Department of Physics

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Subject: search.filters.subject.Supersymmetry

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    Constraining slepton and chargino through compressed top squark search
    (Springer, 2018-04) Mandal, Tanmoy
    We examine the compressed mass spectrum with sub-TeV top squark as lightest colored (s)particle in natural supersymmetry (SUSY). Such spectra are searched along with an additional hard jet, not only to boost the soft decay particles, also to yield enough missing transverse momentum. Several interesting kinematic variables are proposed to improve the probe performance for this difficult region, where we concentrate on relatively clean dileptonic channel of the top squark decaying into lightest neutralino (χ 01 ), which is also the lightest supersymmetric particle. In this work, we investigate the merit of these kinematic variables, sensitive to compressed mass region extending the search by introducing additional states, chargino and slepton (sneutrino) having masses in between the and χ 01 . Enhanced production and lack of branching suppression are capable of providing a strong limit on chargino and slepton/sneutrino mass along with top squark mass. We perform a detailed collider analysis using simplified SUSY spectrum and found that with the present LHC data can be excluded up to 710 GeV right away for χ of 640 GeV for a particular mass gap between different states.
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    Working group report: Beyond the standard model
    (IAS, 2003) Vaidya, Rishikesh
    The working group on Beyond the StandardModel concentrated on identifying interesting physics issues in models of ‘new physics’ which go beyond the standard model. There were two aspects to this activity. One was to familiarise participants with the areas, for which the expertise available among the participants was very useful. The other aspect involved is the identification and formulation of research problems out of these issues, with the ultimate aim of building fruitful collaborations. In view of the range of current interest in the high energy physics community, this working group was organised according to the following focal themes:
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    Radiative B decays in Supersymmetry without R-parity
    (ARXIV, 2004-11) Vaidya, Rishikesh
    We present a systematic analysis of all the contributions at the leading log order to the branching ratio of the inclusive radiative B decay, B --> X_s + gamma in the framework of supersymmetry without R-parity. The relevant set of four-quark operators involved in QCD running are extended from 6 (within SM and MSSM) to 24, with also many new contributions to the Wilson coefficients of (chromo)magnetic penguins for either chiral structure. We present complete analytical results here without any a priori assumptions on the form of R-parity violation. Mass eigenstate expressions are given, hence the results are free from the commonly adopted mass-insertion approximation. In the numerical analysis, we focus here only on the influence of the trilinear lambda-prime couplings and report on the possibility of a few orders of magnitude improvement for the bounds on a few combinations of the lambda-prime couplings. Our study shows that the Wilson coefficients of the current-current operators due to R-parity violation dominate over the direct contributions to the penguins. However, the inter-play of various contributions is complicated due to the QCD corrections which we elaborate here.
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    Radiative B decays in supersymmetry without R parity
    (APS, 2005-03) Vaidya, Rishikesh
    We present a systematic analysis of all the contributions at the leading log order to the branching ratio of the inclusive radiative decay B→Xs+γ in the framework of supersymmetry without R parity. The relevant set of four-quark operators involved in QCD running are extended from six (within the standard model and the minimal supersymmetric standard model) to 24, with also many new contributions to the Wilson coefficients of (chromo)magnetic penguins for either chiral structure. We present complete analytical results here without any a priori assumptions on the form of R-parity violation. Mass-eigenstate expressions are given; hence the results are free from the commonly adopted mass-insertion approximation. In the numerical analysis, we focus here only on the influence of the trilinear λ′ijk couplings and report on the possibility of a few orders of magnitude improvement for the bounds on a few combinations of the λ′ couplings. Our study shows that the Wilson coefficients of the current-current operators due to R-parity violation dominate over the direct contributions to the penguins. However, the interplay of various contributions is complicated due to the QCD corrections which we elaborate here