arXiv subjects

Ahmed M. Hamed

Publications and source records attributed to Ahmed M. Hamed.

8 recordsLinked to original sources

arXiv2025

Particle Identification with Deep Neural Networks Across Collision Energies in Simulated Proton-Proton Collisions

This study demonstrates a proof-of-concept application of a deep neural network for particle identification in simulated high transverse momentum proton-proton collisions, with a focus on evaluating model performance under controlled conditions. A model trained on simulated Large Hadron Collider (LHC) proton-proton collisions at $\sqrt{s} = 13\,\mathrm{TeV}$ is used to classify nine particle species based on seven kinematic-level features. The model is then tested on simulated high transverse momentum Relativistic Heavy Ion Collider (RHIC) data at $\sqrt{s} = 200\,\mathrm{GeV}$ without any transfer learning, fine-tuning, or weight adjustment. It maintains accuracy above 91% for both LHC and RHIC sets, while achieving above 96% accuracy for all RHIC sets, including the $p_T > 7\,\mathrm{GeV}/c$ set, despite never being trained on any RHIC data. Analysis of per-class accuracy reveals how quantum chromodynamics (QCD) effects, such as leading particle effect and kinematic overlap at high $p_T$, shape the model's performance across particle types. These results suggest that the model captures physically meaningful features of high-energy collisions, rather than simply overfitting to kinematics of the training data. This study demonstrates the potential of simulation-trained deep neural networks to remain effective across lower energy regimes within a controlled environment, and motivates further investigation in realistic settings using detector-level features and more advanced network architectures.

hep-ex↗

arXiv2021

Limitations of the Geiger-Nuttall Law in heavy cluster decay

Geiger-Nuttall Law is the simplest relation in radioactive decay relating the half-life and the decay energy. Initially restricted to $α$ decay of individual isotopes, generalizations unifying different isotopes and decay modes under a single set of constant coefficients were subsequently achieved. This motivates investigating to what extent such generalizations are possible. We also examine whether there exists a universal Geiger-Nuttall Law that can simultaneously describe all decay modes and nuclei including heavy clusters. We show that the validity of Geiger-Nuttall Law and its generalizations hinges on the assumption that half-life can be approximated linearly as a function of the square root of the ratio of the decay energy to the Coulomb barrier height. Systematic calculation of the ratio across the nuclear chart for 12 decay modes reveals that it varies over its whole range between 0 and 1. Consequently, no linear approximation can unify all the nuclei and decay modes under a single set of coefficients, and thus no universal Geiger-Nuttall Law is possible in contrast to previous claims. In cluster decay, the ratio varies within 0.6-1 where non-linearity becomes significant such that no generalized Geiger-Nuttall description of heavy clusters is possible. In the ongoing attempts of unification, it might be necessary to go beyond the Geiger-Nuttall Law and incorporate additional terms proportional to the decay energy and/or its square root.

nucl-th↗

arXiv2014

High-$p_{_{T}}$ Direct Photon Azimuthal Correlation Measurements

The azimuthal correlations of direct photons ($γ_{_{dir}}$) with high transverse momentum ($p_{_{T}}$), produced at mid-rapidity ($|η^{γ_{_{dir}}}|<1$) in Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$~GeV, are measured and compared to those of neutral pions ($π^{0}$) in the same kinematic range. The measured azimuthal elliptic anisotropy of direct photon, $v_{_{2}}^{γ_{_{dir}}}(p_{_{T}})$, at high $p_{_{T}}$ ($8< p_{_{T}}^{γ_{_{dir}}}<20$~GeV/$c$) is found to be smaller than that of $π^{0}$ and consistent with zero when using the forward detectors ($2.4 <|η|< 4.0$) in reconstructing the event plane. The associated charged hadron spectra recoiled from $γ_{_{dir}}$ show more suppression than those recoiled from $π^{0}$ $(I_{AA}^{γ_{_{dir}}-h^{\pm}} < I_{AA}^{π^{0}-h^{\pm}})$ in the new measured kinematic range $12< p_{_{T}}^{γ_{_{dir}},π^{0}}<24$~GeV/$c$ and $3< p_{_{T}}^{assoc}<24$~GeV/$c$.

nucl-ex↗

arXiv2014

Azimuthal elliptic anisotropy ($v_{_{2}}$) of high-$p_{_{T}}$ direct $γ$ in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

Preliminary results from the STAR collaboration for the azimuthal elliptic anisotropy $(v_{_{2}})$ of high transverse momentum ($p_{_{T}}$) direct photons ($γ_{_{dir}}$) produced at mid-rapidity ($|η^{γ_{_{dir}}}|<1$) in Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$~GeV are presented, and compared to the measured $(v_{_{2}})$ of neutral pions ($π^{0}$) in the same kinematic range. The electromagnetic transverse shower profile is used to distinguish $π^{0}$ from direct photons. The measured $v_{_{2}}^{γ_{_{dir}}}(p_{_{T}})$ at high $p_{_{T}}$ ($8< p_{_{T}}^{γ_{_{dir}}}<20$~GeV/$c$) is found to be smaller than that of $π^{0}$ and consistent with zero when using the forward detectors in determining the event plane.

nucl-ex↗

arXiv2010

Azimuthal anisotropy ($v_{2}$) of high-p$_{T}$ $π^{0}$ and direct $γ$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

Preliminary results from the STAR collaboration of the azimuthal anisotropy $(v_{2})$ of $π^{0}$ and direct photon ($γ_{dir}$) at high transverse momentum (p$_{T}$) from Au+Au collisions at center-of-mass energy $\sqrt{s_{_{NN}}}=200$~GeV are presented. A shower-shape analysis is used to select a sample free of direct photons ($π^0$) and a sample rich in direct photons $γ_{rich}$. The relative contribution of background in the $γ_{rich}$ sample is determined assuming no associated charged particles nearby $γ_{dir}$. The $v_{2}$ of direct photons ($v_{2}^{γ_{dir}}$) at mid-rapidity ($|η^{γ_{dir}}|<1$) and high p$_{T}$ ($8< p_{T}^{γ_{dir}}<16$~GeV/$c$) is extracted from those of $π^{0}$ and neutral particles measured in the same kinematic range. In mid-central Au+Au collisions (10-40$\%$), the $v_{2}$ of $π^0$ ($v_{2}^{π^{0}}(p_{T})$) and charged particles ($v_{2}^{ch}(p_{T})$) are found to be $\sim$ 0.12 and nearly independent of p$_{T}$. The measured $v_{2}^{γ_{dir}}(p_{T})$ is positive finite and systematically smaller than that of $π^{0}$ and charged particles by a factor of $\sim$ 3. Although the large $v_{2}^{π^{0}}$ at such high p$_{T}$ might be partially due to the path-length dependence of energy loss, the non-zero value of $v_{2}^{γ_{dir}}$ indicates a bias of the reaction plane determination due to the presence of jets in the events. Systematic studies are currently in progress.

nucl-ex↗

arXiv2009

Direct photon-charged hadron coincidence measurements in STAR

The multiplicities of charged particle with transverse momentum (3 $<$ $p_T^{h^{\pm}}$ $<$ 16 $\mathrm GeV/c$) and pseudorapidity ($\midη\mid$ $\leq$ 1.0) associated with direct photons and $π^{0}$ of high transverse momentum (8 $<$ $p_T^{γ, π^{0}}$ $<$ 16 $\mathrm GeV$) at mid-rapidity ($\midη\mid$ $\leq$ 0.9) have been measured over a broad range of centralities for $Au+Au$ collisions and $p+p$ collisions at $\sqrt{s_{NN}}$ = 200 $\mathrm GeV$ in the STAR experiment. A transverse shower-shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum Detector is used to discriminate between the shower of single photon and that of photons from the decays of high $p_T$ $π^{0}$s. The relative azimuthal positions of the associated particles with respect to the trigger particle are constructed, and the associated charged hadron yields per direct $γ$ are extracted. An agreement is observed between the measured suppression for direct $γ$-trigger associated-particle yields in $Au+Au$ compared to that in $p+p$ and theoretical calculations, although the uncertainties are large. Within the current uncertainties, the suppression is similar to the previously observed suppression in single-particle yields as well as in hadron-triggered associated-particle yields.

nucl-ex↗

arXiv2008

Modified Fragmentation Function in Heavy Ion Collisions at RHIC via Direct photon-Jet Measurements

The presented results are the first measurements at RHIC for direct $γ$-charged hadron azimuthal correlations in heavy ion collisions. We use these correlations to study the color charge density of the medium through the medium-induced modification of high-p$_T$ parton fragmentation. Azimuthal correlations of direct photons at high transverse energy (8 $<$ p$_T$ $<$ 16 GeV) with away-side charged hadrons of transverse momentum (3 $<$ p$_T$ $<$ 6 GeV/c) have been measured over a broad range of centrality for $Au+Au$ collisions and $p+p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. A transverse shower shape analysis in the STAR Barrel Electromagnetic Calorimeter Shower Maximum Detector is used to discriminate between the direct photons and photons from the decays of high p$_T$ $π^{0}$. The per-trigger away-side yield of direct $γ$ is smaller than from $π^{0}$ trigger at the same centrality class. Within the current uncertainty the I$_{CP}$ of direct $γ$ and $π^{0}$ are similar.

nucl-ex↗

arXiv2008

Direct photon-charged hadron azimuthal correlations

Azimuthal correlations of direct photons at high transverse energy (8 $<$ E$_T$ $<$ 16 GeV) with away-side hadrons of transverse momentum (3 $<$ p$_T$ $<$ 6 GeV/c) have been measured over a broad range of centrality for $Au+Au$ collisions and $p+p$ collisions at $\sqrt{s_{NN}}$ = 200 GeV. The presented results are the first measurements at RHIC for $γ$-hadron azimuthal correlations in $Au+Au$ collisions.

nucl-ex↗