ATLAS

Abstract:

We present measurements of the structure function F2 in e⁺p scattering at HERA in the range 3.5 GeV² < Q² < 5000 GeV². A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At Q² < 35 GeV² the range in x now spans 6.3 · 10^-5 < x < 0.08 providing overlap with measurements from fixed target experiments. At values of Q² above 1000 GeV² the x range extends to 0.5. Systematic errors below 5% have been achieved for most of the kinematic region. The structure function rises as x decreases; the rise becomes more pronounced as Q² increases. The behaviour of the structure function data is well described by next-to-leading order perturbative QCD as implemented in the DGLAP evolution equations. © Springer-Verlag 1996.

Abstract:

We have searched for a heavy neutral gauge boson, Z′, using the decay channel Z′ → ee. The data were collected with the DØ detector at the Fermilab Tevatron during the 1992-1993 pp̄ collider run at √s = 1.8 TeV from an integrated luminosity of 15 ± 1 pb^-1. Limits are set on the cross section times branching ratio for the process pp̄ → Z′ → ee as a function of the Z′ mass. We exclude the existence of a Z′ of mass less than 490 GeV/c², assuming a Z′ with the same coupling strengths to quarks and leptons as the standard model Z boson.

Abstract:

Jet photoproduction, where the two highest transverse energy (ETjet) jets have ETjet above 6 GeV and a jet-jet invariant mass above 23 GeV, has been studied with the ZEUS detector at the HERA ep collider. Resolved and direct photoproduction samples have been separated. The cross section as a function of the angle between the jet-jet axis and the beam direction in the dijet rest frame has been measured for the two samples. The measured angular distributions differ markedly from each other. They agree with the predictions of QCD calculations, where the different angular distributions reflect the different spins of the quark and gluon exchanged in the hard subprocess.

Abstract:

In deep inelastic neutral current scattering of positrons and protons at the center of mass energy of 300 GeV, we observe, with the ZEUS detector, events with a high energy neutron produced at very small scattering angles with respect to the proton direction. The events constitute a fixed fraction of the deep inelastic, neutral current event sample independent of Bjorken x and Q² in the range 3 · 10^-4 < xBJ < 6 · 10^-3 and 10 < Q² < 100 GeV².