ATLAS

Abstract:

Diffractive scattering of γ^∗p → X + N, where N is either a proton or a nucleonic system with MN < 4 GeV has been measured in deep inelastic scattering (DIS) at HERA. The cross section was determined by a novel method as a function of the γ^∗p c.m. energy W between 60 and 245 GeV and of the mass MX of the system X up to 15 GeV at average Q² values of 14 and 31 GeV². The diffractive cross section dσ^{di f f} /dMX is, within errors, found to rise linearly with W. Parameterizing the W dependence by the form dσ^{di f f} /dMX ∞ (W²)^{(2αIP - 2)} the DIS data yield for the pomeron trajectory αIP = 1.23±0.02(stat)±0.04(syst) averaged over t in the measured kinematic range assuming the longitudinal photon contribution to be zero. This value for the pomeron trajectory is substantially larger than αIP extracted from soft interactions. The value of αIP measured in this analysis suggests that a substantial part of the diffractive DIS cross section originates from processes which can be described by perturbative QCD. From the measured diffractive cross sections the diffractive structure function of the proton F2 ^D(3) (β,Q², xIP) has been determined, where β is the momentum fraction of the struck quark in the pomeron. The form F2 ^D(3) = constant·(1/xIP)^a gives a good fit to the data in all β and Q² intervals with a = 1.46 ± 0.04(stat) ± 0.08(syst).

Abstract:

We measure the mass of the B0s meson by reconstructing the decay chain B0s→J/ψφ, J/ψ→µ+µ-, and φ→K+K-. The data are obtained from 19.3 pb-1 of integrated luminosity of pp collisions at √s=1.8 TeV using the Collider Detector at Fermilab. A sample of 80 000 inclusive J/ψ→µ+µ- events is used to study systematic biases in track reconstruction and to calibrate the momentum scale. We reconstruct the kinematically similar decays B+→J/ψK+ and B0→J/ψK*0 to study the mass measurement technique used for the B0s meson. Based on the observation of 32 ± 6 candidates, the mass of the B0s meson is measured to be 5369.9 ± 2.3 ± 1.3 MeV/c2 and the mass difference between B0s and the average mass of B+ and B0 is determined to be 89.7 ± 2.7 ± 1.2 MeV/c2. © 1996 The American Physical Society.

Abstract:

We present a study of events with Z bosons and hadronic jets produced in ¯p p collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 Z → e⁺e^- decays from 106pb^-1 of integrated luminosity collected using the CDF detector at the Fermilab Tevatron Collider. The Z+ ≥ n jet cross sections and jet production properties have been measured for n = 1 to 4. The data are compared to predictions of leading-order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation. © 1996 The American Physical Society.

Abstract:

We report a measurement of the ratios of the decay rates of the B+, B0, and B0s mesons into exclusive final states containing a J/Ψ meson. The final states were selected from 19.6 pb-1 of pp collisions recorded by the Collider Detector at Fermilab. These data are interpreted to determine the b quark fragmentation fractions fu, fd, and fs. We also determine the branching fractions for the decay modes (formula presented). We discuss the implications of these measurements to B meson decay models. © 1996 The American Physical Society.

Abstract:

We report on the reconstruction of the decay mode B0→J/ΨKS0 using 19.3pb-1 of data collected by the Collider Detector at Fermilab in p-p collisions at √s=1.8TeV. A signal of 41.8±6.9 events, with a signal-to-background ratio of 9:1, is observed. Three additional decay modes B+→J/ΨK+, B0→J/ΨK*(892)0, and B+→J/ΨK*(892)+ are reconstructed. We measure three ratios of branching ratios, each one relative to the B+→J/ΨK+ mode. We also report the ratio of decay rates, γ(B→J/ΨK*)/γ(B→J/ΨK), for the vector-vector relative to the vector-pseudoscalar modes, to be 1.32±0.23(stat)±0.16(syst). © 1996 The American Physical Society.