Abstract
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: |ηγ|<1.37 and 1.56<|ηγ|<2.37. The measurement covers photon transverse energies 25<ETγ<400 GeV and 25<ETγ<350 GeV respectively for the two |ηγ| regions. For each jet flavour, the ratio of the cross sections in the two |ηγ| regions is also measured. The measurement is corrected for detector effects and compared to leading-order and next-to-leading-order perturbative QCD calculations, based on various treatments and assumptions about the heavy-flavour content of the proton. Overall, the predictions agree well with the measurement, but some deviations are observed at high photon transverse energies. The total uncertainty in the measurement ranges between 13% and 66%, while the central γ+b measurement exhibits the smallest uncertainty, ranging from 13% to 27%, which is comparable to the precision of the theoretical predictions.
Highlights
The production of isolated prompt photons in association with a jet containing a b- or c-hadron provides a testing ground for perturbative quantum chromodynamics, the content of the proton and the treatment of heavy quarks in matrix element (ME) and parton shower (PS) computations
Comparisons of the γ + b measurement to NLO + PS predictions from MadGraph5_aMC@NLO in both the 5F and 4F schemes are shown in Figs. 2(a) and 2(b), for the central and forward regions respectively
Differential cross sections as a function of for isolated prompt photons in association with a b-jet or a c-jet are measured with the√ATLAS detector at the Large Hadron Collider (LHC) using a dataset of pp collisions at s = 8 TeV corresponding to an integrated luminosity of up to 20.2 fb−1
Summary
The production of isolated prompt photons in association with a jet containing a b- or c-hadron provides a testing ground for perturbative quantum chromodynamics (pQCD), the content of the proton and the treatment of heavy quarks in matrix element (ME) and parton shower (PS) computations. Global parton distribution function (PDF) fits show that HF quarks in the proton are almost entirely extrinsic, non-zero values of the intrinsic contribution have not been ruled out [22]. Theoretical predictions using leading-order (LO) and next-toleading-order (NLO) pQCD matrix element calculations, interfaced to a PS, are computed using different PDF sets and compared to the measurement. This Letter presents a fiducial differential measurement of the production cross section of a prompt isolated photon in association with a b-jet or a c-jet in pp collisions using the ATLAS detector. The measurement is pwreeigrtihfoonr|mηwγei|dth
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