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تسجيل مستخدم جديدUpgraded photon calorimeter with integrating readout for Hall A Compton Polarimeter at Jefferson Lab
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The photon arm of the Compton polarimeter in Hall A of Jefferson Lab has been upgraded to allow for electron beam polarization measurements with better than 1% accuracy. The data acquisition system (DAQ) now includes an integrating mode, which eliminates several systematic uncertainties inherent in the original counting-DAQ setup. The photon calorimeter has been replaced with a Ce-doped GSO crystal, which has a bright output and fast response, and works well for measurements using the new integrating method at electron beam energies from 1 to 6 GeV.
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A wide range of nucleon and nuclear structure experiments in Jefferson Labs Hall A require precise, continuous measurements of the polarization of the electron beam. In our Compton polarimeter, electrons are scattered off photons in a Fabry-Perot cav
ity; by measuring an asymmetry in the integrated signal of the scattered photons detected in a GSO crystal, we can make non-invasive, continuous measurements of the beam polarization. Our goal is to achieve 1% statistical error within two hours of running. We discuss the design and commissioning of an upgrade to this apparatus, and report preliminary results for experiments conducted at beam energies from 3.5 to 5.9 GeV and photon rates from 5 to 100 kHz.
A high-finesse Fabry-Perot cavity with a frequency-doubled continuous wave green laser (532~nm) has been built and installed in Hall A of Jefferson Lab for high precision Compton polarimetry. The infrared (1064~nm) beam from a ytterbium-doped fiber a
mplifier seeded by a Nd:YAG nonplanar ring oscillator laser is frequency doubled in a single-pass periodically poled MgO:LiNbO$_{3}$ crystal. The maximum achieved green power at 5 W IR pump power is 1.74 W with a total conversion efficiency of 34.8%. The green beam is injected into the optical resonant cavity and enhanced up to 3.7~kW with a corresponding enhancement of 3800. The polarization transfer function has been measured in order to determine the intra-cavity circular laser polarization within a measurement uncertainty of 0.7%. The PREx experiment at Jefferson Lab used this system for the first time and achieved 1.0% precision in polarization measurements of an electron beam with energy and current of 1.0~GeV and 50~$mu$A.
The performances of the calorimeter of the Jlab Hall A Compton Polarimeter have been measured using the Mainz tagged photon beam.
This document describes the technical design concept of a compact high intensity, multi-GeV photon source. Capable of producing 10^12 equivalent photons per second this novel device will provide unprecedented access to physics processes with very sma
ll scattering probabilities such as hard exclusive reactions on the nucleon. When combined with dynamic nuclear polarized targets, its deployment will result in a large gain in polarized experiment figure-of-merit compared to all previous measurements. Compared to a traditional bremsstrahlung photon source the proposed concept presents several advantages, most significantly in providing a full intensity in a small spot at the target and in taking advantage of the narrow angular spread associated with high energy bremsstrahlung compare to the wide angular distribution of the secondary radiation to minimize the operational prompt and activation radiation dose rates.
The electromagnetic calorimeters of the various magnetic spectrometers in Hall C at Jefferson Lab are presented. For the existing HMS and SOS spectrometers design considerations, relevant construction information, and comparisons of simulated and exp
erimental results are included. The energy resolution of the HMS and SOS calorimeters is better than $sigma/E sim 6%/sqrt E $, and pion/electron ($pi/e$) separation of about 100:1 has been achieved in energy range 1 -- 5 GeV. Good agreement has been observed between the experimental and simulated energy resolutions, but simulations systematically exceed experimentally determined $pi^-$ suppression factors by close to a factor of two. For the SHMS spectrometer presently under construction details on the design and accompanying GEANT4 simulation efforts are given. The anticipated performance of the new calorimeter is predicted over the full momentum range of the SHMS. Good electron/hadron separation is anticipated by combining the energy deposited in an initial (preshower) calorimeter layer with the total energy deposited in the calorimeter.
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