arXiv subjects

Sanjoy Biswas

Publications and source records attributed to Sanjoy Biswas.

25 records · Page 2Linked to original sources

arXiv2012

Light neutralino dark matter in the MSSM and its implication for LHC searches for staus

It 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}.

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arXiv2012

Exploring novel correlations in trilepton channels at the LHC for the minimal supersymmetric inverse seesaw model

We investigate signatures of the minimal supersymmetric inverse seesaw model at the large hadron collider (LHC) with three isolated leptons and large missing energy (3\ell + \mET or 2\ell + 1τ+ \mET, with \ell=e,μ) in the final state. This signal has its origin in the decay of chargino-neutralino (\chpm1\ntrl2) pair, produced in pp collisions. The two body decays of the lighter chargino into a charged lepton and a singlet sneutrino has a characteristic decay pattern which is correlated with the observed large atmospheric neutrino mixing angle. This correlation is potentially observable at the LHC by looking at the ratios of cross sections of the trilepton + \mET channels in certain flavour specific modes. We show that even after considering possible leading standard model backgrounds these final states can lead to reasonable discovery significance at the LHC with both 7 TeV and 14 TeV center-of-mass energy.

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arXiv2011

Signatures of supersymmetry with non-universal Higgs mass at the Large Hadron Collider

We 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 ($\simeq 10^6 {\rm ~GeV^2}$) 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 use this feature to distinguish between non-universal Higgs masses (NUHM) and mSUGRA by two methods. First, we study final states with same-sign ditaus. We find that an asymmetry parameter reflecting the polarization 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, which sets apart an NUHM scenario of the above kind.

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arXiv2010

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 $\sim 1~{keV}$) and the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP). The NLSP decays dominantly into a photon and a gravitino within the detector with a decay length ranging from $cτ_{\tildeχ}\sim$ 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 $E_{cm}=14 ~{TeV}$ 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.

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arXiv2010

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). Due to 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 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.

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arXiv2009

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.

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arXiv2009

Neutralino reconstruction in supersymmetry with long-lived staus

We consider a supergravity (SUGRA) 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 a 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 in 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 SUGRA 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.

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