Showing papers by "Brad Abbott published in 2004"

Observation and properties of the X(3872) decaying to J/ψπ+π- in pp̄ collisions at √s = 1.96 TeV

Abstract: We report the observation of the X(3872) in the J/psipi(+)pi(-) channel, with J/psi decaying to mu(+)mu(-), in p (p) over bar collisions at roots=1.96 TeV. Using approximately 230 pb(-1) of data collected with the Run II D0 detector, we observe 522+/-100 X(3872) candidates. The mass difference between the X(3872) state and the J/psi is measured to be 774.9+/-3.1(stat)+/-3.0(syst) MeV/c(2). We have investigated the production and decay characteristics of the X(3872) and find them to be similar to those of the psi(2S) state.

Combination of CDF and D0 results on the W boson mass and width

Abstract: The results based on 1992–95 data (Run 1) from the CDF and D0 experiments on the measurements of the W boson mass and width are presented, along with the combined results. We report a Tevatron collider average MW = 80.456±0.059 GeV. We also report the Tevatron collider average of the directly measured W boson width GammaW = 2.115±0.105 GeV. We describe a new joint analysis of the direct W mass and width measurements. Assuming the validity of the standard model, we combine the directly measured W boson width with the width extracted from the ratio of W and Z boson leptonic partial cross sections. This combined result for the Tevatron is GammaW = 2.135±0.050 GeV. Finally, we use the measurements of the direct total W width and the leptonic branching ratio to extract the leptonic partial width Gamma(W-->enu) = 224±13 MeV.

Search for Doubly Charged Higgs Boson Pair Production in the Decay to μ+μ+μ-μin pp̄ Collisions at √s = 1.96 TeV

Abstract: A search for pair production of doubly charged Higgs bosons in the process p (p) over bar -->H++H---->mu(+)mu(+)mu(-)mu(-) is performed with the D0 run II detector at the Fermilab Tevatron The analysis is based on a sample of inclusive dimuon data collected at an energy of roots=196 TeV, corresponding to an integrated luminosity of 113 pb(-1) In the absence of a signal, 95% confidence level mass limits of M(H-L(+/-+/-))>1184 GeV/c(2) and M(H-R(+/-+/-))>982 GeV/c(2) are set for left-handed and right-handed doubly charged Higgs bosons, respectively, assuming 100% branching into muon pairs

Search for new particles in the two-jet decay channel with the DØ detector

Abstract: We present the results of a search for the production of new particles decaying into two jets in p p collisions at sqrt[s]=1.8 TeV, using the DO 1992–1995 data set corresponding to 109 pb-1. We exclude at the 95% confidence level the production of excited quarks (q*) with masses below 775 GeV/c2, the most restrictive limit to date. We also exclude standard-model-like W′ (Z′) bosons with masses between 300 and 800 GeV/c2 (400 and 640 GeV/c2). A W′ boson with mass <786 GeV/c2 has been excluded by previous measurements, and our lower limit is therefore the most stringent to date.

Search for Narrow tt̄ Resonances in pp̄ Collisions at √(s)=1.8 TeV

Abstract: A search for narrow resonances that decay into tt pairs has been performed using 130 pb(-1) of data in the lepton + jets channel collected by the Dphi detector in pp collisions at square root of (s)=1.8 TeV. There is no significant deviation observed from the standard-model predictions at a top-quark mass of 175 GeV/c2. We therefore present upper limits at the 95% confidence level on the product of the production cross section and branching fraction to tt for narrow resonances as a function of the resonance mass MX. These limits are used to exclude the existence of a leptophobic top-color particle with mass MX<560 GeV/c2, using a theoretical cross section for a width GammaX=0.012MX.

Measurement of the $W W$ production cross section in $p\bar p $ collisions at $\sqrt s 1.96$ TeV

Abstract: We present a measurement of the W boson pair-production cross section in p anti-p collisions at a center-of-mass energy of sqrt{s}=1.96 TeV. The data, collected with the Run II DO detector, correspond to an integrated luminosity of 224-252 pb^-1 depending on the final state (ee, emu or mumu). We observe 25 candidates with a background expectation of 8.1+/-0.6(stat)+/-0.6(syst)+/-0.5(lum) events. The probability for an upward fluctuation of the background to produce the observed signal is 2.3x10^-7, equivalent to 5.2 standard deviations.The measurement yields a cross section of 13.8+4.3/-3.8(stat)+1.2/-0.9(syst)+/-0.9(lum) pb, in agreement with predictions from the standard model.

Search for pair production of light scalar top quarks in pp collisions at √s = 1.8 TeV,

Abstract: Using 85.2+/-3.6 pb(-1) of p (p) over bar collisions collected at roots=1.8 TeV with the D0 detector at Fermilab's Tevatron Collider, we present the results of a search for direct pair production of scalar top quarks ((t) over bar), the supersymmetric partners of the top quark. We examined events containing two or more jets and missing transverse energy, the signature of light scalar top quark decays to charm quarks and neutralinos. After selections, we observe 27 events while expecting 31.1+/-6.4 events from known standard model processes. Comparing these results to next-to-leading-order production cross sections, we exclude a significant region of (t) over tilde and neutralino phase space. In particular, we exclude the (t) over tilde mass m((t) over tilde)<122 GeV/c(2) for a neutralino mass of 45 GeV/c(2).

New measurement of the top quark mass in lepton + jets $t\bar{t}$ events at D\O

Abstract: We present a new measurement of the mass of the top quark using lepton + jets ttbar events collected by the DO experiment in Run I of the Fermilab Tevatron Collider The mass is extracted through a comparison of each event with a leading-order matrix element that depends on the top quark mass The result is M_t=1801 +/- 36 (stat) +/- 39 (sys) GeV/c^2 Combining this improved measurement with our previous value from dilepton channels yields the new DO result M_t=1790 +/- 35 (stat) +/- 38 (sys) GeV/c^2