Niklaus Berger

(1)

Searching for

charged lepton flavour violation in muon decays

Niklaus Berger

Institut für Kernphysik, Johannes-Gutenberg Universität Mainz Flavour & Dark Matter

Karlsruhe, September 2018

(2)

Charged lepton flavour violation experiments:

• μ → e γ

MEG and MEG II

• μ to e conversion in Nuclei DeeMee, Comet, Mu2e

• μ → eee Mu2e

Overview

11

LXe Calorimeter with higher granularity.

Muon Beam More than twice intense beam

Radiative Decay Counter Identify muon radiative-decays Timing Counter

Higher time resolution with highly segmented detector Drift chamber

Higher tracking performance with long single tracking volume

Target Thinner target Active target option

recurl pixel

layers Scintillating

tiles

(3)

Niklaus Berger – Flavour & Dark Matter, Karlsruhe, September 2018 – Slide 3

Standard Model branching fractions of

10 ^-50ish

Lepton flavour violation experiments

Only limited by number of muons and background suppression:

Experimental/technical challenge

(4)

History of cLFV experiments

90 % –C L b ou nd

10^–14 10^–12 10^–10 10^–8 10^–6 10^–4 10^–2 10⁰

e 3e

N eN

3

10^–16

SINDRUM SINDRUM II

MEG

MEG II Mu3e Phase I

Mu3e Phase II Comet/Mu2e μ

μ μ

γ

γ τ

τ

(5)

LFV Muon Decays

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

(6)

LFV Muon Decays: Experimental Situation

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

MEG (PSI) SINDRUM II (PSI) SINDRUM (PSI)

B(μ

⁺

→ e

⁺

γ) < 4.2 ∙ 10

^-13

(2016) B(μ

^-

Au → e

^-

Au) < 7 ∙ 10

^-13

(2006) B(μ

⁺

→ e

⁺

e

^-

e

⁺

) < 1.0 ∙ 10

^-12

(1988)

(7)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back

(8)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

(9)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

• Radiative decay

Kinematics

• Quasi 2-body decay

• Monoenergetic e

^-

• Single particle detected

(10)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

Kinematics

• Quasi 2-body decay

• Monoenergetic e

^-

• Single particle detected Background

• Decay in orbit

(11)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

• Radiative decay

Kinematics

• Quasi 2-body decay

• Monoenergetic e

^-

• Single particle detected Background

• Decay in orbit

• Antiprotons, pions, cosmics

Kinematics

• 3-body decay

• Invariant mass constraint

• Σ p

_i

= 0

(12)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

Kinematics

• Quasi 2-body decay

• Monoenergetic e

^-

• Single particle detected Background

• Decay in orbit

Kinematics

• 3-body decay

• Invariant mass constraint

• Σ p

_i

= 0 Background

• Internal conversion decay

(13)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

• Radiative decay

Kinematics

• Quasi 2-body decay

• Monoenergetic e

^-

• Single particle detected Background

• Decay in orbit

• Antiprotons, pions, cosmics

Kinematics

• 3-body decay

• Invariant mass constraint

• Σ p

_i

= 0 Background

• Internal conversion decay

• Accidental background

(14)

LFV Muon Decays: Experimental signatures

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back Background

• Accidental background

Kinematics

• Quasi 2-body decay

• Monoenergetic e

^-

• Single particle detected Background

• Decay in orbit

Kinematics

• 3-body decay

• Invariant mass constraint

• Σ p

_i

= 0 Background

• Radiative decay

tinuous Be am

tinuous Be am Pul sed Be

am

(15)

Searching for μ → eγ with

MEG and MEG II

(16)

MEG Signal and background

μ ⁺ → e ⁺ γ

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back

Measure

• Photon energy

• Positron momentum

• Opening angle (in two projections)

• Time difference

(17)

MEG Signal and background

μ ⁺ → e ⁺ γ

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back

Accidental Background

• Not exactly in time

• Not exactly same vertex

• e

⁺

, γ energies somewhat off

• Not exactly back-to-back

(18)

MEG Signal and background

μ ⁺ → e ⁺ γ

Kinematics

• 2-body decay

• Monoenergetic e

⁺

, γ

• Back-to-back

Accidental Background

• Not exactly in time

• Not exactly same vertex

• e

⁺

, γ energies somewhat off

• Not exactly back-to-back

Radiative Decay

• e

⁺

, γ energies somewhat off

• Not exactly back-to-back

(19)

The MEG Detector

J. Adam et al. EPJ C 73, 2365 (2013)

(20)

MEG Results

(21)

• 2009-2013 data

• Blue: Signal PDF, given by detector resolution

• No signal seen

• Upper limit at 90% CL:

BR(μ→eγ) < 4.2 × 10 ^-13

A. M. Baldini et al. Eur.Phys.J. C76 (2016) no.8, 434

MEG Results

(MeV)

e+

E

50 51 52 53 54 55 56

(MeV)γE

48 50 52 54 56 58

γ e+

Θ cos

−1 −0.9995 −0.999 −0.9985 (ns) γ+et

−2

−1.5

−1

−0.5 0 0.5 1 1.5 2

(22)

Introduction

Y

• X

Angela Papa (Mainz Seminar)

(23)

MEG Upgrade

Angela Papa, NuFact 2018

MEG II

(24)

MEG II - Calorimeter

• ~4000 VUV sensitive SiliconPMs on entry face (new development with Hamamatsu)

• Better position and energy resolution

• Better efficiency

(25)

MEG II - Calorimeter

(26)

MEG II - Drift Chamber

• New single volume drift chamber

• Lower Z gas mixture

• More space points per track

• Better rate capability

• Less material in front of timing counters

(27)

MEG II - Drift Chamber

• Assembly completed

(28)

MEG II - Drift Chamber

• Assembly completed

• at PSI

(29)

MEG II - Timing Counter

• Many small scintillators

• Read-out by SiliconPMs

• On average eight counters hit by track

• 30 ps timing resolution per track

(30)

MEG II - Timing Counter

(31)

MEG II - Timing Counter

(32)

MEG II - Radiative Decay Counter

• Detect low energy positrons from

radiative decays with high energy gammas

(33)

Angela Papa (Mainz Seminar)

MEG II

(34)

Searching for μ → e conversion with

Mu2e, DeeMee, COMET,

PRISM

(35)

Backgrounds:

Anything that can produce a 105 MeV/c electron

• Primary proton beam

• Decay in Orbit (DIO)

• Nuclear capture (AlCap effort at PSI)

• Cosmics

Conversion Signal and Background

μ ^- N → e ^- N

• Single 105 MeV/c electron observed

(36)

• Proton beam produces pions, photons, (antiprotons) etc.

• Wait until things become better...

• Makes it hard to use high Z targets

Beam induced background

(37)

• Nuclear recoil allows for electron ener- gies above m

_μ

/2

• Calculation by Czarnecki, Garcia i Tormo and Marciano, Phys. Rev. D84 (2011)

• Requires excellent momentum resolution

Deacy-in-orbit background

100 101 102 103 104 105

10 ²⁰ 10 ¹⁸ 10 ¹⁶ 10 ¹⁴

E_e MeV

1 0

d dEeMeV1

Without recoil With nuclear

recoil

(38)

• Re-use part of the Tevatron infrastructure

• Proton pulses every 1700 ns

• > 10

¹⁰

μ/s

• PIP-II would give another 2 orders of magnitude at an energy below the antiproton threshold

Muons from Fermilab...

(39)

... and J-PARC

• 10

¹¹

μ/s from 8 GeV/c protons

(40)

Experimental concept - DeeMee

(41)

Experimental concept - DeeMee

Yohei Nakatsugawa, NuFACT2014

(42)

• Expect 2.1×10

^-14

single event sensitivity for one year running

• Beamline under construction

Sensitivity - DeeMee

Natsuki Teshima,

(43)

First DIO Measurement - DeeMee

Dakai Nagao, NuFACT2018

• Very first measurements:

Different setup and different beamline

(44)

Production target inside a solenoid

(45)

Experimental layout - COMET Phase I

Stopping Target

Production Target

Detector Section Pion-Decay and

Muon-Transport Section Pion Capture Section

A section to capture pions with a large solid angle under a high solenoidal magnetic field by superconducting maget

A detector to search for muon-to-electron conversion processes.

A section to collect muons from decay of pions under a solenoidal magnetic field.

Comet CDR

High solenoidal field

Capture pions with large

solid angle

(46)

Introduction

Y

• X

Y. Kuno

Curved solenoid

Drift chamber

(47)

Cylindrical Detector System

• Large drift chamber for momentum measurements

• Trigger hodoscope

Manabu Moritsu,

NuFACT2018

(48)

Cylindrical Detector System

• Large drift chamber for momentum measurements

• Trigger hodoscope

(49)

Experimental layout - COMET Phase II

Detector Section

Pion-Decay and

Muon-Transport Section

Pion Capture Section

A section to capture pions with a large solid angle under a high solenoidal magnetic field by superconducting maget

A detector to search for muon-to-electron conversion processes.

A section to collect muons from decay of pions under a solenoidal magnetic field.

Stopping Target Production

Target

Comet CDR

Separate muon decay and detector region

One more bend

(50)

• Straw tubes in vacuum

• LYSO calorimeter

COMET Phase II Detector System

Manabu Moritsu,

(51)

• Separate muon production and conversion target

• Not shown: cosmic ray veto and absorbers

Experimental layout - Mu2e

Conversion Target

Mu2e CDR

(52)

• Charge selection in curved solenoid

Experimental layout - Mu2e

Steven Boi, NuFact 2018

(53)

• Straw tubes in vacuum

• Outside of radius of Michel electrons

Mu2e Tracker

Mu2e CDR

(54)

• Straw tubes in vacuum

• Outside of radius of Michel electrons

Mu2e Tracker

(55)

Y

• X

Mu2e Calorimeter

Steven Boi, NuFact 2018

(56)

Mu2e Cosmic Ray Veto

Steven Boi, NuFact 2018

• Without veto:

(57)

• J-PARC : Comet/DeeMee Fermilab: Mu2e

• Comet Phase I and DeeMee might get to ~10 ^-14 as early as 2019

• Both Comet Phase II and Mu2e will start around 2022

• Should get single event sensitivities well below 10 ^-16

• Paths to 10 ^-18 being explored

Conversion: Expected sensitivities

(58)

Searching for μ ⁺ → e ⁺ e ^- e ⁺ with

Mu3e

(59)

• μ

⁺

→ e

⁺

e

^-

e

⁺

• Two positrons, one electron

• From same vertex

• Same time

• Σ p

_e

= m

_μ

• Maximum momentum: ½ m

_μ

= 53 MeV/c

The signal

(60)

• Combination of positrons from ordinary muon decay with electrons from:

- photon conversion,

- Bhabha (electron-positron) scattering, - Mis-reconstruction

• Need very good timing, vertex and momentum resolution

Accidental Background

(61)

• Allowed radiative decay with internal conversion:

μ ⁺ → e ⁺ e ^- e ⁺ νν

• Only distinguishing feature:

Missing momentum carried by neutrinos

Internal conversion background

• Need excellent

momentum resolution _Br ^{anching R}

atio

10

^-12

10

^-16

10

^-18

10

^-14

e

⁺

e

^-

e

⁺

mass (MeV/c

²

)

105 106 104

103 102

101 Internal conversion background

Signal

(62)

Need excellent momentum resolution

for very low momentum electrons

(63)

• 1 T magnetic field

• Resolution dominated by multiple scattering

• Momentum resolution to first order:

Σ _P /P ~ θ ^MS /Ω

• Precision requires large lever arm (large bending angle Ω) and low multiple scattering θ

_MS

Momentum measurement

Ω MS

θ _MS

B

(64)

Precision vs. Acceptance

50 MeV/c 25 MeV/c 12 MeV/c B

^→

33 cm

(65)

Precision vs. Acceptance

50 MeV/c 25 MeV/c 12 MeV/c

B

^→

(66)

Precision vs. Acceptance

50 MeV/c 25 MeV/c 12 MeV/c

B

^→

(67)

Precision vs. Acceptance

50 MeV/c 25 MeV/c 12 MeV/c

B

^→

(68)

Precision vs. Acceptance

50 MeV/c 25 MeV/c 12 MeV/c B

^→

Ω ~ π MS

θ

_MS

B

(69)

Detector Design

muon beam

target

(70)

Detector Design

muon beam

target

(71)

Detector Design

muon beam

target

inner pixel layers

(72)

Detector Design

outer pixel layers

muon beam

target

inner pixel layers

(73)

Detector Design

scintillating ﬁbres

outer pixel layers

muon beam

target

inner pixel layers

(74)

Detector Design

outer pixel layers

muon beam

target

inner pixel layers recurl pixel

layers

recurl pixel layers

(75)

Detector Design

outer pixel layers

muon beam

target

inner pixel layers recurl pixel

layers

recurl pixel layers

scintillating ﬁbres

Scintillating tiles

(76)

Detector Design

outer pixel layers

muon beam

target inner pixel layers recurl pixel

layers

recurl pixel layers

scintillating

Scintillating

tiles

(77)

Detector Design

outer pixel layers

muon beam

target inner pixel layers recurl pixel

layers

recurl pixel layers

scintillating ﬁbres

Scintillating tiles

Challenges:

• Thin detectors

• Services (and beam) inside detector

• Cooling with gaseous Helium

(78)

Detector Design

• Full CAD with wires and pipes

• Mechanics being fabricated

• Cooling working in simulation

(79)

Very thin and fast silicon pixel sensors:

HV-MAPS

(80)

High voltage monolithic active pixel sensors - Ivan Perić

• Use a high voltage commercial process (automotive industry)

Fast and thin sensors: HV-MAPS

N-well E field

(81)

High voltage monolithic active pixel sensors - Ivan Perić

• Use a high voltage commercial process (automotive industry)

• Small active region, fast charge collection via drift

Fast and thin sensors: HV-MAPS

P-substrate N-well

Particle

E field

(82)

High voltage monolithic active pixel sensors - Ivan Perić

• Use a high voltage commercial process (automotive industry)

• Small active region, fast charge collection via drift

Fast and thin sensors: HV-MAPS

N-well E field

• Implement logic directly in N-well in the pixel - smart diode array

• Can be thinned down to < 50 μm

(I.Perić, NIM A 582 (2007) 876 )

(83)

Developed a series of HV-MAPS prototypes

• Goal: Detection and signal processing with just 50 μm silicon

• 6th chip, MuPix7, is a full system-on-a-chip

• Well characterized, working very nicely

• Now: Going “big” 2 x 1 cm

²

MuPix8 with 80 by 80 μm pixels under test

The MuPix Prototypes

(84)

MuPix8: First results

threshold / mV 40 60 80 100 120 140 160 180

efficiency

0.8 0.85 0.9 0.95

1 Preliminary

High efficiency

(85)

MuPix8: First results

threshold / mV 40 60 80 100 120 140 160 180

efficiency

0.8 0.85 0.9 0.95

1 Preliminary

/ ndf

χ2 5.161e+04 / 22

Constant 1.966e+05 ± 2.352e+02 Mean 0.07103 ± 0.01919 Sigma 18.92 ± 0.01

time resolution / ns

−300 −200 −100 0 100 200 300 400

entries

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

106

× χ² / ndf 3.216e+04 / 22

Constant 1.621e+05 ± 1.903e+02

Mean 19.33 ± 0.02

Sigma 23.3 ± 0.0

High efficiency

Decent timing

Large chip leads to

delays

(86)

MuPix8: First results

threshold / mV 40 60 80 100 120 140 160 180

efficiency

0.8 0.85 0.9 0.95

1 Preliminary

Entries

0.05 0.1 0.15

0.2 0.25

106

× χ² / ndf 8.117e+04 / 22

Constant 2.668e+05 ± 3.377e+02 Mean 1.568 ± 0.014 Sigma 13.39 ± 0.01

High efficiency

Decent timing

Large chip leads to delays

Can be corrected:

< 14 ns resolution Chip subset:

< 6 ns

(87)

Better timing:

Scintillating fibres and tiles

(88)

• 4 layers of 250 μm scintillating fibres

• Read-out by silicon photomultipliers (SiPMs) and custom ASIC (MuTRiG)

• Timing resolution < 400 ps including ASIC (using a Sr

⁹⁰

source)

Timing Detector: Scintillating Fibres

outer pixel layers

muon beam

target

inner pixel layers

(89)

Timing Detector: Scintillating tiles

• ~ 0.5 cm

³

scintillating tiles

• Read-out by silicon photomultipliers (SiPMs) and custom ASIC (MuTRiG)

Time Difference [ps]

-7500 -500 -250 0 250 500 750

2000 4000 6000 8000 10000

σ = 79.2 ps

• Test beam with tiles, SiPMs and readout ASIC

• Timing resolution better 80 ps

(90)

Phased experiment:

Phase I uses the existing PiE5 beam line at PSI, shared with MEG II, 10 ⁸ muons/s

Phase II requires a High Intensity Muon Beamline

(HiMB, > 2∙10 ⁹ muons/s)

(91)

• No trigger

• ~ 1 Tbit/s

• FPGA-based switching network

• 12 PCs with GPUs reconstruct tracks and vertices

• Only save things that look like μ

⁺

→ e

⁺

e

^-

e

⁺

Phase I Data Acquisition and Filter Farm

2844 Pixel Sensors

up to 45 1.25 Gbit/s links

FPGA FPGA FPGA

...

86 FPGAs 1 6 Gbit/s

link each

GPU

PC GPU

12 PCs PC 4 12 Gbit/s

links per

16 Inputs each

3072 Fibre Readout Channels

FPGA FPGA

...

12 FPGAs

6272 Tiles

FPGA FPGA

...

14 FPGAs

Data Collection

Server

Mass Storage Gbit Ethernet

Switching Board Switching

Board

Front-end(inside magnet)

Switching Board

Switching

Board Switching

Board

(92)

Phase I Performance Simulation

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 10 2

at 10 -12

→ eee µ

at 10 -13

→ eee µ

at 10 -14

→ eee µ

at 10 -15

→ eee µ

ν ν

→ eee µ

Bhabha +Michel

muons/s muon stops at 10 8

10 15

Mu3e Phase I

(93)

Sensitivity - Mu3e Phase I

Data taking days

0 50 100 150 200 250 300

eee) → µ BR(

−15

10

−14

10

−13

10

−12

10

−11

10

-15

× 2

SES 90% C.L. 95% C.L.

Mu3e Phase I 10

⁸

muon stops/s

19.7% signal efficiency

SINDRUM 1988

• Start 2020

• Phase II with a high intensity muon beam

line at PSI under study

(94)

If we find something...

(95)

(96)

• Models can be discriminated using Z-dependence

• However: low lifetime at high Z

Conversion: Z-dependence

0 0.5 1 1.5 2 2.5

B

µN->eN

( Z ) / B

µN->eN

( Z= 13)

dipole

scalar

vector

(97)

Mu3e: Decay distributions!

Ann-Kathrin Perrevoort

(98)

• Exciting range of experiments going on-line:

New lepton flavour violation limits upcoming

• MEG II starting engineering run now, data taking from next year

• DeeMee and Comet Phase I almost ready

• Mu3e Phase I starting 2020

• Mu2e and Comet Phase II from 2022

Summary

11

LXe Calorimeter with higher granularity.

Muon Beam More than twice intense beam

Radiative Decay Counter Identify muon radiative-decays Timing Counter

Higher time resolution with highly segmented detector Drift chamber

Higher tracking performance with long single tracking volume

Target Thinner target Active target option

outer pixel layers

muon beam

target inner pixel layers recurl pixel

layers

recurl pixel layers

scintillating ﬁbres

Scintillating tiles

(99)

Backup Material

(100)

History of LFV experiments

90 %– CL bound

10^–14 10^–12 10^–10 10^–8 10^–6 10^–4 10^–2 10⁰

μ eγ

μ 3e

μN eN

τ μγ

τ 3μ

10^–16

SINDRUM SINDRUM II

MEG

MEG II Mu3e I

Mu3e II

Comet II/Mu2e DeeMee/

Comet I

(101)

Lepton flavour violating Τ-decays

●

HFAG−Tau

Summer 2016

10

⁻⁸

10

⁻⁶

−eγ

−µγ

−e⁰π

−µ⁰π⁻eη

−µη

−eη′(958 )

−µη′(958 )

−e⁰K^S

−µ⁰K^S

−ef⁰(980 )

−µf⁰(980 )

−e⁰ρ

−µ⁰ρ

−e^∗K(892

0)

−µ^∗K(892

0)

−e^∗K(892

0)

−µ^∗K(892

0)

−eφ

−µφ

−eω

−µω

−e⁺e⁻e

−µ⁺e⁻e

−e⁺µ⁻µ

−µ⁺µ⁻µ

−e⁺µ⁻e

−µ⁺e⁻µ

−e⁺π⁻π

−µ⁺π⁻π

−e⁺π⁻K

−µ⁺π⁻K

−e⁺K⁻π

−µ⁺K⁻π

−e⁺K⁻K

−µ⁺K⁻K

−e⁰K⁰K^S^S

−µ⁰K⁰K^S^S

+e⁻π⁻π

+µ⁻π⁻π

+e⁻π⁻K

+µ⁻π⁻K

+e⁻K⁻K

+µ⁻K⁻K ⁻πΛ

−πΛ

−KΛ

−KΛ p⁻µ⁻µ

p⁺µ⁻µ

90% CL upper limits

●

ATLAS BaBar Belle CLEO LHCb

(102)

Y

• X

Belle II at Super KEKB

(103)

• Beam induced background

• Muon rates

Limitations of last experiment: SINDRUM II

(104)

Add a muon storage ring

Further steps: Prism/Prime Capture Solenoid

Matching Section Solenoid

RF Power Supply RF AMP

RF Cavity

C-shaped FFAG Magnet Ejection System Injection System

Niklaus Berger

Searching for

charged lepton flavour violation in muon decays

Niklaus Berger

Institut für Kernphysik, Johannes-Gutenberg Universität Mainz Flavour & Dark Matter

Karlsruhe, September 2018

Charged lepton flavour violation experiments:

• μ → e γ

MEG and MEG II

• μ to e conversion in Nuclei DeeMee, Comet, Mu2e

• μ → eee Mu2e

Overview

Standard Model branching fractions of

10 -50ish

Lepton flavour violation experiments

Only limited by number of muons and background suppression:

Experimental/technical challenge

History of cLFV experiments

90 % –C L b ou nd

LFV Muon Decays

μ + → e + γ μ - N → e - N μ + → e + e - e +

LFV Muon Decays: Experimental Situation

μ + → e + γ μ - N → e - N μ + → e + e - e +

MEG (PSI) SINDRUM II (PSI) SINDRUM (PSI)

B(μ

→ e

γ) < 4.2 ∙ 10

(2016) B(μ

Au → e

Au) < 7 ∙ 10

(2006) B(μ

→ e

e

e

) < 1.0 ∙ 10

(1988)

LFV Muon Decays: Experimental signatures

μ + → e + γ μ - N → e - N μ + → e + e - e +

Kinematics

• 2-body decay

• Monoenergetic e

, γ

• Back-to-back

LFV Muon Decays: Experimental signatures

μ + → e + γ μ - N → e - N μ + → e + e - e +

Kinematics

• 2-body decay

• Monoenergetic e

, γ

• Back-to-back Background

• Accidental background

LFV Muon Decays: Experimental signatures

μ + → e + γ μ - N → e - N μ + → e + e - e +

Kinematics

• 2-body decay

• Monoenergetic e

, γ

• Back-to-back Background

• Accidental background

• Radiative decay

Kinematics

• Quasi 2-body decay

• Monoenergetic e

• Single particle detected

LFV Muon Decays: Experimental signatures

μ + → e + γ μ - N → e - N μ + → e + e - e +

Kinematics

• 2-body decay

• Monoenergetic e

, γ

• Back-to-back Background

• Accidental background

Kinematics

• Quasi 2-body decay

• Monoenergetic e

• Single particle detected Background

• Decay in orbit

LFV Muon Decays: Experimental signatures

μ + → e + γ μ - N → e - N μ + → e + e - e +

Kinematics

10 ^-50ish

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺

μ ⁺ → e ⁺ γ μ ^- N → e ^- N μ ⁺ → e ⁺ e ^- e ⁺