Measurements of differential cross sections of Z/γ∗+jets+X events in pp

Abstract

We present cross section measurements for Z /γ * + jets + X production, differential in the transverse momenta of the three leading jets. The data sample was collected with the DØ detector at the Fermilab Tevatron pp collider at a center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 1 fb −1 . Leading and next-to-leading order perturbative QCD predictions are compared with the measurements, and agreement is found within the theoretical and experimental uncertainties. We also make comparisons with the predictions of four event generators. Two parton-shower-based generators show significant shape and normalization differences with respect to the data. In contrast, two generators combining tree-level matrix elements with a parton shower give a reasonable description of the shapes observed in data, but the predicted normalizations show significant differences with respect to the data, reflecting large scale uncertainties. For specific choices of scales, the normalizations for either generator can be made to agree with the measurements. Letters B 678 (2009) [45][46][47][48][49][50][51][52][53][54] The production of jets in association with vector bosons (V + jets) in hadron collisions is an important process in quantum chromodynamics (QCD) and is a significant source of background for many standard model measurements (e.g., tt production) and in searches for new phenomena (e.g., supersymmetry). Such measurements at the Fermilab Tevatron collider and the CERN Large Hadron Collider (LHC) rely on accurate descriptions of V + jets production by particle-level event generators. These models require validation with measurements of the properties of the V + jets system, especially as a function of jet multiplicity. DØ Collaboration / PhysicsIn In particular, we have investigated to what extent the differential p T distributions for the higher jet multiplicities can be described by parton-shower-based event generators like pythia [6] and herwig [7], and how they compare to event generator predictions where matrix element and parton shower merging procedures are adopted, as in alpgen + pythia [8] and sherpa [9]. For each prediction, the renormalization and factorization scale uncertainties are evaluated, and the choices of scales are modified to achieve an improved description of the measurements. The presented studies are of vital importance to understand the predictive power of the various event generator models for V + jets processes at both the Tevatron and the LHC.The data set was recorded using the DØ Run II detector, which is described in detail elsewhere [10]. Here we give a brief overview of the most relevant components for this analysis. The trajectories of charged particles are reconstructed using a silicon vertex tracker and a scintillating fiber tracker located inside a superconducting solenoidal coil that provides a magnetic field of approximately 2 T. The tracking volume is surrounded by a liquidargon and uranium calorimeter, divided into electromagnetic and hadronic sections with...

A critical appraisal of NLO+PS matching methods

“…A further measurement of Z+jet production in the electron channel was presented by the DØ collaboration in [89]. Each electron is required to have p ⊥ > 25 GeV and Transverse momentum of leading jet in pp → W + jet + X dσ/dp ⊥ (jet MC/data Figure 21.…”

“…Therefore, the analysis strategy of a measurement presented by the DØ collab- MC/data Figure 23. Transverse momentum distributions of the three hardest jets in Drell-Yan production in association with at least one jet compared to DØ data [89]. All SHERPA predictions are scaled with a common factor to account for the unknown normalisation to the inclusive process.…”

Recent QCD results from the Tevatron

“…These include measurements of jet p T spectra and angular distributions of the jet or the jet-Z/W system [21,22,23,24]. Further analyses have measured the production rates of a Z/W accompanied by a heavy (c or b quark) jet [25,26,27,28].…”

Measurement of Z/γ∗+jet+X angular distributions in pp¯

“…Previous measurements at the Tevatron have studied the kinematics of inclusive Z /γ * production [6][7][8], of the Z /γ * in events with at least one jet [9], of the jets in Z /γ * and W events [9][10][11][12][13], and of the production of Z /γ * and W in association with heavy flavor [14][15][16][17]. In this Letter, we describe the first measurements of the angular correlations between the Z /γ * and leading jet in Z /γ * + jet + X production.…”