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DOE OSTI2023

The Mu2e Experiment at Fermilab

The Muon-to-Electron-Conversion (Mu2e) Experiment is a high-precision, intensity-frontier experiment being developed at Fermilab that will search for coherent, neutrino-less muon to electron conversion in the presence of an atomic nucleus. Such a process would exhibit charged lepton flavor violation (CLFV), which has not yet been observed. Continuing the search for CLFV, Mu2e will improve the sensitivity by four orders of magnitude over the present limits. In the search for beyond the standard model (BSM) physics, Mu2e is uniquely sensitive to a wide range of models by indirectly probing mass scales up to the energy scale of 10^4 TeV. While muon-to-electron-conversion is permissible in an extension of the standard model through neutrino oscillations, the rate is extremely low at about one event in 10^52. By design, the background for the experiment will be well-understood and kept at a sub-event level, which will mean the observation of muon-to-electron conversion is a dire ct confirmation of BSM physics. The physics motivation, the design, and the current status of the experiment will be presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Testing Explanations of Short Baseline Neutrino Anomalies

The experimental observation of neutrino oscillations profoundly impacted the physics of neutrinos, from being well understood theoretically to requiring new physics beyond the standard model of particle physics. Indeed, the mystery of neutrino masses implies the presence of new particles never observed before, often called sterile neutrinos, as they would not undergo standard weak interactions. And while neutrino oscillation measurements entered the precision era, reaching percent-level precision, many experimental results show significant discrepancies with the standard model, at baselines much shorter than typical oscillation baselines, like LSND, MiniBooNE, gallium experiments, and reactor antineutrino measurements. These short baseline anomalies could be explained by the addition of a light sterile neutrino, with mass in the $1-10~\text{eV}$ range, however, in strong tension with many null experimental observations. Other explanations that rely on sterile neutrinos with masses in the $1-500~\text{MeV}$ could resolve the tension. Here we test both classes of models. On the one hand, we look for datasets collected at a short baseline which can constrain heavy sterile neutrino models. We find that the minimal model is fully constrained, but several extensions of this model could weaken the current constraint and be tested with current and future datasets. On the other hand, we test the presence of neutrino oscillations at short baselines, induced by a light sterile state, with the data collected by the MicroBooNE experiment, a liquid argon time projection chamber specifically designed to resolve the details of each neutrino interaction. We report null results from both analyses, further constraining the space of possible explanations for the short baseline anomalies. If new physics lies behind the short baseline anomaly puzzle, it is definitely not described by a simple model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Measurement and interpretation of same-sign W boson pair production in association with two jets in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

This paper presents the measurement of fiducial and differential cross sections for both the inclusive and electroweak production of a same-sign W-boson pair in association with two jets (W ± W ± jj) using 139 fb –1 of proton-proton collision data recorded at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed by selecting two same-charge leptons, electron or muon, and at least two jets with large invariant mass and a large rapidity difference. The measured fiducial cross sections for electroweak and inclusive W ± W ± jj production are 2.92 ± 0.22 (stat.) ± 0.19 (syst.) fb and 3.38 ± 0.22 (stat.) ± 0.19 (syst.) fb, respectively, in agreement with Standard Model predictions. The measurements are used to constrain anomalous quartic gauge couplings by extracting 95% confidence level intervals on dimension-8 operators. A search for doubly charged Higgs bosons H ±± that are produced in vector-boson fusion processes and decay into a same-sign W boson pair is performed. The largest deviation from the Standard Model occurs for an H ±± mass near 450 GeV, with a global significance of 2.5 standard deviations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Search for dark matter in association with an energetic photon in pp collisions at $ \sqrt{s} $ = 13 TeV with the ATLAS detector

A search for dark matter is conducted in final states containing a photon and missing transverse momentum in proton-proton collisions at s√ = 13 TeV. The data, collected during 2015–2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb -1 . No deviations from the predictions of the Standard Model are observed and 95% confidence-level upper limits between 2.45 fb and 0.5 fb are set on the visible cross section for contributions from physics beyond the Standard Model, in different ranges of the missing transverse momentum. The results are interpreted as 95% confidence-level limits in models where weakly interacting dark-matter candidates are pair-produced via an s-channel axial-vector or vector mediator. Dark-matter candidates with masses up to 415 (580) GeV are excluded for axial-vector (vector) mediators, while the maximum excluded mass of the mediator is 1460 (1470) GeV. In addition, the results are expressed in terms of 95% confidence-level limits on the parameters of a model with an axion-like particle produced in association with a photon, and are used to constrain the coupling g a Z γ of an axion-like particle to the electroweak gauge bosons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Inclusive and differential measurements of the $\textrm{t}\overline{\textrm{t}}\mathcal{γ}$ cross section and the $\textrm{t}\overline{\textrm{t}}\mathcal{γ}/\textrm{t}\overline{\textrm{t}}$ cross section ratio in proton-proton collisions at $\sqrt{s}=13$ TeV

Inclusive and differential cross section measurements of top quark pair $(\textrm{t}\overline{\textrm{t}})$ production in association with a photon (γ) are performed as a function of lepton, photon, top quark, and $\textrm{t}\overline{\textrm{t}}$ kinematic observables, using data from proton-proton collisions at $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 138 fb −1 , collected at the CERN LHC with the CMS detector. Events containing two leptons (electrons or muons) and a photon in the final state are considered. The fiducial cross section of $\textrm{t}\overline{\textrm{t}}$γ is measured to be 137 ± 8 fb, in a phase space including events with a high momentum, isolated photon. The fiducial cross section of $\textrm{t}\overline{\textrm{t}}$γ is also measured to be 56 ± 5 fb when considering only events where the photon is emitted in the production part of the process. Both measurements are in agreement with the theoretical predictions, of 126 ± 19 fb and 57 ± 5 fb, respectively. Differential measurements are performed at the particle and parton levels. Additionally, inclusive and differential ratios between the cross sections of $\textrm{t}\overline{\textrm{t}}$γ and $\textrm{t}\overline{\textrm{t}}$ production are measured. The inclusive ratio is found to be 0.0133 ± 0.0005, in agreement with the standard model prediction of 0.0127 ± 0.0008. The top quark charge asymmetry in $\textrm{t}\overline{\textrm{t}}$γ production is also measured to be −0.012 ± 0.042, compatible with both the standard model prediction and with no asymmetry.

Hadron-Hadron Scattering↗
DOE OSTI2021

Explaining (g-2) μ with multi-TeV sleptons

We present a supersymmetric extension of the Standard Model in which the new physics contributions to the anomalous magnetic moment of the muon can be more than an order of magnitude larger than in the minimal supersymmetric Standard Model. The extended electroweak symmetry breaking sector of the model can consistently accommodate Higgs bosons and Higgsinos with O (1) couplings to muons. We find that sleptons with masses in the multi-TeV range can comfortably explain the recently confirmed discrepancy in the anomalous magnetic moment of the muon. We discuss additional phenomenological aspects of the model, including its effects on tau flavor changing decays.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Measurement of the Higgs boson width and evidence of its off-shell contributions to ZZ production

Since the discovery of the Higgs boson in 2012, detailed studies of its properties have been ongoing. Besides its mass, its width - related to its lifetime - is an important parameter. One way to determine this quantity is by measuring its off-shell production, where the Higgs boson mass is far away from its nominal value, and relating it to its on-shell production, where the mass is close to the nominal value. Here, we report evidence for such off-shell contributions to the production cross section of two Z bosons with data from the CMS experiment at the CERN Large Hadron Collider. We constrain the total rate of the off-shell Higgs boson contribution beyond the Z boson pair production threshold, relative to its standard model expectation, to the interval [0.0061, 2.0] at 95% confidence level. The scenario with no off-shell contribution is excluded at a p-value of 0.0003 (3.6 standard deviations). We measure the width of the Higgs boson as $\Gamma_{\mathrm{H}}$ = 3.2 $_{-1.7}^{+2.4}$ MeV, in agreement with the standard model expectation of 4.1 MeV. In addition, we set constraints on anomalous Higgs boson couplings to W and Z boson pairs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Lepton flavor violation by three units

The conservation of lepton flavor is a prediction of the Standard Model and is still an excellent approximate symmetry despite our observation of neutrino oscillations. Lepton flavor violation by one or two units has been discussed for decades, with several dedicated experiments exploring the vast model landscape but no discoveries so far. Here, we explore operators and processes that violate at least one lepton flavor by three units and identify testable signatures. In the Standard Model effective field theory, such operators already arise at mass dimension 7 and can be tested through their contributions to Michel parameters in leptonic decays. True neutrinoless charged-lepton flavor violation arises at mass dimension 10 and can realistically only be seen in the tau decay channels 𝜏 → $𝑒⁢𝑒⁢𝑒⁢\bar{𝜇}⁢\bar{𝜇}$ or 𝜏 → $𝜇⁢𝜇⁢𝜇\bar{𝑒}\bar{𝑒}$, for example in Belle II. Testable rates for these tau decays require light new particles and subsequently predict an avalanche of remarkably clean but so-far unconstrained collider signatures.

Feynman diagrams↗
DOE OSTI2022

Tripling down on the W boson mass

A new precision measurement of the W boson mass has been announced by the CDF collaboration, which strongly deviates from the Standard Model prediction. In this article, we study the implications of this measurement on the parameter space of the SU(2) L triplet extension (with hypercharge Y=1) of the Standard Model Higgs sector, focusing on a limit where the new triplet is approximate Z 2 -odd while the SM is Z 2 -even. We study the compatibility of the triplet spectrum preferred by the W boson mass measured by the CDF-II experiment with other electroweak precision observables and Higgs precision data. We comprehensively consider the signals of new Higgs states at the LHC and highlighted the promising search channels. In addition, we also investigate the cosmological implications of the case in which the lightest new Higgs particle is either late decaying or cosmologically stable.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Search for electroweak production of supersymmetric particles in final states with two or three leptons at $\sqrt{s}=13 \hbox {TeV}$ with the ATLAS detector

A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb -1 of √s=13 TeV proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Long distance effects in inclusive rare B decays and phenomenology of $ \overline{B} $→ Xdℓ + ℓ -

Rare inclusive B decays such as $ \overline{B} $ → Xs(d)ℓ + ℓ - are interesting probes for physics beyond the Standard Model. Due to the complementarity to their exclusive counterparts, they might shed light on the anomalies currently seen in exclusive b → s transitions. Distinguishing new-physics effects from the Standard Model requires precise predictions and necessitates the control of long distance effects. In the present work we revisit and improve the description of various long distance effects in inclusive decays such as charmonium and light-quark resonances, nonfactorizable power corrections, and cascade decays. We then apply these results to a state-of-the-art phenomenological study of $ \overline{B} $ → Xdℓ + ℓ - , including also logarithmically enhanced QED corrections and the recently calculated fivebody contributions. To fully exploit the new-physics potential of inclusive flavour-changing neutral current decays, the $ \overline{B} $ → Xdℓ + ℓ - observables should be measured in a dedicated Belle II analysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Search for the Higgs boson decay to a Z boson and a photon in pp collisions at $\sqrt{s}$ = 13 TeV and 13.6 TeV with the ATLAS detector

A search for the Higgs boson decay to a Z boson and a photon in the ℓℓγ (ℓ = 𝑒,𝜇) final state is performed using pp collisions at $\sqrt{s}$ = 13.6 TeV recorded with the ATLAS detector at the Large Hadron Collider during 2022–2024, corresponding to an integrated luminosity of 165 fb−1. The signal yield, normalised to the Standard Model prediction, is measured to be 𝜇 = 0.9$^{+0.7}_{−0.6}$, compatible with the expected value of 𝜇 = 1.0 ± 0.7. This corresponds to an observed (expected) signal significance of 1.4 (1.5) standard deviations under the background-only hypothesis. This result is combined with that of a similar search performed with 140 fb −1 of $\sqrt{s}$ = 13 TeV pp collisions to provide the best expected sensitivity to date to this rare decay, namely an observed (expected) signal strength of 𝜇 = 1.3$^{+0.6}_{−0.5}$ (𝜇 = 1.0$^{+0.6}_{−0.5}$), corresponding to an observed (expected) significance of 2.5 (1.9) standard deviations. The measurement is consistent with the Standard Model expectation.

Aad, G. (ORCID:0000000266654934)↗
DOE OSTI2014

Tests of Lorentz and CPT Violation with MiniBooNE Neutrino Oscillation Excesses

Violation of Lorentz invariance and CPT symmetry is a predicted phenomenon of Planck-scale physics. Various types of data are analyzed to search for Lorentz violation under the Standard-Model Extension (SME) framework, including neutrino oscillation data. MiniBooNE is a short-baseline neutrino oscillation experiment at Fermilab. The measured excesses from MiniBooNE cannot be reconciled within the neutrino Standard Model (νSM); thus it might be a signal of new physics, such as Lorentz violation. We have analyzed the sidereal time dependence of MiniBooNE data for signals of the possible breakdown of Lorentz invariance in neutrinos. In this brief review, we introduce Lorentz violation, the neutrino sector of the SME, and the analysis of short-baseline neutrino oscillation experiments. We then present the results of the search for Lorentz violation in MiniBooNE data. This review is based on the published result.

Lorentz Violation↗
DOE OSTI2013

Handbook of LHC Higgs Cross Sections: 3. Higgs Properties

This Report summarizes the results of the activities in 2012 and the first half of 2013 of the LHC Higgs Cross Section Working Group. The main goal of the working group was to present the state of the art of Higgs Physics at the LHC, integrating all new results that have appeared in the last few years. This report follows the first working group report Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002) and the second working group report Handbook of LHC Higgs Cross Sections: 2. Differential Distributions (CERN-2012-002). After the discovery of a Higgs boson at the LHC in mid-2012 this report focuses on refined prediction of Standard Model (SM) Higgs phenomenology around the experimentally observed value of 125-126 GeV, refined predictions for heavy SM-like Higgs bosons as well as predictions in the Minimal Supersymmetric Standard Model and first steps to go beyond these models. The other main focus is on the extraction of the characteristics and properties of the newly discovered particle such as couplings to SM particles, spin and CP-quantum numbers etc.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Measurement of the inclusive and differential $t\overline{t}γ$ cross sections in the single-lepton channel and EFT interpretation at $\sqrt{s}$ = 13 TeV

The production cross section of a top quark pair in association with a photon is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The data set, corresponding to an integrated luminosity of 137 fb -1 , was recorded by the CMS experiment during the 2016–2018 data taking of the LHC. The measurements are performed in a fiducial volume defined at the particle level. Events with an isolated, highly energetic lepton, at least three jets from the hadronization of quarks, among which at least one is b tagged, and one isolated photon are selected. The inclusive fiducial $t\overline{t}γ$ cross section, for a photon with transverse momentum greater than 20 GeV and pseudorapidity |η| < 1.4442, is measured to be 798 ± 7(stat) ± 48(syst) fb, in good agreement with the prediction from the standard model at next-to-leading order in quantum chromodynamics. The differential cross sections are also measured as a function of several kinematic observables and interpreted in the framework of the standard model effective field theory (EFT), leading to the most stringent direct limits to date on anomalous electromagnetic dipole moment interactions of the top quark and the photon.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

The Heavy Photon Search experiment at Jefferson Laboratory

Many beyond Standard Model theories predict a new massive gauge boson, a.k.a. 'dark' or 'heavy photon', directly coupling to hidden sector particles with dark charge. The heavy photon is expected to mix with the Standard Model photon through kinetic mixing and therefore couple weakly to normal charge. The Heavy Photon Search (HPS) experiment will search for the heavy photon at the Thomas Jefferson National Accelerator Facility (JLab), in the mass range 20-1000 MeV/c 2 and coupling to electric charge ϵ 2 = α'/α in the range 10 -5 to 10 -10 . HPS will look for the e + e - decay channel of heavy photons radiated by electron Bremsstrahlung, employing both invariant mass search and detached vertexing techniques. The experiment employs a compact forward spectrometer comprising silicon microstrip detectors for vertexing and tracking and an electromagnetic calorimeter for particle identification and triggering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗