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GlueX Experiment Document 5987-v1

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Lawrence Ng
Updated by:
Lawrence Ng
Document Created:
19 Apr 2023, 09:40
Contents Revised:
19 Apr 2023, 09:40
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27 Feb 2024, 13:42
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The reaction, gamma p -> eta pi0 p, is studied in this dissertation at Egamma=8.5 GeV at GlueX. The eta pi decay channel is one of the ``golden channels'' to search for the pi_1 spin-exotic meson. The yield of the pi1 is expected to be only a few percent of the a2(1320) yield, which dominates the
M(etapi0) spectrum observed at GlueX. Exotic signatures from the pi1 can also be mimicked by the double Reggeon exchange (DREx) process. Therefore, searching for the pi1 in the etapi0 channel necessitates a detailed understanding of nearby a2(1320) meson and the DREx process. A measurement will be presented in this dissertation to characterize each of these features.

An analysis will be presented of the first measurement of the differential photoproduction cross section, dsigma/dt, of the a2(1320) meson at photon beam energies of 8.2-8.8 GeV and in the four-momentum transfer range of 0.1 to 1.0 GeV2 is performed. A full partial wave analysis is carried out in the etapi0 invariant mass region around 1.3 GeV/c2 using amplitudes that depend on the polarization of the incoming photon beam, which allows us to separate the contributions of natural and unnatural parity exchange to the differential cross section. The partial wave analysis suggests that the a2(1320) differential cross section contains a dip around -~05 GeV2 with total cross-section equal to 68.34.6+-7.1 nb over the measured interval. These values correspond to the central estimate, the statistical uncertainty, and the systematic uncertainty.

Additionally, an analysis will be presented of this reaction beyond the resonance region at Metapi > 1.6 GeV where the DREx process contributes significantly. As input for the development of models to describe polarized photoproduction in this mass range at GlueX energies, we measure the Sigma beam asymmetry for individual eta and pi mesons for the above reaction, Sigma_eta and Sigma_pi, as functions of several kinematic variables including baryon sensitive ones. This allows a separation of contributions of the DREx process from baryon production. The measurements performed at large M(etapi) can be used to constrain the contributions of the DREx process in the resonance region where the pi1 is expected to populate. A comparison is made to measurements of the complementary reaction, gamma p -> etapiDelta++.

Lawrence's Dissertation was defended on April 7 2023

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