Status of the Mu3e Experiment https://www.psi.ch/mu3e/ Search for µ + → e + e + e - CLFV 2019 Conference “Charged Lepton Flavor Violation” 17.-20.6. 2019, Fukuoka (Kyushu) A. Schöning on behalf of Mu3e 1 CLFV19 Conference
Mu3e Collaboration Germany ● University Heidelberg ● Karlsruhe Institute of Technology ● University Mainz Switzerland ● University of Geneva ● Paul Scherrer Institute ● ETH Zurich ● University Zurich ● [University of Applied Sciences Northwestern Switzerland] United Kingdom ● Bristol ● Liverpool ● Oxford ● UC London about 60 members; ~15 PhD students A. Schöning on behalf of Mu3e 2 CLFV19 Conference
HiPA @ PSI & PiE5 Area World’s most intense continuous muon beam (f=50MHz) World’s most intense continuous muon beam (f=50MHz) 2.4 mA protons at 590 MeV → 1.5 MW 2.4 mA protons at 590 MeV → 1.5 MW Compact Muon Beamline for Mu3e: HiPA and Experimental Hall: MEG expect 1.4 ∙ 10 8 μ + 7s at 2.4 mA for a 60 mm target Mu3e ● Low momentum muons 29 MeV/c ● PiE5 beamline will be shared between MEGII and Mu3e A. Schöning on behalf of Mu3e 3 CLFV19 Conference
Mu3e Experiment Aiming for a sensitivity (SES) requires: BR(μ → e e e ) < 2·10 -15 → 10 8 muons/s (PiE5) (phase I) BR(μ → e e e ) < 10 -16 → >10 9 muons/s (HiMB) (phase II) HiMB = High intensity Muon Beamline (under study) Pixel Tracker Scintillating Fibers Scintillating Tiles A. Schöning on behalf of Mu3e 4 CLFV19 Conference
LFV Decay μ + →fe + e + e - LFV Decay μ + →fe + e + e - Exotic Physics loop diagrams (similar to µ → e γ ) tree diagram (Mu3e specific) 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 on behalf of Mu3e 5 CLFV19 Conference
Matrix Element Dependence Matrix Element Dependence use effective operator framework e.g. A. Crivellin et al. JHEP 05 (2017) 117. generator level: m 1 (e + e - ) vs m 2 (e + e - ) O D O S RR or O V RR O V R RL thesis A.-K.Perrevoort thesis A.-K.Perrevoort Very distinct signal distributions! A. Schöning on behalf of Mu3e 6 CLFV19 Conference
Matrix Element Dependence Matrix Element Dependence use effective operator framework e.g. A. Crivellin et al. JHEP 05 (2017) 117. reconstructed: m 1 (e + e - ) vs m 1 (e + e - ) O D O S RR or O V RR O V R RL thesis A.-K.Perrevoort Very distinct signal distributions! (also after full reco) A. Schöning on behalf of Mu3e 7 CLFV19 Conference
Irreducible Background Irreducible Background radiative decay with internal conversion e - ν e + Mu3e signal e - e + ν e + μ + →f e + e + e - B( μ + →f e + e + e - νν ) = 3.4 ·10 - 5 e + ∑ i E i = m μ p i = 0 ∑ i ⃗ A. Schöning on behalf of Mu3e 8 CLFV19 Conference
Irreducible Background Irreducible Background radiative decay with internal conversion e - ν e + missing energy from two neutrinos R.M.Djilkibaev, steeply falling! R.V.Konoplich PRD79 (2009) ν e + B( μ + →f e + e + e - νν ) = 3.4 ·10 - 5 missing energy taken by neutrinos very good momentum + total energy resolution required! A. Schöning on behalf of Mu3e 9 CLFV19 Conference
Accidental Backgrounds 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 A. Schöning on behalf of Mu3e 10 CLFV19 Conference
Expected Electron Backgrounds Expected Electron Backgrounds Bhabha IC Compton γ conversion Momentum distribution of electrons produced in target region A. Schöning on behalf of Mu3e 11 CLFV19 Conference
Mu3e Baseline Design 10 8 muons per second (phase I) p=28 MeV/c A. Schöning on behalf of Mu3e 12 CLFV19 Conference
Mu3e Baseline Design 80 x 80 µm 2 pixel ● ultra thin silicon pixel detector (HV-MAPS) with 1 per mill radiation length / layer A. Schöning on behalf of Mu3e 13 CLFV19 Conference
Mu3e Baseline Design σ(t) < 1 ns ● ultra thin silicon pixel detector (HV-MAPS) with 1 per mill radiation length / layer ● fast timing detectors ( scintillating fibers ) A. Schöning on behalf of Mu3e 14 CLFV19 Conference
Mu3e Baseline Design Long cylinder! ~180 cm ~15 cm σ(t) < 100 ps not to scale! recurl stations with silicon pixel detector (HV-MAPS) and scintillating tiles A. Schöning on behalf of Mu3e 15 CLFV19 Conference
Mu3e Baseline Design transverse view: + strong magnetic field (B=1T) helium atmosphere + helium gas cooling A. Schöning on behalf of Mu3e 16 CLFV19 Conference
Momentum Resolution Momentum Resolution Standard spectrometer: “Half turn” spectrometer: multiple-scattering angle σ p P ∼ Θ MS σ p 2 ) (linearised) P ∼ O (Θ MS Ω requires large lever arm best precision for half turn tracks large bending angle Ω measure recurlers A. Schöning on behalf of Mu3e 17 CLFV19 Conference
(Outer) Pixel Tracker Module Ultra-thin pixel sensor modules with a radiation length of X/X 0 = 1.15 per mil MuPix (HV-MAPS) High Density Interconnect (< 100 µm) (LTU, Ukraine) 50 µm Monolithic pixel sensor in 180 nm HV-CMOS A. Schöning on behalf of Mu3e 18 CLFV19 Conference
Pixel Detector Technology MuPix8 prototype (2018) High Voltage-Monolithic Active Pixel Sensor (HV-MAPS) transistor logic embedded in N-well (“smart diode array”) 2 cm I.Peric et al., NIM A 582 (2007) 876 ● active sensors →f hit finding + digitisation + readout pixel size 80 x 80 μm 2 ● HV-CMOS 180nm: 60-120 V ● low cost process (AMS, TSI ) MuPix has been fully characterized in the lab and in several test beams ● “thinned” to ~ 50 μm (~ 0.0005 X 0 ) ● efficiency ● noise + rate ● (radiation hardness) ● temperature-dependence A. Schöning on behalf of Mu3e 19 CLFV19 Conference
Mupix8 Performance Plots Mupix 8 beam telescope (4 layers) efficiency noise ~99.9% ~1Hz/pixel time resolution ~ 6.5ns → Mupix10 submission (20x20 mm 2 ) in summer A. Schöning on behalf of Mu3e 20 CLFV19 Conference
Mupix10 Specification not to scale! Mupix10 will implement three design variations for final sensor decision → Mupix11 A. Schöning on behalf of Mu3e 21 CLFV19 Conference
Thermo-Mechanical Prototype Mu3e Vertex layer steel plates used to test: ● assembly procedures ● mechanical stability (vibrations) ● helium cooling A. Schöning on behalf of Mu3e 22 CLFV19 Conference
Pixel Detector + Helium Gas Cooling pixel tracker: central and two recurl stations ~15 cm ~ 200 million pixels He gas cooling simulation He gas cooling concept → temperatures 20-50 °C → no extra material in active volume! A. Schöning on behalf of Mu3e 23 CLFV19 Conference
Timing Detectors Scintillating Fibres Scintillating Tiles ● tiles � 6.5 × 6.5 × 5mm 3 ● SiPM 3 x 3 mm 2 ● Readout with MuTrig ASIC ● time resolution < 100ps ● 3 staggered layers of 250 µm scintillating fibres (SCSF-78MJ from Kuraray) ● very thin ~0.2% X 0 ● 128 channel SiPM array from Hamamatsu ● Readout with MuTrig ASIC ● time resolution < 500ps A. Schöning on behalf of Mu3e 24 CLFV19 Conference
Timing Performance Scintillating Fibres Scintillating Tile Sub-Module 3-layer ribbon in test beam DESY test beam 4-layer ribbon in test beam Time resolution ~ 370ps Time resolution < 100ps A. Schöning on behalf of Mu3e 25 CLFV19 Conference
Simulation and Performance A. Schöning on behalf of Mu3e 26 CLFV19 Conference
Charge Identification Main process: μ + → e + ν e ν μ Time difference vs path length Δ t=t 2 - t 1 [ns] positron loopers → charge confusion transverse positrons view t 1 t 2 X electrons X Δ s/c [n s] Significant reduction of BG for: μ + → e + e + e - A. Schöning on behalf of Mu3e 27 CLFV19 Conference
Simulation and Performance Track Reconstruction Efficiency Track Momentum Resolution limited acceptance σ p /p= 1% DS US excellent! gaps between pixel track stations A. Schöning on behalf of Mu3e 28 CLFV19 Conference
Mu3e Mass Plot (Phase I) hypothetical signal Simulation 10 -12 10 -13 10 -14 (upper limit) 10 -15 A. Schöning on behalf of Mu3e 29 CLFV19 Conference
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