The ultra-light Mu3e Tracker & possibilities for future trackers

A.Schöning University of Heidelberg

https://www.psi.ch/mu3e/

FCC-ee Workshop CERN 8.-11. January 2019

A. Schöning 1 FCC-ee, CERN, 9. January 2019 History of LFV Decay experiments

4 orders of Mu3e I magnitude Mu3e II

A. Schöning 2 FCC-ee, CERN, 9. January 2019 LFV Decay μ+ →ee+e+e-

Exotic Physics

loop diagrams tree diagram

Supersymmetry Higgs Triplet Model Little Higgs Models New Heavy Vector bosons (Z') Seesaw Models Extra Dimensions (KK towers) GUT models (Leptoquarks) many other models

Most models “naturally” induce lepton flavor violation!

A. Schöning 3 FCC-ee, CERN, 9. January 2019 Mu3e Experiment @ PSI

● World’s most intense continuous muon beam (fcycl. = 50MHz) ● 2.4 mA protons at 590 MeV = 1.5 MW → O(1010-11) muons

Aiming for sensitivity (SES) requires: BR(μ → e e e ) < 2·10-15 (phase I) → 108 muons/s (PiE5)

-16 9 BR(μ → e e e ) < 10 (phase II) → >10 muons/s (→new HiMB)

A. Schöning 4 FCC-ee, CERN, 9. January 2019 PiE5 Muon Beamline @ PSI

● O(108) muons per second ● Low momentum muons 28 MeV/c ● PiE5 beamline shared between MEG2 and Mu3e

A. Schöning 5 FCC-ee, CERN, 9. January 2019 PiE5 Area Compact Muon Beamline (CMBL) for Mu3e

MEG

Mu3e

A. Schöning 6 FCC-ee, CERN, 9. January 2019 Signal μ+ →ee+e+e-

● 3-prong signature ● muons decay at rest: ➔ two positrons and electron in common plane

- e e+

e+

Exotic Physics E = m ∑i i μ p⃗ = 0 signal ∑i i

A. Schöning 7 FCC-ee, CERN, 9. January 2019 Irreducible Background

Radiative decay with internal conversion

- e ν e+

- signal e e+

ν e+ B(μ+ →e e+e+e- νν) = 3.4 ·10- 5 e+

E = m ∑i i μ p⃗ = 0 ∑i i

A. Schöning 8 FCC-ee, CERN, 9. January 2019 Irreducible Background

Radiative decay with internal conversion

- e ν e+

missing energy from two neutrinos R.M.Djilkibaev, steeply falling! R.V.Konoplich ν e+ PRD79 (2009) B(μ+ →e e+e+e- νν) = 3.4 ·10- 5 missing energy taken by neutrinos

very good momentum + total energy resolution required! A. Schöning 9 FCC-ee, CERN, 9. January 2019 Accidental Backgrounds

Overlays of two ordinary µ+ decays with a (fake) electron (e-) Electrons from: Bhabha scattering, photon conversion, mis-reconstruction

Need excellent: Vertex resolution Timing resolution Kinematic reconstruction + little material (avoid high Z)

A. Schöning 10 FCC-ee, CERN, 9. January 2019 Tracking Resolution & Multiple Scattering

Muon decay (m = 105.6 MeV): → electrons at low momentum:

limited hit p < 53 MeV/c resolution regime Multiple scattering is dominant!

Need thin, fast and high resolution tracking detectors operated at high rate (>109 particles/s @ phase II)

1 Θ ∼ X / X MS P √ 0 mutiple scattering regime

A. Schöning 11 FCC-ee, CERN, 9. January 2019 Mu3e Experiment Aiming for a sensitivity (SES) requires: BR(μ → e e e ) < 2·10-15 (phase I) →e 108 muons/s (PiE5)

BR(μ → e e e ) < 10-16 (phase II) →e>10 9 muons/s (→e HiMB)

Pixel Tracker Scintillating Fibers Scintillating Tiles timing

A. Schöning 12 FCC-ee, CERN, 9. January 2019 Momentum Resolution in MS Regime

Standard spectrometer:

multiple-scattering angle σ Θ X p ∼ MS ∼ √ (linearised) P Ω Ω

precision requires large lever arm →e large bending angle Ω

Ω

A. Schöning 13 FCC-ee, CERN, 9. January 2019 Momentum Resolution in MS Regime

“Half turn” spectrometer:

σ p 2 X ∼ O(ΘMS ) ∼ P X 0

Ω ~ π best precision for half turn tracks measure recurlers

A. Schöning 14 FCC-ee, CERN, 9. January 2019 Tracking Design Considerations

muon mass ~ 105 MeV/c2

A. Schöning 15 FCC-ee, CERN, 9. January 2019 Tracking Design Considerations

A. Schöning 16 FCC-ee, CERN, 9. January 2019 Tracking Design Considerations

A. Schöning 17 FCC-ee, CERN, 9. January 2019 Tracking Design Considerations

A. Schöning 18 FCC-ee, CERN, 9. January 2019 Mu3e Baseline Design

108 muons per second (phase I)

p=28 MeV/c

A. Schöning 19 FCC-ee, CERN, 9. January 2019 Mu3e Baseline Design

A. Schöning 20 FCC-ee, CERN, 9. January 2019 Mu3e Baseline Design

A. Schöning 21 FCC-ee, CERN, 9. January 2019 Mu3e Baseline Design

Long cylinder!

~180 cm

~15 cm

not to scale!

A. Schöning 22 FCC-ee, CERN, 9. January 2019 Mu3e Baseline Design

solenoid B=1 T

A. Schöning 23 FCC-ee, CERN, 9. January 2019 Mu3e Design Features: ● surface muons (p=29 MeV/c, DC) stopped on target at high rate: 108 - 109 /s ● ultra thin silicon pixel detector (HV-MAPS) with 1 per mill radiation length / layer ● high precision tracking using recurling tracks in strong magnetic field ● fast timing detectors (scintillating fibers & tiles) ● helium gas cooling transverse view:

Ek~ 4 MeV

B = 1 Tesla

helium atmosphere

A. Schöning 24 FCC-ee, CERN, 9. January 2019 A light-weight pixel tracker

Mu3e: SES scales with the third power of the tracker material!

3 Experiment Material per layer X layer SES ∼ ATLAS IBL 1.9% X0 ( X 0 ) ALICE ITS mid/outer 0.8% X0

ALICE ITS inner 0.3% X0 ➔ goal Mu3e: X/X = 0.001 0 STAR 0.4% X0

● 50 µm HV-MAPS BELLE II vertex 0.2% X0

● ~150 mu flexprint Mu3e (all layers) 0.1% X0 + mechanical support

In addition: ● helium atmosphere → reduces multiple scattering ● cooling of pixel tracker with helium gas

A. Schöning 25 FCC-ee, CERN, 9. January 2019 (Outer) Pixel Tracker Module

MuPix (HV-MAPS)

High Density Interconnect (LTU, Ukraine)

50 µm

180 nm HV-CMOS (AMS) A. Schöning 26 FCC-ee, CERN, 9. January 2019 Mechanical Mockups

Ultra-thin mechanical mockup: ● sandwich of 25 µm Kapton® ● 50 µm glass (instead of Si)

Even larger stable structures possible

36 cm

by using Kapton V-folds

A. Schöning 27 FCC-ee, CERN, 9. January 2019 Flexprint Production and Bonding

spTAB = single point tape automated bonding FPC Production by LTU Ltd (Ukraine) FPC = flexible printed circuit

→ bonding yield 100%

FPC spTAB-bonded on test board and qualified

spTAB bond zoomed in

6.85 cm

A. Schöning 28 FCC-ee, CERN, 9. January 2019 Ultralight Pixel Ladder

2 Al layers

pixel layer: ~ 1.15 per mille radiation length

A. Schöning 29 FCC-ee, CERN, 9. January 2019 Pixel Detector Technology

High Voltage-Monolithic Active Pixel Sensor MuPix8 prototype (HV-MAPS) transistor logic embedded in N-well (“smart diode array”)

2 cm

N-well P-substrate Particle I.Peric et al., NIM A 582 (2007) 876

● active sensors MuPix has been characterized →e hit finding + digitisation + readout in the lab and at test beams ● HV-CMOS: 60-120 V, commercial process ● efficiency (AMS, GlobalFaundry, TSI) ● noise ● ● different substrates possible 20-1000 Ω cm rate ● temperature-dependence ● thickness ~50 μm (~ 0.0005 X ) 0 ● (radiation hardness)

A. Schöning 30 FCC-ee, CERN, 9. January 2019 MuPix Chip Design s l e x i “active” cells pixel matrix P y r e h p

i “mirror” cells r periphery e P State state machine (5-10% total area): machine VCO, PLL, ...

A. Schöning 31 FCC-ee, CERN, 9. January 2019 MuPix Chip Design

Sensor analog cell: Source follower ● Charge reverse biased ~ 85V sensitive ● charge sensitive amplifier amp ● source follower s l e x i P y r e h p i r e P State machine

A. Schöning 32 FCC-ee, CERN, 9. January 2019 MuPix Chip Design

transmission line: ● send signal to Transmission line corresponding mirror cell s l e x i P y r e h p i r e P State machine

A. Schöning 33 FCC-ee, CERN, 9. January 2019 MuPix Chip Design

mirror cell: ● comparator for discrimination ● threshold and baseline by tune DACs s l e x i P amp baseline

tune DAC global threshold y r e h p i r e P State machine

A. Schöning 34 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation s l e x i P y r e h p i r e P State machine

A. Schöning 35 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation ● amplification s l e x i P y r e h p i r e P State machine

A. Schöning 36 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation ● charge amplified ● received in mirror pixel s l e x i P y r e h p i r e P State machine

A. Schöning 37 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation ● charge amplified ● received in mirror pixel s l e x i P ● discriminated y r e h p i r e P State machine

A. Schöning 38 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation ● charge amplified ● received in mirror pixel s l e x i P ● discriminated ● scaler generated from clk

y 1 2 3 4 r e h p i r e P State machine

A. Schöning 39 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation ● charge amplified ● received in mirror pixel s l e x i P ● discriminated ● scaler generated from clk ● timestamp generation Time- stamp y r e h p i r e P State machine

A. Schöning 40 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

hit sequence: ● signal generation ● charge amplified ● received in mirror pixel s l e x i P ● discriminated ● scaler generated from clk ● timestamp generation Time- ● hit address and timestamp stamp are sent to serializer y r e h p i r

e Data P State machine Serialiser

A. Schöning 41 FCC-ee, CERN, 9. January 2019 MuPix Hit Detection

Finally, all detected hits are sent out via a 1.25 (1.6) Gbit/s serial link s l e x i P

Time- stamp

y Eye diagram measured r e h

p with Mupix7 prototype i r

e Data P State machine Serialiser Maximum readout rate is Data stream 33 Mhits/s per link

A. Schöning 42 FCC-ee, CERN, 9. January 2019 Integration & Connectivity

High Density Interconnect (HDI) has only two metal layers! Mupix7 prototype ~100 pins (incl. test) → Routing of power, control and signal lines is critical!

HDI design (prel.)

Requires high level of chip integration: ● power regulators Mupix pinout with ~ 21 pins ● state machine ● clock management including 3 serial links ● etc. A. Schöning 43 FCC-ee, CERN, 9. January 2019 MuPix8 Performance Maps

Efficiency Noise

Mupix8 is the first large scale prototype

16 mm

A. Schöning 44 FCC-ee, CERN, 9. January 2019 MuPix8 Efficiency and Noise

untuned & unmasked sensor

1000 e

→ almost 100% efficient

A. Schöning 45 FCC-ee, CERN, 9. January 2019 MuPix8 Timing Resolution

time over threshold

After offline timewalk correction:

all pixels delay

σtime = 6.4 ns

A. Schöning 46 FCC-ee, CERN, 9. January 2019 Pixel Detector + Helium Gas Cooling

Phase I design

~15 cm

● about 200 million pixels ● power dissipation: ~200-300 mW/cm2 He cooling in gaps between layers and detectors 100 Layer 4

Layer 3 Modules 50 Layer 2 of 4 ladders

Layer 1

m 0 m Target Target Half-shells –50 MuPix chips 4 or 5 ladders

–100

–200 –100 0 mm 100 200

A. Schöning 47 FCC-ee, CERN, 9. January 2019 V-Fold Cooling Channels

A. Schöning 48 FCC-ee, CERN, 9. January 2019 Mechanics Prototype with V-folds

kapton support V-shapes for local cooling channels

Cooling outlets V-shape

Helium cooling: ● global flow ● flow between layers ● flow in V-shapes

PIXEL 2016 Sebastianearly pixel Dittmeier module Ultra-low prototype material pixel layers for the Mu3e experiment 10

A. Schöning 49 FCC-ee, CERN, 9. January 2019 Preliminary Simulation Results M. Deflorin (FHNW) Velocity map layer 4 Temperature map layers 1+2

max flow 20 m/s

→ goal ΔT= 20-50 °C

CFD Simulationsare validated by lab-measurements

➔ Targeted power consumption (P=250 mW/cm2)

➔ Maximum allowed power consumption (P=400 mW/cm2)

A. Schöning 50 FCC-ee, CERN, 9. January 2019 Light-Weight Gas Cooling System

Considerations

● Gas supply lines (pipes) require significant space He in/out in grey ● Significant pressure drop of 50-100 mbar in detector areas ● He-gas needs to be pumped in and out

Example: Mu3e cross section ● Mupix power dissipation is max. 4 kW in Mu3e 1 150 mm ● For 1m2 active area and <ΔT>=15K → 50 g/s He

(corresponds to about 20 m3 per minute at atmospheric pressure)

I believe up to 100 m3 per minute (or maybe more) could be realized in future experiments → 20 kW cooling power!

A. Schöning 51 FCC-ee, CERN, 9. January 2019 Lessons and Final Remarks

Mu3e ultralight pixel tracker is based on

● monolithic pixel sensors → HV-MAPS ● ultra-light polyimide/aluminium HDIs ● polyimide mechanical support ● He-gas cooling system

Critical points: mockup: Mu3e inner pixel layers ● precision of pixel modules + vibration due to gas cooling ➔ vibrations measured in lab to be < 5µm ➔ Mu3e will constantly monitor alignment online (studied in PhD thesis)

● Aging of polyimide in helium atmosphere in presence of radiation ➔ currently under study

● Would like to have longer modules (>36 cm) for Mu3e phase II ➔ we believe that is possible if modules are strained (tbc)

A. Schöning 52 FCC-ee, CERN, 9. January 2019 Last Comment I

Momentum resolution in Mu3e is 100 keV/c for 20 MeV/c positrons due to the recurler design

Similar “trick” works also for HEP experiments → next page

A. Schöning 53 FCC-ee, CERN, 9. January 2019 Last Comment II Momentum resolution of an “ATLAS-like” detector with B=2T for different designs of barrel layers

AS (unpublished)

considered “clusters” of barrel layers recurlers (equid. layouts) s u i d a r

recurlers in gaps

large gaps allow for recurling tracks

… might be interesting for physics at the “soft scale” ... A. Schöning 54 FCC-ee, CERN, 9. January 2019 Mu3e Status and Plans

B=1 Tesla ~3m homogeneous field

~35 tons Phase I ● Comprehensive R&D (HV-MAPS, SciFi) program completed ● Detector construction starting this year ● Magnet will be delivered by Cryogenic Ltd. mid 2019 ● First data taking in 2020

Phase II ● requires design and approval of High Intensity Muon Beam Line (HiMB)

➔ not before 2025, physics program up to ~2030

A. Schöning 55 FCC-ee, CERN, 9. January 2019 Backup

A. Schöning 56 FCC-ee, CERN, 9. January 2019 Mu3e Mass Plot (Phase I)

Simulation

10-12

10-13

10-14 (upper limit) 10-15

A. Schöning 57 FCC-ee, CERN, 9. January 2019 Mu3e Collaboration Germany (Deutsche Forschungsgemeinschaft, Germany) ● University Heidelberg ● Karlsruhe Institute of Technology ● University Mainz

Switzerland (Swiss National Font, Switzerland) ● University of Geneva ● Paul Scherrer Institute ● ETH Zurich ● University Zurich

United Kingdom (STFC Council, UK) ● Bristol ● Liverpool ● Oxford ● UC London

about 60 members including 14 PhD students

A. Schöning 58 FCC-ee, CERN, 9. January 2019 High Intensity Muon Beamline (HiMB)

HiMB Studies: proton cyclotron ● refurbish target M ➔ µ rates >> 109/s Ip =2.4 mA @ 590 MeV ➔ promising!

● SINQ target: ➔ rates >1010/s possible world-highest ➔ but extremely difficult intensity beam!

X

PiE5 beamline: MEG+Mu3e experiments A. Schöning 59 FCC-ee, CERN, 9. January 2019