Measurement of the W + jet cross section at CDF

Abstract

A measurement of W → eν + n−jet cross sections in pp collisions at √ s = 1.96 TeV using the Collider Detector at Fermilab in Run II is presented. The measurement is based on an integrated luminosity of 320 pb −1 , and includes events with jet multiplicity from ≥ 1 to ≥ 4. In each jet multiplicity sample the differential and cumulative cross sections with respect to the transverse energy of the n th −leading jet are measured. For W + ≥ 2 jets the differential cross section with respect to the 2-leading jets invariant mass m j 1 j 2 and angular separation ∆R j 1 j 2 is also reported. The data are compared to predictions from Monte Carlo simulations.Keywords: QCD; Jet; Collider physics; TevatronThe study of jets produced in events containing a W bosons provides a useful test of Quantum Chromo-Dynamics (QCD) at high momentum transfers. Recently a lot of work [1] has been invested to develop sophisticated Monte Carlo programs capable of handling more particle in the final state at the leading order (LO), or in some cases, next-to-leading order (NLO) in perturbative QCD. Measurements of W + jet cross sections are an important test of QCD and may be used to validate these new approaches. A good understanding of W + jet production is vital to reduce the uncertainty on the background to top pair production and to increase the sensitivity to higgs and new physics searches at the Tevatron and the LHC.This contribution describes a measurement of the W → eν+ ≥ n−jet production cross section in pp collisions at a center of mass energy of 1.96 TeV. The cross section is presented for four inclusive n-jets samples (n = 1, 2, 3, 4) as a function of the n th −leading jet transverse energy (E jet T ). For W + ≥ 2 jets the differential cross section with respect to the 2-leading jets invariant mass m j 1 j 2 and angular separation ∆R j 1 j 2 is also reported. Cross sections have been corrected to particle level jets, and are defined within a limited W decay phase space, closely matching that which is experimentally accessible. This definition, easily reproduced theoretically, minimizes the model dependence that can enter a correction back to the full W cross-section. These results thus offer the potential for extensive tuning of W+jet(s) Monte Carlo approaches at the hadron-level. This analysis is based on 320 ± 18 pb −1 of data collected by the upgraded Collider Detector at Fermilab (CDF II) during the Tevatron Run II period.The CDF II detector [2] is an azimuthally and forwardbackward symmetric apparatus situated around the pp interaction region, consisting of a magnetic spectrometer surrounded by calorimeters and muon chambers.W → eν candidate events are selected from a high E T electron trigger (E e T ≥ 18 GeV, |η e | < 1.1) by requiring one good quality electron candidate (E e T ≥ 20 GeV) and the missing transverse energy (E / T ) to be greater than 30 GeV. To further reduce background contamination, the W transverse mass is required to satisfy m W T > 20 GeV/c 2 . In addition, Z → e + e − are rejected with a veto algorithm des...

Model Independent Search For New Physics At The Tevatron

“…The value of this correction factor is determined primarily by the number of events in the Vista final states bj and bb. The value of these corrections factors are consistent with other trigger efficiency measurements made using additional information [92]. i!…”

Summary talk for ISMD 06

“…1 There were presentations showing the agreement of NLO computations with photon-gluon fusion and photon-quark scattering to produce pairs of jets in deep inelastic scattering, by Efremenko, as seen in the H1 experiment [10]. Messina from CDF presented data on associated jet production in the production of W bosons [11]. In both cases the agreement with pQCD is quite good.…”

Top Quark Pair in Association with an Extra Jet: Phenomenological Analysis at the Tevatron

“…It is worthwhile to mention at this point that because of the extreme complexity of modeling the QCD background, a pure data-based approach is used instead. Specifically, we use an anti-electron data set to model the QCD as described in [118,119].…”

“…starting point for the heavy flavor fraction and mistag estimate. To perform the fit in the pre-tagged sample, we take the / E T distribution of W +jets MC events as the template for signal and for the QCD template we use the anti-electron sample as described previously in [118,119]. Both templates are fitted to the / E T distribution of isolated pretag data events using a binned likelihood fitter to calculate the QCD fraction.…”