• Energy Research

This Letter presents the measurement of differential cross sections of isolated prompt photons produced in association with a b-jet or a c-jet. These final states provide sensitivity to the heavy-flavour content of the proton and aspects related to the modelling of heavy-flavour quarks in perturbative QCD. The measurement uses proton--proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of up to 20.2 fb$^{-1}$. The differential cross sections are measured for each jet flavour with respect to the transverse energy of the leading photon in two photon pseudorapidity regions: $|\eta^\gamma|<1.37$ and $1.56 Journal of high energy physics 1, 38 (2017). Published by Springer, Berlin

AbstractThis 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.