1. Journée de réflexion DPNC 18 June ‘12 Alessandro Bravar Lepton Flavor Violation  3e @ PSI UniGE @ PSI Lepton Flavor Violation The  3e experiment (   → e  e  e  ) Sci-Fi ToF Tracker UniGE planned contributions

2. Lepton Flavor Conservation Origin of Lepton Flavor Number / Conservation the neutrino produced along with a  + (e  ) in  + decay, when interacting with matter will produced only   s (e  s), →  is different from e ; → Lepton Flavor (Family) Conservation Neutrino oscillations, however, violate this ansatz: after traveling some distance the  can produce a   (OPERA) or an e  (T2K) Flavor Conservation in the charge lepton sector: Processes like  A → e A  → e +   → e e e have not been observed yet. The mechanism and size of LFV remain elusive. In the quark sector the situation is quite different: quarks decay, mix, … only the baryonic number is conserved. However Flavor Changing Neutral Currents (FCNC) have not been observed.

3. Lepton Flavor Violation in  eee Lepton Flavor Violation in  → eee neutrino oscillations SUSY exotic particles Current experimental limit BR(  → eee) < 10  12 (90% c.l., SINDRUM 1988) This experiment (  3e @ PSI) BR(  → eee) < 10  15 (90% c.l. exclusion) phase I (2015 – 2017) BR(  → eee) < 10  16 (90% c.l. exclusion) phase II (2018 – 2020) BR(  → eee) = 3  10  16 (5  discovery) Explore physics up to the PeV scale Complementary to direct searches at LHC

4. LFV in the Standard Model process is heavily suppressed due to the small mass difference of neutrinos (  m 2 ~ 10 -3 eV 2 ) ! BR (   → e  e  e  ) < 10  50 → measurement not affected by SM processes

5. Beyond the Standard Model LFV addressesissues like  origin of flavor  neutrino mass generation  CP violation LFV predicted by many BSM models: Supersymmetry Higgs triplet models Little Higgs models New heavy Vector Bosons (Z’) Leptoquark (GUT models) Extra dimensions In many models sizeable and therefore observable LFV effects are expected: BR(  → eee) ~ 10  12 possible (just beyond SINDRUM limit)

6. LFV Searches : Current Situation The best limits on LFV come from PSI muon experiments  → eee BR < 10  12 SINDRUM 1988   + Au → e  + Au BR < 7  10  13 SINDRUM II 2006  → e +  BR < 2.4  10  12 MEG 2011 BR(  → eee) / BR(  → e  ) ~ o(  em /  ) BR(  A → eA) / BR(  → e  ) ~ o(  em /  ) SINDRUM SINDRUM II MEG

7. Comparison  e  and  eee Comparison  → e  and  → eee Effective charge LFV Lagrangian (“toy” model) (Kuno and Okada)  effective mass scale (including coupling)  – “contact” vs “loop” amplitude contribution (parameter of “toy” model)  → e  1 PeV +

8. UniGE @ PSI (MuLAN and FAST) Measurement of the   lifetime and G F “search” for W propagator effects on G F MuLAN FAST

9. Mu3e @ PSI an experiment to search for Lepton Flavor Violation in   e  e  e  using the most intense surface muon beam (p ~ 28 MeV/c) in the world sensitivity ~10 -16 (PeV scale !)  observe ~10 17  decays (over a reasonable time scale) rate ~ 2  10 9  decays / sec (1 y ~  10 7 sec) 200 M HV-MAPS (Si pixels w/ embedded ampli.) channels 10 k ToF channels acceptance ~ 70% for m → eee decay (3 tracks!) B ~ 1 – 2 T surface  p ~ 28 MeV/c

10. How to Find  eee decays How to Find  → eee decays 50 nsec time frames (Si “resolution”) → 100  decays @ 2  10 9  stops / sec challenge : isolate  → eee events  t ~ few 100 ps Time of Flight ~ few 100 ps

11. Backgrounds irreducible backgroundsaccidental backgrounds (pileup) signal BR(  → eee ) = 3.4  10  5 precise timing (ToF):  t ~few 100 ps precise kinematics (p and E resolution):  p / p < 0.5% (i.e. ~ 100 keV/c) precise vertexing:  x ~0.1 mm to suppress backgrounds

12. Silicon Pixel Detector HV-MAPS High Voltage Monolithic Active Pixel Sensors < 50  m thickness active sensors standard CMOS process low noise radiation tolerant low power ~ 20  20  m 2 pixels 200 M channels transistor logic embedded in N-well Heidelberg

13. The ToF Tracker 3000 Sci-Fi channels 250  m  fibers readout with Si-PM arrays 6000 scint. tiles readout with Si-PMs rate ~ several MHz / Sci-Fi channels time resolution ~ few 100 ps readout with wave-form digitizers real time analysis pileup separation background rejection huge data rate ! ~12 cm diameter 24 ribbons 16 mm wide Hamamatsu MPPC array 5883 250  effective pitch UniGE + ?

14. Sci-Fi Arrays 5 staggered layers of 250  m  fibers double cladding Kuraray scintillating fibers SCSF-81M peak ~ 437 nm  decay ~ 2.4 ns att > 3.5 m minimize thickness to reduce multiple scattering minimal thickness for good time resolution (light output) effective thickness ~ 1 mm (+ glue and / or TiO 2 paint and / or support structure) track “topologies” light propagation in multicladding fibers

15. Si-PMs Demystified ADC ch. distance between peaks is constant -> gain from ADC spectra gain vs. HV linear in +-0.5 V window effect of cross talk part of Labo III program (A. Bravar and S. Orsi) peak #15

16. Si-PM Photo Detection Efficiency Hamamatsu KETEK max (SciFi) ~ 440 nm P.D.E. ~ 30 %P.D.E. ~ 60% detect 2  more photons → gain ~  2 in time resolution SciFi 55-60% PDE =  geometrical  QE   Geiger (50–70 %)  (60–90%)

17. Read-Out amplifier ~10x flash ADC or SCA FPGA CFD algorithm (real time) optical link Si-PM > 1 GHz > 10 -12 bit several MHz rate → very fast amplifier  rise ~ 1 nsec  decay ~ 10 nsec (noise not critical because read-out with WFD) digitizer:start with DRS4 switched capacitor array (phase I) and later DRS5 (phase II) SCA  time stretcher: GHz sampling → MHz readout best timing can be obtained using waveform digitizing (e.g. real-time algorithms simulating the functioning of a constant fraction discriminator) huge data rate → processing of DRS information in real time (on board) data reduction (hit processing and matching) also in real time UniGE + PSI

18. DRS4 @ PSI DRS4 @ PSI http://drs.web.psi.ch DRS4 Evaluation Board 4 channels 1 – 5 GSPS 12 bit USB power S. Ritt again part of Labo III equipment

19. Next Generation SCA (DRS5) Short sampling depth Deep sampling depth only short segments of waveform need fast sampling and readout PSI (S. Ritt)

20. UniGE plans Mu3e collaboration: Geneva, Heidelberg, PSI, Zurich, ETHZ, + … Develop ToF system (SciFi and scintillating tiles) hardware (SciFi ribbons, Si-PMs, …) in coll. with UniZH electronics (amplifiers, DRS, firmware, …) in coll. with PSI digitizing electronics: possible synergy with NA61 and AIDA Simulations and optimization of Mu3e detector, in particular ToF system in coll. with ALL More concrete (next 6 months) - build SciFi array prototype and test / optimize for time resolution rate capabilities - develop fast amplifiers, readout based on commercial DRS electronics - develop (offline → real time) algorithms for DRS electronics - R&D on Si-PM PDE FNS request: 1 PostDoc + 1 CanDoc

21. ADDITIONAL TECHNICAL STUFF

22. Late ’80s – Early ’90s (the beginning) first Position-Sensitive PMs with “crossed wires” anode before the advent of multi-anode PMs 16 x 16 wires (channels) delay line readout RD-17 / FAROS

23. Sci-Fi arrays and Si-PMTs Hamamatsu MPPC 5883 alternative solutions single fiber readout Zecotek linear array of 18 1mm 2 MAPDs (CMS HCAL upgrade) green light ! could use Hamamatsu Si-PMs can couple (glue) Sci-Fi ribbon directly to the photosensor + direct mapping of the Sci-Fi array + best optical transmission - limited sensor size monolithic photosensor (no dead regions) blue light ! total surface ~ 10 mm 2 note: this is max surface for Si-PM 50 x 50  m 2 pixels 5 columns of pixels grouped in a single readout ch. instead of a single ch. effective readout pitch 250  m

24. How To Measure Best Timing J.-F. Genat et al., arXiv:0810.5590 (2008)D. Breton et al., NIM A629, 123 (2011) Simulation with realistic noise and best discriminators beam measurements @ SLAC and FNAL 17 ps (  ) can be achieved with waveform digitizing and 40 photoelectrons (no jitter from scintillator  decay )

25. Switched Capacitor Array (DRS Chip) Shift Register Clock IN Out “Time stretcher” GHz  MHz Waveform stored Inverter “Domino” ring chain 0.2 - 2 ns FADC 33 MHz

26. The DRS5 Digitizer 100 ps sample time. 3.1 ns hold time 2  times better timing resolution data driven readout (almost) dead-time-less waveform digitizing 2 MHz sustained event rate planned for 2013 S. Ritt