ATLAS

Abstract:

We present a measurement of the B⁰ ↔ B^-0 oscillation frequency using a flavor tagging method based on correlations of B meson flavor with the charge of other particles produced in pp collisions at √ s = 1.8 TeV. Such correlations are expected to arise from b quark hadronization and from B** decays. We partially reconstruct B mesons using the semileptonic decays B⁰ → l⁺D^(*)-X and B⁺ → l⁺D^-0X. From the oscillation frequency, we obtain the mass difference between the two B⁰ mass eigenstates, Δmd = 0.471^+0.078 -0.068(stat) ± 0.034(syst) ħps^-1, and measure the efficiency and purity of this flavor tagging method for both charged and neutral B mesons. © 1998 The American Physical Society.

Abstract:

We present a measurement of the time-dependent asymmetry in the rate for B^-0 d versus B⁰ d decays to J/ψK⁰ S. A nonzero asymmetry would be an indication of CP violation, and within the standard model this may be used to measure the CP-violation parameter sin(2β)2. A total of 198 ± 17 B⁰ d/B¯⁰ d decays were observed in 99¯ collisions at √s = 1.8 TeV by the CDF detector at the Fermilab Tevatron. B⁰ d and B¯⁰ d are distinguished by a technique based on charge correlations from hadronization of the b quark. Our analysis results in sin(2β) = 1.8 ± 1.1(stat) ± 0.3(syst). © 1998 The American Physical Society.

Abstract:

We present a measurement of the W boson mass using data collected by the D0 experiment at the Fermilab Tevatron during 1994–1995. We identify W bosons by their decays to [Formula Presented] final states. We extract the W mass [Formula Presented] by fitting the transverse mass and transverse electron momentum spectra from a sample of 28 323 [Formula Presented] decay candidates. We use a sample of 3563 dielectron events, mostly due to [Formula Presented] decays, to constrain our model of the detector response. From the transverse mass fit we measure [Formula Presented] GeV. Combining this with our previously published result from data taken in 1992–1993, we obtain [Formula Presented]. © 1998 The American Physical Society.

Abstract:

This paper presents the first analysis of diffractive photon dissociation events in deep inelastic positron-proton scattering at HERA in which the proton in the final state is detected and its momentum measured. The events are selected by requiring a scattered proton in the ZEUS leading proton spectrometer (LPS) with xL > 0.97, where xL is the fraction of the incoming proton beam momentum carried by the scattered proton. The use of the LPS significantly reduces the contamination from events with diffractive dissociation of the proton into low mass states and allows a direct measurement of t, the square of the four-momentum exchanged at the proton vertex. The dependence of the cross section on t is measured in the interval 0.073 < \t\ < 0.4 GeV² and is found to be described by an exponential shape with the slope parameter b = 7.2 ± 1.1(stat.)^+0.7 -0.9(syst.) GeV^-2. The diffractive structure function F^D(4) 2 is presented as a function of xIP, ≃ 1 - xL and β, the momentum fraction of the struck quark with respect to xIP, and averaged over the t interval 0.073 < \t\ < 0.4 GeV² and the photon virtuality range 5 < Q² < 20 GeV². In the kinematic range 4 x 10^-4 < xIP < 0.03 and 0.015 < β < 0.5, the xIP dependence of F^D(4) 2 is fitted with a form (1/xIP)^a , yielding a = 1.00 ± 0.09 (stat.)^+0.11 -0.05(syst.). Upon integration over t, the structure function F^D(3) 2 is determined in a kinematic range extending to higher xIP and lower β compared to our previous analysis; the results are discussed within the framework of Regge theory.

Abstract:

We present a measurement of the differential cross section dσ/dΣE^jetT for the production of multijet events in pp collisions where the sum is over all jets with transverse energy E^jetT > E^minT. The measured cross section for events with E^jetT > 320 GeV is compared to O(α³s) perturbative QCD predictions and QCD parton shower Monte Carlo predictions. The agreement between the O(α³s) predicted and observed event rates is reasonable for E^minT = 100 GeV, but poorer for E^minT = 20 GeV. © 1998 The American Physical Society.