The Isolated Photon Cross Section in p pbar Collisions at sqrt(s) = 1.8 TeV

We report a new measurement of the cross section for the production of isolated photons, with transverse energies (ET) above 10 GeV and pseudorapidities |eta| < 2.5, in p pbar collisions at sqrt{s} = 1.8 TeV. The results are based on a data sample of 107.6 pb-1 recorded during 1992--1995 with the D0 detector at the Fermilab Tevatron collider. The background, predominantly from jets which fragment to neutral mesons, was estimated using the longitudinal shower shape of photon candidates in the calorimeter. The measured cross section is in good agreement with the next-to-leading order (NLO) QCD calculation for ET > 36 GeV.Comment: 12 pages, 4 figures, LaTeX. Submitted to Physical Review Letter

Measurement of the W boson mass using large rapidity electrons

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.62.092006.We present a measurement of the W boson mass using data collected by the DØ experiment at the Fermilab Tevatron during 1994–1995. We identify W bosons by their decays to eν final states where the electron is detected in a forward calorimeter. We extract the W boson mass M(W) by fitting the transverse mass and transverse electron and neutrino momentum spectra from a sample of 11 089 W⃗ eν decay candidates. We use a sample of 1687 dielectron events, mostly due to Z⃗ ee decays, to constrain our model of the detector response. Using the forward calorimeter data, we measure M(W)=80.691±0.227 GeV. Combining the forward calorimeter measurements with our previously published central calorimeter results, we obtain M(W)=80.482±0.091 GeV

Limits on quark compositeness from high energy jets in p-bar p collisions at 1.8 TeV

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.62.031101.Events in p-bar p collisions at s√=1.8TeV with total transverse energy exceeding 500 GeV are used to set limits on quark substructure. The data are consistent with next-to-leading order QCD calculations. We set a lower limit of 2.0 TeV at 95% confidence on the energy scale ΛLL for compositeness in quarks, assuming a model with a left-left isoscalar contact interaction term. The limits on ΛLL are found to be insensitive to the sign of the interference term in the Lagrangian

Search for first-generation scalar and vector leptoquarks

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.64.092004.We describe a search for the pair production of first-generation scalar and vector leptoquarks in the eejj and eνjj channels by the DØ Collaboration. The data are from the 1992–1996 pp-bar run at s√=1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the eejj and eνjj channels are combined with those from a previous DØ analysis of the ννjj channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of β, the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 GeV/c(2) for β=1, 12, and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 GeV/c(2) are set on the mass for β=1, 12, and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings

New limits for neutrinoless tau decays

Neutrinoless 3-prong tau lepton decays into a charged lepton and either two charged particles or one neutral meson have been searched for using 4.79fb^(-1) of data collected with the CLEO II detector at Cornell Electron Storage Ring. This analysis represents an update of a previous study and the addition of six decay channels. In all channels the numbers of events found are compatible with background estimates and branching fraction upper limits are set for 28 different decay modes. These limits are either more stringent than those set previously or represent the first attempt to find these decays

Search for right-handed W bosons in top quark decay

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.72.011104.We present a measurement of the fraction f(+) of right-handed W bosons produced in top quark decays, based on a candidate sample of tt-bar events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230  pb(−1), collected by the D0 detector at the Fermilab Tevatron pp-bar Collider at s√=1.96  TeV. We use a constrained fit to reconstruct the kinematics of the tt-bar and decay products, which allows for the measurement of the leptonic decay angle θ∗ for each event. By comparing the cosθ∗ distribution from the data with those for the expected background and signal for various values of f(+), we find f(+(=0.00±0.13(stat)±0.07(syst). This measurement is consistent with the standard model prediction of f(+)=3.6×10(−4)

Direct Limits on the B(0)(s) Oscillation Frequency

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.021802.We report results of a study of the B(0)(s) oscillation frequency using a large sample of B(0)(s) semileptonic decays corresponding to approximately 1  fb(−1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider in 2002–2006. The amplitude method gives a lower limit on the B(0)(s) oscillation frequency at 14.8  ps(−1) at the 95% C.L. At Δms=19  ps(−1), the amplitude deviates from the hypothesis A=0 (1) by 2.5 (1.6) standard deviations, corresponding to a two-sided C.L. of 1% (10%). A likelihood scan over the oscillation frequency, Δms, gives a most probable value of 19  ps(−1) and a range of 17<Δms<21  ps(−1) at the 90% C.L., assuming Gaussian uncertainties. This is the first direct two-sided bound measured by a single experiment. If Δms lies above 22  ps(−1), then the probability that it would produce a likelihood minimum similar to the one observed in the interval 16–22  ps(−1) is (5.0±0.3)%

Search for a heavy resonance decaying into a Z+jet final state in pp-bar collisions at s√=1.96 TeV using the D0 detector

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.74.011104.We have searched for a heavy resonance decaying into a Z+jet final state in pp-bar collisions at a center of mass energy of 1.96  TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370  pb(−1). We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production

Search for new physics using QUAERO: A general interface to D0 event data

We describe QUAERO, a method that (i) enables the automatic optimization of searches for physics beyond the standard model, and (ii) provides a mechanism for making high energy collider data generally available. We apply QUAERO to searches for standard model WW, ZZ, and t (t) over bar production, to searches for these objects produced through a new heavy resonance, and to the first direct search for W' --> WZ. Through this interface, we make three data sets collected by the D0 experiment at roots = 1.8 TeV publicly available

Electronic branching ratio of the τ lepton

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.45.3976.Using data accumulated by the CLEO I detector operating at the Cornell Electron Storage Ring, we have measured the ratio R=Γ(τ→eν¯(e)ν(τ)) / Γ(1) where Γ(1) is the τ decay rate to final states with one charged particle. We find R=0.2231±0.0044±0.0073 where the first error is statistical and the second is systematic. Together with the measured topological one-charged-particle branching fraction, this yields the branching fraction of the τ lepton to electrons, Be=0.192±0.004±0.006