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
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.
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.
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.
121313738
Particle Production in de Sitter Space-Time
The definition of vacuum in curved space–time is a delicate object. With Minkowski-like vacuum definition, the current has a characteristic behavior in Robertson–Walker space–time. In this work we study the behavior of Dirac current in a de Sitter space–time. The rapid oscillations of current is observed with respect to time and indicate vigorous instability in initial vacuum and is interpreted as vigorous particle production.
120497919
Radiochemical measurements of 10Be and 7Be formation cross sections in oxygen by 135 and 550 MeV protons
Abstract Radiochemical measurements of the activities of 10 Be and 7 Be in oxygen due to the bombardment of water samples by protons of energies 135 and 550 MeV are reported. The ratios σ( 10 Be ) σ( 7 Be ) of the cross sections in oxygen are found to be 0.19 ± 0.01 and 0.32 ± 0.02 for 135 and 550 MeV protons, respectively, based on t 1 2 ( 10 Be) = 2.7 × 10 6 y and t 1 2 ( 7 Be) = 53.6 d . Using the best estimate of the excitation function of 7 Be in oxygen, the formation cross sections for 10 Bein oxygen are estimated to be 1.0 ± 0.06 and 2.9 ± 0.2 mb for protons of energies 135 and 550 MeV respectively. Cross sections for 10 Be in oxygen, averaged over the energy spectrum of cosmic rays, and based on the observations of its activity in meteorites and deep-sea sediments are discussed. The implication of the present measurements for the use of the 10 Be isotope as a “clock” to estimate the “age” of cosmic rays is briefly noted.
121046658
Aharonov-Bohm effect from five dimensional space-time
We present an alternative non-quantum mechanical description of Aharonov-Bohm effect.
121340460
Particle production, back reaction and singularity avoidance
We consider particle production in Robertson-Walker spacetime as particle-antiparticle rotation. We thereby obtain a scale factor that guarantees particle production. We then study quantum field effects in spatially flat homogeneous and isotropic spacetime with energy density of created particles and one loop quantum correction as back reaction. In the numerical solution initial values are determined from particle production simulated scale factor and obtain the evolution of the universe both at early and late times having a bounce.
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.