The Mu3e Experiment A new search for μ eee with unprecedented sensitivity Kolloquium in Freiburg, November 29, 2017 André Schöning Universität Heidelberg 1
SM of Particle Physics SM Physics after the electroweak epoch is described by the SM 2
Questions in (Particle) Physics bullet cluster Sloan digital Sky Survey Matter Dark Matter Neither we understand the observation of ordinary matter nor the observation of dark matter. Must be understood! 3
Fermions in the Standard Model Higgs field Why 3 generations of fermions? 4
Fermion Masses in the SM Top Quark m = 171 GeV/c2 Proton: m 1 GeV/c2 Elektron: m 0.5 MeV/c2 Why Higgs couplings so different? Neutrinos: m 0.01-0.1 ev/c2 5
Fermion Masses in the SM yt~1 (within 1%) PLOT with YUKAWA? 6
Experimental Observations Matter-antimatter asymmetry in universe CP-Violation Observation Dark matter require new particles or interactions beyond the SM Unknowns Fermion generations nature of neutrinos (Dirac or Majorana?) Fermion masses (Yukawa couplings) no explanation yet Problems Physics Beyond the SM (BSM) hierarchy problem, etc.... requires new particles (interactions) 7
Search Strategies High Energy Frontier Direct searches of new resonances or interactions in the mass reach of colliders LHC, Future Circular Colliders,... High Intensity and Precision Frontier LHC picture LHC accelerator (Geneva) Indirect searches via precision measurements and searches for rare processes Electric Dipole Moments (EDM) Anomalous magnetic moments (g-2) Flavor Changing Neutral Current (FCNC) Charged Lepton Flavor Violation (clfv) Muon g-2 @ Fermilab 8
Overview Standard Model and Lepton Physics (charged) Lepton Flavor Violation (clfv) Mu3e experiment tracking concept detector systems Sensitivity studies 9
Flavor Physics f f Z0, γ H f f Neutral Current Higgs-Yukawa coupling f u d c s t b νe e νμ μ ντ τ ( )( )( ) ( )( )( ) W± f 10 Charged Current
Flavor Mixing Matrices Leptons Quarks Cabibbo Kobayashi Maskawa (CKM) Pontecorvo Maki Nakagawa Sakata (PMNS) v ud v us v ub d d' s ' = v cd v cs v cb s b' v td v ts v tb b νe v e 1 v e 2 v e 3 ν1 νμ = v μ 1 v μ 2 v μ 3 ν 2 v τ 1 v τ 2 v τ 3 ν3 ντ ()( )( ) weak mass Q=-1/3 ()( weak Q=0 Q=+2/3 11 )( ) mass Q=-1
Flavor Changing Processes Flavor Changing Charged Currents are allowed. (on tree level) Flavor Changing Neutral Currents (FCNC) are forbidden! Quarks Leptons Q=-1 Q=+2/3 μ νi (W+)* Q=-1/3 μ eγ Q=0 t b t c 12
Discovery of Neutrino Oscillations W W ν1 ν2 ν3 µ l P(να νβ ) = sin 2(2Θ) sin 2 (Δm2αβ EL ) ν Neutrino Oscillations: solar neutrinos reactor neutrinos atmospheric neutrinos neutrino beams 13
FCNC via Quantum Loops μ e via ν-oscillation W W ν1 ν2 ν3 µ e L P(να νβ) = sin 2(2Θ) sin 2 (Δm2αβ EL ) ν 14
FCNC via Quantum Loops μ e via ν-oscillation W W ν1 ν2 ν3 µ e μ e γ via loop νμ νe μ e W γ L P(να νβ) = sin 2(2Θ) sin 2 (Δm2αβ EL ) ν 15
FCNC via Quantum Loops μ e via ν-oscillation W μ e γ via loop νμ νe μ e W γ W ν1 ν2 ν3 µ e L P(να νβ) = sin 2(2Θ) sin 2 (Δm2αβ EL ) ν B(μ e γ) sin 2 (2Θ) (Δ m2αβ /m2w )2 L 1/ mw E ν mw 16
Lepton Flavor Violation in the SM Higher Order! μ νμ W γ νe e μ eγ τ ντ W γ νμ LFV in generated from lepton mixing: BR(l j l k γ) μ ( i V ij (V jk ) m 2 2 νi 2 MW Δm 2 2 ν jk ) ( ) 2 MW 4 yν τ μγ τ ντ W γ νe e τ eγ 17
Lepton Flavor Violation in the SM Higher Order! μ νμ W γ νe e μ eγ τ ντ W γ νμ BR(l j l k γ) μ τ W γ νe ( i V ij (V jk ) suppression factor for µ e: m 2 2 νi 2 MW Δm 2 2 ν jk ) ( ) 2 MW 4 yν ~ 10-50 unobservable high sensitivity to new physics!!! τ μγ ντ LFV in generated from lepton mixing: e τ eγ 18
Lepton Flavor Violation in the SM Higher Order! μ νμ W γ νe e μ eγ τ ντ W γ νμ BR(l j l k γ) μ τ W γ νe ( i V ij (V jk ) suppression factor for µ e: m 2 2 νi 2 MW Δm 2 2 ν jk ) ( ) 2 MW 4 yν ~ 10-50 unobservable high sensitivity to new physics!!! τ μγ ντ LFV in generated from lepton mixing: e τ eγ FCNC in SM ~ 10-10 19 2 m2c u c.t. quark mixing: 2 MW ~10 7
Lepton Flavor Conservation is an Accidental Symmetry! 20
History of LFV Decay experiments Mu3e I Mu3e II 21
LFV Muon Decays μ+ e+ γ μ- N e- N e+ + Au μ- μ+ μ+ e+e+ee+ e- μ+ γ e- MEG (PSI) SINDRUM II (PSI) B(μ+ e+γ) 4.2 10-13 (2016) B(μ Au e Au) 7 10-13 (2006) e+ SINDRUM (PSI) B(μ+ e+e+e-) 10-12 (1988) being upgraded 22
SM Loop Diagrams μ+ e+ γ μ- N e- N e+ + Au e+ e- μ- μ+ μ+ e+e+eμ+ γ e+ e- SM: LFV loops Au branching ratios suppressed by (Δ m2ν )2 50 10 m4w 23
LFV Muon Decays and SUSY Loops μ+ e+ γ μ- N e- N e+ + Au e+ e- μ- μ+ μ+ e+e+eμ+ γ e+ e- SUSY loops Au Most BSM models (e.g. SUSY) induce naturally LFV 24
LFV Muon Decays and SUSY Loops μ+ e+ γ μ- N e- N e+ + Au e+ e- μ- μ+ μ+ e+e+eμ+ γ e+ e- SUSY loops Au enhanced by coherent conversion in nucleus field for Q2(γ*)~0 25 suppressed by extra vertex with respect to μ+ e+ γ
LFV Tree Diagrams μ+ e+ γ μ- N e- N e+ μ+ e+e+e- + Au e- μ- μ+ e+ μ+ γ e+ eq q LQ e μ not allowed e.g. Leptoquarks extra Z', LFV Higgs, etc. Additional BSM tree diagrams in μn en and μn eee 26
first version (not published yet) 27
Search for μ+ e+e+e- at PSI proton cyclotron Ip=2.4 ma @ 590 MeV world-highest intensity beam! project approved in Jan 2013 Aiming for a sensitivity of BR(μ e e e ) ~ 2 10-15 (phase I) BR(μ e e e ) < 10-16 (phase II) 28
How Big is 10-16? Number of grains of sand at all beaches in Germany ~ 10 16 Find THE grain of sand which violates lepton flavor! 29
Backgrounds for Mu3e Irreducible BG: radiative decay with internal conversion (IC) e- ν e+ signal: B(μ+ e+e+e-) eν B(μ+ e+ e+ e+e+e- νν) = 3.4 10-5 e+ i i 30 E i = mμ p i = 0
Backgrounds Irreducible BG: radiative decay with internal conversion (IC) e- ν e+ missing energy from two neutrinos steeply falling! ν B(μ+ e+ R.M.Djilkibaev, R.V.Konoplich PRD79 (2009) e+e+e- νν) = 3.4 10-5 very good momentum + total energy resolution required! 31
Accidental Backgrounds Overlays of two ordinary µ+ decays with a (fake) electron (e-) Electrons from: Bhabha scattering, photon conversion, mis-reconstruction Detector requirements: Vertex resolution Timing resolution Kinematic reconstruction 32
Tracking Resolution + Multiple Scattering limited hit resolution regime Muon decay (m=105.6 MeV): electrons in low momentum range p < 53 MeV/c Multiple scattering is dominant! Need thin, fast and high resolution tracking detectors operated at high rate (>109 particles/s @ phase II) 1 Θ MS P X / X0 mutiple scattering regime 33
Mu3e Design Concept 34
Momentum Resolution in MS Regime Standard spectrometer: multiple-scattering angle σ p Θ MS Ω P (linearised) precision requires large lever arm large bending angle Ω 35
Momentum Resolution in MS Regime Half turn spectrometer: σp O(Θ2MS ) P best precision for half turn tracks measure recurlers 36
Tracking Design Considerations muon mass ~ 105 MeV/c2 37
Tracking Design Considerations 38
Tracking Design Considerations 39
Tracking Design Considerations 40
Mu3e Baseline Design 108 muons per second (phase I) p=28 MeV/c 41
Mu3e Baseline Design 42
Mu3e Baseline Design 43
Mu3e Baseline Design Long cylinder! ~180 cm ~15 cm not to scale! 44
Mu3e Baseline Design solenoid B=1 T 45
Mu3e CAD Drawings µ minimum material budget in active region! multiple scattering is the enemy! 46
Mu3e Detector Pixel Tracker Scintillating Fibers Scintillating Tiles 47
Compact Muon Beamline (Phase I) πe5 Mu3e MEG muon rates of up to 8.4 107/s at solenoid entrance achieved in 2016 further optimizations might be possible aiming for: 108/s muons on target 48
Compact Muon Beamline (CMB) First CMB beam commissioning in December 2014 49
The Mu3e (MEG) PiE5 Area New skywalk New platforms New PSYS access Area Proposal 50
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Mu3e Magnet B=1 Tesla homogeneous field ~3m ~35 tons Magnet (up to 2.6T) expected beginning of 2019 52
Pixel Tracker TRACKING LAYERS MUST BE THIN! 53
ATLAS Pixel Module MCC sensor FE-Chip FE-Chip 54
ATLAS Pixel Module HV-MAPS 50 µm MCC sensor FE-Chip FE-Chip 55
Pixel Detector Technology High Voltage-Monolithic Active Pixel Sensor (HV-MAPS) MuPix8 prototype transistor logic embedded in N-well ( smart diode array ) 2 cm I.Peric et al., NIM A 582 (2007) 876 active sensors hit finding + digitisation + readout HV-CMOS: 60-85 V low cost process (Austria-Micro-Systems) thinned to ~50 μm (~ 0.0005 X0) 56 MuPix has been fully characterized in the lab and in several test beams efficiency noise rate (radiation hardness) temperature-dependence
Recent Mupix8 Performance Plots Mupix8 delivered end of August test beams ad DESY x2, CERN Mupix 8 beam telescope (4 layers) efficiency noise time resolution 57
(Outer) Pixel Tracker Module MuPix7 High Density Interconnect (LTU) 50 µm 58
Ultralight Pixel Ladder module: ~ 1 per mille radiation length 59
Pixel Tracker Endrings Power Readout Control Signals He-Cooling 60
V-Fold Cooling Channels 61
Simulation of Helium Cooling to be validated (again) by measurements with mock-up power budget 62
Timing 63
Pileup 109 muon stops/second (phase II) 64
Tracks in Pixel Detector 65
Tracks in Pixel Detector additional timing detectors needed < 1ns 66
Mu3e Time Timing Detector Scintillating tiles Scintillating fibers fibres background suppression factor of 100! tiles (and fibres) 67
Scintillating Fibre Detector Scintillating Fibers 68
Scintillating Fibres Single fibre time resolutions round Two types of scintillating 250µm fibres studied: round (Kuraray SCSF-81M) squared (Saint Gobain BC 418) (coated with Al) SiPM: Hamatsu S12571-050P (LHCb) SiPM array 1 x 1 mm2, 50 µm pitch squared MuTRig readout chip time resolution 50 ps 32 channels bandwidth 1.25 Gbit/s chip received January 2017 69
Scintillating Fibre Test Beams OR condition > 0.5 Nphe Requirements and expectations fulfilled in test beams! 70 eff. ~ 98%
Scintillating Tile Detector Scintillating tiles Scintillating fibers design sketch 56 x 56 tiles (6.5 x 6.5 x 5.0 mm3) 3 x 3 mm2 single SiPM timing resolution of 100 ps mixed mode ASIC (MuTRig) 71
Scintillating Tile Detector Very promising results from test beam measurements (4 x 4 array) Time resolution < 100 ps Now testing new MuTRig readout ASIC 72
Simulation and Performance 73
Simulation and Performance Track Reconstruction Efficiency Track Momentum Resolution limited acceptance US σp/p= 1% DS excellent! gaps between pixel track stations 74
Charge Identification Main process: μ+ e+ νe νμ Time difference vs path length Δt (ns) positron loopers charge confusion positrons t1 t2 X X electrons Δs/c (ns) Significant reduction of BG for: 75 μ+ e+ e+ e
Bhabha Scattering Background Bhabha vertices target region e+ e- e+ e- Accidental background due to Bhabha scattering is difficult to simulate Bhabha's can be cut away with only small loss in signal efficiency 76
Mu3e Mass Plot 10-12 10-13 10-14 (upper limit) 10-15 77
Sensitivity versus Time 78
Mu3e Collaboration Germany University Heidelberg Karlsruhe Institute of Technology University Mainz Switzerland University of Geneva Paul Scherrer Institute ETH Zurich University Zurich United Kingdom Bristol Liverpool Oxford UC London 79
Mu3e Summary Technical Design Report Detector R&D is concluding pre production is starting First beam in 2019/20 (Phase I) More muons with High Intensity Muon Beamline (HiMB Project) Aim: B(μ+ e+e+e-) 10-16 (90% CL) Unique discovery potential for New Physics 80