119189999
Signatures of supersymmetry with non-universal Higgs mass at the Large Hadron Collider
A bstractWe discuss large non-universality in the Higgs sector at high scale in supersymmetric theories, in the context of the Large Hadron Collider (LHC). In particular, we note that if $$ {{m}_{{{{H}_u}}}}^2 - {{m}_{{{{H}_d}}}}^2 $$ is large and negative $$ ( \simeq {1}{{0}^{{6}}}{\text{Ge}}{{\text{V}}^{{2}}}) $$ at high scale, the lighter slepton mass eigenstates at the electroweak scale are mostly left chiral, in contrast to a minimal supergravity (mSUGRA) scenario. We utilise this feature to explore different chiral structures of the lowest-lying sleptons, using two methods. First, we study final states with same-sign ditaus. We find that an asymmetry parameter reflecting the polarisation of the taus provides a notable distinction. In addition, we study a charge asymmetry in the jet-lepton invariant mass distribution, arising from decay chains of left-chiral squarks leading to leptons of the first two families.
8990987
Neutralino reconstruction in supersymmetry with long-lived staus
We consider a supergravity 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 the 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 of 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 supergravity 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.
118827075
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). Because of 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 that 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.
119294936
Multi-photon signal in supersymmetry comprising non-pointing photon(s) at the LHC
We study a distinct supersymmetric signal of multi-photons in association with jets and missing transverse energy. At least one of these photons has the origin in displaced vertex, thus delayed and non-pointing. We consider a supersymmetric scenario in which the gravitino is the lightest supersymmetric particle (LSP) (with a mass � 1 keV) and the lightest neutralino is the nextto-lightest supersymmetric particle (NLSP). The NLSP decays dominantly into a photon and a gravitino within the detector with a decay length ranging from c�˜ � 50-100 cm. In addition, we assume that the second lightest neutralino and the lightest neutralino are nearly degenerate and this leads to a prompt radiative decay of the next-to-lightest neutralino into a photon and a lightest neutralino with a large branching ratio. Such degenerate neutralinos can be realised in various representations of the SU(5), SO(10), and E(6) Grand Unified Theories (GUTs). The non-pointing photons can be reconstructed at the electromagnetic calorimeter of the ATLAS inner-detector, which have been designed with good timing and directional resolution. We find that with a centre-of-mass energy Ecm = 14 TeV at an integrated luminosity of 100 fb 1 one may see evidence of hundreds of tri-photon events and a few four-photons events at the LHC, in addition to several thousands di-photon events. We also predict the event rates even at the early phase of LHC run.
119294153
Light neutralino dark matter in the MSSM and its implication for LHC searches for staus
A bstractIt was shown in a previous study that a lightest neutralino with mass below 30 GeV was severely constrained in the minimal supersymmetric standard model (MSSM), unless it annihilates via a light stau and thus yields the observed dark matter abundance. In such a scenario, while the stau is the next-to-lightest supersymmetric particle (NLSP), the charginos and the other neutralinos as well as sleptons of the first two families are also likely to be not too far above the mass bounds laid down by the Large Electron Positron (LEP) collider. As the branching ratios of decays of the charginos and the next-to-lightest neutralino into staus are rather large, one expects significant rates of tau-rich final states in such a case. With this in view, we investigate the same-sign ditau and tri-tau signals of this scenario at the Large Hadron Collider (LHC) for two MSSM benchmark points corresponding to light neutralino dark matter. The associated signal rates for these channels are computed, for the centre-of-mass energy of 14 TeV. We find that both channels lead to appreciable rates if the squarks and the gluino are not too far above a TeV, thus allowing to probe scenarios with light neutralinos in the 14 TeV LHC run with 10–100 fb−1.
117459729
A STUDY OF THE FOURTH-GENERATION QUARKS AND FCNC
The decay of the fourth-generation down-type quark b bγ and b bg has been studied as an extension of the standard model using evolution of the mass-based fourth generation CKM matrix with CP violation phase equal to zero. Range of the masses of fourth generation down-type quark b and up-type quark t have been taken with due observance of the constraint imposed by the present experimental value of the ρ parameter, keeping in view the mass difference of the fourth generation quark doublet. The decay width of b bγ also has been studied, however, with correction up to the leading QCD logarithms for six active fla vours after the W boson, t and t quarks have been integrated out using operator product expansion. Strong interaction coupling constant is taken on matching scale of Z boson mass.
116438584
Particle Production in Expanding Spacetime
The complex time WKB (CWKB) approximation has been an effective technique to study particle production in expanding space time. The success of the approximation technique both in time and space dependent gauge has motivated us to study the method in relation to the time dependent approximation. In this work we try to understand the adiabatic and non-adiabatic transition within the framework of complex time WKB approximation. We find that the emergence of thermal radiation is due to some topological characteristics of cosmological spacetime that separates the spacetime into Euclidean and non-Euclidean region. This applies also to blackhole spacetime. The complex WKB trajectory approach shows that the Euclidean vacuum fluctuation is root cause of thermal particle production and is basically a Hawking effect. We also study here the sensitivity of particle production on the rise of scale factor at early times. It is found that the tunneling paths are responsible for the origin of thermal radiation whereas the slope of the scale factor determines the magnitude of the temperature of the thermal particle production. We also substantiate Hu's assertion in this connection.
122130966
Constraint on three-Higgs-doublet model parameters by b → sγ decay considering possibility of the fourth generation in quark sector
Weak radiative B-meson decay has been studied to find plausible constraints on the complex coupling constants that arise from the diagonalization of the charged scalar mixing matrix in Weinberg three-Higgs-doublet model considering possibility of the fourth generation in quark sector. We examined the range of these complex coupling constants taking in to account corrections up to leading QCD logarithms, using evolution of fourth-generation CKM matrix with CP violation phase approximately equal to zero. Range of the mass of fourth generation down-type quark b′ and that of fourth-generation uptype quark t′ have been taken with due consideration of the constraint imposed by the present experimental value of theρ parameter keeping in view the mass difference of the fourth-generation quark doublet.
119282156
Study of the characteristics of GEM detectors for the future FAIR experiment CBM
Abstract Characteristics of triple GEM detector have been studied systematically. The variation of the effective gain and energy resolution of GEM with variation of the applied voltage has been measured with Fe 55 X-ray source for different gas mixtures and with different gas flow rates. Long-term test of the GEM has also been performed.
121767595
Particle production in de Sitter space
Partial creation in de Sitter spacetime is studied in a complex-time WKB approximation. It is found that the particle production parallels the description of particle creation by a collapsing spherical body. The appropriate vacuum for an inflationary early universe is the Hartle--Hawking vacuum; this is also a general feature of expanding spacetimes. The effect of particle production back on the metric is treated in a way that differs from the standard semiclassical approach.