Speaker
Description
Polarized antiprotons provide unique opportunities to investigate spin-dependent antiproton-proton interactions, annihilation mechanisms, and spectroscopy of hadrons. However, no practical method has yet been stablished for producing an intense polarized antiproton beam. In this work, we propose a novel method for producing polarized antiprotons through the sequential reaction $\bar{p}p\to \bar{\Lambda}\Lambda$, followed by the weak decay $\bar\Lambda \to \pi^+ \bar{p}$. In this scheme, the polarization of the daughter antiprotons originates from both the polarization of the parent antihyperons and the parity-violating nature of the weak decay.
The polarization transfer is formulated using the Lorentz-covariant polarization four-vector together with the Lee-Yang formalism [1-3] for hyperon weak decays. Monte Carlo simulations are performed using the differential cross sections and induced polarizations measured by the PS185 experiment at CERN [4] as phenomenological inputs. The momentum, angular, and polarization distributions of the secondary antiprotons are evaluated for the proposed $\pi20$ and K10 beamlines at the J-PARC Hadron Experimental Facility.
The simulation shows that the momentum and angular distributions of the daughter antiprotons closely follow those of the parent antihyperons, while being moderately broadened by the decay kinematics. The polarization consists of longitudinal self-polarization generated by parity violation and transverse components arising from spin transfer from the parent antihyperon. By selecting suitable decay kinematics in the antihyperon rest frame, antiprotons with large transverse polarization can be obtained.
The proposed method offers a realistic route to producing polarized antiprotons without requiring polarized primary beams, spin filtering, or polarized storage rings. Such a source would significantly expand future studies of spin-dependent antiproton-proton reactions, nucleon-antinucleon interactions, and hadron spectroscopy. In this presentation, the feasibility of the proposed production scheme and its expected performance at the future J-PARC secondary beamlines will be discussed.
[1] T. D. Lee and C. N. Yang, Phys. Rev. 108, 1645–1647 (1957).
[2] K. B. Luk et al. (E756 Collaboration), Phys. Rev. Lett. 85, 4860–4863 (2000).
[3] M. Huang et al. (HyperCP Collaboration), Phys. Rev. Lett. 93, 011802 (2004).
[4] P. D. Barnes et al., Phys. Rev. C 54, 1877–1886 (1996).