2,215 research outputs found
Severe storms forecast systems
Two research tasks are described: (1) the improvement and enhancement of an existing mesoscale numerical simulation system, and (2) numerical diagnostic studies associated with an individual case of severe storm development (April 10, 1979 in the Red River Valley of Texas and Oklahoma)
Isolated leptons from heavy flavor decays: Theory and data
Events with isolated leptons play a prominent role in signatures of new
physics phenomena at high energy collider physics facilities. In earlier
publications, we examine the standard model contribution to isolated lepton
production from bottom and charm mesons and baryons through their semileptonic
decays (b, c -> l + X), showing that this source can overwhelm the effects of
other standard model processes in some kinematic domains. In this paper, we
show that we obtain good agreement with recent Tevatron collider data, both
validating our simulations and showing that we underestimate the magnitude of
the heavy-flavor contribution to the isolated lepton yields. We also show that
the isolation requirement acts as a narrow bandpass filter on the momentum of
the isolated lepton, and we illustrate the effect of this filter on the
background to Higgs boson observation in the dilepton mode. We introduce and
justify a new rule of thumb: isolated electrons and muons from heavy flavor
decay are produced with roughly the same distributions as b and c quarks, but
with 1/200 times the rates of b and c production, respectively.Comment: 12 pg, revtex, 5 fig, corrected typo
Angular correlations in single-top-quark and Wjj production at next-to-leading order
I demonstrate that the correlated angular distributions of final-state
particles in both single-top-quark production and the dominant Wjj backgrounds
can be reliably predicted. Using these fully-correlated angular distributions,
I propose a set of cuts that can improve the single-top-quark discovery
significance by 25%, and the signal to background ratio by a factor of 3 with
very little theoretical uncertainty. Up to a subtlety in t-channel
single-top-quark production, leading-order matrix elements are shown to be
sufficient to reproduce the next-to-leading order correlated distributions.Comment: 22 pages, 23 figs, RevTex4, fixed typos, to appear in Phys. Rev.
Standard model explanation of a CDF dijet excess in Wjj
We demonstrate the recent observation of a peak in the dijet invariant mass
of the Wjj signal observed by the CDF Collaboration can be explained as the
same upward fluctuation observed by CDF in single-top-quark production. In
general, both t-channel and s-channel single-top-quark production produce
kinematically induced peaks in the dijet spectrum. Since CDF used a Monte Carlo
simulation to subtract the single-top backgrounds instead of data, a peak in
the dijet spectrum is expected. The D0 Collaboration has a small upward
fluctuation in their published t-channel data; and hence we predict they would
see at most a small peak in the dijet invariant mass spectrum of Wjj if they
follow the same procedure as CDF.Comment: 3 pg., 2 figs, revtex, minor clarifications, to appear in Phys. Rev.
Missing heavy flavor backgrounds to Higgs boson production
We investigate characteristics of the signal and backgrounds for Higgs boson
decay into WW at the Fermilab Tevatron and CERN Large Hadron Collider. In the
the lepton-pair-plus-missing-energy final state, we show that the background
receives an important contribution from semileptonic decays of heavy flavors.
Lepton isolation cuts provide too little suppression of these heavy flavor
contributions, and an additional 4 to 8 orders-of-magnitude suppression must
come from physics cuts. We demonstrate that an increase of the minimum
transverse momentum of nonleading leptons in multilepton events is one
effective way to achieve the needed suppression, without appreciable loss of
the Higgs boson signal. Such a cut would impact the efficiency of searches for
supersymmetry as well. We emphasize the importance of direct measurement of the
lepton background from heavy flavor production.Comment: 23 pgs., 10 figs, revtex4, 1 Ref. added, minor typos corrected, to
appear in Phys. Rev.
Development of a severe local storm prediction system: A 60-day test of a mesoscale primitive equation model
The progress and problems associated with the dynamical forecast system which was developed to predict severe storms are examined. The meteorological problem of severe convective storm forecasting is reviewed. The cascade hypothesis which forms the theoretical core of the nested grid dynamical numerical modelling system is described. The dynamical and numerical structure of the model used during the 1978 test period is presented and a preliminary description of a proposed multigrid system for future experiments and tests is provided. Six cases from the spring of 1978 are discussed to illustrate the model's performance and its problems. Potential solutions to the problems are examined
Catalogue of lunar craters cross sections. I - Craters with peaks Research report no. 16
Lunar craters with centrally located peaks - tables and profile graph
Recent examples of mesoscale numerical forecasts of severe weather events along the east coast
Mesoscale numerical forecasts utilizing the Mesoscale Atmospheric Simulation System (MASS) are documented for two East Coast severe weather events. The two events are the thunderstorm and heavy snow bursts in the Washington, D.C. - Baltimore, MD region on 8 March 1984 and the devastating tornado outbreak across North and South Carolina on 28 March 1984. The forecasts are presented to demonstrate the ability of the model to simulate dynamical interactions and diabatic processes and to note some of the problems encountered when using mesoscale models for day-to-day forecasting
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