Measurement of the cross section of high transverse momentum $Z\rightarrow b\bar{b}$ production in proton--proton collisions at $\sqrt{s}=8 TeV$ with the ATLAS Detector

TL;DR

This paper reports the first observation and measurement of the high transverse momentum Z boson decaying into b-quark pairs in proton-proton collisions at 8 TeV, using data from the ATLAS detector, with results consistent with theoretical predictions.

Contribution

The study provides the first measurement of the Z→bb̄ production cross section at high pT in proton-proton collisions at 8 TeV, employing a data-driven background estimation method.

Findings

Measured fiducial cross section: 2.02 ± 0.33 pb.

Observation of Z→bb̄ signal at high pT.

Results agree with next-to-leading-order predictions.

Abstract

This Letter reports the observation of a high transverse momentum $Z\rightarrow b\bar{b}$ signal in proton-proton collisions at $\sqrt{s}=8$ TeV and the measurement of its production cross section. The data analysed were collected in 2012 with the ATLAS detector at the LHC and correspond to an integrated luminosity of 19.5 fb$^{-1}$. The $Z\rightarrow b\bar{b}$ decay is reconstructed from a pair of b-tagged jets, clustered with the anti-$k_t$ jet algorithm with $R = 0.4$, that have low angular separation and form a dijet with $p_T > 200$ GeV. The signal yield is extracted from a fit to the dijet invariant mass distribution, with the dominant, multi-jet background mass shape estimated by employing a fully data-driven technique that reduces the dependence of the analysis on simulation. The fiducial cross section is determined to be \[ \sigma^\mathrm{fid}_{Z\rightarrow b\bar{b}} = 2.02 \pm 0.20 ({\rm stat.}) \pm0.25 ({\rm syst.)}\pm 0.06 ({\rm lumi.}){\rm\,pb} = 2.02 \pm{0.33}{\rm\,pb}, \] in good agreement with next-to-leading-order theoretical predictions.