arXiv subjects

K. Sridhar

Publications and source records attributed to K. Sridhar.

At least 19 recordsLinked to original sources

arXiv2025

Probing charmonia resonances in proton-lead collisions at the LHC

After achieving a successful description of charmonia production in proton-proton (pp) collisions within Non-Relativistic Quantum Chromodynamics (NRQCD) and modified NRQCD (MNRQCD) frameworks, we now extend our study to proton-lead (p-Pb) collisions at the Large Hadron Collider (LHC). In this context, theoretical predictions for the production cross-section, the nuclear modification factor $R_{pPb}$ and forward -to-backward production ratio $R_{FB}$ of $J/ψ$ have been made as a function of transverse momentum and rapidity at the LHC. MNRQCD provides a reasonable agreement with the available LHC data for $J/ψ$ production. Furthermore, using the heavy quark symmetry relation, we have estimated the production cross sections and expected number of events of $η_{c}$ and $h_{c}$ production in both NRQCD and MNRQCD. Notably, the predictions exhibit substantial differences in the integrated cross-sections as well as in the $p_T$ distributions for these states at the LHC, highlighting the importance of further experimental and theoretical studies of these resonances to advance our understanding of quarkonium production.

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arXiv2024

Predictions for $h_c$ and $h_b$ production at the LHC

The production cross sections of $h_c$ and $h_b$, the ${}^1P_1$ quarkonia can be predicted in Non-Relativistic Quantum Chromodynamics (NRQCD) using heavy quark symmetry. Our study includes predictions for both the integrated cross-section and the transverse momentum ($p_T$) distribution of $h_c$ ($h_b$) production at the Large Hadron Collider (LHC), using the decay process $h_c (h_b) \rightarrow η_c (η_b) + γ$, $η_c (η_b) \rightarrow p \overline{p}$. We demonstrate substaintial discrepancies in integrated cross-section and the $p_T$ distribution of ${}^1P_1$ quarkonia production at the LHC using Colour-Singlet Model (CSM), NRQCD and modified NRQCD. Measuring these resonances at the LHC could discriminate between these models, thereby offering further insights into the dynamics of quarkonium production. In addition, we compare the recent LHCb data for the integrated cross-section of $h_c$ production at $\sqrt{s}$ = 13 TeV in the kinematic range 5.0 $<$ $p_T$ $<$ 20.0 GeV and 2.0 $<$ $y$ $<$ 4.0 with the theoretical predictions using NRQCD and modified NRQCD. Modified NRQCD gives an agreement with the recent LHCb experimental data.

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arXiv2023

Bottomonia production in Modified NRQCD

Motivated by the success of Modified Non-Relativistic Quantum Chromodynamics (Modified NRQCD) in explaining data from experiments at the Large Hadron Collider (LHC) for charmonia, we now turn to the study of bottomonium production at the LHC. Modified NRQCD does very well in explaining $Υ$ data from the LHC. But this is true also of NRQCD which explains the $Υ$ data equally well. Where the two models differ substantially is in their predictions for $η_b$ production. As was the case with $η_c$, the measurement of $η_b$ production at the LHC will be another decisive test of Modified NRQCD.

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arXiv2023

Resolution of the LHCb $η_c$ anomaly

Due to the heavy-quark symmetry of Non-Relativistic Quantum Chromodynamics (NRQCD), the cross-section for the production of $η_c$ can be predicted. This NRQCD prediction when confronted with data from the LHCb is seen to fail miserably. We address this LHCb $η_c$ anomaly in this paper using a new approach called modified NRQCD, an approach that has been shown to work extremely well for studying $J/ψ$, $ψ^{\prime}$ and $χ_c$ production at the LHC. We show, in the present paper, that the predictions for $η_c$ production agrees very well with LHCb measurements at the three different values of energy that the experiment has presented data for. Modified NRQCD also explains the intriguing agreement of the LHCb $η_c$ data with the colour-singlet prediction. The remarkable agreement of the theoretical predictions with the LHCb data suggests that modified NRQCD is closer to apprehending the true dynamics of quarkonium production.

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arXiv2022

Testing charge-radius coupling of the composite Higgs boson at hadron colliders

We explore the collider relevance of a charge-radius coupling among light mesons in composite Higgs models. In particular, we focus of a coupling of the photon to the composite Higgs and a composite singlet, arising from isospin violation in the underlying theory. This coupling offers a deep probe of the composite nature of the Higgs mechanism, being sensitive to the electromagnetic and weak isospin structure of its constituents. The main collider effect consists in the production of the Higgs boson in association with a light composite pseudo-scalar. We present an exploratory cut-and-count analysis at hadron colliders, like the LHC, showing that an efficient background suppression can be achieved. More sophisticated techniques, however, are necessary to select a sufficient number of signal events, due to the small production rates. This justifies further investigation of this channel, which is highly complementary to other searches for compositeness in the Higgs sector.

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arXiv2022

$χ_c$ production in modified NRQCD

In a previous paper, we had modified Non-Relativistic QCD as it applies to quarkonium production by taking into account the effect of perturbative soft-gluon emission from the colour-octet quarkonium states. We tested the model by fitting the unknown non-perturbative parameter in the model from Tevatron data and using that to make parameter-free predictions for $J/ψ$ and $ψ'$ production at the LHC. In this paper, we study $χ_c$ production: we fit as before the unknown matrix-element using data from Tevatron. We, then, extend the results of the previous paper for $J/ψ$ production by calculating the effect of $χ_c$ feed-down to the $J/ψ$ cross-section, which, by comparing with CMS results at $\sqrt{s}=$ 13 TeV, we demonstrate to be small. We have also computed $χ_c^1$ and $χ_c^2$ at $\sqrt{s}=$7 TeV and find excellent agreement with data from the ATLAS experiment.

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arXiv2022

Understanding $J/ψ$ and $ψ'$ production using a modified version of Non-Relativistic Quantum Chromodynamics

There is serious disagreement between the predictions of Non-Relativistic Quantum Chromodynamics (NRQCD) and the data on $J/ψ$ polarisation which has persisted for almost a quarter of a century. We find that if we account for the effect of perturbative soft gluons on the intermediate charm-anticharm octet states in NRQCD then the polarisation problem can be resolved. In addition, this model, when used to fit the Run 1 data on $J/ψ$ and $ψ'$ production from the CDF experiment at Tevatron, gives good fits and yields values of (energy-independent) non-perturbative parameters. These, in turn, can be used to make parameter-free predictions for $J/ψ$ and $ψ'$ data from the CMS experiment at the Large Hadron Collider and the predictions are in excellent agreement with the CMS data.

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arXiv2021

Di-Higgs production ($γγ\to h h$) in Composite Models

In Standard Model (SM) Higgs Boson pair production initiated by photons ($γγ\to h h$) is loop-generated process and thereby very sensitive to any new couplings and particles that may come in loops. The Composite Higgs Models provide an alternate mechanism to address the hierarchy problem of SM where Higgs instead of being an elementary field could be a bound state of a strongly interacting sector. These set of models apart from modifying the SM Higgs couplings could also introduce new effective couplings that can have substantial impact on the loop processes. In this work we have studied the impact of such modifications by Composite Higgs models in $γγ\to h h$ production process.

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arXiv2021

Composite Higgs revealed in Higgs pair photo-production at future colliders

The next generation electron-positron colliders are designed for precision studies of the Standard Model and its extensions, in particular in the Higgs sector. We consider the potential for discovery of composite Higgs models in Higgs pair production through photon collisions. This process is loop-generated, thus it provides access to all Higgs couplings and can show new physics effects in polarized and unpolarized cross-sections starting at relatively low collider energies. It is, therefore, relevant for all electron-positron colliders planned or in preparation. Sizeable deviations from the Standard Model predictions are present in a general class of composite Higgs models, as couplings of one or more Higgs bosons to fermions, or fermionic and scalar resonances, modify the destructive interference present in the Standard Model. In particular, large effects are due to the new quartic coupling of the Higgs to tops and to the presence of a light scalar resonance.

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arXiv2021

Tera-Zooming in on light (composite) axion-like particles

The Tera-Z phase of future $e^+ e^-$ colliders, FCC-ee and CepC, is a goldmine for exploring $Z$ portal physics. We focus on axion-like particles (ALPs) that can be produced via $Z$ decays with a monochromatic photon. As a template model, we consider composite Higgs models with a light pseudo-scalar that couples through the Wess-Zumino-Witten term to the electroweak gauge bosons. For both photophilic and photophobic cases, we show that the Tera-Z can probe composite scales up to $100$s of TeV, well beyond the capability of the LHC and current precision physics. Our results also apply to generic ALPs and, in particular, severely constrain models that explain the muon $g-2$ anomaly.

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arXiv2019

KK Higgs produced in association with a top quark pair in the bulk RS Model

We present a search strategy for the first Kaluza-Klein (KK) mode of the Higgs boson in the framework of the Randall-Sundrum (RS) model with a deformed metric. We study the production of this massive excitation in association with a ttbar pair at the Large Hadron Collider (LHC). The KK Higgs primarily decays into a boosted ttbar final state and we then end up with an interesting four-top final state of which two are boosted. The boosted products in the final state improve the sensitivity for the search of the KK Higgs in this channel whose production cross-section is otherwise rather small. Our results suggest that masses of the KK Higgs resonance upto about 1.2 TeV may be explorable at the highest planned luminosities of the LHC. Beyond this mass, the KK Higgs cross-section is too tiny for it to be explored at the LHC and may be possible only at a future higher energy collider.

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arXiv2018

Unearthing the electroweak structure of warped 5D models

Heavy charged bosons, with masses in the range of a few TeV, are a characteristic of warped extra-dimensional models with bulk gauge fields. Rendering the latter consistent with electroweak precision tests typically requires either a deformation of the metric or extension of the gauge symmetry. We make here the first attempt at finding empirical discriminants which would tell these models apart. Demonstrating the power of simple kinematic observables involving same-sign leptons, we construct simple yet powerful statistical discriminants.

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arXiv2018

The bulk Higgs in the Deformed RS Model

The Randall-Sundrum model with a deformed metric can generate light Kaluza-Klein (KK) Higgs modes consistent with the electroweak precision analysis for a certain range of parameters. The first KK mode of the Higgs ($h_{1}$) in such a model could lie in the mass range varying from 800 GeV to 1.3 TeV. We find that the $h_{1}$ is gaugephobic and decays dominantly into a $t\bar{t}$ pair. The search strategy for $h_{1}$ decaying to $t\bar{t}$ at the Large Hadron Collider (LHC) in this low mass range has been studies. We have used substructure tools to suppress the large QCD background associated with this channel. We find that $h_{1}$ can be probed at the LHC.

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arXiv2017

Constraining compressed versions of MUED and MSSM using soft tracks at the LHC

A compressed spectrum is an anticipated hideout for many beyond standard model scenarios. Such a spectrum naturally arises in the minimal universal extra dimension framework and also in supersymmetric scenarios. Low $p_T$ leptons and jets are characteristic features of such situations. Hence, a monojet with $\not E_T$ has been the conventional signal at the Large Hadron Collider (LHC). However, we stress that inclusion of $p_T$-binned track observables from such soft objects provide very efficient discrimination of new physics signals against various SM backgrounds. We consider two benchmark points each for minimal universal extra dimension (MUED) and minimal supersymmetric standard model (MSSM) scenarios. We perform a detailed cut-based and multivariate analysis (MVA) to show that the new physics parameter space can be probed in the ongoing run of LHC at 13 TeV center-of-mass energy with an integrated luminosity $\sim$ 20-50 fb$^{-1}$. When studied in conjunction with the dark matter relic density constraint assuming standard cosmology, we find that compressed MUED (with $ΛR=2$) can be already excluded from the existing data. Also, MVA turns out to be a better technique than regular cut-based analysis since tracks provide uncorrelated observables which would extract more information from an event.

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arXiv2016

Exploring the Inert Doublet Model through the dijet plus missing transverse energy channel at the LHC

In this study of the Inert Doublet Model (IDM), we propose that the dijet + missing transverse energy channel at the Large Hadron Collider (LHC) will be an effective way of searching for the scalar particles of the IDM. This channel receives contributions from gauge boson fusion, and $t-$channel production, along with contributions from $H^+$ associated production. We perform the analysis including study of the Standard Model (SM) background with assumed systematic uncertainty, and optimise the selection criteria employing suitable cuts on the kinematic variables to maximise the signal significance. We find that with high luminosity option of the LHC, this channel has the potential to probe the IDM in the mass range of up to about 400 GeV, which is not accessible through other leptonic channels. In a scenario with light dark matter of mass about 65 GeV, charged Higgs in the mass range of around 200 GeV provides the best possibility with a signal significance of about $2σ$ at an integrated luminosity of about 3000 fb$^{-1}$.

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arXiv2016

A Higgs in the Warped Bulk and LHC signals

Warped models with the Higgs in the bulk can generate light Kaluza-Klein (KK) Higgs modes consistent with the electroweak precision analysis. The first KK mode of the Higgs (h_{1}) could lie in the 1-2 TeV range in the models with a bulk custodial symmetry. We find that the h_{1} is gaugephobic and decays dominantly into a t\bar{t} pair. We also discuss the search strategy for h_{1} decaying to t\bar{t} at the Large Hadron Collider. We used substructure tools to suppress the large QCD background associated with this channel. We find that h_{1} can be probed at the LHC run-2 with an integrated luminosity of 300 fb^{-1}.

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arXiv2016

Bulk RS models, Electroweak Precision tests and the 125 GeV Higgs

We present upto date electroweak fits of various Randall Sundrum (RS) models. We consider the bulk RS model, deformed RS and the custodial RS models. For the bulk RS case we find the lightest Kaluza Klein (KK) mode of the gauge boson to be $\sim 8$ TeV while for the custodial case it is $\sim 3$ TeV. The deformed model is the least fine tuned of all which can give a good fit for KK masses $< 2$ TeV depending on the choice of the model parameters. We also comment on the fine tuning in each case.

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arXiv2016

Kaluza-Klein gluon + jets associated production at the Large Hadron Collider

The Kaluza-Klein excitations of gluons offer the exciting possibility of probing bulk Randall-Sundrum (RS) models. In these bulk models either a custodial symmetry or a deformation of the metric away from AdS is invoked in order to deal with electroweak precision tests. Addressing both these models, we suggest a new channel in which to study the production of KK-gluons ($g_{KK}$): one where it is produced in association with one or more hard jets. The cross-section for the $g_{KK}+$ jets channel is significant because of several contributing sub-processes. In particular, the 1-jet and the 2-jet associated processes are important because at these orders in QCD the $qg$ and the $gg$ initial states respectively come into play. We have performed a hadron-level simulation of the signal and present strategies to effectively extract the signal from what could potentially be a huge background. We present results for the kinematic reach of the LHC Run-II for different $g_{KK}$ masses in bulk-RS models.

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