81 research outputs found
Refining light stop exclusion limits with cross sections
If light supersymmetric top (stop) quarks are produced at the LHC and decay
via on- or off-shell -bosons they can be expected to contribute to a
precision cross section measurement. Using the latest results of the
CMS experiment, we revisit constraints on the stop quark production and find
that this measurement can exclude portions of the parameter space not probed by
dedicated searches. In particular we can exclude light top squarks up to
230~GeV along the line separating three- and four-body decays, . We also study the exclusion limits in the case
when the branching ratio for these decays is reduced and we show significant
improvement over previously existing limits.Comment: 5 pages, 2 figures; references updated, minor changes; to appear in
Phys. Lett.
Long-lived bino and wino in supersymmetry with heavy scalars and higgsinos
We point out that there is a parameter region in supersymmetry with heavy
scalars and higgsinos, in which the heavier of bino and wino becomes long-lived
as a consequence of the heavy higgsinos. In this region these electroweak
gaugino sectors are secluded from each other with very small mixings that are
inversely proportional to the higgsino mass. We revisit the bino and bino
decays and provide simple formulae for the partial decay rates and the
lifetimes in the limit of heavy higgsinos. We discuss the collider signatures
of the long-lived binos and winos in this scenario.Comment: 23 pages, 9 figures, text clarified, additional formulas, comparison
with SDecay; to appear in JHE
Tau-Sneutrino NLSP and Multilepton Signatures at the LHC
In models with gravitino as the lightest supersymmetric particle(LSP), the
next to lightest supersymmetric particle (NLSP) can have a long lifetime and
appear stable in collider experiments. We study the leptonic signatures of such
a scenario with tau-sneutrino as the NLSP, which is realized in the
non-universal Higgs masses scenario. We focus on an interesting trilepton
signature with two like-sign taus and an electron or a muon of opposite sign.
The neutralinos and charginos are quite heavy in the model considered, and the
trilepton signal comes mostly from the slepton-sneutrino production. We
identify the relevant backgrounds, taking into account tau decays, and devise a
set of cuts to optimize this trilepton signal. We simulate signal and
backgrounds at the LHC with 14 TeV center-of-mass energy. Although the sleptons
in this model are relatively light, O(100 GeV), discovery is more demanding
compared to typical neutralino LSP scenarios. The trilepton signal requires
large amount of accumulated data, at least ~80 fb^-1, at the CM energy of 14
TeV.Comment: 25 pages, 6 figures, minor changes to match the version published in
Phys.Rev.
Can R-parity violation hide vanilla supersymmetry at the LHC?
Current experimental constraints on a large parameter space in supersymmetric
models rely on the large missing energy signature. This is usually provided by
the lightest neutralino which stability is ensured by the R-parity. However, if
the R-parity is violated, the lightest neutralino decays into the standard
model particles and the missing energy cut is not efficient anymore. In
particular, the UDD type R-parity violation induces the neutralino decay to
three quarks which potentially leads to the most difficult signal to be
searched at hadron colliders. In this paper, we study the constraints on the
R-parity violating supersymmetric model using a same-sign dilepton and a
multijet signatures. We show that the gluino and squarks lighter than a TeV are
already excluded in constrained minimal supersymmetric standard model with
R-parity violation if their masses are approximately equal. We also analyze
constraints in a simplified model with R-parity violation. We compare how
R-parity violation changes some of the observables typically used to
distinguish a supersymmetric signal from standard model backgrounds.Comment: 14 pages, 4 figure
Neutralinos betray their singlino nature at the ILC
It is one of the most challenging tasks at the Large Hadron Collider and at a
future Linear Collider not only to observe physics beyond the Standard Model,
but to clearly identify the underlying new physics model. In this paper we
concentrate on the distinction between two different supersymmetric models, the
MSSM and the NMSSM, as they can lead to similar low energy spectra. The NMSSM
adds a singlet superfield to the MSSM particle spectrum and simplifies
embedding a SM-like Higgs candidate with the measured mass of about 125.5 GeV.
In parts of the parameter space the Higgs sector itself does not provide
sufficient indications for the underlying model. We show that exploring the
gaugino/higgsino sectors could provide a meaningful way to distinguish the two
models. Assuming that only the lightest chargino and neutralino masses and
polarized cross sections ,
are accessible at the linear collider, we
reconstruct the fundamental MSSM parameters , , ,
and study whether a unique model distinction is possible based on this
restricted information. Depending on the singlino admixture in the lightest
neutralino states, as well as their higgsino or gaugino nature, we define
several classes of scenarios and study the prospects of experimental
differentiation.Comment: 20 pages, 11 figure
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