805 research outputs found
Standard Model Higgs boson searches with the ATLAS detector at the Large Hadron Collider
The investigation of the mechanism responsible for electroweak symmetry
breaking is one of the most important tasks of the scientific program of the
Large Hadron Collider. The experimental results on the search of the Standard
Model Higgs boson with 1 to 2 fb^-1 of proton proton collision data at sqrt s=7
TeV recorded by the ATLAS detector are presented and discussed. No significant
excess of events is found with respect to the expectations from Standard Model
processes, and the production of a Higgs boson is excluded at 95% Confidence
Level for the mass regions 144-232, 256-282 and 296-466 GeV.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in
"Pramana - journal of phsyics". 11 pages, 13 figure
Squark anti-squark pair production at the LHC: the electroweak contribution
We present the complete NLO electroweak contribution of
to the production of diagonal
squark--anti-squark pairs in proton--proton collisions. Compared to the
lowest-order electroweak terms, the
NLO contributions are also significant. We discuss the LO and NLO electroweak
effects in cross sections and distributions at the LHC for the production of
squarks different from top squarks, in various supersymmetric benchmark
scenarios.Comment: 38 pages, 21 figures. Replaced with the version published in JHE
Searching for the Kaluza-Klein Graviton in Bulk RS Models
The best-studied version of the RS1 model has all the Standard Model
particles confined to the TeV brane. However, recent variants have the Standard
Model fermions and gauge bosons located in the bulk five-dimensional spacetime.
We study the potential reach of the LHC in searching for the lightest KK
partner of the graviton in the most promising such models in which the
right-handed top is localized very near the TeV brane and the light fermions
are localized near the Planck brane. We consider both detection and the
establishment of the spin-2 nature of the resonance should it be found.Comment: 17 pages, 6 figures - JHEP published version, figures added,
branching ratio correcte
Leptoquark Single and Pair production at LHC with CalcHEP/CompHEP in the complete model
We study combined leptoquark (LQ) single and pair production at LHC at the
level of detector simulation. A set of kinematical cuts has been worked out to
maximize significance for combined signal events.
It was shown that combination of signatures from LQ single and pair
production not only significantly increases the LHC reach, but also allows us
to give the correct signal interpretation. In particular, it was found that the
LHC has potential to discover LQ with a mass up to 1.2 TeV and 1.5 TeV for the
case of scalar and vector LQ, respectively, and LQ single production
contributes 30-50% to the total signal rate for LQ-l-q coupling, taken equal to
the electromagnetic coupling.
This work is based on implementation of the most general form of scalar and
vector LQ interactions with quarks and gluons into CalcHEP/CompHEP packages.
This implementation, which authors made publicly available, was one the most
important aspects of the study.Comment: LaTeX, 27 pages, 15 figure
Radiative corrections to the semileptonic and hadronic Higgs-boson decays H -> W W/Z Z -> 4 fermions
The radiative corrections of the strong and electroweak interactions are
calculated for the Higgs-boson decays H -> WW/ZZ -> 4f with semileptonic or
hadronic four-fermion final states in next-to-leading order. This calculation
is improved by higher-order corrections originating from heavy-Higgs-boson
effects and photonic final-state radiation off charged leptons. The W- and
Z-boson resonances are treated within the complex-mass scheme, i.e. without any
resonance expansion or on-shell approximation. The calculation essentially
follows our previous study of purely leptonic final states. The electroweak
corrections are similar for all four-fermion final states; for integrated
quantities they amount to some per cent and increase with growing Higgs-boson
mass M_H, reaching 7-8% at M_H \sim 500 GeV. For distributions, the corrections
are somewhat larger and, in general, distort the shapes. Among the QCD
corrections, which include corrections to interference contributions of the
Born diagrams, only the corrections to the squared Born diagrams turn out to be
relevant. These contributions can be attributed to the gauge-boson decays, i.e.
they approximately amount to \alpha_s/\pi for semileptonic final states and
2\alpha_s/\pi for hadronic final states. The discussed corrections have been
implemented in the Monte Carlo event generator PROPHECY4F.Comment: 29 pages, LaTeX, 30 postscript figure
NLO electroweak contributions to gluino pair production at hadron colliders
We calculate the full corrections to the
process of gluino pair production at hadron colliders in the framework of the
real MSSM. We show that these contributions can be neglected at the LHC
performing a scan over a wide region of the parameter space. The impact of
these corrections in the parameter range investigated at the Tevatron is small.Comment: 26 pages, 12 figure
Dark matter searches at LHC
Besides Standard Model measurements and other Beyond Standard Model studies,
the ATLAS and CMS experiments at the LHC will search for Supersymmetry, one of
the most attractive explanation for dark matter. The SUSY discovery potential
with early data is presented here together with some first results obtained
with 2010 collision data at 7 TeV. Emphasis is placed on measurements and
parameter determination that can be performed to disentangle the possible SUSY
models and SUSY look-alike and the interpretation of a possible positive
supersymmetric signal as an explanation of dark matter.Comment: 15 pages, 14 figures, Invited plenary talk given at DISCRETE 2010:
Symposium On Prospects In The Physics Of Discrete Symmetries, 6-11 Dec 2010,
Rome, Ital
Theoretical uncertainties in sparticle mass predictions from computational tools
We estimate the current theoretical uncertainty in sparticle mass predictions
by comparing several state-of-the-art computations within the minimal
supersymmetric standard model (MSSM). We find that the theoretical uncertainty
is comparable to the expected statistical errors from the Large Hadron Collider
(LHC), and significantly larger than those expected from a future e+e- Linear
Collider (LC). We quantify the theoretical uncertainty on relevant sparticle
observables for both LHC and LC, and show that the value of the error is
significantly dependent upon the supersymmetry (SUSY) breaking parameters. We
also present the theoretical uncertainty induced in fundamental-scale SUSY
breaking parameters when they are fitted from LHC measurements. Two regions of
the SUSY parameter space where accurate predictions are particularly difficult
are examined in detail: the large tan(beta) and focus point regimes.Comment: 22 pages, 6 figures; comment added pointing out that 2-loop QCD
corrections to mt are incorrect in some of the programs investigated. We give
the correct formul
Three-body decays of sleptons in models with non-universal Higgs masses
We compute the three-body decays of charged sleptons and sneutrinos into
other sleptons. These decays are of particular interest in SUSY-breaking models
with non-universal Higgs mass parameters, where the left-chiral sleptons can be
lighter than the right-chiral ones, and lighter than the lightest neutralino.
We present the formulas for the three-body decay widths together with a
numerical analysis in the context of gaugino-mediated SUSY breaking with a
gravitino LSP.Comment: Version published in JHEP. See http://cern.ch/kraml/papers/ for
high-res figure
Light neutralino in the MSSM: An update with the latest LHC results
We discuss the scenario of light neutralino dark matter in the minimal
supersymmetric standard model, which is motivated by the results of some of the
direct detection experiments --- DAMA, CoGENT, and CRESST. We update our
previous analysis with the latest results of the LHC. We show that new LHC
constraints disfavour the parameter region that can reproduce the results of
DAMA and CoGENT.Comment: 4 pages, 4 figures, to appear in the conference proceedings of TAUP
2011, Munich Germany, 5-9 September 201
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