Modelling exclusive meson pair production at hadron colliders

Abstract

We present a study of the central exclusive production of light meson pairs, concentrating on the region of lower invariant masses of the central system and/or meson transverse momentum, where perturbative QCD cannot be reliably applied. We describe in detail a phenomenological model, using the tools of Regge theory, that may be applied with some success in this regime, and we present the new, publicly available, Dime Monte Carlo (MC) implementation of this for ππ, K K and ρρ production. The MC implementation includes a fully differential treatment of the survival factor, which in general depends on all kinematic variables, as well as allows for the so far reasonably unconstrained model parameters to be set by the user. We present predictions for the Tevatron and LHC, discuss and estimate the size of the proton-dissociative background, and show how future measurements may further test this Regge-based approach, as well as the soft hadronic model required to calculate the survival factor, in particular in the presence of tagged protons.

Measurement of central exclusiveπ+π−production inpp¯collisions atAaltonen1, Albrow2, Amerio3 et al. 2015Phys. Rev. D

“…Cross section values restricted to the kinematic range of this measurement with MðππÞ > 2600 MeV=c 2 have been calculated in the DIME Monte Carlo [23]. There are large uncertainties arising from the unknown ππP form factor in this regime, but while this MC with an exponential form factor agrees with the data at 3000 MeV=c 2 , it predicts a steeper MðππÞ dependence and is lower than the data by a factor of 3 at 5000 MeV=c 2 .…”

Exclusive physics at the LHC with SuperChic 2

“…As expected, the soft suppression factor depends on the proton transverse momenta, and so may have an important effect on the distributions of the outgoing proton momenta, via (10), see e.g. [39,40]. Besides the effect of eikonal screening S eik , there is some suppression caused by the rescatterings of the protons with the intermediate partons [38,41,42].…”

Central exclusive diffractive production of two-pion continuum at hadron colliders

“…Also we show some nuances of the calculations, which we should take into account (elastic amplitudes for virtual particles, off-shell pion form factor, pion-pion elastic amplitude at low energies, nonlinearity of the pion trajectory). Amplitude of the process of double pion LM CEDP p + p → p + π + + π − + p in the KMR approach [7]- [9]. Central part of the diagram is the Born amplitude (with Pomeron and two reggeons).…”