# Exclusive J/ψ and ψ(2S) production in pp collisions at √s=7 TeV

The paper is available here.

J. Phys. G40 (2013) 045001

arXiv:1301.7084

More detailed information: ANA note 2012-059

## Abstract

Exclusive $J/\psi$ and $\psi(2S)$ vector meson production has been observed in the dimuon channel using the LHCb detector. The cross-section times branching fractions to two muons with pseudorapidities between 2.0 and 4.5 are measured to be

$\sigma_{pp\rightarrow J/\psi (\rightarrow \mu^{+} \mu^{-})} (2.0 <\eta_{\mu^{\pm}}< 4.5) = 307 \pm 21 \pm 36~\text{pb},$

$\sigma_{pp\rightarrow \psi(2S) (\rightarrow \mu^{+} \mu^{-})} (2.0 <\eta_{\mu^{\pm}}< 4.5) = 7.8 \pm 1.3 \pm 1.0~\text{pb},$

where the first uncertainties are statistical and the second are systematic. The measurements are found to be in good agreement with results from previous experiments and theoretical predictions. The $J/\psi$ photoproduction cross-section has been measured as a function of the photon-proton centre-of-mass energy. The results are consistent with measurements obtained at HERA and confirm a similar power law behaviour for the photoproduction cross-section.

## Figures

Caption Figure

 Number of tracks in the forward region for dimuon triggered events which in the backward region have one or more tracks. Number of tracks in the forward region for dimuon triggered events which in the backward region have no tracks. Invariant mass distribution in the region of the $J/\psi$ mass peak for events with exactly two tracks, no photons and a dimuon with pt below 900 MeV. The overall fit to the data is shown by the full curve while the dashed curve shows the background contribution. Invariant mass distribution in the region of the $\psi(2S)$ mass peak for events with exactly two tracks, no photons and a dimuon with pt below 900 MeV. The overall fit to the data is shown by the full curve while the dashed curve shows the background contribution. Feynman diagrams displaying (a) exclusive $J/\psi$ photoproduction and (b) inelastic $J/\psi$ photoproduction where a small number of additional particles are produced due to gluon radiation and (c,d) proton dissociation. Transverse momentum distribution for exclusive $J/\psi$ candidates with exactly two tracks and no photons. The points represent the data. The fit contains an exclusive signal component (short-dashed green curve) as estimated by SuperChic and an inelastic background component (long-dashed red curve) as estimated from data. Transverse momentum distribution in $J/\psi$ events with no backward tracks and no photons when there are three (black squares) and eight (red open circles) forward tracks. The results of fitting a Novosibirsk function to the three and eight forward track data are represented by the dashed black and the full red curves respectively. The values for P0 of the $J/\psi$ pt distribution are shown as a function of the number of forward tracks. The values for sigma of the $J/\psi$ pt distribution are shown as a function of the number of forward tracks. The values for alpha of the $J/\psi$ pt distribution are shown as a function of the number of forward tracks. Dependence of $J/\psi$ photoproduction cross-section on the centre-of-mass energy of the photon-proton system.The blue (red) triangles represent the data from H1 (ZEUS). The black dots and squares are derived from the LHCb differential cross-section as a function of rapidity. The dashed and full lines are the power law dependences determined from the HERA and LHCb data, respectively.The uncertainty on the LHCb power law determination is shown by the shaded band.

-- Main.Dermot Moran - 05 Feb 2013

Topic attachments
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pdf Fig1a.pdf r1 manage 14.3 K 2013-02-05 - 12:01 DermotMoran1
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