Study of W boson production in association with beauty and charm

The paper is available here.

arXiv: 1505.04051, LHCB-PAPER-2015-021

More detailed information: ANA note 2014-076

Abstract

The associated production of a W boson with a jet originating from either a light parton or heavy-flavor quark is studied in the forward region using proton-proton collisions. The analysis uses data corresponding to integrated luminosities of 1.0 and 2.0 fb^-1 collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, respectively. The W bosons are reconstructed using the W → μν decay and muons with a transverse momentum, p_T, larger than 20 GeV in the pseudorapidity range 2.0 < η < 4.5. The partons are reconstructed as jets with p_T > 20 GeV and 2.2 < η < 4.2. The sum of the muon and jet momenta must satisfy p_T > 20 GeV. The fraction of W+jet events that originate from beauty and charm quarks is measured, along with the charge asymmetries of the W+b and W+c production cross-sections. The ratio of the W+jet to Z+jet production cross-sections is also measured using the Z → μμ decay. All results are in agreement with Standard Model predictions.

Figures

(Note, eps versions are available under attachments).

Caption	Figure
Figure 1: Distributions of pT(μ)/pT (jμ ) with fits overlaid from (top) √s = 7 TeV and (bottom) 8 TeV data for (left) μ+ and (right) μ−.
Figure 2: (top) Two-dimensional SV-tag BDT distribution and (bottom) fit for events in the subsample with pT (μ)/pT (jμ) > 0.9. Combined data for s = √7 and 8 TeV for both muon charges are shown.
Figure 2 cont: Projections onto the (top) BDT(bc|udsg) and (bottom) BDT(b|c) axes. Combined data for s = √7 and 8 TeV for both muon charges are shown.
Figure 3: (Top) Two-dimensional SV-tag BDT distribution and (bottom) fit for events in the subsample with 0.5 < pT(μ)/pT(jμ ) < 0.6, projected onto the (3rd) BDT(bc|udsg) and (4th) BDT(b c) axes. Combined data for s = √7 and 8 TeV for both muon charges are shown.
Figure 3 cont: Projections onto the (top) BDT(bc|udsg) and (bottom) BDT(b|c) axes for the subsample with 0.5 < pT(μ)/pT(jμ ) < 0.6. Combined data for s = √7 and 8 TeV for both muon charges are shown.
Figure 4: Projections of simultaneous fits of (top) Mcor and (bottom) SV track multiplicity for the SV-tagged subsample with BDT(bc |udsg) > 0.2 and pT(μ)/pT (jμ) > 0.9. The highest Mcor bin includes candidates with Mcor > 10 GeV. Combined data for √s = 7 and 8 TeV for both muon charges are shown.
Figure 5: Fits to pT (μ)/pT(jμ ) distributions for c-tagged data samples for s = √7 and 8 TeV.
Figure 5 cont: Fits to pT (μ)/pT(jμ ) distributions for b-tagged data samples for s = √7 and 8 TeV.
Figure 6: Fits to the pT(SV)/pT (j) distributions in (left) 7 TeV and (right) 8 TeV data for candidates with pT(μ)/pT (jμ ) > 0.9 and BDT(bc|udsg) > 0.2.

-- KatharinaMueller - 2015-06-04