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Two-gluon rapidity correlations of strong colour field in $pp$, $pA$ and $AA$ collisions  [PDF]
Ye-Yin Zhao,Ming-Mei Xu,Heng-Ying Zhang,Yuan-Fang Wu
Physics , 2015,
Abstract: Using the CGC formalism, we calculate the two-gluon rapidity correlations of strong colour fields in $pp$, $pA$ and $AA$ collisions, respectively. If one trigger gluon is fixed at central rapidity, a ridge-like correlation pattern is obtained in symmetry $pp$ and $AA$ collisions, and a huge bump-like correlation pattern is presented in asymmetry $pA$ collisions. It is demonstrated that the ridge-like and the bump-like correlation patterns are caused by different-$x$ degree of freedom and their correlations. The transverse momentum and incident energy dependence of the ridge-like correlation pattern is systematically studied.
Perturbative QCD Results on Pion Production in pp, pA and AA Collisions  [PDF]
G. G. Barnafoldi,P. Levai,G. Papp,G. Fai,Y. Zhang
Physics , 2002, DOI: 10.1556/APH.18.2003.1.9
Abstract: We summarize new pQCD results on pion production in proton-proton (pp), proton-nucleus (pA) and nucleus-nucleus (AA) collisions. Our calculation introduces intrinsic parton transverse momentum (k_T) and is performed effectively at next-to-leading order (NLO), applying a K factor extracted for jet events. Two different factorization scales, Q=p_{T,jet}/2 and p_{T,jet} are used. Experimental data in pA collisions imply a preference for the latter choice at NLO level. We display our results at CERN SPS for AA collisions.
Photoproduction of heavy quarks in ultraperipheral pp, pA, and AA collisions at the CERN Large Hadron Collider  [PDF]
Adeola Adeluyi,Trang Nguyen
Physics , 2012,
Abstract: Photoproduction of heavy quarks in ultraperipheral collisions can help elucidate important features of the physics of heavy quarks in Quantum Chromodynamics (QCD). Due to the dependence on parton distributions it can also potentially offer some constraining ability in the determination of nuclear parton distributions. In the present study we consider next-to-leading order (NLO) photoproduction of heavy quarks in ultraperipheral proton-proton (pp), proton-nucleus (pA), and nucleus-nucleus (AA) collisions at the CERN Large Hadron Collider (LHC). Total cross sections and rapidity distributions are considered and the influence of nuclear modifications of parton distributions on these quantities are explored for pA and AA collisions. We find that photoproduction of heavy quarks in PbPb collisions exhibit significant sensitivity to nuclear effects, and in conjunction with photoproduction in pPb collisions, affords good constraining potential for gluon shadowing determination.
Measurements of electrons from heavy-flavour hadron decays in pp, p-Pb and Pb-Pb collisions with ALICE at the LHC  [PDF]
E. Pereira de Oliveira Filho
Physics , 2014, DOI: 10.1016/j.nuclphysa.2014.09.069
Abstract: Heavy-flavour hadrons, i. e. hadrons carrying charm or beauty quarks, are a well-suited probe to study the Quark-Gluon Plasma (QGP) in relativistic heavy-ion collisions. For this reason, measurements of electrons from heavy-flavour hadron decays have been performed in pp, p-Pb and Pb-Pb collisions at the LHC with the ALICE detector. Results for the nuclear modification factors ($R_{\rm{pA}}$ and $R_{\rm{AA}}$) support a final-state energy loss of heavy quarks in central Pb-Pb collisions and, in semi-central collisions a positive elliptic flow coefficient $v_{2}$ of electrons from heavy-flavour hadron decays was observed. Furthermore, a double-ridge structure was observed in the measured two-particle angular correlation distribution, triggered by heavy-flavour decay electrons, in high-multiplicity p-Pb collisions relative to low-multiplicity p-Pb collisions and to pp collisions.
Strangeness Production in pp,pA,AA Interactions at SPS Energies.HIJING Approach  [PDF]
V. Topor Pop,A. Andrighetto,M. Morando,F. Pellegrini,R. A. Ricci,G. Segato
Physics , 1994,
Abstract: In this report we have made a systematic study of strangeness production in proton-proton(pp),proton-nucleus(pA) and nucleus- nucleus(AA) collisions at CERN Super Proton Synchroton energies, using$\,\,\, HIJING\,\,\, MONTE \,\,\,CARLO \,\,\,MODEL $ \\ (version $HIJ.01$). Numerical results for mean multiplicities of neutral strange particles ,as well as their ratios to negatives hadrons($$) for p-p,nucleon-nucleon(N-N),\,\,p-S,\,\,p-Ag,\,\,p-Au('min. bias')collisions and p-Au,\,\,S-S,\,\,S-Ag,\,\,S-Au ('central')collisions are compared to experimental data available from CERN experiments and also with recent theoretical estimations given by others models. Neutral strange particle abundances are quite well described for p-p,N-N and p-A interactions ,but are underpredicted by a factor of two in A-A interactions for $\Lambda,\bar{\Lambda}, K^{0}_{S}$ in symmetric collisions(S-S,\,\,Pb-Pb)and for $\Lambda,\bar{\Lambda}\,\,$in asymmetric ones(S-Ag,\,\,S-Au,\,\,S-W). A qualitative prediction for rapidity, transverse kinetic energy and transverse momenta normalized distributions are performed at 200 GeV/Nucleon in p-S,S-S,S-Ag and S-Au collisions in comparison with recent experimental data. HIJING model predictions for coming experiments at CERN for S-Au, S-W and Pb-Pb interactions are given. The theoretical calculations are estimated in a full phase space.
Hard scattering cross sections at LHC in the Glauber approach: from pp to pA and AA collisions  [PDF]
D. d'Enterria
Physics , 2003,
Abstract: The scaling rules of the invariant yields and cross sections for hard scattering processes in proton-nucleus ($pA$) and nucleus-nucleus ($AB$) reactions at LHC energies relative to those of nucleon-nucleon $NN$ (isospin averaged $pp$) collisions are reviewed within the Glauber geometrical formalism. The number of binary inelastic collisions for different centrality classes in p+Pb and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 8.8 TeV and 5.5 TeV respectively, as obtained from a Glauber Monte Carlo, are also given.
A unified description of the reaction dynamics from pp to pA to AA collisions  [PDF]
K. Werner,B. Guiot,I. Karpenko,T. Pierog
Physics , 2014, DOI: 10.1016/j.nuclphysa.2014.08.093
Abstract: There is little doubt that in heavy ion collisions at the LHC and RHIC, we observe a hydrodynamically expanding system, providing strong evidence for the formation of a Quark Gluon Plasma (QGP) in the early stage of such collisions. These observations are mainly based on results on azimuthal anisotropies, but also on particle spectra of identified particles, perfectly compatible with a hydrodynamic evolution. Surprisingly, in p-Pb collisions one observes a very similar behavior, and to some extent even in p-p. We take these experimental observations as a strong support for a unified approach to describe proton-proton (p-p), proton-nucleus (p-A), and nucleus-nucleus (A-A) collisions, with a plasma formation even in tiny systems as in p-p scatterings.
Transverse momentum spectra of hadrons in pp, pA and AA collisions  [PDF]
Bedangadas Mohanty
Physics , 2003,
Abstract: The transverse momentum spectra of the produced hadrons have been compared to a model which is based on the assumption that a nucleus-nucleus collision is a superposition of isotropically decaying thermal sources at a given freeze out temperature. The freeze-out temperature in nucleus-nucleus collisions is fixed from the inverse slope of the transverse momentum spectra of hadrons in nucleon-nucleon collision. The successive collisions in the nuclear reaction leads to gain in transverse momentum, as the nucleons propagate in the nucleus following a random walk pattern. The average transverse rapidity shift per collision is determined from the nucleon-nucleus collision data. Using these information we obtain parameter free result for the transverse momentum distribution of produced hadrons in nucleus-nucleus collisions. It is observed that such a model is able to explain the transverse mass spectra of produced pions at SPS energies. However it fails to satisfactorily explain the transverse mass spectra of kaons and protons. This indicates the presence of collective effect which cannot be accounted for by the initial state collision broadening of transverse momentum of produced hadrons, the basis of random walk model.
Universal anti-baryon density in $e^+e^-$,$γp$, pp, pA and AA collisions  [PDF]
Haidong Liu,Zhangbu Xu
Physics , 2006,
Abstract: We compiled the systematical measurements of anti-nucleus production in ultra-relativistic heavy ion collisions as well as those in $pp$, $p\bar{p}$, $\gamma p$ and $e^{+}e^{-}$ at various beam energies. The anti-baryon phase space density inferred from $\bar{d}/\bar{p}$ ratio in $A+A$, $p+A$, $pp(\bar{p})$ and $\gamma p$ collisions is found to follow a universal distribution as a function of center of mass of beam energy and can be described in a statistical model. We demonstrated that anti-baryon density in all the collisions is the highest when the collisions are dominated by the processes of $g+g$ or $\bar{q}+g$. In $e^+e^-$ collisions at LEP, the cross section of $q\bar{q}g$ is suppressed by a factor of strong coupling constant $\alpha_s$ relative to $q\bar{q}$. This can consistently explain the $\bar{d}$ suppression observed by ALEPH relative to that in $e^+e^-\to ggg$ by ARGUS. We discuss the implications to the baryon enhancement at high transverse momentum at RHIC when jet is quenched.
Interplay of soft and hard processes and hadron $p_T$ spectra in $pA$ and $AA$ collisions  [PDF]
Enke Wang,Xin-Nian Wang
Physics , 2001, DOI: 10.1103/PhysRevC.64.034901
Abstract: Motivated by a schematic model of multiple parton scattering within the Glauber formalism, the transverse momentum spectra in $pA$ and $AA$ collisions are analyzed in terms of a nuclear modification factor with respect to $pp$ collisions. The existing data at the CERN Super Proton Synchrotron (SPS) energies are shown to be consistent with the picture of Glauber multiple scattering in which the interplay between soft and hard processes and the effect of absorptive processes lead to nontrivial nuclear modification of the particle spectra. Relative to the additive model of incoherent hard scattering, the spectra are enhanced at large $p_T$ (hard) by multiple scattering while suppressed at low $p_T$ (soft) by absorptive correction with the transition occurring at around a scale $p_0\sim 1-2$ GeV/$c$ that separates soft and hard processes. Around the same scale, the $p_T$ spectra in $pp$ collisions also change from an exponential form at low $p_T$ to a power-law behavior at high $p_T$. At very large $p_T\gg p_0$, the nuclear enhancement is shown to decrease like $1/p_T^2$. Implications of these nuclear effects on the study of jet quenching, parton thermalization and collective radial flow in high-energy $AA$ collisions are discussed.
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