Session FK: Hadron Spectroscopy with Electron, Photon, and Hadron Beams III

Experimental search for eta-prime mesic nuclei using WASA at GSI/FAIR

We are preparing an experimental to search for an eta' meson bound to a nucleus, an eta' mesic nucleus in GSI/FAIR. eta' meson is known to have a much larger mass than other pseudo scalar mesons in the same multiplet. The large mass is thoretically understood in terms of combined contributions from spontaneous chiral symmetry breaking of the QCD vacuum and axial U(1) anomaly. We investigate the origin of the mass of eta' mesons by making spectroscopy of eta' meson bound to a nucleus. We have been working on the experiment in GSI/FAIR in Darmstadt, Germany.
The experiment utlizes 12C(p,d) reactions to produce eta' mesic nuclei. We have performed first experimental search by the inclusive reactions as reported in Refs. [1,2]. We make use of a large detector apparatus for detecting their decays mainly into eta'NN -> NN, where N denotes a nucleon. A large acceptance charged particle detector of WASA is in preparation at GSI. We will report the present status of the project.

References
1. Y.K. Tanaka et al., PRL 117, 202501 (2016)
2. Y.K. Tanaka et al., PRC 97, 015202 (2018)

  

Abstract Withdrawn

The Light Meson Decay (LMD) program in CLAS at Jefferson Lab was formed to analyze decays of light mesons produced in the photoproduction reaction $\gamma p\to pX$, where $X = \pi^0,\eta,\omega, \eta'$ and $\phi$. While the two photon decays of the light mesons are described by the triangle anomaly, we focus on the radiative decay of $\eta\to\pi^+\pi^-\gamma$ which proceeds from the less understood box anomaly. We present preliminary results of the radiative decay of $\eta$ from CLAS6 data collected at the Thomas Jefferson National Accelerator Facility.   

A Precision Measurement of the Proton and Neutron $g_{2}$ and $d_{2}$ with SoLID

We propose a precision measurement of the proton and neutron spin structure function $g_{2} (x,Q^{2})$ by using a Solenoidal Large Intensity Device (SoLID) at Jefferson Lab (JLab) Hall A with the 12 GeV upgrade. We will obtain data with high statistics and large kinematic coverage for Bjorken $0.1 < x < 0.9 $ and four momentum transfer $ 1<Q^{2}<10\;GeV^{2}$ by a longitudinally polarized electron beam scattering on polarized $NH_{3}$ and $^{3}He$ targets. In addition to mapping out the $x$ and $Q^{2}$ evolution of $g_{2}$, we will extract the twist-3 matrix element $d_{2}(Q^{2})$, which is connected to the quark-gluon correlations within the nucleon. This quantity has been calculated in Lattice QCD and different nucleon structure models, which is one of the cleanest observables that can be used to test the theory.      

The upcoming high-Q2 polarization transfer measurement of the proton electromagnetic form factor ratio using the new Super BigBite Spectrometer in Jefferson Lab's Hall A

The nucleon electromagnetic form factors (EMFFs) are centrally important quantities in the characterization of nucleon structure. Elastic EMFF measurements at large values of the invariant four-momentum transfer Q² have experienced a resurgence of interest since precise polarization transfer measurements in Jefferson Lab's Halls A and C revealed the strong decrease of the proton form factor ratio G_Ep/G_Mp with Q² for Q²≥1 GeV², revolutionizing our understanding of nucleon structure. In addition to being benchmark quantities for testing theoretical models of nucleon structure and dynamics, precise knowledge of the high-Q² form factors is required for the interpretation of a diverse range of phenomena in nuclear and hadronic physics. Measurements of nucleon EMFFs up to and beyond Q² ≈ 10 GeV² present special challenges, and are presently a unique worldwide capability of Jefferson Lab's Continuous Electron Beam Accelerator Facility. The new Super BigBite Spectrometer (SBS) in Jefferson Lab's Hall A is designed specifically to facilitate high-Q² EMFF measurements. In this talk, I will give an overview of the planned SBS measurement of the proton form factor ratio GEp/GMp to Q² = 12 GeV² using the polarization transfer method.