The measurement of parity violation in proton-proton scattering at 221 MeV

Abstract

An experiment to measure the parity violating analyzing power, $A\sb{z}$, in proton-proton scattering at 221 MeV is in progress using the TRIUMF cyclotron. At this beam energy, a unique opportunity exists to isolate the $\sp3P\sb2$-$\sp1D\sb2$ parity mixed partial wave amplitude, which has not been measured before. In terms of the single meson exchange model for the weak nucleon-nucleon interaction, this experiment will determine the weak $\rho$-proton-proton coupling constant, $h\sbsp{\rho}{pp}$. The scale of $A\sb{z}$, which is set by the relative strength of the weak interaction, is of order 10$\sp{-7}$. The goal of the TRIUMF experiment is to determine $A\sb{z}$ to ${\pm}0.2 \times 10\sp{-7}$, which has been achieved in existing measurements at lower energies. The experiment is made extremely challenging by the need to control and minimize coherent fluctuations in the properties of the polarized proton beam, which can introduce large systematic effects to the measured analyzing power. The first result from the experiment, based on 105 hours of data taken in February 1997, is $A\sb{z} = (0.34 \pm 0.67) \times10\sp{-7}$. This result includes corrections for helicity correlated beam fluctuations. It was found that one correction term, due to an intrinsic first moment of transverse polarization, dominated the total correction for the February 1997 data.