Accelerator Neutrinos

Abstract:

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Ξ⁰→Λγ have been found with an estimated background of 58±8 events. From these events the Ξ⁰→Λγ decay asymmetry has been determined to α(Ξ⁰→Λγ)=-0.78±0.18stat±0.06 syst, which is the first evidence of a decay asymmetry in Ξ ⁰→Λγ. The branching fraction of the decay has been measured to be Br(Ξ⁰→Λγ)=(1.16±0.05 stat±0.06syst)×10^-3. © 2004 Elsevier B.V. All rights reserved.

Abstract:

The MINOS light-injection calibration system has been fully documented in a previous article (Nucl. Instr. and Meth. A 492 (2002) 353). Upon commissioning in the MINOS detectors, the system was found to give a non-linear response to variations in the intensity of injected light. The source of this non-linearity has been traced to a small change in the spectrum of the injected light as a function of the current applied to the original blue LEDs, in combination with a rapidly varying spectral response function of the wavelength-shifting fibre used in the detector. Both aspects of the problem have been addressed successfully by use of LEDs with different spectral characteristics, and the system now has a linear response. © 2003 Elsevier B.V. All rights reserved.

Abstract:

We use a neural-network technique to search for standard model single-top-quark production in the [Formula Presented] dataset accumulated by the Collider Detector at Fermilab detector during the 1992–1995 collider run (“run I”). Using a sample of 64 [Formula Presented] 2, 3 jets events, we set a 95% confidence level upper limit of 24 pb on the W-gluon and [Formula Presented] combined single-top cross section. © 2004 The American Physical Society.

Abstract:

We have searched for the signature of 3- and 4-body decays of pair-produced scalar top quarks (stop) in the inclusive final state containing an electron, a muon, and significant missing transverse energy using a sample of pp̄ events corresponding to 108.3 pb-1 of data collected with the DØ detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the neutralino (χ̃10) is the lightest supersymmetric particle and is stable. No evidence for a signal is found and we derive cross-section upper limits as a function of stop (t̃) and neutralino masses in different decay scenarios leading to the bℓνχ̃10 final state. © 2004 Published by Elsevier B.V.

Abstract:

Using the NA48 detector at the CERN SPS, 31 KS → π ⁰γγ candidates with an estimated background of 13.7 ± 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS → π⁰γγ) z>0.2 = (4.9 ± 1.6stat ± 0.9 syst) × 10^-8 in agreement with Chiral Perturbation Theory predictions. © 2003 Elsevier B.V. All rights reserved.