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.
124380925
Development of High Resolution Gas Filled Detector for High Energy Physics Experiments
Resistive Plate Chamber (RPC) is one of the most widely used large area gas filled detectors in experimental high energy physics with a potential to be used in PET imaging. Main characteristics of RPC, which have made it highly attractive are excellent time resolution (∼ 1-2 ns for single-gap and ∼ 50 ps for multi-gap) and good position resolution (1 cm to ∼ 100 μm) coupled with the low cost of fabrication. Till now, RPCs have found their applications in HEP experiments like STAR, ALICE, ATLAS, CMS, BELLE, BaBar, BESIII and neutrino experiments e.g. OPERA. The single gap RPC, first developed by R. Santonico and R. Cardarelli is a gas-filled charged particle detector consisting of two parallel plate electrodes made of resistive materials such as bakelite or glass (bulk resistivity ∼ 10 10 Ω cm) enclosing the gas volume [1]. A uniform gap of 2 mm is maintained by spacers made of materials like polycarbonate whose resistivity is more than the resistivity of the electrode plates. By applying a d.c. high voltage to these electrodes, an electric field is generated across the gas gap. A passing charged particle creates an avalanche in the gas. High resistivity of the electrodes prevents discharge to spread over entire gas volume. The created electron and positive ion pairs while traveling towards the respective electrodes induces signal on the pickup strips placed over the electrode plates. The generated charge is deposited on a small region of the electrode plate and the spot is slowly recharged by current flowing through the plate. If the electric field is even more intense, a ’spark’ breakdown can be initiated by the avalanche.
126259637
Necessity of Non-Boltzmann Statistics for Finite System in Equilibrium at Ultra Low Temperatures
116908997
On Production of `Soft' Particles in Au+Au and Pb+Pb Collisions at High Energies
Production of low-$p_T$ (soft) hadronic particles in high energy collisions constitutes a significant corner of special interests and problems, as the perturbative quantum chromodynamics (pQCD) does not work in this region. We have probed here into the nature of the light particle production in two symmetric nuclear collisions at two neighbouring energies with the help of two non-standard models. The results are found to be in good agreement with data. Despite this, as the models applied here are not intended to provide deep insights into the actual physical processes involved in such collisions, the phenomenological bounds and constraints which cannot be remedied for the present continue to exist.
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.
117182698
Does Operator Ordering Need Wormhole Dominance in the Wavefunction of the Universe?
In dealing with the wavefunction of the universe there is a debate on the various proposals about the boundary condition of the wavefunction of the universe. At present we have three proposals, namely, the Hartle-Hawking proposal, the tunneling proposal and the Linde proposal. Recently it has been argued that the operator ambiguity factor has a decisive role in deciding the consequences of the various wavefunction at the zero scale factor region. In the present paper we discuss the role of operator ordering in the light of wormhole dominance proposal proposed by one of the authors and compare the results with that of others obtained earlier. We present an interpretation of operator ordering as a contribution of some sort of matter fields and discuss the role of complex path WKB analysis in avoiding the initial singularity and allowing us to incorporate the contribution of wormhole in the wavefunction of the universe.