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LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS

Carlo Bemporad Venezia 5/12/2003. LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS. The MEG Experiment at PSI. http://meg.pi.infn.it.   e g. An experiment which was repeated many times, each time with improved sensitivity (about a factor of 100/decade)

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LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS

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  1. Carlo Bemporad Venezia 5/12/2003 LEPTON-FLAVOUR VIOLATIONANDNEUTRINO OSCILLATIONS TheMEG Experiment at PSI http://meg.pi.infn.it

  2. eg An experiment which was repeated many times, each time with improved sensitivity (about a factor of 100/decade) Like the measurement of the (g-2), it provided, several times, important constraints to theory Lepton-flavour violation experiments which are closely related: Muon-electron conversion in a muonic atom Muon-decay into three electrons Muonium-Antimuonium conversion

  3. HISTORY neutrino hypothesis for -decay Pauli (1930) weak interaction theory Fermi (1934) proposed method for n detection Pontecorvo (1946) nediscovery Reines and Cowan (1956) DOES A  e EXISTS? if equal, THEORY: (  eg)/TOT branching ratio  10-4 Feinberg (1958), Gell-Mann and Feynman (1958) EXPERIMENTS: no gammas Hincks and Pontecorvo (1947) B< 2 10-6 90% C.L. Berley, Lee, Bardon (1959) B< 1.9 10-7 90 C.L. Frankel et al. (1962) B< 6 10-8 90 C.L. Bartlett, Devons, Sachs (1962) ………………………………(1999) MEGA B< 1.2 10-11 Experiment by Danby at al. directly proves  e (1962)

  4. Physics motivations Previous measurements and related experiments General description of the MEG experiment The New Liquid Xenon Calorimetry Test Beam verification of detector performances Achievable sensitivity and time schedule SUMMARY

  5. LEPTON FLAVOUR VIOLATION IS NOW AN ESTABLISHED FACT ! Atmospheric, accelerator, solar, reactor neutrino oscillations First measurement of some mixing parameters BEYOND THE STANDARD MODEL New experiments in Neutrino Physics, under way or close by, on Neutrino Oscillations, Double  Decay, etc. but after a decade of great advances one probably needs new facilities Superbeams, Large-Mass Exps., Neutrino Factories….. While waiting for them LOOK AT SIMPLE PROCESSES IN WHICH THE “NEW PHYSICS” CAN MANIFEST ITSELF (Constraints to Theory even if the e decay is not seen !)

  6. SUSY SU(5) predictions BR (e)  10-14  10-13 SUSY SO(10) predictions BRSO(10) 100 BRSU(5) Experimental limit Our goal SUGRA indications LFV induced by finite sleptonmixing through radiative corrections R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 combinedLEP results favour tan>10

  7. Combined LEP experiments: SUGRA MSSM

  8. SO10 Kuno, Okada Rev.Mod.Phys. 73, 151 (2001)

  9. Experimental limit Our goal CONNECTIONS WITH NEUTRINO-OSCILLATIONS J. Hisano, N. Nomura, Phys. Rev. D59 (1999) Additional contribution toslepton mixingfrom V21 (the matrix element responsible for solar neutrino deficit) tan(b)=30 tan(b)=1 After SNO After Kamland in the Standard Model !

  10. Vast Recent Literature on SUSY and Connection between Neutrino-oscillations, LFV rare decays, EDM, g-2. Examples: Hisano, Nomura, PRD 59, 116005 (1999) Casas, Ibarra, hep-ph0103065 Lavignac, Masina, Savoy, hep-ph/0106245 Babu, Pati, hep-ph/0207289 Raidal, Strumia, PLB 553, 72 (2003) Barr, hep-ph/0307372 Blažek, King, NPB 662, 359 (2003) Masiero, Vempati, hep-ph/0209303 Petcov, Profumo, Takanishi, Yaguna, NPB9187 in press Rather technical papers Constraints from new experimental information Even the full knowledge of neutrino masses and mixing angles is able to determine the seesaw parameters like: the neutrino Yukawa coupling h and the heavy right-handed neutrino Maiorana mass MR(and therefore e…). Complementary informations. (Masiero, Vempati hep-ph/0209303) Predictions for measurable quantities often within reach of experiments in preparation.Possibilities of important contraints to models !

  11. MOTIVATIONS FOR A NEW EXPERIMENT NOW • LARGE CONSENSUS ON THE DESIRABILITY OF A NEW MEASUREMENT WITH IMPROVED SENSITIVITY • IT CAN BE DONE, MAINLY WITH EXISTING TECHNIQUES AND SOME VITAL R&D (TO BE MADE OVER A DEFINITE PERIOD OF TIME) • IF THE PROMISED SENSITIVITY IS REACHED, THE EXPERIMENT IS GOING TO BE IMPORTANT EVEN IF IT DOES NOT SEE THE EXPECTED EFFECT

  12. Previousm+  e+gExperiments Comparison with other LFV searches: Two orders of magnitude improvement is required: toughexperimental challenge!

  13. e+ +g e+ +g n n n n e+ + SIGNAL AND BACKGROUND background signal eg accidental en n egn n ee  gg eZ  eZg correlated egn n qeg = 180° Ee= Eg=52.8MeV Te = Tg g

  14. qeg = 180° e+ +g Ee= Eg=52.8MeV • Stopped beam of >107/sec • in a 150 mm target • Liquid Xenon calorimeter for  detection (scintillation) • fast:4 / 22 / 45 ns • high LY: ~ 0.8 * NaI • short X0:2.77 cm • Solenoid spectrometer & drift chambers fore+ momentum • Scintillation counters for e+ timing DETECTION METHOD signal selection with+at rest

  15. REQUIRED PERFORMANCES The sensitivity is limited by the accidental background The 310-14 allowsBR (meg) 10-13 but one needs FWHM

  16. THE MEG COLLABORATION INFN & Genova UniversityS. Dussoni, F. Gatti, P. Ottonello, D. Pergolesi, R. Valle INFN & Lecce UniversityS. Spagnolo, C. Chiri, P. Creti, G. Palama’, M. Panareo INFN & Pavia UniversityA.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Pisa UniversityA. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli INFN Roma ID. Zanello ICEPP, University of TokyoT. Mashimo, S. Mihara, T. Mitsuhashi, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamashita KEK, TsukubaT. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Osaka UniversityY. Kuno Waseda UniversityT. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamashita, T. Yoshimura PSI, VilligenJ. Egger, P. Kettle, H. Molte, S. Ritt Budker Institute, NovosibirskL.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

  17. DETECTOR CONSTRUCTION Switzerland Drift Chambers Beam Line DAQ Russia LXe Tests Purification Italy e+ counter (Pv+Ge) Trigger (Pisa) LXe Calorimeter(Pisa) Splitters (Lecce) Japan LXe Calorimeter,Magneticspectrometer

  18.  / e separation sV  6.5mm,sH  5.3mm primary proton beam • 1.8 mA of 590 MeV/c protons • 28 MeV/c muons from  stop at rest BEAM TESTS GO ON ! SEPARATOR SOLENOID UNDER CONSTRUCTION

  19. Uniform field Gradient field Gradient field Uniform field COBRA spectrometer COnstantBendingRAdius(COBRA) spectrometer • Constant bending radius independent of emission angles • High pT positrons quickly swept out

  20. Michel Spectrum, Magnetic Field Shape and Positron Rates in Drift Chambers e+ Rate in D.C. Michel Spectrum Magnetic Field Shape

  21. THE MAGNET (Japan) • Bc = 1.26T current = 359A • Five coils with three different diameters • Compensation coils to suppress the stray field around the LXe detector • High-strength aluminum stabilized superconductor • thin magnet • (1.46 cm Aluminum, 0.2 X0) • Ready: already shipped to PSI during summer 2003

  22. POSITRON TRACKER (PSI) • 17 chamber sectors aligned radially at 10°intervals • Two staggered arrays of drift cells • Chamber gas: He-C2H6 mixture • Vernier pattern to measure z-position made of 15 m kapton foils (X,Y) ~200 mm (drift time)(Z) ~ 300 mm (charge division vernier strips)

  23. FULL SCALE TEST IN DECEMBER 2003 Improved vernier strips structure(more uniform resolution) Summary of Drift Chamber simulation DRIFTCHAMBERS preliminary test on prototype and no magnetic field gave: FWHM

  24. Positron Timing Counter (Italy) BC404 • Two crossed layers of scintillator (0.5, 2.0 cm thick). • Hamamatsu R6504S PMT in 3 kG stray field. • Outer: timing measurement Inner: additional trigger information. • Goaltime~ 40 psec (100 ps FWHM)

  25. TIMING COUNTER R&D CORTES: cosmic ray test facility. Microstrip Chambers.  • Scintillator bar (5cm x 1cm x 100cm long) • Telescope of 8 x MSGC • Measured resolutions • time~60psec independent of impact point position • time improves as ~1/√Npe 2 cm thick

  26. 800 l of Liquid Xe 800 PMT immersed in LXe Only scintillation UV light High light emission Unsegmented volume H.V. Refrigerator Signals Cooling pipe Vacuum for thermal insulation Al Honeycomb Liq. Xe window PMT filler Plastic 1.5m LIQUID XENON CALORIMETER (Italy + Japan) Experimental verification

  27. LXe CALORIMETER PERFORMANCE Energy resolution strongly depends on optical properties of LXe • Complete MC simulations • At abs the resolution is dominated by photostatistics FWHM(E)/E 2.5%(including edge effects) • At abs det limits from shower fluctuations + detector response  need of reconstruction algorithms • FWHM(E)/E  4% FWHM(E)/E (%)

  28. LXe CALORIMETER PROTOTYPE(the largest in the world) • The Large Prototype (LP) • 40 x 40 x 50 cm3 • 228 PMTs, 100 litres LXe • Purpose • Test cryogenic operation on a long term and on a large volume • Measure the LXe properties • Check the reconstruction methods • Measure the Energy, Position and Timing resolutions • Use of : • Cosmic rays • -sources • e+ (60 MeV) in Japan • Back-Compton facility TERAS • 50 MeV  from°at PSIpresently going on

  29. HAMAMATSU PMTs Q.E. improved to 15 %

  30. -sources THE LARGE PROTOTYPE LEDs

  31. STUDY OF LXe OPTICAL PROPERTIES • First tests showed that the number of scintillation photons was MUCH LESS than expected • It improved with Xe cleaning: Oxysorb + gas getter + re-circulation (took time) • There was a strong absorption due to contaminants (mainly H2O) March 2002 Present... labs> 1m

  32. SIMULATION OF EFFECTS OF O2 AND H2O CONTAMINATIONS IN LIQUID XENON

  33. Timing resolution test t = (z2 + sc2)1/2 = (802 + 602)1/2 ps = 100 ps (FWHM) z Time-jitter due to photon interaction point sc Scintillation time and photon statistics our goal Measurement ofsc2with 60 MeV electron beam • weighted average of the PMT TDCs time-walk corrected • scvsph.el. • extrapolation at 52.8Mev is ok • new PMT with good QE • 5 15% 52.8 MeV peak 5% 10% 15%QE

  34. ON-GOING TEST AT PSI  - (essentially) at rest captured on protons:  - p  0 n  - p  n  0   Photon spectrum 129 MeV 54.9 82.9 selection of approx. back-to-back photons by collimators

  35. 1999 measurements (R&D) with a NaI+CsI 8%FWHM • D=100 cm • 10 x 10 window • 9.5 hours • 60 cm (NaI) 75 cm (CsI) • 11 x 13 window

  36. November 2003 for target ZmH f%(CH2)=1.2

  37. R&D IN XENON CALORIMETRY Many projects, but few existing “large size” detectors The reaching of the resolution goals, i.e.: FWHM(E)/E  4% at  50MeVdepends on quantities still poorly known : refractive index, attenuation length, absorption length at 178 nm real photon desappearance Difficult measurements. Some data on dif are available, not always in mutual agreement. Gain extra information from rich data in gas and in the visible region

  38. FIRST EXPERIMENTAL LOWER LIMIT ON ABSORPTION LENGTH  1 m

  39. MEASUREMENT OF NEUTRON BACKGROUND thermal and non-thermal neutrons

  40. Cryostat (PMT test facility: Pisa)

  41. CRYOSTAT (Italy)

  42. 2 boards LXe inner face (312 PMT) . . . . . . 10 boards 20 boards 1 board LXe lateral faces (488 PMT: 4 to 1 fan-in) 1 board 2 x 48 Type1 Type1 Type1 Type1 Type1 Type1 Type1 Type1 Type1 12 boards 2 boards 3 16 16 3 16 3 . . . Timing counters (160 PMT) Type2 Type2 Type2 Type2 Type2 Type2 2 VME 6U 1 VME 9U 2 x 48 4 x 48 20 x 48 12 x 48 10 x 48 TRIGGER ELECTRONICS • It uses quantities like: •  energy • Positron-  coincidence in time and direction • Built on a FADC-FPGA architecture • (field programmable gate array) • More complex algorithms implementable • Beam rate 108 s-1 • Fast LXe energy sum > 45MeV 2103 s-1  interaction point (PMT of max charge) e+ hit point in timing counter • time correlation  – e+ 200 s-1 • angular correlation  – e+ 20 s-1 prototype board under test “on beam”

  43. READOUT ELECTRONICS (PSI) • Waveform digitizing for all channels • Custom domino sampling chip designed at PSI • 2.5 GHz sampling speed @ 40 ps timing resolution • Sampling depth 1024 bins • Readout similar to trigger prototypes under test

  44. Detector parameters Signal Single Event Sensitivity  410-14 Cuts at 1,4FWHM  210-14 Backgrounds  310-15 SUMMARY FOR THE SENSITIVITY OF MEG Upper Limit at 90% CLBR (meg) 110-13 Discovery 4 events (P = 210-3) correspond BR = 210-13

  45. SUMMARY AND TIME SCALE • This experiment may provide a clean indication of New Physics • Measurements and detector simulation make us confident that we can reach the SES of 4 x 10-14 for e (BR 10-13) • Final prototypes are under test now • Large Prototype for energy, position and timing resolutions on ’s • Full scale Drift Chamber • -Transport and degrader-target • Tentative time profile Revised document now LoI Proposal (<LHC) Planning R & D Data Taking Assembly 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp More details at

  46. TOTAL COST Xe Calorimeter Drift chambers Timing counter S. Solenoid Transport Magnet HV Trigger Readout & DAQ Xe 0.9 PMT 1.7 Vessel 0.4 Storage/ 0.4 purif./vacuum 0.14 0.7 1.3 0.14 0.12 0.45 0.43 6.7 (M€)

  47. PHYSICAL PROPERTIES OF LIQUID RARE GASES • If impurities are not present the absorption is neglegible • The light is attenuated according to: Scintillation mechanism: VUV Photons Exited excimer formation One must determine the attenuation lengthand Transparent to its own scintillation light the diffusion length

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