Measurement of jet production in Z0/γ∗→μ+μ− events at LHCb in √s=7 TeV pp collisions

Note:this result is superseded by the paper PAPER-2013-058

The conference note is available here (LHCb-CONF-2012-016).

More detailed information ANA note 2012-006

Abstract

The first LHCb measurement of Z0/γ∗ + jet production is presented. This measurement is performed in the Z0/γ∗→μ+μ− channel, and is normalised to the total inclusive Z0/γ∗→μ+μ− cross-section, based on 1.020.04 fb−1 of data collected in 2011. The results are given for a fiducial acceptance inside the LHCb acceptance, defined as 2.0 ≤ η(μ) ≤ 4.5, pT(μ) ≥ 20 GeV, and with the reconstructed dimuon mass in the range 60 ≤ M ≤ 120 GeV. Jets are reconstructed using the anti-kT algorithm with R = 0.5, and corrected to the hadron level. Jets in our fiducial acceptance are required to have 2.0 ≤ η ≤4.5 and pT ≥ 10 GeV, and be separated from decay muons of the Z0/γ∗ by a distance ΔR(μ,jet)≥0.4 in η−ϕ space. The cross-section ratio of Z0/γ∗(→μ+μ−) + jet(s) events to Z0/γ∗→μ+μ− events is measured as 0.2290.011. We also present the jet multiplicity distribution, and the Z0/γ∗ rapidity and pT distributions for the Z0/γ∗ + jet(s) events. Comparisons are made to NLO predictions. Our results are consistent with Standard Model predictions.

Figures

(Note, eps versions are available under attachments).

Caption Figure
The reconstructed pT distribution of the leading jet in each Z0 + jet candidate in data (black) and the Pythia Monte Carlo simulation (red). Simulation is scaled to have the same integral as data in the range presented. This distribution is not corrected for inefficiencies in detection. The jet energy energy correction has been applied in both data and simulation. Fig1.png
The reconstructed pseudorapidity distribution of the leading jet in each Z0 + jet candidate in data (black) and the Pythia Monte Carlo simulation (red). Simulation is scaled to have the same integral as data in the range presented. This distribution is not corrected for inefficiencies in detection. The jet energy correction has been applied in both data and simulation. Fig2.png
The plot shows the dimuon mass spectrum in data, for Z0 + jet events (blue) and all Z0 events (red) scaled to the same integral (unity) and overlaid. This distribution is not corrected for any inefficiencies in Z0 or jet detection. Fig3_top.png
The plot shows the ratio of the number of Z0 events to the number of Z0 + jet events seen as a function of the dimuon invariant mass. A straight line fit, p0 + p1 M(μ+μ−), returns p0 = 0.170.02 and p1 = 0.000010.00022 GeV−1. This distribution is not corrected for any inefficiencies in Z0 or jet detection. Fig3_bottom.png
Measured jet multiplicity distribution of Z0 events in data. Error bars show the combination of statistical and systematic uncertainties in quadrature. Fig4.png
The normalised Z0 rapidity distribution measured in Z0 + jet events in data (blue points), with the FEWZ+MSTW08 predictions overlaid (the red line gives the central value, whilst the shaded area gives the PDF errors and scale uncertainties combined in quadrature). Data error bars show the combination of statistical and systematics errors in quadrature (linear scale). Fig5_top.png
The normalised Z0 rapidity distribution measured in Z0 + jet events in data (blue points), with the FEWZ+MSTW08 predictions overlaid (the red line gives the central value, whilst the shaded area gives the PDF errors and scale uncertainties combined in quadrature). Data error bars show the combination of statistical and systematics errors in quadrature (logarithmic scale). Fig5_bottom.png
The normalised Z0 pT distribution measured in Z0 + jet events in data. Error bars show the combination of statistical and systematics errors in quadrature. Fig6.png
Mean energy fraction of the input particles used in the particle flow algorithm with respect to the jet transverse momentum. Fig7.png
Efficiency of the jet reconstruction and identification measured in simulation. Jets were selected in Z0 + jet events, where the jet is back-to-back with the Z0. The jet identification cuts used are those outlined in Section 5.2. Two cuts on the jet transverse momentum are shown. Fig8.png
Efficiency of the jet reconstruction and identification measured in simulation. Jets were selected in Z0 + jet events, where the jet is back-to-back with the Z0. The jet identification cuts used are those outlined in Section 5.2. Two regions of jet pseudorapidity are shown. Fig9.png
Angular separation between the Z0 and the jet in the transverse plane. The Z0 is identified in muon decays and the jet is reconstructed with the particle flow algorithm, us- ing the selections outlined in Section 5, as well as requiring that pT(Z0) ≥ 10 GeV and that pT(Second Leading Jet)/pT(Leading Jet) ≤ 0.25. Fig10.png
Jet transverse momentum divided by Z0 transverse momentum, for the cuts detailed in Figure 10 and the requirement that the modulus of (∆φ(Z0, Jet)) > 7π/8. The Z0 is identified in muon decays. Good agreement between data and simulation is observed. Fig11.png
An event display from 2011 data of a Z0 + jet candidate. The reconstructed candidates have pT(Z0) = 75 GeV and pT(jet) = 64 GeV. Fig12.png

-- TaraShears - 18-Sep-2012

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