Mechanics and Cooling of the Mu3e Detector

Mechanics and Cooling of the Mu3e Detector

Adrian Herkert

on behalf of the Mu3e collaboration

Physikalisches Institut Heidelberg University

02.03.2016

The Mu3e Experiment

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

B = 1 T

ˆ Standard Model:

BR < 10 ⁻⁵⁴

ˆ Current upper BR limit:

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

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

ˆ Mu3e sensitivity goal:

1 in 10 ¹⁶ µ-decays

ˆ µ -rate:

10 ⁷ − 10 ^{9 1} _s

Backgrounds

Internal Conversion

ˆ µ ⁺ → e ⁺ e ⁻ e ⁺ ν _e ν _µ

R. M. Djilkibaev, R. V. Konoplich, Phys. Rev. D 79, 073004, 2009

Accidentals

ˆ Ordinary Michel decays plus additional e ⁻

→ High momentum resolution needed

→ High momentum, time, and

vertex resolution needed

Detector Design for Minimum Material Budget

Target Inner pixel layers

Scintillating f bres

Outer pixel layers Recurl pixel layers

Scintillator tiles μ Beam

ˆ Pixel tracker: 4 barrels of thin pixel sensors

ˆ Timing detectors:

ˆ Fibre tracker inside central detector

ˆ Scintillating tiles inside recurl stations

ˆ 1 T solenoid

Pixel Tracker Mechanics

→ x/X ₀ ≈ 0.1 %

ˆ HV-MAPS

ˆ can be read out fast

ˆ can be thinned to 50 µm

L. Huth, T99.5

ˆ Flexprint

ˆ Kapton support structure

ˆ 25 µm thin

36 cm

Cooling Concept

Goal: T _HV-MAPS < 70 ^◦ C

Layer 4 Layer 3

Layer 1 Layer 2 FPGA

Water

Global He flow Gap He flow

Local He flow

Local Cooling Channels

CFD Simulations of the Cooling System

Detector Model

End wheel

Layer 1 Layer 2 Layer 3 Layer 4

Beam pipe Front-end electronics

CFD Simulations of the Cooling System

Results

0 10 20 30 40 50 60 70

0 20 40 60 80 100 120

P/A = 250 mW/cm² PFPGA = 25 W vglobal ≈ vgap ≈ 4 m/s vlocal ≈ 16 m/s v_water ≈ 1.4 m/s

ΔT [°C]

Position [cm]

Layer 1 Layer 2 Layer 3 Layer 4

Measurement of Flow-induced Vibrations

Michelson Interferometer

Laser

Photo diode

Mirror 2 (vibrating) Mirror 1

Oscilloscope Beam

splitter

-1 -0.5 0 0.5 1

0 0.5 1 1.5 2 2.5 3

Intensity [a.u.]

t [ms]

Ideal signal for an oscillating mirror

Beam splitter

Photo diode Laser

Mirror

Loudspeaker

Lens

Module prototype Helium in

Measurement of Flow-induced Vibrations

Setup

Measurement of Flow-induced Vibrations

Results

Superpositions?

→ Alternating sum

0 2 4 6 8 10 12 14 16 18

14 16 18 20 22 24 26 28

Amplitude [µm]

Local He flow velocity [m/s]

Max. observed amplitude Average amplitude

-5 0 5 10 15 20

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Displacement [µm]

time [s]

Alternating sum

FFT

10^-4 10^-3 10^-2 10^-1 10⁰ 10¹ 10²

0 50 100 150 200

Amplitude [µm]

Frequency [Hz]

FFT

Summary

ˆ Minimum material cooling system was designed

ˆ CFD simulations give promising results

ˆ Flow-induced vibrations were measured to be of neglectable size

Outlook

ˆ Lab tests of helium cooling of layers 1 & 2 are planned

ˆ Modifications of interferometer setup are planned for more

reliable results