The Rare and Forbidden:
Testing Physics beyond the SM with the Mu3e
Ann-Kathrin Perrevoort for the Mu3e Collaboration
NIKHEF, Amsterdam (formerly Physics Institute, Heidelberg)
Tau Workshop Amsterdam September 28, 2018
Mu3e Experiment (Phase I)
• Background-free search for µ → eee
• Observe some 1015muon decays
• Precise tracking of e+/e− and large acceptance
... more details in A. Bravar’s talk
A. Perrevoort (NIKHEF) BSM Physics with Mu3e Tau 2018 1 / 5
µ → eee in Effective Theories
• Dipole operator: ϵ=11% ⇒BR≥8.5⋅10−15 at 90% CL
] [MeV2 2ee
0 2 4 6 8 m10 12×103
]2[MeV 2 eem
0 2 4 6 8 10 12×103
1 10 102 103
generated
] [MeV2 2ee
0 2 4 6 8 m10 12×103
]2[MeV2 eem
0 2 4 6 8 10 12×103
1 10 102 103
reconstructed
• Vector operator: ϵ=17% ⇒BR≥4.6⋅10−15 at 90% CL
2] [MeV 2ee
0 2 4 6 8 m10 12×103
]2[MeV 2 eem
0 2 4 6 8 10 12×103
0 100 200 300 400 500 600 700 800 generated 900
2] [MeV 2ee
0 2 4 6 8 m10 12×103
]2[MeV 2 eem
0 2 4 6 8 10 12×103
0 50 100 150 200 reconstructed 250
Dark Photon Searches
• e+e−resonances in µ → eeeνν
• Same data set as for µ → eee searches
[GeV]
mA'
−2
10 10−1 1 10
2ε
8
10− 7
10−
−6
10
5
10−
−4
10
(g-2)e
KLOE 2013 KLOE 2015
KLOE 2016 KLOE 2014 WASA
HADES PHENIX 2σ
µ± (g-2)
favored
E774
E141
APEX
A1 NA48/2
BABAR 2009
BABAR 2014
BESIII Mu3e Phase I
Mu3e Phase II
Mu3e: Work in progress adapted from 1705.04265
A. Perrevoort (NIKHEF) BSM Physics with Mu3e Tau 2018 3 / 5
Familon Searches
µ → e X: narrow peak onpe spectrum
10 20 30 40 50
0 0.2 0.4 0.6 0.8 1
Michel spectrum (leading order) μ→eX signal (mX=60MeV)
pe [MeV]
entries/dpe [a.u.]
[MeV]
mX
0 10 20 30 40 50 60 70 80 90
Branching Fraction at 90% CL
−9
10
−8
10
−7
10
−6
10
−5
10
−4
10
−3
10 Mu3e Phase I SIM: 2.6×1015µstops
TWIST 2014
Mu3e online reco. (ext.calib.) Mu3e online reco. (sim. calib.)
Mu3e: Work in progress
BSM Searches with Mu3e
• Characteristic decay distributions ofµ → eee can reveal type of BSM interaction
(... in case of discovery)
• Can search for more than µ → eee
▸ Dark photons in µ → eeeνν
▸ Familons in µ → e X
⇒ Significant improvements in all these channels expected
A. Perrevoort (NIKHEF) BSM Physics with Mu3e Tau 2018 5 / 5
