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DOE OSTI2018

It’s all right(-handed neutrinos): a new W ' model for the R D ( ∗ ) anomaly

The measured B-meson semi-leptonic branching ratios R D and R D ∗ have long-standing deviations between theory and experiment. We introduce a model which explains both anomalies through a single interaction by introducing a right-handed neutrino as the missing energy particle. This interaction is mediated by a heavy charged vector boson (W ') which couples only to right-handed quarks and leptons of the Standard Model through the mixing of these particles with new vector-like fermions. Previous W ' models for the R D ( ∗ ) anomaly were strongly constrained from flavor changing neutral currents and direct collider searches for Z' → τ τ resonances. We show that relying on right-handed fermion mixing enables us to avoid these constraints, as well as other severe bounds from electroweak precision tests and neutrino mixing.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Representation of ideal magnetohydrodynamic modes

One of the most fundamental properties of ideal magnetohydrodynamics is the condition that plasma motion cannot change magnetic topology. The conventional representation of ideal magnetohydrodynamic modes by perturbing a toroidal equilibrium field through {delta}B(vector sign)={nabla} Multiplication-Sign ({xi}(vector sign) Multiplication-Sign B(vector sign)) ensures that {delta}B(vector sign){center_dot}{nabla}{psi}=0 at a resonance, with {psi} labelling an equilibrium flux surface. Also useful for the analysis of guiding center orbits in a perturbed field is the representation {delta}B(vector sign)={nabla} Multiplication-Sign {alpha}B(vector sign). These two representations are equivalent, but the vanishing of {delta}B(vector sign){center_dot}{nabla}{psi} at a resonance is necessary but not sufficient for the preservation of field line topology, and a indiscriminate use of either perturbation in fact destroys the original equilibrium flux topology. It is necessary to find the perturbed field to all orders in {xi}(vector sign) to conserve the original topology. The effect of using linearized perturbations on stability and growth rate calculations is discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

Weak production of strange particles and η mesons off the nucleon

The strange particle production induced by (anti)neutrino off nucleon has been studied for |ΔS| = 0 and |ΔS| = 1 channels. The reactions those we have considered are for the production of single kaon/antikaon, eta and associated particle production processes. We have developed a microscopical model based on the SU(3) chiral Lagrangian. The basic parameters of the model are f{sub π}, the pion decay constant, Cabibbo angle, the proton and neutron magnetic moments and the axial vector coupling constants for the baryons octet. For antikaon production we have also included Σ*(1385) resonance and for eta production S{sub 11}(1535) and S{sub 11}(1650) resonances are included.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Effective theories of dark mesons with custodial symmetry

Dark mesons are bosonic composites of a new, strongly-coupled sector beyond the Standard Model. We consider several dark sectors with fermions that transform under the electroweak group, as arise from a variety of models including strongly-coupled theories of dark matter (e.g., stealth dark matter), bosonic technicolor (strongly-coupled indcued electroweak symmetry breaking), vector-like confinement, etc. We consider theories with two and four flavors under an SU(N) strong group that acquire variously chiral, vector-like, and mixed contributions to their masses. We construct the non-linear sigma model describing the dark pions and match the ultraviolet theory onto a low energy effective theory that provides the leading interactions of the lightest dark pions with the Standard Model. We uncover two distinct classes of effective theories that are distinguishable by how the lightest dark pions decay: “Gaugephilic”: where π 0 → Zh, π ± → W h dominate once kinematically open, and “Gaugephobic”: where π 0 →$\bar{f}f$, π ± →$\bar{f'}f$ dominate. Custodial SU(2) plays a critical role in determining the “philic” or “phobic” nature of a model. In dark sectors that preserve custodial SU(2), there is no axial anomaly, and so the decay π 0 → γγ is highly suppressed. In a companion paper, we study dark pion production and decay at colliders, obtaining the constraints and sensitsivity at the LHC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2014

The in-medium effects on the neutrino reaction in dense matter

The nucleon form factors in free space are usually thought to be modified when a nucleon is bound in a nucleus or immersed in a nuclear medium. We investigated effects of the density-dependent axial and weak-vector form factors on the electro-neutrino (ν{sub e}) and anti-electro-neutrino (¯ν{sub e}) reactions with incident energy E{sub v} ≤ 80 MeV via neutral current (NC) and charged current (CC) for a nucleon in a nuclear medium or ¹²C. For the density-dependent form factors, we exploited the quark-meson-coupling (QMC) model, and apply them to the ν{sub e} and ¯ν{sub e} induced reactions by NC and CC. In CC reaction, about 5 % decrease of the electro neutrino (ν{sub e}) reaction cross section on the nucleon is shown to be occurred in normal density, ρ=ρ{sub 0}~0.15fm⁻³, and also about 5 % reduction of total ν{sub e} cross section on ¹²C is obtained by the modification of the weak form factors for bound nucleons. Density effects for both cases are relatively small, but they are as large as the effect by the Coulomb distortion of outgoing leptons in the ν-reaction. However, density effects in the anti-electro neutrino (¯ν{sub e}) reaction reduced significantly about 30 % the cross sections for both the nucleon and ¹²C cases. For NC, about 12 % decrease of the total cross section by the ν{sub e} reaction on the nucleon is obtained at normal density, ρ=ρ₀~0.15fm⁻³, as well as about 18 % reduction of the total ν{sub e} cross section on ¹²C, by the modification of the weak form factors of the bound nucleon. However, similarly to the CC reaction, effects of the nucleon property change in the ¯ν{sub e} reaction reduce significantly the cross sections about 30 % for the nucleon in matter and ¹²C cases. In this talk, we address that such a large asymmetry in the ¯ν{sub e} cross sections in both reactions is originated from the different helicities of ¯ν{sub e} and ν{sub e}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

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↗

DOE OSTI2025

High-energy $η^{(')}π$ photoproduction and the nature of exotic waves

The observation of hybrid mesons in photoproduction experiments can provide essential insight into the inner workings of quantum chromodynamics in the strong coupling regime. In particular, the study of final $η^{(')}π$ states is of great interest due to the presence of the lowest lying hybrid candidate with manifestly exotic quantum numbers, the $π_1$(1600). In this work, a double-vector exchange model with Reggeized $ρ$ and $ω$ trajectories is developed to describe the photoproduction of $η^{(')}π$ in the high-mass region. Results are presented for the differential cross sections and forward-backward asymmetries in the energy region of interest to the GlueX experiment. The model contains no free parameters, and reproduces the magnitude and t-dependence of existing CLAS data at $E_γ$ = 5 GeV. The model predicts a stronger asymmetry in the $η'π$ channel than in the $ηπ$ channel, consistent with what has previously been observed in pion beam experiments. This suggests that the sizeable production of exotic odd waves in $η'π$ is not necessarily related to the presence of gluon-rich environments. Confirmation of these predicted asymmetries from forthcoming GlueX data would enable further predictions of the low-energy spectrum.

Montaña, Glòria [Thomas Jefferson National Acceler↗

DOE OSTI2018

A light Higgs at the LHC and the B-anomalies

After the Higgs discovery, the LHC has been looking for new resonances, decaying into pairs of Standard Model (SM) particles. Recently, the CMS experimen observed an excess in the di-photon channel, with a di-photon invariant mass of about 96 GeV. This mass range is similar to the one of an excess observed in the search for the associated production of Higgs bosons with the Z neutral gauge boson at LEP, with the Higgs bosons decaying to bottom quark pairs. On the other hand, the LHCb experiment observed a discrepancy with respect to the SM expectations of the ratio of the decay of B -mesons to K -mesons and a pair of leptons, $ {R}_{K^{\left(\ast \right)}}=BR\left(B\to {K}^{\left(\ast \right)}{\mu}^{+}{\mu}^{-}\right)/BR\left(B\to {K}^{\left(\ast \right)}{e}^{+}{e}^{-}\right) $ . This observation provides a hint of the violation of lepton-flavor universality in the charged lepton sector and may be explained by the existence of a vector boson originating form a $ U{(1)_{L_{\mu}}}_{-{L}_{{}_{\tau }}} $ symmetry and heavy quarks that mix with the left-handed down quarks. Since the coupling to heavy quarks could lead to sizable Higgs di-photon rates in the gluon fusion channel, in this article we propose a common origin of these anomalies identifying a Higgs associated with the breakdown of the $ U{(1)_{L_{\mu}}}_{-{L}_{{}_{\tau }}} $ symmetry and at the same time responsible to the quark mixing, with the one observed at the LHC. We also discuss the constraints on the identification of the same Higgs with the one associated with the bottom quark pair excess observed at LEP.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Azimuthal distributions in radiative decay of a polarized τ lepton

We investigate various distributions over emitted photon angles, especially over the azimuthal angle, in the one-meson radiative decay of the polarized τ lepton, τ{sup –} → π{sup –}γν{sub τ}. In connection with this, the photon phase space is discussed in more detail because it is nontrivial in the case of a polarized τ lepton. The decay matrix element contains both the inner bremsstrahlung and the resonance (structural) contributions. The azimuthal dependence of some observables are calculated. They are the asymmetry of the differential decay width caused by the τ-lepton polarization, the Stokes parameters of the emitted photon itself, and the correlation parameters describing the influence of τ-lepton polarization on the photon Stokes parameters. A numerical estimation is done in the τ-lepton rest frame for an arbitrary direction of the τ-lepton polarization 3-vector. The vector and axial-vector form factors describing the structure-dependent part of the decay amplitude are determined using the chiral effective theory with resonances (RχT). It is found that the features of the azimuthal distributions allows separating various terms in the spin-dependent contribution. The so-called up–down and right–left asymmetries are also calculated.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

The scattering of spinning hadrons from lattice QCD

Hadron spectroscopy is predominantly the study of resonances that decay via the strong interaction into a multitude of stable hadrons, such as the pion. The vast majority of resonances decay via an intermediate hadron with non-zero intrinsic spin. In this thesis, I will present the results of scattering calculations featuring mesons with non-zero intrinsic spin. Before doing so, I will first give a brief introduction to QCD and review the framework necessary to perform lattice QCD calculations in Chapters 1 and 2. In Chapter 3, I present the first lattice calculation of ?? scattering in isospin-2. Here, ?? features in dynamically-coupled 3S1 and 3D1 partial-waves with JP=1+. No resonance enhancement is anticipated in the flavour exotic isospin-2 channel and as such it provides an ideal testing ground for this first calculation. I work at heavier than physical quark masses at the SU(3)F point where the up, down and strange quarks are mass degenerate. Finite-volume spectra are calculated and, utilising the relationship between the discrete energy spectrum and the infinite-volume scattering amplitudes, partial-wave amplitudes with J?3 and the degree of dynamical mixing between the coupled 3S1 and 3D1 channels are determined. In Chapter 4, I investigate ?? in isospin-1 where the a1 axial-vector resonance is expected to feature. Here, I present a discussion on G-parity and Bose-symmetry at the SU(3)F point. Working at heavier than physical quark masses, the resulting finite volume spectrum suggests that the a1 is a bound-state and that the 3S1- and 3D1-wave, ?? scattering amplitudes are similar to those in isospin-2. I present the first calculation of coupled ?? and ?? scattering in Chapter 5 where resonant enhancement is seen experimentally in the JP=1+ channel. Working at a somewhat lighter pion mass than in previous chapters, the finite-volume spectra are determined and the scattering amplitudes are calculated. Analytically continuing the amplitudes into the complex energy plane, a resonance pole is found, interpreted as the analogue of the b1 axial-vector, which couples dominantly to 3S1-wave ??, with a much-suppressed coupling to 3D1-wave ??, and a negligible coupling to ??. In Chapter 6, the exotic JPC=1?+ channel is studied. These quantum numbers are not allowed in the quark model but can be obtained, for example, through a gluonic excitation coupled to a quark-antiquark pair. In this exploratory calculation, performed at the SU(3)F point, the finite-volume spectra and coupled-channel scattering amplitudes are presented. A single resonance pole is found, interpreted as the exotic ?1, and couplings to meson-meson channels, including for example ??{1P1}, ???{1P1} and ??{3P1}, are calculated for the first time in lattice QCD. In order to minimally present the contents of a unitary n-channel scattering matrix, I introduce, in Chapter 7, an n-channel generalisation of the traditional two-channel Stapp parameterisation.

Woss, Antoni↗

DOE OSTI2016

Explaining dark matter and B decay anomalies with an L μ - L τ model

We present a dark sector model based on gauging the L μ - L τ symmetry that addresses anomalies in b→ sμ + μ - decays and that features a particle dark matter candidate. The dark matter particle candidate is a vector-like Dirac fermion coupled to the Z' gauge boson of the L μ - L τ symmetry. We compute the dark matter thermal relic density, its pair-annihilation cross section, and the loop-suppressed dark matter-nucleon scattering cross section, and compare our predictions with current and future experimental results. We demonstrate that after taking into account bounds from Bs meson oscillations, dark matter direct detection, and the CMB, the model is highly predictive: B physics anomalies and a viable particle dark matter candidate, with a mass of ~ (5 - 23) GeV, can be accommodated only in a tightly-constrained region of parameter space, with sharp predictions for future experimental tests. The viable region of parameter space expands if the dark matter is allowed to have L μ - L τ charges that are smaller than those of the SM leptons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

B s → K ℓ ν decay from lattice QCD

We use lattice QCD to calculate the form factors f+(q 2 ) and f 0 (q 2 ) for the semileptonic decay Bs→Kℓν. Our calculation uses six MILC asqtad 2+1 flavor gauge-field ensembles with three lattice spacings. At the smallest and largest lattice spacing the light-quark sea mass is set to 1/10 the strange-quark mass. At the intermediate lattice spacing, we use four values for the light-quark sea mass ranging from 1/5 to 1/20 of the strange-quark mass. We use the asqtad improved staggered action for the light valence quarks, and the clover action with the Fermilab interpolation for the heavy valence bottom quark. We use SU(2) hard-kaon heavy-meson rooted staggered chiral perturbation theory to take the chiral-continuum limit. A functional z expansion is used to extend the form factors to the full kinematic range. We present predictions for the differential decay rate for both Bs→Kμν and Bs→Kτν. We also present results for the forward-backward asymmetry, the lepton polarization asymmetry, ratios of the scalar and vector form factors for the decays Bs→Kℓν and Bs→Dsℓν. Our results, together with future experimental measurements, can be used to determine the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |$V_{ub}$|.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Decoding the B → K ν ν excess at Belle II: Kinematics, operators, and masses

An excess in the branching fraction for B + → K + ν ν recently measured at Belle II may be a hint of new physics. We perform thorough likelihood analyses for different new physics scenarios such as B → K X with a new invisible particle X , or B → K χ χ through a scalar, vector, or tensor current with χ being a new invisible particle or a neutrino. We find that vector-current three-body decay with m X ≃ 0.6 GeV—which may be dark matter—is most favored, while two-body decay with m X ≃ 2 GeV is also competitive. The best-fit branching fractions for the scalar and tensor cases are a few times larger than for the two-body and vector cases. Past measurements provide further discrimination, although the best-fit parameters stay similar. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Electromagnetic properties of baryons

We discuss the chiral behavior of the nucleon and {Delta}(1232) electromagnetic properties within the framework of a SU(2) covariant baryon chiral perturbation theory. Our one-loop calculation is complete to the order p{sup 3} and p{sup 4}/{Delta} with {Delta} as the {Delta}(1232)-nucleon energy gap. We show that the magnetic moment of a resonance can be defined by the linear energy shift only when an additional relation between the involved masses and the applied magnetic field strength is fulfilled. Singularities and cusps in the pion mass dependence of the {Delta}(1232) electromagnetic moments reflect a non-fulfillment. We show results for the pion mass dependence of the nucleon iso-vector electromagnetic quantities and present preliminary results for finite volume effects on the iso-vector anomalous magnetic moment.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Role of the chiral anomaly in polarized deeply inelastic scattering. III. Wess-Zumino-Witten contributions and chiral Ward identities for finite quark mass

We extend our prior results on the worldline computation of the axial vector-vector-vector (AVV) triangle anomaly in polarized deeply inelastic scattering (DIS) to the finite mass case by computing in addition the pseudoscalar-vector-vector (PVV) triangle graph. For the well-studied QED case, we show explicitly how the off-forward AVV pole exactly cancels an identical PVV pole. We then demonstrate the dramatic difference in QCD due to the chiral condensate, which qualitatively modifies anomalous Ward identities. As in the massless case, the anomaly pole in QCD is canceled by the dynamics of a primordial isosinglet pseudoscalar η ¯ -meson, whose Wess-Zumino-Witten coupling to the topological charge density shifts the pole to the physical η ′ mass, with the finite quark mass contribution differing by O ( 10 % ) from the Witten-Veneziano formula. We obtain a compact analytic expression for the finite mass corrections to Shore and Veneziano’s result that the proton’s net quark helicity Δ Σ ∝ χ QCD ′ | m = 0 ( 0 ) , the forward slope of the topological susceptibility in the chiral limit, and show they are of the order of a few percentages. Our prior prediction that the polarized DIS structure function g 1 is quenched by sphaleronlike topological transitions at small x is unaffected by quark mass effects. Our results illustrate how worldline computations of anomalous processes, in synergy with lattice computations and nonet chiral perturbation theory, can uncover novel nonperturbative features of QCD at the Electron-Ion Collider. Published by the American Physical Society 2025

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2019

Dispersion relations for γγ → ππ: helicity amplitudes, subtractions, and anomalous thresholds

We present a comprehensive analysis of the dispersion relations for the doubly-virtual process γ * γ * → ππ . Starting from the Bardeen-Tung-Tarrach amplitudes, we first derive the kernel functions that define the system of Roy-Steiner equations for the partial-wave helicity amplitudes. We then formulate the solution of these partial-wave dispersion relations in terms of Omnès functions, with special attention paid to the role of subtraction constants as critical for the application to hadronic light-by-light scattering. In particular, we explain for the first time why for some amplitudes the standard Muskhelishvili-Omnès solution applies, while for others a modified approach based on their left-hand cut is required unless subtractions are introduced. In the doubly-virtual case, the analytic structure of the vector-resonance partial waves then gives rise to anomalous thresholds, even for space-like virtualities. We develop a strategy to account for these effects in the numerical solution, illustrated in terms of the D -waves in γ * γ * → ππ , which allows us to predict the doubly-virtual responses of the f 2 (1270) resonance. In general, our results form the basis for the incorporation of two-meson intermediate states into hadronic light-by-light scattering beyond the S -wave contribution.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2013

Elastic and transition form factors of the Δ(1232)

Predictions obtained with a confining, symmetry-preserving treatment of a vector Ⓧ vector contact interaction at leading-order in a widely used truncation of QCD’s Dyson–Schwinger equations are presented for Δ and Ω baryon elastic form factors and the γN → Δ transition form factors. This simple framework produces results that are practically indistinguishable from the best otherwise available, an outcome which highlights that the key to describing many features of baryons and unifying them with the properties of mesons is a veracious expression of dynamical chiral symmetry breaking in the hadron bound-state problem. The following specific results are of particular interest. The Δ elastic form factors are very sensitive to m Δ . Hence, given that the parameters which define extant simulations of lattice-regularised QCD produce Δ-resonance masses that are very large, the form factors obtained therewith are a poor guide to properties of the Δ(1232). Considering the Δ-baryon’s quadrupole moment, whilst all computations produce a negative value, the conflict between theoretical predictions entails that it is currently impossible to reach a sound conclusion on the nature of the Δ-baryon’s deformation in the infinite momentum frame. Furthermore, results for analogous properties of the Ω baryon are less contentious. In connection with the N → Δ transition, the Ash-convention magnetic transition form factor falls faster than the neutron’s magnetic form factor and nonzero values for the associated quadrupole ratios reveal the impact of quark orbital angular momentum within the nucleon and Δ; and, furthermore, these quadrupole ratios do slowly approach their anticipated asymptotic limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

The Jefferson Lab Eta Factory (JEF) experiment

The Jefferson Lab Eta Factory (JEF) experiment is an upcoming experiment designed to run in Hall D at Jefferson Lab using an upgraded GlueX spectrometer to study various decays of the ? meson. The GlueX spectrometer consists of a ?2 Tesla solenoid magnet housing a liquid hydrogen target and drift chambers used for tracking charged particles and an array of lead glass blocks (the Forward Calorimeter (FCAL)) downstream of the magnet for detecting neutral particles. The decays of the ? meson can be used to measure the light quark mass ratio via the ???+???0 channel and allow access to higher-order terms in Chiral Perturbation Theory via the ???0?? channel. The decays can also be used to constrain new charge-conjugation violating/parity conserving (CVPC) reactions and to search for signatures of dark matter. In particular, the ???0?? channel can be used to search for lepto-phobic dark vector (B) bosons in the reaction ??B? (B??0?) or dark scalar (S) bosons in the reaction ???0S (S???). Studying the rare radiative decay channel ???0?? requires replacing the 4×4×45 cm3 lead glass blocks in the inner region of the FCAL with 2×2×20 cm3 lead tungstate crystals, which will provide twice better position and energy resolution. This talk will describe the JEF physics program and the upgrade to the FCAL.

Taylor, Simon↗