Experimental Concept

(1)

Searching for Lepton Flavour Violation

Ann-Kathrin Perrevoort

Physics Institute, Heidelberg University

IHEP, October 26, 2016

(2)

Searching for New Physics in the Decayµ eee

Lepton Flavour conserved in Standard Model

. . . but νoscillations

(3)

Lepton Flavour conserved in Standard Model

. . . but νoscillations

Expectation from lepton mixing: BR_µ _eee ^∆m_m2²^ν

W ²@10⁵⁴

(4)

Observation of µ eee is a clear sign for New Physics

SUSY, GUTs, extended Higgs sector, . . .

Current limit: BR_µ _eee@1.0 10¹²at 90%CL[SINDRUM, 1988]

Mu3e: New experiment sensitive to BR’s of 10¹⁵(10¹⁶)

(5)

300 400 500 600 700 800 900 1000 2000 3000 4000 5000 6000 7000

10^-2 10^-1 1 10 10²

!

" (TeV)

EXCLUDED (90% CL) B(µ # e$)=10^-13

B(µ # e$)=10^-14

B(µ # eee)=10^-14 B(µ # eee)=10^-16

LCLFV _κ^m₁^µ_Λ2µRσµνeLF^µν

dipole-like κ

κ1Λ²µLγµeLeLγ^µeL

four-fermion

A. Gouvˆea, P. Vogel, Prog.Part.Nucl.Phys. 71 (2013)

(6)

History of LFV Searches inµandτDecays

1940 1960 1980 2000 2020

Year

90%–CL bound

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

Adapted from Marciano et al. [Ann.Rev.Nucl.Part.Sci.58, 2008]

(7)

Signal Decayµ eee

Signature forµ decay at rest Common vertex

Coincident in time PE_e m_µc² P Ñpe 0

All particles in one decay plane E_e 053MeV

Multiple Coulomb scattering limits momentum resolution

(8)

Background: Combinatorial Background

e⁺

e⁺ e^-

e⁺

e^- e⁺

(e⁺)

Overlays of Michel decay µ eνν, Bhabha scattering, photon conversion, . . .

No common vertex Not coincident PE_exm_µc² P Ñpex0

Increases with beam intensity

(9)

Background: Radiative Decay with Internal Conversionµ eeeνν

BR_µ eeeνµνe 3.40.4 10⁵[Nucl.Phys.B260, 1985]

Common vertex Coincident in time PE_e@m_µc² P Ñpex0

Missing energy due to neutrinos Need very good momentum resolution

(10)

Background: Radiative Decay with Internal Conversionµ eeeνν

BR_µ eeeνµνe 3.40.4 10⁵[Nucl.Phys.B260, 1985]

Branching Ratio

m_μ - E_tot (MeV)

0 1 2 3 4 5 6

10^-12

10^-16

10^-18 10^-13

10^-17 10^-15 10^-14

10^-19 μ3e

[Djilkibaev, Konoplich, Phys.Rev.D79, 2009 ]

Common vertex Coincident in time PEe@m_µc² P Ñpex0

Missing energy due to neutrinos Need very good momentum resolution

(11)

Requirements

High muon stopping rates: 10⁸µ~s toA10⁹µ~s

Very good vertex (200µm) and time resolution (100 ps)

Excellent momentum resolution (0.5 MeV)

Minimal material amount

Triggerless data acquisition

Fast online reconstruction for data rate reduction

(12)

Muon Beam

Paul-Scherrer Institute in Switzerland

2.2 mA proton beam with 590 MeV Secondary beamlines: µwith 28 MeV 10⁸muons~s at existing beamline 10⁹muons~s at future beamline

(under investigation)

(13)

Muon Beam

Paul-Scherrer Institute in Switzerland

(14)

Detector

Tracking detector:

Thin Si pixel sensors (HV-MAPS)

+ Timing detector:

Scintillating fibres and tiles

(15)

Detector

Target Inner pixel layers

Scintillating fibres

Outer pixel layers Recurl pixel layers

Scintillator tiles

μ Beam

Tracking detector:

Thin Si pixel sensors (HV-MAPS)

+ Timing detector:

Scintillating fibres and tiles

(16)

Multiple Coulomb Scattering

Ω MS

θMS

B

Decay electrons have low momentum@53 MeV~c

Momentum resolution is dominated by multiple scattering

σp

p ^θ^MS_Ω with θMS ¹_p¼ _x

X0

reduce material thickness x increase opening angleΩ

(17)

Ω ~ π MS

θ

MS

B

σp

p ^θ^MS_Ω with θ_MS ¹_p¼ _x

X0

reduce material thickness x increase opening angleΩ atΩπ ^σ_p^p Oθ²_MS

(18)

σp

p ^θ^MS_Ω with θMS ¹_p¼ _x

X0

reduce material thickness x increase opening angleΩ

(19)

Target

Extended hollow double-cone target made of mylar (80µm)

Length 10 cm, diameter 3.9 cm High muon stopping fraction

Vertex separation over a large surface Low distortion for ‘escaping’ electrons

(20)

Pixel Sensors: HV-MAPS

High Voltage Monolithic Active Pixel Sensors

180 nm HV-CMOS process

N-well in p-substrate

Reverse bias of 60 to 90 V

L Fast charge collection via drift

L Depletion zone of10µm Thinning possible (ß50µm)

Transistor logic embedded in N-well

“smart diode array”

Pixel size 8080µm² Sensor size 22cm² Thin and granular

P-substrate N-well

Particle E field

I. Peri´c, NIM A 582 (2007)

(21)

Pixel Sensors: HV-MAPS

Pixel Periphery State Machine

readout state machine

VCO

&

PLL

8b/10b

encoder serializer LVDS ...

other pixels

sensor CSA

comparator tune

DAC

threshold baseline source

follower

test-pulse injection

readout 2^nd amplifier

integrate charge

amplification line driver

digital output AC coupling

via CR filter per pixel threshold adjustment

Hit finding, digitisation, zero-suppression and readout on-chip Continuous and fast readout at 1.25 Gbit~s

(22)

Pixel Sensors: MuPix Prototype

MuPix7 is the latest HV-MAPS prototype for Mu3e 3240 pixels `a 10380µm²

2.93.2mm² of active area 50µm thin

‘System-on-chip’

Zero-suppressed hit addresses and timestamps

(23)

Beam telescope with 4 layers of MuPix7 and scintillating tiles One MuPix layer used as DUT

(24)

Experimental Concept

Testbeam at DESY: 4 GeV ebeam

Threshold [V]

0.7 0.71 0.72 0.73 0.74 0.75

Efficiency

0.95 0.96 0.97 0.98 0.99 1

Efficiency Noise 99 %

Preliminary

Noiserate per pixel [1/s]

−1

10 1 10

102

103

104

(25)

Testbeam at DESY: 4 GeV ebeam; using DESY Duranta telescope

row-axis [mm]

0 0.5 1 1.5 2 2.5 3

column-axis [mm]

0 0.5 1 1.5 2 2.5 3

efficiency_pixeluv

Entries 900390

Mean x 1.557

Mean y 1.803

RMS x 0.922

RMS y 0.8324

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

efficiency_pixeluv

Entries 900390

Mean x 1.557

Mean y 1.803

RMS x 0.922

RMS y 0.8324

Mupix7, 735 mV threshold, HV = -85 V

(26)

Experimental Concept

Testbeam at DESY: 4 GeV ebeam; DUT rotated by 60° wrt to beam axis

Threshold [V]

0.67 0.68 0.69 0.7 0.71 0.72 0.73 0.74 0.75

Efficiency

0.984 0.986 0.988 0.99 0.992 0.994 0.996 0.998 1

Efficiency Noise 99 %

Preliminary

Noiserate per pixel [1/s]

1 10

102

(27)

Testbeam at DESY: 4 GeV ebeam Timing resolution of 17.41.1ns

td1

Entries 2694

Mean −7.894

RMS 14.46

/ ndf

χ2 0.09802 / 1

Constant 179.8 ± 11.4 Mean −11.12 ± 0.06 Sigma 1.086 ± 0.066

HitTime layer 0-TriggerTime [16 ns]

−30 −20 −10 0 10 20

Entries

0 20 40 60 80 100 120 140 160

180 td1

Entries 2694

Mean −7.894

RMS 14.46

/ ndf

χ2 0.09802 / 1

Constant 179.8 ± 11.4 Mean −11.12 ± 0.06 Sigma 1.086 ± 0.066

(28)

MuP ix8

ATL AS

Reticle

~10 mm

~22 mm

~26 mm

~21 mm

Next prototype: MuPix8

First large MuPix sensor 21cm²

4 serial links

Time walk correction

Diﬀerent substrates 20Ωcm and 80Ωcm Submission in November

(29)

Pixel Detector: Lightweight Mechanics

50µm silicon sensor

80µm Flexible printed circuit board (FPC)

25µm Kapton support structure

0.1%of radiation length

Aluminium 14 um

Aluminium 14 um Glue 5 um Glue 5 um Polyimide 25 um Polyimide 10 um

Polyimide 10 um MuPix 50 um

Kapton frame 25 um

Bus signals Power distribution Sensor signals Ground SpTAB pads Dielectric spacer layer

{

FPC

Mechanical support

Sensor

Glue 5 um Glue 5 um

(30)

Cooling

Cooling with gaseous helium Power consumption of Si pixel sensors is 250 mW~cm²

Layer 4 Layer 3

Layer 1 Layer 2 FPGA

Water

Global he flow Gap he flow

Local he flow

(31)

Time Measurement

Tracks expected within readout frame of 50 ns

Matching with time information of scintillating fibres and tiles

(32)

Scintillating Fibres

-4 -3 -2 -1 0 1 2 3 4

Events/200ps

0 1000 2000 3000 4000 5000

σ = (412 x √2)ps

t1-t2[ns]

Time resolution of squared fibres

2 to 4 layers of fibres with g 250µm

Round and squared fibres under investigation

Photon detection at both ends with SiPM array

Readout with custom-designed STiC chip

Time resolution:

σ_round

º2 1.5 ns

σ_squared

º2 B500 ps

(33)

Scintillating Tiles

Time Difference [ps]

-400 -200 0 200 400

# Entries

0 5 10 15 20 25 30

103

×

TWC No TWC ) ps

× 2 = (56 σ

) ps

× 2 = (70 σ

Size 111cm³

Each tile has a SiPM

Readout with custom-designed STiC chip

Time resolution ß100 ps

(34)

Data Acquisition

2928 Pixel Sensors

up to 36 1.25 Gbit/s links

FPGA FPGA FPGA

...

86 FPGAs 1 6 Gbit/s

link each

GPU

PC GPU

PC

GPU PC 12 PCs 12 10 Gbit/s

links per

8 Inputs each

~ 3072 Fibre Readout Channels

FPGA FPGA

...

48 FPGAs

~ 3500 Tiles

FPGA FPGA

...

48 FPGAs

Data Collection

Server

StorageMass Gbit Ethernet

Switching

Board Switching

Board

Front-end(inside magnet)

Switching Board

(35)

Data Acquisition

Triggerless data acquisition Front-end board

L Slow control

L Buﬀer and merge data

L Time-sorting Readout board

L Switch between front-end and filterfarm

L Merge data of sub-detectors GPU filterfarm

L Fast track finding and online reconstruction

L Reduce data rate from 1 Tbit~s to100 MB~s

~ 1000 Pixel Sensors

up to 45 1.25 Gbit/s links

FPGA FPGA FPGA

...

RO Boards 1 6.4 Gbit/s link each

GPU PC

GPU 12 PCs PC 12 6.4 Gbit/s ...

links per RO Board 4 Inputs each

Data Collection

Server

Mass Storage Gbit Ethernet

2 RO Boards

~40 FPGAs Front-end boards

Readout boards

Filterfarm

(36)

Detector construction in 2 phases

Starting with central Si pixel tracking detector 10⁷µ~s

(37)

Improve time resolution with scintillators

(38)

Improve momentum resolution by measuring re-curling particles

Increase acceptance for re-curlers 10⁸µ~s

(39)

Full-size detector

New beamline with 2 10⁹µ~s

reach design sensitivity of BRµ eee10¹⁶

(40)

h1

ϕ01 ϕ12

x y

d01

d12

ϕM S

c1 c2

rT ,01

rT ,12

h0

h2

3D multiple scattering fit for track reconstruction

Spatial uncertainties of hit positions are ignored as MS dominates

Hits in 3 layers form a ‘triplet’

Join triplets by minimizing MS angles

Subsequent vertex fit with 3 trajectories of correct charge

(41)

Full Geant4-based detector simulation Generators for SM and BSM decays

Track and vertex reconstruction Analysis tools

Reconstructed Mass [MeV]

96 98 100 102 104 106 108 110

Events per 100 keV

10-4

10-3

10-2

10-1

1 10

Internal Conversion Background

eee at 10-12

→

µ

eee at 10-13

→

µ

eee at 10-14

→

µ

eee at 10-15

→

µ

+ Michel e+ e- Bhabha e+

Mu3e: 1·10¹⁵ μ on Target; Rate 10⁸ μ/s

SIMULATION

(42)

µ eee

EFT approach with LFV dim6 operators L a Pi ci

Λ²O_i

Other LFV decays µ eγ,µ e X

Searches for dark photons µ eννA and A ee

(43)

µ eee

Λ²O_i

2] (high) [MeV

2ee

m

0 2 4 6 8 10 12

103

× ]2 (low) [MeV

2 eem

0 1 2 3 4 5 6 103

×

Dalitz plot for 4-fermion operator

(44)

µ eee

Λ²Oi

p [MeV]

0 10 20 30 40 50 60 70 80

Events per 100keV

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 1012

×

= 60MeV eX, mX

→ µ SM background

μ⁺

e⁺

X⁰

(45)

DPNC, Geneva University KIP, Heidelberg University

Physics Institute, Heidelberg University IPE, Karlsruhe Institute of Technology Institute for Nuclear Physics, JGU Mainz Paul Scherrer Institute

Institute for Particle Physics, ETH Z¨urich Physics Institute, Z¨urich University

(46)

Summary

Mu3e Search for LFV decay µ eee with a sensitivity of BR@10¹⁶ (90%CL)

Low-material tracking detector operated at high muon rates

Status Research proposal approved in 2013 Research and development on subsystems Preparation of detector construction

(47)

(48)

Tracking in MS-dominated Environment

(49)

LFV in Higgs Triplet Models

Models with Higgs triplet responsible for neutrino mass generation

Projections for LFV processes shown for diﬀerent neutrino mass hierarchies

Mu3e

M. Kakizaki, Y. Ogura, F. Shima, Phys.Lett. B566 (2003) (Plotted BR depens on mass scale M and can thus vary)

(50)

Signal and Background

Signal Background

Signalµ eee Accidental combinations Internal conversion µ eeeνµνe

Common vertex Coincident PEe m_µ P Ñpe 0

No common vertex Not coincident PEexm_µ P Ñpex0

Common vertex Coincident PEe@m_µ P Ñpex0

(51)

Full Readout Scheme

...

4860 Pixel Sensors

up to 56 800 Mbit/s links

FPGA FPGA FPGA

...

142 FPGAs

RO

Board RO

Board 1 6 Gbit/s

link each

Group A Group B Group C Group D

GPU

PC GPU

12 PCs PC

Subfarm A 12 10 Gbit/s ...

links per RO Board 8 Inputs each

GPU

PC GPU

12 PCs PC

Subfarm D 4 Subfarms

~ 4000 Fibres

FPGA FPGA

...

48 FPGAs

~ 7000 Tiles

FPGA FPGA

...

48 FPGAs

RO

Board RO

Board Group A Group B Group C Group D

RO

Board RO

Board Group A Group B Group C Group D

Data Collection

Server

Mass Storage Gbit Ethernet

(52)

Experimental Concept

(53)

Experimental Concept

Cooling

Finite elements simulation of temperature distribution at 250 mW~cm²

(54)

Experimental Concept

Cooling

(55)

MuPix: Pixel Layout

(56)

MuPix: Pixel Layout

(57)

MuPix7 Prototype

High Voltage Monolithic Active Pixel Sensor

Integrated signal processing

L Amplification and signal shaping

L Hit detection

Internal state machine

L Column-wise readout time structure is ‘lost’

L 8b/10b encoded data:

hit: time stamp, pixel address or counter

L LVDS link at up to 1.25 Gbit~s up to 30 Mhits~s can be read out

expectedB8 Mhits~s on busiest sensor at 10⁸µ~s

(67)

Front-End for the MuPix Telescope

Receiver

Receive data via LVDS at 1.25 Gbit~s

Align to word boundary using K-words

8b/10b decoding

“Unpacker”

Disentangle hit and counter data

Remove K-words Hit sorter

Merge data from 4 sensors to one datastream

Sort hit data by time stamp

Data transfer to PC via PCIe ^{to PC}

PCIe

MuPix MuPix MuPix MuPix

LVDS LVDS LVDS LVDS