Photoproduction of $D^{*\pm}$ mesons associated with a leading neutron

TL;DR

This paper reports the observation of $D^{* ext{±}}$ mesons produced alongside leading neutrons in electron-proton collisions at HERA, highlighting the role of a hard scale in such peripheral scattering events.

Contribution

First measurement of $D^{* ext{±}}$ mesons with leading neutrons in ep collisions, demonstrating the influence of a hard scale on neutron production.

Findings

Neutron carries >20% of proton energy at small angles.

$D^*$ mesons are centrally produced with high transverse momentum.

Neutron-tagged $D^*$ production ratio is approximately 8.85%.

Abstract

The photoproduction of $D^{*\pm} (2010)$ mesons associated with a leading neutron has been observed with the ZEUS detector in $ep$ collisions at HERA using an integrated luminosity of 80 pb$^{-1}$. The neutron carries a large fraction, {$x_L>0.2$}, of the incoming proton beam energy and is detected at very small production angles, {$\theta_n<0.8$ mrad}, an indication of peripheral scattering. The $D^*$ meson is centrally produced with pseudorapidity {$|\eta|<1.5$}, and has a transverse momentum {$p_{\it T} > 1.9$ GeV}, which is large compared to the average transverse momentum of the neutron of 0.22 GeV. The ratio of neutron-tagged to inclusive $D^*$ production is $8.85\pm 0.93({\rm stat.})^{+0.48}_{-0.61}({\rm syst.})\%$ in the photon-proton center-of-mass energy range {$130 <W<280$ GeV}. The data suggest that the presence of a hard scale enhances the fraction of events with a leading neutron in the final state.