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Dear Colleagues,
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<div class="">Please find below an abstract prepared by my graduate student Tianqi Hu for a contributed talk at the SESAPS (SouthEastern Section of the APS) meeting in Tallahassee, November 18-20. </div>
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<div class="">Best wishes,</div>
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<div class=""> Volker</div>
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<p class=""><b class=""><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">Measurements of
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">η </span>
<span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">and </span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω
</span></b><span style="font-size: 11.000000pt; font-family: 'CMR10'" class=""><b class="">photoproduction beyond the nucleon resonance regime</b> </span></p>
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<p class=""><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">Measurements of light-meson photoproduction are critical for understanding the underlying production mechanism in photon-nucleon interaction. At low energies, nucleon resonances
have been extensively studied using techniques such as partial wave analysis. However, scarcities of cross section and polarization data over the photon energy range 3-6 GeV have thus far hindered our understanding of the transition from the nucleon resonance
regime to a description of the reaction mechanism in terms of t-channel Pomeron and Regge exchanges. In this talk, we will present recent measurements of
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">η </span>
<span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">and </span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω
</span><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">meson differential cross sections, and
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω </span>
<span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">meson spin density matrix elements (SDMEs) from close to the production thresholds up to about 5 GeV using the data collected at Jefferson Lab during the CLAS-g12 run period. The circularly
polarized </span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω
</span><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">SDMEs have been measured for the first time. The production mechanism will be discussed in comparison with various models. The
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">η </span>
<span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">and </span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω
</span><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">differential cross sections have been fairly well described by the
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">η</span><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">-MAID 2018 and Laget models, respectively. The observed flip-sign discrepancy of the
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω </span>
<span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">SDME </span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ρ</span><span style="font-size: 8.000000pt; font-family: 'CMR8'; vertical-align: 4.000000pt" class="">0</span><span style="font-size: 8.000000pt; font-family: 'CMR8'; vertical-align: -3.000000pt" class="">1</span><span style="font-size: 8.000000pt; font-family: 'CMSY8'; vertical-align: -3.000000pt" class="">−</span><span style="font-size: 8.000000pt; font-family: 'CMR8'; vertical-align: -3.000000pt" class="">1
</span><span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">with the JPAC model implies that the potential contribution of the unnatural-parity t-channel exchanges to the
</span><span style="font-size: 11.000000pt; font-family: 'CMMI10'" class="">ω </span>
<span style="font-size: 11.000000pt; font-family: 'CMR10'" class="">photoproduction is smaller than the model predicted.</span></p>
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