Measurements of b-jet Nuclear Modification Factors in pPb and PbPb Collisions with CMS

TL;DR

This paper measures how b-jet production is modified in lead-lead and proton-lead collisions at the LHC, revealing significant suppression in lead-lead and no suppression in proton-lead, which informs understanding of quark-gluon plasma effects.

Contribution

First measurement of b-jet nuclear modification factors in PbPb and pPb collisions at the LHC using CMS detector data.

Findings

Significant suppression of b jets in PbPb collisions.

RpA(PYTHIA) for b jets in pPb is consistent with unity.

Results align with inclusive-jet suppression, suggesting negligible mass-dependent energy loss at high pT.

Abstract

We present measurements of the nuclear modification factors RAA and RpA(PYTHIA) of b jets in lead-lead and proton-lead collisions, respectively, using the CMS detector. Jets from b-quark fragmentations are found by exploiting the long lifetime of the b-quark through tagging methods using distributions of the secondary vertex displacement. From these, b-jet cross-sections are calculated and compared to the pp cross-section from the 2.76 TeV pp data collected in 2013 and to a PYTHIA simulation at 5.02 TeV, where these center-of-mass energies correspond to those of the PbPb and pPb data. We observe significant suppression for b jets in PbPb, and a RpA(PYTHIA) value consistent with unity for b jets in pPb. Results from both collision species show remarkable correspondence with inclusive-jet suppression measurements, indicating that mass-dependent energy-loss effects are negligible at pT values greater than around 50 GeV/c. We use 150 inverse {\mu}b of lead-lead data and 35 inverse nb of proton-lead data collected at the LHC.