arXiv subjects

Dipan Sengupta

Publications and source records attributed to Dipan Sengupta.

48 records · Page 3Linked to original sources

arXiv2015

Closing in on compressed gluino-neutralino spectra at the LHC

A huge swath of parameter space in the context of the Minimal Supersymmetric Standard Model (MSSM) has been ruled at after run I of the LHC. Various exclusion contours in the $m_{\tilde{g}}-\m_{\tildeχ_{1}^{0}}$ plane were derived by the experimental collaborations, all based on three-body gluino decay topologies. These limits are however extremely model dependent and do not always reflect the level of exclusion. If the gluino-neutralino spectrum is compressed, then the current mass limits can be drastically reduced. In such situations, the radiative decay of the gluino $\gino \ra g \neut{1}$ can be dominant and used as a sensitive probe of small mass splittings. We examine the sensitivity of constraints of some Run I experimental searches on this decay after recasting them within the \texttt{MadAnalysis5} framework. The recasted searches are now part of the \texttt{MadAnalysis5} Public Analysis Database. We also design a dedicated search strategy and investigate its prospects to uncover this decay mode of the gluino at run II of the LHC. We emphasize that a multijet search strategy may be more sensitive than a monojet one, even in the case of very small mass differences.

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arXiv2015

Confronting the Inert Doublet Model with results from Run 1 of the LHC

The Inert Doublet Model (IDM) is a simple extension of the Standard Model (SM) that aims to address the naturalness problem, electroweak baryogenesis and accommodate a viable dark matter (DM) candidate, along with a rich phenomenlogy in terms of collider signatures. In this note, we address the constraints on the IDM by recasting dilepton + missing energy searches performed for Supersymmetry at LHC run-1 using Madanalysis5.

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arXiv2015

Probing the NMSSM via Higgs boson signatures from stop cascade decays at the LHC

Higgs signatures from the cascade decays of light stops are an interesting possibility in the next to minimal supersymmetric standard model (NMSSM). We investigate the potential reach of the light stop mass at the 13 TeV run of the LHC by means of five NMSSM benchmark points where this signature is dominant. These benchmark points are compatible with current Higgs coupling measurements, LHC constraints, dark matter relic density and direct detection constraints. We consider single and di-lepton search strategies, as well as the jet-substructure technique to reconstruct the Higgs bosons. We find that one can probe stop masses up to 1.2 TeV with 300 $\rm fb^{-1}$ luminosity via the di-lepton channel, while with the jet-substructure method, stop masses up to 1 TeV can be probed with 300 $\rm fb^{-1}$ luminosity. We also investigate the possibility of the appearance of multiple Higgs peaks over the background in the fat-jet mass distribution, and conclude that such a possibility is viable only at the high luminosity run of 13 TeV LHC.

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arXiv2013

Probing the flavor violating scalar top quark signal at the LHC

The Large Hadron Collider(LHC) has completed its run at 8 TeV with the experiments ATLAS and CMS having collected about 25 $\rm fb^{-1}$ of data each. Discovery of a light Higgs boson, coupled with lack of evidence for supersymmetry at the LHC so far, has motivated studies of supersymmetry in the context of naturalness with the principal focus being the third generation squarks. In this work, we analyze the prospects of the flavor violating decay mode $\rm \tilde{t}_1\to cχ_{1}^{0}$ at 8 and 13 TeV center of mass energy at the LHC. This channel is also relevant in the dark matter context for the stop-coannihilation scenario, where the relic density depends on the mass difference between the lighter stop quark ($\tilde{t}_1$) and the lightest neutralino($χ_{1}^{0}$) states. This channel is extremely challenging to probe, specially for situations when the mass difference between the lighter stop quark and the lightest neutralino is small. Using certain kinematical properties of signal events we find that the level of backgrounds can be reduced substantially. We find that the prospect for this channel is limited due to the low production cross section for top squarks and limited luminosity at 8 TeV, but at the 13 TeV LHC with 100 $fb^{-1}$ luminosity, it is possible to probe top squarks with masses up to $\sim$ 450 GeV. We also discuss how the sensitivity could be significantly improved by tagging charm jets.

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arXiv2013

Stop and sbottom search using dileptonic $M_{T2}$ variable and boosted top technique at the LHC

The ATLAS and CMS experiments at the CERN LHC have collected about 20 $fb^{-1}$ of data each at the end of their 8 TeV run, and ruled out a huge swath of parameter space in the context of Minimally Supersymmetric Standard Model(MSSM). Limits on masses of the gluino ($\tilde{g}$) and the squarks of the first two generations($\tilde{q}$) have been pushed to the TeV range. Light third generation squarks namely stop and sbottom of sub-TeV masses, on the other hand, are still allowed by their direct search limits. Interestingly, the discovery of a Standard Model(SM) higgs boson like particle with a mass of $\sim$ 125 GeV favours a light third generation which is also motivated by naturalness arguments. Decays of stop and sbottom quarks can in general produce a number of distinct final states which necessitate different search strategies in the collider experiments. In this paper we, on the other hand, propose a general search strategy to look for third generation squarks in the final state which contains a top quark in the sample along with two additional hard leptons and substantial missing transverse momentum. We illustrate that a search strategy using the dileptonic $M_{T2}$, the effective mass $m_{eff}$ and jet substructure to reconstruct the hadronic top quark can be very effective to reduce the SM backgrounds. With the proposed search strategy, we estimate that the third generation squarks with masses up to about 800 GeV can be probed at the 14 TeV LHC with a 100 $fb^{-1}$ data set. We also interpret our results in two simplified scenarios where we consider the stop (sbottom) pair production followed by their subsequent decay to a top quark and the second lightest neutralino (lightest chargino). In this case also we find that stop (sbottom) mass up to 1 TeV (0.9 TeV) can be discovered at the 14 TeV LHC with 100 $fb^{-1}$ integrated luminosity.

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arXiv2013

Looking for an Invisible Higgs Signal at the LHC

While the recent discovery of a Higgs-like boson at the LHC is an extremely important and encouraging step towards the discovery of the {\it complete} standard model(SM), the current information on this state does not rule out possibility of beyond standard model (BSM) physics. In fact the current data can still accommodate reasonable values of the branching fractions of the Higgs into a channel with `invisible' decay products, such a channel being also well motivated theoretically. In this study we revisit the possibility of detecting the Higgs in this invisible channel for both choices of the LHC energies, 8 and 14 TeV, for two production channels; vector boson fusion(VBF) and associated production($ZH$). In the latter case we consider decays of the $Z$ boson into a pair of leptons as well as a $b \bar b$ pair. For the VBF channel the sensitivity is found to be more than $5 σ$ at both the energies up to an invisible branching ratio ${\cal B}r_{invis} \sim 0.80$, with luminosities $\sim 20/30 {\rm fb}^{-1}$. The sensitivity is further extended to values of ${\cal B}r_{invis} \sim 0.25$ for $300 {\rm fb}^{-1}$ at 14 TeV. However the reach is found to be more modest for the $ZH$ mode with leptonic final state; with about $3.5 σ$ for the planned luminosity at 8 TeV, reaching $8 σ$ only for 14 TeV for $50 {\rm fb}^{-1}$. In spite of the much larger branching ratio of the $Z$ into a $b \bar b$ channel compared to the dilepton case, the former channel, can provide useful reach upto ${\cal B}r_{invis} \gsim 0.75$, only for the higher luminosity ($300{\rm fb}^{-1}$) option using jet-substructure and jet clustering methods for $b$-jet identification.

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arXiv2013

Searching the sbottom in the four lepton channel at the LHC

Direct searches at the Large Hadron Collider (LHC) have pushed the lower limits on the masses of the gluinos ($\tilde{g}$) and the squarks of the first two generations ($\tilde{q}$) to the TeV range. On the other hand, the limits are rather weak for the third generation squarks and masses around a few hundred GeV are still allowed. A comparatively light third generation of squarks is also consistent with the lightest Higgs boson with mass $\sim$ 125 GeV. In view of this, we consider the direct production of a pair of sbottom quarks ($\tilde{b}_1$) at the LHC and study their collider signatures. We focus on the scenario where the $\tilde{b}_1$ is not the next-to-lightest supersymmetric particle (NLSP) and hence can also decay to channels other than the commonly considered decay mode to a bottom quark and the lightest neutralino ($\tildeχ^0_1$). For example, we consider the decay modes containing a bottom quark and the second neutralino ($\tilde{b}_1 \to b \tildeχ^0_2$) and/or a top quark and the lightest chargino ($\tilde{b}_1 \to t \tildeχ^{\pm}_1$) following the leptonic decays of the neutralino, chargino and the top quark giving rise to a 4 leptons ($\ell$) + 2 $b$-jets + missing transverse momentum ($\PMET$) final state. We show that an sbottom mass $\lesssim$ 550 GeV can be probed in this channel at the 14 TeV LHC energy with integrated luminosity $\lesssim$ 100 fb$^{-1}$.

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arXiv2012

Probing Supersymmetry using Event Shape variables at 8 TeV LHC

We have revisited the prospects of Supersymmetry(SUSY) searches at the LHC with 7 TeV energy along with the prediction of the discovery potential at 8 TeV energy assuming an integrated luminosity 5 $fb ^{-1}$ and 20 $\invfb$ with mSUGRA/CMSSM as a model framework. We discuss further optimization of our selection strategy which is based on the hadronic event shape variables. Evaluating the standard model backgrounds and signal rates in detail we predict the discovery reach in the $m_0 - m_{1/2}$ plane for 7 TeV with 5$\invfb$ luminosity. We also present the discovery reach for 8 TeV energy with an integrated luminosity 5$\invfb$ and 20 $\invfb$. A comparison is made between our results and the exclusion plots obtained by CMS and ATLAS. Finally, discovery reach in the gluino and squark mass plane at the 7 TeV and 8 TeV energy is also presented.

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arXiv2012

Higgs signal in Chargino-Neutralino production at the LHC

We have analyzed the prospect of detecting a higgs signal in mSUGRA/CMSSM based Supersymmetric(SUSY) model via chargino-neutralino($\CH_1\N0_2$) production at 8 TeV and 14 TeV LHC energy. The signal is studied in the channel with $\ell + b \bar b + \PMET$ following the decays, $\CH_1 \to W^\pm \N0_1$, $\N0_2 \to \N0_1 h$ and $h \to b \bar b$. In this analysis reconstruction of the higgs mass out of two b-jets plays a very crucial role in determining the signal to background ratio. We follow two techniques to reconstruct higgs mass: (A) using two identified b-jets, (B) using jet substructure technique. In addition, imposing a certain set of selection cuts we observe the significance is better for the latter method. We find that a viable signal can be obtained for the higgs mass $\sim$ 125 GeV with an integrated luminosity 100 $\lumi$ for both 8 and 14 TeV LHC energy.

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arXiv2012

How Constrained is the cMSSM?

We study the allowed parameter space of the constrained minimal supersymmetric Standard Model (cMSSM) in the light of direct searches, constraints from $B$-physics (including the recent measurement of the branching ratio for $B_s \to μ^+μ^-$) and the dark matter relic density. For low or moderate values of $\tanβ$, the strongest constraints are those imposed by direct searches, and therefore, large areas of the parameter space are still allowed. In the large $\tan β$ limit, however, the $B$-physics constraints are more restrictive, effectively forcing the squark and gluino masses to lie close to or above a TeV. A light Higgs boson could dramatically change the allowed parameter space, but we need to know its mass precisely for this to be effective. We emphasize that it is still too early to write off the cMSSM, even in the large $\tanβ$ limit. Finally we explore strategies to extend the LHC search for cMSSM signals beyond the present reach of the ATLAS and CMS Collaborations.

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arXiv2011

Probing a Mixed Neutralino Dark Matter Model at the 7 TeV LHC

We have analyzed the prospect of probing a non-universal gaugino mass model of mixed bino-higgsino dark matter at the current 7 TeV run of LHC. It provides cosmologically compatible dark matter relic density over two broad bands of parameters, corresponding to $m_{\gl} < m_{\sq}$ and $m_{\gl} \sim m_{\sq}$. The SUSY spectrum of this model has two distinctive features : (i) an approximate degeneracy among the lighter chargino and neutralino masses, and (ii) an inverted mass hierarchy of squark masses. We find that these features can be exploited to obtain a viable signal upto $m_{\gl} \sim$ 800 GeV over both the parameter bands with an integrated luminosity 5/fb.

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arXiv2011

Event-shape selection cuts for supersymmetry searches at the LHC with 7 TeV energy

We investigate the prospects of supersymmetry searches at the LHC with 7 TeV energy. A new set of selection cuts is proposed based on event shapes to control backgrounds. Our preliminary studies show that it is possible to minimize backgrounds to a significantly low level and conservative estimate suggests that the mass reach can be extended to $\sim$ 1.1 TeV for luminosity 1/fb with a reasonable signal-to-background ratio.

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