Measurement of subjet multiplicities in neutral current deep inelastic scattering at HERA and determination of $\alpha_s$

TL;DR

This paper measures subjet multiplicities in neutral current deep inelastic scattering at HERA, compares results with QCD predictions, and determines the strong coupling constant alpha_s with high precision.

Contribution

It provides the first detailed measurement of subjet multiplicities in neutral current DIS and extracts alpha_s(M_Z) from these measurements.

Findings

Measured mean subjet multiplicity for jets with E_T > 15 GeV.

Next-to-leading-order QCD describes the measurements well.

Determined alpha_s(M_Z) = 0.1187 with quantified uncertainties.

Abstract

The subjet multiplicity has been measured in neutral current e+p interactions at Q**2 > 125 GeV**2 with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb-1. Jets were identified in the laboratory frame using the longitudinally invariant K_T cluster algorithm. The number of jet-like substructures within jets, known as the subjet multiplicity, is defined as the number of clusters resolved in a jet by reapplying the jet algorithm at a smaller resolution scale y_cut. Measurements of the mean subjet multiplicity, < n_sbj >, for jets with transverse energies E_T,jet >15 GeV are presented. Next-to-leading-order perturbative QCD calculations describe the measurements well. The value of alpha_s(M_Z), determined from < n_sbj > at y_cut=10**-2 for jets with 25 < E_T,jet < 71 GeV, is alpha_s (M_Z) = 0.1187 +/- 0.0017 (stat.) +0.0024 / -0.0009 (syst.) +0.0093 / -0.0076 (th.).