ATLAS

Abstract:

A large sample (96) of epitaxial Si PIN photodiodes has been irradiated by approximately 1 MeV neutrons and 24 GeV protons with fluences up to 10¹⁵ equivalent 1 MeV neutrons cm^-2 in order to test their suitability for use in the optical readout of the ATLAS semiconductor tracker and pixel detector at the CERN Large Hadron Collider. After an initial reduction of 30% the responsivity remains constant up to the maximum fluence. The rise and fall times are not significantly affected and remain below 1 ns. Although the dark current increases linearly with increasing neutron fluence, its level remains below 100 nA which is negligible in comparison to the operating photocurrent which is above 100 μA. Enhanced ageing studies at 60 °C have also been carried out and no failure has occurred after an equivalent of 360 years of operation.

Abstract:

We report on a search for supersymmetry using the DØ detector. The 1994-1996 data sample of √s = 1.8 TeV pp̄ collisions was analyzed for events containing two leptons (e or μ), two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with A0 = 0 and μ < 0, various thresholds were employed to optimize the search. No events were found beyond expectation from the background. We set a lower limit at the 95% C.L. of 255 GeV/c2 for equal mass squarks and gluinos for tan β = 2, and present exclusion contours in the (m0, m1/2) plane for tan β = 2-6.

Abstract:

We describe a search for the pair production of first-generation scalar and vector leptoquarks in the [Formula Presented] and [Formula Presented] channels by the DØ Collaboration. The data are from the 1992–1996 [Formula Presented] run at [Formula Presented] at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the [Formula Presented] and [Formula Presented] channels are combined with those from a previous DØ analysis of the [Formula Presented] channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of [Formula Presented] the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 [Formula Presented] for [Formula Presented] [Formula Presented] and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 [Formula Presented] are set on the mass for [Formula Presented] [Formula Presented] and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings. © 2001 The American Physical Society.

Abstract:

A study of the v̄-jet mass spectrum in e+p→v̄X events at a center-of-mass energy 300 GeV has been performed with the ZEUS detector at the HERA collider at DESY using an integrated luminosity of 47.7 pb-1. The mass spectrum is in good agreement with that expected from standard model processes over the v̄-jet mass range studied. No significant excess attributable to the decay of a narrow resonance is observed. By using both e+p→>e+X and e+p-vX data, mass-dependent limits are set on the s-channel production of scalar and vector resonant states. Couplings to first-generation quarks are considered and limits are presented as a function of the e+q and v̄q branching ratios. These limits are used to constrain the production of leptoquarks and A-parity violating squarks. © 2001 The American Physical Society.