MEG II: Status and Francesco Renga Upgrades INFN Roma for the MEG II Collaboration 1
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 Sensitivity to New Physics A. Crivellin et al. , JHEP 1705 (2017) 117 G. M. Pruna, 2019 PSI User Meeting Operators in EFT mix at the loop level: • the naive view (i .e. µ -> e γ only sensitive to dipole operators ) has to be abandoned • µ -> e γ also sensitive to 4-fermion operators and can give the strongest bounds in some scenario - 2
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 µ -> e γ searches e + Positron and photon are monochromatic (52.8 MeV), µ + back-to-back and produced at the same time ; γ Accidental Background Radiative Muon Decay (RMD) e e DOMINANT µ µ ν µ ν ν γ γ ν 3
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 µ -> e γ searches e + Positron and photon are monochromatic (52.8 MeV), µ + back-to-back and produced at the same time ; Γ acc ∝ Γ 2 µ · ε e · ε γ · δ E e · ( δ E γ ) 2 · ( δ Θ e γ ) 2 · δ T e γ γ Accidental Background Radiative Muon Decay (RMD) e e DOMINANT µ µ ν µ ν ν γ γ ν 4
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 The most intense DC muon beam in the world • The ring cyclotron at PSI PSI Aerial View (Villigen, CH) serves the most intense DC muon beam lines in the world π E5 - up to 10 8 µ/s 590 MeV, 2.2 mA PSI Ring Cyclotron 5
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 Ingredients for a search of µ -> e γ Reconstruct the Reconstruct the Positron Energy Relative Angle e + µ + γ Reconstruct the Relative Time Reconstruct the Photon Energy 6
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 The MEG Experiment Reconstruct the LXe calorimeter Reconstruct the Positron Energy Relative Angle e + 16 Drift Chambers in a magnetic field DC TC 30 scintillating bars µ + γ for timing & trigger LXe Reconstruct the Relative Time Reconstruct the Photon Energy 7
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 Likelihood Analysis • Likelihood analysis of 5 discriminating variables (Ee,E γ , θ e γ , φ e γ ,Te γ ): - year-by-year and event-by-event PDFs - careful treatment of correlations (from well understood geometrical effects) • Accidental Background PDFs are fully defined from data sidebands: • very solid determination of the (largely) dominant background • Signal and radiative decay PDFs by combining the results of the calibration procedures • Normalization from the observed number of µ -> e ν ν and RMD 8
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 The final MEG result (I) 7.5 x 10 14 µ on target N ACC = 7684 ± 103 N RMD = 663 ± 59 N SIG (best fit) = -2.2 BR < 4.2 x 10 -13 @ 90% C.L. Eur. Phys. J. C76 (2016) no. 8, 434 Magnified signal (BR = 4 x 10 -11 ) 9
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 The final MEG result (II) Toy MC sensitivity Median UL = 5.3 x 10 -13 DATA 10 10
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II • The MEG experiment is undergoing an upgrade that involves all sub-detectors Eur. Phys. J. C78 (2018) no.5, 380 First physics run expected in 2020 UL ~ 6 x 10 -14 in 3 years of run Larger LXe volume with finer light detector granularity Higher beam intensity Unique-volume Drift Chamber RMD Veto Scintillator Tile TC 11
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - The LXe Calorimeter MEG MEG-II First events/spectra from 2017 data We developed large-area (12x12 mm 2 ), UV-sensitive MPPCs to cover the inner face of the LXe calorimeter Better Resolution, better pile-up rejection σ E ~ 1%, σ position ~ 2/5 mm (x,y/z) 12
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - The Timing Counters 5mm-thick Scintillator Tiles read out by 3x3 mm 2 SiPM Detector completed, data taken in 2017 and 2018 Calibration with dedicated laser 13
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - The Timing Counters 5mm-thick Scintillator Tiles read out by 3x3 mm 2 SiPM Detector completed, data taken in 2017 and 2018 σ T ~ 35 ps Already reached the design resolution 14
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - The Drift Chamber The challenge: minimal material budget (to reduce MS of 50 MeV e + ) and very high granularity (to cope with the high rate) —> small cells (down to < 6 mm) + extremely thin wires (20 µm W(Au) + 40-50 µm Al(Ag)) Innovative wiring technique (no feedthroughs) Severe problems of wire fragility in presence of contaminants + humidity σ E ~ 130 keV, σ angles ~ 5 mrad, 2x larger positron efficiency 15
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - The Drift Chamber The challenge: minimal material budget (to reduce MS of 50 MeV e + ) and very high granularity (to cope with the high rate) —> small cells (down to < 6 mm) + extremely thin wires (20 µm W(Au) + 40-50 µm Al(Ag)) Innovative wiring technique (no feedthroughs) Assembly completed in summer 2018 Severe problems of wire fragility in presence of contaminants + humidity First data on beam in fall 2018 σ E ~ 130 keV, σ angles ~ 5 mrad, 2x larger positron efficiency 16
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - The Drift Chamber Low wire elongation in 2018 (50% of elastic limit) to limit the impact of • wire fragility —> electrostatic stability problems (inner layers could not reach the working point) Elongation increased in Spring 2019 New HV tests show that all the chamber can now be operated at the proper working point (1400-1500 V, 5 x 10 5 gain) with 100 V safety margin Working point + 100V green = goal reached 17
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 RDC & Target monitoring 50% of acc. background photons come from RMD w/ positron along the beam line Can be vetoed by detecting the positron in coincidence with the photon RMD Veto A new detector (LYSO + plastic scint.) built and tested in 2017 -> 16% better sensitivity The target position in MEG-II has to be known with an accuracy ~ 100 µm to not compromise the angular resolution A system of photo cameras has been installed to monitor the target position << 100 µm resolution reached 18
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - RDC, DAQ, Trigger Trigger and DAQ will be integrated in a single, compact system (WaveDAQ) Also provides power and amplification for SiPM/MPPC Had to face severe common-noise problems 19 — now fixed — The design and test of the DAQ electronics is going to be finalized in the next few months, mass production will start immediately after 19
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II Highlights - Calibrations 20
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 MEG-II schedule & sensitivity 2013 2014 2015 2018 2019 2020 2016 2017 2021 2022 2023 PROPOSAL R&D Construction & Commissioning Engineering Runs Physics Runs 6 x 10 -14 21
What next? G. Cavoto, A. Papa, FR, E. Ripiccini and C. Voena Eur. Phys. J. C (2018) 78: 37 22
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 Sensitivity to New Physics A. Crivellin et al. , JHEP 1705 (2017) 117 G. M. Pruna, 2019 PSI User Meeting Even just a factor 10 in µ -> e γ can improve its New Physics sensitivity beyond • the reach of the current µ -> e conversion experiments 23
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 The next generation of high intensity muon beams MuSIC Project @ RCNP Thick production target π capture solenoid 4 x 10 8 µ/s at the production target S. Cook et al. , Phys. Rev. Accel. Beams 20 (2017) HiMB Project @ PSI x4 µ capture eff. x6 µ transport eff. 1.3 x 10 10 µ/s A. Knecht, SWHEPPS2016 24
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 The next generation of high intensity muon beams MuSIC Project @ RCNP Thick production target π capture solenoid Possibility for a high intensity 4 x 10 8 µ/s DC muon beam under study at the production target S. Cook et al. , Phys. Rev. Accel. Beams 20 (2017) at PIP-II (FNAL) HiMB Project @ PSI x4 µ capture eff. x6 µ transport eff. 1.3 x 10 10 µ/s A. Knecht, SWHEPPS2016 25
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 Toward the next generation of µ -> e γ searches: Photon Reconstruction Calorimetry BR Exp. UL Photon Conversion High efficiency Calorimetry Good resolutions Improved calorimetry MEG: LXe calorimeter 10% acceptance Photon Conversion Beam Rate Low efficiency (~ %) Reminder: Extreme resolutions Acc. Bkg. ~ R µ2 e γ Vertex + Sens. ~ S/ √ B ~ const. MEGA/Mu3e if non-zero background 26
Francesco Renga - CLFV2019, Fukuoka, 17-19 June 2019 Photon Reconstruction: Limiting Factors CALORIMETRY PHOTON CONVERSION Photon Statistics Interactions in the converter (conversion • • probability, e + e - energy loss and MS) Scintillator time constant • Detector segmentation • LaBr 3 (Ce) looks a very good • candidate: our simulations & tests indicate - that ~ 800 keV resolution can be SIGNAL reached BKG extreme time resolution (~ 30 ps) - large acceptance - VERTEXING very expensive - 27
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