93 research outputs found
Reconstruction of the left-chiral tau-sneutrino in supersymmetry with a right-sneutrino as the lightest supersymmetric particle
We have considered a supersymmetric scenario in which the minimal
supersymmetric standard model is augmented with a right-chiral neutrino
superfield for each generation. Such a scenario can have a lightest
supersymmetric particle (LSP) dominated by the right-chiral sneutrino state and
the lighter stau as the next-to-lightest supersymmetric particle (NLSP). This
can easily be motivated by assuming a high scale framework of supersymmetry
breaking like minimal supergravity (mSUGRA). Due to the extremely small
neutrino Yukawa coupling, the decay of the NLSP to the LSP is suppressed and
consequently the NLSP, here the lighter stau mass eigenstate, becomes stable at
the length scale of the detector. The collider signal in this case consists of
charged tracks of massive stable particles in the muon chamber. Following up on
our earlier studies on neutralino and chargino reconstruction in such a
scenario, we have shown the kinematical information obtained from these charged
tracks allows us to reconstruct the left-chiral tau-sneutrino as well over a
significant region of the mSUGRA parameter space. Two methods for
reconstruction are suggested and their relative merits are discussed.Comment: 18 pages, 7 figures and 5 table
Neutralino reconstruction in supersymmetry with long-lived staus
We consider a supergravity (SUGRA) scenario, with universal scalar and
gaugino masses at high scale, with a right-chiral neutrino superfield included
in the spectrum. Such a scenario can have a lightest supersymmetric particle
(LSP) dominated by the right sneutrino and a stau as the next-to lightest
supersymmetric particle (NLSP). Since decays of all particles into the LSP are
suppressed by the neutrino Yukawa coupling, the signal of supersymmetry
consists in charged tracks of stable particles in the muon chamber. We
demonstrate how a neutralino decaying into a tau and the stau-NLSP can be fully
reconstructed over substantial areas in the SUGRA parameter space. We also
suggest event selection criteria for eliminating backgrounds, including
combinatorial ones, and use a new method for the extraction of the mass of the
stau-NLSP, using its three-momentum as obtained from the curvature of the
charged track.Comment: Version to appear in Phys. Rev.
Multi-leptons and Top-jets in the Hunt for Gluinos in R-parity Violating Supersymmetry
The presence of R-parity () violation offers intersting decay
channels for the gluinos. In this work we present a new search strategy for the
gluinos in the presence of semileptonic violating couplings
and . We consider two scenarios (i)
induced 3-body decay of gluinos to a top quark (), a bottom
quark () and a light lepton () (ii) cascade decay of gluinos to top
quarks and neutralinos () followed by the decay of
to , and through couplings.
We present two different search procedures which are common to both the
scenarios. While the first one involves the traditional approach with
multi-leptons and -tagged jets, the second one employs the more recent
technique to reconstruct highly energetic hadronically decaying top quarks. We
perform a detailed simulation of the signal as well as all the relevant
Standard Model backgrounds to show that the second procedure offers slightly
better sensitivity for gluino discovery. In both the procedures, a
5 discovery is possible for the gluino mass in the range 1.5 -1.7 TeV
at 14 TeV LHC with 50 fb integrated luminosity.Comment: Event selection cuts optimized, results significantly improved, more
discussions added. Version to appear in JHE
Dark-Photon searches via Higgs-boson production at the LHC
Dark photons mediating long-range forces in a dark sector are
predicted by various new physics scenarios, and are being intensively searched
for in experiments. We extend a previous study of a new discovery process for
dark photons proceedings via Higgs-boson production at the LHC. Thanks to the
non-decoupling properties of the Higgs boson, BR()
values up to a few percent are possible for a massless dark photon, even for
heavy dark-sector scenarios. The corresponding signature consists (for a Higgs
boson at rest) of a striking monochromatic photon with energy , and similar amount of missing energy. We perform a model independent
analysis at the LHC of both the gluon-fusion and VBF Higgs production
mechanisms at 14 TeV, including parton-shower effects, and updating our
previous parton-level analysis at 8 TeV in the gluon-fusion channel by a more
realistic background modeling. We find that a sensitivity can be
reached in the gluon-fusion channel for BR(0.1% with an integrated luminosity of . The corresponding VBF reach is instead restricted to 1%. Such decay
rates can be naturally obtained in dark-photon scenarios arising from unbroken
models explaining the origin and hierarchy of the Yukawa couplings,
strongly motivating the search for this exotic Higgs decay at the LHC.Comment: 8 pages, 3 figure
Enhancing the ttH signal through top-quark spin polarization effects at the LHC
We compare the impact of top-quark spin polarization effects in Higgs boson
production in association with top-quark pairs and in corresponding backgrounds
at the LHC. Because of the spin-zero nature of the Higgs boson, one expects, in
the chiral limit for the top quarks, a substantial complementarity in
spin correlations for a Higgs decaying into fermions/gauge-bosons and
spin correlations for the corresponding irreducible backgrounds. Although top mass effects in production are in
general dominant, and seriously spoil the chiral-limit expectations, one can
find observables that capture the angular spin correlations and can
help in separating the signal from irreducible backgrounds. In particular, we
show that, for both and , taking into account
spin correlations in production and irreducible
backgrounds could appreciably improve the LHC sensitivity to the
channel.Comment: 18 pages, 9 figures; implementation of cuts corrected in figures 7-
Higgs-boson production in association with a Dark Photon in collisions
We study the production of a Higgs boson recoiling from a massless invisible
system in collisions. This is a quite distinctive signature that
can arise when the Higgs boson is produced in association with a massless dark
photon, which can happen in BSM scenarios foreseeing an extra unbroken
gauge group. Dark photons can indeed acquire effective couplings to the Higgs
boson as occurs in models recently proposed to generate exponentially-spread
Yukawa couplings. We analyze the signal and corresponding backgrounds for , and estimate ILC and FCC-ee sensitivities in a model-independent
way.Comment: 25 pages, 12 figures; Conclusion Section expandend, to appear in
JHEP; v5: typographical errors correcte
ASSESSMENT OF THE QUADRUPLE INJECTION STRATEGY OVER TRIPLE INJECTIONS TO IMPROVE EMISSIONS, PERFORMANCE AND NOISE OF THE AUTOMOTIVE DIESEL ENGINE
The present study aims at investigating effectiveness of the quadruple (early-pilot-main-after [epMa]) injection strategy over three different triple [early-main-after (eMa), early-pilot-main (epM) and pilot-main-after (pMa)] injection scheduling in terms of emissions, performance [brake specific fuel consumption (BSFC), torque, brake thermal efficiency (BTE) and fuel economy] and noise. The experimentation was carried out on a heavy-duty BS-IV diesel engine with 45% EGR fraction and fixed main injection (Crank-angle) scheduling at eight different RPMs and three loads of engine (20%, 60% and 100%) using design of experiments(DOE). This comprehensive study showed that the quadruple injection strategy provides optimum results in both performance and emissions compared to the promising three triple injection strategy. The quadruple injection strategy exhibits the best BTE at all operating conditions and best BSFC at medium to high-speed zone around 0.5–1% inline to reduce combustion noise (CN) level, especially at low speeds and low to medium load of 0.2–2.2 dBA. Among triple injections, the pMa shows the best performance in BSFC, BTE, smoke and THC emissions. The epM is the best in the CO emissions and torque performance in the low-speed zone. Smoke value is marginally higher for the epMa at low to medium speed than the pMa, although average smoke emissions were the best. Taken together, the overall PM emission level was marginally better than Triple Injections, due to the impact of double pilots in combination with post-injection. In addition, NOx emissions were improved (around 3–6%) significantly with quadruple than with triple injections. The epMa injection scheduling also showed improvement in constant speed fuel economy and in pass-by-noise at the vehicle
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