Deep Inelastic Scattering 2025

Observation and differential cross section measurement of neutral current DIS events with an empty hemisphere in the Breit frame

Not scheduled

20m

QCD with Heavy Flavors and Hadronic Final States WG4: QCD with Heavy Flavors and Hadronic Final States

Speaker

H1 Collaboration (DESY)

Description

The Breit frame provides a natural frame to analyze lepton--proton scattering events. In this reference frame, the parton model hard interactions between a quark and an exchanged boson defines the coordinate system such that the struck quark is back-scattered along the virtual photon momentum direction. In Quantum Chromodynamics (QCD), higher order perturbative or non-perturbative effects can change this picture drastically. As Bjorken-$x$ decreases below one half, a rather peculiar event signature is predicted with increasing probability, where no radiation is present in one of the two Breit-frame hemispheres and all emissions are to be found in the other hemisphere. At higher orders in ${\alpha }_s$ or in the presence of soft QCD effects, predictions of the rate of these events are far from trivial, and that motivates measurements with real data. We report on the first observation of the empty current hemisphere events in electron--proton collisions at the HERA collider using data recorded with the H1 detector at a center-of-mass energy of 319 GeV. The fraction of inclusive neutral-current DIS events with an empty hemisphere is found to be $0.0112\pm 3.9{\mathrm{\%}}_{\text{stat}}\pm 4.5{\mathrm{\%}}_{\text{syst}}\pm 1.6{\mathrm{\%}}_{\text{mod}}$ in the selected kinematic region of $150

Eur.Phys.J.C84 (2024), 720 [arxiv:2403.08982]