We present a measurement of the electron charge asymmetry in ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. The asymmetry is measured as a function of the electron transverse momentum and pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations from next-to-leading order calculations in perturbative quantum chromodynamics. These measurements will allow more accurate determinations of the proton parton distribution functions.
The cross section for the inclusive production of isolated photons has been measured in p anti-p collisions at sqrt{s}=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV and have pseudorapidity |eta|<0.9. The cross section is compared with the results from two next-to-leading order perturbative QCD calculations. The theoretical predictions agree with the measurement within uncertainties.
We present a measurement of the shapes of b-jets using 300 pb-1 of data obtained with the upgraded Collider Detector at Fermilab (CDF II) in p pbar collisions at center of mass energy sqrt{s}=1.96 TeV. This measurement covers a wide transverse momentum range, from 52 to 300 GeV/c. Samples of heavy-flavor enhanced jets together with inclusive jets are used to extract the average shapes of b-jets. The b-jets are expected to be broader than inclusive jets. Moreover, b-jets containing a single b-quark are expected to be narrower than those containing a b bbar pair from gluon splitting. The measured b-jet shapes are found to be significantly broader than expected from the PYTHIA and HERWIG Monte Carlo simulations. This effect may arise from an underestimation of the fraction of b-jets originating from gluon splitting in these simulations.
We present a measurement of the inclusive jet cross section in p-pbar collisions at sqrt{s}=1.96 TeV based on data collected by the CDF II detector with an integrated luminosity of 1.13 fb^-1. The measurement was made using the cone-based Midpoint jet clustering algorithm in the rapidity region of |y|<2.1. The results are consistent with next-to-leading-order perturbative QCD predictions based on recent parton distribution functions (PDFs), and are expected to provide increased precision in PDFs at high parton momentum fraction x. The results are also compared to the recent inclusive jet cross section measurement using the k_T jet clustering algorithm, and we find that the ratio of the cross sections measured with the two algorithms is in agreement with theoretical expectations over a large range of jet transverse momentum and rapidity.
DELPHI results are presented on the inclusive production of the neutral mesons ρ 0 , f 0 (980), f 2 (1270), K ∗0 2 (1430) and f ′ 2 (1525) in hadronic Z 0 decays. They are based on about 2 million multihadronic events collected in 1994 and 1995, using the particle identification capabilities of the DELPHI Ring Imaging Cherenkov detectors and measured ionization losses in the Time Projection Chamber. The total production rates per hadronic Z 0 decay have been determined to be: 1.19±0.10 for ρ 0 ; 0.164±0.021 for f 0 (980); 0.214±0.038 for f 2 (1270); 0.073±0.023 for K ∗0 2 (1430) ; and 0.012±0.006 for f ′ 2 (1525). The total production rates for all mesons and differential cross-sections for the ρ 0 , f 0 (980) and f 2 (1270) are compared with the results of other LEP experiments and with models.
The process $p\bar{p} \to \gamma$ + jet + X is studied using 1.0 $fb^{-1}$ of data collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ collider at a center-of-mass energy $\sqrt{s}$=1.96 TeV. Photons are reconstructed in the central rapidity region |$y^{\gamma}$|< 1.0 with transverse momenta in the range 30<$p^{\gamma}_T$<400 GeV while jets are reconstructed in either the central |$y^{jet}$|< 0.8 or forward 1.5 <|$y^{jet}$|<2.5 rapidity intervals with $p^{jet}_T$> 15 GeV. The differential cross section $d^3\sigma/dp^{\gamma}_T dy^\gamma dy^{jet}$ is measured as a function of $p^{\gamma}_T$ in four regions, differing by the relative orientations of the photon and the jet in rapidity. Ratios between the differential cross sections in each region are also presented. Next-to-leading order QCD predictions using different parameterizations of parton distribution functions and theoretical scale choices are compared to the data. The predictions do not simultaneously describe the measured normalization and Pt_gamma dependence of the cross section in any of the four measured regions.
We describe the properties of six-jet events, with the six-jet mass exceeding 520GeV/c2, produced at the Fermilab proton-antiproton collider operating at a center-of-mass energy of 1.8 TeV. Observed distributions for a set of 20 multijet variables are compared with predictions from the HERWIG QCD parton shower Monte Carlo program, the NJETS leading order QCD matrix element Monte Carlo program, and a phase-space model in which six-jet events are distributed uniformly over the kinematically allowed region of the six-body phase space. In general the QCD predictions provide a good description of the observed six-jet distributions.
The multiplicity distributions of charged particles in restricted rapidity intervals inZ0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, “clans”, fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.
We present a measurement of the differential cross section dσ/dΣETjet for the production of multijet events in pp¯ collisions where the sum is over all jets with transverse energy ETjet>ETmin. The measured cross section for events with ΣETjet>320GeV is compared to O(αs3) perturbative QCD predictions and QCD parton shower Monte Carlo predictions. The agreement between the O(αs3) predicted and observed event rates is reasonable for ETmin=100GeV, but poorer for ETmin=20GeV.
We present new measurements of differential cross sections for Z/gamma*(->mumu)+jet+X production in a 1 fb-1 data sample collected with the D0 detector in proton anti-proton collisions at sqrt{s}=1.96 TeV. Results include the first measurements differential in the Z/gamma* transverse momentum and rapidity, as well as new measurements differential in the leading jet transverse momentum and rapidity. Next-to-leading order perturbative QCD predictions are compared to the measurements, and reasonable agreement is observed, except in the region of low Z/gamma* transverse momentum. Predictions from two event generators based on matrix elements and parton showers, and one pure parton shower event generator are also compared to the measurements. These show significant overall normalization differences to the data and have varied success in describing the shape of the distributions.
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