A Search for the Higgs Boson in its Associated Production with a W Vector Boson in p anti-p Collisions at s**(1/2) = 1.96-TeV (open access)

A Search for the Higgs Boson in its Associated Production with a W Vector Boson in p anti-p Collisions at s**(1/2) = 1.96-TeV

We present the results of a search for the Standard Model Higgs boson in its associated production with a W vector boson in p{bar p} collisions at {radical}s = 1.96 TeV using the complete Run IIA dataset with an integrated luminosity of 1.04 fb{sup -1} collected by the D0 experiment. The salient features of this analysis are the extended geometric acceptance by including the pseudorapidity covered by the end cap calorimeter, optimization in b-tagging and event selection criteria. We observe very good agreement in the data compared to the expectation form the modeling of Standard Model background for the WH signal. No excess events in data are observed over the predicted background. We establish that the evidence for observing the Higgs boson in this channel is inconclusive and proceed to set upper cross section limits on the associated WH production at 95% confidence level. We derive the cross section upper limits for the Higgs mass (m{sub H}) ranging from 105 GeV/c{sup 2} to 145 GeV/c{sup 2}. For m{sub H} = 115 GeV/c{sup 2}, the observed (expected) upper limit is 0.8 (0.9) pb compared to the Standard Model expectation of 0.13 pb.
Date: December 1, 2007
Creator: Kaushik, Venkatesh S. & /Texas U., Arlington
System: The UNT Digital Library
A search for muon neutrino to electron neutrino oscillations at delta(m^2)>0.1 eV^2 (open access)

A search for muon neutrino to electron neutrino oscillations at delta(m^2)>0.1 eV^2

The evidence is compelling that neutrinos undergo flavor change as they propagate. In recent years, experiments have observed this phenomenon of neutrino oscillations using disparate neutrino sources: the sun, fission reactors, accelerators, and secondary cosmic rays. The standard model of particle physics needs only simple extensions - neutrino masses and mixing - to accommodate all neutrino oscillation results to date, save one. The 3.8{sigma}-significant {bar {nu}}{sub e} excess reported by the LSND collaboration is consistent with {bar {nu}}{sub {mu}} {yields}{bar {nu}}{sub e} oscillations with a mass-squared splitting of {Delta}m{sup 2} {approx} 1 eV{sup 2}. This signal, which has not been independently verified, is inconsistent with other oscillation evidence unless more daring standard model extensions (e.g. sterile neutrinos) are considered.
Date: November 1, 2007
Creator: Patterson, Ryan Benton
System: The UNT Digital Library
Atmospheric neutrino observations in the MINOS far detector (open access)

Atmospheric neutrino observations in the MINOS far detector

This thesis presents the results of atmospheric neutrino observations from a 12.23 ktyr exposure of the 5.42 kt MINOS Far Detector between 1st August 2003 until 1st March 2006. The separation of atmospheric neutrino events from the large background of cosmic muon events is discussed. A total of 277 candidate contained vertex {nu}/{bar {nu}}{sub {mu}} CC data events are observed, with an expectation of 354.4{+-}47.4 events in the absence of neutrino oscillations. A total of 182 events have clearly identified directions, 77 data events are identified as upward going, 105 data events are identified as downward going. The ratio between the measured and expected up/down ratio is: R{sup data}{sub u/d}/R{sup MC}{sub u/d} = 0.72{sup +0.13}{sub -0.11}(stat.){+-} 0.04 (sys.). This is 2.1{sigma} away from the expectation for no oscillations. A total of 167 data events have clearly identified charge, 112 are identified as {nu}{sub {mu}} events, 55 are identified as {bar {nu}}{sub {mu}} events. This is the largest sample of charge-separated contained-vertex atmospheric neutrino interactions so far observed. The ratio between the measured and expected {bar {nu}}{sub {mu}}/{nu}{sub {mu}} ratio is: R{sup data}{sub {bar {nu}}{nu}} / R{sup MC}{sub {bar {nu}}{nu}} = 0.93 {sup +0.19}{sub -0.15} (stat.) {+-} 0.12 (sys.). This is …
Date: September 1, 2007
Creator: Chapman, John Derek & U., /Cambridge
System: The UNT Digital Library