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At least 1,765 records · Page 98
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DOE OSTI2021

The proton radius (puzzle?) and its relatives

We review determinations of the electric proton charge radius from a diverse set of low-energy observables. We explore under which conditions it can be related to Wilson coefficients of appropriate effective field theories. This discussion is generalized to other low-energy constants. This provides us with a unified framework to deal with a set of low-energy constants of the proton associated with its electromagnetic interactions. Unambiguous definitions of these objects are given, as well as their relation with expectation values of QCD operators. We show that the proton radius obtained from spectroscopy and lepton–proton scattering (when both the lepton and proton move with nonrelativistic velocities) is related to the same object of the underlying field theory with O ( α ) precision. The model dependence of these analyses is discussed. The prospects of constructing effective field theories valid for the kinematic configuration of present, or near-future, lepton–proton scattering experiments are explored.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Disentangling the various Mechanisms of neutrinoless double beta decay to extract the neutrino mass

It is well known that there exist many mechanisms that may contribute to neutrinoless double beta decay. By exploiting the fact that the associated nuclear matrix elements are target dependent we show that, given definite experimental results on a sufficient number of targets, one can determine or sufficiently constrain all lepton violating parameters including the mass term. As a specific example we show that, given the observation of the 0{nu}{beta}{beta}-decay in three different nuclei, e.g. {sup 76}Ge, {sup 100}Mo and {sup 130}Te, and assuming just three active lepton number violating parameters, e.g. light and heavy neutrino mass mechanisms in left handed currents as well as R-parity breaking SUSY mechanism, one may determine all lepton violating parameters, provided that they are relatively real.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

GAMMA-RAY BURST SPECTRA AND SPECTRAL CORRELATIONS FROM SUB-PHOTOSPHERIC COMPTONIZATION

One of the most important unresolved issues in gamma-ray burst (GRB) physics is the origin of the prompt gamma-ray spectrum. Its general non-thermal character and the softness in the X-ray band remain unexplained. We tackle these issues by performing Monte Carlo simulations of radiation–matter interactions in a scattering dominated photon–lepton plasma. The plasma—initially in equilibrium—is driven to non-equilibrium conditions by a sudden energy injection in the lepton population, mimicking the effect of a shock wave or the dissipation of magnetic energy. Equilibrium restoration occurs due to an energy exchange between the photons and leptons. While the initial and final equilibrium spectra are thermal, the transitional photon spectra are characterized by non-thermal features such as power-law tails, high energy bumps, and multiple components. Such non-thermal features are observed at infinity if the dissipation occurs at small to moderate optical depths, and the spectrum is released before thermalization is complete. We model the synthetic spectra with a Band function and show that the resulting spectral parameters are similar to observations for a frequency range of 2–3 orders of magnitude around the peak. In addition, our model predicts correlations between the low-frequency photon index and the peak frequency as well as between the low- and high-frequency indices. We explore baryon and pair-dominated fireballs and reach the conclusion that baryonic fireballs are a better model for explaining the observed features of GRB spectra.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Two radiative inverse seesaw models, dark matter, and baryogenesis

The inverse seesaw mechanism allows the neutrino masses to be generated by new physics at an experimentally accessible scale, even with O(1) Yukawa couplings. In the inverse seesaw scenario, the smallness of neutrino masses is linked to the smallness of a lepton number violating parameter. This parameter may arise radiatively. In this paper, we study the cosmological implications of two contrasting radiative inverse seesaw models, one due to Ma and the other to Law and McDonald. The former features spontaneous, the latter explicit lepton number violation. First, we examine the effect of the lepton-number violating interactions introduced in these models on the baryon asymmetry of the universe. We investigate under what conditions a pre-existing baryon asymmetry does not get washed out. While both models allow a baryon asymmetry to survive only once the temperature has dropped below the mass of their heaviest fields, the Ma model can create the baryon asymmetry through resonant leptogenesis. Then we investigate the viability of the dark matter candidates arising within these models, and explore the prospects for direct detection. We find that the Law/McDonald model allows a simple dark matter scenario similar to the Higgs portal, while in the Ma model the simplest cold dark matter scenario would tend to overclose the universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Common origin of neutrino mass, dark matter and Dirac leptogenesis

We study the possibility of generating tiny Dirac neutrino masses at one loop level through the scotogenic mechanism such that one of the particles going inside the loop can be a stable cold dark matter (DM) candidate. Majorana mass terms of singlet fermions as well as tree level Dirac neutrino masses are prevented by incorporating the presence of additional discrete symmetries in a minimal fashion, which also guarantee the stability of the dark matter candidate. Due to the absence of total lepton number violation, the observed baryon asymmetry of the Universe is generated through the mechanism of Dirac leptogenesis where an equal and opposite amount of leptonic asymmetry is generated in the left and right handed sectors which are prevented from equilibration due to tiny Dirac Yukawa couplings. Dark matter relic abundance is generated through its usual freeze-out at a temperature much below the scale of leptogenesis. We constrain the relevant parameter space from neutrino mass, baryon asymmetry, Planck bound on dark matter relic abundance, and latest LUX bound on spin independent DM-nucleon scattering cross section. We also discuss the charged lepton flavour violation (μ → e γ) and electric dipole moment of electron in this model in the light of the latest experimental data and constrain the parameter space of the model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Flavor-violating ALPs, electron g − 2 , and the Electron-Ion Collider

We revisit the possibility that light axionlike particles (ALPs) with lepton-flavor-violating couplings could give significant contributions to the electron’s anomalous magnetic moment g e − 2 . Unlike flavor diagonal lepton-ALP couplings, which are exclusively axial, lepton-flavor-violating couplings can have arbitrary chirality. Focusing on the e − τ ALP coupling, we find that the size of the contribution to g e − 2 depends strongly on the chirality of the coupling. A significant part of the parameter space for which such a coupling can explain experimental anomalies in g e − 2 can be probed at the Electron-Ion Collider, which is uniquely sensitive to the chirality of the coupling using the polarization of the electron beam. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Collider signatures of the SO(5)xU(1) gauge-Higgs unification

Collider signatures of the SO(5)xU(1) gauge-Higgs unification model in the Randall-Sundrum warped space are explored. Gauge couplings of quarks and leptons receive small corrections from the fifth dimension whose effects are tested by the precision data. It is found that the forward-backward asymmetries in e{sup +}e{sup -} collisions on the Z pole are well explained in a wide range of the warp factor z{sub L}, but the model is consistent with the branching fractions of Z decay only for large z{sub L} > or approx. 10{sup 15}. Kaluza-Klein (KK) spectra of gauge bosons, quarks, and leptons as well as gauge and Higgs couplings of low-lying KK excited states are determined. Right-handed quarks and leptons have larger couplings to the KK gauge bosons than left-handed ones. Production rates of Higgs bosons and KK states at the Tevatron, LHC, and International Linear Collider are evaluated. The first KK Z has a mass 1130 GeV with a width 422 GeV for z{sub L}=10{sup 15}. The current limit on the Z' production at the Tevatron and LHC indicates z{sub L}>10{sup 15}. A large effect of parity violation appears in the difference between the rapidity distributions of e{sup +} and e{sup -} in the decay of the first KK Z. The first KK gauge bosons decay into light and heavy quarks evenly.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement and Interpretation of Moments of the Combined Hadronic Mass and Energy Spectrum in Inclusive Semileptonic B-Meson Decays

This thesis presents first measurements of moments of the hadronic n X 2 distribution measured in inclusive semileptonic decays of B mesons to final states containing a charm quark, B → X c ℓν. The variable n X 2 is a combination of the invariant mass of the charmed meson m X , its energy in the B-meson rest-frame E X;BRF , and a constant ~Λ = 0.65 GeV, n X 2 = m X 2 c 4 -2~ΛE X,BRF + ~Λ 2 . The moments <n X k > with k = 2,4,6 are measured as proposed by theory to constrain assumptions made in the theoretical description of inclusive observables in semileptonic B-meson decays. This description uses Heavy Quark Expansion (HQE), an effective QCD combined with an Operator Product Expansion. The measurement is based on a sample of 231.6 million e + e - → Υ(4S) {yields} B$\bar{B}$ events recorded with the BABAR experiment at the PEP-II e + e - -storage rings at SLAC. We reconstruct the semileptonic decay by identifying a charged lepton in events tagged by a fully reconstructed hadronic decay of the second B meson. Correction procedures are derived from Monte Carlo simulations to ensure an unbiased measurement of the moments of the n X 2 distribution. All moments are measured requiring minimum lepton momenta between 0.8 GeV/c and 1.9 GeV/c in the rest frame of the B meson. Performing a simultaneous fit to the measured moments <n X k > up to order k = 6 combined with other measurements of moments of the lepton-energy spectrum in decays B → X c ℓν and moments of the photon-energy spectrum in decays B → X s γ, we determine the quark-mixing parameter |V cb |, the bottom and charm quark masses, the semileptonic branching fraction β(B → X c ℓν), and four non-perturbative heavy quark parameters. Using HQE calculations in the kinetic scheme up to order 1/m b 3 we find |V cb | = (41.65 ± 0.43 ± 0.40 ± 0.58) • 10 -3 and m b = (4.570 ± 0.033 ± 0.043) GeV/c 2 , where the first uncertainty refers to experimental contributions, the second to uncertainties in the HQE, and the third to theoretical uncertainties in the calculations of the semileptonic decay rate Λ(B {yields} X c ℓν). All obtained results are consistent with previous determinations. The inclusion of the moments <n X 6 > decreases the uncertainty on the HQE parameters μ π 2 and ρ D 3 . Furthermore, the theoretical treatment of higher order corrections in the HQE used for the moments <m X k > has been verified with these new measurements.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Evidence for $WZ/WW\to \ell \nu$ + Heavy Flavors Vector Boson Production in 7.5 fb$^{-1}$ of CDF Data

This contribution describes a search for the associated production of Standard Model vector bosons WZ where the W boson decays leptonically (W {yields} {ell}{nu}) and the Z boson decays to a heavy flavor quark pair (Z {yields} b{bar b}, c{bar c}). At least one identified ('tagged') heavy flavor jet in the final state is required. Given the small di-jet invariant mass separation between the W and the Z resonances, the production of WW events where one W decays leptonically and the second W decays into an heavy flavor jet (e.i. W{sup + {yields} c{bar s}) contributes to our the signal. This search uses data collected with the CDF II detector at the Tevatron Collider at Fermilab, and corresponding to an integrated luminosity of approximately 7.5 fb{sup -1}. Events consistent with the signature of a charged lepton (electron or muon), large missing transverse energy and exactly two jets, of which at least one is required to contain a secondary vertex displaced from the jet origin, are selected. A multivariate discriminant based on the Support Vector Machine algorithm is used to reduce greatly the multi-jet background contamination. We observe a signal of significance of 3.03{sigma} over the background only hypothesis. A cross section of 1.085{sub -0.40}{sup +0.26} times the expected Standard Model value for the combined WZ/WW production and decay into heavy flavors is measured, consistent with the Standard Model prediction.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Search for LFV in Tau- to L- L+ L- Decays at BaBar

We report the results of search for the neutrinoless lepton-flavor violating decay of the tau lepton into three charged leptons, performed using 376 fb{sup -1} of data collected at an e{sup +}e{sup -} center-of-mass energy around 10.58 GeV with the BaBar detector at the PEP-II. In all six decay modes considered, the number of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (4-8) x 10{sup -8} at 90% confidence level.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Global Fits for PDFs

Constraining the d PDF at large values of x has traditionally relied, in part, on the use of deeply inelastic lepton deuterium scattering data. In order to utilize such data, one must include nuclear corrections which account for Fermi motion, binding, and off-shell effects. The impact of these corrections in the context of a global fit are examined. The uncertainties due to these nuclear effects are large.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Electron-Nucleus Scattering Process at Intermediate Energy Transfers

Many-body approach to the lepton-nucleus scattering is being tested. Preliminary results containing the 1p1h and {Delta}(1232)h excitations from local Fermi gas are shown. Comparisons are made with the selected inclusive electron scattering data. The importance of the different physical channels is discussed. The main attention is paid to the lepton energy range from about 500 to 2000 MeV, which is crucial for the present T2K and future NOvA neutrino oscillation experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Using Neutrino Nucleus Interactions as a Probe of the Strong Interaction

Neutrino scattering experiments have been studying QCD for over 30 years. From the Gargamelle experiments in the early 70's, through the subsequent bubble chamber and electronic detector experiments in the 80's and 90's, neutrino scattering experiments have steadily accumulated increasing statistics and minimized their systematic errors. An example of the more recent studies of QCD with neutrinos is from the TeVatron neutrino beam--the NuTeV {nu}-Fe experiment. The problem the community faces in trying to study QCD with modern neutrino data is that there is no experimentally verified way to scale neutrino-nucleus (for example, Fe) results to the equivalent neutrino-nucleon values making it difficult to combine neutrino nucleus scattering data with charged-lepton nucleus and nucleon scattering data in QCD global fits to extract parton distribution functions. This is particularly crucial since there is now indications that nuclear effects in neutrino nucleus interactions are different than those measured in charged-lepton nucleus scattering. To better understand this situation, the MINER{nu}A neutrino-nucleus scattering experiment at Fermilab, a collaboration of elementary-particle and nuclear physicists, is systematically studying neutrino nuclear effects off of He, C, Fe and Pb for a more thorough A-dependent study of nuclear PDFs and these correction factors.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Nuclear corrections in {nu}A DIS and their compatibility with global NPDF analyses

We perform a global {chi}{sup 2}-analysis of nuclear parton distribution functions using data from charged current neutrino--nucleus({nu}A) deep inelastic scattering (DIS), charged-lepton--nucleus (l{sup {+-}A}) DIS, and the Drell-Yan (DY) process. We show that the nuclear corrections in {nu}A DIS are not compatible with the predictions derived from l{sup {+-}A} DIS and DY data. We quantify this result using a hypothesis-testing criterion based on the {chi}{sup 2} distribution which we apply to the total {chi}{sup 2} as well as to the {chi}{sup 2} of the individual data sets. We find that it is not possible to accommodate the data from {nu}A and l{sup {+-}A} DIS by an acceptable combined fit. Our result has strong implications for the extraction of both nuclear and proton PDFs using combined neutrino and charged lepton data sets.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

EMC effect for light nuclei: new results from Jefferson Lab

High energy lepton scattering has been the primary tool for mapping out the quark distributions of nucleons and nuclei. Measurements of deep inelastic scattering in nuclei show that the quark distributions in heavy nuclei are not simply the sum of the quark distributions of the constituent proton and neutron, as one might expect for a weakly bound system. This modification of the quark distributions in nuclei is known as the EMC effect. I will discuss the results from Jefferson Lab (JLab) experiment E03-103, a precise measurement of the EMC effect in few-body nuclei with emphasis on the large x region. Data from the light nuclei suggests that the nuclear dependence of the high x quark distribution may depend on the nucleon's local environment, rather than being a purely bulk effect. In addition, I will also discuss about a future experiment at the upgraded 12 GeV Jefferson Lab facility which will further investigate the role of the local nuclear environment and the influence of detailed nuclear structure to the modification of quark distributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Low-energy effective field theory below the electroweak scale: anomalous dimensions

We compute the one-loop anomalous dimensions of the low-energy effective Lagrangian below the electroweak scale, up to terms of dimension six. The theory has 70 dimension-five and 3631 dimension-six Hermitian operators that preserve baryon and lepton number, as well as additional operators that violate baryon number and lepton number. The renormalization group equations for the quark and lepton masses and the QCD and QED gauge couplings are modified by dimension-five and dimension-six operator contributions. We compute the renormalization group equations from one insertion of dimension-five and dimension-six operators, as well as two insertions of dimension-five operators, to all terms of dimension less than or equal to six. As a result, the use of the equations of motion to eliminate operators can be ambiguous, and we show how to resolve this ambiguity by a careful use of field redefinitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Search for heavy Majorana neutrinos in same-sign dilepton channels in proton-proton collisions at $ \sqrt{s}=13 $ TeV

A search is performed for a heavy Majorana neutrino (N), produced in leptonic decay of a W boson propagator and decaying into a W boson and a lepton, with the CMS detector at the LHC. The signature used in this search consists of two same-sign leptons, in any flavor combination of electrons and muons, and at least one jet. The data were collected during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The results are found to be consistent with the expected standard model background. Upper limits are set in the mass range between 20 and 1600 GeV in the context of a Type-I seesaw mechanism, on |V$_{eN}$|$^{2}$, |V$_{μN}$|$^{2}$, and |V$_{eN}$V$_{μN}^{*}$ |$^{2}$/(|V$_{eN}$|$^{2}$ + |V$_{μN}$|$^{2}$), where V$_{ℓN}$ is the matrix element describing the mixing of N with the standard model neutrino of flavor ℓ = e, μ. For N masses between 20 and 1600 GeV, the upper limits on |V$_{ℓN}$|$^{2}$ range between 2.3 × 10$^{-5}$ and unity. These are the most restrictive direct limits for heavy Majorana neutrino masses above 430 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗