arXiv subjects

Srimoy Bhattacharya

Publications and source records attributed to Srimoy Bhattacharya.

17 recordsLinked to original sources

arXiv2026

Multi-Lepton Probes of the Drell-Yan Production of Triplet Higgses

Excesses in di-photon, $Zγ$, and $WW$ spectra indicate the existence of a new Higgs boson with mass $152 \pm 1$ GeV. However, no excess is observed in the $ZZ$ channel. This pattern aligns with a Real Higgs Triplet model with hypercharge $Y = 0$ ($Δ$SM). A prediction of this model is the Drell--Yan production of scalars at the LHC, which dominantly decay to electroweak bosons, thus enhancing the cross sections of triboson channels such as $WWZ$, $WZZ$, and $WWW$. Interestingly, both ATLAS and CMS have reported higher-than-expected significances for such processes: $6.4σ$ (observed) vs $4.7σ$ (expected) in the $VVZ$ (where $V = W$ or $Z$) channel and $4.4σ$ vs $3.6σ$ in $WWZ$, suggesting the possibility that these signals may be manifestations of an extended Higgs sector. We investigate whether the $Δ$SM can account for these triboson excesses through electroweak production and decay of triplet scalars. We find that while current data prefers a non-zero new physics signal ($2.6σ$), the $Δ$SM predicts more events than observed, such that it is consistent with data but not preferred over the SM. However, this tension could be clarified with Run~3 and HL-LHC data.

hep-ph↗

arXiv2026

Discovery Prospects for the 150 GeV charged scalar at Future $e^+e^-$ Colliders

The Real Higgs Triplet model, known as the $Δ$SM, is a minimal extension of the Standard Model (SM) obtained by adding a hypercharge 0 triplet ($Δ$). This simple model is motivated by the multi-lepton anomalies and excesses in di-photon, $Zγ$, and $WW$ spectra at $\approx152$ GeV. The model contains, in addition to the SM particle content, a $CP$-even neutral Higgs ($Δ^0$) and a charged state ($Δ^\pm$), which are quasi-degenerate in mass. Observing the charged scalar at the LHC and measuring its mass is very challenging, since it dominantly decays to $WZ$, $tb$, and $τν$. In this article, we consider the discovery prospects of the charged Higgs with mass 150 GeV at future electron-positron colliders. Taking into account $e^+e^- \to γ^*,Z^* \to Δ^\pm Δ^\mp$ as the production mechanism and the dominant decay modes, we define three signal regions (SR) to study the 150 GeV charged Higgs properties: SR1: $\ge 3j + 1\ell$, SR2: $\ge 3\ell + τ_{\text{had}}$, SR3: $\ge 4j + τ_{\text{had}}$. For $m_{Δ^\pm}=150\text{ GeV}$, a $5σ$ significance can be achieved in SR1 with an integrated luminosity of less than $1\text{ fb}^{-1}$. SR2 is very clean with leptonic final states having low background and small systematic uncertainties. Furthermore, SR3 is crucial for reconstructing the charged scalar invariant mass, which can be measured with $\mathcal{O}(1)$ GeV accuracy with an integrated luminosity of $500\text{ fb}^{-1}$.

hep-ph↗

arXiv2025

Emerging Narrow Resonance at 152 GeV

The discovery of the Higgs boson at the LHC completed the Standard Model (SM), yet the possibility of additional scalars remains open, provided their contributions to electroweak symmetry breaking are sufficiently small. Recent analyses of LHC data have revealed statistically significant anomalies in multi-lepton final states - events characterized by multiple leptons, missing transverse energy, and ($b$-)jets. These anomalies provide intriguing hints of physics beyond the SM. In this work, we present the signature of growing excesses for a new scalar resonance with a mass of $152 \pm 1$ GeV, observed in the $γγ$, $Zγ$, and $WW$ channels. The combined global significance reaches a level that points toward the growing signature of this resonance. The findings align with a simplified model in which a heavy scalar boson decays into two lighter scalars, thus providing a consistent framework explaining the observed multi-lepton anomalies. These results significantly advance the search for new scalar bosons at the electroweak scale. Future investigations, including precision studies with upcoming HL-LHC data, will be crucial for confirming the nature of this resonance and exploring its implications for extending the SM.

hep-ph↗

arXiv2025

Axion Icebergs: Clockwork ALPs at hadron colliders

Scenarios with multiple pseudoscalars are interesting as they usually tend to provide a framework to naturally realize a light axion with a large decay constant which has rich applications in cosmology, especially in the context of inflation and light dark matter physics. On the other hand, from a particle physics perspective, this facilitates a solution to the strong CP problem with a low Peccei-Quinn symmetry breaking scale. One such realization is afforded within the framework of the clockwork mechanism where the axion can have suppressed couplings with the gluons or photons while its companion axion-like particles (ALPs) have relatively unsuppressed couplings, thereby facilitating detectability. We study a minimal clockwork model for the QCD axion invoking a KSVZ-like setup and examine the visibility of its unique multi-ALP $(a_n)$ signature at the LHC, the most sensitive channel being $p p \to a_n \, (+ \, {\rm additional \, jets})$ followed by $a_n \to γγ$. In congruence with the astrophysical and cosmological bounds for the axion, a striking feature emerges for the case of light ALPs $(m \sim \mathcal{O}(10 \, {\rm GeV}))$ wherein the mass-splittings among the former are so small that the signal profile mimics that of a single broad resonance, or an $axion$ $iceberg$. The scenario is found to be imminently testable by the end of LHC's Run 3 phase for an integrated luminosity of $\sim 300 {\rm \, fb^{-1}}$. A larger average ALP mass, on the other hand, results in multiple closely-spaced peaks with a characteristic signal profile, and would be expected to be seen at the forthcoming HL-LHC. Possible additional signals are also listed.

hep-ph↗

arXiv2025

Emerging Excess Consistent with a Narrow Resonance at 152 GeV in High-Energy Proton-Proton Collisions

The Higgs boson discovery at the Large Hadron Collider (LHC) at CERN confirmed the existence of the last missing particle of the Standard Model (SM). The existence of new fundamental constituents of matter beyond the SM is of great importance for our understanding of Nature. In this context, indirect (non-resonant) indications for new scalar bosons were found in the data from the first run of the LHC, taken between 2010 and 2012 at CERN: an excess in the invariant mass of muon-electron pairs, consistent with a new Higgs boson ($S$) with a mass of $150\pm5$ GeV. Other processes with multiple leptons in the final state, moderate missing energy, and possibly (bottom quark) jets exhibit deviations from the SM predictions. These anomalies can be explained within a simplified model in which a new heavy Higgs boson $H$ decays into two lighter Higgses $S$. This lighter Higgs $S$ subsequently decays to $W$ bosons, bottom quarks and has also an invisible decay mode. Here, we demonstrate that using this model we can identify narrow excesses in di-photon and $Z$-photon spectra around 152 GeV. By incorporating the latest measurements of di-photons in association with leptons, we obtain a combined global significance of $5.4σ$. This represents the highest significance ever reported for an excess consistent with a narrow resonance beyond the SM (BSM) in high-energy proton-proton collision data at the LHC. Such findings have the potential to usher in a new era in particle physics - the BSM epoch - offering crucial insights into unresolved puzzles of nature.

hep-ph↗

arXiv2023

Accumulating Evidence for the Associated Production of a New Higgs Boson at the Large Hadron Collider

In the last decades, the Standard Model (SM) of particle physics has been extensively tested and confirmed, with the announced discovery of the Higgs boson in 2012 being the last missing puzzle piece. Even though since then the search for new particles and interactions has been further intensified, the experiments ATLAS and CMS at the Large Hadron Collider (LHC) at CERN did not find evidence for the direct production of a new state. However, in recent years deviations between LHC data and SM predictions in multiple observables involving two or more leptons (electrons or muons) have emerged, the so-called ``multi-lepton anomalies'', pointing towards the existence of a beyond the SM Higgs boson $S$. While from these measurements its mass cannot be exactly determined, it is estimated to lay in the range between $130\,$GeV and $160\,$GeV. Motivated by this observation, we perform a search for signatures of $S$, by using existing CMS and ATLAS analyses. Combining channels involving the associate productions of SM gauge bosons ($γγ$ and $Zγ$), we find that a simplified model with a new scalar with $m_S= 151.5\,$GeV is preferred over the SM hypothesis by 4.3$σ$ (3.9$σ$) locally (globally). On the face of it, this provides a good indication for the existence of a new scalar resonance $S$ decaying into photons, in association with missing energy and allows for a connection to the long-standing problem of Dark Matter. Furthermore, because $S$ is always produced together with other particles, we postulate the existence of a second new (heavier) Higgs boson $H$ that decays into $S$ and propose novel searches to discover this particle, which can be performed by ATLAS and CMS.

hep-ph↗

arXiv2023

COVID-19 South African Vaccine Hesitancy Models Show Boost in Performance Upon Fine-Tuning on M-pox Tweets

Very large numbers of M-pox cases have, since the start of May 2022, been reported in non-endemic countries leading many to fear that the M-pox Outbreak would rapidly transition into another pandemic, while the COVID-19 pandemic ravages on. Given the similarities of M-pox with COVID-19, we chose to test the performance of COVID-19 models trained on South African twitter data on a hand-labelled M-pox dataset before and after fine-tuning. More than 20k M-pox-related tweets from South Africa were hand-labelled as being either positive, negative or neutral. After fine-tuning these COVID-19 models on the M-pox dataset, the F1-scores increased by more than 8% falling just short of 70%, but still outperforming state-of-the-art models and well-known classification algorithms. An LDA-based topic modelling procedure was used to compare the miss-classified M-pox tweets of the original COVID-19 RoBERTa model with its fine-tuned version, and from this analysis, we were able to draw conclusions on how to build more sophisticated models.

cs.CL↗

arXiv2023

Searching for Low-Mass Resonances Decaying into $W$ Bosons

In this article, we recast and combine the CMS and ATLAS analyses of the Standard Model Higgs boson decaying to a pair of $W$ bosons in order to search for low-mass resonances in this channel. We provide limits on the corresponding cross section assuming direct production via gluon fusion. For the whole range of masses we consider (90$\,$GeV to 200$\,$GeV), the observed limit on the cross section turns out to be weaker than the expected one. Furthermore, at $\approx95\,$GeV the limit is weakest and a new scalar decaying into a pair of $W$ bosons (which subsequently decay leptonically) with a cross section $\approx0.5\,$pb is preferred over the Standard Model hypothesis by $\gtrsim 2.5\,σ$. In light of the excesses in the $γγ$, $τ^+τ^-$ and $b\bar b$ channels at similar masses, this strengthens the case for such a new Higgs boson. Furthermore, this analysis also gives room for the scalar candidate at 151$\,$GeV decaying into $W$ bosons.

hep-ph↗

arXiv2023

Detecting the Presence of COVID-19 Vaccination Hesitancy from South African Twitter Data Using Machine Learning

Very few social media studies have been done on South African user-generated content during the COVID-19 pandemic and even fewer using hand-labelling over automated methods. Vaccination is a major tool in the fight against the pandemic, but vaccine hesitancy jeopardizes any public health effort. In this study, sentiment analysis on South African tweets related to vaccine hesitancy was performed, with the aim of training AI-mediated classification models and assessing their reliability in categorizing UGC. A dataset of 30000 tweets from South Africa were extracted and hand-labelled into one of three sentiment classes: positive, negative, neutral. The machine learning models used were LSTM, bi-LSTM, SVM, BERT-base-cased and the RoBERTa-base models, whereby their hyperparameters were carefully chosen and tuned using the WandB platform. We used two different approaches when we pre-processed our data for comparison: one was semantics-based, while the other was corpus-based. The pre-processing of the tweets in our dataset was performed using both methods, respectively. All models were found to have low F1-scores within a range of 45$\%$-55$\%$, except for BERT and RoBERTa which both achieved significantly better measures with overall F1-scores of 60$\%$ and 61$\%$, respectively. Topic modelling using an LDA was performed on the miss-classified tweets of the RoBERTa model to gain insight on how to further improve model accuracy.

cs.CY↗

arXiv2023

Growing Excesses of New Scalars at the Electroweak Scale

We combine searches for scalar resonances at the electroweak scale performed by the Large Hadron Collider experiments ATLAS and CMS where persisted excesses have been observed in recent years. Using both the side-bands of Standard Model Higgs analyses as well as dedicated beyond the Standard Model analyses, we find significant hints for new scalars at $\approx 95\,$GeV ($S^\prime$) and $\approx152\,$GeV ($S$). The presence of a $95\,$GeV scalar is preferred over the Standard Model hypothesis by $3.8σ$, while interpreting the $152\,$GeV excesses in a simplified model with resonant pair production of $S$ via a new heavier scalar $H(270)$, a global significance of $\approx5σ$ is obtained. While the production mechanism of the $S^\prime$ cannot yet be determined, data strongly favours the associated production of $S$, i.e. via the decay of a heavier boson $H$ ($pp\to H\to SS^*$). A possible alternative or complementary decay chain is $H\rightarrow SS^{\prime}$, where $S\to WW^*$ ($S^{\prime}$) would be the source of the leptons ($b$-quarks) necessary to explain the multi-lepton anomalies found in Large Hadron Collider data.

hep-ph↗

arXiv2020

'Deep' Dive into $b \to c$ Anomalies: Standardized and Future-proof Model Selection Using Self-normalizing Neural Networks

Noting the erroneous proclivity of information-theoretic approaches, like the Akaike information criterion (AIC), to select simpler models while performing model selection with a small sample size, we address the problem of new physics model selection in $b\to c τν_τ$ decays in this paper by employing a specific machine learning algorithm (self-normalizing neural networks, a.k.a. SNN) for supervised classification and regression, in a model-independent framework. While the outcomes of the classification with real data-set are compared with AIC, with the SNNs outperforming AIC$_c$ in all aspects of model selection, the regression-outcomes are compared with the results from Bayesian analyses; the obtained parameter spaces differ considerably while keeping maximum posterior (MAP) estimates similar. A few of the two-operator scenarios with a tensor-type interaction are found to be the most probable solution for the data. We also test the effectiveness of our trained networks with the expected, more precise data in Belle-II. The trained networks and associated functionalities are supplied for the use of the community.

hep-ph↗

arXiv2020

Exhaustive Model Selection in $b \to s \ell \ell$ Decays: Pitting Cross-Validation against AIC$_c$

In the light of recent data, we study the new physics effects in the exclusive $b \to s \ell^+\ell^-$ decays from a model independent perspective. Different combinations of the dimension six effective operators along with their respective Wilson coefficients are chosen for the analysis. To find out the operator or sets of operators that can best explain the available data in this channel, we simultaneously apply popular model selection tools like cross-validation and the information theoretic approach like Akaike Information Criterion (AIC). There are one, two, and three-operator scenarios which survive the test and a left-handed quark current with vector muon coupling is common among them. This is also the only surviving one-operator scenario. Best-fit values and correlations of the new Wilson coefficients are supplied for all the selected scenarios. We find that the angular observables play the dominant role in the model selection procedure. We also note that while a left-handed quark current with axial-vector muon coupling is the only one-operator scenario able to explain the ratios $R_{K^{(*)}}$ ($R_{K^*}$ for $q^2\in [ 0.045, 1.1] {\rm GeV}^2$ in particular), there are also a couple of two operator scenarios that can simultaneously explain the measured $R_{K^{(*)}}$.

hep-ph↗

arXiv2019

A detailed study of the $Λ_b \to Λ\ell^+ \ell^-$ decays in the Standard Model

Based on the standard model (SM) of particle physics, we study the decays $Λ_b \to Λ\ell^+ \ell^-$ in light of the available inputs from lattice and the data from LHCb. We fit the form-factors of this decay mode using the available theory and experimental inputs after defining different fit scenarios and checking their consistencies. The theory inputs include the relations between the form-factors in heavy quark effective theory (HQET) and soft collinear effective theory (SCET) at the endpoints of di-lepton invariant mass squared $q^2$. Utilizing the fit results, we have predicted a few observables related to this mode. We have also predicted the observable $R_Λ = Br(Λ_b \to Λ\ell_i^+\ell_i^- )/Br(Λ_b \to Λ\ell_j^+\ell_j^-)$ where $\ell_{i}$ and $\ell_j$ are charged leptons of different generations ($i \ne j$). At the moment, we do not observe noticeable differences in the extracted values of the observables in fully data-driven and SM like fit scenarios.

hep-ph↗

arXiv2019

An in-depth analysis of $b\to c(s)$ semileptonic observables with possible $μ- τ$ mixing

In a couple of recent publications ( arXiv:1706.08437 and arXiv:1712.01593 ), the authors attempted to achieve simultaneous explanation of the persistent flavor anomalies in $b\to s$ and $b\to c$ semileptonic decays with a minimal scheme by using only three unknown new parameters. The analysis was obtained with a handful of precise observables. Motivated by their proposal, in this paper we reanalyze the models proposed in the aforementioned papers with a total of 170 observables from those channels including newly available measurements, correlated theoretical results, and constraints. We validate our results by searching for the most influential points and outliers. By analyzing the parameter spaces and their relationship with the constraints, we gain new insight and statistical significance in those models. We also provide a new and precise calculation of $R(J/Ψ)$, obtained during the analysis.

hep-ph↗

arXiv2018

$b \to c τν_τ$ Decays: A Catalogue to Compare, Constrain, and Correlate New Physics Effects

In this article, we have predicted the standard model (SM) values of the asymmetric and angular observables in $B\to D^{(\ast)}τν_τ$ decays, using the results of the new up-to-date analysis in $B\to D^{(*)}\ellν_{\ell}$. We have also revisited the SM prediction of the inclusive ratio $\mathcal{R}_{X_c}$, and have given its values in different schemes of the charm quark mass. This is the first analysis which includes all the known corrections in the SM. In addition, we have analysed the $b\to cτν_τ$ decay modes in a model-independent framework of effective field theory beyond the standard model. Considering all the possible combinations of the effective operators in $b \to c τν_τ$ decays and using the Akaike Information Criterion, we find out the scenarios which can best explain the available data on these channels. In the selected scenarios, best-fit values and correlations of the new parameters are extracted. Using these results, predictions are made on various observables in the exclusive and inclusive semitaunic $b \to c $ decays. The graphical correlations between these observables are shown, which are found to be useful in discriminating various new physics scenarios.

hep-ph↗

arXiv2017

Looking for possible new physics in $B\to D^{(\ast)}τν_τ$ in light of recent data

We study the decays $B\to D^{(\ast)}τν_τ$ in light of the available data from BABAR, Belle and LHCb. We divide our analysis into two parts: in one part we fit the form-factors in these decays directly from the data without adding any additional new physics (NP) contributions and compare our fit results with those available from the decays $B\to D^{(\ast)}\ellν_{\ell}$. We find that the $q^2$-distributions of the form-factors associated with the pseudo-vector current, obtained from $B\to D^{(\ast)}τν_τ$ and $B\to D^{(\ast)}\ellν_{\ell}$ respectively, do not agree with each other, whereas the other form-factors are consistent with each other. In the next part of our analysis, we look for possible new effective operators of dimension 6 amongst new vector, scalar, and tensor-type that can best explain the current data in the decays $B\to D^{(\ast)}τν_τ$. We use the information-theoretic approaches, especially of `Second-order Akaike Information Criterion' (AIC$_c$) in the analysis of empirical data. Normality tests for the distribution of residuals are done after selecting the best possible scenarios, for cross-validation. We find that it is the contribution from the operator involving left or right-handed vector current that passes all the selection criteria defined for the best-fit scenario and can successfully accommodate all the available data set.

hep-ph↗

arXiv2016

Optimal-observable analysis of possible new physics in $B\to D^{(\ast)}τν_τ$

We study all possible observables in $B\to D^{(\ast)}τν_τ$ with new physics (NP), including new vector, scalar and tensor interactions, and investigate the prospects of extracting NP Wilson coefficients with optimal observables. Analysis of the full $q^2$ integrated branching fractions of $B\to D^{(\ast)}τν_τ$ show that the overall sensitivity of the observables of $B\to D τν_τ$ is more towards the scalar current, whereas the bin-by-bin analysis of $q^2$ distribution of the differential branching fraction points to regions of $q^2$ sensitive to tensor interactions. Interestingly, the observables in $B\to D^{\ast}τν_τ$ are more sensitive to tensor interactions, and bin-by-bin analysis of this mode shows the distinct regions of $q^2$ sensitive to vector or scalar interactions. In addition to that, the $τ$ polarisation asymmetry is found to be more sensitive to NP compared to the other observables, in both decay modes.

hep-ph↗