Central exclusive production of W boson pairs in pp collisions at the LHC in hadronic and semi-leptonic final states

We present a phenomenology study on central exclusive production of W+W− boson pairs in proton-proton collisions at the Large Hadron Collider at 14 TeV using the forward proton detectors, such as the ATLAS Forward Proton or the CMS-TOTEM Precision Proton Spectrometer detectors. Final states where at least one of the W bosons decay hadronically in a large-radius jet are considered. The latter extends previous efforts that consider solely leptonic final states. A measurement of exclusive W+W− also allows us to further constrain anomalous quartic gauge boson interactions between photons and W bosons. Expected limits on anomalous quartic gauge couplings $$ {a}_{0,C}^W $$ a 0 , C W associated to dimension-six effective operators are derived for the hadronic, semi-leptonic, and leptonic final states. It is found that the couplings can be probed down to one-dimensional values of $$ {a}_0^W=3.7\times {10}^{-7}{\mathrm{GeV}}^{-2} $$ a 0 W = 3.7 × 10 − 7 GeV − 2 and $$ {a}_C^W=9.2\times {10}^{-7}{\mathrm{GeV}}^{-7} $$ a C W = 9.2 × 10 − 7 GeV − 7 at 95% CL at an integrated luminosity of 300 fb−1 by combining all final states, compared to values of about $$ {a}_0^W=4\times {10}^{-6}{\mathrm{GeV}}^{-2} $$ a 0 W = 4 × 10 − 6 GeV − 2 and $$ {a}_C^W=1\times {10}^{-5}{\mathrm{GeV}}^{-2} $$ a C W = 1 × 10 − 5 GeV − 2 at 95% CL expected for the leptonic channel alone.

Searching for Odderon in Exclusive Reactions

We discuss the possibility to use the pp → ppфф process in identifying the odderon exchange. So far, there is no unambiguous experimental evidence for the odderon, the charge conjugation C = −1 counterpart of the C = +1 pomeron. Last year, the results of the TOTEM collaboration suggest that the odderon exchange can be responsible for a disagreement of theoretical calculations and the TOTEM data for the elastic proton-proton scattering. Here, we present recent studies for the central exclusive production (CEP) of фф pairs in proton-proton collisions. We consider the pomeron-pomeron fusion to фф (PP → фф) through the continuum processes, due to the ^t- and ^u-channel reggeized ф-meson, photon, and odderon exchanges, as well as through the s-channel resonance process (PP → f2(2340) → фф). This f2 state is a candidate for a tensor glueball. The amplitudes for the processes are formulated within the tensor-pomeron and vector-odderon approach. Some model parameters are determined from the comparison to the WA102 experimental data. The odderon exchange is not excluded by the WA102 data for high фф invariant masses. The measurement of large Mфф or Ydiff events at the LHC would therefore suggest the presence of the odderon exchange. The process is advantageous, as here the odderon does not couple to protons.

Central Exclusive Production at LHCb

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.