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Register a new userPredictions for multiplicities and flow harmonics in 5.44 TeV Xe+Xe collisions at the CERN Large Hadron Collider
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We present the next-to-leading-order event-by-event EKRT model predictions for the centrality dependence of the charged hadron multiplicity in the pseudorapidity interval $|eta|le 0.5$, and for the centrality dependence of the charged hadron flow harmonics $v_n{2}$ obtained from 2-particle cumulants, in $sqrt{s_{NN}}=5.44$ TeV Xe+Xe collisions at the CERN Large Hadron Collider. Our prediction for the 0-5 % central charged multiplicity is $dN_{rm ch}/deta =1218pm 46$. We also predict $v_n{2}$ in Xe+Xe collisions to increase more slowly from central towards peripheral collisions than those in a Pb+Pb system. We find that at $10 dots 50$% centralities $v_2{2}$ is smaller and $v_3{2}$ is larger than in the Pb+Pb system while $v_4{2}$ is of the same magnitude in both systems. We also find that the ratio of flow harmonics in Xe+Xe collisions and in Pb+Pb collisions shows a slight sensitivity to the temperature dependence of the shear-viscosity-to-entropy ratio. As we discuss here, the new nuclear mass-number systematics especially in the flow harmonics serves as a welcome further constraint for describing the space-time evolution of a heavy-ion system and for determining the shear viscosity and other transport properties of strongly interacting matter.
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We make predictions for cross sections of $rho$ and $phi$ vector meson photoproduction in ultraperipheral Xe-Xe collisions at $sqrt{s_{NN}}=5.44$ TeV. Analyzing the momentum transfer distribution of $rho$ mesons in this process, we explore the feasibility of extracting the nuclear density of $^{129}$Xe, which is needed in searches for dark matter with Xenon-based detectors.
We analyze the measured spectra of $pi^pm$, $K^pm$, $p$($bar p$) in $pp$ collisions at $sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $Lambda$($bar Lambda$) and $Xi^-$ also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in $pp$ collisions at LHC. Strong transverse radial flow in high multiplicity $pp$ collisions and its comparison with that in $pA$ and $AA$ collisions match with predictions from a very recent theoretical work [Shuryak and Zahed 2013 arXiv:1301.4470] that addresses the conditions for applicability of hydrodynamics in $pp$ and $pA$ collisions.
Based on the recent RHIC and LHC experimental results, the $langle p_Trangle$ dependence of identified light flavour charged hadrons on $sqrt{(frac{dN}{dy})/S_{perp}}$, relevant scale in gluon saturation picture, is studied from $sqrt{s_{NN}}$=7.7 GeV up to 5.02 TeV. This study is extended to the slopes of the $langle p_Trangle$ dependence on the particle mass and the $langlebeta_Trangle$ parameter from Boltzmann-Gibbs Blast Wave (BGBW) fits of the $p_T$ spectra. A systematic decrease of the slope of the $langle p_Trangle$ dependence on $sqrt{(frac{dN}{dy})/S_{perp}}$ from BES to the LHC energies is evidenced. While for the RHIC energies, within the experimental errors, the $langle p_Trangle$/$sqrt{(frac{dN}{dy})/S_{perp}}$ does not depend on centrality, at the LHC energies a deviation from a linear behaviour is observed towards the most central collisions. The influence of the corona contribution to the observed trends is discussed. The slopes of the $langle p_Trangle$ particle mass dependence and the $langlebeta_Trangle$ parameter from BGBW fits scale well with $sqrt{(frac{dN}{dy})/S_{perp}}$. Similar systematic trends for pp at $sqrt{s}$=7 TeV are in a good agreement with the ones corresponding to Pb-Pb collisions at $sqrt{s_{NN}}$=2.76 TeV and 5.02 TeV pointing to a system size independent behaviour.
Tagged jet measurements provide a promising experimental channel to quantify the similarities and differences in the mechanisms of jet production in proton-proton and nucleus-nucleus collisions. We present the first calculation of the transverse momentum asymmetry of Z^0/gamma^*-tagged jet events in sqrt{s}=2.76$ TeV reactions at the LHC. Our results combine the O(G_Falpha_s^2) perturbative cross sections with the radiative and collisional processes that modify parton showers in the presence of dense QCD matter. We find that a strong asymmetry is generated in central lead-lead reactions that has little sensitivity to the fluctuations of the underlying soft hadronic background. We present theoretical model predictions for its shape and magnitude.
The hypothesis of limiting fragmentation (LF) or it is called otherwise recently, as extended longitudinal scaling, is an interesting phenomena in high energy multiparticle production process. This paper discusses about different regions of phase space and their importance in hadron production, giving special emphasis on the fragmentation region. Although it was conjectured as a universal phenomenon in high energy physics, with the advent of higher center-of-mass energies, it has become prudent to analyse and understand the validity of such hypothesis in view of the increasing inelastic nucleon-nucleon cross-section ($sigma_{rm in}$). In this work, we revisit the phenomenon of limiting fragmentation for nucleus-nucleus (A+A) collisions in the pseudorapidity distribution of charged particles at various energies. We use energy dependent $sigma_{rm in}$ to transform the charged particle pseudorapidity distributions ($dN^{rm AA}_{ch}/deta$) into differential cross-section per unit pseudorapidity ($dsigma^{rm AA}/deta$) of charged particles and study the phenomenon of LF. We find that in $dsigma^{rm AA}/deta$ LF seems to be violated at LHC energies while considering the energy dependent $sigma_{rm in}$. We also perform a similar study using A Multi-Phase Transport (AMPT) Model with string melting scenario and also find that LF is violated at LHC energies.
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