Update from the Mu3e Experiment

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1 Update from the Mu3e Experiment Niklaus Berger Physics Institute, University of Heidelberg Charged Lepton Working Group, February 2013

Overview The Challenge: Finding one in 10 16 muon decays

Sensors The Mu3e Detector: Minimum Material, Maximum

2 Overview The Challenge: Finding one in muon decays The Technology: High Voltage Monolithic Active Pixel Sensors The Mu3e Detector: Minimum Material, Maximum Precision Niklaus Berger Charged Leptons, February 2013 Slide 2

3 The Physics: Charged Lepton Flavour Violation Neutrinos have mass Leptons do change flavour However: Standard Model branching ratio for μ eee < e + W + γ * e - ν µ ν e µ + e + Niklaus Berger Charged Leptons, February 2013 Slide 3

4 The Physics: Charged Lepton Flavour Violation µ ~ Neutrinos have mass Leptons do change flavour However: Standard Model branching ratio for μ eee < e ~ + χ ~ 0 e + Can be much bigger with new physics γ */Z e - e + Niklaus Berger Charged Leptons, February 2013 Slide 4

5 The Physics: Charged Lepton Flavour Violation µ + Z µ ~ Neutrinos have mass Leptons do change flavour However: Standard Model branching ratio for μ eee < e ~ + χ ~ 0 e + e + e + e - Can be much bigger with new physics γ */Z e - e + Niklaus Berger Charged Leptons, February 2013 Slide 5

6 Comparison with μ eγ m μ κ L LFV = A R μ R σ μν e L F μν + (μ L γ μ e L ) (e L γ μ e L ) (κ+1)λ 2 (κ+1)λ 2 µ ~ γ*/z e ~ + χ ~ 0 e + e - e + µ + Z e + e + e - Ratio κ between dipole and contact Common mass scale Λ Allows for sensitivity comparisons between μ eee and μ eγ In case of dominating dipole couplings (κ = 0): B(μ eee) = (essentially αem ) B(μ eγ) Niklaus Berger Charged Leptons, February 2013 Slide 6

7 Comparison with μ eγ µ ~ e ~ + χ ~ 0 e + γ */Z e - e + Z-penguins could be important Lots of theory activity Niklaus Berger Charged Leptons, February 2013 Slide 7

8 The Goal: We want to find or exclude μ eee at the level orders of magnitude over previous experiment (SINDRUM 1988) % CL bound μ μ μn eγ 3e en MEG τ τ μγ 3μ SINDRUM SINDRUM II MEG plan Mu3e Phase I Mu3e Phase II Year (Updated from W.J. Marciano, T. Mori and J.M. Roney, Ann.Rev.Nucl.Part.Sci. 58, 315 (2008)) Niklaus Berger Charged Leptons, February 2013 Slide 8

9 The Challenges Observe more than muon decays: 2 Billion muons per second Suppress backgrounds by more than 16 orders of magnitude % CL bound μ μ μn eγ 3e en MEG Be sensitive for the signal τ τ μγ 3μ SINDRUM SINDRUM II MEG plan Mu3e Phase I Mu3e Phase II Year (Updated from W.J. Marciano, T. Mori and J.M. Roney, Ann.Rev.Nucl.Part.Sci. 58, 315 (2008)) Niklaus Berger Charged Leptons, February 2013 Slide 9

Muons from PSI DC muon beams for particle physics at PSI: πe5 beamline: ~ 10 8 muons/s (MEG experiment) SINQ (spallation neutron source) target could even provide ~ 5

10 Muons from PSI DC muon beams for particle physics at PSI: πe5 beamline: ~ 10 8 muons/s (MEG experiment) SINQ (spallation neutron source) target could even provide ~ muons/s The μ eee experiment (final stage) requires muons/s focused and collimated on a ~2 cm spot Niklaus Berger Charged Leptons, February 2013 Slide 10

11 The signal μ + e + e - e + e + Two positrons, one electron From same vertex Same time e - e + Sum of 4-momenta corresponds to muon at rest Maximum momentum: ½ m μ = 53 MeV/c Niklaus Berger Charged Leptons, February 2013 Slide 11

12 Accidental Background e + Combination of positrons from ordinary muon decay with electrons from: - photon conversion, - Bhabha scattering, - Mis-reconstruction e - Need very good timing, vertex and momentum resolution e + Niklaus Berger Charged Leptons, February 2013 Slide 12

13 Internal conversion background µ + ν μ Allowed radiative decay with internal conversion: W + γ* Need excellent momentum resolution ν e } E miss e + e + e - } E tot μ + e + e - e + νν Only distinguishing feature: Missing momentum carried by neutrinos Branching Ratio μ3e (R. M. Djilkibaev, R. V. Konoplich, m μ - E tot (MeV) Phys.Rev. D79 (2009) ) Niklaus Berger Charged Leptons, February 2013 Slide 13

14 Momentum measurement 1 T magnetic field MS Resolution dominated by multiple scattering Momentum resolution to first order: θ MS Σ P / P ~ θ MS/ Ω Ω B Precision requires large lever arm (large bending angle Ω) and low multiple scattering θ MS Niklaus Berger Charged Leptons, February 2013 Slide 14

Fast and thin sensors: HV-MAPS High voltage monolithic active pixel sensors Implement logic directly in N-well in the pixel - smart diode array Use a high voltage commercial process (automotive

15 Fast and thin sensors: HV-MAPS High voltage monolithic active pixel sensors Implement logic directly in N-well in the pixel - smart diode array Use a high voltage commercial process (automotive industry) Small active region, fast charge collection via drift Can be thinned down to < 50 μm (I.Peric, P. Fischer et al., NIM A 582 (2007) 876 ) Niklaus Berger Charged Leptons, February 2013 Slide 15

16 The MUPIX chips 55 Fe peak Module size 6 1 cm (inner layers) 6 2 cm (outer layers) Pixel size μm Goal for thickness: 50 μm 1 bit per pixel, zero suppression on chip ToT [µs] Power: 150 mw/cm 2 Data output up to 3.2 Gbit/s Time stamps every 50 ns SNR Resolution for μm pixels Signal to Noise Threshold [V] Niklaus Berger Charged Leptons, February 2013 Slide 16

17 Introduction Y X Niklaus Berger Charged Leptons, February 2013 Slide 17

18 Mechanics 50 μm silicon 25 μm Kapton flexprint with aluminium traces 25 μm Kapton frame as support Less than 1 of a radiation length per layer Niklaus Berger Charged Leptons, February 2013 Slide 18

19 Niklaus Berger Charged Leptons, February 2013 Slide 19

20 Cooling Add no material: Cool with gaseous Helium ~ 150 mw/cm 2 Simulations: Need ~ 1 m/s flow First measurements: Need several m/s Full scale prototype on the way Niklaus Berger Charged Leptons, February 2013 Slide 20

21 Momentum measurement 1 T magnetic field MS Resolution dominated by multiple scattering Momentum resolution to first order: θ MS Σ P / P ~ θ MS/ Ω Ω B Precision requires large lever arm (large bending angle Ω) and low multiple scattering θ MS Niklaus Berger Charged Leptons, February 2013 Slide 21

22 Precision vs. Acceptance MS B θ MS 50 MeV/c 25 MeV/c 12 MeV/c B Ω ~ π Niklaus Berger Charged Leptons, February 2013 Slide 22

23 Detector Design μ Beam Target Niklaus Berger Charged Leptons, February 2013 Slide 23

24 Detector Design Inner pixel layers μ Beam Target Niklaus Berger Charged Leptons, February 2013 Slide 24

25 Detector Design Inner pixel layers μ Beam Target Outer pixel layers Niklaus Berger Charged Leptons, February 2013 Slide 25

26 Detector Design Inner pixel layers μ Beam Target Scintillating fibres Outer pixel layers Niklaus Berger Charged Leptons, February 2013 Slide 26

27 Detector Design Recurl pixel layers Inner pixel layers μ Beam Target Scintillating fibres Outer pixel layers Niklaus Berger Charged Leptons, February 2013 Slide 27

28 Detector Design Recurl pixel layers Scintillator tiles Inner pixel layers μ Beam Target Scintillating fibres Outer pixel layers Niklaus Berger Charged Leptons, February 2013 Slide 28

Timing measurements 250 μm fibres - O(0.

switched capacitor array (PSI developed DRS5

29 Timing measurements 250 μm fibres - O(0.5 ns) 0.5 cm 3 tiles - O(60 ps) Photosensor: SiPM; high gain, high frequency Readout via switched capacitor array (PSI developed DRS5 chip) or STiC ASIC developed in Heidelberg Niklaus Berger Charged Leptons, February 2013 Slide 29

event reconstruction 10 9 3D track fits/s achieved Data reduction by factor

30 Online filter farm Online software filter farm Continuous front-end readout (no trigger) ~ 1 Tbit/s FPGAs and Graphics Processing Units (GPUs) Online track and event reconstruction D track fits/s achieved Data reduction by factor ~1000 Data to tape < 100 Mbyte/s Niklaus Berger Charged Leptons, February 2013 Slide 30

31 Simulated Performance 4 10 RMS: 0.28 MeV/c D multiple scattering track fit Simulation results: 280 kev single track momentum 520 kev total mass resolution Rec. Momentum - Gen. Momentum [MeV/c] RMS: 0.52 MeV/c 2 s 1 : 0.31 MeV/c 2 s 2 : 0.71 MeV/c 2 s av : 0.37 MeV/c Reconstructed Mass [MeV/c Niklaus Berger Charged Leptons, February 2013 Slide 31 2 ] 2

32 Simulated Performance Events per muon decay and 0.1 MeV µ eeeνν generated -11 µ eeeνν simulated Signal BF Signal BF Signal BF Signal BF Signal BF Signal BF Reconstructed Mass [MeV/c ] Niklaus Berger Charged Leptons, February 2013 Slide 32

33 Sensitivity Recurl pixel layers Scintillator tiles μ Beam Inner pixel layers Target Scintillating fibres Outer pixel layers Phase Ib: Inner pixel layers μ Beam Target Outer pixel layers Phase Ia: Starting 2015 Recurl pixel layers Phase II: New Beam Line Scintillator tiles Inner pixel layers μ Beam Target Scintillating fibres Outer pixel layers Niklaus Berger Charged Leptons, February 2013 Slide 33

34 Current Status The Mu3e Research Proposal was approved by the PSI research committee in January Proposal available on arxiv:1301:6113 Phase I experiment mostly funded Aim for first measurements in 2015 High-intensity beam line under study (earliest availability 2017+) Niklaus Berger Charged Leptons, February 2013 Slide 34

35 Collaboration Participating Institutes: University of Geneva University of Heidelberg (3 Institutes) Paul Scherrer Institut (PSI) University of Zurich ETH Zurich Also in contact with other interested groups Niklaus Berger Charged Leptons, February 2013 Slide 35

36 Backup Material Niklaus Berger Charged Leptons, February 2013 Slide 36

37 Radiation Hardness Requirements not as strict as at LHC Irradiation at PS After 380 MRad ( n eq /cm 2 ) Chip still working (Courtesy Ivan Perić) Niklaus Berger Charged Leptons, February 2013 Slide 37

The Mu3e Experiment. Niklaus Berger. Physics Institute, University of Heidelberg. Charged Lepton Flavour Violation Workshop, Lecce, May 2013

The Mu3e Experiment. Niklaus Berger. Physics Institute, University of Heidelberg. Charged Lepton Flavour Violation Workshop, Lecce, May 2013 The Mu3e Experiment Niklaus Berger Physics Institute, University of Heidelberg Charged Lepton Flavour Violation Workshop, Lecce, May 2013 Overview The Question: Can we observe charged lepton flavour violation?