Probing the pion gluon distribution at small-$x$ in photon-induced interactions at LHC
Victor P. Goncalves, Juciene T. de Souza, Diego Spiering
TL;DR
Investigates the poorly constrained small $x$ pion gluon distribution by proposing heavy quark photoproduction associated with a leading neutron in ultraperipheral $pp$ and $pPb$ collisions as a photon–pion probe. The analysis uses the Sullivan process to connect the photon–pion interaction to the pion gluon density $g^{\pi}(x,\mu^2)$, and evaluates LO cross-sections and rapidity distributions with three pion PDF parameterizations GRV, JAM21, and xFitter. The results show sizable cross-sections and strong sensitivity of $dσ/dY$ to the chosen pion PDF, with the $pPb$ case amplified by the nuclear photon flux; the ratio of charm to bottom rapidity distributions emerges as a robust observable largely independent of absorptive effects. The work highlights a complementary approach to map pion structure at small $x$ and motivates higher-order calculations and Monte Carlo implementations for experimental tests at the LHC and future facilities like EIC/EicC.
Abstract
In this paper we propose the analysis of the heavy quark photoproduction associated with a leading neutron in hadronic collisions at the LHC as an alternative to probe the pion gluon distribution in a kinematical range not covered by previous experiments. We perform an exploratory study of the charm and bottom photoproduction associated with a leading neutron in proton-proton ($pp$) and proton-lead ($pPb$) collisions, and present calculations for the rapidity distributions and cross-sections. Our predictions indicate that experimental studies of these processes are feasible, and that a future measurement of this final state will be useful to constrain the pion gluon distribution at small values of the Bjorken $x$ variable and to improve our understanding of the pion structure.