Experimental determination of the b quark mass in DELPHI

TL;DR

This paper reports the first experimental observation of the running of the b quark mass in the MS-bar scheme at the Z boson scale, using a large dataset from DELPHI at LEP.

Contribution

It provides the first measurement of the b quark mass at the M_Z scale and demonstrates the running of quark masses experimentally.

Findings

Measured m_b(M_Z) = 2.67 +- 0.25 (stat.) +- 0.34 (frag.) +- 0.27 (theo.) GeV/c^2

Observed the difference in b quark mass between the Upsilon and Z scales, confirming the running.

First experimental evidence of quark mass running far from production threshold.

Abstract

The running mass of the b quark as defined in the MS-bar renormalization scheme, m_b, was measured at the M_Z scale using 2.8 million hadronic Z^0 decays collected by the DELPHI experiment at LEP. The result is m_b(M_Z) = 2.67 +- 0.25 (stat.) +- 0.34 (frag.) +- 0.27(theo.) GeV/c^2 which differs from that obtained at the Upsilon scale, by m_b(M_\Upsilon/2)-m_b(M_Z) = 1.49 +- 0.52 GeV/c^2. This measurement, performed far from the $b\bar{b}$ production threshold, provides the first experimental observation of the running of the quark masses.