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We propose a parametrization of the nuclear absorption mechanism relying on the proper time spent by cc¯ bound states travelling in nuclear matter. Our approach could lead to the extraction of charmonium formation time. It is based on a large amount of proton-nucleus data, from nucleon-nucleon center-of-mass energies sNN=27GeV to sNN=5.02TeV, collected in the past 30 years, and for which the main effect on charmonium production must be its absorption by the nuclear matter it crosses.

We outline the many quarkonium-physics opportunities offered by a multi-purpose fixed-target experiment using the p and Pb Large Hadron Collider (LHC) beams extracted by a bent crystal. This provides an integrated luminosity of 0.5 fb −1 per year on a typical 1 cm-long target. Such an extraction mode does not alter the performance of the collider experiments at the LHC. With such a high luminosity, one can analyse quarkonium production in great details in pp , pd and pA collisions at GeV and at GeV in Pb A collisions. In a typical pp ( pA ) run, the obtained quarkonium yields per unit of rapidity are 2–3 orders of magnitude larger than those expected at RHIC and about, respectively, 10(70) times larger than for ALICE. In Pb A , they are comparable. By instrumenting the target-rapidity region, the large negative- x F domain can be accessed for the first time, greatly extending previous measurements by Hera-B and E866. Such analyses should help resolving the quarkonium-production controversies and clear the way for gluon PDF extraction via quarkonium studies. The nuclear target-species versatility provides a unique opportunity to study nuclear matter and the features of the hot and dense matter formed in Pb A collisions. A polarised proton target allows the study of transverse-spin asymmetries in J / ψ and production, providing access to the gluon and charm Sivers functions.

Being used in the fixed-target mode, the multi-TeV LHC proton and lead beams allow for studies of heavy-flavour hadroproduction with unprecedented precision at backward rapidities, far negative Feynman-x, using conventional detection techniques. At the nominal LHC energies, quarkonia can be studied in detail in p+p, p+d, and p+A collisions at sNN≃115 GeV and in Pb + p and Pb + A collisions at sNN≃72 GeV with luminosities roughly equivalent to that of the collider mode that is up to 20 fb−1 yr−1 in p+p and p+d collisions, up to 0.6 fb−1 yr−1 in p+A collisions, and up to 10 nb−1 yr−1 in Pb + A collisions. In this paper, we assess the feasibility of such studies by performing fast simulations using the performance of a LHCb-like detector.

We study the effect of nuclear matter in ϒ production in d Au collisions at RHIC and p Pb collisions at the LHC. We find that the nuclear modification factor, , measured at RHIC is not satisfactorily reproduced by the conventional effects used in the literature, namely the modification of the gluon distribution in bound nucleons and an—effective—survival probability for a bound state to escape the nucleus. In particular, we argue that this probability should be close to 1 as opposed to the J / ψ case. We note that, at backward rapidities, the unexpected suppression of observed by PHENIX hints at the presence of a gluon EMC effect, analogous to the quark EMC effect—but likely stronger. Further nuclear matter effects, such as saturation and fractional energy loss, are discussed, but none of them fit in a more global picture of quarkonium production. Predictions for ϒ ( nS ) for the forthcoming p Pb run at 5 TeV at the LHC are also presented.

We report on the opportunities for spin physics and Transverse-Momentum Dependent distribution (TMD) studies at a future multi-purpose fixed-target experiment using the proton or lead ion LHC beams extracted by a bent crystal. The LHC multi-TeV beams allow for the most energetic fixed-target experiments ever performed, opening new domains of particle and nuclear physics and complementing that of collider physics, in particular that of RHIC and the EIC projects. The luminosity achievable with AFTER@LHC using typical targets would surpass that of RHIC by more that 3 orders of magnitude in a similar energy region. In unpolarised proton-proton collisions, AFTER@LHC allows for measurements of TMDs such as the Boer-Mulders quark distributions, the distribution of unpolarised and linearly polarised gluons in unpolarised protons. Using the polarisation of hydrogen and nuclear targets, one can measure transverse single-spin asymmetries of quark and gluon sensitive probes, such as, respectively, Drell-Yan pair and quarkonium production. The fixed-target mode has the advantage to allow for measurements in the target-rapidity region, namely at large x↑ in the polarised nucleon. Overall, this allows for an ambitious spin program which we outline here.

We study the effect of nuclear matter in γ production in dAu collisions at RHIC and pPb collisions at the LHC. We find that the nuclear modification factor, [R.sup.γ.sub.dAu], measured at RHIC is not satisfactorily reproduced by the conventional effects used in the literature, namely the modification of the gluon distribution in bound nucleons and an-effective--survival probability for a bound state to escape the nucleus. In particular, we argue that this probability should be close to 1 as opposed to the J/ψ case. We note that, at backward rapidities, the unexpected suppression of [R.sup.γ.sub.dAu] observed by PHENIX hints at the presence of a gluon EMC effect, analogous to the quark EMC effect--but likely stronger. Further nuclear matter effects, such as saturation and fractional energy loss, are discussed, but none of them fit in a more global picture of quarkonium production. Predictions for γ(nS) for the forthcoming pPb run at 5 TeV at the LHC are also presented.

We present a new approach to estimate the effect of gluon shadowing in nucleus + nucleus collisions and its consequences on the J / ψ production yield. Using kinematical information available from the measured J / ψ production in proton + proton collisions at  GeV, we build a Glauber Monte Carlo code which takes into account shadowing in two alternative ways: multiple-scattering corrections or Q 2 evolution of parton densities. We exploit the dependence of these different parameterizations to the J / ψ transverse momentum and we give the first predictions on the resulting p T dependence of the nuclear modification factor in deuteron + gold collisions at the same energy.

We study the impact of different cold nuclear matter effects both on J/ψ and ψ' 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 ψ' production in dAu collisions at 200 GeV, which show a strong suppression for central collisions, 5 times larger than the one obtained for J/ψ production at the same energy. We conclude that none of the abovementioned mechanisms can explain this experimental result.

A bstract The cross-sections of exclusive (coherent) photoproduction J/ψ and ψ (2S) mesons in ultra-peripheral PbPb collisions at a nucleon-nucleon centre-of-mass energy of 5 . 02 TeV are measured using a data sample corresponding to an integrated luminosity of 228 ± 10 μb − 1 , collected by the LHCb experiment in 2018. The differential cross-sections are measured separately as a function of transverse momentum and rapidity in the nucleus-nucleus centre-of-mass frame for J/ψ and ψ (2S) mesons. The integrated cross-sections are measured to be σ J / ψ coh = 5 . 965 ± 0 . 059 ± 0 . 232 ± 0 . 262 mb and σ ψ 2 S coh = 0 . 923 ± 0 . 086 ± 0 . 028 ± 0 . 040 mb, where the first listed uncertainty is statistical, the second systematic and the third due to the luminosity determination. The cross-section ratio is measured to be σ ψ 2 S coh / σ J / ψ coh = 0 . 155 ± 0 . 014 ± 0 . 003, where the first uncertainty is statistical and the second is systematic. These results are compatible with theoretical predictions.

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2 fb - 1 , respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80  GeV / c 2 and lifetimes from 5 to 100 ps are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23–198 GeV/ c 2 range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.