arXiv subjects

Arghya Choudhury

Publications and source records attributed to Arghya Choudhury.

36 records · Page 2Linked to original sources

arXiv2017

Blind Spots for Direct Detection with Simplified DM Models and the LHC

Using the existing simplified model framework, we build several dark matter models which have suppressed spin-independent scattering cross section. We show that the scattering cross section can vanish due to interference effects with models obtained by simple combinations of simplified models. For weakly interacting massive particle (WIMP) masses $\gtrsim$10 GeV, collider limits are usually much weaker than the direct detection limits coming from LUX or XENON100. However, for our model combinations, LHC analyses are more competitive for some parts of the parameter space. The regions with direct detection blind spots can be strongly constrained from the complementary use of several Large Hadron Collider (LHC) searches like mono-jet, jets + missing transverse energy, heavy vector resonance searches, etc. We evaluate the strongest limits for combinations of scalar + vector, "squark" + vector, and scalar + "squark" mediator, and present the LHC 14 TeV projections.

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arXiv2016

Revisiting the Exclusion Limits from Direct Chargino-Neutralino Production at the LHC

We revisit the existing limits on the gaugino masses in various Supersymmetric (SUSY) scenarios derived from Run-I data of the LHC. These limits obtained from the various final states rely heavily on the simplified assumptions regarding the masses, compositions and decay branching ratios of the gauginos. The most promising exclusion limits on the gaugino masses are obtained from trilepton final states while the second lightest neutralino ($\widetilde χ_2^0$) decaying into the SM-like Higgs and lightest SUSY particle (LSP) results in the weakest bounds. Our aim is to assess the extent of deviation of these exclusion limits in more realistic scenarios. After a brief discussion on the various decay modes of the $\widetilde χ_2^0$ and the lightest chargino ($\widetilde χ^{\pm}_1$), we proceed to validate the ATLAS exclusion limits obtained from trilepton, $lγγ$ and $lb\bar b$ final states associated with missing energy. We then consider different combinations of the relevant branching ratios to study their impact on the existing bounds. The results are presented alongside the existing exclusion limits to showcase the extent of the obtained deviation. We also observe that the three-body decay modes of $\widetilde χ_2^0$ and $\widetilde χ^{\pm}_1$ via off-shell slepton decays resulting in trilepton final states provide bounds that are far more severe in some parts of the available parameter space than that obtained from the usual two-body decay modes of the aforementioned gauginos.

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arXiv2016

Study of MSSM heavy Higgs bosons decaying into charginos and neutralinos

A multitude of searches have already been performed by the ATLAS and CMS collaborations at the LHC to probe the heavy Higgses of the Minimal Supersymmetric Standard Model (MSSM) through their decay to the Standard Model particles. In this paper, we study the decay of the MSSM heavy Higgses into neutralino and chargino pairs and estimate the maximum possible branching ratios for these `ino' modes being consistent with the present LHC data. After performing a random scan of the relevant electroweakino parameters, we impose the SM 125 GeV Higgs constraints, low energy flavour data as well as current bounds on heavy Higgses from the LHC run-I and run-II data. The present limits on the electroweakino masses and couplings are also considered in our analysis. We choose a few representative benchmark points satisfying all the above-mentioned constraints, and then perform a detailed collider simulation, including fast detector effects, and analyze all the potential SM backgrounds in order to estimate the discovery reach of these heavy Higgses at the LHC. We restrict ourselves within the leptonic cascade decay modes of these heavy Higgses and study the mono-X + MET (X=W,Z) and trilepton + MET signatures in the context of high luminosity run of the 14 TeV LHC.

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arXiv2016

The role of leptonic cascades in $B_c \to B_s$ at the LHC

We study the feasibility and advantages of investigating the $c\to s$ decay channel of the $B_c$ meson through the cascade decay $B_c\to B_sπ$, $B_s\to D_s\ellν$. We take into account possible contaminations coming from the vector excitations (like $B_s^*$, $D_s^*$ or $ρ$ in the intermediate stages of the cascade) too, as well as the opposite cascade $B_c\to B_s\ellν$, $B_s\to D_sπ$. We show how the $p_T$ distribution of the pion and the lepton can possibly help to differentiate between various form factor models, for which we either need more integrated luminosity at the LHC, or a high-luminosity $e^+e^-$ B factory producing $B_c$ mesons too.

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arXiv2016

Di-photon resonance around 750 GeV: shedding light on the theory underneath

Both the ATLAS and CMS collaborations have recently observed an excess in the di-photon invariant mass distribution in the vicinity of 750 GeV with a local significance of $\sim3σ$. In this article we try to investigate this excess in the context of a minimal simplified framework assuming effective interactions of the hinted resonance with photons and gluons. We scrutinise the consistency of this observation with possible accompanying yet hitherto unseen signatures of this resonance. Subsequently, we try to probe the nature of new particles, e.g., spin, electric charge and number of colour, etc., that could remain instrumental to explain this excess through loop-mediation.

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arXiv2016

Less-simplified models of dark matter for direct detection and the LHC

We construct models of dark matter with suppressed spin-independent scattering cross section utilizing the existing simplified model framework. Even simple combinations of simplified models can exhibit interference effects that cause the tree level contribution to the scattering cross section to vanish, thus demonstrating that direct detection limits on simplified models are not robust when embedded in a more complicated and realistic framework. In general for fermionic WIMP masses >10 GeV direct detection limits on the spin-independent scattering cross section are much stronger than those coming from the LHC. However these model combinations, which we call less-simplified models, represent situations where LHC searches become more competitive than direct detection experiments even for moderate dark matter mass. We show that a complementary use of several searches at the LHC can strongly constrain the direct detection blind spots by setting limits on the coupling constants and mediators' mass. We derive the strongest limits for combinations of vector + scalar, vector + "squark", and "squark" + scalar mediator, and present the corresponding projections for the LHC 14 TeV for a number of searches: mono-jet, jets + missing energy, and searches for heavy vector resonances.

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arXiv2015

Reduced LHC constraints for higgsino-like heavier electroweakinos

As a sequel to our earlier work on wino-dominated $\tilde χ_1^{\pm}$ and $\tilde χ_2^{0}$ (wino models), we focus on the pMSSM models where $\tilde χ_1^{\pm}$ and $\tilde χ_{2,3}^{0}$ are either higgsino dominated (higgsino models) or admixtures of significant amount of higgsino and wino components (mixed models), with or without light sleptons. The LHC constraints in the trilepton channel are significantly weaker even in the presence of light sleptons, especially in the higgsino models, compared to those mostly studied by the LHC collaborations with wino-dominated $\tilde χ_1^{\pm}$ and $\tilde χ_2^{0}$. The modes $\tilde χ_{2,3}^{0}\rightarrow h~\tildeχ_1^{0}$ with large branching ratios (BRs) are more common in the higgsino models and may produce spectacular signal in the LHC Run-II. In a variety of higgsino and mixed models we have delineated the allowed parameter space due to the LHC constraints, the observed Dark Matter (DM) relic density of the universe, which gets contributions from many novel DM producing mechanisms i.e., the annihilation/coannihilation processes that lead to the correct range of relic density, and the precise measurement of the anomalous magnetic moment of the muon. In the higgsino models many new DM producing mechanisms, which are not allowed in the wino models, open up. We have also explored the prospects of direct and indirect detection of DM in the context of the LUX and IceCube experiments respectively. In an extended model having only light gluinos in addition to the electroweak sparticles, the gluinos decay into final states with multiple taggable b-jets with very large BRs. As a consequence, the existing ATLAS data in the $0l$ + jets (3b) + $E\!\!\!\!/_T$ channel provide the best limit on $m_{\tilde g}$ ($\approx$ 1.3 TeV). Several novel signatures of higgsino models for LHC Run-II and ILC have been identified.

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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.

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arXiv2015

Non-universal Gaugino mass models under the lamppost of muon (g-2)

In unified $\mathcal{N}=1$ supergravity scenario the gaugino masses can be non-universal. The patterns of these non-universalities are dictated by the vacuum expectation values of non-singlet chiral super-fields in visible sector. Here, we have analysed the model independent correlations among the gaugino masses with an aim to explain the $[1÷3]σ$ excess of muon (g-2) ($Δa_μ$). We have also encapsulated the interconnections among other low and high scale parameters, compatible with the collider constraints, Higgs mass, relic density and flavour data. We have noted that the existing non-universal models are not capable enough to explain $Δa_μ$ at $[1÷2]σ$ level. In the process, we have also shown the impact of recent limits from the searches for disappearing track and long lived charged particles at the LHC. These are the most stringent limits so far ruling out a large parameter space allowed by other constraints. We have also performed model guided analysis where gaugino masses are linear combination of contributions coming from singlet and non-singlet chiral super-fields. Here, a new mixing parameter has been introduced. Following the earlier methodology, we have been able to constrain this mixing parameter and pin down the promising models on this notion.

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arXiv2015

The role of MSSM heavy Higgs production in the self coupling measurement of the 125 GeV Higgs boson at the LHC

Measurement of the self coupling of 125 GeV Higgs boson is one of the most crucial tasks for high luminosity run of the LHC and it can only be measured in the di-Higgs final state. In the minimal supersymmetric standard model, heavy CP even Higgs ($H$) can decay into lighter 125 GeV Higgs boson ($h$) and therefore influence the di-Higgs production. We investigate the role of single $H$ production in the measurement of self coupling of $h$. We find that $H \rightarrow hh$ decay can nontrivially affect the $h$ self coupling measurement in low tan$β$ regime when the mass of the heavy Higgs boson lies between 250 - 600 GeV and depending on the parameter space it may be seen as an enhancement of the self coupling of 125 GeV Higgs boson.

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arXiv2015

Gluino mass limits with sbottom NLSP in coannihilation scenarios

In view of the recent interest in the pMSSM with light third generation squarks, we consider a hitherto neglected scenario where the lighter bottom squark ($\widetilde{b}_1$) is the next lightest supersymmetric particle (NLSP) which co-annihilates with the lightest supersymmetric particle (LSP), the dark matter (DM) candidate. Since the co-annihilation cross section receives contributions from both electroweak and strong vertices, it is relatively large. As a result relatively large NLSP-LSP mass difference (25 - 35 GeV) is consistent with the PLANCK data. This facilitates the LHC signatures of this scenario. We consider several variants of the sbottom NLSP scenario with and without light stops and delineate the parameter space allowed by the PLANCK data. We point out several novel signal (e.g., $\widetilde{t}_1 \rightarrow \widetilde{b}_1 W$) which are not viable in the stop NLSP scenario of DM production. Finally, we consider gluino ($\widetilde g$) decays in this scenario and using the current ATLAS data in the jets (with or without b-tagging) + $\not \!\! E_T$ channel, obtain new limits in the $m_{\widetilde{b}_1} - m_{\widetilde g}$ mass plane. We find that for $m_{\widetilde{b}_1}$ upto 500 GeV, $m_{\widetilde g} \geq$ 1.1 - 1.2 TeV in this scenario.

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arXiv2014

The Electroweak Sector of the pMSSM in the Light of LHC - 8 TeV and Other Data

Using the chargino-neutralino and slepton search results from the LHC in conjunction with the WMAP/PLANCK and $(g-2)_μ$ data, we constrain several generic pMSSM models with decoupled strongly interacting sparticles, heavier Higgs bosons and characterized by different hierarchies among the EW sparticles. We find that some of them are already under pressure and this number increases if bounds from direct detection experiments like LUX are taken into account, keeping in mind the associated uncertainties. The XENON1T experiment is likely to scrutinize the remaining models closely. Analysing models with heavy squarks, a light gluino along with widely different EW sectors, we show that the limits on gluino mass are not likely to be below 1.1 TeV, if a multichannel analysis of the LHC data is performed. Using this light gluino scenario we further illustrate that in future LHC experiments the models with different EW sectors can be distinguished from each other by the relative sizes of the $n$-leptons + $m$-jets + ${\mbox{${E\!\!\!\!/_T}$}}$ signals for different choices of $n$.

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arXiv2014

Compressed SUSY at 14 TeV LHC

In this work we study the collider phenomenology of a compressed supersymmetric model with gluino and the lightest neutralino. All other sparticles are assumed to be heavy. We consider gluino pair production at the 14 TeV LHC and present the mass reach of gluino as a function of mass splitting between gluino and the the lightest neutralino. We find that the gluino mass below 1 TeV can be excluded at 95% CL with integrated luminosity of 100 fb$^{-1}$ for extreme degenerate case where mass separation between gluino and the lightest neutralino is about 20 GeV. On the other hand, the lower bound on the mass of gluino increases to 1.2 - 1.3 TeV if the mass splitting between the gluino and neutralino is about 200 GeV. This result shows that for degenerate gluino, the current mass limit may extend approximately 400-500 GeV at 14 TeV LHC.

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arXiv2013

Neutralino dark matter confronted by the LHC constraints on Electroweak SUSY signals

The supersymmetric particles (sparticles) belonging exclusively to the electroweak sector of the minimal supersymmetric standard model (MSSM) may hold the key to the observed dark matter relic density in the universe even if all strongly interacting sparticles are very heavy. The importance of the light EW sparticles in DM physics and in producing spectacular collider signals is emphasized. It is shown that even the preliminary data on the direct searches of these sparticles at the LHC, significantly constrain the parameter space of the MSSM compatible with the observed relic density and provide useful hints about the future search prospects. If in addition to the electroweak sparticles the gluinos are also within the reach of the LHC experiments, then the gluino mass limits in the light slepton scenario obtained via the canonical jets + $\met$ channel may be relaxed by as much as 25 $%$ compared to the existing limits. But the corresponding same sign dilepton (SSD) + jets + $\met$ signal will yield enhanced limits competitive with the strongest limits currently available. This is illustrated with the help of benchmark scenarios at the generator level using PYTHIA. If the gluinos are just beyond the current reach of the LHC, then the generic n-lepton + m-jets + missing energy signal may discriminate between different DM producing mechanisms by comparing the signals corresponding to different values of n. This is illustrated by simulating the signals for n = 0 and n = 2 (the SSD signal).

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arXiv2012

New limits on top squark NLSP from ATLAS 4.7 $fb^{-1}$ data

Using the ATLAS 4.7 $fb^{-1}$ data on new physics search in the jets + $\met$ channel, we obtain new limits on the lighter top squark ($\tilde t_1$) considering all its decay modes assuming that it is the next to lightest supersymmetric particle (NLSP). If the decay $\lstop$ $\ra c \lspone$ dominates and the production of dark matter relic density is due to NLSP - LSP co-annihilation then the lower limit on $\mlstop $ is 240 GeV. The limit changes to 200 GeV if the decay $\lstop$ $\ra b W \lspone$ dominates. Combining these results it follows that $\lstop $ NLSP induced baryogenesis is now constrained more tightly.

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arXiv2012

Many faces of low mass neutralino dark matter in the unconstrained MSSM, LHC data and new signals

If all strongly interacting sparticles (the squarks and the gluinos) in an unconstrained minimal supersymmetric standard model (MSSM) are heavier than the corresponding mass lower limits in the minimal supergravity (mSUGRA) model, obtained by the current LHC experiments, then the existing data allow a variety of electroweak (EW) sectors with light sparticles yielding dark matter (DM) relic density allowed by the WMAP data. Some of the sparticles may lie just above the existing lower bounds from LEP and lead to many novel DM producing mechanisms not common in mSUGRA. This is illustrated by revisiting the above squark-gluino mass limits obtained by the ATLAS Collaboration, with an unconstrained EW sector with masses not correlated with the strong sector. Using their selection criteria and the corresponding cross section limits, we find at the generator level using Pythia, that the changes in the mass limits, if any, are by at most 10-12% in most scenarios. In some cases, however, the relaxation of the gluino mass limits are larger ($\approx 20%$). If a subset of the strongly interacting sparticles in an unconstrained MSSM are within the reach of the LHC, then signals sensitive to the EW sector may be obtained. This is illustrated by simulating the $blj$$\etslash$, $l= e and μ$, and $bτj$$\etslash$ signals in i) the light stop scenario and ii) the light stop-gluino scenario with various light EW sectors allowed by the WMAP data. Some of the more general models may be realized with non-universal scalar and gaugino masses.

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arXiv2011

Low mass neutralino dark matter in mSUGRA and more general models in the light of LHC data

The $bτj \etslash$ signal at the ongoing LHC experiments is simulated with Pythia in the mSUGRA and other models of SUSY breaking. Special attention is given on the compatibility of this signature with the low mass neutralino dark matter (LMNDM) scenario consistent with WMAP data. In the mSUGRA model the above signal as well as the LMNDM scenario are strongly disfavoured due to the constraints from the on going SUSY searches at the LHC. This tension, however, originates from the model dependent correlations among the parameters in the strong and electroweak sectors of mSUGRA. That there is no serious conflict between the LMNDM scenario and the LHC data is demonstrated by constructing generic phenomenological models such that the strong sector is unconstrained or mildly constrained by the existing LHC data and parameters in the electroweak sector, unrelated to the strong sector,yield DM relic density consistent with the WMAP data. The proposed models, fairly insensitive to the conventional SUSY searches in the jets + $\etslash$ and other channels, yield observable signal in the suggested channel for $\lum \gsim 1 \ifb$ of data. They are also consistent with the LMNDM scenario and can be tested by the direct dark matter search experiments in the near future. Some of these models can be realized by non-universal scalar and gaugino masses at the GUT scale.

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arXiv2011

SUSY signals with small and large trilinear couplings at the LHC 7 TeV runs and neutralino dark matter

We propose the signal $1b+1l+N_j+\etslash$ along with appropriate selection criteria for the LHC 7 TeV run, where the number of jets $(N_j)$ is $\ge$ 2 or 4. These signals can complement the canonical $Jets + \etslash$ signature since they are sensitive to the trilinear soft breaking parameter $(A_0)$ and low values of the parameter tan$β$ in the minimal supergravity (mSUGRA) model. A large region of this mSUGRA parameter space within the reach of the ongoing experiments at the LHC is disfavoured by the bound on the lightest Higgs boson mass ($m_h \ge 114.4 $ GeV) unless $A_0$ has moderate to large negative values. Interestingly this parameter space with $A_0 \ne 0$ is also consistent with the observed dark matter relic density. A natural consequence of large $A_0$ is the existence of a light top squark ($\lstop$). The proposed signals primarily stem from direct $\lstop \lstop^*$ production and/or $\tilde g \ra \tilde t_{1} t $, if all squark-gluino events are considered. A thorough analysis of the signals and the corresponding backgrounds are presented using the event generator Pythia. We finally compare the signal size for $A_0 = 0$ and $A_0 \ne 0$.

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