Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector

Abstract

Abstract This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at

$$\sqrt{s_{_\text {NN}}}=5.02$$

s

NN

= 5.02

TeV with the ATLAS detector at the LHC. The measurement uses 260

$$\text {pb}^{-1}$$

pb

- 1

of pp collisions collected in 2017 and 1.4

$$\text {nb}^{-1}$$

nb

- 1

of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-

$$k_{t}$$

k t

algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters

$$R= 0.2$$

R = 0.2

and

$$R= 0.4$$

R = 0.4

, and only

$$R= 0.2$$

R = 0.2

jets are used in Pb+Pb collisions. For comparison, inclusive

$$R= 0.2$$

R = 0.2

jets are also measured using 1.7

$$\text {nb}^{-1}$$

nb

- 1

of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor,

$$R_\text {AA}$$

R AA

, is calculated for both b-jets and inclusive jets with

$$R= 0.2$$

R = 0.2

over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet

$$R_\text {AA}$$

R AA

to inclusive jet

$$R_\text {AA}$$

R AA

is also presented and suggests that the

$$R_\text {AA}$$

R AA

for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.