18-22 October 2021
Matsue, Shimane Prefecture, Japan
Asia/Tokyo timezone

Optically polarized alkali metal cell for muonic helium measurements

19 Oct 2021, 18:50
Room 401 (Kunibiki Messe)

Room 401

Kunibiki Messe

Parallel Session Presentation Acceleration, Storage and Polarimetry of polarized Beams Polarized Sources and Targets


Dr Takashi Ino (KEK)


Muonic helium is a helium atom with one of the two electrons substituted by a negative muon. This three-body atomic system gives rise to opportunities to precisely study the hyperfine structure interval as well as the negative muon magnetic moment and mass. Muonic helium atoms are formed by stopping a negative muon beam in dense helium gas, but in this formation process, the polarization of muons is lost by a factor of ten or more, remaining only several percent of the muons spin-polarized. They can, however, be repolarized by spin-exchange collisions with polarized alkali metal atoms [1], the same as spin-exchange optical pumping often used to polarize noble gas nuclei [2].
We are studying glass cells containing pressurized helium gas and alkali metals for muonic helium measurements at J-PARC Muon Facility MUSE [3]. The glass cell, helium gas pressure, and polarized alkali metal density are essential to maximize the number of polarized muonic helium atoms. So called hybrid alkali metal optical pumping, which was first developed to achieve a high 3He nuclear polarization [4], can be applied for effective repolarization of muonic helium atoms. In the hybrid optical pumping, Rb is optically pumped conventionally, and the Rb polarization is rapidly passed to K atoms by spin-exchange collisions inside a cell with Rb and K enclosed together. Thanks to the smaller spin-destruction cross section in K-K collisions compared to those between Rb atoms, a higher alkali metal number density with a very high polarization can be obtained by the hybrid method.
We will discuss hybrid alkali metal optical pumping cells for muonic helium measurements.

[1] A. S. Barton et al., Phys. Rev. Lett. 70, 758 (1993).
[2] T. G. Walker and W. Happer, Rev. Mod. Phys. 69, 629 (1997); T. R. Gentile, P. J. Nacher, B. Saam, and T. G. Walker, Rev. Mod. Phys. 89, 045004 (2017).
[3] P. Strasser, K. Shimomura, and H. A. Torii, JPS Conf. Proc. 21, 011045 (2018).
[4] E. Babcock et al., Phys. Rev. Lett. 91, 123003 (2003).

Primary author

Dr Takashi Ino (KEK)


Seiso Fukumura (School of Science, Nagoya University) Patrick Strasser (IMSS, KEK) Masaki Fujita (IMR, Tohoku University) Yoichi Ikeda (IMR, Tohoku University) Sohtaro Kanda (IMSS, KEK) Masaaki Kitaguchi (KMI, Nagoya University) shoichiro Nishimura (IMSS, KEK) Takayuki Oku (JAEA) Takuya Okudaira (School of Science, Nagoya University) Hirohiko Shimizu (School of Science, Nagoya University) koichiro Shimomura (IMSS, KEK)

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