Design and test of the Mu2e undoped CsI + SiPM crystal calorimeter - - PowerPoint PPT Presentation

Design and test of the Mu2e undoped CsI + SiPM crystal calorimeter

Raffaella Donghia

LNF-INFN and Roma Tre University On behalf of the Mu2e calorimeter group May 29, 2018 Frontier Detectors for Frontier Physics 14th Pisa Meeting on Advanced Detectors

FERMILAB-SLIDES-18-801-E

This document was prepared by Mu2e collaboration using the resources of the Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy, Office of Science, HEP User Facility. Fermilab is managed by Fermi Research Alliance, LLC (FRA), acting under Contract No. DE-

AC02-07CH11359.

Talk overview

• Mu2e
• CLFV Introduction
• Experiment layout and detectors
• Calorimeter requirements
• Components
• Single Channel Tests
• Prototypes’ performance
• Production phase

May 29, 2018 Mu2e Calorimeter, R.Donghia 1

Charged Lepton Flavor Violation

• CLFV strongly suppressed in SM: Branching Ratio ≤10-54

à Observation would indicate New Physics

• CLFV@Mu2e:μ- e conversion in a nucleus field

à discovery sensitivity to many NP models

• Goal:

104 improvement w.r.t. current limit (SINDRUM II) (@ 90% CL, with ~ 1018 stopped muons in 3 years of running)

μ-e conversion in the presence of a nucleus

< 8.4 x 10-17

Nuclear captures of muonic Al atoms

µ e Al

More information at mu2e.fnal.gov

ECE = mμc2 – Eb – Erecoil= = 104.97 MeV

May 29, 2018 Mu2e Calorimeter, R.Donghia 2

Mu2e experiment design

25 m

Production Solenoid / Target

• Protons hitting target and

producing mostly π Transport Solenoid

• Selects and transports low

momentum μ-

PS TS

• 1. Generate low momentum μ- beam
• 2. Stop the muons in an Al target à trapped in orbit around the nucleus
• 3. Look for an excess around 105 MeV/c in the electron spectrum

Detector Solenoid: stopping target and detectors

• Stops μ- on Al foils
• Events reconstructed by detectors optimized

for 105 MeV/c momentum

May 29, 2018 Mu2e Calorimeter, R.Donghia 3

DS

Calorimeter requirements

• σE/E = 𝓟(10%) for CE
• σT < 500 ps for CE
• σX,Y ≤ 1 cm
• Fast scintillation signals (τ<40 ns)
• Operate in 1 T and in vacuum at 10-4 Torr
• Redundancy in readout ( 2 sensors+FEE /crystal)
• Radiation hardness (with a safety factor of 3):
• 100 krad (45 krad) dose for crystals (sensors)
• 3x1012 n1MeV/cm2 (1.2x1012 n1MeV/cm2) for crystals (sensors)
• Low radiation induced readout noise < 0.6 MeV

The electromagnetic calorimeter (EMC) should provide high acceptance for reconstructing energy, time and position of CEs for: 1) PID: e/μ separation 2) EMC seeded track finder 3) Standalone trigger

Requirements @ 105 MeV/c

Front Disk Dose – 1 year [krad] May 29, 2018 Mu2e Calorimeter, R.Donghia 4

Simulated performance

ion

• Simulation includes full background

and digitization and cluster-finding, with split-off and pileup recovery

• The overall resolution depends on

crystals features

• Several crystals considered

LRU: RMS/MEAN of Light Output values along axis

May 29, 2018 Mu2e Calorimeter, R.Donghia 5

LYSO BaF2 CsI Radiation Length X0 [cm] 1.14 2.03 1.86 Light Yield [% NaI(Tl)] 75 4/36 3.6 Decay Time[ns] 40 0.9/650 20 Photosensor APD RMD APD SiPM Wavelength [nm] 402 220/300 310 $

Calorimeter Design

2 annular disks with 674 undoped CsI (34 x 34 x 200) mm3 square crystals/each disk

• RIN = 374 mm, ROUT = 660 mm
• Depth = 10 X0 (200 mm), Distance 70 cm
• Redundant readout:

2 UV-extended SiPMs/crystal

• 1 FEE / SiPM , Digital readout on crates
• RA source for energy calibration
• Laser system for monitoring

BETTER PICTURE!!

May 29, 2018 Mu2e Calorimeter, R.Donghia 6

1 year long R&D phase for the final test of the option CsI + UV extended SiPM 72 crystals + 150 SiPM + 150 FEE chips completed in 2016

Small prototype:

Time and Energy resolution

Significant leakage contribution due to block dimensions w.r.t. the shower

σT ~ 110 ps at 100 MeV σE ~ 7 % at 100 MeV

JINST 12 (2017) P05007

PRE-PRODUCTION

h

Entries Mean 0 RMS 0 Energy [GeV] 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 [ns]

t

σ 0.05 0.1 0.15 0.2 0.25 0.3

h

Entries Mean 0 RMS 0 / ndf

2

χ 38 / 17 a 0.00015 ± 0.0049 b 0.0033 ± 0.087 / ndf

2

χ 38 / 17 a 0.00015 ± 0.0049 b 0.0033 ± 0.087

b ⊕ = a/E

t

σ

Single crystal @ 0 deg All crystals above 10 MeV @ 0 deg Cosmics Neighboring crystals @ 50 deg Single crystal @ 50 deg Most energetic crystal @ 50 deg All crystals above 10 MeV @ 50 deg

Total energy [GeV] 0.07 0.075 0.08 0.085 0.09 0.095 0.1 0.105 /E [%]

E

σ 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9

/ ndf

2

χ 2.866 / 3 a 0.3253 ± 1.38 b 1.092 ± 4.911 / ndf

2

χ 2.866 / 3 a 0.3253 ± 1.38 b 1.092 ± 4.911

data Monte Carlo

b ⊕ E [GeV] a = E

E

σ May 29, 2018 Mu2e Calorimeter, R.Donghia 7

Small prototype 3x3 tested @ BTF (LNF) in 2015, 80-120 MeV e-

Normal incidence

/MeV

pe

N 100 110 120 130 140 150 160 170 180 190 200

Entries

2 4 6 8 10 LRU (%) 1 2 3 4 5 6 7 8 9 10

Entries

2 4 6 8 10 12 (%) µ / σ 10 11 12 13 14 15 16 17 18 19 20

Entries

2 4 6 8 10 12 14 16 SICCAS Amcrys Saint Gobain F/T (%) 60 65 70 75 80 85 90 95 100 105

Entries

2 4 6 8 10 12 14

Pre-production Crystals

• 24 crystals from SICCAS, Amcrys, Saint Gobain
• Optical properties tested with 511 keV γ’s along the crystal axis
• 150 µm Tyvek wrapping and UV-extended PMT readout

Energy resolution Light Yield Longitudinal Resp. Uniformity Q(200 ns)/Q(3000 ns)

RMS/MEAN of Light Output values along axis

Fast/Total

Un-doped CsI crystals perform well:

• Excellent LRU and LY:
• 100 pe/MeV
• LRU < 5%

§ τ of 30 ns (small slow component) § Radiation hardness OK LY loss < 40% (@ 100 krad)

May 29, 2018 Mu2e Calorimeter, R.Donghia 8 Entries 72

]

2

/cm

1MeV

Integrated flux [n 100 200 300 400 500 600 700 800

9

10 I [mA] 10 20 30 40 50 60

Entries 102900 Mean 90.04 Mean y 33.18 RMS 63.51 RMS y 33.26

Time [ns] 50 100 150 200 Amplitude [mV] 20 40 60 80 100 120 140 160

Entries 102900 Mean 90.04 Mean y 33.18 RMS 63.51 RMS y 33.26 Entries 102900 Mean 90.09 Mean y 60.63 RMS 63.51 RMS y 110.6

Time [ns] 50 100 150 200 Amplitude [mV] 100 200 300 400 500

Entries 102900 Mean 90.09 Mean y 60.63 RMS 63.51 RMS y 110.6

Pre-production SiPMs

150 sensors: 3×50 Mu2e pre-production SiPMs from Hamamatsu, SenSl and AdvanSiD

• 3×35 were fully characterized for all six cells in the array

Gain Mu2e custom silicon photosensors: à 2 arrays of 3 6 x 6 mm2 UV-extended SiPMs: total area (12x18) mm2 The readout series configuration reduces the overall capacitanceàfaster signals ~ 150 V i1≈ i2 ≈ i3 Ctot ≈ C1/3

6x6 mm2 K1 A1

A1-1 A1-2

Single cell of 6 x 6 mm2 Series of 3 cells

May 29, 2018 Mu2e Calorimeter, R.Donghia 9

We need to cool down SiPMs at 0 ° Neutron test Hamamatsu SenSl AdvanSiD

t wrapped

Module 0

Large EMC prototype: 51 crystals, 102 SiPMs, 102 FEE boards Mechanics and cooling system similar to the final ones!

Goals:

• Integration and assembly procedures
• Test beam May 2017, 60-120 MeV e-

(beam @ 0° and @ 50°)

• Work under vacuum, low temperature, irradiation test

May 29, 2018 Mu2e Calorimeter, R.Donghia 10

Readout: 1 GHz CAEN digitizers (DRS4 chip), 2 boards x 32 channels

F i n a l r e a d

• u

t d e t a i l s i n C a i u l

• ’

s p

• s

t e r

0.05 0.06 0.07 0.08 0.09 0.1 0.11 [GeV]

dep

E 1 2 3 4 5 6 7 8 9 10 [%]

dep

/E σ

/ ndf

2

χ 1.132 / 1 a 0.9182 ± 0.2 b 0.02063 ± 0.3289 c 0.3227 ± 3.807 / ndf

2

χ 1.132 / 1 a 0.9182 ± 0.2 b 0.02063 ± 0.3289 c 0.3227 ± 3.807

− − − − − − − −

§ Single particle selection § Calibration

• MIPs
• 100 MeV e- beam, up to ring 2

§ Threshold applied after noise run @ 3 σ

Module 0 Energy resolution

May 29, 2018 Mu2e Calorimeter, R.Donghia 11 Ebeam = 100 MeV σE ~ 7.3 % Beam @ 50° Perpendicular Beam Ebeam = 100 MeV σE ~ 5.4 %

σE E = a √ E ⊕ b E ⊕ c

Preliminary Good agreement Data - MC

a 0.200 ± 0.092 b 0.329 ± 0.021 c 3.807 ± 0.323

Energy [MeV] 10 20 30 40 50 60 70 80 90 100 [ns]

T

σ 0.05 0.1 0.15 0.2 0.25 0.3 0.35

/ ndf

2

χ 1.631 / 5 a 0.2011 ± 6.29 b 0.006919 ± 0.08285 / ndf

2

χ 1.631 / 5 a 0.2011 ± 6.29 b 0.006919 ± 0.08285 / ndf

2

χ 2.776 / 3 a 0.1399 ± 4.85 b 0.004284 ± 0.06402 / ndf

2

χ 2.776 / 3 a 0.1399 ± 4.85 b 0.004284 ± 0.06402

• Beam at 0

Cosmic Rays - Hamamatsu

• Beam at 50

Cosmic Rays - SensL

Module 0 Time resolution

σ (T1+T2)/2 ~ 94 ps @ Ebeam = 100 MeV

• Selection on single particle
• Log-normal fit on leading edge
• Constant Fraction method used

à CF = 5%

TimeHist

/ ndf

2

106.6 / 20 0.0444 0.6526 1.21 17.12 0.7 216.6 N 640.2 8782 t [ns] 200 400 600 800 1000 Amplitude [mV] 50 100 150 200 250 300 350

TimeHist

/ ndf

2

106.6 / 20 0.0444 0.6526 1.21 17.12 0.7 216.6 N 640.2 8782

Χ η σ µ

May 29, 2018 Mu2e Calorimeter, R.Donghia

σT = a/E + b

Entries 1531 / ndf

19.56 / 15 Constant 7.6 240.9 Mean 0.0049 0.1664 Sigma 0.0035 0.1874

t [ns] 1.5 1 0.5 0.5 1 1.5 Entries / (0.075 ns) 50 100 150 200 250

Entries 1531 / ndf

19.56 / 15 Constant 7.6 240.9 Mean 0.0049 0.1664 Sigma 0.0035 0.1874

Central crystal (TSiPM 1 – TSiPM2)

Δ Highest Energy Crystal [MeV]

QA status of basic components

New laboratory built at FNAL. QA tests of all components started on march 2018 M

• r

e i n f

• r

m a t i

• n

i n D i F a l c

• ’

s p

• s

t e r

May 29, 2018 Mu2e Calorimeter, R.Donghia 13

/MeV

N 60 80 100 120 140 160 180 200 220 240 Entries 2 4 6 8 10 12 14 SICCAS Saint Gobain µ / σ 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Entries 10 20 30 40 50 60 LRU 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 Entries 2 4 6 8 10 12 14 16 18 Fast/Total 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 Entries 2 4 6 8 10 12 14 RIN (MeV) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Entries 2 4 6 8 10

SICCAS Saint Gobain

Crystals QA status

May 29, 2018 Mu2e Calorimeter, R.Donghia 14

More than 100 crystals already tested

• SICCAS rate: 60 crystals / month
• SG almost same rate, mechanical problem not fixed yet

LY LRU Eresolution

F/T 0.86 0.88 0.9 0.92 0.94 0.96 0.98 1 RIN 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

F/T RIN

Entries 120

RIN vs F/T

SiPMs QA status

May 29, 2018 Mu2e Calorimeter, R.Donghia 15

RMS (Vbr) RMS (Idark)

SiPM ID
 333 307 490 503 482 SiPM ID
 515 488 516 373 487

About 550 Mu2e SiPMs already characterized

• 300 pieces/month from March 2018
• All the 6 cells tested, measuring Vbr, Idark, Gain x PDE
• 4 % of tested SiPMs rejected (defective or with high Idark RMS)
• Irradiation with ~1x1012 neutrons/cm2 (MTTF) test on 5 (15)

SiPMs/batch

MTTF

• Requirement: grant an MTTF of 1 million hours at 0°
• sensors tested 18 days burn-in at 65°
• SiPM MTTF > 3 million hours

I [mA] I [mA] Elapsed Time [min]

• 10 °

0 ° 20°

Summary and Conclusions

• The Mu2e calorimeter has concluded its prototyping phase satisfying

the Mu2e requirements:

• Un-doped CsI crystals perform well

§ Excellent LRU and LY 100 pe/MeV ( PMT+Tyvek wrapping ) § τ of 30 ns with negligible slow component § Radiation hardness OK for our purposes: 40% LY loss at 100 krad

• Mu2e SiPMs quality OK, high gain, high PDE, small Idark, small spread

inside array

• SiPM performance after irradiation OK
• SiPM MTTF > 3 million hours
• Calorimeter prototypes tested with e- beam

§ Good time and energy resolution achieved @ 100 MeV

• Calorimeter production phase started

In 2020 installation of the calorimeter in the Mu2e experimental all begins!

May 29, 2018 Mu2e Calorimeter, R.Donghia 16

Spares

Raffaella Donghia

LNF-INFN and Roma Tre University On behalf of the Mu2e calorimeter group May 29, 2018 Frontier Detectors for Frontier Physics 14th Pisa Meeting on Advanced Detectors

Entries 1633 / ndf

χ 29.69 / 21 Constant 7.2 ± 225.1 Mean 0.0054 ± 0.1647 Sigma 0.0043 ± 0.2131

t [ns] ∆ 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 Entries / (0.075 ns) 50 100 150 200 250

Entries 1633 / ndf

χ 29.69 / 21 Constant 7.2 ± 225.1 Mean 0.0054 ± 0.1647 Sigma 0.0043 ± 0.2131

Module 0 SiPM-vendors comparison

May 29, 2018 Mu2e Calorimeter, R.Donghia 18

Time [ns] 160 180 200 220 240 260 280 300 320 340 Amplitude [mV] 50 100 150 200

10%max

• T

90%max

=T

rise

T = 29 ns

rise

Hamamatsu - T = 38 ns

rise

SensL - T = 37 ns

rise

AdvanSiD - T

Ebeam = 100 MeV Energy fluctuation C F d i s c r i m i n a t

• r

t [ns] ∆ 2 − 1.5 − 1 − 0.5 − 0.5 1 1.5 2 Entries / (0.075 ns) 50 100 150 200 250

σT ~ 115±2ps SensL σT ~ 106.5±2.1ps

Entries 1531 / ndf

19.56 / 15 Constant 7.6 240.9 Mean 0.0049 0.1664 Sigma 0.0035 0.1874

t [ns] 1.5 1 0.5 0.5 1 1.5 Entries / (0.075 ns) 50 100 150 200 250

Entries 1531 / ndf

19.56 / 15 Constant 7.6 240.9 Mean 0.0049 0.1664 Sigma 0.0035 0.1874

σT ~ 93.5±2ps AdvanSiD

Hamamatsu

Mu2e

Charged Lepton Flavor Violation

• CLFV strongly suppressed in SM: BR ≤10-54

à Observation indicates New Physics

• CLFV@Mu2e:μ- e conversion in a nucleus field

à discovery sensitivity on many NP models

• Goal:

104 improvement w.r.t. current limit (SINDRUM II) (@ 90% CL, with ~ 1018 stopped muons in 3 years of running)

Contact dominated Loop dominated

μ-e conversion in the presence of a nucleus

< 8 x 10-17

Nuclear captures of muonic Al atoms

µ e Al

arXiv: 1303.4907 May 29, 2018 Mu2e Calorimeter, R.Donghia 19

Small prototype: Test Beam

• Small prototype tested @ BTF (Frascati) in April 2015, 80-120 MeV e-
• 3×3 array of 30×30×200 mm2 undoped CsI crystals coupled to one

Hamamatsu SiPM array (12x12) mm2 with Silicon optical grease

• DAQ readout: 250 Msps CAEN V1720 WF Digitizer

JINST 12 (2017) P05007

FOTO matrice

Log-normal fit

May 29, 2018 Mu2e Calorimeter, R.Donghia 20

Pre-production test: SiPMs (2)

• 1 sample per vendor has been exposed to neutron flux up to

8.5×1011 n1MeVeq/cm2 (@ 20 °C)

• 5 samples per vendor have been used to estimate the mean time to failure value

Requirement: obtain an MTTF of 1 million hours when operating at 0 °C

]

2

/cm

1MeV

Integrated flux [n 100 200 300 400 500 600 700 800

9

10 I [mA] 10 20 30 40 50 60

• MTTF evaluated operating SiPMs @

50 °C for 3.5 months

• No dead channels observed

MTTF ≥ 6×105 hours

• SiPMs will operate @ 0 °C: a decrease of

10 °C in SiPMs temperature corresponds to a Id decrease of 50%

• Lower Vop also helps to decrease the Id

MTTF Neutron test Hamamatsu SenSl AdvanSiD

May 29, 2018 Mu2e Calorimeter, R.Donghia 21

SG crystal + Hamamatsu SiPM + FEE Optical coupling in air.

• 22Na source
• TRG: small scintillator readout by a PMT
• Study distance effect for air-coupling

Single channel slice test

Time [ns]

80 100 120 140 160 180 200 220

Amplitude [mV]

5 10 15 20 25

Hamamatsu 4 - DIstance from Crystal 0 mm 1 mm 2 mm

~ 10% loss

• Cosmic ray test à 2 SiPMs readout
• TRG: crystal between 2 small scintillators

2 SiPMs

May 29, 2018 Mu2e Calorimeter, R.Donghia 22

Single channel Cosmic Rays Test

• TRG time resolution ~ 170 ps
• Constant fraction method used
• Pulse height correction applied

(slewing)

After jitter subtraction: SiPM 1 – σT ~ 330 ps SiPM 2 – σT ~ 340 ps T(SiPM1 - SiPM2)/2 à ~ 215 ps @ ~ 23 MeV energy deposition (MIP energy scale from Na22 source peak) Timing result well compares with old tests: à Reduced light output/SiPM (22 vs 30 pe/MeV) à 2 SiPMs/crystal à LY of 44 vs 30 à 215 ps (now) vs 250 ps (old).

Entries 727 Constant 6.2 ± 133.6 Mean 0.0161 ± 0.1234 Sigma 0.012 ± 0.429

Time [ns]

• 3
• 2
• 1

1 2 3 Entries / 25 ps 20 40 60 80 100 120 140

Entries 727 Constant 6.2 ± 133.6 Mean 0.0161 ± 0.1234 Sigma 0.012 ± 0.429

SiPM 1 - SiPM 2 Σ May 29, 2018 Mu2e Calorimeter, R.Donghia 23

Pre-production test: Crystals (2)

Few samples per vendor have been exposed both to ionizing dose and neutrons

• Irradiation test up to 100 krad
• Requirement:

normalized LY after 10/100 krad > 85/60%

• Radiation Induced Noise (RIN) @ 1.8 rad/h required is < 0.6 MeV
• All 72 samples tested. All OK apart some Amcrys crystals that

do not satisfy the required limit

• Negligible LY and LRU variation after 1.6 x 1012 n1MeV/cm2 integrared flux
• Neutron RIN is also smaller than the one from dose

Most crystals have LY larger than 100 p.e./MeV after 100 krad (40% max. loss), promising a robust CsI calorimeter

85% 60%

May 29, 2018 Mu2e Calorimeter, R.Donghia 24

Module 0 Event selection

May 29, 2018 Mu2e Calorimeter, R.Donghia 25

Noise width in the new charge increase linearly with the number of crystals added

Module 0 Event selection

May 29, 2018 Mu2e Calorimeter, R.Donghia 26

Module 0 Event selection

May 29, 2018 Mu2e Calorimeter, R.Donghia 27

Module 0 Event selection

May 29, 2018 Mu2e Calorimeter, R.Donghia 28

20 40 60 80 100 [MeV]

MC

E 200 400 600 800 1000 1200 1400 Q [pC]

/ ndf

2

χ 89.91 / 4 p 0.02236 ± 12.47 / ndf

2

χ 89.91 / 4 p 0.02236 ± 12.47 pC to MeV = 1 / p = 0.0802

PId

29

With a CRV inefficiency of 10-4 an additional rejection factor of ~ 200 is needed to have < 0.1 fake events from cosmics in the signal window

A rejection factor of 200 can be achieved with ~ 95% efficiency for CE

May 29, 2018 Mu2e Calorimeter, R.Donghia 29

Calibration source and laser

• Liquid source FC 770 + DT generator: 6 MeV + 2 escape peaks
• Laser system to monitor SiPM performance

May 29, 2018 Mu2e Calorimeter, R.Donghia 30

Calorimeter Trigger

• Calo info can provide additional trigger capabilities in Mu2e:
• Calorimeter seeded track finder
• Factorized into 3 steps: hit pre-selection, helix serach and track fit
• ε ~ 95% for background rejection of 200
• Standalone calorimeter trigger that uses only calo info
• Ε ~ 65% for background rejection 200

May 29, 2018 Mu2e Calorimeter, R.Donghia 31

Calorimeter seeded track finder

May 29, 2018 Mu2e Calorimeter, R.Donghia 32

Calorimeter radiation damage

• Calorimeter radiation dose driven by beam

flash (interaction of proton beam on target)

• Dose from muon capture is x10 smaller
• Dose is mainly in the inner radius
• Highest dose ~10 krad/year
• Highest n flux on crystals ~ 2×1011 n/cm2/year
• Highest n flux on SiPM ~ 1011 n1MeVeq/cm2/year
• Qualify crystals up to

~ 100 krad, 1012 n/cm2

• Qualify SiPM up to

~ 1012 n1MeVeq/cm2

This includes a safety factor

• f 3 for a 3 year run

May 29, 2018 Mu2e Calorimeter, R.Donghia 33

Calorimeter radiation damage

May 29, 2018 Mu2e Calorimeter, R.Donghia 34

Calorimeter mechanics

Mu2e Collaboration, November 2013

May 29, 2018 Mu2e Calorimeter, R.Donghia 35

Calorimeter Readout electronics

Mu2e Collaboration, November 2013

May 29, 2018 Mu2e Calorimeter, R.Donghia 36

Three years run Expectation by full Simulation

Mu2e Collaboration, November 2013

May 29, 2018 Mu2e Calorimeter, R.Donghia 37

CLFV Lagrangian

Mu2e Collaboration, November 2013 μN→eN μ→eγ μ→eee Loops dominate for κ << 1 Contact terms dominate for κ >> 1 κ μN→eN μ→eγ μ→eee

Λ (TeV)

May 29, 2018 Mu2e Calorimeter, R.Donghia 38