Showing papers by "Mohd Danish Azmi published in 2011"

Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV

Abstract: The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.

Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at root s(NN)=2.76 TeV

Abstract: We report on the first measurement of the triangular nu(3), quadrangular nu(4), and pentagonal nu(5) charged particle flow in Pb-Pb collisions at root s(NN) = 2.76 TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow nu(2) and nu(3) have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients.

Production of pions, kaons and protons in pp collisions at root s=900 GeV with ALICE at the LHC

Abstract: The production of π+, π−, K+, K−, p, and \(\overline{\mathrm{p}}\) at mid-rapidity has been measured in proton-proton collisions at \(\sqrt{s} = 900~\mathrm{GeV}\) with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (pt) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from pt=100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean pt are compared with previous measurements, and the trends as a function of collision energy are discussed.

Strange particle production in proton-proton collisions at root s=0.9 TeV with ALICE at the LHC

Abstract: The production of mesons containing strange quarks ($\Kzs$, $\phi$) and both singly and doubly strange baryons ($\rmLambda$, $\rmAlambda$, and $\Xis$) are measured at central rapidity in pp collisions at $\sqrt{s}$ = 0.9 $\tev$ with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at central rapidities for inelastic pp collisions are presented. For mesons, we report yields ($ $) of $0.184 \pm 0.002 \stat \pm 0.006 \syst$ for $\Kzs$ and $0.021 \pm 0.004 \stat \pm 0.003 \syst$ for $\phi$. For baryons, we find $ = 0.048 \pm 0.001 \stat \pm 0.004 \syst$ for $\rmLambda$, $0.047 \pm 0.002 \stat \pm 0.005 \syst$ for $\rmAlambda$ and $0.0101 \pm 0.0020 \stat \pm 0.0009 \syst$ for $\Xis$. The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions.

Femtoscopy Of Pp Collisions At √s=0.9 And 7 Tev At The Lhc With Two-pion Bose-einstein Correlations

Abstract: We report on the high statistics two-pion correlation functions from pp collisions at root s = 0.9 TeV and root s = 7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant nonfemtoscopic correlations are observed, and are argued to be the consequence of "mini-jet"-like structures extending to low p(t). They are well reproduced by the Monte-Carlo generators and seen also in pi(+)pi(-) correlations.

a Comparative Study of the Experimental and Simulated Values of Multifractal Specific Heat in 14.5A GeV/c Heavy-Ion Collision

Abstract: An attempt is made to study multifractal specific heat from Fq, modified Gq and Takagi moments, which can provide some interesting information about event-by-event fluctuations in heavy-ion collisions at high energies It is an established fact that constancy of the specific heat (CSH) of solids and gases helps explain thermodynamical behavior of intermittency and multifractality in A–A collisions at different projectile energies It is worthmentioning that the present paper deals with multifractal specific heat, c, extracted from Fq, modified Gq and Takagi moments for the experimental as well as FRITIOF generated data on 145A GeV/c28Si-nucleus interactions The results obtained using the three approaches are compared for both the data sets The observed power law behavior reflects self-similar property of the multiparticle production process The common feature of the multifractal specific heat obtained using the three approaches is that there is no systematic variation in its value for different orders of the moments Furthermore, the value of c is found to be different for both the data sets and no strong target mass dependence is observed in any of the cases A noteworthy observation is that a non-zero finite value of the multifractal specific heat may be considered a good signal for the presence of multifractality in the relativistic charged particle multiplicity distribution

Entropy and specific heat as a measure of fluctuations in multiparticle production in relativistic nuclear collisions

Abstract: An analysis to disentangle information about the occurrence of dynamical fluctuations in multiparticle production in high energy nucleus-nucleus collisions has been carried out in terms of fractal moments and entropy for the experimental and simulated data using FRITIOF, UrQMD and HIJING generators. Although there is a possibility to thermodynamically interpret the final state of multiparticle production by calculating the values of specific heat, c, using Gq- and Fq-moments. However, both these moments give markedly different values of c. The constancy observed in the values of specific heats calculated from either Gq- or Fq-moments is in accord with the predictions of constant specific heat approximation. Variations of multifractal and factorial moments and various other parameters calculated from these moments predict the presence of non-statistical fluctuations in high energy nuclear collisions.