<p>The search for heavy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>W</mi><mo>′</mo></msup></math> bosons in their decay modes to a lepton and a heavy neutrino offers a promising avenue for probing new physics beyond the Standard Model. This work focuses on such a signature with an energetic lepton plus a fat jet, originating from the heavy neutrino and containing a lepton. We have employed the jet substructure techniques to isolate the embedded lepton as a subjet of the fat jet. The lepton subjet fraction (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>L</mi><mi>S</mi><mi>F</mi></math>) and lepton mass drop (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>L</mi><mi>M</mi><mi>D</mi></math>) variables constructed from the lepton subjet help in separating the signal region from the background. We further study the polarization properties of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>W</mi><mo>′</mo></msup></math> coupling to the lepton and heavy neutrino through the decay products of the neutrino. Instead of relying on a specific model, we employ generic couplings and explore the discrimination power. Jet substructure-based angular variables <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>z</mi></mrow><mrow><mo>ℓ</mo></mrow></msub></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>z</mi><mi>θ</mi></msub></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>z</mi><mi>k</mi></msub></math> are combined to form BDT scores to obtain a better separation power between the left-chiral (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi><mo>−</mo><mi>A</mi></math>) and right-chiral (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi><mo>+</mo><mi>A</mi></math>) coupling configurations. By using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><msub><mi>L</mi><mi>s</mi></msub></math> type profile likelihood estimator, we could achieve <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1.6</mn><mi>σ</mi><mo>−</mo><mrow><mn>2.8</mn><mi>σ</mi></mrow></mrow></math> significance of excluding one coupling configuration in favor of the other.</p>

India

Songshaptak De

Ireland

Atri Dey

Tousik Samui

Jet substructure analysis for distinguishing left- and right-handed couplings of heavy neutrino in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>W</mi><mo>′</mo></msup></math> decay at the HL-LHC

We study the high-scale validity of two kinds of two Higgs doublet models (2HDM), namely, type-II and type-X, but with a scalar SU(2) singlet dark matter (DM) candidate in addition in each case. The additional quartic couplings involving the DM particle in the scalar potential in both the scenarios bring in additional constraints from the requirement of perturbative unitarity and vacuum stability. DM relic density and direct search constraints play a crucial role in this analysis as the perturbative unitarity of the DM-Higgs portal couplings primarily decide the high scale validity of the model. We find that, within the parameter regions thus restricted, the type-II scenario must have a cutoff at around <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mn>6</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>, while the type-X scenario admits of validity up to the Planck scale. However, only those regions which are valid up to about <math><msup><mn>10</mn><mn>8</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> in type-X 2HDM is amenable to detection at the High-luminosity LHC (up to <math><mrow><mn>3000</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>), while most of the parameter space of the type-II scenario mentioned above is likely to be detectable.

Subhaditya Bhattacharya

Germany

Jayita Lahiri

Biswarup Mukhopadhaya

High scale validity of two-Higgs-doublet scenarios with a real scalar singlet dark matter

We perform a collider search for fatjet signals originating from boosted heavy neutral and charged leptons with masses between a few hundred GeV to a TeV. These heavy leptons originate from the decay of heavy gauge bosons with masses above 4 TeV in a left-right symmetric extension of the Standard Model (SM), which considers a universal seesaw mechanism for the generation of all the SM fermion masses. The fatjet signals arise naturally in this model due to the presence of heavy seesaw partners of the SM fermions which decay to SM gauge bosons carrying large boosts. We employ substructure based variables lepton sub-jet fraction (LSF) and lepton mass drop (LMD) together with kinematic variables of fatjets to look for fatjet signals associated with non-isolated leptons. These variables help in reducing the SM backgrounds while retaining enough statistics for signal events, which leads to a robust discovery potential at the high-luminosity Large Hadron Collider (HL-LHC).

Rafiqul Rahaman

Santosh Rai

Fatjet signatures of heavy neutrinos and heavy leptons in a left-right model with universal seesaw at the HL-LHC

The study of the polarization of heavy particles is an important branch of research in today’s collider physics. The massive W boson has two types of polarization states, which usually are studied via the angular distribution of its decay products. We present a jet substructure-based study on the polarization of a boosted W boson decaying hadronically, which forms a fat jet, in pp collision at the  $$\sqrt{s}$$  <math> <msqrt> <mi>s</mi> </msqrt> </math>   = 14 TeV at the LHC. Two different methods, viz. N-subjettiness and Soft Drop, were used to find the subjets, which are approximately considered to be the two hadronic decay products of W, inside boosted W jets. These subjets were then used to calculate two variables  $$p_\theta =|E_1-E_2|/p_T^W$$  <math> <mrow> <msub> <mi>p</mi> <mi>θ</mi> </msub> <mo>=</mo> <mrow> <mo>|</mo> <msub> <mi>E</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>E</mi> <mn>2</mn> </msub> <mo>|</mo> </mrow> <mo>/</mo> <msubsup> <mi>p</mi> <mi>T</mi> <mi>W</mi> </msubsup> </mrow> </math>   and  $$z_j=\max (p_{T_1},p_{T_2})/p_T^W$$  <math> <mrow> <msub> <mi>z</mi> <mi>j</mi> </msub> <mo>=</mo> <mo>max</mo> <mrow> <mo>(</mo> <msub> <mi>p</mi> <msub> <mi>T</mi> <mn>1</mn> </msub> </msub> <mo>,</mo> <msub> <mi>p</mi> <msub> <mi>T</mi> <mn>2</mn> </msub> </msub> <mo>)</mo> </mrow> <mo>/</mo> <msubsup> <mi>p</mi> <mi>T</mi> <mi>W</mi> </msubsup> </mrow> </math>  , where the subscripts 1 and 2 are for two subjets and W represents the reconstructed W jet. We then prepared the templates for longitudinally and transversely polarized W. These templates were used to extract the fractions of different W polarization in a mixed sample with relatively good accuracy.

Polarization study of a boosted W boson decaying hadronically at the LHC with jet substructures and a multivariate analysis

We study the high-scale validity of a type-X two Higgs doublet scenario, which provides an explanation of the observed value of muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>). This region allows a pseudoscalar physical state, which is well below the observed 125-GeV scalar in mass. A second neutral scalar particle can be both above and below 125 GeV in such a scenario. Admissible regions in the parameter space are obtained by using the most recent data on muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>), theoretical constraints such as low-scale perturbativity and vacuum stability, and also all experimental constraints, including the available LHC results. Among other things, both the aforesaid orders of <math><mi>C</mi><mi>P</mi></math>-even neutral scalar masses are included in our benchmark studies. Two-loop renormalization group equations are used to predict the values of various couplings at high scales, and the regions in the space spanned by low-scale parameters, which retain perturbative unitarity as well as vacuum stability up to various scales are identified. We thus conclude that such a scenario, while successfully explaining the observed muon (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>), can be valid up to energy scales ranging from <math><msup><mn>10</mn><mn>4</mn></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> to the Planck scale, thus opening up directions of thought on its ultraviolet completion.

Muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math> and a type-X two-Higgs-doublet scenario: Some studies in high-scale validity

We consider a scenario where an SU(2) triplet scalar acts as the portal for a scalar dark matter particle. We identify regions of the parameter space, where such a triplet coexists with the usual Higgs doublet consistently with all theoretical as well as neutrino, accelerator and dark matter constraints, and the triplet-dominated neutral state has substantial invisible branching fraction. LHC signals are investigated for such regions, in the final state While straightforward detectability at the high-luminosity run is predicted for some benchmark points in a cut-based analysis, there are other benchmarks where one has to resort to gradient boosting/neural network techniques in order to achieve appreciable signal significance.

Biswarup Mukhopadhyaya

LHC signals of triplet scalars as dark matter portal: cut-based approach and improvement with gradient boosting and neural networks

Though the 125-GeV scalar, as the Higgs boson of the standard model, is disfavoured as a dark matter portal by direct searches and the observations on relic density, a heavier scalar in an extended electroweak sector can fit into that role. We explore this possibility in the context of two Higgs doublet models (2HDM). Taking Type I and Type II 2HDM as illustration, and assuming a scalar gauge singlet dark matter particle, we show that the heavy neutral CP-even scalar (H) can (a) serve as dark matter portal consistently with all data, and (b) have a substantial invisible branching ratio, over a wide region of the parameter space. Using this fact, we estimate rates of LHC signals where H is produced via (i) gluon fusion, in association with a hard jet, and (ii) vector boson fusion. Invisible decays of the H can then lead to monojet + E/  T  in (i), and two forward jets with large rapidity gap + E/T in (ii). The second kind of signal usually yields better significance for the high-luminosity run. We also supplement our cut-based analyses with those based on gradient boosted decision trees (XGboost) and artificial neural network (ANN) techniques, where the statistical significance distinctly improves.

LHC signals of a heavy doublet Higgs as dark matter portal: cut-based approach and improvement with gradient boosting and neural networks

The available data on the 125 GeV scalar h is analysed to explore the room for new physics in the electroweak symmetry breaking sector. The first part of the study is model-independent, with h couplings to standard model particles scaled by quantities that are taken to be free parameters. At the same time, the additional loop contributions to h → γγ and h → Zγ, mediated by charged scalar contributions in the extended scalar sector, are treated in terms of gauge-invariant effective operators. Having justified this approach for cases where the concerned scalar masses are a little above the Z-boson mass, we fit the existing data to obtain marginalized 1σ and 2σ regions in the space of the coefficients of such effective operators, where the limit on the h → Zγ branching ratio is used as a constraint. The correlation between, say, the gluon fusion and vector-boson fusion channels, as reflected in a non-diagonal covariance matrix, is taken into account. After thus obtaining model-independent fits, the allowed values of the coefficients are translated into permissible regions of the parameter spaces of several specific models. In this spirit we constrain four different types of two Higgs doublet models, and also models with one or two Y = 2 scalar triplets, taking into account the correlatedness of the scale factors in h-interactions and the various couplings of charged Higgs states in each extended scenario.