Differential (2+1) Jet Event Rates and Determination of alpha_s in Deep Inelastic Scattering at HERA

TL;DR

This paper measures the rate of (2+1) jet events in deep-inelastic scattering at HERA, compares it with theoretical models, and extracts a precise value of the strong coupling constant alpha_s.

Contribution

It provides a new determination of alpha_s from (2+1) jet event rates using next-to-leading order QCD calculations at HERA.

Findings

Measured (2+1) jet event rates across a wide Q^2 range.

Extracted alpha_s(M_Z^2)= 0.118 with detailed uncertainties.

Compared data with Monte Carlo models and NLO QCD predictions.

Abstract

Events with a (2+1) jet topology in deep-inelastic scattering at HERA are studied in the kinematic range 200 < Q^2< 10,000 GeV^2. The rate of (2+1) jet events has been determined with the modified JADE jet algorithm as a function of the jet resolution parameter and is compared with the predictions of Monte Carlo models. In addition, the event rate is corrected for both hadronization and detector effects and is compared with next-to-leading order QCD calculations. A value of the strong coupling constant of alpha_s(M_Z^2)= 0.118+- 0.002 (stat.)^(+0.007)_(-0.008) (syst.)^(+0.007)_(-0.006) (theory) is extracted. The systematic error includes uncertainties in the calorimeter energy calibration, in the description of the data by current Monte Carlo models, and in the knowledge of the parton densities. The theoretical error is dominated by the renormalization scale ambiguity.