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.