PANIC 2014 - Particles and Nuclei International Conference 2014

Ultra-slow muon production with room-temperature thermal-muonium-emitting material

Not scheduled

Main Building (Hamburg University)

Poster 12) New concepts and techniques for accelerators and particle detectors

Speaker

Dr Shinji Okada (RIKEN)

Description

Ultra-slow muons, which are positively charged muons having an energy of a few eV, are useful tools for producing variable-energy muon beams with extraordinarily small energy spread by accelerating them through an electrostatic field. We will apply this new technique to a measurement of the muon anomalous magnetic moment g-2 and electric dipole moment at J-PARC [1], which requires an intense muon beam having an extremely small transverse momentum. The ultra-slow muon production has been realized by laser ionization of thermal muonium (a Coulomb-bound system formed by a positive muon and an electron), Mu, emitted from a tungsten foil heated to 2300 K [2]. While it is known that silica powder is useful as a Mu-emitting material at room temperature [3], we have investigated the possible use of silica aerogel, a material similar to silica powder, as a room-temperature self-standing Mu-emitting material. The room-temperature target has the following significant merits: 1) experimentally easy to handle (no significant heat), 2) smaller emittance of the ionized source (lower Mu energies), 3) smaller spatial spread and smaller Doppler broadening (thanks to lower Mu energy distribution) leading to a more efficient use of the available laser power. In the TRIUMF S1249 experiment, Mu emission from silica aerogel into vacuum has been observed [4]; and the recent measurement yielded promising results with aerogels having a surface with sub-mm structures such as pores. For practical-scale development, we are now preparing an ultra-slow muon beamline dedicated to the research and development of practical ultra-slow muon production with room-temperature targets at the RIKEN-RAL muon facility at the Rutherford Appleton Laboratory. Here we establish the ultra-slow muon extraction scheme with compact electrostatic beam optics and laser reflection scheme by installing mirrors near the target for more efficient use of laser beam, both of which have been difficult to be realized with hot-tungsten target due to its huge radiant heat. In this presentation we introduce those studies with the preliminary analysis results and a future plan of the room-temperature target study at RIKEN-RAL ultra-slow muon beamline. [1] N. Saito et al., J-PARC E34 proposal, http://j-parc.jp/researcher/Hadron/en/pac_1001/pdf/KEK_J-PARC-PAC2009-12.pdf. [2] K. Nagamine et al., Phys. Rev. Lett. 74 (1995) 4811.; P. Bakule et al., NIM B 266, (2008) 355. [3] G. A. Beer et al., Phys. Rev. Lett. 57 (1986) 671. [4] P. Bakule et al., Prog. Theor. Exp. Phys. (2013) 103C01

Presentation materials

Poster

20140826_PANIC14_UltraSlowMu.pdf