Abstract
The LHCb collaboration has measured central exclusive production of J/ф, ф(2S), and ϒ mesons as well as J/фJ/ф, J/фф(2S), ф(2S)ф(2S), and xcxc meson pairs in proton-proton collisions. The analyses of ϒ and charmonium pairs are performed at the centre-of-mass energies of 7 TeV and 8 TeV, and those of J/ф and ф(2S) are done at 7 TeV and 13 TeV. The analysis at 13 TeV involves the use of new shower counters. These allow a reduction in the background by vetoing events with activity in an extended region in rapidity. The measurements of central exclusive production at LHCb are sensitive to gluon distributions for Bjorken-x values down to 2×10−6 (at 13 TeV). An overview of the LHCb results is presented and compared to existing measurements of other experiments and theoretical calculations.
Highlights
The nucleon structure can be described in three dimensions in terms of the probability to find quarks and gluons as a function of their transverse position inside the nucleon and their longitudinal momentum fraction with respect to the nucleon momentum [1, 2]
They are Fourier transforms of generalised parton distributions (GPDs). These GPDs do not have a probabilistic interpretation. They represent probability amplitudes for a parton with longitudinal momentum fraction x + ξ to be emitted from a nucleon and a parton with longitudinal momentum fraction x − ξ to be absorbed by the nucleon
In central exclusive production of vector mesons in ultra-peripheral collisions, the proton emitting the real photon is to a good approximation not altered detecting charged-particle activity for rapidities between -3.5 and -1.5
Summary
C. Van Hulse, on behalf of the LHCb Collaboration University College Dublin Belfield, Dublin 4, Ireland∗. The LHCb collaboration has measured central exclusive production of J/ψ, ψ(2S), and Υ mesons as well as J/ψJ/ψ, J/ψψ(2S), ψ(2S)ψ(2S), and χcχc meson pairs in proton-proton collisions. The analysis at 13 TeV involves the use of new shower counters. These allow a reduction in the background by vetoing events with activity in an extended region in rapidity. The measurements of central exclusive production at LHCb are sensitive to gluon distributions for Bjorken-x values down to 2 × 10−6 (at 13 TeV). An overview of the LHCb results is presented and compared to existing measurements of other experiments and theoretical calculations
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