The MEG experiment at PSI

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Donato Nicolo`, Universita` di Pisa & INFN 1 NOON 2003, Kanazawa February, 10-14 2003 The MEG experiment at PSI Status and Prospects Donato Nicolo` Dipartimento

1 Donato Nicolo`, Universita` di Pisa & INFN 1 NOON 2003, Kanazawa February, The MEG experiment at PSI Status and Prospects Donato Nicolo` Dipartimento di Fisica dell Universita`di Pisa and Istituto Nazionale di Fisica Nucleare, Pisa (Italy) on behalf of the MEG collaboration NOON 2003 Kanazawa, February

2 Outline Physics motivations SUSY predictions Connection with neutrino oscillations µ eγ signature Signal and Background Sensitivity The detector The e.m. calorimeter (LXe) The positron spectrometer The timing counter Trigger and DAQ Recent progress Calorimeter prototype tests Light transparency Timing resolution Future plans Donato Nicolo`, Universita` di Pisa & INFN 2 NOON 2003, Kanazawa February,

3 Physics Motivations Physics motivation Lepton Flavour Violation (LFV) forbidden (or strongly supprssed) in the Standard Model (BR with massive Dirac neutrinos) Extensions of the SM (SUSY-GUTs) generically predict LFV SUSY SU(5) predictions: BR (µ eγ) LFV induced by finite slepton mixing through radiative corrections (could be large due to top mass) clear evidence for physics beyond the SM Exp. Bound J.Hisano et al.,phys. Lett. B391 (1997) 341 R. Barbieri et al.,nucl. Phys. B445(1995) 215 tan(β) < 3 excluded by LEP results Related issues: µ e conversion (see A. Van der Schaaf s talk) neutron electric dipole Donato Nicolo`, Universita` di Pisa & INFN 3 NOON 2003, Kanazawa February,

ν oscillations+leptogenesis Additional contribution to slepton mixing from V 21 (mixing responsible for solar ν-deficit) SU(5) with right-handed neutrinos J. Hisano, N. Nomura, Phys. Rev.

4 ν oscillations+leptogenesis Additional contribution to slepton mixing from V 21 (mixing responsible for solar ν-deficit) SU(5) with right-handed neutrinos J. Hisano, N. Nomura, Phys. Rev. D59 (1999) Experimental Bound Further enhanced by 3 orders of magnitude to include leptogenesis S. Pascoli, S.T. Petcov, C.E.Yaguna, hep-ph/ Donato Nicolo`, Universita` di Pisa & INFN 4 NOON 2003, Kanazawa February,

5 The MEG Collaboration Donato Nicolo`, Universita` di Pisa & INFN 5 NOON 2003, Kanazawa February, INFN & Pisa University ICEPP, University of Tokyo KEK, Tsukuba A. Baldini C. Bemporad F. Cei M. Grassi D. Nicolò R. Pazzi G. Signorelli F. Sergiampietri INFN & Pavia University A. De Bari P. Cattaneo G. Cecchet INFN & Genoa University F. Gatti T. Mashimo S. Mihara T. Mitsuhashi T. Mori H. Nishiguchi W. Ootani K. Ozone T. Saeki R. Sawada S. Yamashita T. Haruyama A. Maki Y. Makida A. Yamamoto K. Yoshimura Osaka University Waseda University BINP, Novosibirsk PSI, Villigen Y. Kuno T. Doke J. Kikuchi H. Okada S. Suzuki K. Terasawa M. Yamashita T. Yoshimura L. M. Barkov A. A. Grebenuk B. I. Khazin V. P. Smakhtin J. Egger P-R. Kettle S. Ritt

6 Event signature E r p t e e e e γ + = Eγ = mµ c r = pγ = t Backgrounds + e 2 + µ /2 = MeV Correlated: radiative decays Accidental:? Signal and background + + e + µ γ νe ν µ energy position timing Donato Nicolo`, Universita` di Pisa & INFN 6 NOON 2003, Kanazawa February, µ + e γ ν e ν µ from Michel decays γ from radiative decays + e-annihilation in flight pile-up γ

7 Background rate and sensitivity Since 1948 E.P.Hincks and B.Pontecorvo, PR 73 (1948) 257 Limits improved by ~ 2 orders of magnitude per decade µ eγ µ eee µa ea K L 0 µe K + πµe Sensitivity now limited by accidental background BR R E E θ t acc µ e 2 γ eγ eγ After Y. Kuno and Y. Okada Experiment Year E e =E e E =E t e e R BR (%) (ns) (mrad) (s ;1 ) (90% CL) (%) { < 3:6 10 ;9 TRIUMF { < 1:0 10 ;9 SIN : < 1:7 10 ;10 LANL Box < 4:9 10 ;11 Crystal : < 1:2 10 ;11 MEGA PSI ;14 MEG < Donato Nicolo`, Universita` di Pisa & INFN NOON 2003, Kanazawa February,

8 Donato Nicolo`, Universita` di Pisa & INFN 8 NOON 2003, Kanazawa February, Experimental search for µ eγ FWHM resolution needed Ee 0.7% Eγ 1.4% θeγ 12 mrad teγ 150 ps Ω/ 4π 9% Stopped µ-beam: 10 8 µ /sec Liquid Xenon calorimeter for γ detection (scintillation) -fast: 4 / 22 / 45 ns -high LY: ~ 0.8 * NaI -short X 0 : 2.77 cm Solenoid spectrometer & drift chambers (σ r 200 µm) Timing Counter for e + timing

9 Donato Nicolo`, Universita` di Pisa & INFN 9 NOON 2003, Kanazawa February, Present Design Switzerland Drift Chamber, Beam Line, DAQ Russia LXe Tests and Purification Italy taly + counter, Trigger, M.C. Xe Calorimeter Japan LXe Calorimeter, Superconducting Solenoid, M.C.

Donato Nicolo`, Universita` di Pisa & INFN 10 NOON 2003, Kanazawa February, 10-14 2003 Beam Transport The muon System beamat PSI Must provide

10 Donato Nicolo`, Universita` di Pisa & INFN 10 NOON 2003, Kanazawa February, Beam Transport The muon System beamat PSI Must provide continuous 10 8 µ/s with little e + contamination Two separate configurations of the πe5 beam line, U -branch and Z -branch (29 MeV/c µ s) Primary proton beam

11 Donato Nicolo`, Universita` di Pisa & INFN 11 NOON 2003, Kanazawa February, Beam studies Use of: Wien-filter for µ/e separation Solenoid (to be coupled to the spectrometer) + degrader ( momentum reduction) U-branch Z-branch Integral (@4cm target) 1.3*10 8 µ + /s 1.3*10 8 µ + /s After separator 7.3*10 7 µ + /s 9.5*10 7 µ + /s After solenoid σ V 6.5mm, σ H 5.5mm to be studied µ/e separation 11 σ 7 σ Good! Beam time is planned in 2003 Apr/May for last-stage measurements on Z-branch Work on transport solenoid started (0.5 T COBRA)

12 Donato Nicolo`, Universita` di Pisa & INFN 12 NOON 2003, Kanazawa February, COBRA spectrometer COnstant Bending RAdius (COBRA) spectrometer Constant bending radius independent of emission angles Gradient field Uniform field High p T positrons quickly swept out Gradient field Uniform field

Donato Nicolo`, Universita` di Pisa & INFN 13 NOON 2003, Kanazawa February, 10-14 2003 COBRA Magnet B c = 1.

13 Donato Nicolo`, Universita` di Pisa & INFN 13 NOON 2003, Kanazawa February, COBRA Magnet B c = 1.26T, operating current = 359A Five coils with three different diameter to realize gradient field Compensation coils to suppress the residual field around the LXe detector High-strength aluminum stabilized superconductor thin superconducting coil ( 1.46 cm Aluminum, 0.2 X 0 ) Crash Tests completed Winding TOSHIBA To be shipped within this year

intervals Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture

14 Donato Nicolo`, Universita` di Pisa & INFN 14 NOON 2003, Kanazawa February, Positron Tracker 17 chamber sectors aligned radially with 10 intervals Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture Vernier pattern to determine z-position σ(x,y) ~200 µm σ(z) ~ 300 µm(charge division)

15 Donato Nicolo`, Universita` di Pisa & INFN 15 NOON 2003, Kanazawa February, Drift Chamber 90 Sr source Tokyo Univ. σ σ R Z = 93 ± 10µ m = 425 ± 7µ m (no magnetic field here test in PSI)

Donato Nicolo`, Universita` di Pisa & INFN 16 NOON 2003, Kanazawa February, 10-14 2003 Positron Timing Counter BC404 Two layers of

16 Donato Nicolo`, Universita` di Pisa & INFN 16 NOON 2003, Kanazawa February, Positron Timing Counter BC404 Two layers of scintillator read by PMTs placed at right angles with each other Outer: timing measurement Inner: additional trigger information Goal σ time ~ 40 psec

Positron Timing Counter, cont d CORTES: Timing counter test facility with cosmic rays Scintillator bar (5cm x 1cm x 100cm long) Telescope of 8 x MSGC Measured resolutions

17 Positron Timing Counter, cont d CORTES: Timing counter test facility with cosmic rays Scintillator bar (5cm x 1cm x 100cm long) Telescope of 8 x MSGC Measured resolutions σ time ~60psec independent of incident position σ time improves as ~1/ Npe 2 cm thick Donato Nicolo`, Universita` di Pisa & INFN 17 NOON 2003, Kanazawa February,

18 Donato Nicolo`, Universita` di Pisa & INFN 18 NOON 2003, Kanazawa February, Trigger Electronics Uses easily quantities: γ energy cut (N pe ) Positron- γ coincidence in time and direction Built on a FPGA architecture More complex algorithms implementable Trigger system structure VME boards Beam Beam rate rate s -1-1 Fast Fast LXe LXeenergy energy sum sum > > 45MeV 45MeV s -1-1 g g interaction interaction point point (PMT (PMT of of max max charge) charge) e e + + hit hit point point in in timing timing counter counter time time correlation γ γ e e s -1-1 angular correlation γ γ e e s -1-1 Design and simulation of type1 board completed Prototype board delivered by next spring

Donato Nicolo`, Universita` di Pisa & INFN 19 NOON 2003, Kanazawa February, 10-14 2003 Readout electronics Waveform digitizing for all channels Custom domino sampling

19 Donato Nicolo`, Universita` di Pisa & INFN 19 NOON 2003, Kanazawa February, Readout electronics Waveform digitizing for all channels Custom domino sampling chip designed at PSI Cost per DSC ~ 1 US$ 2.5 GHz sampling 40 ps timing resolution Sampling depth 1024 bins Readout similar to trigger Prototypes delivered in autumn

20 Donato Nicolo`, Universita` di Pisa & INFN 20 NOON 2003, Kanazawa February, LXe performance Energy resolution strongly depends on optical properties of LXe Use of MC simulations based on GEANT 3.21 At λ abs the resolution is dominated by photostatistics σ(e)/e (%) σ(e)/e 1.5% (2.5% including edge effects) At λ abs L det it is limited by shower fluctuations+detector response need to use reconstruction algorithms σ(e)/e 4.5% final sensitivity

21 Xenon Calorimeter Prototype Tests on the LXe calorimeter currently under way on a LARGE PROTOTYPE : trigger counters PMT holder inch PMT (x 228) 40 x 40 x 50 cm PMTs, 100 litres Lxe (the largest in the World) Used for the measurement of: Test of cryogenic and long term operation Energy resolution (expected %) Position resolution (few mm) Timing resolution (100 ps) Liquid Xenon trigger counters with: Cosmic rays α-sources 60 MeV eˉ from KSR storage ring 40 MeV γ from TERAS Compton Backscattering (still to be done) Donato Nicolo`, Universita` di Pisa & INFN 21 NOON 2003, Kanazawa February,

Donato Nicolo`, Universita` di Pisa & INFN 22 NOON 2003, Kanazawa February, 10-14 2003

22 Donato Nicolo`, Universita` di Pisa & INFN 22 NOON 2003, Kanazawa February, The LP from inside α-sources and LEDs used for PMT calibrations and monitoring LEDs α-source

23 Donato Nicolo`, Universita` di Pisa & INFN 23 NOON 2003, Kanazawa February, Optical properties First tests showed that the number of scintillation photons was MUCH LESS than expected It improved with every liquefaction/recovery cycle Looks like there is some absorption due to contaminants (mainly H 2 O) May 2002 Present... λ abs > 90% C.L.

24 Donato Nicolo`, Universita` di Pisa & INFN 24 NOON 2003, Kanazawa February, Rayleigh scattering measurement 30 cm 45 cm 60 cm

25 Donato Nicolo`, Universita` di Pisa & INFN 25 NOON 2003, Kanazawa February, Timing resolution test σ t = (σ z2 + σ sc2 ) 1/2 = ( ) 1/2 ps = 100 ps (FWHM) Time-jitter due to photon interaction Scintillation time, photon statistics Measurement of σ sc 2 electron beam Use of Kyoto Syncrotron Ring 60 MeV (2/12/02 6/12/02)

26 Timing resolution 60 MeV e - material degradation only 128 channels (out of 228) had the TDC We estimate the intrinsic timing resolution vs p.e. divide PMTs in two groups: σ sc =RMS[( T L - T R )/2] at center T L,R = weighted average of the PMT TDCs (timewalk corrected) Q sum (MeV) 1/ Q t(tdc) Donato Nicolo`, Universita` di Pisa & INFN 26 NOON 2003, Kanazawa February,

27 Results The resolution scales according to 1/E 1/2 (could be improved by using higher QE PMTs) 52.8 MeV peak Extrapolation to the signal region is satisfactory 5% 10%15%QE Time-walk corrections 1/ Q Analysis still in progress: cross talk position dependence Donato Nicolo`, Universita` di Pisa & INFN 27 NOON 2003, Kanazawa February,

28 Future Plan of LP R&D Nuclear of Tsukuba Preliminary test using a 5inch NaI crystal on 17,18/Feb 7 Li(p, γ) 8 Be Ep=440keV, s=~5mb, Eγ=17.64MeV, Γ 0 =16.7eV 11 B(p, γ) 12 C Ep=7.2 MeV, s=120mb, Eγ=22.6MeV, Γ 0 =2500eV 1.26um 100 na 1kHz reaction rate 9 Be( 3 He, γ) 12 C E he =6.51MeV, s=1.5mb, Eγ=31.16MeV, Γ 0 =2.2MeV Inverse Vacuum problem in wave guides One month for full recovery Next beam time will be after March π 0 γγ from π - p nπ Beam time in autumn requested Donato Nicolo`, Universita` di Pisa & INFN 28 NOON 2003, Kanazawa February,

29 Donato Nicolo`, Universita` di Pisa & INFN 29 NOON 2003, Kanazawa February, Summary and Time Scale All sub-detectors within time scale Near future: Test beam of Large Prototype for E, position and timing with γs µ-transport system test now LoI Proposal now Planning R & D Assembly Data Taking More details at

Lepton Flavour Violation

Lepton Flavour Violation Search for e at Paul Scherrer Institut Satoshi Mihara ICEPP, Univ. of Tokyo http://meg.icepp icepp.s..s.u-tokyo.ac.jp, http://meg.psi psi.ch,http://meg.pi.,http://meg.pi.infn.it