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GlueX Experiment Document 4904-v1

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Photoproduction of the b1(1235) Meson off the proton at Egamma = 6-12 GeV

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Ahmed Foda
Updated by:
Ahmed Foda
Document Created:
05 Feb 2021, 22:30
Contents Revised:
05 Feb 2021, 22:30
Metadata Revised:
15 Mar 2021, 15:41
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The GlueX Experiment at Jefferson Lab directs a linearly polarized photon beam on a liquid hydrogen target surrounded by an almost hermetic detector. The experiment aims to study the meson spectrum in the light-quark sector and search for exotic spin-parity states predicted by lattice QCD calculations. The lightest exotic candidate is the pi1 meson, which is predicted to decay dominantly to b1 pi. In this thesis, we present efforts to characterize the omega pi decay channel of the b1 meson as precursor to an analysis of the sought-after pi1 exotic state.

We present an introduction to the physics involved and an overview of the detector subsystems with a focus on the Barrel Calorimeter gain monitoring system, as part of the service work expected by the GlueX Collaboration.

We discuss the data analysis method used and present two frameworks, for angular moments and partial waves analyses. Details of the simulation used to calculate the detector acceptance. A proof of concept partial wave analysis is presented along with experimental angular moments as first step to a full analysis of the angular distribution. Our partial wave analysis indicates that both S- and D-waves are needed, in qualitative agreement with theoretical expectations. The cross-section of the omega pi channel is extracted to be of the scale of 1 mub in agreement with previous measurements. The differential cross-section indicates the presence of two production processes with p1 = -5.24±0.04 for 0.25 < -t < 0.95 GeV2/c2 and p2 = -1.24±0.05 for 0.95 < -t < 2.0 GeV2/c2, which does not agree with results from previous experiments. The s-channel helicity conservation and helicity amplitudes of the b1 meson are presented as additional experimental observables. Our results confirm that the b1 photoproduction process does not conserve s-channel helicity though they do not align with previous measurements. The helicity amplitude of the omega are extracted to be |F1|2 = 0.3037±0.0003 which does not agree with the expected value of a b1 decay or results from a previous experiment. Future steps in all these analyses will be continued by a new graduate student in the group, culminating in a publication.

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Four-meson final state
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