585 research outputs found
Signals for R-parity-violating Supersymmetry at a 500 GeV e+ e- Collider
We investigate the production of charginos and neutralinos at a 500 GeV
e^+e^- collider (NLC) and study their decays to the lightest neutralino, which
then decays into multi-fermion final states through couplings which do not
conserve R-parity. These couplings are assumed to affect only the decay of the
lightest neutralino. Detailed analyses of the possible signals and backgrounds
are performed for five selected points in the parameter space.Comment: 42 pages, LaTeX, 12 postscript figure
Probing compressed mass spectra in electroweak supersymmetry with Recursive Jigsaw Reconstruction
The lack of evidence for the production of colored supersymmetric particles
at the LHC has increased interest in searches for superpartners of the
electroweak SM gauge bosons, namely the neutralinos and charginos. These are
challenging due to the weak nature of the production process, and the existing
discovery reach has significant gaps in due to the difficulty of separating the
supersymmetric signal from SM diboson events that produce similar final states
and kinematics. We apply the Recursive Jigsaw Reconstruction technique to study
final states enriched in charged leptons and missing transverse momentum,
focusing on compressed topologies with direct production of charginos and
neutralinos decaying to the lightest neutral supersymmetric particle through
the emission of W and Z bosons. After presenting prototype analysis designs for
future LHC runs, we demonstrate that its detectors have the potential to probe
a significant amount of unexplored parameter space for chargino-neutralino
associated production within the next few years, and show that the very
challenging successful search for chargino pair production with compressed
spectra might be possible by the end of the LHC lifetime.Comment: 20 pages, 33 figure
Pulling Out All the Stops: Searching for RPV SUSY with Stop-Jets
If the lighter stop eigenstate decays directly to two jets via baryonic
R-parity violation, it could have escaped existing LHC and Tevatron searches in
four-jet events, even for masses as small as 100 GeV. In order to recover
sensitivity in the face of increasingly harsh trigger requirements at the LHC,
we propose a search for stop pairs in the highly-boosted regime, using the
approaches of jet substructure. We demonstrate that the four-jet triggers can
be completely bypassed by using inclusive jet-H_T triggers, and that the
resulting QCD continuum background can be processed by substructure methods
into a featureless spectrum suitable for a data-driven bump-hunt down to 100
GeV. We estimate that the LHC 8 TeV run is sensitive to 100 GeV stops with
decays of any flavor at better than 5-sigma level, and could place exclusions
up to 300 GeV or higher. Assuming Minimal Flavor Violation and running a
b-tagged analysis, exclusion reach may extend up to nearly 400 GeV.
Longer-term, the 14 TeV LHC at 300/fb could extend these mass limits by a
factor of two, while continuing to improve sensitivity in the 100 GeV region.Comment: 28 pages, 10 figure
Dark Matter Searches with Astroparticle Data
The existence of dark matter (DM) was first noticed by Zwicky in the 1930s,
but its nature remains one of the great unsolved problems of physics. A variety
of observations indicate that it is non-baryonic and non-relativistic. One of
the preferred candidates for non-baryonic DM is a weakly interacting massive
particle (WIMP) that in most models is stable. WIMP self-annihilation can
produce cosmic rays, gamma rays, and other particles with signatures that may
be detectable. Hints of anomalous cosmic-ray spectra found by recent
experiments, such as PAMELA, have motivated interesting interpretations in
terms of DM annihilation and/or decay. However, these signatures also have
standard astrophysical interpretations, so additional evidence is needed in
order to make a case for detection of DM annihilation or decay. Searches by the
Fermi Large Area Telescope for gamma-ray signals from clumps, nearby dwarf
spheroidal galaxies, and galaxy clusters have also been performed, along with
measurements of the diffuse Galactic and extragalactic gamma-ray emission. In
addition, imaging atmospheric Cherenkov telescopes like HESS, MAGIC, and
VERITAS have reported on searches for gamma-ray emission from dwarf galaxies.
In this review, we examine the status of searches for particle DM by these
instruments and discuss the interpretations and resulting DM limits.Comment: Solicited review article to appear in Annual Reviews of Astronomy and
Astrophysics. 52 pages, 10 figures (higher resolution figures will appear in
the journal article
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A Search for New Physics producing Jets, Large MT2, and Disappearing Tracks in 13 TeV Proton-Proton Collisions at CERN’s Large Hadron Collider
This work presents two searches for new physics characterized by pair-production of strongly interacting particles, each decaying to hadronic jets and a particle that is not detectable. The searches use the full 13 TeV proton-proton collision dataset produced by CERN’s Large Hadron Collider and recorded by the CMS detector from 2016 to 2018, with total integrated luminosity 137 fb−1. The presence of particles interacting too weakly to be detected is inferred using imbalance in the transverse momentum of the collision products, and sensitivity to pair- production is enhanced by requiring large values of the kinematic variable MT2 in events with at least two jets. The first search is inclusive, binning events using the total hadronic transverse energy, the total number of jets, the number of jets reconstructed as originating from a bottom quark, and either the value of MT2 in multijet events, or the transverse momentum of the jet in monojet events. The second search extends the first, by requiring the presence of a disappearing track in the event, and adds binning in the length and transverse momentum of the disappearing track. Both searches are sensitive to a variety of extensions to the Standard Model that include dark matter candidates. Of greatest interest, the results set constraints on pair production of squarks and gluinos as predicted by R-parity conserving supersymmetric extensions of the Standard Model, in which the lightest supersymmetric particle is a neutralino. The first search is sensitive to any decay chain terminating in Standard Model hadrons plus the neutralino, while the second specifically targets, with greatly enhanced sensitivity, decay chains containing an intermediate long-lived chargino. These constraints are the most stringent yet produced by any experiment
Angular Structure of Jet Quenching Within a Hybrid Strong/Weak Coupling Model
Within the context of a hybrid strong/weak coupling model of jet quenching,
we study the modification of the angular distribution of the energy within jets
in heavy ion collisions, as partons within jet showers lose energy and get
kicked as they traverse the strongly coupled plasma produced in the collision.
To describe the dynamics transverse to the jet axis, we add the effects of
transverse momentum broadening into our hybrid construction, introducing a
parameter that governs its magnitude. We show that,
because of the quenching of the energy of partons within a jet, even when
the jets that survive with some specified energy in the final state
are narrower than jets with that energy in proton-proton collisions. For this
reason, many standard observables are rather insensitive to . We propose a
new differential jet shape ratio observable in which the effects of transverse
momentum broadening are apparent. We also analyze the response of the medium to
the passage of the jet through it, noting that the momentum lost by the jet
appears as the momentum of a wake in the medium. After freezeout this wake
becomes soft particles with a broad angular distribution but with net momentum
in the jet direction. We show that the particles coming from the response of
the medium to the momentum and energy deposited in it leads to a correlation
between the momentum of soft particles well separated from the jet in angle
with the direction of the jet momentum, and find qualitative but not
quantitative agreement with experimental data on observables designed to
extract such a correlation. By confronting the results that we obtain upon
introducing transverse momentum broadening and the response of the medium to
the jet with available jet data, we highlight the importance of these processes
for understanding the internal, soft, angular structure of high energy jets.Comment: 62 pages, 14 figure
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