25th International Spin Symposium (SPIN 2023)

Measuring Photon Beam Polarization Through Detection of e+e− Pairs at GlueX

Sep 26, 2023, 4:20 PM

20m

Junior Ballroom A3 (Durham Convention Center)

Talk Acceleration, Storage and Polarimetry of Polarized Beams Acceleration, Storage and Polarimetry of Polarized Beams

Speaker

Albert Fabrizi

Description

The Charged and Neutral Pion Polarizability Experiments (CPP and NPP) at GlueX require a precision measurement of the linear polarization of the incident photon beam.The utilization of electron-positron ($e^{+}{e}^{-}$) pair production is a valuable technique for determining photon beam polarizations.Polarization determination from pair production on atomic electrons (the Triplet Polarimeter, TPOL technique) or on a nuclear target with the detection of a single lepton are reliable methods to this end. This talk will show a new technique and the subsequent result for measurement of linear beam polarization through detection of $e^{+}{e}^{-}$ pairs in the GlueX forward drift chambers and calorimeters. The analyzing power for the azimuthal distribution of $e^{+}{e}^{-}$ pairs accessible within GlueX kinematics is approximately $60\mathrm{\%}$. Using a neural net designed for $e/\pi$ separation, the spring 2018 GlueX data set was analyzed and measured to have an average beam polarization of $0.349\pm 0.009$. This result agrees with the TPOL measurement of polarization within $0.85$ standard deviations. This technique to derive linear beam polarization from $e^{+}{e}^{-}$ pairs obtained during data taking can be applied to photo-production experiments where detection of $e^{+}{e}^{-}$ pairs is achieved with good particle identification and good angular acceptance in the forward angles. This work was supported in part by the U.S. Department of Energy award DE-FG02-88ER40415 and by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.

Presentation materials

AFabrizi_BHPairPolarimetryAtGlueX_SPINTalk_TuesSep262023.pdf