LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS Carlo Bemporad Venezia 5/12/2003 LEPTON-FLAVOUR VIOLATION AND NEUTRINO OSCILLATIONS The MEG Experiment at PSI Non ancora a presentazione definitiva 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) 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

if equal, THEORY: (  e g)/TOT branching ratio  10-4 HISTORY neutrino hypothesis for -decay Pauli (1930) weak interaction theory Fermi (1934) proposed method for n detection Pontecorvo (1946) ne discovery Reines and Cowan (1956) DOES A   e EXISTS ? if equal, THEORY: (  e g)/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)

Previous measurements and related experiments SUMMARY 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

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 !)

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

Combined LEP experiments: SUGRA MSSM

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

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

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 !

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

Previous m+  e+ g Experiments Lab. Year Upper limit Experiment or Auth. PSI 1977 < 1.0  10-9 A. Van der Schaaf et al. TRIUMF < 3.6  10-9 P. Depommier et al. LANL 1979 < 1.7  10-10 W.W. Kinnison et al. 1986 < 4.9  10-11 Crystal Box 1999 < 1.2  10-11 MEGA ~2007 ~ 10-13 MEG Comparison with other LFV searches: Two orders of magnitude improvement is required: tough experimental challenge!

background signal SIGNAL AND BACKGROUND   e g accidental   e n n   e g n n ee  g g eZ  eZ g correlated   e g n n e+ + g e+ + g n e+ + n qeg = 180° Ee = Eg = 52.8 MeV Te = Tg g

DETECTION METHOD qeg = 180° e+ + g signal selection with + at rest 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 for e+ momentum Scintillation counters for e+ timing signal selection with + at rest e+ + g Ee = Eg = 52.8 MeV qeg = 180°

REQUIRED PERFORMANCES The sensitivity is limited by the accidental background The  310-14 allows BR (meg)  10-13 but one needs FWHM Exp./Lab Year DEe/Ee (%) DEg /Eg Dteg (ns) Dqeg (mrad) Stop rate (s-1) Duty cyc.(%) BR (90% CL) SIN 1977 8.7 9.3 1.4 - 5 x 105 100 3.6 x 10-9 TRIUMF 10 6.7 2 x 105 1 x 10-9 LANL 1979 8.8 8 1.9 37 2.4 x 105 6.4 1.7 x 10-10 Crystal Box 1986 1.3 87 4 x 105 (6..9) 4.9 x 10-11 MEGA 1999 1.2 4.5 1.6 17 2.5 x 108 (6..7) 1.2 x 10-11 MEG 2007 0.8 4 0.15 19 2.5 x 107 1 x 10-13

THE MEG COLLABORATION INFN & Genova University S. Dussoni, F. Gatti, P. Ottonello, D. Pergolesi, R. Valle INFN & Lecce University S. Spagnolo, C. Chiri, P. Creti, G. Palama’, M. Panareo INFN & Pavia University A.de Bari, P. Cattaneo, G. Cecchet, G. Nardo’, M. Rossella INFN & Pisa University A. Baldini, C. Bemporad, F.Cei, M.Grassi, F. Morsani, D. Nicolo’, R. Pazzi, F. Raffaelli, F. Sergiampietri, G. Signorelli INFN Roma I D. Zanello ICEPP, University of Tokyo T. Mashimo, S. Mihara, T. Mitsuhashi, T. Mori, H. Nishiguchi, W. Ootani, K. Ozone, T. Saeki, R. Sawada, S. Yamashita KEK, Tsukuba T. Haruyama, A. Maki, Y. Makida, A. Yamamoto, K. Yoshimura Osaka University Y. Kuno Waseda University T. Doke, J. Kikuchi, H. Okada, S. Suzuki, K. Terasawa, M. Yamashita, T. Yoshimura Inserire i nomi sotto forma di testo e il numero di fisici equivalenti PSI, Villigen J. Egger, P. Kettle, H. Molte, S. Ritt Budker Institute, Novosibirsk L.M. Barkov, A.A. Grebenuk, D.G. Grigoriev, B, Khazin, N.M. Ryskulov

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, Magnetic spectrometer

 / e separation BEAM TESTS GO ON ! SEPARATOR SOLENOID 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

Constant bending radius independent of emission angles COBRA spectrometer COnstant Bending RAdius (COBRA) spectrometer Constant bending radius independent of emission angles Gradient field Uniform field High pT positrons quickly swept out Gradient field Uniform field

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

Ready: already shipped to PSI during summer 2003 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

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)

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

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)

 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

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

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 (%)

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 PSI presently going on

HAMAMATSU PMTs Q.E. improved to 15 %

THE LARGE PROTOTYPE -sources LEDs

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

SIMULATION OF EFFECTS OF O2 AND H2O CONTAMINATIONS IN LIQUID XENON

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 sc2 with 60 MeV electron beam weighted average of the PMT TDCs time-walk corrected sc vs ph.el. extrapolation at 52.8 Mev is ok new PMT with good QE 5 15% 52.8 MeV peak 5% 10% 15%QE

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

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

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

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  50 MeV depends 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

FIRST EXPERIMENTAL LOWER LIMIT ON ABSORPTION LENGTH

MEASUREMENT OF NEUTRON BACKGROUND thermal and non-thermal neutrons

Cryostat (PMT test facility: Pisa)

CRYOSTAT (Italy)

TRIGGER ELECTRONICS 2 VME 6U 1 VME 9U 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 1 board 2 VME 6U 1 VME 9U Type2 LXe inner face (312 PMT) . . . 20 boards 20 x 48 Type1 16 3 2 boards 10 boards 10 x 48 LXe lateral faces (488 PMT: 4 to 1 fan-in) 12 boards 12 x 48 Timing counters (160 PMT) 2 x 48 4 x 48 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”

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

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

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 Planning R & D Assembly Data Taking (<LHC) 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

TOTAL COST 6.7 (M€) 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 0.12 0.45 0.43 6.7 (M€)

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 length and Transparent to its own scintillation light the diffusion length