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At least 1,513 records · Page 84
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Resonance region structure functions and parity-violating deep inelastic scattering

The primary motive of parity-violating deep inelastic scattering experiments has been to test the standard model, particularly the axial couplings to the quarks, in the scaling region. The measurements can also test for the validity of models for the off-diagonal structure functions ${F}_{1,2,3}^{γZ}$($x,Q^2$) in the resonance region. The off-diagonal structure functions are important for the accurate calculation of the $γZ$-box correction to the weak charge of the proton. Currently, with no data to determine ${F}_{1,2,3}^{γZ}$($x,Q^2$) directly, models are constructed by modifying existing fits to electromagnetic data. Here, we present the asymmetry value for deuteron and proton targets predicted by several different ${F}_{1,2,3}^{γZ}$($x,Q^2$) models and demonstrate that there are notable disagreements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Measurement of the forward-backward asymmetry of μ{sup +}μ{sup −} pairs in CMS

The measurement of the forward-backward asymmetry A{sub FB} and the effective weak mixing angle with the Drell-Yan process at the LHC is presented. The samples of 2011 collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5 fb{sup −1} and 1.1 fb{sup −1}, were used. The results are consistent with the standard model expectations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Search for dark matter in events with heavy quarks and missing transverse momentum in pp collisions with the ATLAS detector

This article reports on a search for dark matter pair production in association with bottom or top quarks in 20.3 fb –1 of pp collisions collected at √s=8 TeV by the ATLAS detector at the LHC. Events with large missing transverse momentum are selected when produced in association with high-momentum jets of which one or more are identified as jets containing b-quarks. Final states with top quarks are selected by requiring a high jet multiplicity and in some cases a single lepton. The data are found to be consistent with the Standard Model expectations and limits are set on the mass scale of effective field theories that describe scalar and tensor interactions between dark matter and Standard Model particles. Limits on the dark-matter–nucleon cross-section for spin-independent and spin-dependent interactions are also provided. These limits are particularly strong for low-mass dark matter. Using a simplified model, constraints are set on the mass of dark matter and of a colored mediator suitable to explain a possible signal of annihilating dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

A search for new phenomena in pp collisions at $\sqrt{s} = 13\,\text {TeV} $ in final states with missing transverse momentum and at least one jet using the $\alpha _{\mathrm {T}}$ variable

A search for new phenomena is performed in final states containing one or more jets and an imbalance in transverse momentum in pp collisions at a centre-of-mass energy of 13 $\,\text {TeV}$ . The analysed data sample, recorded with the CMS detector at the CERN LHC, corresponds to an integrated luminosity of 2.3 $\,\text {fb}^{-1}$ . Several kinematic variables are employed to suppress the dominant background, multijet production, as well as to discriminate between other standard model and new physics processes. The search provides sensitivity to a broad range of new-physics models that yield a stable weakly interacting massive particle. The number of observed candidate events is found to agree with the expected contributions from standard model processes, and the result is interpreted in the mass parameter space of fourteen simplified supersymmetric models that assume the pair production of gluinos or squarks and a range of decay modes. For models that assume gluino pair production, masses up to 1575 and 975 $\,\text {GeV}$ are excluded for gluinos and neutralinos, respectively. For models involving the pair production of top squarks and compressed mass spectra, top squark masses up to 400 $\,\text {GeV}$ are excluded.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Software Quality Metrics for Geant4: An Initial Assessment - Paper 122

In the context of critical applications, such as shielding and radiation protection, ensuring the quality of simulation software they depend on is of utmost importance. The assessment of simulation software quality is crucial both to determine its adoption in experimental applications and to guarantee reproducibility of outcome over time. Geant4 is a simulation system used in a wide range of experimental applications, some of which, such as radiation protection and biomedical studies, may involve critical use cases and would especially profit from an objective assessment of the software quality. In this study, we present the first results from an ongoing analysis of Geant4 code based on established software metrics from the perspective of software engineering. The analysis evaluates the current status of the code to quantify its characteristics with respect to documented quality standards; further appraisals concern evolutions over a series of release distributions. The quantitative assessment of the software is initially focused on a subset of Geant4 packages, which play a key role in scientific applications and are representative of different software development processes. We describe the chosen software metrics that map the entities of a software system to numeric values through mathematical definitions, quantifying software attributes ranging from functionality to maintainability. To measure such metrics, we exploited a set of software metrics tools, i.e. programs that implement a set of software metrics definitions. They allow software engineers to assess a software system by extracting the required attributes from the software and providing the corresponding metric values. To correlate software metrics values in a well-defined way, we used software quality standard models, such as the ISO/IEC 9126 standard, which aggregate numerical values to aid quality analysis and assessment. With this work we aim to create a baseline for evaluating correlations between software quality embedded in the Geant4 development process and simulation observables produced by Geant4-based applications. Furthermore, we intend to highlight what metrics are most effective at evaluating radiation transport software quality. We are confident that the result will provide constructive guidance both to improve key software tools, such as Geant4, and to estimate their contribution in risk analysis concerning sensitive applications. The remainder of this paper is structured as follows. We first discuss the approach adopted to fulfil our assessment. Then, we present the setup of our experiments and the way we collected data. We provide an initial interpretation of a subset of data resulting from measurements made on the selected Geant4 packages. As the analysis is still ongoing at the time of submitting this abstract, some results will be documented in the final paper and in the conference presentation. With this work we aim to create a proper Geant4 data set for evaluating its software characteristics and identifying both strengths and weaknesses. In this initial study, we considered the geometry and processes packages, which play a major role in most simulation applications. The data analysis is in progress at the time of writing; its complexity is related to the differences among software metrics tools, to the large amount of data to be evaluated and to the pioneering character of this project. We are confident that the results will provide valuable indications for the Geant4 user community and constructive guidance to improve key Geant4 packages. Other Monte Carlo codes could profit from the methodology developed in this pilot project for similar assessments of their software quality. At the end of this study, we intend to create a baseline for evaluating correlations between software quality embedded in the Geant4 development process and simulation observables produced by Geant4-based applications. (authors)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2020

Quantum Critical Higgs: from AdS 5 to colliders

We examine distinctive signatures of Quantum Critical Higgs models at the LHC and future higher energy colliders. In these models the Higgs boson is part of a conformal sector that is softly broken at a threshold scale, and generically the scaling dimension of the Higgs is larger than in the Standard Model. In particular we examine the gg → H → ZZ, gg → H → γγ, and gg → Z → H Z channels to see how the cross sections deviate from the Standard Model in the high invariant mass region. In order to perform the calculations we use 5D duals of Quantum Critical Higgs models using the AdS/CFT correspondence, with a soft wall to break the conformal symmetry.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Study of exclusive two-photon production of $W^+W^-$ in $pp$ collisions at $\sqrt{s} = 7$ TeV and constraints on anomalous quartic gauge couplings

A search for exclusive or quasi-exclusive W + W $-$ production by photon-photon interactions, pp → p(*)W + W $-$ p(*), at TeV is reported using data collected by the CMS detector with an integrated luminosity of 5.05 fb $-$1 . Events are selected by requiring a μ ± e ∓ vertex with no additional associated charged tracks and dilepton transverse momentum p T (μ ± e ∓ ) > 30 GeV. Two events passing all selection requirements are observed in the data, compared to a standard model expectation of 2.2 ± 0.4 signal events with 0.84 ± 0.15 background. The tail of the dilepton p T distribution is studied for deviations from the standard model. No events are observed with p T > 100 GeV. Model-independent upper limits are computed and compared to predictions involving anomalous quartic gauge couplings. The limits on the parameters α$W\atop{0,C}$/Λ 2 with a dipole form factor and an energy cutoff Λ cutoff = 500 GeV are of the order of 10 $-$4 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Towards grounding nuclear physics in QCD

Exascale computing could soon enable a predictive theory of nuclear structure and reactions rooted in the Standard Model, with quantifiable and systematically improvable uncertainties. Such a predictive theory will help exploit experiments that use nucleons and nuclei as laboratories for testing the Standard Model and its limitations. Examples include direct dark matter detection, neutrinoless double beta decay, and searches for permanent electric dipole moments of the neutron and atoms. It will also help connect QCD to the properties of cold neutron stars and hot supernova cores. We discuss how a quantitative bridge between QCD and the properties of nuclei and nuclear matter will require a synthesis of lattice QCD (especially as applied to two- and three- nucleon interactions), effective field theory, and ab initio methods for solving the nuclear many-body problem. While there are significant challenges that must be addressed in developing this triad of theoretical tools, the rapid advance of computing is accelerating progress. In particular, we focus this review on the anticipated advances from lattice QCD and how these advances will impact few-body effective theories of nuclear physics by providing critical input, such as constraints on unknown low-energy constants of the effective (field) theories. We also review particular challenges that must be overcome for the successful application of lattice QCD for low-energy nuclear physics. We describe progress in developing few-body effective (field) theories of nuclear physics, with an emphasis on HOBET, a non-relativistic effective theory of nuclear physics, which is less common in the literature. We use the examples of neutrinoless double beta decay and the nuclear-matter equation of state to illustrate how the coupling of lattice QCD to effective theory might impact our understanding of symmetries and exotic astrophysical environments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for Invisible Decays of a Higgs Boson Produced in Association with a Z Boson in ATLAS

A search for evidence of invisible-particle decay modes of a Higgs boson produced in association with a Z boson at the Large Hadron Collider is presented. No deviation from the standard model expectation is observed in 4.5 fb -1 (20.3 fb -1 ) of 7 (8) TeV pp collision data collected by the ATLAS experiment. Assuming the standard model rate for ZH production, an upper limit of 75%, at the 95% confidence level is set on the branching ratio to invisible-particle decay modes of the Higgs boson at a mass of 125.5 GeV. The limit on the branching ratio is also interpreted in terms of an upper limit on the allowed dark matter-nucleon scattering cross section within a Higgs-portal dark matter scenario. Within the constraints of such a scenario, the results presented in this Letter provide the strongest available limits for low-mass dark matter candidates. Limits are also set on an additional neutral Higgs boson, in the mass range 110 < m H < 400 GeV, produced in association with a Z boson and decaying to invisible particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Optimal mass variables for semivisible jets

Strongly coupled hidden sector theories predict collider production of invisible, composite dark matter candidates mixed with standard model hadrons in the form of semivisible jets. Classical mass reconstruction techniques may not be optimal for these unusual topologies, in which the missing transverse momentum comes from massive particles and has a nontrivial relationship to the visible jet momentum. We apply the artificial event variable network, a semisupervised, interpretable machine learning technique that uses an information bottleneck, to derive superior mass reconstruction functions for several cases of resonant semivisible jet production. We demonstrate that the technique can extrapolate to unknown signal model parameter values. We further demonstrate the viability of conducting an actual search for new physics using this method, by applying the learned functions to standard model background events from quantum chromodynamics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Energy Audit of MC-1

The goal of the Muon g-2 project is to measure the muon magnetic anomalous moment to a precision of 140 ppb. This is an unprecedented endeavor that will allow for the comparison of the standard model’s prediction and experimental value of the muon magnetic anomaly. If the difference is statistically significant this could mean there is physics beyond the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Experimental status of top charge asymmetry measurements

The latest measurements of the asymmetry in the angular distributionsof the \ttbar\ events are reviewed. The measurements of the forward-backwardasymmetry \Afb\ in the \ppbar\ 1.98 TeV collisions at the Tevatronshow some tension with the Standard Model calculation, while resultsof the measurements of the charge asymmetry \Ac\ in $pp$ collisionsat 7 TeV and 8 TeV at the LHC are compatible with Standard Model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Overview of the Fermilab Muon g-2 Experiment

The measurement of the anomalous magnetic moment of muon provides a precision test of the Standard Model. The Brookhaven muon g-2 experiment (E821) measured the muon magnetic moment anomaly with 0.54 ppm precision, a more than 3 deviation from the Standard Model predictions, spurring speculation about the possibility of new physics. The new g-2 experiment at Fermilab (E989) will reduce the combined statistical and systematic error of the BNL experiment by a factor of 4. An overview of the new experiment is described in this article.

Kim, SeungCheon↗
DOE OSTI2012

Search for Heavy Neutrinos and W R Bosons with Right-Handed Couplings in a Left-Right Symmetric Model in p p Collisions at s = 7 TeV

Results are presented from a search for heavy, right-handed muon neutrinos, N[mu], and right-handed W[R] bosons, which arise in the left-right symmetric extensions of the standard model. The analysis is based on a 5.0 inverse femtobarn sample of proton-proton collisions at a center-of-mass energy of 7 TeV, collected by the CMS detector at the Large Hadron Collider. No evidence is observed for an excess of events over the standard model expectation. For models with exact left-right symmetry, heavy right-handed neutrinos are excluded at 95% confidence level for a range of neutrino masses below the W[R] mass, dependent on the value of M(W[R]). The excluded region in the two-dimensional (M(W[R]), M(N[mu])) mass plane extends to M(W[R]) = 2.5 TeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Search for the production of a Higgs boson in association with a single top quark in pp collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A search for the production of a Higgs boson in association with a single top quark, tH, is presented. The analysis uses proton-proton collision data corresponding to an integrated luminosity of 140 fb −1 at a centre-of-mass energy of 13 TeV, collected by the ATLAS detector at the LHC. The search targets Higgs-boson decays into $b\bar{b}$, WW * , ZZ * , and ττ, accompanied by an isolated lepton (electron or muon) from the top-quark decay. Multivariate techniques are employed to enhance the separation between signal and background processes. The observed signal strength, μ tH , defined as the ratio between the measured cross-section and the predicted Standard Model value, is μ tH = 8.1 ± 2.6 (stat.) ± 2.0 (syst.). The significance of the observed (expected) signal above the background-only expectation is 2.8 (0.4) standard deviations. The corresponding observed (expected) upper limit at the 95% confidence level on the tH cross-section is found to be 13.9 (6.1) times the value predicted by the Standard Model. An interpretation with an inverted sign of the top-quark Yukawa coupling is performed, and the signal strength and corresponding limit are reported.

Hadron-Hadron Scattering↗
DOE OSTI2014

Constraints on the CMB temperature evolution using multiband measurements of the Sunyaev-Zel'dovich effect with the South Pole Telescope

The adiabatic evolution of the temperature of the cosmic microwave background (CMB) is a key prediction of standard cosmology. We study deviations from the expected adiabatic evolution of the CMB temperature of the form T(z) = T 0 (1 + z) 1 - α using measurements of the spectrum of the Sunyaev–Zel'dovich effect with the South Pole Telescope (SPT). We present a method for using the ratio of the Sunyaev–Zel'dovich signal measured at 95 and 150 GHz in the SPT data to constrain the temperature of the CMB. We demonstrate that this approach provides unbiased results using mock observations of clusters from a new set of hydrodynamical simulations. We apply this method to a sample of 158 SPT-selected clusters, spanning the redshift range 0.05 < z < 1.35, and measure $\alpha = 0.017^{+0.030}_{-0.028}$, consistent with the standard model prediction of α = 0. In combination with other published results, we find α = 0.005 ± 0.012, an improvement of ~10 percent over published constraints. This measurement also provides a strong constraint on the effective equation of state in models of decaying dark energy w eff = -0.994 ± 0.010.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Revisiting 𝐶 and 𝐶⁢𝑃 violation in 𝜂 → 𝜋 + 𝜋 - ⁢𝜋 0 decay

The decay 𝜂 → 𝜋 + ⁢𝜋 − ⁢𝜋 0 is an ideal process in which to study flavor-conserving 𝐶 and 𝐶⁢𝑃 violation beyond the Standard Model. We deduce the 𝐶- and 𝐶⁢𝑃-odd quark operators that contribute to 𝜂 → 𝜋 + ⁢𝜋 − ⁢𝜋 0 originating from the mass-dimension-six Standard Model effective field theory. The corresponding hadron-level operators that generate a nonvanishing 𝐼 = 0 amplitude at order 𝑝 6 in the chiral effective theory are presented for the first time, to the best of our knowledge, in addition to the leading-order operators ascribed to the 𝐼 = 2 final state. By fitting the KLOE-2 and the most recent BESIII experimental data, we determine the coefficients of the lowest-order 𝐼 = 0 and 𝐼 = 2 amplitudes and estimate the potential new physics energy scale. We also perform an impact study of the future 𝜂 → 𝜋 + ⁢𝜋 − ⁢𝜋 0 experiments.

CP violation↗