D$ and $B$ mesons in both RHIC and LHC energies.

hep-ph↗

arXiv2018

A Proof-of-principle for Time-Of-Flight Positron Emission Tomography Imaging

Time-Of-Flight (TOF) is a noble technique that is used in Positron Emission Tomography (PET) imaging worldwide. The scintillator based imaging system that is being used around the world for TOF-PET is very expensive. Multi-gap Resistive Plate Chambers (MRPCs) are gaseous detectors which are easy to fabricate, inexpensive and have excellent position and timing resolution. They can be used as a suitable alternative to highly expensive scintillators. For the sole purpose of TOF-PET, a pair of 18 cm $\times$ 18 cm, 5 gap, glass-based MRPC modules have been fabricated. Our main aim was to determine the shift in the position of the source (Na-22) with these fabricated MRPCs. In this document, the details of the experimental results will be presented.

physics.ins-det↗

arXiv2018

Development and Characterization of 6-gap Bakelite Multi-gap Resistive Plate Chamber

The Multi-gap Resistive Plate Chamber (MRPC) is an advanced form of Resistive Plate Chamber (RPC) detector where the gas gap is divided into sub-gaps. MRPCs are known for their good time resolution and detection efficiency for charged particles. They have found suitable applications in several high energy physics experiments like ALICE in LHC, CERN, Geneva, Switzerland, and STAR in RHIC, BNL, USA. As they have very good time resolution and are of low cost, they can be a suitable replacement for very expensive scintillators used in Positron Emission Tomography Imaging. The MRPCs that are being used nowadays are developed with glass electrodes. We have made an attempt to develop a 6-gap MRPC using bakelite electrodes. The outer electrodes are of dimensions 15 cm $\times$ 15 cm $\times$ 0.3 cm and the inner electrodes are of dimension 14 cm $\times$ 14 cm $\times$ 0.05 cm. The glossy finished electrode surfaces have not been treated with any oil like linseed, silicone for smoothness. The performance of the detector has been studied measuring the efficiency, noise rate and time resolution with cosmic rays. This effort is towards the development of a prototype for Positron Emission Tomography with the Time-Of-Flight technique using MRPCs. Details of the development procedure and performance studies have been presented here.

physics.ins-det↗

arXiv2018

Characterization of quark gluon plasma as seen through the energy loss of heavy quarks

The shear viscosity to entropy density ratio (η/s) of quark gluon plasma produced in ultra- relativistic heavy-ion collisions has been studied from the energy loss of heavy quarks in QGP medium. We have also studied the bulk viscosity to entropy density ratio (ζ/s) and fluidity measure(F) of the medium using the obtained η/s values. In addition to that, we have estimated the heavy quark bound state potential (V) inside this medium. Our finding of η/s agrees well with the results obtained by Lattice QCD (LQCD) and functional renormalization group technique.

hep-ph↗

arXiv2017

Effect of the chromo-electromagnetic field fluctuations on heavy quark propagation at the LHC energies

We consider the effect of the chromo-electromagnetic field fluctuations in addition to the collisional as well as the radiative energy loss suffered by heavy quarks while propagating through the hot and densed deconfined medium of quarks and gluons created in relativistic heavy ion collisions. The chromo-electromagnetic field fluctuations play an important role as it leads to an energy gain of heavy quarks of all momentum, significantly effective at the lower momentum region. With this, we have computed, for the first time, the nuclear modification factor (R_{AA}) of heavy mesons, viz., D-mesons and B-mesons and compared with the those experimental measurements in Pb-Pb collisions at \sqrt{s_{NN}} = 2.76 TeV and \sqrt{s_{NN}} = 5.02 TeV by the CMS and ALICE experiments at the LHC. Our results are found to be in very good agreement with those available data measured by CMS and ALICE experiments.

hep-ph↗

arXiv2017

Measurement of basic characteristics and gain uniformity of a triple GEM detector

Large area Gas Electron Multiplier (GEM) detectors have been the preferred choice for tracking devices in major nuclear and particle physics experiments. Uniformity over surface of the detector in terms of gain, energy resolution and efficiency is crucial for the optimum performance of these detectors. In the present work, detailed performance study of a 10x10 cm^2 triple GEM detector operated using Ar and CO_2 gas mixtures in proportions of 70:30 and 90:10, has been made by making a voltage scan of the efficiency with 106^Ru-Rh beta-source and cosmic rays. The gain and energy resolution of the detector were studied using the X-ray spectrum of 55^Fe source. The uniformity of the detector has been investigated by dividing the detector in 7x7 zones and measuring the gain and energy resolution at the center of each zone. The variations of the gain and energy resolution have been found to be 8.8% and 6.7%, respectively. These studies are essential to characterise GEM detectors before their final use in the experiments.

physics.ins-det↗

arXiv2016

Fabrication and Characterisation of Oil-Free Large High Pressure Laminate Resistive Plate Chamber

A large (240 cm $\times$ 120 cm $\times$ 0.2 cm) oil-free High Pressure Laminate (HPL), commonly referred as "bakelite", Resistive Plate Chamber (RPC) has been developed at VECC-Kolkata using locally available P-302 OLTC grade HPL. The chamber has been operated in streamer mode using Argon, Freon(R134a) and Iso-butane in a ratio of 34:57:9 by volume. The electrodes and glue samples have been characterised by measuring their electrical parameters like bulk resistivity and surface resistivity. The performance of the chamber has been studied by measuring the efficiency, its uniformity and stability in detection of cosmic muons. Timing measurement has been performed at a central location of the chamber. The chamber showed an efficiency $>$95$\%$ and time resolution ($σ$), at the point of measurement, $\sim$0.83 ns at 9000V. Details of the material characterisation, fabrication procedure and performance studies have been discussed.

physics.ins-det↗

arXiv2016

Long Term Performance Studies of Large Oil-Free Bakelite Resistive Plate Chamber

Several high energy physics and neutrino physics experiments worldwide require large-size RPCs to cover wide acceptances. The muon tracking systems in the Iron calorimeter (ICAL) in the INO experiment, India and the near detector in DUNE at Fermilab are two such examples. A (240 cm $\times$ 120 cm $\times$ 0.2 cm) bakelite RPC has been built and tested at Variable Energy Cyclotron Centre, Kolkata, using indigenous materials procured from the local market. No additional lubricant, like oil has been used on the electrode surfaces for smoothening. The chamber is in operation for $>$ 365 days. We have tested the chamber for its long term operation. The leakage current, bulk resistivity, efficiency, noise rate and time resolution of the chamber have been found to be quite stable during the testing peroid. It showed an efficiency $>$ 95$\%$ with an average time resolution of $\sim$0.83 ns at the point of measurement at 9000 V throughout the testing period. Details of the long term performance of the chamber have been discussed.

physics.ins-det↗

arXiv2008

STAR's Measurement of Energy and System Size Dependence of K/$π$ Fluctuations at RHIC

Strangeness enhancement has been predicted to be one of the signatures of the formation of the quark gluon plasma (QGP) and event-by-event fluctuations of strangeness may reveal the nature of such a phase transition. We report results for $K/π$ fluctuations from Cu+Cu at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV and Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4, 130 and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. We compare our results with the results observed in central Pb+Pb collisions at SPS energies at $\sqrt{s_{NN}}$ = 6.3, 7.6, 8.8, 12.3, and 17.3 GeV. We observe the fluctuation strength measured at the highest SPS energy point by the NA49 collaboration in Pb+Pb collisions is similar to our results in Cu+Cu and Au+Au collisions. We also compare our results with HIJING, a statistical hadronization model and a multi-phase transport model.

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