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Ritesh K. Singh

Publications and source records attributed to Ritesh K. Singh.

At least 37 records · Page 2Linked to original sources
arXiv2023

Measuring Electroweak Quantum Numbers of Color Sextet Resonances at the LHC

We study the prospect of measuring the electroweak quantum numbers of beyond the Standard Model (SM) color sextet particles that decay into same-sign top quark pairs. Among these particles, the color sextet scalars give rise to top quarks with the same chirality, while the top quarks coming from the color sextet vector would have opposite chirality. This difference gets encoded in the angular distributions of the bottom quarks and leptons originating from the decays of the top quarks. We utilize this feature and the energy distributions of the final state jets and leptons to distinguish among the three possible color sextet resonances, taking into account various SM background processes at the $13$ TeV LHC.

hep-ph↗
arXiv2023

Emulating the measurement postulates of quantum mechanics via non-Hermitian Hamiltonian

Ever since the formulation of quantum mechanics, there is very little understanding of the process of the collapse of a wavefunction. We have proposed a dynamical model to emulate the measurement postulates of quantum mechanics. We postulate that a non-Hermitian Hamiltonian operates during the process of measurement, which evolves any state to an attracting equilibrium state, thus, mimicking a "collapse". We demonstrate this using a 2-level system and then extend it to an N-level system. For a 2-level system, we also demonstrate that the dynamics generated by the Lindblad master equation can be replicated as an incoherent sum of the evolution by two separate non-Hermitian Hamiltonians.

quant-ph↗
arXiv2023

Novel signals for the Type-X two Higgs doublet scenario at the Large Hadron Collider

We consider, in the context of the Large Hadron Collider, the signals of the Type-X two Higgs doublet model (2HDM) in the parameter region answering to the best possible solution to the muon $(g-2)$ data within this framework. The analysis takes into account all theoretical and observational constraints, and is based on the final state comprising a same-sign dilepton pair and a pair of same-sign $τ$ jets. The crucial ingredient in making the signal clean is the same-sign feature of both the dilepton and the $τ$-jet pair individually. After a detailed estimate of the signal and all noteworthy backgrounds, we show that this channel offers by far the best signal significance among those studied so far, predicting discovery with an integrated luminosity of 3000 fb$^{-1}$, and strong indications even with 1000 fb$^{-1}$ if systematic uncertainies do not exceed about 10%. We also demonstrate that the recently developed dynamic radius jet algorithm is effective in this connection.

hep-ph↗
arXiv2023

Study of anomalous $W^-W^+γ/Z$ couplings using polarizations and spin correlations in $e^-e^+\to W^-W^+$ with polarized beams

We study the anomalous $W^-W^+γ/Z$ couplings in $e^-e^+\to W^-W^+$ followed by semileptonic decay using a complete set of polarization and spin correlation observables of $W$ boson with the longitudinally polarized beam. We consider a complete set of dimension-six operators affecting $W^-W^+γ/Z$ vertex, which are $SU(2)\times U(1)$ gauge invariant. Some of the polarization and spin correlation asymmetries average out if the daughter of $W^+$ is not tagged. We developed an artificial neural network and boosted decision trees to distinguish down-type jets from up-type jets. We obtain bounds on the anomalous couplings for center of mass energy $\sqrt{s} = 250$ GeV with integrated luminosities of~$\mathcal{L}\in\{100~\text{fb}^{-1}, 250~\text{fb}^{-1}, 1000~\text{fb}^{-1}, 3000~\text{fb}^{-1}\}$. We find that using spin-related observables and cross~section in the presence of initial beam polarization significantly improves the bounds on anomalous couplings compared to previous studies.

hep-ph↗
arXiv2023

Breaking down the entire spectrum of spin correlations of a pair of particles involving fermions and gauge bosons

We discuss a formalism for the spin correlations and polarizations in two-particle systems with spins half-half, half-one and one-one, and provide the connections between the polarizations and correlations with the joint angular distributions of decay products identifying the asymmetries for them. We demonstrate the formalism in the processes $e^-e^+\to t\bar{t}$, $gb \to tW^-$ and $e^-e^+\to ZZ$ in the standard model as examples. We investigate the effect of some anomalous couplings on the polarizations and spin correlations in the processes $e^-e^+\to t\bar{t}$, $gb \to tW^-$ and $u\bar{d}\to ZW^+$ at parton level and compare their strengths. The spin correlations have the potential to provide a significant improvement over the polarizations in probing the anomalous couplings.

hep-ph↗
arXiv2023

Dynamic Radius Jet Clustering Algorithm

The study of standard QCD jets produced along with fat jets, which may appear as a result of the decay of a heavy particle, has become an essential part of collider studies. Current jet clustering algorithms, which use a fixed radius parameter for the formation of jets from the hadrons of an event, may be inadequate to capture the differing radius features. In this work, we develop an alternative jet clustering algorithm that allows the radius to vary dynamically based on local kinematics and distribution in the $η$-$ϕ$ plane inside each evolving jet. We present the usefulness of this dynamic radius clustering algorithm through two Standard Model processes, and thereafter illustrate it for a scenario beyond the Standard Model at the 13 TeV LHC.

hep-ph↗
arXiv2023

Role of polarizations and spin-spin correlations of $W's$ in $e^-e^+ \to W^-W^+$ at $\sqrt{s} = 250$ GeV to probe anomalous $W^-W^+Z/γ$ couplings

We study anomalous $W^-W^+Z/γ$ couplings due to dimension-$6$ operators in the production process $e^-e^+ \to W^-W^+$ followed by semi-leptonic decay using polarizations and spin-spin correlations of $W$ bosons. The construction of some of the polarization and spin-spin correlation asymmetries required one to distinguish between two decay quarks coming from $W^+$ decay. We developed an artificial neural network (ANN) and a boosted decision tree (BDT) to distinguish down-type jets from up-type jets and used them to put constraint on anomalous couplings at International Linear Collider (ILC) running at $\sqrt{s} = 250$ GeV with integrated luminosities of $\mathcal{L} \in \{100 \ \text{fb}^{-1}, \ 250 \ \text{fb}^{-1}, \ 1000 \ \text{fb}^{-1}, \ 3000 \ \text{fb}^{-1}\}$. We find that the use of polarization and spin correlation observables, on top of the cross-sections, significantly improves the limits on anomalous coupling compared to the earlier studies.

hep-ph↗
arXiv2022

Exploring the potential of neural networks to predict statistics of solar wind turbulence

Time series datasets often have missing or corrupted entries, which need to be ignored in subsequent data analysis. For example, in the context of space physics, calibration issues, satellite telemetry issues, and unexpected events can make parts of a time series unusable. Various approaches exist to tackle this problem, including mean/median imputation, linear interpolation, and autoregressive modeling. Here we study the utility of artificial neural networks (ANNs) to predict statistics, particularly second-order structure functions, of turbulent time series concerning the solar wind. Using a dataset with artificial gaps, a neural network is trained to predict second-order structure functions and then tested on an unseen dataset to quantify its performance. A small feedforward ANN, with only 20 hidden neurons, can predict the large-scale fluctuation amplitudes better than mean imputation or linear interpolation when the percentage of missing data is high. Although, they perform worse than the other methods when it comes to capturing both the shape and fluctuation amplitude together, their performance is better in a statistical sense for large fractions of missing data. Caveats regarding their utility, the optimisation procedure, and potential future improvements are discussed.

astro-ph.SR↗
arXiv2021

Probing non-standard $b\bar{b}h$ interaction at the LHC at $\sqrt{s}=13$ TeV

In the detailed probe of Higgs boson properties at the Large Hadron Collider, and in looking for new physics signatures in the electroweak symmetry breaking sector, the bottom quark Yukawa coupling has a crucial role. We investigate possible departure from the standard model value of $b\bar{b}h$ coupling, phenomenologically expressed in terms of a modification factor $α_b$, in $b\bar{b}$-associated production of the $125$-GeV scalar at the high-luminosity LHC. In a next-to-leading order estimate, we make use of a gradient boosting algorithm to improve in statistical significance upon a cut-based analysis. It is found possible to probe down to $α_b = 3$ with more than $5~σ$ significance, with ${\cal L} = 3000$ fb$^{-1}$ and $\sqrt{s}$ = 13 TeV, while the achievable limit at $95\%$ C.L. is $\pm 1.95$.

hep-ph↗
arXiv2020

Unravelling the anomalous gauge boson couplings in $ZW^\pm$ production at the LHC and the role of spin-$1$ polarizations

We study the anomalous triple gauge boson couplings (aTGC) in $ZW^\pm$ production in $3l$ + missing $E_T$ channel at the LHC for $\sqrt{s}=13$ TeV. We use cross sections, azimuthal asymmetry, forward-backward asymmetry, and polarization asymmetries of $Z$ and reconstructed $W$ to estimate simultaneous limits on the anomalous couplings for both the effective vertex formalism as well as the effective operator approach using the Markov-chain--Monte-Carlo (MCMC) method for luminosities $35.9$ fb$^{-1}$, $100$ fb$^{-1}$, $300$ fb$^{-1}$, $1000$ fb$^{-1}$, and $3000$ fb$^{-1}$. The trilepton invariant mass ($m_{3l}$)and the transverse momentum of $Z$ ($p_T(Z)$) are found to be sensitive to the aTGC for the cross sections as well as for the asymmetries. We observed that the asymmetries significantly improve the measurement of anomalous couplings at the high-luminosity large hadron collider (LHC) if a deviation from the Standard Model (SM) is observed.

hep-ph↗
arXiv2020

Probing the anomalous triple gauge boson couplings in $e^+e^-\to W^+W^-$ using $W$ polarizations with polarized beams

We study the anomalous $W^+W^-V$ ($V=γ,Z$) couplings in $e^+e^-\to W^+W^-$ using the complete set of polarization observables of $W$ boson with longitudinally polarized electron ($e^-$) and positron ($e^+$) beams. For the effective $W^+W^-V$ couplings, we use the most general Lorentz invariant form factor parametrization as well as $SU(2)\times U(1)$ invariant dimension-$6$ effective operators. We estimate simultaneous limits on the anomalous couplings using the Markov-Chain--Monte-Carlo (MCMC) method for an $e^+e^-$ collider running at center of mass energy of $\sqrt{s}=500$ GeV and the integrated luminosity of ${\cal L}=100$ fb$^{-1}$, $3.2$ ab$^{-1}$ and $4$ ab$^{-1}$. The best limits on the anomalous couplings are obtained for $e^-$ and $e^+$ polarization being $(\pm 0.8,\mp 0.6)$ for both $100$ fb$^{-1}$ and $3.2$ ab$^{-1}$ of luminosity.

hep-ph↗
arXiv2019

Anomalous triple gauge boson couplings in $ZZ$ production at the LHC and the role of $Z$ boson polarizations

We study anomalous couplings among neutral gauge bosons in $ZZ$ production at the LHC for $\sqrt{s}=13$ TeV in $4$-lepton final state. We use the cross section and polarization asymmetries of the $Z$ boson to estimate simultaneous limits on anomalous coupling using Markov-Chain--Monte-Carlo (MCMC) method for luminosities $35.9$ fb$^{-1}$, $150$ fb$^{-1}$, $300$ fb$^{-1}$ and $1000$ fb$^{-1}$. The $CP$-even polarization asymmetry $A_{x^2-y^2}$ is sensitive mainly to the $CP$-odd couplings $f_4^{Z/γ}$ (quadratically) providing a probe to identify $CP$-odd nature of interaction at the LHC. We find that the polarization asymmetries significantly improve the estimation of anomalous couplings should a deviation from the Standard Model (SM) be observed.

hep-ph↗
arXiv2019

Measuring Higgs self couplings in the presence of VVH and VVHH at the ILC

The recent discovery of a Higgs boson at the LHC, while establishing the Higgs mechanism as the way of electroweak symmetry breaking, started an era of precision measurements involving the Higgs boson. In an effective Lagrangian framework, we consider the $e^+e^-\rightarrow ZHH$ process at the ILC running at a centre of mass energy of 500 GeV to investigate the effect of the $ZZH$ and $ZZHH$ couplings on the sensitivity of $HHH$ coupling in this process. Our results show that the sensitivity of the trilinear Higgs self couplings on this process has somewhat strong dependence on the Higgs-gauge boson couplings. Single and two parameter reach of the ILC with an integrated luminosity of 1000 fb$^{-1}$ are obtained on all the effective couplings indicating how these limits are affected by the presence of anomalous $ZZH$ and $ZZHH$ couplings. The kinematic distributions studied to understand the effect of the anomalous couplings, again, show a strong influence of $Z$-$H$ couplings on the dependence of these distributions on $HHH$ coupling. Similar results are indicated in the case of the process, $e^+e^-\rightarrow ν\bar νHH$, considered at a centre of mass energy of 2 TeV, where the cross section is large enough. The effect of $WWH$ and $WWHH$ couplings on the sensitivity of $HHH$ coupling is clearly established through our analyses in this process.

hep-ph↗
arXiv2019

On polarization parameters of spin-$1$ particles and anomalous couplings in $e^+e^-\to ZZ/Zγ$

We study the anomalous trilinear gauge couplings of $Z$ and $γ$ using a complete set of polarization asymmetries for the $Z$ boson in $e^+e^-\to ZZ/Zγ$ processes with unpolarized initial beams. We use these polarization asymmetries, along with the cross section, to obtain a simultaneous limit on all the anomalous couplings using the Markov-Chain--Monte-Carlo (MCMC) method. For an $e^+e^-$ collider running at $500$ GeV center-of-mass energy and $100$ fb$^{-1}$ of integrated luminosity the simultaneous limits on the anomalous couplings are $1\sim3\times 10^{-3}$.

hep-ph↗
arXiv2019

On the choice of beam polarization in $e^+e^-\to ZZ/Zγ$ and anomalous triple gauge-boson couplings

The anomalous trilinear gauge couplings of $Z$ and $γ$ are studied in $e^+e^-\to ZZ/Zγ$ with longitudinal beam polarizations using a complete set of polarization asymmetries for the $Z$ boson. We quantify the goodness of the beam polarization in terms of the likelihood and find the best-choice of $e^-$ and $e^+$ polarizations to be ($+0.16$, $-0.16$), ($+0.09$, $-0.10$) and ($+0.12$, $-0.12$) for $ZZ$, $Zγ$ and combined processes, respectively. Simultaneous limits on anomalous couplings are obtained for these choices of beam polarizations using Markov-Chain--Monte-Carlo (MCMC) for an $e^+e^-$ collider running at $\sqrt{s}=500$ GeV and $\mathcal{L}=100$ fb$^{-1}$. We find the simultaneous limits for these beam polarizations to be comparable with each other and also comparable with the unpolarized beam case.

hep-ph↗
arXiv2018

Polarization of a vector boson produced in decay of a heavy fermion in an arbitrary frame

We consider processes where an electroweak gauge boson ($W$ and $Z$) is produced in the decays of a heavy fermion. The polarization state of the produced gauge boson is given in terms of a vector polarization and a rank-2 tensor polarization. In the rest frame of the mother fermion, these are given directly by the dynamical parameters of the underlying theory. In a frame where the mother particle is moving, the polarization parameters of the gauge boson are dependent additionally upon kinematical factors. We show that these kinematical factors depend only on the magnitude of the velocity of the mother particle and derive analytical expressions for them. We apply the results to pair production of heavy fermions at the LHC with one of the fermions decaying to a gauge boson ($W$, $Z$) and a light Standard Model fermion. We construct estimators of laboratory frame values of polarization parameters of the produced gauge boson. These estimators can be used to estimate the laboratory frame values of polarization parameters of the produced gauge boson without a detailed simulation of the entire process. We validate our expressions with detailed Monte Carlo simulations in the context of beyond the Standard Model scenarios which have a vector-like top partner. We also indicate how to include finite width effects of the heavy fermion in some special cases.

hep-ph↗
arXiv2017

Constraining anomalous gauge boson couplings in $e^+e^-\to W^+W^-$ using polarization asymmetries with polarized beams

We study the anomalous $W^+W^-V$ ($V=γ,Z$) couplings in $e^+e^-\to W^+W^-$ using the complete set of polarization observables of $W$ boson with longitudinally polarized beams. We use most general Lorentz invariant form factors parametrization as well as $SU(2)\times U(1)$ invariant dimension $6$ effective operators for the effective $W^+W^-V$ couplings. We estimate simultaneous limits on the anomalous couplings in both the parametrizations using cross section, forward backward asymmetry and polarization observables of $W$ boson with different kinematical cuts using Markov-Chain--Monte-Carlo (MCMC) method for an $e^+e^-$ collider running at centre of mass energy of $\sqrt{s}=500$ GeV and ${\cal L}=100$ fb$^{-1}$. The best limits on form factors are obtained to be $1 \sim 5 \times 10^{-2}$ for $e^-$ and $e^+$ polarization being $(+0.4,-0.4)$. For operator's coefficients, the best limits are obtained to be $1\sim 16$ TeV$^{-2}$.

hep-ph↗