136 research outputs found
Higgs Boson Decay into a Pair of Leptons
The decay of a Higgs boson into a pair of W bosons h --> W^+W^-, is a
dominant mode for Higgs boson masses above 135 GeV. At hadron colliders,
searches for this decay focus on channels in which both W bosons decay
leptonically into charged leptons, h --> W^+ W^- --> l^+ l^- plus missing
energy. We show that semileptonic decays of heavy flavors are an important
background to this signal. Lepton isolation provides too little suppression of
heavy flavor contributions, and an additional 4 to 8 orders-of-magnitude
suppression must come from physics cuts. An increase of the cut on the the
minimum transverse momentum of non-leading leptons in multilepton events is one
effective way to achieve the needed suppression, without appreciable loss of
the Higgs boson signal.Comment: 4 pages, 2 figures, 1 table. AIP style file. Paper presented by Ed
Berger. To be published in the proceedings of the 9th Conference on the
Intersections of Particle and Nuclear Physics (CIPANP 2006), Rio Grande,
Puerto Rico, May 30-June 3, 200
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
Associated Higgs plus vector boson test of a fermiophobic Higgs boson
Production in association with an electroweak vector boson V is a distinctive
mode of production for a Higgs boson H without tree-level couplings to
fermions, known as a fermiophobic Higgs boson. We focus on HV associated
production with H decay into a pair of photons, and V into a pair of jets, with
the goal of distinguishing a fermiophobic Higgs boson from the standard model
Higgs boson. Performing a simulation of the signal and pertinent QCD
backgrounds, and using the same event selection cuts employed by the LHC ATLAS
Collaboration, we argue that existing LHC data at 7 TeV with 4.9 fb^{-1} of
integrated luminosity may distinguish a fermiophobic Higgs boson from a
standard model Higgs boson near 125 GeV at about 1.9 standard deviation signal
significance (1.9 sigma) per experiment. At 8 TeV we show that associated
production could yield 2.8 sigma significance per experiment with 10 fb^{-1} of
data.Comment: 5 pgs., 4 figs, version 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.
Trilepton production at the CERN LHC: Standard model sources and beyond
Events with three or more isolated leptons in the final state are known to be
signatures of new physics phenomena at high energy collider physics facilities.
Standard model sources of isolated trilepton final states include gauge boson
pair production such as and , and production. We
demonstrate that leptons from heavy flavor decays, such as and , provide sources of trileptons that can be orders-of-magnitude larger
after cuts than other standard model backgrounds to new physics processes. We
explain the physical reason heavy flavor backgrounds survive isolation cuts. We
propose new cuts to control the backgrounds in the specific case of chargino
plus neutralino pair production in supersymmetric models. After these cuts are
imposed, we show that it should be possible to find at least a 4 sigma excess
for supersymmetry parameter space point LM9 with 30 fb of integrated
luminosity.Comment: 33 pgs, 17 figs, revtex; repaired damaged latex sourc
Supersymmetric QCD correction to top-quark production at the Tevatron
We calculate the supersymmetric QCD correction to top-quark production at the
Fermilab Tevatron, allowing for arbitrary left-right mixing of the squarks. We
find that the correction is significant for several combinations of gluino and
squark masses, e.g. +33% for m_{\tilde g}=200 GeV, m_{\tilde t} = m_{\tilde q}
=75 GeV.Comment: To appear Phys. Rev. D, added discussion of some references, two
figures replaced with one, 15 pages, 7 ps figures include
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