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.
120327378
ON PRODUCTION OF SOME NEUTRAL MESONS IN PION-INDUCED REACTIONS AT HIGH ENERGIES AND AT LARGE TRANSVERSE MOMENTA
The measured data on production of π0 and η mesons at large transverse momenta in high energy π-P and π-Be interactions have here been analyzed with the help of a newly-developed phenomenological model, called Combinational Approach(CA). The results so obtained on the basis of the CA are seen to be in fair agreement with the measured data. Furthermore, the results so obtained have been compared with both some previous measuremnts by the same group and some models of the standard variety type, e.g., PYTHIA, HERWIG.
14665554
The CWKB Method of Particle Production in a Periodic Potential
In this work we study the particle production in time dependent periodic potential using the method of complex time WKB (CWKB) approximation. In the inflationary cosmology at the end of the inflationary stage, the potential becomes time dependent as well as periodic. Reheating occurs due to particle production by the oscillating inflaton field. Using CWKB we obtain almost identical results on catastrophic particle production as obtained by others.
122420945
Setup optimization toward accurate ageing studies of gas filled detectors
Abstract An infrastructure has been set up at the GSI detector laboratory to study the influence of construction materials on the ageing properties of gas filled detectors, such as multi-wire proportional chamber (MWPC), gas electron multiplier (GEM). Optimization of an ageing setup was performed by observing the variation of the normalized gain obtained using two identical MWPCs. An accuracy in the relative gain measurement below 1% has been achieved by monitoring environmental conditions and by systematic improvements of the measuring equipment. Ageing test of fiberglass G11 has been performed.
117379664
Evolution of Dynamical Coupling in Scalar Tensor Theory from Noether Symmetry
We present the gravitational coupling function ω(φ) in the vacuum scalar-tensor theory as allowed by the Noether symmetry. We also obtain some exact cosmological solutions in the spatially homogeneous and isotropic background thereby showing that the attractor mechanism is not effective enough to reduce the theory to Einstein theory. It is observed that, asymptotically, the scalar tensor theory goes over to Einstein theory with a finite value of ω. This work thus supports earlier works in this direction.
120084598
Study of the Influence of Construction Materials on the Ageing Properties of High Rate Gas Detectors
Abstract An infrastructure has been set up at the GSI detector laboratory to study the inﬂuence of construction materials on the ageing properties of gas ﬁlled detectors such as multi wire proportional chambers (MWPC), gas electron multipliers (GEM) etc. As a ﬁrst step an ageing test of silicone-based glue (RTV-3145)(Dow Corning) has been performed. In this article details of the experimental set-up and the ﬁrst result on (RTV3145) will be presented.
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.
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.
118476208
Chargino reconstruction in supersymmetry with long-lived staus
We consider a supersymmetric (SUSY) scenario including right-handed neutrinos, one of whose scalar superpartners is the lightest SUSY particle (LSP). The distinguishing feature in the collider signal of SUSY in such a case is not missing energy but a pair of charged tracks corresponding to the next-to-lightest SUSY particle, when it is, as in the case considered, a stau. Following up on our recent work on neutralino reconstruction in such cases, we explore the possibility of reconstructing charginos, too, through a study of transverse mass distributions in specified final states. The various steps of isolating the transverse momenta of neutrinos relevant for this are outlined, and regions of the parameter space where our procedure works are identified. E-mail: sbiswas@mri.ernet.in E-mail: biswarup@mri.ernet.in
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.