Impact of the Nuclear Modification of the Gluon Densities on J/Psi production in pPb collisions at sqrt(s_NN) = 5 TeV

We update our previous studies of nuclear-matter effects on J/Psi production in proton-nucleus for the recent LHC pPb runs at sqrt(s_NN)=5 TeV. We have analysed the effects of the modification of the gluon PDFs in nucleus, using an exact kinematics for a 2->2 process, namely g+g->J/Psi+g as expected from LO pQCD. This allows to constrain the transverse-momentum while computing the nuclear modification factor for different rapidities, unlike with the usual simplified kinematics. Owing to the absence of measurement in pp collisions at the same sqrt(s_NN) and owing to the expected significant uncertainties in yield interpolations which would hinder definite interpretations of nuclear modification factor --R_pPb--, we have derived forward-to-backward and central-to-peripheral yield ratios in which the unknown proton-proton yield cancel. These have been computed without and with a transverse-momentum cut, e.g. to comply with the ATLAS and CMS constraints in the central-rapidity region.Comment: 5 pages, 16 figures, LaTeX. v2: predictions on R_CP and 3 references added; introduction slightly extende

J/\psi\ and \psi' production in proton(deuteron)-nucleus collisions: lessons from RHIC for the proton-lead LHC run

We study the impact of different cold nuclear matter effects both on J/\psi\ and \psi' production, among them the modification of the gluon distribution in bound nucleons, commonly known as gluon shadowing, and the survival probability for a bound state to escape the nucleus --the nuclear absorption. Less conventional effects such as saturation and fractional energy loss are also discussed. We pay a particular attention to the recent PHENIX preliminary data on \psi' production in dAu collisions at sqrt{s}=200 GeV, which show a strong suppression for central collisions, 5 times larger than the one obtained for J/\psi\ production at the same energy. We conclude that none of the abovementioned mechanisms can explain this experimental result.Comment: 4 pages, 2 tables, 2 figures, contribution to Rencontres du Vietnam, 'Heavy Ion Collisions in the LHC Era', 15-21 July 2012, Quy Nhon, Vietna

Open-beauty production in ppPb collisions at sNN\sqrt{s_{NN}}=5 TeV: effect of the gluon nuclear densities

We present our results on open beauty production in proton-nucleus collisions for the recent LHC $p$Pb run at $\sqrt{s_{NN}}$=5 TeV. We have analysed the effect of the modification of the gluon PDFs in nucleus at the level of the nuclear modification factor. Because of the absence of measurement in $pp$ collisions at the same energy, we also propose the study of the forward-to-backward yield ratio in which the unknown proton-proton yield cancel. Our results are compared with the data obtained by LHCb collaboration and show a good agreement.Comment: 6 pages, 3 figures, Proceedings IS2013 submitted to Nuclear Physics

On the theoretical and experimental uncertainties in the extraction of the J/psi absorption cross section in cold nuclear matter

We investigate the cold nuclear matter effects on $J/\psi$ production, whose understanding is fundamental to study the quark-gluon plasma. Two of these effects are of particular relevance: the shadowing of the parton distributions and the nuclear absorption of the $c\bar{c}$ pair. If $J/\psi$'s are not produced {\it via} a $2 \to 1$ process as suggested by recent theoretical works, one has to modify accordingly the way to compute the nuclear shadowing. This naturally induces differences in the absorption cross-section fit to the data. A careful analysis of these differences however requires taking into account the experimental uncertainties and their correlations, as done in this work for $d$Au collisions at \sqrtsNN=200\mathrm{GeV}, using several shadowing parametrisations.Comment: 6 pages, 1 table, 3 figures, Submitted to J. Phys. G, talk given at the International Conference on Strangeness in Quark Matter (SQM2009), Buzios, Brasil, Sep. 27 - Oct. 2, 200

A Fixed-Target ExpeRiment at the LHC (AFTER@LHC) : luminosities, target polarisation and a selection of physics studies

We report on a future multi-purpose fixed-target experiment with the proton or lead ion LHC beams extracted by a bent crystal. The multi-TeV LHC beams allow for the most energetic fixed-target experiments ever performed. Such an experiment, tentatively named AFTER for "A Fixed-Target ExperRiment", gives access to new domains of particle and nuclear physics complementing that of collider experiments, in particular at RHIC and at the EIC projects. The instantaneous luminosity at AFTER using typical targets surpasses that of RHIC by more than 3 orders of magnitude. Beam extraction by a bent crystal offers an ideal way to obtain a clean and very collimated high-energy beam, without decreasing the performance of the LHC. The fixed-target mode also has the advantage of allowing for spin measurements with a polarised target and for an access over the full backward rapidity domain up to xF ~ - 1. Here, we elaborate on the reachable luminosities, the target polarisation and a selection of measurements with hydrogen and deuterium targets.Comment: 6 pages. Proceedings of the Sixth International Conference on Quarks and Nuclear Physics QNP2012 (16-20 April 2012, Ecole Polytechnique, Palaiseau,France

Interpretations of J/ψJ/\psi suppression

We review the two main interpretations of $J/\psi$ suppression proposed in the literature. The phase transition (or deconfining) scenario assumes that below some critical value of the local energy density (or of some other geometrical quantity which depends both on the colliding systems and on the centrality of the collision), there is only nuclear absorption. Above this critical value the absorptive cross-section is taken to be infinite, i.e. no $J/\psi$ can survive in this hot region. In the hadronic scenario the $J/\psi$ dissociates due both to nuclear absorption and to its interactions with co-moving hadrons produced in the collision. No discontinuity exists in physical observables. We show that an equally good description of the present data is possible in either scenario.Comment: 12 pages, LaTeX, uses epsfig and ioplppt; review talk given by A. Capella at the International Symposium on Strangness in Quark Matter, Santorini (Greece), April 1997; Figs. 1 and 2 not available but can be found in Refs. 13 and 6 respectivel

Spin physics at A Fixed-Target ExpeRiment at the LHC (AFTER@LHC)

We outline the opportunities for spin physics which are offered by a next generation and multi-purpose fixed-target experiment exploiting the proton LHC beam extracted by a bent crystal. In particular, we focus on the study of single transverse spin asymetries with the polarisation of the target.Comment: Contributed to the 20th International Spin Physics Symposium, SPIN2012, 17-22 September 2012, Dubna, Russia, 4 pages, LaTe

Prospectives for A Fixed-Target ExpeRiment at the LHC: AFTER@LHC

We argue that the concept of a multi-purpose fixed-target experiment with the proton or lead-ion LHC beams extracted by a bent crystal would offer a number of ground-breaking precision-physics opportunities. The multi-TeV LHC beams will allow for the most energetic fixed-target experiments ever performed. The fixed-target mode has the advantage of allowing for high luminosities, spin measurements with a polarised target, and access over the full backward rapidity domain --uncharted until now-- up to x_F ~ -1.Comment: 6 pages, 1 table, LaTeX. Proceedings of the 36th International Conference on High Energy Physics (ICHEP2012), 4-11 July 2012, Melbourne, Australi