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At least 1,657 records · Page 92
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Multi-Higgs doublet models with local U(1){sub H} gauge symmetry and neutrino physics therein

Multi-Higgs doublet models appear in many interesting extensions of the standard model (SM). But they suffer from Higgs-mediated flavor changing neutral current (FCNC) problem which is very generic. In this talk, I describe that this problem can be resolved or mitigated if we introduce local U(1){sub H} Higgs flavor gauge symmetry. As examples, I describe chiral U(1){sub H} models where the right-handed up-type quarks also carry U(1){sub H} charges and discuss the top forward-backward asymmetry (FBA) and B → D{sup (*)}τν puzzle. Next I describe the two-Higgs doublet models where the usual Z₂ symmetry is implemented to U(1){sub H} and show how the Type-I and Type-II models are extended. One possible extension of Type-II has the same fermion contents with the leptophobic E₆Z´ model by Rosner, and I discuss the neutrino sector in this model briefly.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Search for triple Higgs boson production in the 6⁢𝑏 final state using 𝑝⁢𝑝 collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for the production of three Higgs bosons (𝐻⁡𝐻⁡𝐻) 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 𝐻⁡𝐻⁡𝐻. The resonant interpretations primarily consider a cascade decay topology of 𝑋 →𝑆⁢𝐻 → 𝐻⁡𝐻⁡𝐻 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 𝐻⁡𝐻⁡𝐻 production, with limits on the trilinear and quartic Higgs self-coupling set. No evidence for 𝐻⁡𝐻⁡𝐻 production is observed. An upper limit of 59 fb is set, at the 95% confidence level, on the cross section for Standard Model 𝐻⁡𝐻⁡𝐻 production.

Artificial neural networks↗
DOE OSTI2025

Search for heavy neutral resonances decaying to tau lepton pairs in proton-proton collisions at $\sqrt{s}$=13 TeV

A search for heavy neutral gauge bosons (𝑍′) decaying into a pair of tau leptons is performed in proton-proton collisions at $\sqrt{s}$ =13 TeV at the CERN LHC. The data were collected with the CMS detector and correspond to an integrated luminosity of 138 fb −1 . The observations are found to be in agreement with the expectation from standard model processes. Limits at 95% confidence level are set on the product of the 𝑍′ production cross section and its branching fraction to tau lepton pairs for a range of 𝑍′ boson masses. For a narrow resonance in the sequential standard model scenario, a 𝑍′ boson with a mass below 3.5 TeV is excluded. This is the most stringent limit to date from this type of search.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for associated production of a Z boson with a single top quark and for tZ flavour-changing interactions in pp collisions at $ \sqrt{s}=8 $ TeV

A search for the production of a single top quark in association with a Z boson is presented, both to identify the expected standard model process and to search for flavour-changing neutral current interactions. The data sample corresponds to an integrated luminosity of 19.7 fb$^{−1}$ recorded by the CMS experiment at the LHC in proton-proton collisions at $ \sqrt{s}=8 $ TeV. Final states with three leptons (electrons or muons) and at least one jet are investigated. An events yield compatible with tZq standard model production is observed, and the corresponding cross section is measured to be σ(pp → tZq → ℓνbℓ$^{+}$ ℓ$^{−}$q) = 10$_{− 7}^{+ 8}$ fb with a significance of 2.4 standard deviations. No presence of flavour-changing neutral current production of tZq is observed. Exclusion limits at 95% confidence level on the branching fractions of a top quark decaying to a Z boson and an up or a charm quark are found to be ℬ(t → Zu) < 0.022% and ℬ(t → Zc) < 0.049%.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Constraints on fifth forces and ultralight dark matter from OSIRIS-REx target asteroid Bennu

It is important to test the possible existence of fifth forces, as ultralight bosons that would mediate these are predicted to exist in several well-motivated extensions of the Standard Model. Recent work indicated asteroids as promising probes, but applications to real data are lacking so far. Here we use the OSIRIS-REx mission and ground-based tracking data for the asteroid Bennu to derive constraints on fifth forces. Our limits are strongest for mediator masses m ~ (10 -18 -10 -17 ) eV, where we currently achieve the tightest bounds. These can be translated to a wide class of models leading to Yukawa-type fifth forces, and we demonstrate how they apply to U(1) B dark photons and baryon-coupled scalars. Our results demonstrate the potential of asteroid tracking in probing well-motivated extensions of the Standard Model and ultralight bosons near the fuzzy dark matter range.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

High-Sensitivity Nuclear-Structure Studies of Rare Isotopes and Few-Electron Systems

This final technical report presents the work that was completed during the award period for DE-SC0017649 related to the structure of nuclei for both astrophysics and tests of the Standard Model, namely: Using trapped bare (and few-electron) radioactive ions to probe the nature of elec- troweak decay modes under extreme conditions for structure and astrophysics, Providing experimental nuclear structure guidance to nuclear theory in systems relevant for testing the Standard Model, and Working with the HPGe sub-group of the FRIB decay station collaboration, which includes the technical development of a next-generation γ-ray spectrometer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Neutrino physics beyond the current paradigm

An exciting program of international neutrino experiments aims to complete our understanding of three-neutrino mixing in the Standard Model (SM), which has had great success in describing world neutrino data. However, there exist a number of short-baseline neutrino anomalies that do not fit into this simple picture and could be pointing us instead to phenomena beyond the Standard Model (BSM). Neutrinos and neutrino experiments are excellent laboratories to search for BSM physics for a number a reasons. First, neutrinos mass itself is evidence of BSM physics as it implies the addition of new fields to the SM. In addition, neutrino properties are not well-constrained and allow sizable, new interactions. Finally, accelerator- and reactor-based short-baseline neutrino experiments bring high luminosity sources of photons, nuclear, and meson decays near large, sensitive detectors and can therefore probe a variety of dark sector models. In this talk, I will give an overview of worldwide accelerator- and reactor-based short-baseline neutrino experiments and their efforts to search for physics beyond the current paradigm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

TASI Lectures on WIMPs and Supersymmetry

Weakly interacting massive particles (WIMPs) are an appealing and well studied candidate for dark matter (DM) that arise in many extensions of the standard model. I will discuss where a WIMP sits in the catalogue of DM candidates, its origin as a thermal relic, and the various approaches available to discover it. The prototypical example of a WIMP is the neutralino of the minimal supersymmetric standard model (MSSM). I will give an introduction to the formalism and phenomenology of supersymmetry and the MSSM, with emphasis on DM. These notes are the combination of lectures given at TASI 2018 and a Joint ICTP-Trieste/ICTP-SAIFR School.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1989

On the wavelength dependence of apparent emissivity of asteroid microwave emissions - Ceres and Vesta

Observations of Ceres and Vesta demonstrate the need for modifying the physical parameters of the standard model procedure in treating single-wavelength observations. It is suggested that simultaneous IR and cm-wavelength data should be used in order to determine such properties as the surface dielectric characteristics, layer depth, and radio emissivity. If using the standard model, an emissivity of 0.8 should be adopted for wavelengths of longer than 1 cm.

Webster, William J., Jr.↗
DOE OSTI2012

Top anti-top Asymmetries at the Tevatron and the LHC

The heaviest known elementary particle today, the top quark, has been discovered in 1995 by the CDF and D0 collaborations at the Tevatron proton antiproton collider at Fermilab. Recently, the CDF and D0 collaborations have studied the forward-backward asymmetry in ttbar events, resulting in measured values larger than the standard model prediction. With the start of the LHC at CERN in 2010, a new top quark factory has opened and asymmetry measurements in ttbar have also been performed in a proton proton environment with higher collision energy. No deviations from the standard model have been noticed so far in the measurements of ATLAS and CMS. This article discusses recent results of asymmetry measurements in ttbar events of the ATLAS, CDF, CMS and D0 collaborations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of electroweak $Z\left(\nu \overline{\nu}\right)\gamma jj$ production and limits on anomalous quartic gauge couplings in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

The electroweak production of $Z\left(\nu \overline{\nu}\right)\gamma jj$ in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton–proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb –1 collected by the ATLAS detector during the 2015–2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial $Z\left(\nu \overline{\nu}\right)\gamma jj$ cross section for electroweak production is measured to be ${0.77}_{-0.30}^{+0.34}$ fb and is consistent with the Standard Model prediction. Evidence of electroweak $Z\left(\nu \overline{\nu}\right)\gamma jj$ production is found with an observed significance of 3.2σ for the background-only hypothesis, compared with an expected significance of 3.7σ. The combination of this result with the previously published ATLAS observation of electroweak $Z\left(\nu \overline{\nu}\right)\gamma jj$ production yields an observed (expected) signal significance of 6.3σ (6.6σ). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Erratum to: Constraining couplings of top quarks to the Z boson in $ t\overline{t} $ + Z production at the LHC

We study top quark pair production in association with a Z boson at the Large Hadron Collider (LHC) and investigate the prospects of measuring the couplings of top quarks to the Z boson. To date these couplings have not been constrained in direct measurements. Such a determination will be possible for the first time at the LHC. Our calculation improves previous coupling studies through the inclusion of next-to-leading order (NLO) QCD corrections in production and decays of all unstable particles. We treat top quarks in the narrow-width approximation and retain all NLO spin correlations. To determine the sensitivity of a coupling measurement we perform a binned log-likelihood ratio test based on normalization and shape information of the angle between the leptons from the Z boson decay. The obtained limits account for statistical uncertainties as well as leading theoretical systematics from residual scale dependence and parton distribution functions. We use current CMS data to place the first direct constraints on the ttbZ couplings. We also consider the upcoming high-energy LHC run and find that with 300 inverse fb of data at an energy of 13 TeV the vector and axial ttbZ couplings can be constrained at the 95% confidence level to C_V=0.24^{+0.39}_{-0.85} and C_A=-0.60^{+0.14}_{-0.18}, where the central values are the Standard Model predictions. This is a reduction of uncertainties by 25% and 42%, respectively, compared to an analysis based on leading-order predictions. We also translate these results into limits on dimension-six operators contributing to the ttbZ interactions beyond the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Search for high-mass resonances in final states with a τ-lepton and missing transverse momentum with the ATLAS detector

A search for high-mass resonances decaying into a τ-lepton and a neutrino using proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ =13 TeV is presented. The full run 2 data sample corresponding to an integrated luminosity of 139 fb -1 recorded by the ATLAS experiment in the years 2015–2018 is analyzed. The τ-lepton is reconstructed in its hadronic decay modes and the total transverse momentum carried out by neutrinos is inferred from the reconstructed missing transverse momentum. The search for new physics is performed on the transverse mass between the τ-lepton and the missing transverse momentum. No excess of events above the Standard Model expectation is observed and upper exclusion limits are set on the W' →τ⁢v production cross section. Heavy W' vector bosons with masses up to 5.0 TeV are excluded at 95% confidence level, assuming that they have the same couplings as the Standard Model W boson. For nonuniversal couplings, W' bosons are excluded for masses less than 3.5–5.0 TeV, depending on the model parameters. In addition, model-independent limits on the visible cross section times branching ratio are determined as a function of the lower threshold on the transverse mass of the τ-lepton and missing transverse momentum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Learning new physics from data: A symmetrized approach

Thousands of person years have been invested in searches for new physics (NP), the majority of them motivated by theoretical considerations. Yet, no evidence of beyond the Standard Model physics has been found. This suggests that model-agnostic searches might be an important key to explore NP, and help discover unexpected phenomena which can inspire future theoretical developments. A possible strategy for such searches is identifying asymmetries between data samples that are expected to be symmetric within the Standard Model. We propose exploiting neural networks (NNs) to quickly fit and statistically test the differences between two samples. Our method is based on an earlier work, originally designed for inferring the deviations of an observed dataset from that of a much larger reference dataset. We present a symmetric formalism, generalizing the original one, avoiding fine-tuning of the NN parameters and any constraints on the relative sizes of the samples. Our formalism could be used to detect small symmetry violations, extending the discovery potential of current and future particle physics experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for the Dimuon Decay of the Higgs Boson in p p Collisions at s = 13 TeV with the ATLAS Detector

A search for the dimuon decay of the Higgs boson was performed using data corresponding to an integrated luminosity of 36.1 fb -1 collected with the ATLAS detector in p p collisions at √ s = 13 TeV at the Large Hadron Collider. No significant excess is observed above the expected background. The observed (expected) upper limit on the cross section times branching ratio is 3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a Higgs boson mass of 125 GeV. Finally, when combined with the p p collision data at √ s = 7 TeV and √ s = 8 TeV , the observed (expected) upper limit is 2.8 (2.9) times the Standard Model prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Constraining the Higgs potential with neural simulation-based inference for di-Higgs production

Determining the form of the Higgs potential is one of the most exciting challenges of modern particle physics. Higgs pair production directly probes the Higgs self-coupling and should be observed in the near future at the High-Luminosity LHC. We explore how to improve the sensitivity to physics beyond the Standard Model through per-event kinematics for di-Higgs events. In particular, we employ machine learning through simulation-based inference to estimate per-event likelihood ratios and gauge potential sensitivity gains from including this kinematic information. In terms of the Standard Model Effective Field Theory, we find that adding a limited number of observables can help to remove degeneracies in Wilson coefficient likelihoods and significantly improve the experimental sensitivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Search for WH associated production in pp̄ collisions at √s=1.96 TeV

This report describes a search for associated production of W and Higgs bosons based on data corresponding to an integrated luminosity of L≈5.3 fb⁻¹ collected with the D0 detector at the Fermilab Tevatron pp̄ Collider. Events containing a W→lν candidate (with l corresponding to e or μ) are selected in association with two or three reconstructed jets. One or two of the jets are required to be consistent with having evolved from a b quark. A multivariate discriminant technique is used to improve the separation of signal and backgrounds. Expected and observed upper limits are obtained for the product of the WH production cross section and branching ratios and reported in terms of ratios relative to the prediction of the standard model as a function of the mass of the Higgs boson (M H ). The observed and expected 95% C.L. upper limits obtained for an assumed M H =115 GeV are, respectively, factors of 4.5 and 4.8 larger than the value predicted by the standard model.

Abazov, V. M.↗
DOE OSTI2024

Dark Photon Search at the Short-Baseline Near Detector

Neutrino physics has long been a key field in elementary particle physics, both enhancing our understanding of the Standard Model (SM) and raising new questions. Among these are the so-called "Short-Baseline Anomalies" observed by neutrino experiments, particularly the MiniBooNE experiment at Fermilab, which detected an excess of low-energy electron-like events. In recent years, beyond Standard Model (BSM) explanations have been proposed to address this anomaly, with a focus on neutrino beam-related processes. A novel interpretation involving a dark-sector explanation was recently suggested, introducing a vector portal that connects the SM and dark sectors through a new interaction mediated by a bosonic particle, the Dark Photon. This work investigates the production of dark-sector particles, specifically Dark Photons, in the Booster Neutrino Beam (BNB) at Fermilab and their potential detection at the Short-Baseline Near Detector (SBND). The BNB produces mesons which decay into Dark Photons, detectable via their decay into electron-positron pairs at SBND. By exploiting the temporal structure of the neutrino beam, we propose a method to isolate Dark Photon signals from neutrino backgrounds using time-delayed event detection. In this thesis, the sensitivity of SBND to Dark Photons is assessed using a three-year exposure, demonstrating that SBND has the potential to significantly improve current experimental constraints on Dark Photons. This analysis provides a promising avenue for future dark sector searches in neutrino experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗