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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Measurement of fiducial differential cross sections of gluon-fusion production of Higgs bosons decaying to WW *→eνμν with the ATLAS detector at s = 8 $$ \sqrt{s}=8 $$ TeV

This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the H → W W*→ eνμν channel, using 20.3 fb -1 of proton-proton collision data. The data were produced at a centre-of-mass energy of √=8 TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed H→ W W*→ eνμν signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Measurement of $W^\pm$ boson production in Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\text {Te}\text {V}$ with the ATLAS detector

A measurement of W ± boson production in Pb+Pb collisions at √s NN =5.02 TeV is reported using data recorded by the ATLAS experiment at the LHC in 2015, corresponding to a total integrated luminosity of 0.49nb -1 . The W ± bosons are reconstructed in the electron or muon leptonic decay channels. Production yields of leptonically decaying W ± bosons, normalised by the total number of minimum-bias events and the nuclear thickness function, are measured within a fiducial region defined by the detector acceptance and the main kinematic requirements. These normalised yields are measured separately for W + and W - bosons, and are presented as a function of the absolute value of pseudorapidity of the charged lepton and of the collision centrality. The lepton charge asymmetry is also measured as a function of the absolute value of lepton pseudorapidity. In addition, nuclear modification factors are calculated using the W ± boson production cross-sections measured in pp collisions. The results are compared with predictions based on next-to-leading-order calculations with CT14 parton distribution functions as well as with predictions obtained with the EPPS16 and nCTEQ15 nuclear parton distribution functions. No dependence of normalised production yields on centrality and a good agreement with predictions are observed for mid-central and central collisions. For peripheral collisions, the data agree with predictions within 1.7 (0.9) standard deviations for W - (W + ) bosons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Seeking for sterile neutrinos with displaced leptons at the LHC

We study the signal of long-lived sterile neutrino at the LHC produced through the decay of the W boson. It decays into charged lepton and jets. The characteristic signature is a hard prompt lepton and a lepton from the displaced decay of the sterile neutrino, which leads to a bundle of displaced tracks with large transverse impact parameter. Different from other studies, we neither reconstruct the displaced vertex nor place requirement on its invariant mass to maintain sensitivity for low sterile neutrino masses. Instead, we focus on the displaced track from the lepton. A difficulty for low mass sterile neutrino study is that the displaced lepton is usually non-isolated.Therefore, leptons from heavy flavor quark is the major source of background. We closely follow a search for displaced electron plus muon search at CMS and study their control regions, which is related to our signal regions, in great detail to develop a robust estimation of the background for our signals. After further optimization on the signal limiting the number of jets, low H T and large lepton displacement d 0 to suppress SM background, we reach an exclusion sensitivity of about 10 -8 (10 -5 ) for the mixing angle square at 10 (2) GeV sterile neutrino mass respectively. Thestrategy we propose can cover the light sterile masses complimentary to beam dumpand forward detector experiments

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Muonic force behind flavor anomalies

We develop an economical theoretical framework for combined explanations of the flavor physics anomalies involving muons: (g - 2) μ , R K(*), and b → sμ + μ - angular distributions and branching ratios, that was first initiated by some of us in ref. [1]. The Standard Model (SM) is supplemented with a lepton-flavored U(1) X gauge group. The U(1) X gauge boson with the mass of O(0.1) GeV resolves the (g - 2) μ tension. A TeV-scale leptoquark, charged under the U(1) X , carries a muon number and mediates B-decays without prompting charged lepton flavor violation or inducing proton decay. We explore the theory space of the chiral, anomaly-free U(1) X gauge extensions featuring the above scenario, and identify many suitable charge assignments for the SM+3ν R fermion content with the integer charges in the range X F i $\in$ [-10, 10]. We then carry out a comprehensive phenomenological study of the muonic force in representative benchmark models. Interestingly, we found models which can resolve the tension without conflicting the complementary constraints, and all of the viable parameter space will be tested in future muonic resonance searches. Finally, the catalog of the anomaly-free lepton-non-universal charge assignments motivated us to explore different directions in model building. We present a model in which the muon mass and the (g - 2) μ are generated radiatively from a common short-distance dynamics after the U(1) X breaking. We also show how to charge a vector leptoquark under U(1) μ-τ in a complete gauge model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Observation of $\gamma\gamma\to\tau\tau$ in proton-proton collisions and limits on the anomalous electromagnetic moments of the $\tau$ lepton

The production of a pair of τ leptons via photon–photon fusion, ${{\unicode{x03B3}\unicode{x03B3}\to\unicode{x03C4}\unicode{x03C4}}}$, is observed for the first time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb$^{−1}$. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of ${{\unicode{x03B3}\unicode{x03B3}\to\unicode{x03C4}\unicode{x03C4}}}$ is $\sigma^\text{fid}_\text{obs} = 12.4 ^{+3.8}_{-3.1}\,\textrm{fb}$. Constraints are set on the contributions to the anomalous magnetic moment (${a_{\unicode{x03C4}}}$) and electric dipole moments (${d_{\unicode{x03C4}}}$) of the τ lepton originating from potential effects of new physics on the $\unicode{x03B3}\unicode{x03C4}\unicode{x03C4}$ vertex: ${a_{\unicode{x03C4}}} = 0.0009_{-0.0031}^{+0.0032}$ and $|{d_{\unicode{x03C4}}}| \lt 2.9\times 10^{-17}\,{e}\,\textrm{cm}$ (95% confidence level), consistent with the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Measurements of differential cross sections of top quark pair production as a function of kinematic event variables in proton-proton collisions at $ \sqrt{s}=13 $ TeV

Measurements of differential $ \mathrm{t}\overline{\mathrm{t}} $ production cross sections are presented in the single-lepton decay channel, as a function of a number of kinematic event variables. The measurements are performed with proton-proton collision data at $ \sqrt{s}=13 $ TeV, collected by the CMS experiment at the LHC during 2016, with an integrated luminosity of 35.9 fb$^{−1}$. The data are compared to a variety of state-of-the-art leading-order and next-to-leading-order $ \mathrm{t}\overline{\mathrm{t}} $ simulations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

New vector-like fermions and flavor physics

We study renormalizable extensions of the standard model that contain vector-like fermions in a (single) complex representation of the standard model gauge group. There are 11 models where the vector-like fermions Yukawa couple to the standard model fermions via the Higgs field. These models do not introduce additional fine-tunings. They can lead to, and are constrained by, a number of different flavor-changing processes involving leptons and quarks, as well as direct searches. An interesting feature of the models with strongly interacting vector-like fermions is that constraints from neutral meson mixings (apart from CP violation in $ {K}^0-{\overline{K}}^0 $ mixing) are not sensitive to higher scales than other flavor-changing neutral-current processes. We identify order 1/(4πM) 2 (where M is the vector-like fermion mass) one-loop contributions to the coefficients of the four-quark operators for meson mixing, that are not suppressed by standard model quark masses and/or mixing angles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1984

Cosmic-ray antiprotons as a probe of a photino-dominated universe

Observational tests of the hypothesis that the universe is flat and dominated by dark matter in the form of massive photinos include the production of significant fluxes of cosmic rays and gamma rays in our galactic halo. Specification of the cosmological photino density and the masses of scalar quarks and leptons determines the present annihilation rate. The predicted number of low-energy cosmic-ray antiprotons is comparable to the observed flux.

Silk, J.↗
DOE OSTI2016

Measurement of fiducial differential cross sections of gluon-fusion production of Higgs bosons decaying to W W ∗ → e ν μ ν with the ATLAS detector at s = 8 TeV

CERN-LHC. This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the H->WW*->e nu mu nu channel, using 20.3 fb^{-1} of proton--proton collision data. The data were produced at a centre-of-mass energy of sqrt(s) = 8 TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed H->WW*->e nu mu nu signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Precise measuring mass and spin of dark matter particles at ILC via singularities in the single lepton energy spectrum

We consider models, in which stability of Dark Matter particles D is ensured by the conservation of the new quantum number, called D-parity here. Our models contain also charged D-odd particle D{sup ±}. We propose method for precision measuring masses and spin of D-particles via the study of energy distribution of single lepton (e or μ) in the process e{sup +} e{sup −} → D{sup +} D{sup −} → DDW{sup +} W{sup −} with the observable state dijet + μ (or e) + nothing. It is shown that this distribution has kinematically determined singular points (upper edge and kinks or peak). Measuring of their positions allow to determine precisely masses of D and D{sup ±}. After this, even a rough measuring of corresponding cross section allows to determine the spin of D particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

13 TeV pp collisions, SM type, PYTHIA8 generator: tev13pp_pythia8_qcd_em

Filtered QCD multijet events (2->2 process) using a electron and muon filters. PDF: LHAPDF6:NNPDF23_lo_as_0130_qed. The sample was created using the Pythia8 tune Tune:pp = 14, similar to ATLAS. The sample was created for ATLAS studies of dijet+lepton event topologies. EM filters: Events contain at least one final state electron or muon from QCD dijet events. The leptons are isolated to make sure there is no hadronic activity around. This was done by using a cone of 0.2 around the lepton, and by requiring that the lepton carries at least 90% of energy of the 0.2 cone in eta and phi. In addition, fake lepton and muon rates were simulated. It is assumed that an antiKT4 jet with less than 10 numbers of constituents have 10% chance to be electron, and 1% chance to be a muon. Such fake leptons were put at the end of the event records. The particles that were used for fake leptons were subtracted from the original event record. How to use weights: This is weighted events to obtain good statistics up to very large pT. This feature is set via PhaseSpace:bias2Selection and PhaseSpace:bias2SelectionPow = 5.0. Use event weights to obtain correct pT distribution. Slimmed as: Particle records are slimmed (all stable with pT>0.3 GeV) and (PID=5 || PID=6) or PID>22 && PID<38) or PID>10 && PID<17). Note: Created for ATLAS BSM analysis

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Search for Baryon Number Violation in Top Quark Production and Decay Using Proton-Proton Collisions at $\sqrt{𝑠}$ = 13 TeV

A search is presented for baryon number violating interactions in top quark production and decay. The analysis uses data from proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC with an integrated luminosity of 138 fb −1 . Candidate events are selected by requiring two oppositely charged leptons (electrons or muons) and exactly one jet identified as originating from a bottom quark. Multivariate discriminants are used to separate the signal from the background. No significant deviation from the standard model prediction is observed. Upper limits are placed on the strength of baryon number violating couplings. For the first time the production of single top quarks via baryon number violating interactions is studied. This allows the search to set the most stringent constraints to date on the branching fraction of the top quark decay to a lepton, an up-type quark (𝑢 or 𝑐), and a down-type quark (𝑑, 𝑠, or 𝑏). The results improve the previous bounds by 3 to 6 orders of magnitude based on the fermion flavor combination of the baryon number violating interactions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Search for new physics in same-sign dilepton events in proton-proton collisions at √s = 13 TeV

A search for new physics is performed using events with two isolated same-sign leptons, two or more jets, and missing transverse momentum. The results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 2.3 fb 1 . Multiple search regions are defined by classifying events in terms of missing transverse momentum, the scalar sum of jet transverse momenta, the transverse mass associated with a W boson candidate, the number of jets, the number of b quark jets, and the transverse momenta of the leptons in the event. The analysis is sensitive to a wide variety of possible signals beyond the standard model. No excess above the standard model background expectation is observed. Constraints are set on various supersymmetric models, with gluinos and bottom squarks excluded for masses up to 1300 and 680 GeV, respectively, at the 95% confidence level. Upper limits on the cross sections for the production of two top quark-antiquark pairs (119 fb) and two same-sign top quarks (1.7 pb) are also obtained. Furthermore, selection efficiencies and model independent limits are provided to allow further interpretations of the results.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Three-dimensional core-collapse supernova models with phenomenological treatment of neutrino flavor conversions

Abstract We perform three-dimensional supernova simulations with a phenomenological treatment of neutrino flavor conversions. We show that the explosion energy can increase to as high as $\sim 10^{51}$ erg depending on the critical density for the onset of flavor conversions, due to a significant enhancement of the mean energy of electron antineutrinos. Our results confirm previous studies showing such energetic explosions, but for the first time in three-dimensional configurations. In addition, we predict neutrino and gravitational wave (GW) signals from a nearby supernova explosion aided by flavor conversions. We find that the neutrino event number decreases because of the reduced flux of heavy-lepton neutrinos. In order to detect GWs, next-generation GW telescopes such as Cosmic Explorer and the Einstein Telescope are needed even if the supernova event is located at the Galactic Center. These findings show that the neutrino flavor conversions can significantly change supernova dynamics and highlight the importance of further studies on the quantum kinetic equations to determine the conditions of the conversions and their asymptotic states.

Mori, Kanji↗
DOE OSTI2021

Measurements of differential cross-sections in four-lepton events in 13 TeV proton-proton collisions with the ATLAS detector

Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb -1 of $ \sqrt{s} $ = 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single Z boson production, Higgs boson production and on-shell ZZ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The Z → 4 ℓ branching fraction is extracted, giving a value of (4.41 ± 0.30) × 10 -6 . Constraints on effective field theory parameters and a model based on a spontaneously broken B – L gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for new physics in events with same-sign dileptons and jets in pp collisions at $\sqrt{s}$ = 8 TeV

A search for new physics is performed based on events with jets and a pair of isolated, same-sign leptons. The results are obtained using a sample of proton-proton collision data collected by the CMS experiment at a centre-of-mass energy of 8 TeV at the LHC, corresponding to an integrated luminosity of 19.5 inverse femtobarns. In order to be sensitive to a wide variety of possible signals beyond the standard model, multiple search regions defined by the missing transverse energy, the hadronic energy, the number of jets and b-quark jets, and the transverse momenta of the leptons in the events are considered. No excess above the standard model background expectation is observed and constraints are set on a number of models for new physics, as well as on the same-sign top-quark pair and quadruple-top-quark production cross sections. As a result, information on event selection efficiencies is also provided, so that the results can be used to confront an even broader class of new physics models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

$L_\mu - L_\tau$ theory of Higgs flavor violation and $(g-2)_\mu$

Several experiments reported hints for the violation of lepton flavor or lepton flavor universality in processes involving muons. Most prominently, there is the hint for a nonzero rate of the flavor violating Higgs decay h→τμ at the LHC, as well as the hint for lepton flavor universality violation in rare B meson decays at the LHCb. In addition, also the long-standing discrepancy in the anomalous magnetic moment of the muon motivates new physics connected to muons. A symmetry which violates lepton flavor universality is Lμ-Lτ: the difference of muon number and tau number. We show that adding vectorlike fermions to a Lμ-Lτ theory generates naturally an effect in the anomalous magnetic moment of the muon and h→τμ, while effects in other τ→μ transitions are systematically suppressed by symmetry arguments. We find that if Lμ-Lτ is gauged it is possible to also accommodate the discrepant b→sμμ data while predicting a τ→3μ and a modified h→μμ rate within reach of upcoming experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for B + → K + τ + τ - at the BaBar Experiment

We search for the rare flavor-changing neutral current process B + → K + τ + τ - using data from the BABAR experiment. The data sample, collected at the center-of-mass energy of the Υ ( 4 S ) resonance, corresponds to a total integrated luminosity of 424 fb - 1 and to 471 × 1 0 6 B$\bar{B}$ pairs. We reconstruct one B meson, produced in the Υ ( 4 S ) → B + B - decay, in one of many hadronic decay modes and search for activity compatible with a B + → K + τ + τ - decay in the rest of the event. Each τ lepton is required to decay leptonically into an electron or muon and neutrinos. Comparing the expected number of background events with the data sample after applying the selection criteria, we do not find evidence for a signal. The resulting upper limit, at the 90% confidence level, is B ( B + → K + τ + τ - ) < 2.25 × 10 - 3 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗