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DOE OSTI2019

Latest results from GlueX

The GlueX experiment is housed in the newest experimental hall at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. It was successfully commissioned in 2015 and is in its third year of data taking. GlueX uses a 12 GeV electron beam incident on a diamond radiator, producing a linearly polarized, coherent Bremsstrahlung photon beam. The ultimate goal of GlueX is to search for exotic hybrid mesons (e.g. $q\bar{q}g$), with either exotic or conventional quantum numbers, whose existence, or lack thereof, would allow for the exploration of the gluon-gluon coupling present in QCD through the manifestation of hadrons with gluonic degrees of freedom. Photo-production at these energies is fairly unexplored and the linear beam polarization allows GlueX to discriminate between various production mechanisms which may be an effective way to identify such exotic hybrid mesons. In addition to exotic mesons, GlueX will also be poised to map out the conventional meson spectrum and to study the spectrum of excited vector mesons, which are often poorly understood. Here in these proceedings, we will present an overview of the GlueX experiment, its goals, current physics results, and future plans.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

Latest results from GlueX

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Interacting mesons as degrees of freedom in a chiral model

Here, we study the equation of state of hot and dense hadronic matter using an extended chiral mean field (CMF) model framework where the addition is the inclusion of interactions of thermally excited mesons. This is implemented by calculating the in-medium masses of pseudoscalar and vector mesons, obtained through the explicit chiral symmetry-breaking and vector-interaction terms in the Lagrangian, respectively, prior to applying the mean-field approximation. As a result, the in-medium meson contributions generate a feedback term to the CMF’s equations of motion, which then modifies the equation of state. With this improvement, we quantify the effect on the equation of state of strongly interacting matter through comparisons with state-of-the-art lattice QCD results and other hadronic models like the hadron resonance gas model. We find that the results of the updated hadronic CMF model with an improved meson description (mCMF) provide a better agreement with lattice-QCD data for thermodynamic state variables across a wide range of temperatures and baryon chemical potentials.

phenomenology↗

DOE OSTI2025

Polarization of the 𝜙 meson in the hadronic phase with nucleon scatterings and a viscous hydrodynamic background

We extend our previous work on the spin alignment of the ϕ vector meson in the hadronic phase of the quark gluon plasma, by including effects of nucleon scatterings. The emission rates are calculated in a realistic hydrodynamic background simulated with the code FLUIDuM , for different beam energies. We find that all the effects taken into account cannot explain the out-of-plane spin alignment of the ϕ meson observed experimentally.

Polarization phenomena↗

DOE OSTI2019

Light hidden mesons through the Z portal

Confining hidden sectors are an attractive possibility for physics beyond the Standard Model (SM). They are especially motivated by neutral naturalness theories, which reconcile the lightness of the Higgs with the strong constraints on colored top partners. We study hidden QCD with one light quark flavor, coupled to the SM via effective operators suppressed by the mass M of new electroweak-charged particles. This effective field theory is inspired by a new tripled top model of supersymmetric neutral naturalness. The hidden sector is accessed primarily via the Z and Higgs portals, which also mediate the decays of the hidden mesons back to SM particles. We find that exotic Z decays at the LHC and future Z factories provide the strongest sensitivity to this scenario, and we outline a wide array of searches. For a larger hidden confinement scale Λ ~ O (10) GeV, the exotic Z decays dominantly produce final states with two hidden mesons. ATLAS and CMS can probe their prompt decays up to M ~ 3 TeV at the high luminosity phase, while a TeraZ factory would extend the reach up to M ~ 20 TeV through a combination of searches for prompt and displaced signals. For smaller Λ ~ O (1) GeV, the Z decays to the hidden sector produce jets of hidden mesons, which are long-lived. LHCb will be a powerful probe of these emerging jets. Furthermore, the light hidden vector meson could be detected by proposed dark photon searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Peripheral transverse densities of the baryon octet from chiral effective field theory and dispersion analysis

The baryon electromagnetic form factors are expressed in terms of two-dimensional densities describing the distribution of charge and magnetization in transverse space at fixed light-front time. In this paper, we calculate the transverse densities of the spin-1/2 flavor-octet baryons at peripheral distances b=O(M$-1\atop{π}$) using methods of relativistic chiral effective field theory (χ EFT) and dispersion analysis. The densities are represented as dispersive integrals over the imaginary parts of the form factors in the timelike region (spectral functions). The isovector spectral functions on the two-pion cut t > 4 M$2\atop{π}$ are calculated using relativistic χEFT including octet and decuplet baryons. The χEFT calculations are extended into the ρ meson mass region using an N/D method that incorporates the pion electromagnetic form factor data. The isoscalar spectral functions are modeled by vector meson poles. We compute the peripheral charge and magnetization densities in the octet baryon states, estimate the uncertainties, and determine the quark flavor decomposition. Finally, the approach can be extended to baryon form factors of other operators and the moments of generalized parton distributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Spin density matrix elements in exclusive $\rho ^0$ meson muoproduction

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $\rho ^0$ meson muoproduction at COMPASS using 160 GeV/c polarised μ + and μ – beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/c 2 < W < 17.0 GeV/c 2 , 1.0 (GeV/c) 2 < $\mathrm{Q}$ 2 < 10.0 (GeV/c) 2 and 0.01 (GeV/c) 2 < $p_{\textrm{T}}^2$ < 0.5 (GeV/c) 2 . Here, W denotes the mass of the final hadronic system, $\mathrm{Q}$ 2 the virtuality of the exchanged photon, and $p_{\textrm{T}}$ the transverse momentum of the $\rho ^0$ meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ($\gamma ^*_T \rightarrow V^{ }_L$) indicate a violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive $\rho ^0$ production.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Algebraic model to study the internal structure of pseudoscalar mesons with heavy-light quark content

The internal structure of all lowest-lying pseudoscalar mesons with heavy-light quark content is studied in detail using an algebraic model that has been applied recently, and successfully, to the same physical observables of pseudoscalar and vector mesons with hidden-flavor quark content, from light to heavy quark sectors. The algebraic model consists on constructing simple and evidence-based of the meson’s Bethe-Salpeter amplitude (BSA) and quark’s propagator in such a way that the Bethe-Salpeter wave function (BSWF) can then be readily computed algebraically. Its subsequent projection onto the light front yields the light front wave function (LFWF) whose form allows us a simple access to the valence-quark parton distribution amplitude (PDA) by integrating over the transverse momentum squared. We exploit our current knowledge of the PDAs of lowest-lying pseudoscalar heavy-light mesons to compute their generalized parton distributions (GPDs) through the overlap representation of LFWFs. From these three dimensional knowledge, different limits/projections lead us to deduce the related parton distribution functions (PDFs), electromagnetic form factors (EFFs), and impact parameter space GPDs (IPS-GPDs). When possible, we make explicit comparisons with available experimental results and earlier theoretical predictions. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Doubly virtual ( π 0 , η , η ' ) → γ * γ * transition form factors in the light-front quark model

We report our investigation on the doubly virtual transition form factors (TFFs) F P γ * ( Q 1 2 , Q 2 2 ) for the P → γ * ( q 1 ) γ * ( q 2 ) ( P = π 0 , η , η ' ) transitions using the light-front quark model (LFQM). Performing a LF calculation in the exactly solvable manifestly covariant Bethe-Salpeter (BS) model as the first illustration, we use the q 1 + = 0 frame and find that both LF and manifestly covariant calculations produce exactly the same results for F P γ * ( Q 1 2 , Q 2 2 ) . This confirms the absence of the LF zero mode in the doubly virtual TFFs. We then map this covariant BS model to the standard LFQM using the more phenomenologically accessible Gaussian wave function provided by the LFQM analysis of meson mass spectra. For the numerical analyses of F P γ * ( Q 1 2 , Q 2 2 ) , we compare our LFQM results with the available experimental data and the perturbative QCD (pQCD) and vector meson dominance (VMD) model predictions. As ( Q 1 2 , Q 2 2 ) → ∞ , our LFQM result for doubly virtual TFF is consistent with the pQCD prediction, i.e., F P γ * ( Q 1 2 , Q 2 2 ) ~ 1 / ( Q 1 2 + Q 2 2 ) , while it differs greatly from the result of the VMD model, which behaves as F P γ * VMD ( Q 1 2 , Q 2 2 ) ~ 1 / ( Q 1 2 Q 2 2 ) . Our LFQM prediction for F η ' γ * ( Q 1 2 , Q 2 2 ) shows an agreement with the very recent experimental data obtained from the BABAR Collaboration for the ranges of 2 < ( Q 1 2 , Q 2 2 ) < 60 GeV 2 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Deeply pseudoscalar meson production and Generalized Transversity Distributions

A longstanding goal in nuclear and particle physics has been to describe the three dimensional structure of the nucleon in terms of the quarks and gluon fields. Exclusive electron scattering at high momentum transfers Q^2 directly related to the Generalized Parton Distributions (GPDs). Most reactions studied, such as DVCS or vector meson electroproduction, are primarily sensitive to the chiral-even GPDs. Very little is known about the chiral-odd GPDs, except that H_T becomes the transversity function h_1 in the forward limit. It turns out that pseudoscalar meson electroproduction, and especially pi^0 and eta production, were identified as especially sensitive to the parton helicity-flip subprocesses. Dedicated experiments to study Deeply Virtual Meson Production have been carried out in Hall B at Jefferson Lab. The cross sections and asymmetries of the exclusive pseudoscalar meson electroproduction processes in a very wide kinematic range of Q^2, x_B and t have been measured with CLAS. The Generalized form factors H^pi,eta_T and E-bar^pi,eta_T were extracted directly form the experimental observables. These combined pi^0 and eta data will provide the way for the flavor decomposition of the transversity GPDs.

Kubarovsky, Valery↗

DOE OSTI2018

Poincaré-covariant analysis of heavy-quark baryons

We use a symmetry-preserving truncation of meson and baryon bound-state equations in quantum field theory in order to develop a unified description of systems constituted from light and heavy quarks. In particular, we compute the spectrum and leptonic decay constants of ground-state pseudoscalar and vector mesons: q'(q) over bar, Q'(Q) over bar, with q', q = u, d, s and Q', Q = c, b, and the masses of J P = 3/2 + baryons and their first positive-parity excitations, including those containing one or more heavy quarks. This Poincare covariant analysis predicts that such baryons have a complicated angular momentum structure. For instance, the ground states are all primarily S wave in character, but each possesses P -, D - and F -wave components, with the P -wave fraction being large in the qqq states, and the first positive-parity excitation in each channel having a large D -wave component, which grows with increasing current-quark mass, but also exhibits features consistent with a radial excitation. In conclusion, the configuration space extent of all such baryons decreases as the mass of the valence-quark constituents increases.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Detector-size upper bounds on dark hadron lifetime from cosmology

We show that in a confining hidden valley model where the lightest hidden particles are dark hadrons that have mass splittings larger than $ \mathcal{O}(0.1) $ GeV, if the lightest dark hadron is either stable or decays into Standard Model (SM) hadrons/charged leptons during the big-bang nucleosynthesis (BBN), at least one of the heavier dark hadrons needs to decay into SM particles within $ \mathcal{O}(10) $ nanosec. Once being produced at collider experiments, this heavier dark hadron is likely to decay within $ \mathcal{O}(10) $ meter distance, which strengthens the motivation of searching for long-lived particles with sub-meter scale decay lengths at colliders. To illustrate the idea, we study the lifetime constraint in scenarios where the lightest dark particle is a pseudo-scalar meson, and dark hadrons couple to SM particles either through kinetic mixing between the SM and dark photons or by mixing between the SM and dark Higgs. We study the annihilation and decay of dark hadrons in a thermal bath and calculate upper bounds on the lightest vector meson (scalar hadron) lifetime in the kinetic mixing (Higgs portal) scenario. We discuss the application of these lifetime constraints in long-lived particle searches that use the LHCb VELO or the AT-LAS/CMS inner detectors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2019

Isoscalar and Isovector Kaon Form Factors from e{sup +}e{sup –} and τ Data

The recent precise measurements of the e{sup +}e{sup –} → K{sub S}K{sub L} and e{sup +}e{sup –} → K{sup +}K{sup –} cross sections and the hadronic spectral function of the τ{sup –} → K{sup –}K{sub S}ν{sub τ} decay are used to extract the isoscalar and isovector electromagnetic kaon form factors and their relative phase in a model-independent way. The experimental results are compared with a fit based on the vector-meson-dominance model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Production of $\omega $ mesons in pp collisions at $\mathbf {\sqrt{s}=7\,\text {TeV}}$

The invariant differential cross section of inclusive $\omega (782)$ meson production at midrapidity ( $|y|<0.5$ ) in pp collisions at $\sqrt{s}=7\,\hbox {TeV}$ was measured with the ALICE detector at the LHC over a transverse momentum range of $2< p_{\mathrm {T}}< 17\,\hbox {GeV}/c$ . The $\omega $ meson was reconstructed via its $\omega \rightarrow \pi ^+\pi ^-\pi ^0$ decay channel. The measured $\omega $ production cross section is compared to various calculations: PYTHIA 8.2 Monash 2013 describes the data, while PYTHIA 8.2 Tune 4C overestimates the data by about 50%. A recent NLO calculation, which includes a model describing the fragmentation of the whole vector-meson nonet, describes the data within uncertainties below $6\,\hbox {GeV}/c$ , while it overestimates the data by up to 50% for higher $p_{\mathrm {T}}$ . The $\omega /\pi ^0$ ratio is in agreement with previous measurements at lower collision energies and the PYTHIA calculations. In addition, the measurement is compatible with transverse mass scaling within the measured $p_{\mathrm {T}}$ range and the ratio is constant with $C^{\omega /\pi ^{0}}= 0.67 \pm 0.03 \text {~(stat)~} \pm 0.04 \text {~(sys)~}$ above a transverse momentum of $2.5\,\hbox {GeV}/c$ .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

𝐽/𝜓-meson–nucleon scattering length from threshold photoproduction on light nuclei

The quality of recent Short-Range Correlations/Color-Transparency (SRC/CT) Collaboration 𝐽/𝜓 photoproduction data off a 4 He target from Hall D at Jefferson Laboratory, combined with the feasibility of measuring the reaction close to the free-nucleon energy threshold, opens the door to using incoherent 𝐽/𝜓 photoproduction to explore a variety of interesting physics aspects. An example is the estimation of the 𝐽/𝜓 𝑝 scattering length |𝛼 𝐽/𝜓 𝑝 | on the bound proton, obtained using the vector meson dominance model. The new experiment E12–25–002, conducted by the SRC/CT Collaboration, was recently approved in Hall D with the GlueX spectrometer, which will significantly enhance the number of reconstructed 𝐽/𝜓 mesons. Using a plane-wave theoretical model to generate quasidata, we estimated that the experiment could achieve a result of |𝛼 𝐽/𝜓 𝑝 | = 3.08 ± 0.45 mfm. This value can be compared to an extraction based on the free proton data from the GlueX Collaboration, |𝛼 𝐽/𝜓 𝑝 | = 3.08 ± 0.55 mfm. A comparison between the two would provide an opportunity to evaluate the effects of medium modification in light nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Hazma meets HERWIG4DM: precision gamma-ray, neutrino, and positron spectra for light dark matter

Herein we present a new open-source package, Hazma 2, that computes accurate spectra relevant for indirect dark matter searches for photon, neutrino, and positron production from vector-mediated dark matter annihilation and for spin-one dark matter decay. The tool bridges across the regimes of validity of two state of the art codes: Hazma 1, which provides an accurate description below hadronic resonances up to center-of-mass energies around 250 MeV, and Herwig4DM, which is based on vector meson dominance and measured form factors, and accurate well into the few GeV range. The applicability of the combined code extends to approximately 1.5 GeV, above which the number of final state hadrons off of which we individually compute the photon, neutrino, and positron yield grows exceedingly rapidly. We provide example branching ratios, particle spectra and conservative observational constraints from existing gamma-ray data for the well-motivated cases of decaying dark photon dark matter and vector-mediated fermionic dark matter annihilation. Finally, we compare our results to other existing codes at the boundaries of their respective ranges of applicability. Hazma 2 is freely available on GitHub athttps://github.com/LoganAMorrison/Hazma.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

Light-Meson Spectroscopy at GlueX

GlueX at Jefferson Lab aims to study the light meson spectrum with an emphasis on the search for light hybrid mesons. To this end, a linearly-polarized 9 GeV photon beam impinges on a hydrogen target contained within a hermetic detector with near-complete neutral and charged particle coverage. In 2016, the experiment completed its commissioning and subsequently started to take data in its design configuration. With the size of the data set so far, GlueX already exceeds previous experiments for polarized photoproduction in this energy regime. A selection of early results will be presented, focusing on beam asymmetries for pseudo-scalar and vector mesons. The potential to make significant contributions to the field of light-meson spectroscopy is highlighted by the observation of several known meson resonances. As a result, the strategy to map the light meson spectrum with amplitude analysis tools will be outlined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Charm and strange quark masses and f D s from overlap fermions

We use overlap fermions as valence quarks to calculate meson masses in a wide quark mass range on the 2 + 1 -flavor domain-wall fermion gauge configurations generated by the RBC and UKQCD Collaborations. The well-defined quark masses in the overlap fermion formalism and the clear valence quark mass dependence of meson masses observed from the calculation facilitate a direct derivation of physical current quark masses through a global fit to the lattice data, which incorporates O($a^2$) and O($m^4a^4$) corrections, chiral extrapolation, and quark mass interpolation. Using the physical masses of D s , D$^*_s$ and J/ψ as inputs, Sommer's scale parameter r 0 and the masses of charm quark and strange quark in the $\overline{MS}$ scheme are determined to be r 0 = 0.465 (4) (9) fm, $m^{\overline{MS}}_c$ (2 GeV ) = 1.118 (6) (24) GeV (or $m^{\overline{MS}}_c(m_c)$ = 1.304 (5) (20) GeV), and $m^{\overline{MS}}_s$ (2 GeV ) = 0.101 (3) (6) GeV, respectively. Furthermore, we observe that the mass difference of the vector meson and the pseudoscalar meson with the same valence quark content is proportional to the reciprocal of the square root of the valence quark masses. The hyperfine splitting of charmonium, M J/ψ -$M_{η_c}$, is determined o be 119(2)(7) MeV, which is in good agreement with the experimental value. Finally, we also predict the decay constant of D s to be $f_{D_S}$ = 254 (2) (4) MeV. The masses of charmonium P-wave states χ c0 , χ c1 and $h_c$ are also in good agreement with experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗