Study of b-quark mass effects in multijet topologies with the DELPHI detector at LEP

TL;DR

This paper investigates how the b-quark mass influences multijet event rates at LEP, measuring jet ratios and extracting the b-quark mass using experimental data and theoretical models, confirming consistency with previous results.

Contribution

It provides a novel measurement of the b-quark mass at the Z boson energy scale using multijet topologies and compares experimental data with theoretical predictions after hadronisation.

Findings

Measured b-quark to light-quark jet rate ratios in multijet events.

Extracted b-quark mass at the Z scale: 3.76 GeV/c^2 with uncertainties.

Results agree with previous measurements and QCD evolution.

Abstract

The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and light quark jets (l = uds) in events with n = 2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, R_n^bl, have been measured with a double-tag technique using the CAMBRIDGE jet-clustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R_4^bl, a measurement of the b-quark mass using massive leading-order calculations gives: m_b(M_Z) = 3.76 +/- 0.32 (stat) +/- 0.17 (syst) +/- 0.22 (had) +/- 0.90 (theo) GeV/c^2 . This result is compatible with previous three-jet determinations at the M_Z energy scale and with low energy mass measurements evolved to the M_Z scale using QCD Renormalisation Group Equations.