Identified particle transverse momentum spectra in p+p and d+Au collisions at sqrt{s_NN} = 200 GeV

The transverse momentum ($p_{\mathrm T}$) spectra for identified charged pions, protons and anti-protons from $p$+$p$ and $d$+Au collisions are measured around midrapidity ($\mid$y$\mid$ $<$ 0.5) over the range of 0.3 $<$ $p_{\mathrm T}$ $<$ 10 GeV/$c$ at $\sqrt{s_{\mathrm {NN}}}$ = 200 GeV. The charged pion and proton+anti-proton spectra at high p_{T} in p+p collisions have been compared with the next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations with a specific fragmentation scheme. The p/pi^{+} and pbar/pi^{-}has been studied at high p_{T}. The nuclear modification factor (R_{dAu}) shows that the identified particle Cronin effects around midrapidity are significantly non-zero for charged pions and to be even larger for protons at intermediate p_{T} (2 < p_{T} < 5 GeV/c).Comment: Talk given at Particles and Nuclei International Conference, Santa Fe,NM-October 24-28,200

The width of the rapidity distribution in heavy ion collisions

We have studied the widths of the rapidity distributions of particles produced in nucleus-nucleus collisions at various center of mass energies and as a function of centrality at SPS energies. We show that the width of the rapidity distribution is sensitive to longitudinal flow, velocity of sound in the medium, and rescattering of particles. We explore the possibility of distinguishing the initial hard scattering regime from final state effects by studying the variation in the width of the rapidity distribution of the particles with centrality for various pT values.Comment: 4 pages, 6 figures, to appear in Physical Review

Selected Experimental Results from Heavy Ion Collisions at LHC

We review a subset of experimental results from the heavy-ion collisions at the Large Hadron Collider (LHC) facility at CERN. Excellent consistency is observed across all the experiments at the LHC (at center of mass energy of 2.76 TeV) for the measurements such as charged particle multiplicity density, azimuthal anisotropy coefficients and nuclear modification factor of charged hadrons. Comparison to similar measurements from the Relativistic Heavy Ion Collider (RHIC) at lower energy (center of mass energy of 200 GeV) suggests that system formed at LHC has a higher energy density, larger system size, and lives for a longer time. These measurements are compared to model calculations to obtain physical insights on the properties of matter created at the RHIC and LHC.Comment: 19 pages and 26 figures. Accepted for publication in the special issue of Advances in High Energy Physics dedicated to Physics of Quark Gluon Plasma: An Update and Status Repor

Energy dependence of elliptic flow from heavy-ion collision models

We have compared the experimental data on charged particle elliptic flow parameter (v2) in Au+Au collisions at midrapidity for \surd sNN = 9.2, 19.6, 62.4 and 200 GeV with results from various models in heavy-ion collisions like UrQMD, AMPT, and HIJING. We observe that the average from the transport model UrQMD agrees well with the measurements at \surd sNN = 9.2 GeV but increasingly falls short of the experimental values as the beam energy increases. The difference in being of the order of 60% at \surd sNN = 200 GeV. The results from HIJING is consistent with zero, while those from AMPT with default settings, a model based on HIJING with additional initial and final state rescattering effects included, gives a value of about 4% for all the beam energies studied. This is in contrast to increase in with beam energy for the experimental data. A different version of the AMPT model, which includes partonic effects and quark coalescence as a mechanism of hadronization, gives higher values of among the models studied and is in agreement with the measured values at \surd sNN = 200 GeV. These studies show that the experimental has substantial contribution from partonic interactions at \surd sNN = 200 GeV whose magnitude reduces with decrease in beam energy. We also compare the available data on the transverse momentum and pseudorapidity dependence of v2 to those from the above models.Comment: 5 pages, 6 figures, accepted in Physical Review

Addressing the physics of the ridge by 2- and 3-particle correlations at STAR

We present new results on 2-particle azimuthal ($\Delta\phi$) correlation relative to event plane and 3-particle pseudorapidity ($\Delta\eta$) correlation at mid-rapidity in Au+Au collisions at $\sqrt{{\it s}_{NN}}$ = 200 GeV, measured by the STAR experiment. While jet-like correlation is symmetric, ridge is found to be asymmetric when trigger particle azimuth is between in- and out-of-plane. The charge ordering properties between associated and trigger particles are exploited to separate jet-like and ridge contributions in 3-particle $\Delta\eta$-$\Delta\eta$ correlations. We found that like-sign triplets are dominated by ridge. The separated ridge, while narrow in $\Delta\phi$, is extremely broad in $\Delta\eta$. The ridge particles are not only uncorrelated to the trigger particle in $\Delta\eta$, but also uncorrelated between themselves.Comment: 4 pages, 4 Figures, Quark Matter 200

Longitudinal scaling of observables in heavy-ion collision models

Longitudinal scaling of pseudorapidity distribution of charged particles ($dN_{\mathrm {ch}}/d\eta$) is observed when presented as a function of pseudorapidity ($\eta$) shifted by the beam rapidity ($\eta$ - $y_{\mathrm {beam}}$) for a wide range of collision systems ($e^{+}+e^{-}$, p+p, $d$+A and A+A) and beam energies. Such a scaling is also observed for the elliptic flow ($v_{2}$) of charged hadrons in A+A collisions. This is a striking observation, as $v_{2}$ is expected to be sensitive to the initial conditions, the expansion dynamics and the degrees of freedom of the system, all of which potentially varies with collision system and colliding energies. We present a study of the longitudinal scalings of $dN_{\mathrm {ch}}/d\eta$, average transverse momentum () and $v_{2}$ using transport models UrQMD and AMPT for Au+Au collisions at center of mass energies ($\sqrt{s_{\mathrm {NN}}}$) of 19.6, 62.4, 200 GeV and Pb+Pb collisions at 2760 GeV. Only the AMPT models which includes partonic effects and quark coalescence as a mechanism of hadronization, shows longitudinal scaling for $dN_{\mathrm {ch}}/d\eta$, $< p_{\mathrm T}>$ and $v_{2}$. Whereas the UrQMD and AMPT default versions show longitudinal scaling only for $dN_{\mathrm {ch}}/d\eta$ and . We also discuss the possibility of longitudinal scaling of $v_{2}$ within two extreme scenarios of models with hydrodynamic and collisionless limits. We find the longitudinal scaling of bulk observables to be an important test for the underlying physics mechanism in models of particle production.Comment: 5 pages, 3 figures, accepted for publication in Physical Review

Improving the dE/dx calibration of the STAR TPC for the high-pT hadron identification

We derive a method to improve particle identification (PID) at high transverse momentum ($p_T$) using the relativistic rise of the ionization energy loss ($rdE/dx$) when charged particles traverse the Time Projection Chamber (TPC) at STAR. Electrons triggered and identified by the Barrel Electro-Magnetic Calorimeter (BEMC), pure protons and pions from $\Lambda\to p+\pi^{-}$ ($\bar{\Lambda}\to \bar{p}+\pi^{+}$), and $K^{0}_{S}\to\pi^{+}+\pi^{-}$ decays are used to obtain the $dE/dx$ value and its width at given $\beta\gamma=p/m$. We found that the deviation of the $dE/dx$ from the Bichsel function can be up to $0.4\sigma$ ($\sim3$) in p+p collisions at $\sqrt{s_{NN}}=200$ GeV taken and subsequently calibrated in year 2005. The deviation is approximately a function of $\beta\gamma$ independent of particle species and can be described with a function of $f(x) = A+\frac{B}{C+x^{2}}$. The deviations obtained with this method are used to re-calibrate the data sample from p+p collision for physics analysis of identified hadron spectra and their correlations up to transverse momentum of 15 GeV/$c$. The ratio of $e^{-}/e^{+}$ (dominantly from $\gamma$-conversion) is also used to correct the residual asymmetry in the negative and positive charged hadrons due to momentun distortion in the STAR TPC.Comment: 18pages, 10 figure

Optimasi Portofolio Resiko Menggunakan Model Markowitz MVO Dikaitkan dengan Keterbatasan Manusia dalam Memprediksi Masa Depan dalam Perspektif Al-Qur`an

Risk portfolio on modern finance has become increasingly technical, requiring the use of sophisticated mathematical tools in both research and practice. Since companies cannot insure themselves completely against risk, as human incompetence in predicting the future precisely that written in Al-Quran surah Luqman verse 34, they have to manage it to yield an optimal portfolio. The objective here is to minimize the variance among all portfolios, or alternatively, to maximize expected return among all portfolios that has at least a certain expected return. Furthermore, this study focuses on optimizing risk portfolio so called Markowitz MVO (Mean-Variance Optimization). Some theoretical frameworks for analysis are arithmetic mean, geometric mean, variance, covariance, linear programming, and quadratic programming. Moreover, finding a minimum variance portfolio produces a convex quadratic programming, that is minimizing the objective function ðð¥with constraintsð ð 𥠥 ðandð´ð¥ = ð. The outcome of this research is the solution of optimal risk portofolio in some investments that could be finished smoothly using MATLAB R2007b software together with its graphic analysis