Muonium-Antinuonium転換過程探索実験

Mu anti-Mu変換実験
~MUWG in 熱海~
J-PARC MLFディビジョンミュオン
河村成肇
物質・生命科学実験施設
中性子分光器
ミュオン生成標的
ミュオン科学実験施設
=陽子ビームライン
＋ミュオンビームライン
中性子生成標的
中性子分光器
第二期ミュオン施設建設
崩壊ミュオンビームライン（第一期建設分）
汎用性の高い崩壊ミュオンビームライン
正負ミュオン（30-120MeV/c）の輸送
大立体角ミュオンビームライン（第二期）
表面ミュオン（30MeV/c）に特
化し、軸収束のビームラインで
大立体角、高輸送効率を狙う。
大立体角ミュオンビームライン
大立体角ビーム
実験エリア
ミュオンビーム強度
 崩壊ミュオンビームライン（１ＭＷ時）



30MeV/c
60MeV/c
120MeV/c
3×107 m+/秒
5×106 m+/秒
2×107 m+/秒
6×105 m-/秒
1×106 m-/秒
1×107 m-/秒
 大立体角ミュオンビームライン（第二期計画）

30MeV/c
5×108 m+/秒
1×107 m-/秒
 大立体角ビームラインによる高強度化
NuFact’00 青木
物理のイントロ
 Lepton

Flavor Violation (LFV)
|DLi| = 1
m   e 
m   e e e 
m   e  conversion

|DLi| = 2
Mu  Mu conversion
m   e  m  e
NuFact’00 青木
モデル
L. Willm ann, et al. Phys . Rev. Lett. 82 (1999) 49-52
(a) doubly charged Higgs boson, (b) heavy Majorana neutrinos, (c) a
neutral scalar, e.g., a supersymmetric τ-sneutrino, or (d) a bileptonic
flavor diagonal gauge boson
NuFact’00 青木
PSIでの実験
 Setup
 Surface muon (26 MeV/c)
 Nm   8  106 m  /s
 Beam Time: 1290 hours

NMu  5.6  10 10
L. Willmann, et al. Phys. Rev. Lett. 82 (1999) 49-52
NuFact’00 青木
PSIでの実験
 Result
PMM  8.3  10 11
(90%C.L.)
NBG  1.7
 Bhabha scattering of e

m  e e ee  m BR  3.4 10 5
NuFact’03 松田
Slow muons

Slow muons : muons which are (re-)accelerated from
the muons which are almost at a rest.
Beam energy is tunable, and its spread is very small.
a The range in the material is tunable down to sub mm.
 Emittance is very small.
a Small sample can be used.



New application of mSR for thin films
Possible application towards future muon/neutrino
sources
NuFact’03 松田
Two methods to generate slow muon beam

Cryogenic moderator method (PSI)




Use a layer of solid rare gas as a moderator.
Initial energy is 10-100eV, and its spread is around
10eV.
Time structure is determined by initial beam.
Laser resonant ionization method
Obtain slow muons by ionizing thermal muoniums
emitted from a hot tungsten film.

Initial energy is around 0.2eV, and its spread is less
than 1eV.

Time structure is determined by laser timing.
g Gives better time resolution for pulsed beam.
g Possible use for Mu anti-Mu conversion experiment
as a sensitive detection method of anti-Mu and
background suppression.

NuFact’03 松田
Slow-muon beam-line at RIKEN-RAL
NuFact’03 松田
Slow-muon beam-line at RIKEN-RAL
slow muons
Main Chamber
(1x1011 hPa)
Ionizing Lasers
High purity Tungsten film (45mm; 87mg/cm2)
Tungsten degrader (20mm; 39mg/cm2)
SUS foil (50mm; 40mg/cm2)
Kapton foils
Degrader chamber
(1x10 hPa)
surface muons
Port 3 beam line
(1x10 hPa)
NuFact’03 松田
Efficiency of slow muon generation
Observed slow muon signal :
3.3 m/sec
(MCP efficiency 66%) a 5.0 m/sec
(Decay in flight 43%)
a 8.6 m/sec
(Transport efficiency unknown. assume 100%)
a >8.6 m/sec at the source
Initial surface muon beam : 1.0x106 m/sec
Efficiency 8.6/1.0x106 = 8.6x106 (still low…)
NuFact’03 松田
Future plan for slow muon

Beam study


mSR study



Beam profile measurement ( Segmented MCP, Slit, emittance
measurement)
Scintillator telescopes installation around the MCP chamber.
Helmholtz coil installation
Thinking of fundamental physics…




Mu1anti-Mu conversion experiment : double coincidence between laser
irradiation and anti-Mu detection will reduce background significantly.
PSI experiment accumurated 5.7x1010 muonium decays. We need
significant improvement of slow muon yield.
Muon intensity improvement : J-PARC, new proton driver, new
design of capture channel.
Muon to muonium conversion improvement : cyclotron trap
NuFact’03 松田
Cyclotron trap

PSI & LEAR application
 Winding up the range path of stopping particles inside a
weak focusing cyclotron field. It has been used for producing
low energy negative muons beams, pions and anti-protons.
 Moderator can be gas (typically ~1mbar Hydrogen), or thin
metal foils.
 Application for positive muons have been limited because of
high capture rate of electron.

Cyclotron trap + laser ionization
 Can expect increase of muon stopping density at the nearsurface of Tungsten foil.
 We will lose muon polarization. This will limit application for
mSR, but is good for Mu 1 anti-Mu oscillation experiment.
 Recover muon polarization with polarized laser light?
まとめ
 J-PARC
MLFの大立体角ミュオンビームラインを
使い、Mu-antiMu実験ができる。超低速ミュオン
ビームラインとほとんど同じ装置で逆のpolarity。
 5×108 surface m+/s ×10-5 (m+→slow m+)
5×1010 Mu/0.5y
（2×107 Mu/s=2×1012 Mu/d）
 現状(1MW)でも、半年程度でPSIと同程度の統計。
Laserとの同期で散乱からくるBGはなし。ただし、
in-flightでのm-e崩壊などが問題になる？
 Mu-antiMu変換はいつ起こる？Laserを打つタイミ
ングは？

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