arXiv subjects

Rhitaja Sengupta

Publications and source records attributed to Rhitaja Sengupta.

18 recordsLinked to original sources

arXiv2026

The ABC of RPV III: Classification of R-parity Violating Signatures from LQD Couplings and their Coverage at the LHC

We consider the R-parity violating Minimal Supersymmetric Standard Model (RPV-MSSM) with its wide range of signatures as a test model for the coverage of beyond the Standard Model searches at the LHC. Here we present a systematic study of the phenomenological and experimental status of specifically the R-parity violating $LQ\bar D$ operators, as the third study in the ABC of RPV series, following our previous analyses of the $LL\bar E$ and $\bar U\bar D\bar D$ operators. We classify the distinct collider signatures for all possible LSPs and for eight representative $LQ\bar D$ couplings, considering both direct LSP production and production through gauge cascades. Assuming one non-zero $LQ\bar D$ coupling at a time, we assess the current LHC coverage using ATLAS and CMS searches implemented in $\texttt{CheckMATE 2}$, and identify recent searches relevant for future recasting. We find substantial sensitivity to the colored sector, while gaps remain for wino- and higgsino-like LSPs for couplings involving $\tau$ leptons, when the LSP is the only sparticle within the LHC kinematic limit. Slepton LSPs remain unconstrained in their direct production at the LHC, although some sensitivity is found for slepton NLSPs with a bino-like LSP. These results highlight gaps in the $\texttt{CheckMATE 2}$ search database, as well as the need for targeted LHC searches for specific $LQ\bar D$ signatures.

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arXiv2026

A new approach to long-lived particle detection at hadron colliders: the $\textsf{DELIGHT-SHIELD}$ concept

We propose a fundamental shift in the search for beyond the Standard Model long-lived particles (LLPs) at high-luminosity hadron colliders by prioritizing physical background suppression over traditional inner tracking. We introduce $\textsf{DELIGHT-SHIELD}$, a dedicated detector design for a 100 TeV Future Circular Collider at a dedicated interaction point for LLP searches. By replacing the inner parts of the detector with a multi-layered composite shield, followed by tracking volumes, we estimate a suppression of Standard Model hadronic and electromagnetic backgrounds by up to seven orders of magnitude analytically. Full Geant4 simulations validate the effectiveness of this design. Although the achieved suppression is somewhat lower than the analytical estimate, primarily due to secondary particle production within the shield, the residual background remains at a level that is manageable for LLP analyses. It can be further mitigated by applying energy thresholds, as well as vertexing and timing cuts in the downstream detector. Benchmarking against dark scalar model, we show that this shielding based detector concept achieves sensitivity to branching ratios as low as $\mathcal{O}(10^{-9})$ for $h\rightarrow\phi\phi$ process under zero background condition $-$ outperforming general-purpose detector baselines. This strategy not only expands the discovery reach for neutral LLPs but also provides a rigorous experimental handle to distinguish new physics from Standard Model punch-through backgrounds. We further discuss a phased implementation at the High-Luminosity LHC as a critical testbed for this novel detection concept.

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arXiv2025

Colliders are not Testing Locality via Bell's Inequality nor Providing an Unconditional Proof of Entanglement

Recently there has been an increased interest in possible tests of locality via Bell's inequalities, as well as separately tests of entanglement at colliders, in particular at the LHC. These have involved various physical processes, such as $t\bar t$, or $\tau^+\tau^-$ production, or the decay of a Higgs boson to two vector bosons $H\to VV^*$. We argue that $\textit{none}$ of these proposals constitute a test of locality via Bell's inequality or promise unconditional observational evidence of entanglement. In all cases what is measured are the momenta of the final state particles. Using the construction proposed by Kasday (1971) in a different context, and adapted to collider scenarios by Abel, Dittmar, and Dreiner (1992), it is straightforward to construct a local hidden variable theory (LHVT) which exactly reproduces the data. This construction is only possible as the final state momenta all commute. We show that this LHVT satisfies Bell's inequality or the related CHSH inequality as appropriate for all the proposed LHC collider tests in the literature. Thus a test of locality via Bell's inequality is not possible at colliders. The LHVT is also by construction local, $\textit{i.e.}$ all correlations are separable. Thus an unconditional proof of entanglement is also inherently $\textit{not}$ possible at colliders. It can only be shown that the entanglement within the Standard Model consistently describes the data.

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arXiv2025

Proposal for a shared transverse LLP detector for FCC-ee and FCC-hh and a forward LLP detector for FCC-hh

As the particle physics community has explored most of the conventional avenues for new physics, the more elusive areas are becoming increasingly appealing. One such potential region, where new physics might be hiding, involves light and weakly interacting long-lived particles (LLPs). To probe deeper into this region, where the possibility of highly displaced scenarios weakens the role of general-purpose collider detectors, dedicated LLP detectors are our best option. However, their potential can only be fully realized if we optimize their position and dimensions to suit our physics goals. This is possible at the upcoming Future Circular Collider (FCC) facility, where the feasibility and design studies are still ongoing and can accommodate new proposals focused specifically on LLP searches. We propose optimized dedicated detectors in both the transverse and forward directions, DELIGHT and FOREHUNT, significantly enhancing the sensitivity to previously uncharted regions of the new physics parameter space. Our proposed DELIGHT detector can additionally serve as a shared transverse detector during both the FCC-ee and FCC-hh runs. The concept of a shared transverse detector is novel and sustainable, utilizing the same interaction points of the lepton and hadron colliders at the FCC. This minimizes costs and boosts the LLP physics case at the FCC.

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arXiv2025

From obstacle to opportunity: uncovering the silver lining of pileup

The lack of evidence for Beyond Standard Model (BSM) particles might be due to their light mass and very weak interactions, as exemplified by BSM long-lived particles (LLPs). Such particles can be produced from $B$ or $D$ hadron decays. Typically, the high values of pileup (PU) in hadron colliders are expected to pose a major challenge in light new physics searches. We propose a fresh perspective that counters this conventional wisdom: instead of viewing PU solely as an impediment, we highlight its potential benefits in searches for light LLPs from $B$ or $D$ hadron decays at HL-LHC and FCC-hh. In particular, certain forward detectors in LHC experiments, such as the Zero Degree Calorimeters (ZDC), which are currently not utilized for LLP searches, can be repurposed with strategic modifications to play a crucial role in this endeavor. Leveraging a combination of forward and central detectors, along with smart strategies for triggering and offline analysis, we demonstrate the potential for exploring light LLPs in high PU scenarios.

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arXiv2025

Long-lived Light Mediators in a Higgs Portal Model at the FCC-ee

In the search for beyond the Standard Model (SM) physics, long-lived particles (LLPs) have emerged as potential candidates and are being explored in various ongoing experiments. Future lepton colliders, such as the FCC-ee, shall provide an excellent opportunity to probe LLPs, owing to their clean environment and improved particle identification. This study investigates the potential of the proposed \textbf{I}nnovative \textbf{D}etector for an \textbf{E}lectron-Positron \textbf{A}ccelerator (IDEA) detector at FCC-ee in the detection of LLPs produced from $B$-meson and Higgs boson decays. We explore benchmark scenarios for different final states resulting from LLP decays, including a detailed analysis of the SM long-lived hadronic background. Additionally, we propose dedicated LLP detectors with different configurations, dimensions, and locations with respect to the IDEA detector. DELIGHT B, originally proposed as a dedicated LLP detector for the FCC-hh, stands out as the detector with the maximum efficiency for detecting LLPs produced at FCC-ee. We find that cylindrical detector configurations, if feasible to construct around the IDEA detector, would also enhance sensitivity for LLPs mostly decaying outside it.

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arXiv2025

The ABC of RPV II: Classification of R-parity Violating Signatures from UDD Couplings and their Coverage at the LHC

We perform a detailed study of the current phenomenological status of baryon number violating operators within the framework of the $R$-parity violating Minimal Supersymmetric Standard Model (RPV-MSSM). This study aims to identify any gaps in the experimental coverage of the RPV landscape. We identify the unique final states for all possible LSPs decaying via four different benchmark UDD operators. Both the direct production of the LSP and its production via gauge-cascades are considered. For each LSP, we assume that only one UDD coupling is non-zero at a time and confront the signals with existing ATLAS and CMS searches implemented in the recasting framework \texttt{CheckMATE\;2}. We find that the UDD colored LSP sector is well covered with the mass bounds on the gluino LSP being the strongest, and with possible improvements for some of the right-handed squark LSPs. We also point out that there is limited coverage for electroweakino and slepton LSPs with UDD decays. This limitation may be due to the lack of targeted experimental searches for these specific final states or the appropriate recasting of existing searches.

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arXiv2024

Exploring $Z'$ and Right-Handed Neutrinos in the BLSM at the Large Hadron Collider

We study the collider phenomenology of the $B$-$L$ extension of the Standard Model (BLSM), focusing on the production and decay of a heavy neutral gauge boson ($ Z' $) at the Large Hadron Collider (LHC). In this framework, the $ Z' $ can decay into pairs of heavy right-handed neutrinos ($ \nu_R $), which subsequently decay into charged leptons and $ W $ bosons. These processes give rise to three distinctive final states: (i) two leptons plus four jets ($ 2\ell + 4j $), (ii) four leptons plus missing transverse energy ($ 4\ell + \text{MET} $), and (iii) three leptons plus two jets and MET ($ 3\ell + 2j + \text{MET} $). % To enhance signal sensitivity and suppress Standard Model backgrounds, we employ multivariate analysis techniques based on Boosted Decision Trees (BDTs), as well as selection optimizations using the \texttt{XGBOOST} framework. The classifiers are trained on kinematic observables sensitive to the masses of the $ Z' $ and $ \nu_R $. We demonstrate that all three final states offer significant discovery potential for both the $ Z' $ and heavy $ \nu_R $ at the High-Luminosity LHC. Our results highlight the testability of the BLSM at current and future collider experiments, and provide a promising avenue for probing the origin of neutrino masses and the baryon asymmetry of the Universe.

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arXiv2024

Current status of the light neutralino thermal dark matter in the phenomenological MSSM

In a previous publication, we studied the parameter space of the phenomenological Minimal Supersymmetric Standard Model (pMSSM) with a light neutralino thermal dark matter ($M_{\tilde{\chi}_1^0} \leq M_h/2$) and observed that the recent results from the dark matter and collider experiments put strong constraints on this scenario. In this work, we present in detail the arguments behind the robustness of this result against scanning over the large number of parameters in pMSSM. The Run-3 of LHC will be crucial in probing the surviving regions of the parameter space. We further investigate the impact of light staus on our parameter space and also provide benchmarks which can be interesting for Run-3 of LHC. We analyse these benchmarks at the LHC using the machine learning framework of \texttt{XGBOOST}. Finally, we also discuss the effect of non-standard cosmology on the parameter space.

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arXiv2023

Is the light neutralino thermal dark matter in the pMSSM ruled out?

We explore the parameter space of the phenomenological Minimal Supersymmetric Standard Model (pMSSM) with a light neutralino thermal dark matter ($m_{\tildeχ_1^0} \leq m_h/2$) that is consistent with current collider and astrophysical constraints. We consider both positive and negative values of the higgsino mass parameter ($μ$). Our investigation shows that the recent experimental results from the LHC as well as from direct detection searches for dark matter by the LUX-ZEPLIN (LZ) collaboration rule out the $Z$-funnel region for the $μ>0$ scenario. The same results severely restrict the $h$-funnel region for positive $μ$, however, the allowed points can be probed easily with few more days of data from the LZ experiment. In the $μ<0$ scenario, we find that very light higgsinos in both the $Z$ and $h$ funnels might survive the present constraints from the electroweakino searches at the LHC, and dedicated efforts from experimental collaborations are necessary to make conclusive statements about their present status.

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arXiv2023

Light long-lived particles at the FCC-hh with the proposal for a dedicated forward detector FOREHUNT and a transverse detector DELIGHT

In this paper, we propose a dedicated forward detector, FOREHUNT (FORward~Experiment~for~HUNdred~TeV), for 100 TeV FCC-hh for the detection of light long-lived particles (LLP) coming from $B$-meson decay. We calculate the signal acceptance as a function of mass and proper decay length of the LLP for 100 TeV and interpret our result in terms of model parameters for models of dark Higgs scalar and heavy neutral leptons. We also compare the sensitivity with proposed transverse detectors like MATHUSLA, CODEX-b for HL-LHC, and DELIGHT (Detector for long-lived particles at high energy of 100 TeV) for FCC-hh. Our analysis reveals that if the LLP is light ($\lesssim 4.4$ GeV) and has a low proper decay length ($<10$ m), a forward detector like FOREHUNT is the best option to look for the decaying LLP, while DELIGHT is preferable for higher proper decay lengths.

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arXiv2022

Long-Lived Light Mediators from Higgs boson Decay at HL-LHC, FCC-hh and a Proposal of Dedicated LLP Detectors for FCC-hh

We study the pair production of the long-lived mediator particles from the decay of the SM Higgs boson and their subsequent decay into standard model particles. We compute the projected sensitivity, both model-independently and with a minimal model, of using the muon spectrometer of the CMS detector at the HL-LHC experiment for ggF, VBF, and Vh production modes of the Higgs boson and various decay modes of the mediator particle, along with dedicated detectors for LLP searches like CODEX-b and MATHUSLA. Subsequently, we study the improvement with the FCC-hh detector at the 100\,TeV collider experiment for such long-lived mediators, again focusing on the muon spectrometer. We propose dedicated LLP detector designs for the 100\,TeV collider experiment, DELIGHT (\textbf{De}tector for \textbf{l}ong-l\textbf{i}ved particles at hi\textbf{gh} energy of 100\,\textbf{T}eV), and study their sensitivities.

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arXiv2022

Boosted top tagging and its interpretation using Shapley values

Top tagging has emerged as a fast-evolving subject due to the top quark's significant role in probing physics beyond the standard model. For the reconstruction of top jets, machine learning models have shown a substantial improvement in the classification performance compared to the previous methods. In this work, we build top taggers using $N$-Subjettiness ratios and several Energy Correlation observables as input features to train the eXtreme Gradient BOOSTed decision tree (XGBOOST). The study finds that tighter parton-level matching lead to more accurate tagging. However, in real experimental data, where the parton level data are unknown, this matching cannot be done. We train the XGBOOST models without performing this matching and show that this difference impacts the taggers' effectiveness. Additionally, we test the tagger under different simulation conditions, including changes in center-of-mass energy, parton distribution functions (PDFs), and pileup effects, demonstrating its robustness with performance deviations of less than 1%. Furthermore, we use the SHapley Additive exPlanation (SHAP) framework to calculate the importance of the features of the trained models. It helps us to estimate how much each feature of the data contributed to the model's prediction and what regions are of more importance for each input variable. Finally, we combine all the tagger variables to form a hybrid tagger and interpret the results using the Shapley values.

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arXiv2021

Dedicated Triggers for Displaced Jets using Timing Information from Electromagnetic Calorimeter at HL-LHC

In this paper, we study the prospect of ECAL barrel timing to develop triggers dedicated to long-lived particles decaying to jets, at the level-1 of HL-LHC. We construct over 20 timing based variables, and identify three of them which have better performances and are robust against increasing PU. We estimate the QCD prompt jet background rates accurately using the "stitching" procedure for varying thresholds defining our triggers, and compute the signal efficiencies for different LLP scenarios for a permissible background rate. The trigger efficiencies can go up to $\mathcal{O}(80\%)$ for the most optimal trigger for pair-produced heavy LLPs having high decay lengths, which degrades with decreasing mass and decay length of the LLP. We also discuss the prospect of including the information of displaced L1 tracks to our triggers, which further improves the results, especially for LLPs characterised by lower decay lengths.

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arXiv2021

XENON1T Excess: Some Possible Backgrounds

This work is a study of some possible background sources in the XENON1T environment which might affect the energy spectrum of electronic recoil events in the lower side and might contribute to the observed excess. We have identified some additional possible backgrounds, like $^{41}$Ca, $^{49}$V, $^{63}$Ni, $^{106}$Ru and $^{125}$Sb coming from cosmogenic production, where the former two emit monoenergetic $X$-rays and the latter three have $β$ decays, or isotopes, like $^{210}$Pb, from the decay chain of $^{222}$Rn emanated in liquid xenon from the materials, or isotopes, like $^{137}$Cs, produced due to neutron capture. We perform a $χ^2$ fitting of the ER spectrum from these backgrounds along with tritium to the observed excess events by varying their individual rates to understand whether they can be present to contribute to the low energy excess or their presence is constrained from the data. We also study the possibility of simultaneous presence of more than one such backgrounds, and how this affects the rates required by individual backgrounds to explain the excess.

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arXiv2021

Determining the lifetime of long-lived particles at the HL-LHC

We examine the capacity of the Large Hadron Collider to determine the mean proper lifetime of long-lived particles assuming different decay final states. We mostly concentrate on the high luminosity runs of the LHC, and therefore, develop our discussion in light of the high amount of pile-up and the various upgrades for the HL-LHC runs. We employ model-dependent and model-independent methods in order to reconstruct the proper lifetime of neutral long-lived particles decaying into displaced leptons, potentially accompanied by missing energy, as well as charged long-lived particles decaying ihnto leptons and missing energy. We also present a discussion for lifetime estimation of neutral long-lived particles decaying into displaced jets, along with the challenges in the high PU environment of HL-LHC. After a general discussion, we illustrate and discuss these methods using several new physics models. We conclude that the lifetime can indeed be reconstructed in many concrete cases. Finally, we discuss to which extent including timing information, which is an important addition in the Phase-II upgrade of CMS, can improve such an analysis.

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arXiv2020

Triggering long-lived particles in HL-LHC and the challenges in the first stage of the trigger system

Triggering long-lived particles at the first stage of the trigger system is very crucial in LLP searches to ensure that we do not miss them at the very beginning. The future High Luminosity runs of the Large Hardron Collider will have increased number of pile-up events per bunch crossing. There will be major upgrades in hardware, firmware and software sides, like tracking at level-1 (L1) as well as inclusion of the MIP timing detector. The L1 trigger menu will also be modified to cope with pile-up and maintain the sensitivity to physics processes. In our study we found that the usual level-1 triggers, mostly meant for triggering prompt particles, will not be very efficient for LLP searches in the 140 PU environment of HL-LHC, thus pointing to the need to include dedicated L1 triggers in the menu for LLPs. We consider the decay of the LLP into jets and develop dedicated jet triggers using the track information and if available, the regional timing information at L1 to select LLP events. We show in our work that these triggers give promising results in identifying LLP events with moderate trigger rates.

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arXiv2019

Study of energy deposition patterns in hadron calorimeter for prompt and displaced jets using convolutional neural network

Sophisticated machine learning techniques have promising potential in search for physics beyond Standard Model in Large Hadron Collider (LHC). Convolutional neural networks (CNN) can provide powerful tools for differentiating between patterns of calorimeter energy deposits by prompt particles of Standard Model and long-lived particles predicted in various models beyond the Standard Model. We demonstrate the usefulness of CNN by using a couple of physics examples from well motivated BSM scenarios predicting long-lived particles giving rise to displaced jets. Our work suggests that modern machine-learning techniques have potential to discriminate between energy deposition patterns of prompt and long-lived particles, and thus, they can be useful tools in such searches.

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