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Lewis, Ian M.

Publications and source records attributed to Lewis, Ian M..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Resonant multiscalar production in the generic complex singlet model in the multi-TeV region

We develop benchmarks for resonant discalar production in the generic complex singlet scalar extension of the Standard Model (SM) with no additional symmetries, which contains two new scalars. These benchmarks maximize discalar resonant production modes at future 𝑝⁒𝑝 colliders: 𝑝⁒𝑝 β†’ β„Ž 2 β†’ β„Ž 1⁑ β„Ž 1 , 𝑝⁒𝑝 β†’ β„Ž 2 β†’ β„Ž 1 β‘β„Ž 3 , and 𝑝⁒𝑝 β†’ β„Ž 2 β†’ β„Ž 3 β‘β„Ž 3 , where β„Ž 1 is the observed SM-like Higgs boson and β„Ž 2,3 are new scalars. The decays β„Ž 2 β†’ β„Ž 1 β‘β„Ž 3 and β„Ž 2 β†’ β„Ž 3 β‘β„Ž 3 may be the only way to discover β„Ž 3 , leading to a discovery of two new scalars at once. Current LHC and projected future collider (HL-LHC, FCC-ee+HL-LHC, IL⁒C⁒500+HL-LHC) constraints on this model are used to produce benchmarks at the HL-LHC for β„Ž 2 masses between 250 GeV and 1 TeV and a future 𝑝⁒𝑝 collider (FCC-hh) for β„Ž 2 masses between 250 GeV and 12 TeV. We update the current LHC bounds on the singlet-Higgs boson mixing angle for these benchmarks. As the mass of β„Ž 2 approaches the multi-TeV region, certain limiting behaviors of the maximum rates are uncovered due to theoretical constraints on the parameters. These limits, which can be derived analytically, are BR⁑(β„Ž 2 β†’ β„Ž 1⁑ β„Ž 1 ) β†’ 0.25, BR⁑(β„Ž 2 β†’ β„Ž 3 β‘β„Ž 3 ) β†’ 0.5, and BR⁑(β„Ž 2 β†’ β„Ž 1⁑ β„Ž 3 ) β†’ 0. It can also be shown that the maximum rates of 𝑝⁒𝑝 β†’ β„Ž 2 β†’ β„Ž 1 β‘β„Ž 1 and 𝑝⁒𝑝 β†’ β„Ž 2 β†’ β„Ž 3⁑ β„Ž 3 approach the same value. Hence, all three β„Ž 2 β†’ β„Ž 𝑖 β‘β„Ž 𝑗 decays are promising discovery modes for β„Ž 2 masses at and below π’ͺ⁑(1 TeV), while above π’ͺ⁑(1 TeV) the decays β„Ž 2 β†’ β„Ž 1 β‘β„Ž 1 and β„Ž 2 β†’ β„Ž 3 β‘β„Ž 3 are more encouraging. We choose benchmark masses for β„Ž 3 to produce a large range of decay signatures including multi-𝑏, multivector boson, and multi-SM-like Higgs production. As we will show, the behavior of the maximum rates leads to the surprising conclusion that in the multi-TeV region this model may be discovered in the Higgs quartet production mode via β„Ž 2 β†’ β„Ž 3 β‘β„Ž 3 β†’ 4β’β„Ž 1 decays before Higgs triple production is observed. The maximum di- and four Higgs production rates are similar in the multi-TeV range.

Extensions of Higgs sector↗
DOE OSTI2024

Probing the CP structure of the top quark Yukawa at the future muon collider

We study the top-Higgs coupling with a CP violating phase ΞΎ at a future multi-TeV muon collider. We focus on processes that are directly sensitive to the top quark Yukawa coupling: $t$$\overline{t}$$h$, $tbhΞΌΞ½$, and $t$$\overline{t}$$h$$v$$\overline{v}$ with $h$ β†’ $b$$\overline{b}$ and semileptonic top decays. At different energies, different processes dominate the cross section, providing complementary information. At and above an energy of $\mathcal{O}$(10) TeV, vector boson fusion processes dominate. As we show, in the Standard Model there is destructive interference in the vector boson fusion processes $t$$\overline{t}$$h$$v$$\overline{v}$ and $tbhΞΌΞ½$ between the top quark Yukawa and Higgs-gauge boson couplings. A CP-violating phase changes this interference, and the cross section measurement is very sensitive to the size of the CP-violating angle. Although we find that the cross sections are measured to $\mathcal{O}$(50%) statistical uncertainty at 1Οƒ, a 10 and 30 TeV muon collider can bound the CP-violating angle |ΞΎ| ≲ 9.0Β° and |ΞΎ| ≲ 5.4Β°, respectively. However, cross section measurements are insensitive to the sign of the CP-violating angle. To determine that the coupling is truly CP violating, observables sensitive to CP-violation must be measured. We find in the $t$$\overline{t}$$h$ process the azimuthal angle between the $t$ + $\overline{t}$ plane and the initial state muon+Higgs plane shows good discrimination for ΞΎ = Β±0.1Ο€.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

A guide to diagnosing colored resonances at hadron colliders

We present a comprehensive study on how to distinguish the properties of heavy dijet resonances at hadron colliders. A variety of spins, chiral couplings, charges, and QCD color representations are considered. Distinguishing the different color representations is particularly difficult at hadron colliders. To determine the QCD color structure, we consider a third jet radiated in a resonant dijet event. We show that the relative rates of three-jet versus two-jet processes are sensitive to the color representation of the resonance. We also show analytically that the antennae radiation pattern of soft radiation depends on the color structure of dijet events and develops an observable that is sensitive to the antennae patterns. Finally, we exploit a Convolutional Neural Network with Machine Learning techniques to differentiate the radiation patterns from different colored resonances and find encouraging results to discriminate them. We demonstrate our results numerically at a 14 TeV LHC, and the methodology presented here should be applicable to other future hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Higgs production in association with a dark-Z at future electron positron colliders

In recent years there have been many proposals for new electron–positron colliders, such as the circular electron–positron collider, the international linear collider, and the future circular collider in electron–positron mode. Much of the motivation for these colliders is precision measurements of the Higgs boson and searches for new electroweak states. Hence, many of these studies are focused on energies above the hZ threshold. However, there are proposals to run these colliders at the lower WW threshold and Z -pole energies. In this paper, we study a new search for Higgs physics accessible at lower energies: e + e – β†’ hZ d , where Z d is a new light gauge boson such as a dark photon or dark- Z . Such searches can be conducted at the WW threshold, i.e. energies below the hZ threshold where exotic Higgs decays can be searched for in earnest. Additionally, due to very good angular and energy resolution at future electron–positron colliders, these searches will be sensitive to Z d masses below 1 GeV, which is lower than the current direct LHC searches. Here, we will show that at $\sqrt{s}=160$ GeV with 10 ab –1 , a search for e + e – β†’ hZ d is sensitive to h – Z – Z d couplings of Ξ΄ ~ 9 Γ— 10 –3 and cross sections of $\sim 2-3$ ab for Z d masses below 1 GeV. The results are similar at $\sqrt{s}=240$ GeV with 5 ab –1 . These limits are better than those expected from limits on the HL-LHC limits on Higgs branching ratio into generic non-standard model final states and comparable to meson decay limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Higgs troika for baryon asymmetry

To explain the baryon asymmetry of the Universe, we extend the Standard Model (SM) with two additional Higgs doublets with small vacuum expectation values. The additional Higgs fields interact with SM fermions through complex Yukawa couplings, leading to new sources of $CP$ violation. We propose a simple flavor model with $\mathcal{O}$(1) or less Yukawa couplings for quarks and charged leptons, consistent with current flavor constraints. To generate neutrino masses and the baryon asymmetry, right-handed neutrinos in the ~ 0.1 - 10 TeV range couple to the "Higgs Troika." The new Higgs doublet masses are at or above the TeV scale, allowing for asymmetric decays into SM lepton doublets and right-handed neutrinos. The asymmetry in lepton doublets is then processed into a baryon asymmetry, similar to leptogenesis. Since the masses of the new fields could be near the TeV scale, there is potentially a rich high energy collider phenomenology, including observable deviations in the 125 GeV Higgs decay into muons and taus, as well as detectable low energy signals such as the electron EDM or $Β΅ β†’ eΞ³$. Hence, this is in principle a testable model for generation of baryon asymmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗