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Photon asymmetry measurement in radiative muon capture on calcium-40 Pouladdej, Ali


A photon asymmetry measurement in radiative muon capture (RMC) on ⁴⁰Ca has been carried out in order to determine a value for the induced-pseudoscalar coupling constant (ցƿ), thereby allowing us to investigate the possible renormalisation effect for this coupling constant inside nuclear matter. Negative muons from the M20A channel at TRIUMF were stopped in a ⁴⁰Ca target. The resulting RMC photons were then converted by a 5 cm thick Nal converter placed immediately in front of our main detector, a Nal crystal of size 46 cm∅x51 cm. The purpose of the converter was to provide discrimination against the prolific high energy neutron background. From a fit to our time spectrum for the high-energy (57 MeV< E⋎ <95 MeV) photons, we were able to extract a value for the RMC photon asymmetry (⍺⋎). This time spectrum, with 5200 "clean" photons and a signal to noise ratio of ~7, showed the photon asymmetry quite clearly. With our measured value for the photon asymmetry: ⍺⋎ = 1.00±0.23, the predicted value of the induced-pseudoscalar coupling constant becomes: ցƿ = (0.0±⁸‧⁰₆․₇) ցA;, this range contains the (theoretical) unrenormalised value of Goldberger-Treiman: ցƿ ≈ 7 ցA⋅

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