Lepton Number Violation: Seesaw Models and Their Collider Tests
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Results for “LEPTONS”
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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Ab initio Calculations of Lepton-Nucleus Scattering
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Dispersion And Energy Compensation in High-Gradient Linacs for Lepton Colliders
The shape of an rf pulse is distorted due to dispersion encountered in acceleration through traveling-wave linear accelerator structures. Simulations are made to ascertain the severity of this distortion in cavities designed to operate at various group velocities. The pulse suffers maximum degradation when propagated through accelerating cavities with a phase advance per cell in the vicinity of {pi}, where the group velocity reaches its minimum value. Several cavities are simulated to study the pulse distortion and compared with experiments performed on a high phase advance structure H60VG3, which has a phase advance of 5{pi}/6 per cell. A circuit model and a mode matching code are used to perform these simulations on accelerating structures consisting of multiple cells. Beam loading is taken into account and the implications on energy dispersion are also analyzed. Means of mitigating for this energy deviation are discussed.
43 PARTICLE ACCELERATORS↗
Search for lepton flavour violation in the emu continuum with the ATLAS detector in sqrt(s) = 7 TeV pp collisions at the LHC
This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark (tilde-(t)) in the e{sup {+-}} {mu}{sup {+-}} continuum using 2.1 fb{sup -1} of data collected by the ATLAS detector in {radical}s=7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95% C.L. are calculated as a function of the scalar top mass (m{sub [tilde-(t)]}). The upper limits on the production cross section for pp{yields}e{mu}X, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m{sub [tilde-(t)]}=95 GeV to 30 fb for m{sub [tilde (t)]}=1000 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for lepton flavour violation in the e mu continuum with the ATLAS detector in root s=7 TeV pp collisions at the LHC
This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ({tilde t}) in the e{sup {+-}} {mu}{sup {-+}} continuum using 2.1 fb{sup -1} of data collected by the ATLAS detector in {radical}s = 7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95% C.L. are calculated as a function of the scalar top mass (m{sub {tilde t}}). The upper limits on the production cross section for pp {yields} e{mu}X, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m{sub {tilde t}} = 95 GeV to 30 fb for m{sub {tilde t}} = 1000 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Muon g-2 and lepton flavor violation in a two Higgs doublets model for the fourth generation
N/A
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the branching fractions of radiative leptonic τ decays τ → ℓγν anti-ν (ℓ=e,μ) at BABAR
We perform a measurement of the branching fractions for τ → ℓγν anti ν, (ℓ = e, μ) decays for a minimum photon energy of 10 MeV in the τ rest frame using 430 fb -1 of e + e - collisions collected at the center-of-mass energy of the Υ(4S) resonance with the BABAR detector at the PEP-II storage rings. We find B(τ → μγνν) = (3.69±0.03±0.10)×10 3 and B(τ → eγνν) = (1.847 ± 0.015 ± 0.052) × 10 -2 where the first quoted error is statistical and the second is systematic. These results represent a substantial improvement with respect to existing measurements for both channels.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Leptonic B- and D-Meson Decay Constants with 2+1 Flavors of Asqtad Fermions
We present the status of our updated D- and B-meson decay-constant analysis, based on the MILC N f =2+1 asqtad gauge ensembles. Heavy quarks are incorporated using the Wilson clover action with the Fermilab interpretation. This analysis includes ensembles at five lattice spacings from α ≈ 0.045 to 0.15 fm, and light sea-quark masses down to 1/20 th of the strange-quark mass. Projected error budgets for ratios of decay constants, in particular between bottom- and charm-meson decay constants, are presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for heavy quarks decaying into a top quark and a W or Z boson using lepton + jets events in pp collisions at $ \sqrt{s}=7 $ TeV
Results are presented from a search for the pair-production of heavy quarks, Q Q-bar, that decay exclusively into a top quark and a W or Z boson. The search is performed using a sample of proton-proton collisions at $\sqrt{s}$ = 7 TeV corresponding to an integrated luminosity of 5.0 inverse femtobarns, collected by the Compact Muon Solenoid experiment. The signal region is defined using a sample of events containing one electron or muon, missing transverse momentum, and at least four jets with large transverse momenta, where one jet is likely to originate from the decay of a bottom quark. No significant excess of events is observed with respect to the standard model expectations. Assuming a strong pair-production mechanism, quark masses below 675 (625) GeV decaying into tW (tZ) are excluded at the 95% confidence level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the W W + W Z cross section and limits on anomalous triple gauge couplings using final states with one lepton, missing transverse momentum, and two jets with the ATLAS detector at $ \sqrt{s}=7 $ TeV
The production of a W boson decaying to eν or μν in association with a W or Z boson decaying to two jets is studied using 4.6 fb -1 of proton-proton collision data at $ \sqrt{s}$ =7 TeV recorded with the ATLAS detector at the LHC. The combined WW + WZ cross section is measured with a significance of 3.4σ and is found to be 68 ± 7 (stat.)±19 (syst.) pb , in agreement with the Standard Model expectation of 61.1 ± 2.2 pb . The distribution of the transverse momentum of the dijet system is used to set limits on anomalous contributions to the triple gauge coupling vertices and on parameters of an effective-field-theory model.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
“Unification” of BSM searches and SM measurements: the case of lepton+E T and m W
We develop the idea that the unprecedented precision in Standard Model (SM) measurements, with further improvement at the HL-LHC, enables new searches for physics Beyond the Standard Model (BSM). As an illustration, we demonstrate that the measured kinematic distributions of the ℓ + E T final state not only determine the mass of the W boson, but are also sensitive to light new physics. Such a search for new physics thus requires a simultaneous fit to the BSM and SM parameters, “unifying” searches and measurements at the LHC and Tevatron. In this paper, we complete the program initiated in our earlier work [1]. In particular, we analyze (i) novel decay modes of the W boson with a neutrinophilic invisible scalar or with a heavy neutrino; (ii) modified production of W bosons, namely, associated with a hadrophilic invisible Z′ gauge boson; and (iii) scenarios without an on-shell W boson, such as slepton-sneutrino production in the Minimal Supersymmetric Standard Model (MSSM). Here, we complement our previous MSSM analysis in [1] by considering a different kinematic region. Our results highlight that new physics can still be directly discovered at the LHC, including light new physics, via SM precision measurements. Furthermore, we illustrate that such BSM signals are subtle, yet potentially large enough to affect the precision measurements of SM parameters themselves, such as the W boson mass.
Electroweak Precision Physics↗
Collins-type fragmentation energy correlator in semi-inclusive deep inelastic lepton-hadron scattering
We initiate a systematic study of fragmentation energy correlators (FECs), which generalize traditional fragmentation functions and encode non-perturbative information about transverse dynamics in parton fragmentation processes. We define boost-invariant, non-perturbative FECs and derive a corresponding collinear factorization formula. A spin decomposition of the FECs is carried out, analogous to that of transverse-momentum-dependent fragmentation functions. In this work we focus particularly on the Collins-type quark FEC, which is sensitive to chiral symmetry breaking and characterizes the azimuthal asymmetry in the fragmentation of a transversely polarized quark. We perform a next-to-leading-order calculation of the corresponding hard coefficient in semi-inclusive deep-inelastic scattering for the quark non-singlet component, thereby validating the consistency of our theoretical framework.
Deep Inelastic Scattering or Small-x Physics↗
Search for charged Higgs bosons through the violation of lepton universality in t(t)over-bar events using pp collision data at root s=7 TeV with the ATLAS experiment
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for heavy resonances decaying into a W or Z boson and a Higgs boson in final states with leptons and b -jets in 36 fb -1 of $ \sqrt{s}=13 $ TeV pp collisions with the ATLAS detector
Here, a search is conducted for new resonances decaying into a W or Z boson and a 125 GeV Higgs boson in the $v\bar{v}$$b\bar{b}$, ℓ ± ν$b\bar{b}$, and ℓ + ℓ - $b\bar{b}$ final states, where ℓ ± = e ± or μ ± , in pp collisions at $\sqrt{s}$ =13 TeV. The data used correspond to a total integrated luminosity of 36.1 fb -1 collected with the ATLAS detector at the Large Hadron Collider during the 2015 and 2016 data-taking periods. The search is conducted by examining the reconstructed invariant or transverse mass distributions of W h and Zh candidates for evidence of a localised excess in the mass range of 220 GeV up to 5 TeV. No significant excess is observed and the results are interpreted in terms of constraints on the production cross-section times branching fraction of heavy W' and Z' resonances in heavy-vector-triplet models and the CP-odd scalar boson A in two-Higgs-doublet models. Upper limits are placed at the 95% confidence level and range between 9.0 × 10 -4 pb and 7.3 × 10 -1 pb depending on the model and mass of the resonance.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Search for $\mathrm{t\overline{t}}$H production in the H $\rightarrow$ $\mathrm{b\overline{b}}$ decay channel with leptonic $\mathrm{t\overline{t}}$ decays in proton-proton collisions at $\sqrt{s} =$ 13 TeV
A search is presented for the associated production of a standard model Higgs boson with a top quark-antiquark pair ($\mathrm{t\overline{t}}$H), in which the Higgs boson decays into a b quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy $\sqrt{s} =$ 13 TeV. The data correspond to an integrated luminosity of 35.9 fb$^{-1}$ recorded with the CMS detector at the CERN LHC. Candidate $\mathrm{t\overline{t}}$H events are selected that contain either one or two electrons or muons from the $\mathrm{t\overline{t}}$ decays and are categorised according to the number of jets. Multivariate techniques are employed to further classify the events and eventually discriminate between signal and background. The results are characterised by an observed $\mathrm{t\overline{t}}$H signal strength relative to the standard model cross section, $\mu = \sigma$ / $\sigma_{\mathrm{SM}}$, under the assumption of a Higgs boson mass of 125 GeV. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit on $\mu$ of 1.5 (0.9) at 95% confidence level, and a best fit value of 0.72 $\pm$ 0.24 (stat) $\pm$ 0.38 (syst), corresponding to an observed (expected) signal significance of 1.6 (2.2) standard deviations above the background-only hypothesis.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the inclusive and differential Higgs boson production cross sections in the leptonic WW decay mode at $\sqrt{s} =$ 13 TeV
Measurements of the fiducial inclusive and differential production cross sections of the Higgs boson in proton-proton collisions at $ \sqrt{s} $ = 13 TeV are performed using events where the Higgs boson decays into a pair of W bosons that subsequently decay into a final state with an electron, a muon, and a pair of neutrinos. The analysis is based on data collected with the CMS detector at the LHC during 2016–2018, corresponding to an integrated luminosity of 137 fb$^{−1}$. Production cross sections are measured as a function of the transverse momentum of the Higgs boson and the associated jet multiplicity. The Higgs boson signal is extracted and simultaneously unfolded to correct for selection efficiency and resolution effects using maximum-likelihood fits to the observed distributions in data. The integrated fiducial cross section is measured to be 86.5 ± 9.5 fb, consistent with the Standard Model expectation of 82.5 ± 4.2 fb. No significant deviation from the Standard Model expectations is observed in the differential measurements.[graphic not available: see fulltext]
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Lepton-pair production at hadron colliders at N 3 LO in QCD
We compute for the first time the complete corrections at N 3 LO in the strong coupling constant to the inclusive neutral-current Drell-Yan process including contributions from both photon and Z-boson exchange. Our main result is the computation of the QCD corrections to the inclusive production cross section of an axial-vector boson to third order in the strong coupling in a variant of QCD with five massless quark flavours. Since the axial anomaly does not cancel for an odd number of flavours, we also consistently include non-decoupling effects in the top-quark mass through three loops. We perform a phenomenological study of our results, and we present for the first time predictions for the inclusive Drell-Yan process at the LHC at this order in QCD perturbation theory.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing the fermionic Higgs portal at lepton colliders
Here, we study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator H † Hχ¯χ. Measurements of precision electroweak S and T parameters and the e + e – → Zh cross-section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also provide full one-loop results for S and T in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗