Differential cross section measurements for the production of a W boson in association with jets in proton-proton collisions at sqrt(s) = 7 TeV

TL;DR

This CMS study delivers fiducial differential cross sections for W boson production in association with jets at 7 TeV, using data corresponding to 5.0 fb^-1. Observables span jet multiplicities up to six and include jet kinematics, HT, and jet–muon angular separations, all unfolded to particle level for direct theory comparisons. Results are contrasted with MG5+Pythia, SHERPA, and BlackHat+SHERPA predictions, showing general agreement but with notable discrepancies in high-$p_T$ tails and HT distributions, particularly for low jet multiplicities. The work provides a rigorous test of pQCD and informs MC tuning and background modeling for SM and new physics searches.

Abstract

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pt) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 inverse femtobarns. The measured cross sections are compared to predictions from Monte Carlo generators, MADGRAPH + PYTHIA and SHERPA, and to next-to-leading-order calculations from BLACKHAT + SHERPA. The differential cross sections are found to be in agreement with the predictions, apart from the pt distributions of the leading jets at high pt values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.

Figures (8)

• Figure 1: The jet multiplicity in data and simulation before (left) and after (right) the b-jet veto. The $\mathrm{W}$+jets contribution is modelled with MadGraph 5.1.1+ Pythia 6.424. The solid band indicates the total statistical and systematic uncertainty in the $\mathrm{W}$+jets signal and background predictions, as detailed in Section \ref{['systematics']}. This includes uncertainties in the jet energy scale and resolution, the muon momentum scale and resolution, the pileup modelling, the b-tagging correction factors, the normalisations of the simulations, and the efficiencies of reconstruction, identification, and trigger acceptance. A substantial reduction in the expected ${t}\overline{{t}}\xspace$ background is observed in the right plot.
• Figure 2: The dominant systematic uncertainties in the measurement of the $\mathrm{W}$+jets cross section as a function of the exclusive jet multiplicity. The systematic uncertainties displayed include the jet energy scale and resolution (JES, JER), the choice of generator used in the unfolding procedure (Generator), the statistical uncertainty in the data minus the background, propagated through the unfolding procedure (Statistical), the uncertainty due to a finite number of simulated events used to construct the response matrix (MC stat.), and all other systematic uncertainties (Other) detailed in Section \ref{['systematics']}, including pileup, integrated luminosity, background normalisation, b-tagging, muon momentum and resolution, trigger efficiency, muon identification. The uncertainties presented here correspond to the weighted average of the values shown in Table \ref{['tab:sysranges']}.
• Figure 3: The cross section measurement for the exclusive and inclusive jet multiplicities, compared to the predictions of MadGraph 5.1.1 + pythia 6.426, sherpa 1.4.0, and BlackHat+sherpa (corrected for hadronisation and multiple-parton interactions). Black circular markers with the grey hatched band represent the unfolded data measurement and its uncertainty. Overlaid are the predictions together with their statistical uncertainties (Theory stat.). The BlackHat+sherpa uncertainty also contains theoretical systematic uncertainties (Theory syst.) described in Section \ref{['results']}. The lower plots show the ratio of each prediction to the unfolded data.
• Figure 4: The differential cross section measurement for the leading four jets' transverse momenta, compared to the predictions of MadGraph 5.1.1 + pythia 6.426, sherpa 1.4.0, and BlackHat+sherpa (corrected for hadronisation and multiple-parton interactions). Black circular markers with the grey hatched band represent the unfolded data measurement and its uncertainty. Overlaid are the predictions together with their statistical uncertainties (Theory stat.). The BlackHat+sherpa uncertainty also contains theoretical systematic uncertainties (Theory syst.) described in Section \ref{['results']}. The lower plots show the ratio of each prediction to the unfolded data.
• Figure 5: The differential cross section measurement for $H_{\mathrm{T}}$ for inclusive jet multiplicities 1--4, compared to the predictions of MadGraph 5.1.1 + pythia 6.426, sherpa 1.4.0, and BlackHat+sherpa (corrected for hadronisation and multiple-parton interactions). Black circular markers with the grey hatched band represent the unfolded data measurement and its uncertainty. Overlaid are the predictions together with their statistical uncertainties (Theory stat.). The BlackHat+sherpa uncertainty also contains theoretical systematic uncertainties (Theory syst.) described in Section \ref{['results']}. The lower plots show the ratio of each prediction to the unfolded data.