Studies of the Electromagnetic Structure of Mesons at Jefferson Lab

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The Jefferson Laboratory Hall B PrimEx Collaboration is using tagged photons to perform an absolute 1.4% level cross section measurement of the photoproduction of neutral pions in the Coulomb field of a nucleus. The absolute cross section for this process is directly proportional to the neutral pion radiative decay width and consequently the uncertainty in the luminosity is directly reflected in the final error bar of the measurement. The PI has taken primary responsibility for the photon flux determination and in this technical report, we outline the steps taken to limit the uncertainty in the tagged photon flux to the ... continued below

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Dale, Daniel, S. November 11, 2012.

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The Jefferson Laboratory Hall B PrimEx Collaboration is using tagged photons to perform an absolute 1.4% level cross section measurement of the photoproduction of neutral pions in the Coulomb field of a nucleus. The absolute cross section for this process is directly proportional to the neutral pion radiative decay width and consequently the uncertainty in the luminosity is directly reflected in the final error bar of the measurement. The PI has taken primary responsibility for the photon flux determination and in this technical report, we outline the steps taken to limit the uncertainty in the tagged photon flux to the 1% level. These include the use of a total absorption counter for absolute flux calibration, a pair spectrometer for online relative flux monitoring, and updated procedures for postbremsstrahlung electron counting. The photon tagging technique has been used routinely in its various forms to provide quasimonochromatic photons for absolute photonuclear cross section measurements. The analysis of such experiments in the context of bremsstrahlung photon tagging was summarized by Owens in 1990. Since then, a number of developments have made possible significant improvements in the implementation of this technique. Here, we describe the steps taken by the PrimEx Collaboration in Hall B of Jefferson Laboratory to limit the systematic uncertainty in the absolute photon flux to 1%. They include an absolute flux calibration at low intensity with a total absorption counter, online relative flux monitoring with a pair spectrometer, and the use of multihit time to digital converters for post bremsstrahlung electron counting during production data runs. While this discussion focuses on the analysis techniques utilized by the PrimEx Collaboration which involves a bremsstrahlung based photon tagging system to measure the neutral pion lifetime, the methods described herein readily apply to other types of photon tagging systems.

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  • Report No.: DOEER41523
  • Grant Number: FG02-07ER41523
  • Office of Scientific & Technical Information Report Number: 1054527
  • Archival Resource Key: ark:/67531/metadc842673

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  • November 11, 2012

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  • May 19, 2016, 9:45 a.m.

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  • June 20, 2016, 1:06 p.m.

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Dale, Daniel, S. Studies of the Electromagnetic Structure of Mesons at Jefferson Lab, report, November 11, 2012; United States. (digital.library.unt.edu/ark:/67531/metadc842673/: accessed September 26, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.