4,788 research outputs found
Strong Interaction Effects in Stop Pair Production at Colliders
We discuss perturbative and non-perturbative strong interaction effects in
the pair production of stop squarks () at colliders.
Events with an additional hard gluon allow to detect or exclude stop pair
production even in scenarios with very small mass splitting between
and an invisible lightest supersymmetric particle (LSP). Such
events can also help to establish that transforms as a triplet
under . We also carefully study non-perturbative
fragmentation, which is currently not well understood: not only is the
fragmentation function not known very well, but also there are
ambiguities in the algorithm employed to model fragmentation. We present
numerical results both for CERN LEP-183 and for a proposed future
collider operating at center-of-mass energy GeV.Comment: 16 pages and 4 figure
Lepton Flavours at the Early LHC Experiments as the Footprints of the Dark Matter Producing Mechanisms
The mSUGRA parameter space corresponding to light sleptons well within the
reach of LHC and relatively light squarks and gluinos (mass 1 TeV) has
three regions consistent with the WMAP data on dark matter relic density and
direct mass bounds from LEP 2. Each region can lead to distinct leptonic
signatures from squark-gluino events during the early LHC experiments
(integrated luminosity or even smaller). In the much studied
stau-LSP coannihilation region with a vanishing common trilinear coupling
() at the GUT scale a large fraction of the final states contain electrons
and / or muons and - - universality holds to a good
approximation. In the not so well studied scenarios with non-vanishing
both LSP pair annihilation and stau-LSP coannihilation could contribute
significantly to the dark matter relic density for even smaller squark-gluino
masses. Our simulations indicate that the corresponding signatures are final
states rich in -leptons while final states with electrons and muons are
suppressed leading to a violation of lepton universality. These features may be
observed to a lesser extent even in the modified parameter space (with non-zero
) where the coannihilation process dominates. We also show that the
generic -leptons + -jets+ signatures without flavour tagging
can also discriminate among the three scenarios. However, the signals become
more informative if the and -jet tagging facilities at the LHC
experiments are utilized.Comment: 28 page
SUSY darkmatter at the LHC - 7 TeV
We have analysed the early LHC signatures of the minimal supergravity
(mSUGRA) model. Our emphasis is on the 7 - run corresponding to an
integrated luminosity of although we have also discussed
briefly the prospects at LHC-10 . We focus on the parameter space yielding
relatively light squark and gluinos consistent with the darkmatter relic
density data and the LEP bounds on the lightest Higgs scalar mass. This
parameter space is only allowed for non-vanishing trilinear soft breaking term
. A significant region of the parameter space with large to moderate
negative values of consistent with the stability of the scalar potential
and relic density production via neutralino annihilation and/or neutralino -
stau coannihilation yields observable signal via the jets + missing transverse
energy channel. The one lepton + jets + missing energy signal is also viable
over a smaller but non-trivial parameter space. The ratio of the size of the
two signals - free from theoretical uncertainties - may distinguish between
different relic density generating mechanisms. With efficient -tagging
facilities at 7 the discriminating power may increase significantly. We
also comment on other dark matter relic density allowed mSUGRA scenarios and
variants there of in the context of LHC-7 .Comment: Brief comments on signals at 7 TeV in the Higgs funnel region of
mSUGRA, models with non universal scalar and gaugino masses have been added.
Accepted for publication in PR
Electroweak Contributions to Squark Pair Production at the LHC
In this paper we compute electroweak contributions to the production of
squark pairs at hadron colliders. These include the exchange of electroweak
gauge bosons in the s-channel as well as electroweak gaugino exchange in the t-
and/or u-channel. In many cases these can interfere with the dominant QCD
contributions. As a result, we find sizable contributions to the production of
two SU(2) doublet squarks. At the LHC, they amount to 10 to 20% for typical
mSUGRA (or CMSSM) scenarios, but in more general scenarios they can vary
between -40 and +55%, depending on size and sign of the SU(2) gaugino mass. The
electroweak contribution to the total squark pair production rate at the LHC is
about 3.5 times smaller.Comment: 28 pages, 9 figure
Inference on the tail process with application to financial time series modelling
To draw inference on serial extremal dependence within heavy-tailed Markov
chains, Drees, Segers and Warcho{\l} [Extremes (2015) 18, 369--402] proposed
nonparametric estimators of the spectral tail process. The methodology can be
extended to the more general setting of a stationary, regularly varying time
series. The large-sample distribution of the estimators is derived via
empirical process theory for cluster functionals. The finite-sample performance
of these estimators is evaluated via Monte Carlo simulations. Moreover, two
different bootstrap schemes are employed which yield confidence intervals for
the pre-asymptotic spectral tail process: the stationary bootstrap and the
multiplier block bootstrap. The estimators are applied to stock price data to
study the persistence of positive and negative shocks.Comment: 22 page
Non-zero trilinear parameter in the mSUGRA model - dark matter and collider signals at Tevatron and LHC
Phenomenologically viable and interesting regions of parameter space in the
minimal super-gravity (mSUGRA) model with small and small
consistent with the WMAP data on dark matter relic density and the bound on the
mass of the lightest Higgs scalar 114 GeV from LEP2 open up if the
rather adhoc assumption =0, where is the common trilinear soft
breaking parameter, employed in most of the existing analyses is relaxed. Since
this region corresponds to relatively light squarks and gluinos which are
likely to be probed extensively in the very early stages of the LHC
experiments, the consequences of moderate or large negative values of are
examined in detail. We find that in this region several processes including
lightest supersymmetric particle (LSP) pair annihilation, LSP - lighter tau
slepton () coannihilation and LSP - lighter top squark
() coannihilation contribute to the observed dark matter relic
density. %\sout{The possibility that a relic density producing
can be %observed at the current experiments at the Tevatron is wide open.} The
possibility that a that can participate in coannihilation with
the lightest neutralino to satisfy the WMAP bound on relic density and at the
same time be observed at the current experiments at the Tevatron is wide open.
At the LHC a large number of squark - gluino events lead to a very distinctive
semi-inclusive signature +X (anything without a tau lepton)
with a characteristic size much larger than +X or +X
events.Comment: Some minor changes made in the text. To appear in Phys Rev
Determining the Mass of Dark Matter Particles with Direct Detection Experiments
In this article I review two data analysis methods for determining the mass
(and eventually the spin-independent cross section on nucleons) of Weakly
Interacting Massive Particles with positive signals from direct Dark Matter
detection experiments: a maximum likelihood analysis with only one experiment
and a model-independent method requiring at least two experiments.
Uncertainties and caveats of these methods will also be discussed.Comment: 24 pages, 10 figures, 1 reference added, typos fixed, published
version, to appear in the NJP Focus Issue on "Dark Matter and Particle
Physics
Supersymmetric Higgs Boson Decays in the MSSM with Explicit CP Violation
Decays into neutralinos and charginos are among the most accessible
supersymmetric decay modes of Higgs particles in most supersymmetric extensions
of the Standard Model. In the presence of explicitly CP--violating phases in
the soft breaking sector of the theory, the couplings of Higgs bosons to
charginos and neutralinos are in general complex. Based on a specific benchmark
scenario of CP violation, we analyze the phenomenological impact of explicit CP
violation in the Minimal Supersymmetric Standard Model on these Higgs boson
decays. The presence of CP--violating phases could be confirmed either directly
through the measurement of a CP--odd polarization asymmetry of the produced
charginos and neutralinos, or through the dependence of CP--even quantities
(branching ratios and masses) on these phases.Comment: 14 pages, latex, 4 eps figure
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