3,635 research outputs found

### Overview of physics at the Large Hadron Collider

The Large Hadron Collider has produced during the run from 2010 to 2012, proton-proton collision to a center-of-mass energy up to 8TeV. The data delivered to the experiments placed along the ring allowed studies of the hadron
collision physics at this unprecedent energy scale, and accurate checks of the Standard Model have been performed. An overview of the most representative physics results achieved are briefly presented and discussed, with emphasis to the most recent studies made. In particular, an update on the first measurements of the new resonance with mass around 125 GeV is reported

### Phenomenology of the minimal supersymmetric $U(1)_{B-L}\times U(1)_R$ extension of the standard model

We discuss the minimal supersymmetric $U(1)_{B-L}\times U(1)_R$ extension of
the standard model. Gauge couplings unify as in the MSSM, even if the scale of
$U(1)_{B-L}\times U(1)_R$ breaking is as low as order TeV and the model can be
embedded into an SO(10) grand unified theory. The phenomenology of the model
differs in some important aspects from the MSSM, leading potentially to rich
phenomenology at the LHC. It predicts more light Higgs states and the mostly
left CP-even Higgs has a mass reaching easily 125 GeV, with no constraints on
the SUSY spectrum. Right sneutrinos can be the lightest supersymmetric
particle, changing all dark matter constraints on SUSY parameter space. The
model has seven neutralinos and squark/gluino decay chains involve more
complicated cascades than in the MSSM. We also discuss briefly low-energy and
accelerator constraints on the model, where the most important limits come from
recent $Z'$ searches at the LHC and upper limits on lepton flavour violation.Comment: 46 pages, 11 figure

### Structure of dimension-six derivative interactions in pseudo Nambu-Goldstone N Higgs doublet models

We derive the general structure of dimension-six derivative interactions in
the N Higgs doublet models, where Higgs fields arise as pseudo Nambu-Goldstone
modes of a strongly interacting sector. We show that there are several
relations among the dimension-six operators, and therefore the number of
independent operators decreases compared with models on which only SU(2)_L x
U(1)_Y invariance is imposed. As an explicit example, we derive scattering
amplitudes of longitudinal gauge bosons and Higgs bosons at high energy on
models involving two Higgs doublets, and compare them with the amplitudes in
the case of one Higgs doublet.Comment: 49 pages, 10 figure

### 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

### Implications of a high mass light MSSM Higgs scalar for SUSY searches at the LHC

The Atlas and CMS collaborations have both reported an excess of events in
the WW\star \rightarrow \ell+\ell- + ETmiss search channel, which could be the
first evidence for the Higgs boson. In the context of the MSSM, the lightest
SUSY Higgs scalar h is expected to occur with mass mh = 135 GeV, depending on
the range of SUSY parameters scanned over. Since the h \rightarrow WW\star
branching fraction falls swiftly with decreasing mh, a signal in the WW\star
channel would favor an h at the high end of its predicted mass range. We scan
over general GUT scale SUSY model parameters to find those which give rise to
mh > 130 GeV. A value of m0 \sim 10 - 20 TeV is favored, with A0 \sim \pm2m0,
while the lower range of m1/2 < 1 TeV is also slightly favored. This gives rise
to an "effective SUSY" type of sparticle mass spectrum. For low m1/2, gluino
pair production followed by three-body gluino decay to top quarks may
ultimately be accesible to LHC searches, while for higher m1/2 values, the SUSY
spectra would likely be out of range of any conceivable LHC reach. Since the
thermal neutralino relic abundance tends to be very high, late-time entropy
dilution or neutralino decay to light axinos would be required to gain accord
with the measured dark matter abundanceComment: 12 pages, 3 figures, some references added, accepted in PR

### Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC

In supersymmetric scenarios with a long-lived stau, the LHC experiments
provide us with a great environment for precise mass measurements of
superparticles. We study a case in which the mass differences between the
lightest stau and other sleptons are about 10 GeV or larger, so that the decay
products of heavier sleptons are hard enough to be detected. We demonstrate
that the masses of neutralinos, sleptons, and squarks can be measured with a
good accuracy.Comment: 20 pages, 6 figure

### Interactions of Heavy Hadrons using Regge Phenomenology and the Quark Gluon String Model

The search for stable heavy exotic hadrons is a promising way to observe new
physics processes at collider experiments. The discovery potential for such
particles can be enhanced or suppressed by their interactions with detector
material. This paper describes a model for the interactions in matter of stable
hadrons containing an exotic quark of charges $\pm {1/3}e$ or $\pm {2/3}e$
using Regge phenomenology and the Quark Gluon String Model. The influence of
such interactions on searches at the LHC is also discussed

### Proceedings of the Workshop on Monte Carlo's, Physics and Simulations at the LHC PART II

These proceedings collect the presentations given at the first three meetings
of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC",
held at the Frascati National Laboratories in 2006. The first part of these
proceedings contains pedagogical introductions to several basic topics of both
theoretical and experimental high pT LHC physics. The second part collects more
specialised presentations.Comment: 157 pages, 136 figures; contribution by M. Grazzini has been adde

### Calculation of the One W Loop $H \to \gamma \gamma$ Decay Amplitude with a Lattice Regulator

There has been a controversial recent claim that the standard result on the
Higgs to two photon decay rate is incorrect, with the use of dimensional
regularization fingered as the alleged culprit. Given the great importance of
the $H\to \gamma \gamma$ process as a possible Standard Model Higgs discovery
channel at the LHC if the Higgs mass is light, it is critical to find a way to
check the correctness of the results of dimensional regularization for this
process. Here we report the results of a perturbative calculation of the $H\to
\gamma \gamma$ decay amplitude using a spacetime lattice as a UV regulator,
which is the only known gauge-invariant regulator for non-Abelian gauge
theories other than dimensional regularization. We find that the decay
amplitude calculated using lattice-regularized perturbation theory is
consistent to very high statistical accuracy with the decay amplitude obtained
using dimensional regularization.Comment: 5 pages, 4 figure

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