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 present results from a search for anomalous WW and WZ production in pp^¯ collisions at √s = 1.8 TeV. We used pp^¯ → evjjX events observed during the 1992-1993 run of the Fermilab Tevatron collider, corresponding to an integrated luminosity of 13.7 ± 0.7pb⁻¹. A fit to the transverse momentum spectrum of the W boson yields direct limits on the CP-conserving anomalous WWγ and WWZ coupling parameters of −0.9 < Δk < 1.1 (with λ = 0) and −0.6 < λ < 0.7 (with Δk = 0) at the 95% confidence level, for a form factor scale Λ = 1.5 TeV, assuming that the WWγ and WWZ coupling parameters are equal. © 1996 The American Physical Society.

Abstract:

We present a search for pair produced top squarks, the supersymmetric partners of the top quark, using the D0 detector at the Fermilab Tevatron p¯p collider. We consider a scenario in which the lighter of the two top squarks ˜t1 decays with 100% branching fraction to a charm quark and the lightest neutralino ˜χ⁰ 1 yielding a signal of two acollinear jets with missing transverse energy. We observe 3 events while we expect 3.5 α 1.2 events from the known standard model processes. We exclude at the 95% confidence level a significant region of the mt1 - mχ1 ⁰ parameter space. The highest mt1 value we exclude is 93GeV/c² with a corresponding mχ1 ⁰ value of 8GeV/c². © 1996 The American Physical Society.

Abstract:

We have searched for associated production of the lightest chargino ¯W1 and next-to-lightest neutralino ¯Z2 of the minimal supersymmetric standard model in p¯p collisions at √s=1.8 TeV using the D0 detector at the Fermilab Tevatron collider. Data corresponding to an integrated luminosity of 12.5±0.7pb⁻¹ were examined for events containing three isolated leptons. No evidence for ¯W1¯Z2 pair production was found. Limits on σ(¯W1¯Z2)B(¯W1→ℓν¯Z1)B(¯Z1→ℓℓ¯Z2) are presented. © 1996 The American Physical Society.

Abstract:

The global topologies of inclusive three- and four-jet events produced in pp interactions are described. The three- and four-jet events are selected from data recorded by the D0 detector at the Fermilab Tevatron Collider operating at a center-of-mass energy of √1800 GeV. The measured, normalized distributions of various topological variables are compared with parton-level predictions of tree-level QCD calculations. The parton-level QCD calculations are found to be in good agreement with the data. The studies also show that the topological distributions of the different subprocesses involving different numbers of quarks are very similar and reproduce the measured distributions well. The parton-shower Monte Carlo generators provide a less satisfactory description of the topologies of the three- and four-jet events. © 1996 The American Physical Society.