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Register a new userPhenomenological NLO analysis of eta(c) production at the LHC in the collider and fixed-target modes
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In view of the good agreement between the LHCb prompt-eta(c) data at sqrt(s)=7 and 8 TeV and the NLO colour-singlet model predictions --i.e. the leading v^2 NRQCD contribution--, we provide predictions in the LHCb acceptance for the forthcoming 13 TeV analysis bearing on data taken during the LHC Run2. We also provide predictions for sqrt(s)=115 GeV for proton-hydrogen collisions in the fixed-target mode which could be studied during the LHC Run3. Our predictions are complemented by a full theoretical uncertainty analysis. In addition to cross section predictions, we elaborate on the uncertainties on the p bar-p branching ratio --necessary for data-theory comparison-- and discuss other usable branching fractions for future studies.
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We investigate the potentialities offered by the study of J/psi exclusive photo-production in ultra-peripheral collisions at a fixed-target experiment using the proton and lead LHC beams (generically denoted as AFTER@LHC) on hydrogen targets and at RHIC in the collider mode. We compare the expected counting rates in both set-ups. Studying Single-Transverse-Spin Asymmetries (A_N) in such a process provides a direct path to the proton Generalised Parton Distribution (GPD) E_g(x,xi,t). We evaluate the expected precision on A_N for realistic conditions with the LHCb detector in pH(pol) and PbH(pol) collisions. We also discuss prospects with polarised deuterium and helium targets in the case of AFTER@LHC.
We review the hadro-production data presently available on open charm and beauty absolute production cross-sections, collected by experiments at CERN, DESY and Fermilab. The published charm production cross-section values are updated, in particular for the time evolution of the branching ratios. These measurements are compared to LO pQCD calculations, as a function of the collision energy, using recent parametrisations of the parton distribution functions. We then estimate, including nuclear effects of the parton densities, the charm and beauty production cross-sections relevant for measurements at SPS and RHIC energies, in proton-proton, proton-nucleus and nucleus-nucleus collisions. The calculations are also compared with measurements of single D and B kinematical distributions, and DDbar pair correlations. We finish with two brief comments, concerning the importance of beauty production as a feed-down source of J/psi production, and open charm measurements performed using leptonic decays.
We present an analysis of hadroproduction of $J/psi$ and $psi(2S)$ at fixed-target energies in the framework of non-relativistic QCD (NRQCD). Using both pion- and proton-induced data, a new determination of the color-octet long-distance matrix elements (LDMEs) is obtained. Compared with previous results, the contributions from the $q bar{q}$ and color-octet processes are significantly enhanced, especially at lower energies. A good agreement between the pion-induced $J/psi$ production data and NRQCD calculations using the newly obtained LDMEs is achieved. We find that the pion-induced charmonium production data are sensitive to the gluon density of pions, and favor pion PDFs with relatively large gluon contents at large $x$.
We compute the energy dependence of the P_T-integrated cross section of directly produced quarkonia in pp collisions at next-to-leading order (NLO), namely up to alpha_s^3, within nonrelativistic QCD (NRQCD). Our analysis is based on the idea that the P_T-integrated and the P_T-differential cross sections can be treated as two different observables. The colour-octet NRQCD parameters needed to predict the P_T-integrated yield can thus be extracted from the fits of the P_T-differential cross sections at mid and large P_T. For the first time, the total cross section is evaluated in NRQCD at full NLO accuracy using the recent NLO fits of the P_T-differential yields at RHIC, the Tevatron and the LHC. Both the normalisation and the energy dependence of the J/psi, psi and Upsilon(1S), we obtained, are in disagreement with the data irrespective of the fit method. The same is true if one uses CEM-like colour-octet NRQCD parameters. If, on the contrary, one disregards the colour-octet contribution, the existing data in the TeV range are well described by the alpha_s^3 contribution in the colour-singlet model --which, at alpha_s^4, however shows an unphysical energy dependence. A similar observation is made for eta(c,b). This calls for a full NNLO or for a resummation of the initial-state radiation in this channel. In any case, past claims that colour-octet transitions are dominantly responsible for low-P_T quarkonium production are not supported by our results. This may impact the interpretation of quarkonium suppression in high-energy proton-nucleus and nucleus-nucleus collisions.
The pair production of a $W$ and a $Z$ boson at the LHC is an important process to study the triple-gauge boson couplings as well as to probe new physics that could arise in the gauge sector. In particular the leptonic channel $p p to W^pm Zto 3ell + u + X$ is considered by ATLAS and CMS collaborations. Polarisation observables can help pinning down new physics and give information on the spin of the gauge bosons. Measuring them requires high statistics as well as precise theoretical predictions. We define in this contribution fiducial polarisation observables for the $W$ and $Z$ bosons and we present theoretical predictions in the Standard Model at next-to-leading order (NLO) including QCD as well as NLO electroweak corrections, the latter in the double-pole approximation. We also show that this approximation works remarkably well for $W^pm Z$ production at the LHC by comparing to the full results.
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