A Thin Silicon Pixel Tracker for the Mu3e Experiment

A Thin Silicon Pixel Tracker for the Mu3e Experiment

Adrian Herkert

on behalf of the Mu3e collaboration Physics Institute Heidelberg

29.03.2017

The Mu3e Experiment

Search for the decay µ ⁺ → e ⁺ e − e ⁺

B = 1 T

• Standard Model:

BR < 10 ^{− 54}

• Current upper BR limit:

1.0 × 10 ^{− 12} at 90 % CL (SINDRUM, 1988)

U. Bellgardt et al., Nucl. Phys. B 299 1, 1988.

• Mu3e sensitivity goal:

1 in 10 ¹⁶ µ-decays

• µ-rate:

∼ 10 ^{9 1} s

The Signal

µ ⁺ → e ⁺ e − e ⁺

B = 1 T

• Common vertex

• Coincident in time

• P 3

i =1 p i

2

= m ² _µ

•

P 3 i =1 ~ p i

= 0

Background

Internal Conversion

• µ ⁺ → e ⁺ e ⁻ e ⁺ ν e ν _µ

R. M. D j ilkibaev , R. V. Konoplich, Phy s. Rev . D 79, 073004, 2009.

Accidentals

• Ordinary Michel decays plus additional e ⁻

→ High momentum resolution needed

→ High momentum, time, and

vertex resolution needed

Background

Internal Conversion

• µ ⁺ → e ⁺ e ⁻ e ⁺ ν e ν _µ

R. M. D j ilkibaev , R. V. Konoplich, Phy s. Rev . D 79, 073004, 2009.

Accidentals

• Ordinary Michel decays plus additional e ⁻

→ High momentum resolution needed

→ High momentum, time, and vertex resolution needed E e ≤ 53 MeV

→ Multiple scattering

→ Need low material budget!

Detector Design for Minimum Material Budget

Target Inner pixel layers

Scintillating f bres

Outer pixel layers Recurl pixel layers

Scintillator tiles μBeam

i

• Pixel tracker: 4 barrels of thin pixel sensors

• Timing detectors:

• Fibre tracker inside central detector

• Scintillating tiles inside recurl stations

• 1 T solenoid

Pixel Tracker Mechanics

→ x/X ₀ ≈ 0.1 %

• HV-MAPS

• thinned to 50 µm

• Flexprint (T46.6)

• Kapton support structure

• 25 µm thin

36 cm

Helium Gas Cooling System

• CFD simulation

• P/A = 400 mW/cm ²

• ∆T _max < 50 ^◦ C

Detector Readout (T94.9) and Online Track Reconstruction (T46.5, T116.1)

1056 Pixel Sensors

up to 36 1.25 Gbit/s links

FPGA FPGA FPGA

...

34 FPGAs

Switching Boards 1 6 Gbit/s link each

GPU PC

GPU PC

GPU 12 PCs PC ...

12 10 Gbit/s links per Switching Board

2 Inputs each

Data Collection

Server

Mass Storage Gbit Ethernet

Front-end(inside magnet)

High-Voltage Monolithic Active Pixel Sensors

P-substrate N-well

Particle E field

I. Peri´c, NIM A 582, 3, 2007.

• Deep n-well in p-substrate

• Reverse bias voltage (-85 V)

• Depletion zone: ca. 10 - 20 µm (20 Ωcm substrate)

• Can be thinned to < 50 µm

• Fast charge collecion via drift

The MuPix7

• Commercial 180 nm

High-Voltage CMOS process

• Thinned to 50 µm

• Active area: 3.3 x 3.2 mm ²

• 32 x 40 pixels

• Pixel size: 103 x 80 µm ²

• Readout state machine on chip

• Clock generation on chip

• Fast serial output of up to

1.6 Gbits/s

The MuPix7

Layout

Pixel

Digital cell

The MuPix7

Full readout system on chip

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

MuPix7 Test Results

EUDET Telescope at DESY

• E e = 4 GeV

• 6 MIMOSA planes

• Scintillator triggers in front and back

• DUT: MuPix7 on rotation stage

• Analysis:

• Straight tracks fit to MIMOSA hits

• Matched hits from DUT

Efficiency Map with Sub-Pixel Resolution

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

D. v. Bruch, 2016.

Efficiency Map for Reduced Bias Voltage

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 1267281

Mean x 1.557

Mean y 1.806

RMS x 0.9219

RMS y 0.833

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

efficiency_pixeluv

Entries 1267281

Mean x 1.557

Mean y 1.806

RMS x 0.9219

RMS y 0.833

Mupix7, 730 mV threshold, HV = -40 V

D. v. Bruch, 2016.

Efficiency Map for Reduced Bias Voltage Folded on 2x2 Pixels

pixels in column direction

−1.5 −1 −0.5 0 0.5 1 1.5 2 2.5

pixels in row direction

−1.5

−1

−0.5 0 0.5 1 1.5 2

2.5 efficiency_pixel_uv_folded

Entries 1047236

Mean x 0.4995

Mean y 0.4994

RMS x 0.5757

RMS y 0.5757

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 efficiency_pixel_uv_folded 1 Entries 1047236

Mean x 0.4995

Mean y 0.4994

RMS x 0.5757

RMS y 0.5757

Mupix7, 730 mV threshold, HV = -40 V

D. v. Bruch, 2016.

Efficiency Map for Nominal Bias Voltage Folded on 2x2 Pixels

pixels in column direction

−1.5 −1 −0.5 0 0.5 1 1.5 2 2.5

pixels in row direction

−1.5

−1 0.5

− 0 0.5 1 1.5

2

2.5 efficiency_pixel_uv_folded

Entries 743583 Mean x 0.4997 Mean y 0.4998 RMS x 0.5771 RMS y 0.577

0.9 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1

efficiency_pixel_uv_folded Entries 743583 Mean x 0.4997 Mean y 0.4998 RMS x 0.5771 RMS y 0.577

Mupix7, 735 mV threshold, HV = -85 V

D. v. Bruch, 2016.

Efficiency Map Folded on 2x2 Pixels for DUT Rotated by 45 ^◦

pixels in column direction

−

1.5

1

0.5 0 0.5 1 1.5 2 2.5

pixels in row direction

−

1.5

−

1

−

0.5 0 0.5 1 1.5 2

2.5

Entries 622567 Mean x 0.5 Mean y 0.5 RMS x 0.5772 RMS y 0.5773

0.98 0.982 0.984 0.986 0.988 0.99 0.992 0.994 0.996 0.998

efficiency_pixel_uv_folded

1

D. v. Bruch, 2016.

The MuPix Telescope

Efficiency Averaged over Full Sensor

Threshold [V]

0.7 0.71 0.72 0.73 0.74 0.75

Efficiency [%]

96 96.5 97 97.5 98 98.5 99 99.5

Efficiency [%]

Noise

99 %

Noiserate per pixel [1/s]

−1

10 1 10 10

10

10

10

L. Huth, 2016.

Efficiency at 60 ° Rotation

Threshold [V]

0.66 0.68 0.7 0.72 0.74 0.76

Efficiency [%]

98.4 98.6 98.8 99 99.2 99.4 99.6 99.8

Efficiency [%]

Noise

99 %

Noiserate per pixel [1/s]

1 10 10

L. Huth, 2016.

MuPix7 Time Resolution

−600 −500 −400 −300 −200 −100 0

Entries [1/run]

102 103 104

Time diffrence between hit and scintillator time [ns]

σ= 14.3 ns

L. Huth, 2016.

Summary and Outlook

Specification MuPix7 MuPix8 Sensor size [mm

] 20 × 22 3.2 × 3.3 10.7 × 19.5 Sensor thickness [µm] 50 50, 63, 75, 250 50, 100

LVDS links 3 1 4

Bandwidth [Gbit/s] 3.75 1.6 6.4

Power consumption [mW/cm

] ≤ 350 ≈ 300 250 − 300

Time resolution [ns] ≤ 20 ≈ 14 ≈ 5 − 10

Efficiency at 20 Hz noise [%] ≥ 99 99.5 ≥ 99.9

Substrate resistance [Ωcm] no spec. ≈ 20 ≈ 80

Acknowledgements

The measurements leading to beam test results have been performed at the Test Beam Facility at DESY Hamburg (Germany), a member of the Helmholtz Association (HGF).

We would like to thank the PSI for providing high rate test beams under excellent conditions.

We owe our SPS test beam time to the SPS team and our LHCb colleagues, especially Heinrich, Kazu and Martin.

We thank the Institut f¨ur Kernphysik at the JGU Mainz for giving

us the opportunity to take data at MAMI.