Polarimeters for the SPASCHARM Experiment

Abstract

A beam channel of polarized protons and antiprotons produced from decays of Λ-and anti-Λ-hyperons for the SPASCHARM experiment is to be built at IHEP U-70 accelerator in Protvino, Russia. The methods for tagging and measuring polarization of the beam (anti)protons are discussed in this report. The fast on-line beam tagging exploits the correlations between polarization and kinematics of (anti)protons originated from (anti)Λ-decays. In the intermediate focus of primary target, decay (anti)protons of different transverse polarizations are spatially dispersed transversely with respect to the beam axis. The tagging system, consisting of fast beam detectors with good spatial resolution, measures the momentum and trajectory of each beam particle, including its position at the intermediate focus, thus allowing instant (on-line) assignment of the transverse polarization value to each (anti)proton. This system is also extremely useful for the beam channel tuning. While being fast and convenient, the polarization tagging fully relies on computing of particle transportation in the beam channel. In order to verify the real beam polarization and operating of the tagging system and beam channel, the independent absolute beam polarimetry is to be used. It is based on measuring the spin asymmetries in elastic scattering of beam (anti)protons in Coulomb-Nuclear Interference (CNI) and diffractive kinematic regions. It is estimated that less than one week of data taking would allow measuring an absolute beam polarization at the statistical accuracy of ∼4-5%.Keywords: Spin; polarization; asymmetry; decays; protons; antiprotons; tagging; elastic scattering.PACS numbers: 13.88.+e, 13.85.Dz This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 3.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited.

Measurements of the Beam and Target Analyzing Powers and Spin Correlation Parameter ANN in Elastic pp Scattering at 45 Gev/c

“…We plan to do these measurements using the 45 Gev/c polarized proton beam with the narrow momentum width Δp/p=1,2% to fit into the polarized target of a diameter 18 mm [9].The beam properties are as follows: an average beam polarization P =40%, transverse dimensions σ(x)×σ(y) = 11×8.7 mm 2 , angular divergences σ(x')×σ(y)=1.4×1.7 mrad 2 , intensity I=5×10 6 protons per cycle hitting the target. The beam-tagging system will be used for measuring the polarization of each particle at the accuracy of about 1% [10]. The beam-tagging system will also be used for the polarized beam tune up at commissioning time.…”

The polarized proton and antiproton beam project at U-70 accelerator

“…Thus, the measurement of the position y for each proton (antiproton) trajectory in the intermediate focus is equivalent to measuring the mean polarization associated with each particular trajectory. This is the essence of the beam-tagging method [5,16], using a number of fast beam hodoscopes for tracing the beam particles and measuring their momenta. The beamtagging hodoscopes will also be used for tuning the beam.…”