Exclusive and semiexclusive production of $\mu^+ \mu^-$ pairs with $\Delta$ isobars and other resonances in the final state and the size of absorption effects

Abstract

We include $p p \to p \Delta^{+} \mu^{+} \mu^{-}$ and $p p \to \Delta^{+} \Delta^{+} \mu^{+} \mu^{-}$ processes in addition to the standard $p p \to p p \mu^{+} \mu^{-}$ process both in equivalent-photon approximation (EPA) and in exact $2 \to 4$ calculations. For comparison we calculate also the continuum proton dissociation in a recently developed $k_{t}$-factorization approach to $\gamma \gamma$-involved processes with parametrizations of $F_{2}$ structure function known from the literature. The calculated cross section including all the processes is considerably larger than the one measured recently by the ATLAS collaboration. We calculate absorption effects for $p p \to p p \mu^{+} \mu^{-}$ process in the momentum space. The final cross section with absorption effects is by 10\% larger than the one measured by the ATLAS collaboration which is difficult to explain. Several differential distributions with the ATLAS experimental cuts are presented. It is shown that the processes with electromagnetic $p \to \Delta(1232)$ and $p \to N(1440)$ transitions, that have similar characteristics as the $p p \to p p \mu^+ \mu^-$ process, increase the cross section for $\mu^+ \mu^-$ production and thus can affect its theoretical interpretation when the leading baryons are not detected as is the case for the CMS and ATLAS measurements. The mechanism of dissociation into hadronic continuum is not under full control as the corresponding absorption effects are not fully understood. We present first predictions for future ATLAS experiment with the ALFA sub-detectors and discuss observables relevant for this measurement.