Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session PK: Hadron Structure I |
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Chair: Efrain Segarra, MIT Room: Arlington |
Thursday, October 14, 2021 9:30AM - 9:42AM |
PK.00001: High precision measurements of the proton Generalized Polarizabilities at Jefferson Lab Nikos Sparveris, Ruonan Li, HAMZA ATAC, Michael Paolone, Mark Jones, Alexandre Camsonne The Generalized Polarizabilities (GPs) are fundamental properties of the nucleon. They characterize the nucleon's response to an applied electromagnetic field, offering access to the polarization densities inside the nucleon, and as such they represent an essential part for a complete understanding of the nucleon structure and dynamics. The GPs can be explored through the measurement of the Virtual Compton Scattering reaction. Previous measurements of the proton electric GP at intermediate four-momentum transfer squared have challenged the predictions of theoretical calculations, raising questions in regard to the underlying reasons responsible for a local enhancement of the electric GP. The measurement of the magnetic GP, on the other hand, allows to quantify the interplay of the paramagnetism and diamagnetism inside the proton. The VCS experiment (E12-15-001) at JLab has accessed the proton GPs with high precision in the intermediate four-momentum transfer squared region, namely from Q2=0.3 (GeV2) to Q2=0.7 (GeV2). Preliminary results from the Hall C VCS experiment will be presented and future prospects will be discussed in this talk. |
Thursday, October 14, 2021 9:42AM - 9:54AM |
PK.00002: Measurements of charged pion and neutral pion electromagnetic polarizabilities at GlueX Rory A Miskimen Electromagnetic polarizabilities are fundamental properties of composite systems such as molecules, atoms, nuclei and hadrons, with polarizabilities being sensitive to the 'stiffness' of the system and the spectrum of excited states. Measurements of hadron polarizabilities provide a test of effective field theories, dispersion theories, and lattice calculations, and the charged pion polarizability tests fundamental symmetries at leading order. While significant progress has been made in measurements of nucleon polarizabilities, with uncertainties ≅ ± 0.4 x 10-4 e fm3 for the proton, experimental constraints on the charged and neutral pion polarizabilities (CPP and NPP) are much weaker, ≅ ± 2 x 10-4 e fm3 for the charged pion and no measurement for the neutral pion. The upcoming CPP and NPP experiments at GlueX utilize a new technique to measure pion polarizability, Primakoff photo-production of π+π- and π0π0 pairs on a high Z target. Details of the technique and experimental setup will be presented in the talk, including the commissioning of a muon detection system constructed for the measurement. The CPP and NPP experiments are scheduled to run at JLab in mid-2022. |
Thursday, October 14, 2021 9:54AM - 10:06AM |
PK.00003: Exploring photoproduced meson states that decay K+K-π0 with an emphasis on events where the K+K- pair are from a0 decay Alan Gardner Mesons that have K+K-π0 decay products are potentially interesting as exotic states, however many non-exotics have the same decay products. On the way towards uncovering exotic meson states, a major goal of the GlueX experiment is to map the non-exotic light mesons into their respective nonets. This endeavor requires that methods utilized can sufficiently measure well known states. As a step towards uncovering the richness possessed for mesons that have K+K− 0 decay products is to search for low mass states decaying a0 0 that include K+K-π0 non-resonant contributions. Utilizing GlueX data for K+K-π0 photoproduction from the proton I will show a sharp peak in invariant mass K+K-π0 near the f1(1285) and η(1295) mass along with angular distribution of the decay products. |
Thursday, October 14, 2021 10:06AM - 10:18AM |
PK.00004: Status of the PrimEx‑eta radiative decay width experiment in Hall D at Jefferson Lab Tyler J Hague The first run of a new experiment, PrimEx-eta (E12-10-011), was carried out in Hall D at Jefferson Lab using the GlueX experimental setup. Its goal is to precisely extract the η→γγ radiative decay width from the photoproduction of η‑mesons at extreme forward angles using the so-called Primakoff effect. The two-photon decay of the η‑meson proceeds predominantly due to Chiral anomaly in QCD. The projected 3.2% accuracy of the η decay width measurement will significantly impact the η-sector of the Particle Data Group’s (PDG) compilation, sizably improving the average value on Γ(η→γγ) and significantly improving the rest of the η partial decay widths which, in turn, will positively impact the extraction of the light quark mass ratio and the η—η′ mixing angle. The first run of this experiment was completed in the spring of 2019 to test the capability of the experimental setup and also yielded a rich and good statistics initial experimental data set. The second run of the experiment will take place from August to October 2021. We are currently analyzing the data to check the experimental method and to prepare for the second run. Preliminary physics distributions will be presented and discussed in this talk as well as discussing the status of the second run that will have just concluded. |
Thursday, October 14, 2021 10:18AM - 10:30AM |
PK.00005: Partial wave analysis of K*K Sebastian Cole What meson states contribute to the 1400 MeV mass region has been a topic of debate in the particle physics community since the 1960s. It began with conflicting evidence of a pseudoscalar or axial vector meson with a mass of ∼1420 MeV, an issue that became known as the E/ι puzzle. By the late 1990s, it was generally accepted that this was in fact two states, the f1(1420) and η(1405), respectively. However, the controversy did not end with resolution to this problem. Currently, it is a topic of debate as to whether two pseudoscalar mesons exist in the 1400 MeV mass region, specifically the η(1405) and η(1475). The GlueX experiment can assist in settling this debate by further establishing the nonet for the first radially excited pseudoscalar mesons and the nonet for the axial vector mesons. To contribute to this effort, a partial wave analysis of K*K has been conducted to determine what meson states exist in this mass region. Furthermore, this work lays a foundation to search for the η'1 hybrid meson candidate in the γp → pK+K-γγ reaction topology. |
Thursday, October 14, 2021 10:30AM - 10:42AM |
PK.00006: Abstract Withdrawn
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Thursday, October 14, 2021 10:42AM - 10:54AM |
PK.00007: Octet and decuplet baryon sigma terms in relativistic SU(3) chiral effective theory Marston M Copeland, Chueng-Ryong Ji, Wally Melnitchouk We present a new comprehensive analysis of the SU(3) octet and decuplet baryon masses and sigma terms. Chiral extrapolations are made to high precision 2+1 flavor lattice QCD data using the latest relativistic SU(3) chiral effective theory framework with finite range regularization. The effects of various systematic uncertainties are explored, such as different scale setting schemes for the lattice data as well as the model dependence from the chiral expansion of the baryon masses. Good agreement is found between all schemes. The quark fractions of the baryon masses are also presented and their implications on the trace anomalies of the energy momentum tensors and heavy quark sigma terms are discussed. |
Thursday, October 14, 2021 10:54AM - 11:06AM |
PK.00008: Very First Measurement of the Two-Photon Exchange Contribution to the Elastic Electron-Neutron Scattering Cross Section using BigBite and Super BigBite Spectrometers in Jefferson Lab's Hall A Provakar Datta The electromagnetic form factors of the nucleon can be measured experimentally either by using the polarization transfer technique or by using the Rosenbluth technique. Experimental data have shown that the values of the ratio of proton Sachs form factors, $G^{p}_{E}/G^{p}_{M}$, obtained using these two methods have significant discrepancy. This inconsistency is believed to be due to the two-photon exchange (TPE) contribution to the $e-N$ elastic scattering process. The contribution of TPE increases with increasing $Q^2$ and for the case of neutron it has been pedicted to reach about $30\%$ of the Rosenbluth slope value at $Q^{2}=5\,\text{(GeV/c)}^2$. Hence, the precise assessment of the impact of TPE in elastic $e-N$ scattering is extremely important for the better understanding of the nucleon form factors. This effect has been studied extensively for $e-p$ scattering but has never been examined experimentally for $e-n$ scattering. In this talk, I will present an overview of one of the currently approved experiments to measure TPE contribution to the $e-n$ elastic scattering cross section with high precision, using the new Super BigBite Spectrometer (SBS) and the upgraded BigBite Spectrometer in JLab's experimental Hall A. |
Thursday, October 14, 2021 11:06AM - 11:18AM |
PK.00009: New results from CLAS on the ep→e'pπ0 beam spin asymmetry in the resonance region Evgeny Isupov, Valery Klimenko The N* program in Jefferson Lab is crucial for understanding the strong interaction in the non-perturbative regime and the emergence of hadron mass. Studies of resonance electroexcitation in Nπ electroproduction represent an important part of these efforts. The data on beam spin asymmetry provide unique information on the imaginary part of the interference terms between the electroproduction amplitudes with the longitudinally and transversely polarized virtual photons. The new CLAS results on beam spin asymmetry and polarized structure function σLT' for π0p electroproduction at invariant masses of the final hadrons from the threshold and up to 1.8 GeV and at photon virtualities 0.4 GeV2<Q2<1.0 GeV2 will be presented in the talk. Analyses of these results demonstrated sensitivity of the Legendre moments of the σLT' structure function to the electroexcitation amplitudes of the nucleon resonances in the mass range > 1.6 GeV. Combined studies of beam spin asymmetries and unpolarized cross sections for π0p electroproduction channel will allow us to improve knowledge on Q2-evolution of the resonance electroexcitation amplitudes, in particular, for the resonances in the third resonance region. |
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