1,209 research outputs found
The forward-backward asymmetry of top quark production at the Tevatron in warped extra dimensional models
The CDF and D0 experiments have reported on the measurement of the
forward-backward asymmetry of top quark pair production at the Tevatron and the
result is that it is more than 2 standard deviations above the predicted value
in the Standard Model. This has to be added to the longstanding anomaly in the
forward-backward asymmetry for bottom quark production at LEP which is 3
standard deviations different from the Standard Model value. The discrepancy in
the bottom asymmetry can be accounted for by the contributions of Kaluza-Klein
excitations of electroweak gauge bosons at LEP in warped extra dimensional
models in which the fermions are localized differently along the extra
dimension so that the gauge interactions of heavy third generation fermions are
naturally different from that of light fermions. In this paper, we show that it
is more difficult to elaborate a model generating a significant top asymmetry
in a similar way -- through exchanges of Kaluza-Klein gluons at the Tevatron --
due to the indirect constraints originating from precision electroweak data.Comment: 4 pages, 1 figure, published versio
Search for a Higgs Boson Decaying into Two Photons with the L3 Detector at LEP
A search is performed for a Higgs boson, decaying into two photons, using the
L3 data collected at centre of mass energies between = 189 and 202
GeV, corresponding to an integrated luminosity of 400 pb. The processes
, , are considered. The observed data are found to be consistent with the
expected background from standard physics processes. Limits on the branching
fraction of the Higgs boson decay into two photons as a function of the Higgs
mass are shown and a lower mass limit on a fermiophobic Higgs is derived.Comment: 3 pages, 2 postscript figures, Presented at the DPF2000 Conference,
August 9-12, 2000, The Ohio State University, Columbus, Ohi
e+ e- -> t anti-t H including decays: on the size of background contributions
We present results for the lowest order cross sections, calculated with the
complete set of the standard model Feynman diagrams, of all possible detection
channels of the associated production of the top quark pair and the light Higgs
boson, which may be used for determination of the top-Higgs Yukawa coupling at
the future e+e- linear collider. We show that, for typical particle
identification cuts, the background contributions are large. In particular, the
QCD background contributions are much bigger than could be expected when taking
into account a possibly low virtuality of exchanged gluons. Moreover, we
include the initial state radiation effects and discuss the dependence of the
cross sections on the Higgs boson and top quark masses.Comment: 13 pages, 1 figure; substantially revised version, accepted for
publication in Eur.Phys.J.
Probing the spin-parity of the Higgs boson via jet kinematics in vector boson fusion
Determining the spin and the parity quantum numbers of the recently
discovered Higgs-like boson at the LHC is a matter of great importance. In this
paper, we consider the possibility of using the kinematics of the tagging jets
in Higgs production via the vector boson fusion (VBF) process to test the
tensor structure of the Higgs-vector boson () interaction and to determine
the spin and CP properties of the observed resonance. We show that an anomalous
vertex, in particular its explicit momentum dependence, drastically
affects the rapidity between the two scattered quarks and their transverse
momenta and, hence, the acceptance of the kinematical cuts that allow to select
the VBF topology. The sensitivity of these observables to different spin-parity
assignments, including the dependence on the LHC center of mass energy, are
evaluated. In addition, we show that in associated Higgs production with a
vector boson some kinematical variables, such as the invariant mass of the
system and the transverse momenta of the two bosons and their separation in
rapidity, are also sensitive to the spin--parity assignments of the Higgs--like
boson.Comment: 15 pages, 5 figure
The Search for Higgs particles at high-energy colliders: Past, Present and Future
I briefly review the Higgs sector in the Standard Model and its minimal
Supersymmetric extension, the MSSM. After summarizing the properties of the
Higgs bosons and the present experimental constraints, I will discuss the
prospects for discovering these particle at the upgraded Tevatron, the LHC and
a high-energy linear collider. The possibility of studying the
properties of the Higgs particles will be then summarized.Comment: 28 pages, latex, 15 figures, talk at WHEPP VII, Allahabad, Indi
The Higgs sector of the phenomenological MSSM in the light of the Higgs boson discovery
The long awaited discovery of a new light scalar at the LHC opens up a new
era of studies of the Higgs sector in the SM and its extensions. In this paper
we discuss the consequences of the observation of a light Higgs boson with the
mass and rates reported by the ATLAS and CMS collaborations on the parameter
space of the phenomenological MSSM, including also the so far unsuccessful LHC
searches for the heavier Higgs bosons and supersymmetric particle partners in
missing transverse momentum as well as the constraints from B physics and dark
matter. We explore the various regimes of the MSSM Higgs sector depending on
the parameters MA and tan beta and show that only two of them are still allowed
by all present experimental constraints: the decoupling regime where there is
only one light and standard--like Higgs boson and the supersymmetric regime in
which there are light supersymmetric particle partners affecting the decay
properties of the Higgs boson, in particular its di-photon and invisible
decays.Comment: 21 pages, 9 figures v2 - Discussion of the impact of LHC data
extended, scan statistics increased, a few figures added and typos correcte
Model Independent Determination of the Top Yukawa Coupling from LHC and LC
We show how a measurement of the process pp-->t tbar H + X at the LHC and a
measurement of the Higgs boson branching ratios BR(H-->b bar) and BR(H-->W+W-)
at a future linear electron positron collider can be combined to extract a
model-independent measurement of the top quark Yukawa coupling. We find that
for 120 GeV < m_H < 200 GeV a measurement precision of 15% including systematic
uncertainties can be achieved for integrated luminosities of 300 fb-1 at the
LHC and 500 fb-1 at the LC at a centre-of-mass energy of 350 GeV.Comment: A contribution to the LHC / LC Study Group document, 7 pages, 3
figure
Three-Body Decays of Top and Bottom Squarks
We investigate the decays of third generation scalar quarks in the Minimal
Supersymmetric extension of the Standard Model, focusing on the three-body
modes. We calculate the partial widths of the decays of heavier top and bottom
squarks into the lighter ones and a fermion pair [through virtual vector boson,
Higgs boson or gaugino exchanges] and the partial widths of the three-body
decays of both top squarks into bottom quarks and a pair of fermion and scalar
fermion [we consider the case of lighter or states]
and into a bottom quark, the lightest neutralino and a or a charged Higgs
boson . Some of these decay modes are shown to have substantial
branching ratios in some areas of the parameter space.Comment: 24 pages with 4 psfigures, late
Higgs Physics: Theory
I review the theoretical aspects of the physics of Higgs bosons, focusing on
the elements that are relevant for the production and detection at present
hadron colliders. After briefly summarizing the basics of electroweak symmetry
breaking in the Standard Model, I discuss Higgs production at the LHC and at
the Tevatron, with some focus on the main production mechanism, the gluon-gluon
fusion process, and summarize the main Higgs decay modes and the experimental
detection channels. I then briefly survey the case of the minimal
supersymmetric extension of the Standard Model. In a last section, I review the
prospects for determining the fundamental properties of the Higgs particles
once they have been experimentally observed.Comment: 21 pages, 15 figures. Talk given at the XXV International Symposium
on Lepton Photon Interactions at High Energies (Lepton Photon 11), 22-27
August 2011, Mumbai, Indi
Higgs Physics at Future Colliders: recent theoretical developments
I review the physics of the Higgs sector in the Standard Model and its
minimal supersymmetric extension, the MSSM. I will discuss the prospects for
discovering the Higgs particles at the upgraded Tevatron, at the Large Hadron
Collider, and at a future high--energy linear collider with
centre--of--mass energy in the 350--800 GeV range, as well as the possibilities
for studying their fundamental properties. Some emphasis will be put on the
theoretical developments which occurred in the last two years.Comment: 20 pages, latex, 12 figures. Talk given at PASCOS 2003 (Bombay,
India
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