Accelerator Neutrinos

Abstract:

We present a preliminary study of a new technique for measuring B-s(0) mixing and CP violation using the decay Bs0 --> J/phi phi, phi --> K+K-, J/phi --> mu(+)mu(-). This technique utilizes the unequal lifetimes of the B-s(0) CP even and odd eigenstates, and an angular variable decomposition of the CP content of the final state. This study is based on CDF Run-I observations and Run-II projections, and predicts that the B-s(0) mixing parameter x(s) can be measured with high accuracy in untagged samples if this approach is adopted. A large CP asymmetry may also be possible to measure. The accuracy of this method is shown to increase for higher values of x(s) as the lifetime splitting of the CP eigenstates increases. The measurement of x(s) does nor depend on tagging, whereas the observation of a CP-violating asymmetry does.

Abstract:

We report on measurements on inclusive cross sections times branching fractions into electrons for W and Z bosons produced in pp̄ collisions at s=1.8 TeV. From an integrated luminosity of 84.5 pb-1 recorded in 1994-1995 using the DØ detector at the Fermilab Tevatron, we determine σ(pp̄→W+X)×B(W→eν) = 2310±10(stat)±50(syst)±100(lum)pb and σ(pp̄→Z+X)×B(Z→ee)=221±3(stat)±4(syst) ±10(lum) pb. From these, we derive σ(pp̄→W+X)×B(W→eν)/σ(pp̄→Z+X) ×B(Z→ee)=10.43±0.15(stat) ±0.20(syst)±0.10(NLO), B(W→eν)=0.1044±0.0015(stat)±0.0020(syst)±0. 0017(theory)±0.0010(NLO), and Γ W=2.169±0.031(stat)±0.042(syst)±0.041(theory) ±0.022(NLO)GeV. We use the latter to set a 95% confidence level upper limit on the partial decay width of the W boson into nonstandard model final states, ΓWinv, of 0.213 GeV. Combining these results with those from the 1992-1993 data gives σ(pp̄→W+X) ×B(W→eν)/σ(pp̄→Z+X)×B(Z→ee)=10. 51±0.25,ΓW=2.152±0.066 GeV, and a 95% C.L. upper limit on ΓWinv of 0.191 GeV. Using a sample with a luminosity of 505 nb-1 taken at s=630 GeV, we measure σ(pp̄→W+X)×B(W→eν)=658±67 pb. ©2000 The American Physical Society.

Abstract:

Milagrito, a detector sensitive to very high energy gamma rays, monitored the northern sky from 1997 February through 1998 May. With a large field of view and a high duty cycle, this instrument was well suited to perform a search for TeV gamma-ray bursts (GRBs). We report on a search made for TeV counterparts to GRBs observed by BATSE. BATSE detected 54 GRBs within the field of view of Milagrito during this period. An excess of events coincident in time and space with one of these bursts, GRB 970417a, was observed by Milagrito. The excess has a chance probability of 2.8x10-5 of being a fluctuation of the background. The probability for observing an excess at least this large from any of the 54 bursts is 1.5x10-3. No significant correlations were detected from the other bursts.