Bounds on QCD Instantons from HERA

TL;DR

This paper searches for QCD instanton signals in HERA deep-inelastic scattering data, setting upper limits on their occurrence and providing constraints on instanton models within specific kinematic ranges.

Contribution

It provides the first experimental upper bounds on QCD instanton-induced processes in HERA data, refining previous theoretical predictions.

Findings

Instanton-induced events are limited to less than a few percent of the total in the studied kinematic range.

Multiplicity distributions offer the most stringent constraints on instanton signals.

Results set new bounds on the presence of QCD instantons in high-energy scattering.

Abstract

Signals for processes induced by QCD instantons are searched for in HERA data on the hadronic final state in deep-inelastic scattering. The maximally allowed fraction of instanton induced events is found at 95% confidence level to be on the percent level in the kinematic domain 0.0001<x<0.01 and 5 < Q-squared < 100 GeV-squared. The most stringent limits are obtained from the multiplicity distributions.