Abstract
Central Exclusive Production (CEP) is a unique process at hadron machines in which particles are produced via colourless propagators, and several measurements at the LHC are directly comparable with past and future electron-ion colliders. LHCb have measured the cross-sections for the CEP of vector mesons, J /ψ,ψ (2S ),ϒ(1S ), ϒ(2S ) and ϒ(3S ), which are photo-produced. In the double Pomeron exchange process, preliminary measurements have been made of χ c 0 , χ c 1 , χ c 2 meson production while the first observations of the CEP of pairs of charmonia, J /ψJ /ψ and J/ψψ (2S ), have been made and limits obtained on the pair production of other charmonia.
Highlights
Central exclusive production (CEP) at the LHC is characterised by an isolated system of particles surrounded by two rapidity gaps that extend down to the intact colliding protons; see [1] and the papers referenced in [2] for a recent survey of the field
In J/ψ CEP at LHC central rapidities, parton fractional momenta, x, of about 5 × 10−4 are probed, similar to that examined at HERA
I concentrate on measurements of the photoproduction of single charmonium and bottomium as well as the production of double charmonia, which is principally produced by exchange
Summary
Central exclusive production (CEP) at the LHC is characterised by an isolated system of particles surrounded by two rapidity gaps that extend down to the intact colliding protons; see [1] and the papers referenced in [2] for a recent survey of the field. Charged activity in the backward region, in the approximate range −3.5 < η < −1.5, can be vetoed due to the presence of a silicon strip detector that surrounds the interaction point. LHCb is designed to trigger on particles produced at low transverse momentum. CEP events are selected by triggering on muons with transverse momentum, pT , above 400 MeV/c or electromagnetic or hadronic energy above 1000 MeV, in coincidence with a total event charged multiplicity of less than 10 as recorded by a scintillating pad detector. About 20% of the total luminosity has a single interaction and is suitable for searching for the CEP signature of low multiplicity and large rapidity gaps
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