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Register a new userPredictions for p+Pb at 4.4A TeV to Test Initial State Nuclear Shadowing at energies available at the CERN Large Hadron Collider
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G. G. Barnafoldi
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Collinear factorized perturbative QCD model predictions are compared for p+Pb at 4.4A TeV to test nuclear shadowing of parton distribution at the Large Hadron Collider (LHC). The nuclear modification factor (NMF), R_{pPb}(y=0,p_T<20 GeV/c) = dn_{p Pb} /(N_{coll}(b)dn_{pp}), is computed with electron-nucleus (e+A) global fit with different nuclear shadow distributions and compared to fixed Q^2 shadow ansatz used in Monte Carlo Heavy Ion Jet Interacting Generator (HIJING) type models. Due to rapid DGLAP reduction of shadowing with increasing Q^2 used in e+A global fit, our results confirm that no significant initial state suppression is expected (R_{pPb} (p_T) = 1 pm 0.1) in the p_T range 5 to 20 GeV/ c. In contrast, the fixed Q^2 shadowing models assumed in HIJING type models predict in the above p_T range a sizable suppression, R_{pPb} (p_T) = 0.6-0.7 at mid-pseudorapidity that is similar to the color glass condensate (CGC) model predictions. For central (N_{coll} = 12) p+ Pb collisions and at forward pseudorapidity (eta = 6) the HIJING type models predict smaller values of nuclear modification factors (R_{pPb}(p_T)) than in minimum bias events at mid-pseudorapidity (eta = 0). Observation of R_{pPb}(p_T= 5-20 GeV/c) less than 0.6 for minimum bias p+A collisions would pose a serious difficulty for separating initial from final state interactions in Pb+Pb collisions at LHC energies.
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Collinear factorized perturbative quantum chromodynamics (pQCD) model predictions are compared for $p+{rm Pb}$ at 5.02$A$ TeV to test nuclear shadowing of parton distribution at the Large Hadron Collider (LHC). The pseudorapidity distribution the nuclear modification factor (NMF), $R_{p{rm Pb}}(y=0,p_T<20;{rm GeV}/{it c}) = dn_{p{rm Pb}} /(N_{rm coll}(b)dn_{pp})$ and the pseudorapidity asymmetry $Y_{asym}^{h}(p_T)=R^h_{pPb}(p_T, eta<0)/R^h_{pPb}(p_T,eta>0)$ are computed using {small HIJING/B=B v2.0 model} and a pQCD improved parton model kTpQCD_v2.0 which embedded generalized parton distribution functions (PDFs). These results are updated calculations of those presented in Phys. Rev. C {bf 85}, 024903 (2012).
Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. To study the implications of such a scenario, the dynamical evolution of a chemically nonequilibrated system is described by the ideal (2+1)-dimensional hydrodynamics with a time dependent (anti)quark fugacity. The equation of state interpolates linearly between the lattice data for the pure gluonic matter and the lattice data for the chemically equilibrated quark-gluon plasma. The spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the CERN Large Hadron Collider energy of $sqrt{s_{_{rm NN}}} = 2.76$ TeV. We test the sensitivity of the results to the choice of equilibration times, including also the case where the complete chemical equilibrium of partons is reached already at the initial stage. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the $p_T$-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state.
We study the diffusion of charm and beauty in the early stage of high energy nuclear collisions at RHIC and LHC energies, considering the interaction of these heavy quarks with the evolving Glasma by means of the Wong equations. In comparison with previous works, we add the longitudinal expansion as well as we estimate the effect of energy loss due to gluon radiation. We find that heavy quarks diffuse in the strong transverse color fields in the very early stage (0.2-0.3 fm/c) and this leads to a suppression at low $p_T$ and enhancement at intermediate low $p_T$. The shape of the observed nuclear suppression factor obtained within our calculations is in qualitative agreement with the experimental results of the same quantity for $D-$mesons in proton-nucleus collisions. We compute the nuclear suppression factor in nucleus-nucleus collisions as well, for both charm and beauty, finding a substantial impact of the evolving Glasma phase on these, suggesting that initialization of heavy quarks spectra in the quark-gluon plasma phase should not neglect the early evolution in the strong gluon fields.
Effects of strong longitudinal colour electric fields (SCF), shadowing, and quenching on the open prompt charm mesons (D$^0$, D$^+$, D$^{*+}$, D${_s}{^+}$) production in central Pb + Pb collisions at $sqrt{s_{rm NN}}$ = 2.76 TeV are investigated within the framework of the {small HIJING/B=B v2.0} model. We compute the nuclear modification factor $R_{rm PbPb}^{rm D}$, and show that the above nuclear effects constitute important dynamical mechanisms in the description of experimental data. The strength of colour fields (as characterized by the string tension $kappa$), partonic energy loss and jet quenching process lead to a suppression factor consistent with recent published data. Predictions for future beauty mesons measurements have been included. Ratios of strange to non-strange prompt charm mesons in central Pb + Pb and minimum bias (MB) $ p + p$ collisions at 2.76 TeV are also discussed. Minimum bias $p + p$ collisions which constitute theoretical baseline in our calculations are studied at the centre of mass energies $sqrt{s}$ = 2.76 TeV and 7 TeV.
The kaon to pion ratio $K^+/pi^+$ and the scaled variance $omega^-$ for fluctuations of negatively charged particles are studied within the statistical hadron resonance gas (HRG) model and the Ultra relativistic Quantum Molecular Dynamics (UrQMD) transport model. The calculations are done for p+p, Be+Be, Ar+Sc, and Pb+Pb collisions at the CERN Super Proton Synchrotron energy range to reveal the system size dependence of hadron production. For the HRG calculations the canonical ensemble is imposed for all conserved charges. In the UrQMD simulations the centrality selection in nucleus-nucleus collisions is done by calculating the forward energy $E_{rm F}$ deposited in the Projectile Spectator Detector, and the acceptance maps of the NA61/SHINE detectors are used. A comparison of the HRG and UrQMD results with the data of the NA61/SHINE Collaboration is done. To understand a difference of the event-by-event fluctuations in p+p and heavy ion collisions the centrality selection procedure in the sample of all inelastic p+p events is proposed and analyzed within the UrQMD simulations.
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