Exclusive physics at the LHC with SuperChic 2

Abstract

We present a range of physics results for central exclusive production processes at the LHC, using the new SuperChic 2 Monte Carlo event generator. This includes significant theoretical improvements and updates, most importantly a fully differential treatment of the soft survival factor, as well as a greater number of generated processes. We provide an overview of the latest theoretical framework, and consider in detail a selection of final states, namely exclusive 2 and 3 jets, photoproduced vector mesons, two-photon initiated muon and W boson pairs and heavy χ c,b quarkonia.

The production of a diphoton resonance via photon-photon fusion

“…This is in a regime where the proton optical density Ω(b t ), which is required to calculate the survival factor (see appendix A), is well constrained to be small in size. This means that any allowed variation in its value results in a very small change in the probability of no inelastic production exp(−Ω(b t )); in [49] various models for Ω(b t ) are taken for a range of photon-induced processes, and the variation in the resulting cross sections is found to be at the ∼ % level. Thus in this exclusive case the expected theoretical uncertainty is extremely small, of order a few percent.…”

“…where V µν is the usual γγ → R vertex, see [49] for further discussion, and q i ⊥ are the photon transverse momenta. Comparing to the coupling of R to external photons, we can see that the q i ⊥ play the role of the photon polarisation vectors, which are therefore directed along their transverse momenta.…”

“…This is seen in figure 4, where we plot the predicted φ distribution for scalar (left) and pseudoscalar (right) particles. These are calculated using a modified version of the SuperChic 2 MC [49], with model 4 of [54] taken for the survival factor (the resulting distributions are not sensitive to this precise choice). The difference between the scalar and pseudoscalar cases is clear, with the distinct azimuthal distributions resulting from (3.7) and (3.8) remaining even after survival effects are included.…”

“…• The SuperChic 2 MC [49], gives a state of the art and precise treatment of a range of exclusive γγ-initiated processes, including soft survival effects.…”

“…The above considerations therefore imply that the survival factor should be treated differentially: this was achieved within the SuperChic 2 MC framework in [49], and we give a brief summary of how this is done for γγ-initiated processes below. The diagram in figure 5 (left) corresponds to the usual so-called 'bare' amplitude, prior to including any survival effects.…”