Accelerator Neutrinos

Abstract:

The standard model of particle physics contains parameters--such as particle masses--whose origins are still unknown and which cannot be predicted, but whose values are constrained through their interactions. In particular, the masses of the top quark (M(t)) and W boson (M(W)) constrain the mass of the long-hypothesized, but thus far not observed, Higgs boson. A precise measurement of M(t) can therefore indicate where to look for the Higgs, and indeed whether the hypothesis of a standard model Higgs is consistent with experimental data. As top quarks are produced in pairs and decay in only about 10(-24) s into various final states, reconstructing their masses from their decay products is very challenging. Here we report a technique that extracts more information from each top-quark event and yields a greatly improved precision (of +/- 5.3 GeV/c2) when compared to previous measurements. When our new result is combined with our published measurement in a complementary decay mode and with the only other measurements available, the new world average for M(t) becomes 178.0 +/- 4.3 GeV/c2. As a result, the most likely Higgs mass increases from the experimentally excluded value of 96 to 117 GeV/c2, which is beyond current experimental sensitivity. The upper limit on the Higgs mass at the 95% confidence level is raised from 219 to 251 GeV/c2.

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:

The results of a search for the direct production of Kaluza-Klein (KK) graviton modes using the rate of events with one or two energetic jets and large ET at the Collider Detector at Fermilab (CFD) were reported. The search was based on 84±4 pb^-1 of integrated luminosity recorded with the CDF detector. The final state of large missing transverse energy and one or two high energy jets was also investigated. The calculation of graviton emission was based on the effective low-energy theory that was valid below the scale MD.