3 electron
www.psi.ch/mu3e
[MeV]
mee
0 20 40 60 80 100 120
dN/N per 1 MeV
3
10− 2
10− 1
10−
1 both
All tracks: mee
= 20 MeV mA'
= 45 MeV mA'
= 70 MeV mA'
[GeV]
mA' 2
10− 10−1 1 10
2 ε
8
10− 7
10− 6
10− 5
10− 4
10−
(g-2)e
KLOE 2013 KLOE 2015
KLOE 2016 KLOE 2014 WASA
HADES PHENIX σ
2
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
2] [MeV
2ee
0 2 4 6 8 m10 12×103
]2 [MeV
2 eem
0 2 4 6 8 10 12×103
0 100 200 300 400 500 600 700 800 900
4-fermion interaction
Se nsitiv ity to μ → ee e Eff ective Field Theor y A pp roach Sensit ivit y in Phase I
[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
Sensit ivit y in Phase I Famil ons
2] [MeV
2ee
0 2 4 6 8 m10 12×103
]2[MeV
2 eem
0 2 4 6 8 10 12×103
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4103
×
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
2] [MeV
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
2] [MeV
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
2] [MeV
2ee
0 2 4 6 8 m10 12×103
]2[MeV
2 eem
0 2 4 6 8 10 12×103
0 50 100 150 200 250
Dipole interaction
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]
mee
0 20 40 60 80 100 120
N per 1 MeV
1 10 102
103
104
105
106
107
108 All tracks: mbothee
Combined background Internal conversion Bhabha
Background
SM μ eeeνν, Bhabha scattering, γ conversion
Sensit ivit y (90% CL)
Simulation Simulation
After reconstruction
ε=11%
Br≥8.510-15 ε=19%
Br≥4.610-15 ε=17%
Br≥5.210-15 Phase space
Familon is a neutral light pseudo-Goldstone boson from an additional broken flavour symmetry,
emitted in flavour-changing processes e.g. μ eX
Wilczek, PRL 49 (1982) 1549
Michel edge is preferred
means of calibration Limited
acceptance at low pT
Signal
A' ee resonance in μ eeeνν
by Echenard et al., JHEP 01 (2015) 113
SM background μ→eeeνν (Br = 3.4⋅10-5)
→ suppress by good momentum resolution
Pruna et al., (2016) arXiv:1611.03617
Backg rou nd
Combinations of Michel decays with Bhabhascattering, photon conversion, ...
→ suppress by good vertex and timing resolution
μ→eeeνν @ NLO
Mu3e
s from a common vertex with ΣPe = (mμ, 0)
Signat ure
Lepton-flavour violating (LFV) decay μ→eee in the Standard Model (SM) possible via neutrino mixing, but suppressed to a branching ratio Br < 10-54
Observation of μ→eee ⇒ Physics beyond SM e.g. SUSY, GUT, extended electro-weak sector
Standard Model (υ mixing)
De cay μ → eee
SupersymmetryMot iv at ion
Test μ → eee with a sensitivity of
Br ≤ 10 -16
Challenges
- -
→
High muon rates > 108μ/s to 109μ/s Excellent momentum resolution
despite low momentum of electrons Extremely low material budget
(low multiple scattering)
Long detector tube (L = 1.1m to 2m, Ø = 16cm) in solenoidal magnetic field of 1T
→ high acceptance for recurling tracks
μ stop on extended hollow double cone target
→ vertex separation
8 9
28 MeV/c μ beam at PSI Phase I: 10 μ/s
Phase II: 10 μ/s
Triggerless DAQ system &
online reconstruction on GPU based filter farm
→ reduce data rate
Lightweight tracking detector Thinned Si pixel
sensors (~50μm)
Mechanical support made of Kapton Readout via Aluminium- Kapton Flexprint
→0.1% of X0 per layer + Cooling by gaseous He
High Voltage
Monolithic Active Pixel Sensors
-- -
Reverse bias of ~85V Fast charge collection
Integrated readout electronics
developed by Ivan Perić (KIT) NIM A582 (2007) 876-885
Phase I detector design
De te ct or De sign Su mmary
Searching for New Physics with
The Mu3e Experiment
Niklaus Berger
1)and Ann-Kathrin Perrevoort
2)on behalf of the Mu3e Collaboration
3)PRISMA+ Cluster of Excellence and Institute of Nuclear Physics, JGU Mainz Nikhef, Amsterdam, formerly Physics Institute, Heidelberg University
Paul Scherrer Institute (PSI), Uni Bristol, Uni Geneva, Uni Heidelberg, KIT Karlsruhe, Uni Liverpool, UCL London, JGU Mainz, Uni Oxford, ETH Zürich, Uni Zürich
2)
1)
3)
The Mu3e Experiment at PSI is designed to search for the lepton-flavour violating decay of a positive muon to two positrons and an electron with a branching ratio sensitivity of order 10
-15(phase I) and order 10
-16(phase II). The
detector is based on ultra-thin high-voltage monolithic active pixel sensors combined with scintillating fibres and tiles for precise timing measurement. We present sensitivity studies performed for the Mu3e detector, both for
the main signal decay in different models of new physics, as well as for electron-positron resonances, motivated by dark photon models, and two-body decays of the muon, motivated by Familon models .
Scintillating fibres
→ Timing < 500 ps σ Scintillating tiles
→ Timing < 70 ps σ
1T superconducting magnet Winding completed
2] [MeV/c mrec
96 98 100 102 104 106 108 110
2 Events per 0.2 MeV/c
4
10− 3
10− 2
10− 1
10−
1 10 102
at 10-12
eee
→ µ
at 10-13
eee
→ µ
at 10-14
eee
→ µ
at 10-15
eee
→ µ ν
eeeν
→ µ
Bhabha +Michel
muons/s muon stops at 108
1015
Mu3e Phase I
Background-free operation:
Measure or exclude BR(μ→eee) ≥ 5.2 ‧ 10-15 @ 90% C.L.
Type of interaction determines kinematics and affects signal reconstruction efficiency
Decay distributions
differential BRs by Kuno et al., Rev.Mod.Phys.73 (2001) 151; Crivellin et al., JHEP 05 (2017) 117
After reconstruction
Re sonances in e + e - Dar k Phot ons in Muon Decay Sensist ivit y (90% C.L.)
Phase I: 2.6·1015μ Phase II: 5.5·1016μ
Simulation Simulation
Dark Photon A´
interacting with SM particles via kinetic mixing
Background:
SM µ → eeeυυ, Bhabha scattering, γ conversion Signal:
A´ → e+e- resonance in µ → eeeυυ
L by Echenard et al., JHEP 01 (2015) 113
LFV Two-Bod y De cays μ → eX Familons Sensit ivit y in Phase I
Familon is a neutral light pseudo-Goldstone boson from an additional broken flavour symmetry
emitted in flavour-changing processes, e.g. µ→eX
Wilczek, PRL 49 (1982) 1549
Signature:
Narrow peak on smooth pe spectrum from SM µ decays
Full track information cannot be stored:
Search for peaks in momentum histograms of the
online reconstruction (limited momentum resolution)
Michel edge is preferred means of calibration
Limited acceptance at low pT
10 cm
