Abstract
A beam channel of polarized protons and antiprotons produced from decays of [Formula: see text]- and anti-[Formula: see text]-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)[Formula: see text]-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 [Formula: see text]4–5%.
Highlights
The new experimental program SPASCHARM [1, 2] for 70 GeV proton synchrotron (U-70) is currently under development at the Institute for High Energy Physics (IHEP), Protvino, Russia
The main physics motivation for the SPASCHARM experiment is the systematic study of spin phenomena for a wide range of inclusive and exclusive reactions in collisions of high-energy polarized hadrons
We address the issue of tagging the polarization of beamprotons as well as independent measurements of absolute polarization of the selected beam samples in order to verify the tagging validity and performance
Summary
2. Polarized Proton and Anti-Proton Beams The polarized protons and antiprotonsa in the proposed beams for the 2nd stage of SPASCHARM experiment are produced by parity-violating decays of Λ-hyperons: Λ → pπ− or Λ → pπ+. Polarized Proton and Anti-Proton Beams The polarized protons and antiprotonsa in the proposed beams for the 2nd stage of SPASCHARM experiment are produced by parity-violating decays of Λ-hyperons: Λ → pπ− or Λ → pπ+ This method had been suggested ∼ 45 years ago by Overseth and Sandweiss [4, 5] and successfully used in E581/E704 experiment [6] at Fermilab and FODS experiment [7] at IHEP. For the SPASCHARM beam, the computed dependences of vertical transverse proton polarization on the vertical position at the virtual source are presented in Table 1 for two momentum spreads ∆p/p. The total intensity of the 14 GeV/c antiproton beam is expected to be up to ∼4 · 105 antiprotons/cycle
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