arXiv subjects

Shankha Banerjee

Publications and source records attributed to Shankha Banerjee.

43 records · Page 3Linked to original sources

arXiv2015

Searching for a Heavy Higgs boson in a Higgs-portal B-L Model

We study the discovery prospects of a heavy neutral scalar arising from a $U(1)_{B-L}$ extension of the Standard Model (SM) during the Large Hadron Collider's high luminosity runs (HL-LHC). This heavy neutral scalar mixes with the SM Higgs boson through a Higgs portal and interacts with the SM particles with an interaction strength proportional to the sine of the mixing angle. The mixing between the two Higgs bosons is constrained by direct and indirect measurements. We choose an experimentally viable mixing angle and explore in detail the $ZZ$ and $WW$ decay modes of the heavy Higgs boson. For the $ZZ$ case, we focus on the cleanest $4\ell$ and $2\ell 2j$ final states and find that a heavy Higgs boson of mass smaller than 500 GeV can be discovered at the HL-LHC. For the $WW$ decay mode, we analyze the $\ell jj \slashed{E}_T$ signature. We implement novel background reduction techniques in order to tackle the huge background by performing both cut-based and multivariate analyses. However, large backgrounds render this channel challenging. We briefly discuss the discovery prospects of the heavy $Z'$-boson arising in this model.

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arXiv2015

Cornering dimension-6 $HVV$ interactions at high luminosity LHC: the role of event ratios

We suggest a way of improving the probes on dimension-6 CP-conserving $HVV$ interactions ($V$ = $W$, $Z$, $γ$), from the LHC data on the Higgs boson to be available in the 14 TeV run with an integrated luminosity of $3000$ fb$^{-1}$. We find that the ratios of total rates in different channels can be quite useful in this respect. This includes ratios of event rates in (a) different final states for the Higgs produced by the same production mechanism, and (b) the same final state from two different production modes. While most theoretical uncertainties cancel in the former, the latter helps in the case of those operators which shift the numerator and denominator in opposite directions. Our analysis, incorporating theoretical, systematic and statistical uncertain, leads to projected limits that are better than the strongest ones obtained so far from precision electroweak as well as LHC Higgs data. Moreover, values of the coefficients of the dimension-6 operators, which are allowed in disjoint intervals, can have their ranges narrowed down substantially in our approach.

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arXiv2015

Exploration of the Tensor Structure of the Higgs Boson Coupling to Weak Bosons in $e^+e^-$ Collisions

Probing signatures of anomalous interactions of the Higgs boson with pairs of weak vector bosons is an important goal of an $e^+e^-$ collider commissioned as a Higgs factory. We perform a detailed analysis of such potential of a collider operating at $250 - 300$ GeV. Mostly using higher dimensional operators in a gauge-invariant framework, we show that substantial information on anomalous couplings can be extracted from the total rates of $s$-and $t$-channel Higgs production. The most obvious kinematic distributions, based on angular dependence of matrix elements, are relatively less sensitive with moderate coefficients of anomalous couplings, unless one goes to higher centre-of-mass energies. Some important quantities to use here, apart from the total event rates, are the ratios of event rates at different energies, ratios of $s$ and $t$-channel rates at fixed energies, and under some fortunate circumstances, the correlated changes in the rates for $W$-boson pair-production. A general scheme of calculating rates with as many as four gauge-invariant operators is also outlined. At the end, we perform a likelihood analysis using phenomenological parametrization of anomalous $HWW$ interaction, and indicate their distinguishability for illustrative values of the strength of such interactions.

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arXiv2014

Higgs data confronts Sequential Fourth Generation Fermions in the Higgs Triplet Model

We investigate the effect of introducing a sequential generation of chiral fermions in the Higgs Triplet Model with nontrivial mixing between the doublet and triplet Higgs. We use the available LHC data for Higgs boson production and decay rates, the constraints on the fourth generation masses, and impose electroweak precision constraints from the S, T and U parameters. Our analysis shows that an SM-like Higgs boson state at ~125 GeV can be accommodated in the Higgs Triplet Model with four generations, and thus, that four generations survive collider and electroweak precision constraints in models beyond SM.

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arXiv2014

Higher dimensional operators and LHC Higgs data : the role of modified kinematics

The inclusion of higher-dimensional gauge invariant operators induces new Lorentz structures in Higgs couplings with electroweak gauge boson pairs. This in principle affects the kinematics of Higgs production and decay, thereby modifying the efficiencies of the experimental cuts compared to what simulations based on the standard model interactions yield. Taking some sample cases, we perform a rigorous analysis of how the efficiencies differ for various strengths of the additional operator vis-a-vis the standard model interactions, scanning over the values of both of them. While the response to cuts can be markedly different in some regions, we find that the sensitivity to new operator structures is relatively limited, so long as we remain confined to the 2-sigma regions around the best fit signal strengths measured at the Large Hadron Collider. We also show modifications to certain kinematical distributions including the new operators in the diphoton final state.

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arXiv2013

Invisible Higgs Decay in a Supersymmetric Inverse Seesaw Model with Light Sneutrino Dark Matter

Within the framework of a constrained Minimal Supersymmetric Standard Model (cMSSM) augmented by an MSSM singlet-pair sector to account for the non-zero neutrino masses by inverse seesaw mechanism, the lightest supersymmetric particle (LSP) can be a mixed sneutrino with mass as small as 50 GeV, satisfying all existing constraints, thus qualifying as a light dark matter candidate. We study the possibility of the lightest neutral Higgs boson in this model decaying invisibly into a pair of sneutrino LSPs, thereby giving rise to novel missing energy signatures at the LHC. We perform a two-parameter global analysis of the LHC Higgs data available till date to determine the optimal invisible Higgs branching fraction in this scenario, and obtain a $2σ(1σ)$ upper limit of 0.23 (0.12). A detailed cut-based analysis is carried out thereafter, demonstrating the viability of our proposed signal vis-a-vis backgrounds at the LHC.

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arXiv2012

New Higgs interactions and recent data from the LHC and the Tevatron

We perform a multi-parameter global analysis of all data available till date from the ATLAS, CMS and Tevatron experiments, on the signals of a Higgs boson, to investigate how much scope exists for departure from the standard model prediction. We adopt a very general and model-independent scenario, where separate deviations from standard model values are possible for couplings of the observed scalar with up-and down-type fermions, W-and Z-boson pairs, as well as gluon and photon pair effective interactions. An arbitrary phase in the coupling with the top-pair, and the provision for an invisible decay width for the scalar are also introduced. After performing a global fit with seven parameters, we find that their values at 95% confidence level can be considerably different from standard model expectations. Moreover, rather striking implications of the phase in top-quark coupling are noticed. We also note that the invisible branching ratio can be sizeable, especially when the couplings of the Higgs to W-and Z-pairs are allowed to be different.

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