Measurement of the cross section for production of b b-bar X, decaying to muons in pp collisions at sqrt(s)=7 TeV

TL;DR

This CMS study measures the inclusive cross section for pp → bb̄ X → μμ X′ at √s = 7 TeV using 27.9 pb−1, selecting dimuon events within |η| < 2.1 and applying pT thresholds of 4 or 6 GeV. A template-based method leveraging two-dimensional muon impact-parameter distributions separates muon sources (B, C, prompt, decays in flight) and yields the BB fraction in data, combined with data-driven efficiency corrections to extract the cross section. The measured values, 26.4 nb (pT > 4 GeV) and 5.12 nb (pT > 6 GeV), are compared to LO PYTHIA and NLO MC@NLO QCD predictions, with the data lying above LO and broadly compatible with NLO within uncertainties. The analysis demonstrates a robust approach to heavy-flavor production measurements at the LHC and provides a precise benchmark for QCD calculations in a regime where gluon-splitting contributions are suppressed.

Abstract

A measurement of the inclusive cross section for the process pp to b b-bar X to muon muon X' at sqrt(s) = 7 TeV is presented, based on a data sample corresponding to an integrated luminosity of 27.9 inverse picobarns collected by the CMS experiment at the LHC. By selecting pairs of muons each with pseudorapidity abs(eta)<2.1, the value of the cross section for pp to b b-bar X to muon muon X' is found to be 26.4 +/- 0.1 (stat.) +/- 2.4 (syst.) +/- 1.1 (lumi.) nb is obtained for muons with transverse momentum greater than 4 GeV, and 5.12 +/- 0.03 (stat.) +/- 0.48 (syst.) +/- 0.20 (lumi.) nb for transverse momenta greater than 6 GeV. These results are compared to QCD predictions at leading and next-to-leading orders.

Figures (3)

• Figure 1: Comparison, for muons with $p_{\mathrm{T}}\xspace>4\,\text{Ge\spaceV}\xspace$, between the template $d_{xy}$ histogram (red) and the fitted function (black) for muons coming from B hadrons (class B, top left), charmed hadrons (class C, top right), prompt tracks (class P, bottom left), and decays in flight (class D, bottom right). The templates for B, C, and D come from simulation. For the prompt tracks, the distribution is obtained from data. An enlargement of the prompt-track distribution for $d_{xy}>0.05\,\text{cm}\xspace$ is shown on a linear scale as an insert in the lower-left plot. For each template, the ratio of the $d_{xy}$ histogram to the fitted function is shown at the bottom.
• Figure 2: 1D projections of the $d_{xy}$ templates used in the fit for muons with $p_{\mathrm{T}}\xspace>4\,\text{Ge\spaceV}\xspace$, for the BB, CC, PP, DD categories (left) and the BC, BD, CD ones (right).
• Figure 3: Top: The projected $d_{xy}$ distributions from data with the results of the fit for muons with $p_{\mathrm{T}}\xspace>4\,\text{Ge\spaceV}\xspace$ (left) and $p_{\mathrm{T}}\xspace>6\,\text{Ge\spaceV}\xspace$ (right). The distribution from each dimuon source is shown by the histograms. Bottom: The pull distribution from the fit.