arXiv subjects

A. M. Hamed

Publications and source records attributed to A. M. Hamed.

7 recordsLinked to original sources

arXiv2024

Benchmarking the Non-flow Contributions to the Elliptic Flow Parameter ($v_{_2}$) in Proton-Proton Collisions

This manuscript reports on the elliptic flow parameter, $v_{_2}$, in proton-proton (p-p) collisions using PYTHIA8 event generator simulations. The typical Event Plane ($EP$) method $v_{_2}$($EP$) as the one used for the real data analysis has been adopted to measure the $v_{_2}$ of particles composed of different quark flavors, and produced at mid-pseudorapidity $|η| \le 1$ at center-of-mass energy $\sqrt{s}$ = 200 GeV and $\sqrt{s}$ = 13 TeV. The event plane has been constructed using the soft charged particles with transverse momentum ($p{_{_T}} < $ 2 GeV/c) produced in various $η$ ranges. The pseudorapidity gap technique ($Δη$) between the particle of interest and the soft charged particles contributed to the event plane constructions has been utilized to benchmark the non-flow contributions. The $v_{_2}^{π^{^\pm,}π^{^0}}$, $v_{_2}^{J/ψ,Υ, K, D, B}$, and the $v_{_2}^{γ_{dir}}$ show similar pattern dependence on the transverse momentum for the same $Δη$, at both $\sqrt{s}$ = 200 GeV and $\sqrt{s}$ = 13 TeV. At each center-of-mass energy, the measured $v_{_2}$ shows obvious dependence on the quark flavor contents where $v_{_2}^{γ_{dir}}$ $\le$ $v_{_2}^{J/ψ, Υ, K, D, B}$ $\le$ $v_{_2}^{π^{^\pm,}π^{^0}}$ for similar $Δη$ gap. The measured $v_{_2}$ shows slightly higher values at smaller $\sqrt{s}$ for particles of similar values of $Δη$ gaps, particularly at small $Δη$ gap. The measured $v_{_2}$ for all particles shows systematic decreases with increasing the $Δη$ gap as expected from the previous experimental results. Because PYTHIA8 simulations do not incorporate final state interactions, the $v_{_2}(EP)$ values reported here primarily reflect the non-flow contributions and its dependence on the quark contents, pseudorapidity gap as a function on $p_{T}$ at each center of mass-energy.

hep-ph↗

arXiv2019

Quark Gluon Plasma Formation in Proton-Proton Collisions Using PYTHIA

The aim of this study is to investigate the possibility of the Quark Gluon Plasma (QGP) formation in proton-proton (p-p) collisions. The p-p collisions at center of mass energies $\sqrt{s_{_{NN}}} = 200$ $GeV$ and $\sqrt{s_{_{NN}}} = 13$ $TeV$ were simulated using PYTHIA. These are the available energies of the current collider experiments; the Relativistic Heavy Ion Collider (RHIC), and the Large Hadron Collider (LHC). To search for the QGP Phase, the near-side yield to the away-side yield ratios were calculated for high transverse momentum particles. These ratios were then compared for the low and high multiplicity events as a function of transverse momentum. At the LHC energy in the high multiplicity events, the away-side yields show suppression compared with the near-side yields. This suppression might indicate the possibility of forming the QGP at the high-energy and high-multiplicity events in p-p collisions.

hep-ex↗

arXiv2019

The Onset of Jet Quenching Phenomenon

The aim of this study is to set a baseline for the jet quenching measurements of the Quark Gluon Plasma (QGP) formed in the large system size Nucleus-Nucleus (A-A) at top central collisions, via studying simulated small system size, Nucleon-Nucleon (N-N) collisions. The proton-proton (p-p) collisions were simulated using PYTHIA, at center of mass energies $\sqrt{s_{_{NN}}} = 200$ $GeV$ and $\sqrt{s_{_{NN}}} = 13$ $TeV$ corresponding to the available energies at the current collider experiments; the Relativistic Heavy Ion Collider (RHIC), and the Large Hadron Collider (LHC). At both energies, the two-particle azimuthal correlation functions have been considered, and the yield associated with the high transverse momentum ($p_{_{T}}$) particles were extracted at its near-side ($Δϕ\approx 0$) and away-side ($Δϕ\approx π$) at mid pseudo rapidity ($|η| \le 2$). The ratio between the near-side yields in the high multiplicity events to these of the low multiplicity events ($I_{_{HL}}^{^{N}}$), as well as, the ratio of the away-side yields ($I_{_{HL}}^{^{A}}$) were calculated at both energies as a function of the hadron fractional energy $z_{_{T}}$ of the high-$p_{_{T}}$ particle. At both energies, the values of $I_{_{HL}}^{^{N}}$ and $I_{_{HL}}^{^{A}}$ were less than unity, and of trivial dependence on $z_{_{T}}$. The values of $I_{_{HL}}^{^{A}}$ are always less than these of $I_{_{HL}}^{^{N}}$ at the same multiplicity and energy, and both quantities show a pattern of systematic decreases with the multiplicity. Such multiplicity dependence cannot be used neither to exclude the jet quenching nor to prove it in the high multiplicity events in p-p collisions, as the suppressions have been found at both sides, near and away of the high-$p_{_{T}}$ particle.

hep-ex↗

arXiv2010

Upsilon Productions at STAR

The $Υ(1S+2S+3S)\to e^{+}e^{-}$ cross section is measured at mid-rapidity ($y$) in $p+p$ collisions and in d$+Au$ collisions at center-of-mass energy $\sqrt{s}$ = 200 GeV with the STAR detector at RHIC. In $p+p$, the measured cross section is found to be consistent with the world data trend as a function of $\sqrt{s}$, in agreement with the Color Evaportaion Model (CEM), and underestimated by the Color Singlet Model (CSM) up to the Next-to-Leading-Order Quantum Chromodynamics (NLO QCD) calculations. In d+$Au$, the measured cross section is in agreement with the CEM prediction with anti-shadowing effects, and the nuclear modification factor indicates that $Υ(1S+2S+3S)$ production follows binary scaling within the current uncertainties. These measurements provide a benchmark for the future measurements of $Υ$ production in $Au+Au$ collisions.

nucl-ex↗

arXiv2009

Exploration of jet energy loss via direct $γ$-charged particle azimuthal correlation measurements

The multiplicities of charged particles azimuthally associated with direct photons and $π^{0}$ have been measured for Au+Au, p+p, and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. Charged particles with transverse momentum 0.5 $<$ $p_T^{h^{\pm}}$ $<$ 16 GeV/c for p+p and d+Au, and 3 $<$ $p_T^{h^{\pm}}$ $<$ 16 GeV/c for Au+Au and pseudorapidity $\midη\mid$ $\leq$ 1.5 in coincidence with direct photons and $π^{0}$ of high transverse momentum 8 $<$ $p_T^{γ,π^{0}}$ $<$ 16 GeV/c at $\midη\mid$ $\leq$ 0.9 have been used for this analysis. Within the considered range of kinematics, the observed suppressions of the associated yields per direct $γ$ in central Au+Au relative to p+p and d+Au are similar and constant with direct photon fractional energy $z_{T}$ ($z_{T}=p_{T}^{h^{\pm}}/p_{T}^γ$). The measured suppressions of the associated yields with direct $γ$ are comparable to those with $π^{0}$. The data are compared to theoretical predictions.

nucl-ex↗

arXiv2008

Azimuthal correlations between charged hadrons and direct photons at high-p$_{t}$ in $p+p$ and $Au+Au$ collisions at $\sqrt{s_{NN}}$ = 200 GeV

Recent results at STAR for direct $γ$-charged hadron azimuthal correlations in heavy-ion collisions are presented. These correlations are used 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 $<$ E$_T$ $<$ 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. The per-trigger away-side yield of direct $γ$ is smaller than from $π^{0}$ triggers in the same centrality class.

nucl-ex↗

arXiv2008

One more ingredient for energy loss quantification

The recent results at RHIC for direct $γ$-charged hadron azimuthal correlations in heavy-ion collisions are presented. 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 $<$ E$_T$ $<$ 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 $π^{0}$ triggers in the same centrality class. Within the current uncertainty the recoil suppression in central $Au+Au$ collisions I$_{CP}$ of direct $γ$ and $π^{0}$ are similar.

nucl-ex↗