Probing long-lived axions at the KOTO experiment
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Results for “Extensions of scalar sector”
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Search for a new pseudoscalar decaying into a pair of muons in events with a top-quark pair at $\sqrt{s} = 13$ $\mathrm{TeV}$ with the ATLAS detector
A search for a new pseudoscalar a-boson produced in events with a top-quark pair, where the a-boson decays into a pair of muons, is performed using $\sqrt{s}$=13 TeV pp collision data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb -1 . The search targets the final state where only one top quark decays to an electron or muon, resulting in a signature with three leptons eμμ and μμμ. No significant excess of events above the Standard Model expectation is observed and upper limits are set on two signal models: $pp→t\bar{t}a$ and $pp→t\bar{t}$ with $t→H^±b, H^±→W^±a$, where $a→μμ$, in the mass ranges 15 GeV a <72 GeV and 120 GeV≤m H± ≤160 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Astrophysical consequences of an electroweak 𝜂 𝑤 pseudoscalar
Recently, it has been suggested that the spectrum of physical states in the Standard Model may include an ultralight pseudoscalar, denoted by 𝜂 w , in analogy with the 𝜂′ state arising from the strong interactions. We find that typical expectations for the properties of 𝜂 w get challenged by astrophysical constraints on the couplings of ultralight bosons. Our strongest limit sets a lower bound of 𝒪(100 TeV) on the decay constant of the hypothesized pseudoscalar. We also briefly discuss whether 𝜂 w could be a dark matter candidate, or the origin of dark energy, but conclude that those identifications appear unlikely. Given the important implications of a potentially overlooked 𝜂 w state for a more complete understanding of the electroweak interactions and a fundamental description of nature, further theoretical and phenomenological investigations of this possibility and its associated physics are warranted.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Low mass Higgs Portal Scalars at the MicroBooNE Detector in the NuMI Beam
The MicroBooNE experiment exploits Liquid Argon Time Projection Chamber (LArTPC) technology to detect neutrinos from two beams at Fermilab, Chicago: on-axis Booster Neutrino Beam (BNB) and the off-axis Neutrinos at the Main Injector (NuMI) beam. While the aim of the experiment is to study the low-energy excess of electron neutrino events observed by the MiniBooNE experiment, to search for eV-scale sterile neutrinos and to characterise neutrino interactions on argon, it could also be exploited to probe Beyond Standard Model (BSM) Physics. This thesis presents a BSM search for low-mass Higgs Portal Scalars at MicroBooNE in the NuMI beam using data collected during the Run 1 and Run 3 data-taking periods with a total exposure corresponding to $7.01 \times 10^{20}$ protons on target (POT). The Higgs Portal Model is an extension to the Standard Model in which a dark-sector scalar, $S$, mixes with the Higgs boson with mixing angle $\theta$ and acquires a coupling to the Standard Model fermions via the Higgs Yukawa coupling. We search for low-mass Higgs Portal scalars, in the mass range $100-200$ MeV, at MicroBooNE via the production channel $K \rightarrow \pi + S$, where scalars are produced from kaons decaying at rest in the NuMI target and beam dump, as well as kaons decaying in flight in the decay pipe of the NuMI beam. In the MicroBooNE detector, we search for the decay channel $S \rightarrow e^+e^-$, which is the only decay channel available to the scalars in the mass range of our search. The results are expressed as limits, at the 95\% confidence level, on the scalar-Higgs mixing angle $\theta$ for scalars in the mass range $100-200$ MeV.Date of Award1 Aug 2023Original languageEnglishAwarding InstitutionThe University of ManchesterSupervisorStefan Soldner-Rembold (Supervisor) & Justin Evans (Supervisor)
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Search for triple Higgs boson production in the 6𝑏 final state using 𝑝𝑝 collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector
A search for the production of three Higgs bosons (𝐻𝐻𝐻) in the $b\bar{b}b\bar{b}b\bar{b}$ final state is presented. The search uses 126 fb −1 of proton-proton collision data at $\sqrt{s}$ =13 TeV collected with the ATLAS detector at the Large Hadron Collider. The analysis targets both nonresonant and resonant production of 𝐻𝐻𝐻. The resonant interpretations primarily consider a cascade decay topology of 𝑋 →𝑆𝐻 → 𝐻𝐻𝐻 with masses of the new scalars 𝑋 and 𝑆 up to 1.5 and 1 TeV, respectively. In addition to scenarios where 𝑆 is off-shell, the nonresonant interpretation includes a search for Standard Model 𝐻𝐻𝐻 production, with limits on the trilinear and quartic Higgs self-coupling set. No evidence for 𝐻𝐻𝐻 production is observed. An upper limit of 59 fb is set, at the 95% confidence level, on the cross section for Standard Model 𝐻𝐻𝐻 production.
Artificial neural networks↗
Search for New Resonances Decaying to Pairs of Merged Diphotons in Proton-Proton Collisions at $\sqrt{s}$ = 13 TeV
A search is presented for an extended Higgs sector with two new particles, 𝑋 and 𝜙, in the process 𝑋 → 𝜙𝜙 → (𝛾𝛾)(𝛾𝛾). Novel neural networks classify events with diphotons that are merged and determine the diphoton masses. The search uses LHC proton-proton collision data at $\sqrt{s}$ = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 138 fb −1 . No evidence of such resonances is seen. Upper limits are set on the production cross section for 𝑚 𝑋 between 300 and 3000 GeV and 𝑚 𝜙 /𝑚 𝑋 between 0.5% and 2.5%, representing the most sensitive search in this channel.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Scalar-induced neutrinoless double beta decay in SU(5)
We discuss the role of heavy scalar fields in mediating neutrinoless double beta decay (0νββ) within the SU(5) Grand Unified Theory framework, extended suitably to include neutrino mass. In such a minimal realistic SU(5) setup for fermion masses, the scalar contributions to 0νββ are extremely suppressed as a consequence of the proton decay bound. We circumvent this problem by imposing a discrete Z 3 symmetry. However, the scalar contributions to 0νββ remain suppressed in this SU(5) x Z 3 model due to the neutrino mass constraint. We find that the 0νββ contribution can be enhanced by extending the scalar sector with an additional 15-dimensional scalar representation with suitable Z 3 charge. Such an extension not only yields realistic fermion mass spectra but also leads to experimentally testable predictions in upcoming ton-scale 0νββ searches, which can be used as a sensitive probe of the new scalars across a broad range, from LHC-accessible scales up to ∼ 10 10 GeV.
Baryon/Lepton Number Violation↗
Impact of new experimental data on the C2HDM: the strong interdependence between LHC Higgs data and the electron EDM
The complex two-Higgs doublet model (C2HDM) is one of the simplest extensions of the Standard Model with a source of CP-violation in the scalar sector. It has a $\mathbb{Z}$ 2 symmetry, softly broken by a complex coefficient. There are four ways to implement this symmetry in the fermion sector, leading to models known as Type-I, Type-II, Lepton Specific and Flipped. In the latter three models, there is a priori the surprising possibility that the 125 GeV Higgs boson couples mostly as a scalar to top quarks, while it couples mostly as a pseudoscalar to bottom quarks. This “maximal” scenario was still possible with the data available in 2017. Since then, there have been more data on the 125 GeV Higgs boson, direct searches for CP-violation in angular correlations of $τ$-leptons produced in Higgs boson decays, new results on the electron electric dipole moment, new constraints from LHC searches for additional Higgs bosons and new results on $b$ → $sγ$ transitions. Highlighting the crucial importance of the physics results of LHC’s Run 2, we combine all these experiments and show that the “maximal” scenario is now excluded in all models. Still, one can have a pseudoscalar component in $hτ\overline{τ}$ couplings in the Lepton-Specific case as large as 87% of the scalar component for all mass orderings of the neutral scalar bosons.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in 𝑝𝑝 collisions at $\sqrt{𝑠}$ = 13 TeV
A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using 140 fb −1 of proton-proton collision data at $\sqrt{𝑠}$ =13 TeV recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than 𝒪(10) cm.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in p p collisions at s = 13 TeV
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Tree-level Unitarity in $$ \textrm{SU}{(2)}_L\times \textrm{U}{(1)}_Y\times \textrm{U}{(1)}_{Y^{\prime }} $$ Models
Abstract In models with a U(1) gauge extension beyond the Standard Model, one can derive sum rules for the couplings of the theory that are a consequence of tree-level unitarity. In this paper, we provide a comprehensive list of coupling sum rules for a general$$ \textrm{SU}{(2)}_L\times \textrm{U}{(1)}_Y\times \textrm{U}{(1)}_{Y^{\prime }} $$ SU 2 L × U 1 Y × U 1 Y ′ gauge theory coupled to an arbitrary set of fermion and scalar multiplets. These results are of particular interest for models of dark matter that employ an extended gauge sector mediated by a new (dark)Z ′ gauge boson. For the case of a minimal extension of the Standard Model with a$$ \textrm{U}{(1)}_{Y^{\prime }} $$ U 1 Y ′ gauge boson, we clarify the definitions of the weak mixing angle and the electroweakρparameter. We demonstrate the utility of a generalizedρparameter (denoted byρ ′ ) whose definition naturally follows from the unitarity sum rules developed in this paper.
Physics↗
Search for cascade decays of charged sleptons and sneutrinos in final states with three leptons and missing transverse momentum in 𝑝𝑝 collisions at $\sqrt{𝑠} = 13$ TeV with the ATLAS detector
A search for cascade decays of charged sleptons and sneutrinos using final states characterized by three leptons (electrons or muons) and missing transverse momentum is presented. The analysis is based on a dataset with 140 fb −1 of proton-proton (pp) collisions at a center-of-mass energy of $\sqrt{𝑠} = 13$ TeV recorded by the ATLAS detector at the Large Hadron Collider. This paper focuses on a supersymmetric scenario that is motivated by the muon anomalous magnetic moment observation, dark-mattter relic density abundance, and electroweak naturalness. A mass spectrum involving light Higgsinos and heavier sleptons with a bino at intermediate mass is targeted. No significant deviation from the Standard Model expectation is observed. This search enables us to place stringent constraints on this model, excluding at the 95% confidence level charged slepton and sneutrino masses up to 450 GeV when assuming a lightest neutralino mass of 100 GeV and mass-degenerate selectrons, smuons and sneutrinos.
extensions of Higgs sector↗
Depleted Higgs boson: Searches for universal coupling suppression, invisible decays, and mixed-in scalars
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Neutral and doubly charged scalars at future lepton colliders
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Toward UV models of kinetic mixing and portal matter. VI. A more complex dark matter sector?
Portal matter (PM), having both Standard Model (SM) and dark sector charges, can induce kinetic mixing between the 𝑈(1) 𝐷 dark photon and the SM gauge fields at the 1-loop level offering an attractive mechanism by which light (≲1 GeV) thermal dark matter (DM) can interact with visible matter and obtain its observed relic density. In doing so, if the DM is fermionic, the CMB and other astrophysical observations inform us that it must be Majorana/pseudo-Dirac in nature to avoid velocity/temperature-independent 𝑠-wave annihilation to SM final states. How does this idea fit into a more UV-complete picture also including the SM interactions? There are some reasons to believe that at least a first step along this path may not lie too far away in energy due to the renormalization group equations running of the dark gauge coupling, which for a significant range of parameters, becomes nonperturbative at/before the ∼10’s of TeV energy range. This implies that 𝑈(1) 𝐷 must become embedded in an asymptotically free, non-Abelian group, 𝐺 𝐷 , before this can occur. The breaking of this larger group then produces the masses for the PM and the additional gauge fields associated with 𝐺 𝐷 then can lead to new interactions between the SM and the dark sector. Following several bottom-up approaches, we have examined a set of distinctive and testable phenomenological features associated with this general setup, based upon a number of simplifying assumptions. Clearly, it behooves us to explore the impact of these specific assumptions on these predictions for the array of possible experimental tests of this class of models. In most past analyses it has been assumed that DM is a vectorlike, complex singlet under the group 𝐺 𝐷 . If this assumption is relaxed, the dark sector must be augmented by additional fermion(s) and the associated scalar fields needed to break the gauge symmetries while generating the needed Majorana-like mass terms for the DM. In this paper, we analyze the simplest extension of this kind wherein the DM lies in a vectorlike doublet of 𝐺 𝐷 , which we take to have the structure 𝑆𝑈(2) 𝐼 ×𝑈(1) 𝑌 𝐼 as in earlier work, leading to new phenomenological implications. We find, for example, that given the current LHC search constraints on the masses of heavy gauge bosons, the production of these new dark states with large rates is unlikely to occur at colliders unless they are produced singly in 𝑔𝑔 fusion or their pair production cross sections are resonantly enhanced. Here, we also find that an additional mechanism arises to generate hierarchal neutrino masses in such a setup.
Extensions of Higgs sector↗
Accommodating hints of new heavy scalars in the framework of the flavor-aligned two-Higgs-doublet model
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79 ASTRONOMY AND ASTROPHYSICS↗
CFTs blueshift tensor fluctuations universally
The strong constraints of conformal symmetry cause any nearly-conformal sector to blueshift tensor fluctuations in cosmology. Hidden sectors with approximate conformal symmetry, which may be quite large, are a well-motivated extension of physics beyond the Standard Models of particle physics and cosmology. They can therefore lead to a detectable shift in the tensor tilt for next-generation CMB and gravitational wave experiments. Here, we compute the leading-order contribution to the in-in graviton two-point function from virtual loops in such sectors to demonstrate this universal effect. In units where a single conformally-coupled scalar is 1, limits from Stage-IV CMB experiments could bound the size of this extra sector to be smaller than ~10 15 , under a plausible calculational assumption backed by a simple power counting argument. This would be sufficient to rule out N-Naturalness as a complete resolution of the hierarchy problem.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Fermion mass, axion dark matter, and leptogenesis in SO(10) GUT
SO(10) grand unified theory with minimum parameters in the Yukawa sector employs the Peccei-Quinn symmetry that solves the strong C P problem. Such an economical Yukawa sector is highly appealing and has been extensively studied in the literature. However, when the running of the renormalization group equations of the Yukawa couplings are considered, this scenario shows some tension with the observed fermion masses and mixing. In this work, we propose an extension of the minimal framework that utilizes lower dimensional representations and alleviates this tension by introducing only a few new parameters. The proposed model consists of a fermion in the fundamental and a scalar in the spinorial representations. While the latter is needed to implement the Peccei-Quinn symmetry successfully, the presence of both is essential in obtaining an excellent fit to the fermion mass spectrum. In our model, axions serve the role of dark matter, and the out-of-equilibrium decays of the right-handed neutrinos successfully generate the matter-antimatter symmetry of the Universe. Published by the American Physical Society 2024
Astronomy & Astrophysics↗