Speaker
Description
A new DAQ system for the 200 MeV proton-carbon polarimeter at the BNL Linac has been commissioned during the polarized proton RHIC Run 2024. The polarimeter measures the asymmetry of the vertically polarized 200 MeV proton beam scattering off a thin carbon target at $12^\circ$ and $16.2^\circ$. For the $16.2^\circ$ elastic scattering, the analyzing power is close to $100\%$, allowing for precision absolute calibration of the beam polarization. To optimize the isolation of elastic events, a variable-thickness copper absorber is used. The new Data Acquisition system, based on 14-bit, 200 MHz Waveform Digitizers (WFDs), records full $\sim300\,\mathrm{\mu{s}}$ beam bunch signal waveforms in the scintillator detectors. An exhaustive data analysis requires less than $50\,\rm{ms}$ and is performed between the beam bunches (typically repeated every $4.2\,\rm{s}$). The dead-time-free measurements allow us to accurately control systematic errors ($\lesssim 0.1\%$) in the value of the elastic asymmetry for the $16.2^\circ$ scattering, and consequently determine the beam polarization with systematic uncertainties better than $0.5\%$. For the combined data, including elastic and inelastic events at $12^\circ$ and $16.2^\circ$, the statistical accuracy of the measured beam polarization is about $0.5\%$ for a 1-hour measurement.
