Semi-inclusive photon-hadron production in pp and pA collisions at RHIC and LHC

We investigate semi-inclusive photon-hadron production in the color glass condensate (CGC) framework at RHIC and the LHC energies in proton-proton (pp) and proton-nucleus (pA) collisions. We calculate the coincidence probability for azimuthal correlation of pairs of photon-hadron and show that the away-side correlations have a double-peak or a single-peak structure depending on trigger particle selection and kinematics. This novel feature is unique for semi-inclusive photon-hadron production compared to a similar measurement for double inclusive dihadron production in pA collisions. We obtain necessary conditions between kinematics variables for the appearance of a double-peak or a single peak structure for the away-side photon-hadron correlations in pp and pA collisions at forward rapidities and show that this feature is mainly controlled by the ratio p_T^hadron/p_T^photon. Decorrelation of away-side photon-hadron production by increasing the energy, rapidity and density, and appearance of double-peak structure can be understood by QCD saturation physics. We also provide predictions for the ratio of single inclusive prompt photon to hadron production, and two-dimensional nuclear modification factor for the semi-inclusive photon-hadron pair production at RHIC and the LHC at forward rapidities.Comment: 16 pages, 20 figures; v2: latex Compilation problem in Figs. 3,4 correcte

Particle Production in pA Collisions and QCD Saturation

The forthcoming LHC measurements in proton-nucleus (pA) collisions at forward rapidities can discriminate between the color glass condensate (CGC) and alternative approaches including standard collinear factorization one. We report some of our recent predictions based on gluon saturation/CGC formalism for pA collisions at the LHC including the charged hadron multiplicity distribution, the nuclear modification factor for single inclusive hadron and prompt photon production, and the azimuthal angle correlation of the semi-inclusive hadron-photon production.Comment: 4 pages, 8 figures; v2: a typo corrected. Talk given at "Hard Probes 2012", 27 May - 1 June, 2012, Cagliari, Ital

Gluon saturation effects at forward rapidities at LHC in pp collisions

We investigate hadrons and direct photon production in pp collisions at the LHC energy within the color-dipole approach. We show that greatest sensitivity to gluon saturation effects is reached at very forward rapidities in pp collisions at LHC (\sqrt{s}=14 TeV). The discrepancies among various saturation models (fitted to HERA data) results can be about a factor of 2-3 at forward rapidities. We found that the ratio of direct-photon to pion production can be about 20-10 at forward rapidities \eta=7-8. Therefore, direct photon production at forward rapidities should provide a rather clean probe as the background from radiative hadronic decays is significantly suppressed.Comment: 4 pages, 6 figures, Contributed to "Lepton-Photon 2009 (LP09)", Hamburg, German

Charged particle multiplicities in pA interactions at the LHC from the Color Glass Condensate

The forthcoming LHC measurement of hadron multiplicity in proton-nucleus collisions is a crucial test of the k_t factorization and gluon saturation based models. Here, we provide quantitative predictions for the pseudorapidity distribution of charged particles produced in minimum bias proton-nucleus collisions at the LHC based on the idea of gluon saturation in the color-glass condensate framework. Our formulation gives good descriptions of the LHC and RHIC data for the charged-hadron multiplicities in both proton-proton and nucleus-nucleus collisions, and also the deep inelastic scattering at HERA at small Bjorken-x.Comment: 5 pages, 3 figures; v2: version improved. The version to appear in PR

Hadron production at the LHC: Any indication of new phenomena

We confront soft Pomeron and gluon saturation models with the first LHC data on inclusive hadron production. We claim that while the first type of models are not able to describe some part of the LHC data, the Colour-Glass-Condensate (gluon saturation) approach gives an adequate description of the data. Here, we compare our published predictions with the recently available 7 TeV data. We firmly believe that if further experimental measurements confirm that the gluon saturation works, it will be a major discovery.Comment: 8 pages, 12 figure, Based on two talks given by authors at Diffraction 2010, Otranto (Lecce), Italy, September 10-15, 201