2,662 research outputs found
New probes for bino dark matter with coannihilation at the LHC
It has been widely known that bino-like dark matter in supersymmetric
theories suffers from over-production. The situation can be improved if the
gluino or wino has a mass of O(10) GeV heavier than the bino, sufficiently
reducing the bino abundance through co-annihilation. In this scenario, the
gluino decays to the bino via squark exchange, and the wino decays to the bino
via higgsino exchange. In split SUSY models favoured after the Higgs discovery,
the intermediate particles in these decays would be much heavier than gauginos,
suppressing the decay of the gluino and wino. This, in addition to the small
mass differences, results in long lifetimes for the gluino and wino. We show
that searches performed at the LHC for long-lived particles with displaced
vertices offer a powerful method to test this scenario.Comment: 6 pages, 3 figures, contributed to "The European Physical Society
Conference on High Energy Physics - EPS-HEP 2015" (22 - 29 July 2015, Vienna,
Austria
Probing Bino-Wino Coannihilation at the LHC
We study bino-wino coannihilation scenario in the so-called spread or
mini-split supersymmetry. We show that, in this model, a neutral wino has a
macroscopic decay length in a wide range of parameter space. This
characteristic feature could be observed as a displaced vertex plus missing
transverse energy event at the LHC. In this paper, we study the current
constraints and future prospects on the scenario based on the displaced vertex
search performed by the ATLAS collaboration. It is found that a sizable
parameter region can be probed at the 8 TeV LHC run. This search strategy will
considerably extend its reach at the next stage of the LHC running, and thus
play a crucial role to examine a possibility of bino dark matter in the
mini-split type supersymmetric models.Comment: 21 pages, 7 figures; version accepted for publication in JHE
Higgsino Dark Matter or Not: Role of Disappearing Track Searches at the LHC and Future Colliders
Higgsino in supersymmetric standard models is known to be a promising
candidate for dark matter in the Universe. Its phenomenological property is
strongly affected by the gaugino fraction in the Higgsino-like state. If this
is sizable, in other words, if gaugino masses are less than TeV,
we may probe the Higgsino dark matter in future non-accelerator experiments
such as dark matter direct searches and measurements of electric dipole
moments. On the other hand, if gauginos are much heavier, then it is hard to
search for Higgsino in these experiments. In this case, due to a lack of
gaugino components, the mass difference between the neutral and charged
Higgsinos is uniquely determined by electroweak interactions to be around
MeV, which makes the heavier charged state rather long-lived, with a decay
length of about cm. In this letter, we argue that a charged particle with a
flight length of cm can be probed in disappearing-track searches
if we require only two hits in the pixel detector. Even in this case, we can
reduce background events with the help of the displaced-vertex reconstruction
technique. We study the prospects of this search strategy at the LHC and future
colliders for the Higgsino dark matter scenario. It is found that an almost
pure Higgsino is indeed within the reach of the future TeV collider
experiments. We then discuss that the interplay among collider and
non-accelerator experiments plays a crucial role in testing the Higgsino dark
matter scenarios. Our strategy for disappearing-track searches can also enlarge
the discovery potential of pure wino dark matter as well as other
electroweak-charged dark matter candidates.Comment: 7 pages, 3 figure
Extending the LHC Reach for New Physics with Sub-Millimeter Displaced Vertices
Particles with a sub-millimeter decay length appear in many models of physics
beyond the Standard Model. However, their longevity has been often ignored in
their LHC searches and they have been regarded as promptly-decaying particles.
In this letter, we show that, by requiring displaced vertices on top of the
event selection criteria used in the ordinary search strategies for
promptly-decaying particles, we can considerably extend the LHC reach for
particles with a decay length of . We discuss a way of
reconstructing sub-millimeter displaced vertices by exploiting the same
technique used for the primary vertex reconstruction on the assumption that the
metastable particles are always pair-produced and their decay products contain
high- jets. We show that, by applying a cut based on displaced
vertices on top of standard kinematical cuts for the search of new particles,
the LHC reach can be significantly extended if the decay length is . In addition, we may measure the lifetime of the target
particle through the reconstruction of displaced vertices, which plays an
important role in understanding the new physics behind the metastable
particles.Comment: 18 pages, 6 figure
Looking for the left sneutrino LSP with displaced-vertex searches
We analyze a displaced dilepton signal expected at the LHC for a tau left
sneutrino as the lightest supersymmetric particle with a mass in the range
- GeV. The sneutrinos are pair produced via a virtual , or
in the channel and, given the large value of the tau Yukawa
coupling, their decays into two dileptons or a dilepton plus missing transverse
energy from neutrinos can be significant. The discussion is carried out in the
SSM, where the presence of -parity violating couplings involving
right-handed neutrinos solves the problem and can reproduce the neutrino
data. To probe the tau left sneutrinos we compare the predictions of the SSM with the ATLAS search for long-lived particles using displaced lepton
pairs in collisions at TeV, allowing us to constrain the
parameter space of the model. We also consider an optimization of the trigger
requirements used in existing displaced-vertex searches by means of a High
Level Trigger that exploits tracker information. This optimization is
generically useful for a light metastable particle decaying into soft charged
leptons. The constraints on the sneutrino turn out to be more stringent. We
finally discuss the prospects for the TeV LHC searches as well as further
potential optimizations.Comment: Version published in PRD, discussions expanded, references added, LEP
and LHC constraints discussed in more detail, 29 pages, 9 figures, 9 table
On the basic mechanism of Pixelized Photon Detectors
A Pixelized Photon Detector (PPD) is a generic name for the semiconductor
devices operated in the Geiger-mode, such as Silicon PhotoMultiplier and
Multi-Pixel Photon Counter, which has high photon counting capability. While
the internal mechanisms of the PPD have been intensively studied in recent
years, the existing models do not include the avalanche process. We have
simulated the multiplication and quenching of the avalanche process and have
succeeded in reproducing the output waveform of the PPD. Furthermore our model
predicts the existence of dead-time in the PPD which has never been numerically
predicted. For serching the dead-time, we also have developed waveform analysis
method using deconvolution which has the potential to distinguish neibouring
pulses precisely. In this paper, we discuss our improved model and waveform
analysis method.Comment: 4pages, 5figures, To appear in the proceedings of 5th International
Conference on New Developments in Photodetection (NDIP08), Aix-les-Bains,
France, 15-20 Jun 200
Cornering Higgsino: Use of Soft Displaced Track
Higgsino has been intensively searched for in the LHC experiments in recent
years. Currently, there is an uncharted region beyond the LEP Higgsino mass
limit where the mass splitting between the neutral and charged Higgsinos is
around - GEV, which is unexplored by either the soft di-lepton or
disappearing track searches. This region is, however, of great importance from
a phenomenological point of view, as many supersymmetric models predict such a
mass spectrum. In this letter, we propose a possibility of filling this gap by
using a soft micro-displaced track on top of the mono-jet event selection,
which allows us to discriminate a signature of the charged Higgsino decay from
the Standard Model background. It is found that this new strategy is
potentially sensitive to a Higgsino mass of GeV at the
LHC Run 2 (HL-LHC) for a charged-neutral mass splitting of GeV.Comment: 6 pages, 2 figure
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