505 research outputs found
Maximum Significance at the LHC and Higgs Decays to Muons
We present a new way to define and compute the maximum significance
achievable for signal and background processes at the LHC, using all available
phase space information. As an example, we show that a light Higgs boson
produced in weak--boson fusion with a subsequent decay into muons can be
extracted from the backgrounds. The method, aimed at phenomenological studies,
can be incorporated in parton--level event generators and accommodate
parametric descriptions of detector effects for selected observables.Comment: 7 pages, 2 figures, changes to wording and new references, published
versio
Dark Matter and Collider Phenomenology with two light Supersymmetric Higgs Bosons
Recently, it has been pointed out that two different excesses of events
observed at LEP could be interpreted as the CP-even Higgs bosons of the MSSM
with masses of approximately 98 and 114 GeV. If this is the case, the entire
MSSM Higgs sector is required to be light. In this article, we explore such a
scenario in detail. We constrain the Higgs and supersymmetric spectrum using
physics constraints as well as the magnetic moment of the muon. We then
point out the implications for neutralino dark matter -- next generation direct
detection experiments will be sensitive to all MSSM models with such a Higgs
sector. Finally, we find that all models outside of a very narrow corridor of
the parameter space have a charged Higgs boson which will be observed at the
LHC. In those exceptional models which do not contain an observable charged
Higgs, a light top squark will always be seen at the LHC, and likely at the
Tevatron.Comment: 12 pages, 18 figure
Weak boson fusion production of supersymmetric particles at the LHC
We present a complete calculation of weak boson fusion production of
colorless supersymmetric particles at the LHC, using the new matrix element
generator SUSY-MadGraph. The cross sections are small, generally at the
attobarn level, with a few notable exceptions which might provide additional
supersymmetric parameter measurements. We discuss in detail how to consistently
define supersymmetric weak couplings to preserve unitarity of weak gauge boson
scattering amplitudes to fermions, and derive sum rules for weak supersymmetric
couplings.Comment: 24 p., 3 fig., 9 tab., published in PRD; numbers in Table IV
corrected to those with kinematic cuts cite
Charged Higgs Boson Pairs at the LHC
We compute the cross section for pair production of charged Higgs bosons at
the LHC and compare the three production mechanisms. The bottom-parton
scattering process is computed to NLO, and the validity of the bottom-parton
approach is established in detail. The light-flavor Drell-Yan cross section is
evaluated at NLO as well. The gluon fusion process through a one-loop amplitude
is then compared with these two results. We show how a complete sample of
events could look, in terms of total cross sections and distributions of the
heavy final states.Comment: 15 pages with 8 figure
Precision Measurements of Higgs Couplings: Implications for New Physics Scales
The measured properties of the recently discovered Higgs boson are in good
agreement with predictions from the Standard Model. However, small deviations
in the Higgs couplings may manifest themselves once the currently large
uncertainties will be improved as part of the LHC program and at a future Higgs
factory. We review typical new physics scenarios that lead to observable
modifications of the Higgs interactions. They can be divided into two broad
categories: mixing effects as in portal models or extended Higgs sectors, and
vertex loop effects from new matter or gauge fields. In each model we relate
coupling deviations to their effective new physics scale. It turns out that
with percent level precision the Higgs couplings will be sensitive to the
multi-TeV regime.Comment: Invited review for Journal of Physics G, 33pp; v2: references added
and improved discussion of operator basis in section 2.
Single scalar top production with polarized beams in ep collisions at HERA
From the point of view of the R-parity breaking supersymmetric model, we
propose a scalar top (stop) search with longitudinally polarized electron (e-)
and positron(e+) beams which will soon be available at the upgraded HERA. Fully
polarized e- or e+ beams could produce the stop two times as much as
unpolarized beams, while they increase background events due to the process of
the standard model by about 30% in comparison with unpolarized ones. We show
that right-handed e+ beams at HERA is efficient to produce the stop in the
model. With 1 fb**(-1) of integrated luminosity we estimate reach in the
coupling constant lambda'(131) for masses of the stop in the range 160-400 GeV.
We can set a 95% confidence-level exclusion limit for lambda'(131) > 0.01-0.05
in the stop mass range of 240-280 GeV if no singal of the stop is observed. We
also point out that y(=Q**2/sx) distributions of e+ coming from the stop shows
the different behavior from those of the standard model.Comment: 12 pages, 6 eps figure
Fittino, a program for determining MSSM parameters from collider observables using an iterative method
Provided that Supersymmetry (SUSY) is realized, the Large Hadron Collider
(LHC) and the future International Linear Collider (ILC) may provide a wealth
of precise data from SUSY processes. An important task will be to extract the
Lagrangian parameters. On this basis the goal is to uncover the underlying
symmetry breaking mechanism from the measured observables. In order to
determine the SUSY parameters, the program Fittino has been developed. It uses
an iterative fitting technique and a Simulated Annealing algorithm to determine
the SUSY parameters directly from the observables without any a priori
knowledge of the parameters, using all available loop-corrections to masses and
couplings. Simulated Annealing is implemented as a stable and efficient method
for finding the optimal parameter values. The theoretical predictions can be
provided from any program with SUSY Les Houches Accord interface. As fit
result, a set of parameters including the full error matrix and two-dimensional
uncertainty contours are obtained. Pull distributions can automatically be
created and allow an independent cross-check of the fit results and possible
systematic shifts in the parameter determination. A determination of the
importance of the individual observables for the measurement of each parameter
can be performed after the fit. A flexible user interface is implemented,
allowing a wide range of different types of observables and a wide range of
parameters to be used.Comment: 32 pages, 6 figures, accepted by Comp. Phys. Com
Determining the Structure of Higgs Couplings at the LHC
Higgs boson production via weak boson fusion at the CERN Large Hadron
Collider has the capability to determine the dominant CP nature of a Higgs
boson, via the tensor structure of its coupling to weak bosons. This
information is contained in the azimuthal angle distribution of the two
outgoing forward tagging jets. The technique is independent of both the Higgs
boson mass and the observed decay channel.Comment: 5 pages, 4 figures, version accepted for publication in PR
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