arXiv subjects

Biplob Bhattacherjee

Publications and source records attributed to Biplob Bhattacherjee.

At least 73 records · Page 4Linked to original sources

arXiv2013

Natural SUSY's Last Hope: R-parity Violation via UDD Operators

Here, we give a broad overview of the more natural spectra allowed by the LHC when UDD R-parity violation is allowed. Because R-parity violation removes the missing energy signals in colliders, the experimental constraints on the gluino, stops, sbottoms and higgsinos are relatively mild. We also show that UDD R-parity violation and lepton number conservation can be made consistent with grand unification. This feat is achieved through the product unification, SU(5) X U(3). In this model, mixing of the SM quarks with additional quark like particles charged under the U(3) generate a UDD R-parity violating operator. Furthermore, these models are also capable of generating a "natural" spectra. The emergence of these more natural low-scale spectra relies heavily on the fact that the gaugino masses are non-universal, a natural consequence of product unification.

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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.

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arXiv2012

Degenerate SUSY search at the 8 TeV LHC

ATLAS and CMS collaborations have searched for the supersymmetry (SUSY) in different channels with 7 TeV center-of-mass energy and their search strategies are optimized for the SUSY scenarios with fairly large mass splittings among the sparticles. In absence of any significant deviation of the data from the Standard Model (SM) prediction, stringent bounds are imposed on the squarks and gluino masses in the context of different SUSY scenarios. Since the exact SUSY breaking mechanism is not known, some part of the SUSY spectrum may be degenerate. In this paper, we consider two particular cases of degenerate SUSY spectrum and discuss the impact of ATLAS and CMS SUSY searches on these scenarios. We found that present SUSY search strategies of the ATLAS and CMS collaborations are not optimized for the degenerate SUSY scenarios. Even the LHC with 8 TeV center-of-mass energy can not probe large part of the parameter space of degenerate SUSY scenarios with the present search strategies.

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arXiv2012

Pure Gravity Mediation of Supersymmetry Breaking at the LHC

Supersymmetric theories which can allow for a 125 GeV Higgs mass and also solve the naturalness and susy flavor problems now require a fair degree of complexity. Here we consider the simplest possibility for supersymmetry near the weak scale, but with the requirement of naturalness dropped. In "pure gravity mediation", all supersymmetric particles except for the gauginos lie at tens to thousands of TeV, with the gauginos obtaining loop suppressed masses automatically by anomaly mediation and higgsino threshold corrections. The gauginos are the lightest superpartners, and we investigate the current collider constraints on their masses, as well as the future reach of the LHC. We consider gluino pair production with a jets + missing energy signature, as well as events with disappearing charged tracks caused by charged winos decaying into their neutral partners. We show that presently, gluino masses less than about 1 TeV and wino masses less than about 300 GeV are excluded, and that the 14 TeV LHC can probe gluino masses up to about 2 TeV and wino masses up to 1 TeV.

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arXiv2011

Can Flavor Physics Hint at Distinctive Signals for R-parity Violation at the LHC?

Observation of some low-energy processes in the flavor physics regime may require the existence of supersymmetry with two relatively large R-parity-violating couplings of the LQD-type, together with reasonably light superparticles. At the LHC, such interactions would be expected to give rise to clear signals with convenient leptonic triggers, including some multileptons of the same sign. We undertake a detailed investigation of these signals taking care to correlate with low-energy requirements and taking proper account of the Standard Model backgrounds as well as the R-parity-conserving sector of the supersymmetric model. We find clear indications that R-parity violation as envisaged in this scenario can be detected at the LHC - even, perhaps, in the early runs.

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arXiv2011

Revealing the footprints of squark gluino production through Higgs search experiments at the Large Hadron Collider at 7 TeV and 14 TeV

The invariant mass distribution of the di-photons from the decay of the lighter scalar Higgs boson(h) to be carefully measured by dedicated h search experiments at the LHC may be distorted by the di-photons associated with the squark-gluino events with much larger cross sections in Gauge Mediated Supersymmetry Breaking (GMSB) models. This distortion if observed by the experiments at the Large Hadron Collider at 7 TeV or 14 TeV, would disfavour not only the standard model but various two Higgs doublet models with comparable h - masses and couplings but without a sector consisting of new heavy particles decaying into photons. The minimal GMSB (mGMSB) model constrained by the mass bound on h from LEP and that on the lightest neutralino from the Tevatron, produce negligible effects. But in the currently popular general GMSB(GGMSB) models the tail of the above distribution may show statistically significant excess of events even in the early stages of the LHC experiments with integrated luminosity insufficient for the discovery of h. We illustrate the above points by introducing several benchmark points in various GMSB models - minimal as well as non-minimal. The same conclusion follows from a detailed parameter scan in a simplified GGMSB model recently employed by the CMS collaboration to interpret their searches in the di-photon + $\etslash$ channel. Other observables like the effective mass distribution of the di-photon + X events may also reveal the presence of new heavy particles beyond the Higgs sector. The contamination of the h mass peak and simple remedies are also discussed.

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arXiv2011

Boosted top quarks in supersymmetric cascade decays at the LHC

At the LHC, a generic supersymmetric cascade can be a source of top quark. Specifically third generation squarks and gluino are the major sources of top quark which could also be boosted. In this article, we have shown that jet substructure algorithm can be very useful in identifying such boosted top quarks in the cascade. We take inclusive three jets plus zero lepton plus missing energy final state and try to reconstruct at least one hadronically decaying top quark by using top tagging techniques which has good prospect at the LHC.

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arXiv2011

Tevatron Signal for an Unmixed Radion

The recent observation by the CDF Collaboration of an excess in $W$ plus dijet events, where the dijet invariant mass shows a 3.2$σ$ peak around $144 \pm 5$ GeV, is shown to be consistent with the production of a radion $Φ$ of mass in this range, in association with a $W$ boson. It is shown that the $Φ$, which is known to be similar to the Higgs boson in many aspects, differs from it in having a much larger cross-section for $q\bar q \to WΦ$ and in decaying principally to gluons, rather than $b\bar b$ pairs. These appear to be the precise features demanded by the new particle interpretation of the CDF events. No modifications of the underlying model are required.

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arXiv2011

Do new data on [B+ -> tau+ nu_tau] decays point to an early discovery of supersymmetry at the LHC?

The recent Belle and BaBar measurements of the branching ratio of $B^+ \to τ^+ ν_τ$ indicate a significant deviation from the Standard Model prediction. We demonstrate that this measurement has a serious impact on models with minimal flavor violation involving a charged Higgs boson, ruling out a large portion of the currently-allowed parameter space. In the constrained minimal supersymmetric standard model, this creates a tension between the measurements of $B^+ \to τ^+ ν_τ$ and the anomalous magnetic moment of the muon, unless $\tanβ$ is small, $μ> 0$, and $A_0$ takes a large negative value. In fact, a very small region of the parameter space of this model, with small values of $m_0$ and $m_{1/2}$, survives all the constraints at 95% C.L.. It is remarkable that this specific region is still consistent with the lightest supersymmetric particle as the dark matter. Moreover, it predicts observable SUSY signals in the early runs of the LHC, even perhaps at 7 TeV. We also show that a consistent explanation for the deviation of the $B^+ \to τ^+ ν_τ$ branching ratio from the Standard Model can be achieved in a non-universal Higgs mass model, which could also predict early signals of supersymmetry at the LHC.

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arXiv2011

Top quark forward-backward asymmetry at Tevatron and its implications at the LHC

The measurement of forward-backward asymmetry in the top and anti-top quark ($t \bar{t}$) production has been recently reconfirmed by the CDF Collaboration and shows a more than $3σ$ deviation from the Standard Model(SM) prediction in the large $t \bar{t}$ invariant mass region. Models with new W$^{\prime}$ or Z$^{\prime}$ bosons have been invoked to explain this deviation. In the context of these models we perform a $χ^2$ analysis with all the available experimental numbers in different $ΔY$ and $M_{t \bar{t}}$ bins. We show that for the $Z^{\prime}$ model the region of parameter space which explain the Tevatron asymmetry can be probed in the same sign top production channel by Tevatron itself. Moreover, we consider a recently proposed observable, the one sided forward-backward asymmetry ($A_{OFB}$) at the LHC and conclude that both the W$^{\prime}$ and Z$^{\prime}$ models can lead to sizable $A_{OFB}$ even at the LHC running at a center of mass energy of 7 TeV for the model parameters consistent with the Tevatron measurements.

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arXiv2010

Boosted Top Quark Signals for Heavy Vector Boson Excitations in a Universal Extra Dimension Model

In view of the fact that the $n = 1$ Kaluza-Klein (KK) modes in a model with a Universal Extra Dimension (UED), could mimic supersymmetry signatures at the LHC, it is necessary to look for the $n = 2$ KK modes, which have no analogues in supersymmetry. We discuss the possibility of searching for heavy $n = 2$ vector boson resonances -- especially the $g_2$ -- through their decays to a highly-boosted top quark-antiquark pair using recently-developed top-jet tagging techniques in the hadronic channel. It is shown that $t\bar{t}$ signals from the $n = 2$ gluon resonance are as efficient a discovery mode at the LHC as dilepton channels from the $γ_2$ and $Z_2$ resonances.

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arXiv2010

Search for the minimal universal extra dimension model at the LHC with $\sqrt{s}$=7 TeV

Universal Extra Dimension (UED) model is one of the popular extension of the Standard Model (SM) which offers interesting phenomenology. In the minimal UED (mUED) model, Kaluza-Klein (KK) parity conservation ensures that $n=1$ KK states can only be pair produced at colliders and the lightest KK particle is stable. In most of the parameter space, first KK excitation of SM hypercharge gauge boson is the lightest one and it can be a viable dark matter candidate. Thus, the decay of $n=1$ KK particles will always involve missing transverse energy as well as leptons and jets. The production cross sections of $n=1$ KK particles are large and such particles may be observed at the Large Hadron Collider (LHC). We explore the mUED discovery potential of the LHC with $\sqrt{s}$ = 7 TeV in the multileptonic final states. Since in the early LHC run, precise determination of missing transverse energy may not be possible, we examine the LHC reach with and without using missing transverse energy information. We observe that missing transverse energy cut will not improve mUED discovery reach significantly. We have found that opposite sign di-lepton channel is the most promising discovery mode and with first $fb^{-1}$ of collected luminosity, LHC will be able to discover the strongly interacting $n=1$ KK particles with masses upto 800 to 900 GeV.

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arXiv2009

Multijet Discriminators for New Physics in Leptonic Signals at the LHC

Some of the cleanest signals for new physics in the early runs of the LHC will involve strongly-produced particles which give rise to multiple leptons by undergoing cascade decays through weakly-interacting states to stable particles. Some of the most spectacular final states will involve three or more leptons, multiple jets and generally missing energy-momentum as well. A triad of the most interesting models of new physics which induce such signals is known to consist of (i) supersymmetry with R-parity conservation, (ii) a universal extra dimension with conservation of KK-parity and (iii) little Higgs models with conserved T-parity. Similar signals could also arise if the Standard Model is augmented with a fourth sequential generation of heavy fermions. We study all these possibilities and show that a judiciously chosen set of observables, critically involving the number of identifiable jets and leptons, can collectively provide distinct footprints for each of these models. In fact, simple pairwise correlation of such observables can enable unambiguous identification of the underlying model, even with a relatively small data sample.

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arXiv2009

Search for Higgs bosons of the Universal Extra Dimensions at the Large Hadron Collider

The Higgs sector of the Universal Extra Dimensions (UED) has a rather involved setup. With one extra space dimension, the main ingredients to the construct are the higher Kaluza-Klein (KK) excitations of the Standard Model Higgs boson and the fifth components of the gauge fields which on compactification appear as scalar degrees of freedom and can mix with the former thus leading to physical KK-Higgs states of the scenario. In this work, we explore in detail the phenomenology of such a Higgs sector of the UED with the Large Hadron Collider (LHC) in focus. We work out relevant decay branching fractions involving the KK-Higgs excitations. Possible production modes of the KK-Higgs bosons are then discussed with an emphasis on their associated production with the third generation KK-quarks and that under the cascade decays of strongly interacting UED excitations which turn out to be the only phenomenologically significant modes. It is pointed out that the collider searches of such Higgs bosons face generic hardship due to soft end-products which result from severe degeneracies in the masses of the involved excitations in the minimal version of the UED (MUED). Generic implications of either observing some or all of the KK-Higgs bosons at the LHC are discussed.

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arXiv2009

Universal extra dimension: Violation of Kaluza-Klein parity

The minimal Universal Extra Dimension (mUED) model respects the Kaluza-Klein (KK) parity $(-1)^n$, where $n$ is the KK number. However, it is possible to have interactions located at only one of the two fixed points of the $S_1/\ztwo$ orbifold. Such asymmetric interactions violate the KK parity. This kills the cold dark matter component of UED but also removes the upper bound on the inverse compactification radius, and thus non-observation of the KK excitations even at the Large Hadron Collider does not necessarily invalidate the model. Apart from the decay of the lightest $n=1$ KK excitation, this leads to collider signals which are markedly different from those in the mUED scenario. The phenomenological consequences of such KK-parity violating terms are explored.

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arXiv2007

Production of Higgs boson excitations of universal extra dimension at the Large Hadron Collider

The Kaluza-Klein excitations of the Higgs bosons of the universal extra dimension model are extremely challenging to detect. We discuss the production and possible detection mechanisms of such excited scalars at the LHC. The dominant production mechanism of such scalars is from the decay of the excited third generation quarks. In particular, the charged Higgs boson has a large production cross-section over most of the parameter space. We highlight how one may detect these excited scalars. We also comment on the production and detection of excited neutral scalars.

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arXiv2006

Signals of Universal Extra Dimension at the ILC

In the minimal Universal Extra Dimension model, single production of n=2 gauge bosons provides a unique discriminating feature from supersymmetry. We discuss how the proposed International Linear Collider can act as a n=2 factory, much in the same vein as LEP.

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arXiv2006

The Excited Scalars of the Universal Extra Dimension Model

In the minimal Universal Extra Dimension (mUED) model, there are four physical scalar particles at the n=1 level, two charged and two neutral. Due to the almost degenerate nature of the spectrum, the detection of these scalars is a major challenge, perhaps the greatest experimental challenge if UED-type new physics is observed at the Large Hadron Collider (LHC). We explore the possibility of detecting these particles at the International Linear Collider (ILC), and emphasise the need of having an excellent soft tau detection efficiency.

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