arXiv subjects

Amit Chakraborty

Publications and source records attributed to Amit Chakraborty.

62 records · Page 4Linked to original sources

arXiv2015

Status of MSSM Higgs Sector using Global Analysis and Direct Search Bounds, and Future Prospects at the HL-LHC

In this paper, we search for the regions of the phenomenological minimal supersymmetric standard model (pMSSM) parameter space where one can expect to have moderate Higgs mixing angle ($α$) with relatively light (up to 600 GeV) additional Higgses after satisfying the current LHC data. We perform a global fit analysis using most updated data (till December 2014) from the LHC and Tevatron experiments. The constraints coming from the precision measurements of the rare b-decays $B_s \to μ^+ μ^-$ and $b\to s γ$ are also considered. We find that low $M_{A}$ $(\lesssim 350)$ and high $\tanβ$ $(\gtrsim 25)$ regions are disfavored by the combined effect of the global analysis and flavour data. However, regions with Higgs mixing angle $α\sim$ 0.1 - 0.8 are still allowed by the current data. We then study the existing direct search bounds on the heavy scalar/pseudoscalar ($\rm H/A$) and charged Higgs boson ($\rm H^\pm$) masses and branchings at the LHC. It has been found that regions with low to moderate values of $\tanβ$ with light additional Higgses (mass $\le$ 600 GeV) are unconstrained by the data, while the regions with $\tanβ>$ 20 are excluded considering the direct search bounds by the LHC-8 data. The possibility to probe the region with $\tanβ$ $\le$ 20 at the high luminosity run of LHC are also discussed, giving special attention to the $\rm H \to hh$, $\rm H/{A} \to t \bar t$ and $\rm H/{A} \to τ^{+}τ^{-}$ decay modes.

hep-ph↗

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.

hep-ph↗

arXiv2014

HIPAD - A Hybrid Interior-Point Alternating Direction algorithm for knowledge-based SVM and feature selection

We consider classification tasks in the regime of scarce labeled training data in high dimensional feature space, where specific expert knowledge is also available. We propose a new hybrid optimization algorithm that solves the elastic-net support vector machine (SVM) through an alternating direction method of multipliers in the first phase, followed by an interior-point method for the classical SVM in the second phase. Both SVM formulations are adapted to knowledge incorporation. Our proposed algorithm addresses the challenges of automatic feature selection, high optimization accuracy, and algorithmic flexibility for taking advantage of prior knowledge. We demonstrate the effectiveness and efficiency of our algorithm and compare it with existing methods on a collection of synthetic and real-world data.

stat.ML↗

arXiv2014

The 125 GeV Higgs signal at the LHC in the CP Violating MSSM

The ATLAS and CMS collaborations have observed independently at the Large Hadron Collider (LHC) a new Higgs-like particle with a mass $M_h \sim$ 125 GeV and properties similar to that predicted by the Standard Model (SM). Although the measurements indicate that this Higgs-like boson is compatible with the SM hypothesis, however due to large uncertainties in some of the Higgs detection channels, one still has the possibility of testing this object as being a candidate for some Beyond the SM (BSM) physics scenarios, for example, the Minimal Supersymmetric Standard Model (MSSM), in the CP-conserving version (CPC-MSSM). In this paper, we evaluate the modifications of these CPC-MSSM results when CP-violating (CPV) phases are turned on explicitly, leading to the CP-violating MSSM (CPV-MSSM). We investigate the role of the CPV phases in (some of) the soft Supersymmetry (SUSY) terms on both the mass of the lightest Higgs boson $h_1$, and the rates for the processes $gg \rightarrow h_1 \rightarrow γγ$, $gg \rightarrow h_1 \rightarrow ZZ^*\rightarrow 4l$, $gg \rightarrow h_1 \rightarrow WW^*\rightarrow l νl ν$, $pp \rightarrow V h_1 \rightarrow V b\bar b$ and $pp \rightarrow V h_1 \rightarrow V τ^+τ^-$, ($V \equiv W^\pm, Z$) at the LHC, considering the impact of the flavor constraints as well as the constraints coming from the Electric Dipole Moment (EDM) measurements. We find that the imaginary part of the top and bottom Yukawa couplings can take very small but non-zero values even after satisfying the recent updates from LHC. Our study shows that the CPV-MSSM provides an equally potential solution (like its CP-conserving (CPC) counterpart) to the recent LHC Higgs data. Improvement in different Higgs coupling measurements is necessary in order to test the possibility of probing the small dependence on these CPV phases in the Higgs sector of the MSSM.

hep-ph↗

arXiv2014

Study of Baryonic R-Parity Violating MSSM Using Jet Substructure Technique at the 14 TeV LHC

We study the discovery reach of the gluino ($\widetilde{g}$) and the lightest stop squark ($\widetilde{t}_1$) with baryonic R-parity violation (UDD type) in the context of Minimal Supersymmetric Standard Model (MSSM) at the 14 TeV run of the LHC. We consider the gluino pair production process followed by its decay to a top quark and a real or virtual stop squark. The top quark produced from the decay of the gluino can have sufficient transverse momentum to appear as a single fat jet. We apply the jet substructure technique to tag such a hadronically decaying boosted top quark and find that gluino mass up to 1.65 TeV can be discovered whereas exclusion limit extends up to 1.9 TeV at the 14 TeV LHC with 300 $\rm fb^{-1}$ luminosity. We also briefly discuss the discovery prospect of the boosted stop squark which may be identified as a narrow resonance in the jet mass distribution.

hep-ph↗

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.

hep-ph↗

arXiv2013

Implications of 98 GeV and 125 GeV Higgs scenario in non-decoupling SUSY with updated ATLAS, CMS and PLANCK data

We discuss both MSSM and NMSSM scenarios in which the lightest Higgs boson with $m_h=98$~GeV is consistent with the small excess ($\sim 2.3 σ$) observed at the LEP in $e^+ e^-\rightarrow Zh$, with $h \rightarrow b {\bar b}$ process and the heavier Higgs boson of mass close to 125~GeV as the observed candidate of the SM Higgs like particle at the LHC. We show the allowed regions in the non-decoupling Higgs zone of MSSM parameter space which are consistent with several low energy constraints coming from heavy flavour physics, latest experimental data on Higgs signals and lower limit on superparticle masses from 7~TeV and 8~TeV LHC run. We also implement the constraints from the relic density of the cold dark matter as obtained from the recent PLANCK data. Additionally, we discuss the possibility of observing the light Higgs boson of mass 98~GeV at the 14~TeV LHC run via $pp \rightarrow V h$, with $h \rightarrow b \bar b$ using the technique of jet substructure. Our analysis shows that at 14~TeV LHC run with 300 ${\rm fb}^{-1}$ luminosity the signal efficiency of such a light Higgs boson is at most 2.5$σ$. Finally, we make a comment on the prospect of proposed $e^+ e^-$ ILC to discover/exclude this light Higgs boson.

hep-ph↗

arXiv2012

Using Jet Substructure at the LHC to Search for the Light Higgs Bosons of the CP-Violating MSSM

The CP-violating version of the Minimal Supersymmetric Standard Model (MSSM) is an example of a model where experimental data do not preclude the presence of light Higgs bosons in the range around 10 -- 110 GeV. Such light Higgs bosons, decaying almost wholly to b-bbar pairs, may be copiously produced at the LHC, but would remain inaccessible to conventional Higgs searches because of intractable QCD backgrounds. We demonstrate that a significant number of these light Higgs bosons would be boosted strongly enough for the pair of daughter $b$-jet pairs to appear as a single `fat' jet with substructure. Tagging such jets could extend the discovery potential at the LHC into the hitherto-inaccessible region for light Higgs bosons.

hep-ph↗