Measurement of beauty-hadron decay electrons in Pb–Pb collisions at = 2.76 TeV with ALICE

Martin Völk

doi:10.1088/1742-6596/612/1/012037

Abstract

The ALICE Collaboration at the LHC studies heavy-ion collisions to investigate the properties of the Quark-Gluon Plasma (QGP). Heavy quarks (charm and beauty) are effective probes for this purpose. Both their energy loss in the medium as well as their possible thermalization yield information about the medium properties. In ALICE, the reconstruction of exclusive decays is currently accessible for charm, but not for beauty hadrons. For hadrons with beauty valence quarks a promising strategy is the measurement of their decay electrons. To separate these from the background electrons (mainly from charm hadron decays, photon conversions or light-meson decays) the large decay length of beauty hadrons can be utilized. It leads to a relatively large typical impact parameter of the decay electrons. By comparing the impact parameter distribution of the signal electrons with those from the background sources, the signal can be statistically separated from the background. For this purpose a maximum likelihood fit is employed using impact parameter distribution templates from simulations. The resulting nuclear modification factor for electrons from beauty-hadron decays shows a sizeable suppression for pT > 3 GeV/c, albeit still with large uncertainties.

Highlights

The measurement of hadrons with heavy valence quarks via their decay products in heavy-ion collisions can give insight into the properties of the Quark-Gluon Plasma
Use can be made of the large branching ratios (≈ 10%) of decays with an electron in the final state
A comparison of the pT distributions of electrons from beautyhadron decays in Pb–Pb and pp collisions based on the nuclear modification factor (RAA) is sensitive to the medium effects on b-quarks

Summary

Introduction

The measurement of hadrons with heavy valence quarks (charm or beauty) via their decay products in heavy-ion collisions can give insight into the properties of the Quark-Gluon Plasma. A comparison of the pT distributions of electrons from beautyhadron decays in Pb–Pb and pp collisions based on the nuclear modification factor (RAA) is sensitive to the medium effects on b-quarks. The remaining hadron contamination was studied and was found not to contribute strongly to the systematic uncertainty of the measured spectrum of beauty-hadron decay electrons.

Results

Conclusion