A study of the b-quark fragmentation function with the DELPHI detector at LEP I and an averaged distribution obtained at the Z Pole

TL;DR

This paper investigates b-quark fragmentation using DELPHI data at LEP, measuring the distribution of weakly decaying b-hadrons and comparing it with theoretical models to extract non-perturbative parameters.

Contribution

It provides new measurements of the b-quark fragmentation function and refines parameters of the Lund model using combined LEP data, enhancing understanding of b-hadron production.

Findings

Average x^weak_B = 0.699 +/- 0.011 at DELPHI

Lund model parameters determined: a=1.84, b=0.642 GeV^-2

Combined data yields x^weak_B = 0.7092 +/- 0.0025

Abstract

The nature of b-quark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying b-hadrons, E^weak_B. The average value of x^weak_B = E^weak_B/E_beam is measured to be 0.699 +/- 0.011. The resulting x^weak_B distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of b-hadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA~6.156 from DELPHI data: a= 1.84^{+0.23}_{-0.21} and b=0.642^{+0.073}_{-0.063} GeV^-2, with a correlation factor rho = 92.2%. Combining the data on the b-quark fragmentation distributions with those obtained at the Z peak by ALEPH, OPAL and SLD, the average value of x^weak_B is found to be 0.7092 +/- 0.0025 and the non-perturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a= 1.48^{+0.11}_{-0.10} and b=0.509^{+0.024}_{-0.023} GeV^-2, with a correlation factor rho = 92.6%.