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.
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.
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.
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.
18233616
Neutrino Oscillation as Coupled vibration
Neutrino oscillation is visualized as coupled vibrations. Unlike existing models describing neutrino oscillations, our model involving a single fundamental mass parameter $m$ and first discussed in the context of a possible boson oscillation demonstrates that for a self consistent theory there should be three types of bosons paired with maximal mixing. The argument is easily extended to neutrinos (fermions) with the exception that in the case of boson oscillation means periodic variation of particle number, whereas in the case of fermions the particle number does not change, only the mass oscillates. The fermionic vacuum is not really empty but filled with zero energy fermions. The oscillation length calculated perturbatively conforms to the experimental findings. Also there is no fermionic number violation in our model.
14676562
Paradigm Shifts and a Possible Resolution of the PAMELA-Paradox in Astroparticle Physics
Very recently, PAMELA Collaboration has formally reported two sets of data on positron and antiproton flux measurements done at very high energies and with unprecedented accuracy. The reports reveal a puzzle of great topical interest and importance : it is decisively found that there is a sharp smooth rise of the positron fraction, whereas for antiproton production no such rises occur; rather the fraction either flattens, or shows signs of falling off gradually with increasing energies. The present work is just an attempt to decipher the riddle with the help of a host of radically new ideas about the particle-structure, the multiparticle-production mechanisms and the concept of nucleon break-downs into the constituent partons. The application of these ideas found remarkable successes in the past; exactly similar or more striking are the findings by the present study.
126259637
Necessity of Non-Boltzmann Statistics for Finite System in Equilibrium at Ultra Low Temperatures
73560476
FLAVOUR-CHANGING RADIATIVE TOP QUARK DECAY
Top quark has now come into existence [1]. The top quark mass is approximately lying in the range 160 GeV to 180 GeV as measured by CDF and DO/ [2,3]. Transition for heavy quarks flavour-changing neutral process attracts much interest recently. The radiative b quark decay attracts much attention for last few years and the theoretical calculations are more or less synchronized with experimental observations. It has been argued that the experimental data provides more informations about the restrictions on the standard model (SM) [4], and QCD corrections [5,6]. The predictions of the standard model are in conformity with the CLEO data at the 2σ level. The new results opened the scope for investigations in various classes of models, namely; anomalous top-quark couplings [7], anomalous trilinear gauge couplings [8], fourth generation [9], two-Higgs-doublet model [10], three-Higgs-doublet model [11], supersymmetry [12], extended technicolour [13], leptoquarks [14] and left-right symmetric models [15]. The results are found to be sensitive to the theoretical calculations of such decays.
16527600
The CWKB Method of Particle Production Near the Chronology Horizon
In this paper we investigate the phenomenon of particle production of massles scalar field, in a model of spacetime where the chronology horizon could be formed, using the method of complex time WKB approximation (CWKB). For the purpose, we take two examples in a model of spacetime, one already discussed by Sushkov, to show that the mode of particle production near chronology horizon possesses the similar characteristic features as are found while discussing particle production in time dependent curved background. We get identical results as that obtained by Sushkov in this direction. We find, in both the examples studied, that the total number of particles remain finite at the moment of the formation of the chronology horizon.