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Register a new userA model for gluon production in heavy-ion collisions at the LHC with rcBK unintegrated gluon densities
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This note is a physics manual for a recent numerical implementation of k_t-factorization with running-coupling BK unintegrated gluon distributions. We also compile some results for Pb+Pb collisions at sqrt{s} = 2.75 TeV, such as predictions for the centrality dependence of the charged particle multiplicity and transverse energy. The model can further be used to obtain initial conditions for hydrodynamic simulations of A+A collisions at the LHC.
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We compute the leading order (LO) $qgto q gamma$ and next-to-leading order (NLO) $ggto q{bar q} gamma$ contributions to inclusive photon production in proton-proton (p+p) collisions at the LHC. These channels provide the dominant contribution at LO and NLO for photon transverse momenta $k_{gammaperp}$ corresponding to momentum fractions of $xleq 0.01$ in the colliding protons. Our computations, performed in the dilute-dense framework of the Color Glass Condensate effective field theory (CGC EFT), show that the NLO contribution dominates at small-$x$ because it is sensitive to $k_perp$-dependent unintegrated gluon distributions in both of the protons. We predict a maximal $10%$ modification of the cross section at low $k_{gammaperp}$ as a direct consequence of the violation of $k_perp$-factorization. The coherence effects responsible for this modification are enhanced in nuclei and can be identified from inclusive photon measurements in proton-nucleus collisions. We provide numerical results for the isolated inclusive photon cross section for $k_{gammaperp}leq 20$ GeV in p+p collisions that can be tested in the future at the LHC.
We test several BFKL-like evolution equations for unintegrated gluon distributions against forward-central dijet production at LHC. Our study is based on fitting the evolution scenarios to the LHC data using the high energy factorization approach. Thus, as a by-product, we obtain a set of LHC-motivated unintegrated gluon distributions ready to use. We utilize this application by calculating azimuthal decorrelations for forward-central dijet production and compare with existing data.
We study the relevance of experimental data on heavy-flavor [$D^0$, $J/psi$, $Brightarrow J/psi$ and $Upsilon(1S)$ mesons] production in proton-lead collisions at the LHC to improve our knowledge of the gluon-momentum distribution inside heavy nuclei. We observe that the nuclear effects encoded in both most recent global fits of nuclear parton densities at next-to-leading order (nCTEQ15 and EPPS16) provide a good overall description of the LHC data. We interpret this as a hint that these are the dominant ones. In turn, we perform a Bayesian-reweighting analysis for each particle data sample which shows that each of the existing heavy-quark(onium) data set clearly points --with a minimal statistical significance of 7 $sigma$-- to a shadowed gluon distribution at small $x$ in the lead. Moreover, our analysis corroborates the existence of gluon antishadowing. Overall, the inclusion of such heavy-flavor data in a global fit would significantly reduce the uncertainty on the gluon density down to $xsimeq 7times 10^{-6}$ --where no other data exist-- while keeping an agreement with the other data of the global fits. Our study accounts for the factorization-scale uncertainties which dominate for the charm(onium) sector.
We present an overview of theoretical aspects of the phenomenon of gluon saturation in high energy scattering in Quantum Chromo Dynamics. Then we review the state-of-the-art of saturation-based phenomenological approaches to the study and characterisation of the initial state of ultra-relativistic heavy ion collisions performed at RHIC and the LHC. Our review focuses mostly in the Color Glass Condensate effective theory, although we shall also discuss other approaches in parallel.
We describe the quark gluon plasma (QGP) as a thermalized quark-gluon system, the thermalized QGP phase of QCD. The hadronization of the thermalized QGP phase is given in a way resembling a coalescence model with correlated quarks and anti-quarks. The input parameters of the approach are the spatial volumes of the hadronization. We introduce three dimensionless parameters C_M, C_B and C_bar{B} related to the spatial volumes of the production of low-lying mesons (M), baryons (B) and antibaryons (bar{B}). We show that at the temperature T= 175 MeV our predictions for the ratios of multiplicities agree good with the presently available set of hadron ratios measured for various experiments given by NA44, NA49, NA50 and WA97 Collaborations on Pb+Pb collisions at 158 GeV/nucleon, NA35 Collaboration on S+S collisions and NA38 Collaboration on O+U and S+U collisions at 200 GeV/nucleon.
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