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First results from the MEG/RE12 experiment at PSI

First results from the MEG/RE12 experiment at PSI. A.M. Baldini 29 sep 2009. Hep-ex:0908.2594v1 18 Aug 2009. Most recent m +  e + g Experiments. Two orders of magnitude improvement tough experimental challenge! But

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First results from the MEG/RE12 experiment at PSI

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  1. First results from the MEG/RE12 experiment at PSI A.M. Baldini 29 sep 2009 Hep-ex:0908.2594v1 18 Aug 2009

  2. Most recent m+  e+g Experiments Two orders of magnitude improvement tough experimental challenge! But several SUSY GUT and SUSY see-saw models predict BRs at the reach of MEG

  3. SUSY SU(5) predictions BR (meg)  10-14  10-13 SUSY SO(10) predictions BRSO(10) 100 BRSU(5) Experimental limit Our goal SUSY-GUT (SUGRA) First contribution: VCKM cLFV LFV induced by slepton mixing R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al.,Nucl. Phys. B445(1995) 215 combinedLEP results favour tanb>10

  4. SO10

  5. Experimental limit Our goal VPMNS (n oscillations) cLFV Independent contribution toslepton mixingfrom n masses (see-saw model): V less known J. Hisano, N. Nomura, Phys. Rev. D59 (1999) tan(b)=30 tan(b)=1 After SNO After Kamland in the Standard Model !! If it is seen it is not SM!

  6. e+ +g e+ +g n n n n e+ + Signal and background background signal eg accidental en n egn n ee  g g eZ  eZ g physical egn n qeg = 180° Ee= Eg=52.8MeV Te = Tg g

  7. The sensitivity is limited by theaccidental background The n. of acc. backg events (nacc.b.) depends quadratically on the muon rateand on how well we measure the experimental quantities: e-g relative timing and angle, positron and photon energy Effective BRback (nback/Rm T) Integral on the detector resolutions of the Michel and radiative decay spectra

  8. Required Performances BR (meg) 10-13 reachable BRacc.b. 2 10-14 and BRphys.b.  0.1 BRacc.b.with the following resolutions FWHM Need of a DC muon beam

  9. Experimental method • Detector outline • Stopped beam of 3 107 /sec in a 150 mm target • Solenoid spectrometer & drift chambers fore+ momentum • Scintillation counters for e+ timing • Liquid Xenon calorimeter for  detection (scintillation) • Method proposed in 1998: PSI-RR-99-05: 10-14 possibility • MEG proposal: september 2002: 10-13 goal: A. Baldini and T. Mori spokespersons: Italy, Japan, Switzerland, Russia

  10. Detector Construction Switzerland Drift Chambers Beam Line DAQ Russia LXe Tests Beam line Italy e+ counter Trigger LXe Calorimeter Japan LXe Calorimeter,Spectrometer’s magnet USA(UCI) Calibrations/Target/DC pressure system

  11. Next slides... • The PSI pE5 beamline • The Positron spectrometer • The Liquid Xenon calorimeter • DAQ • The 2008 run • Future

  12. Primary proton beam 1) The PSI pE5 DC beam Particles intensity as a function of the selected momentum m+ • 1.8 mA of 590 MeV/c protons (most intense DC beam in the world) • 29 MeV/c muons from decay of  stop at rest: fully polarized

  13. Beam studies • Optimization of the beam elements: • Wien filterform/e separation • Degrader to reduce the momentum stopping in a150mmCH2target • Solenoid to couplebeam with COBRA spectrometer • Results (4 cm target): • Z-version • Rm(total)1.3*108m+/s • Rm(after W.filter & Coll.) 1.1*108m+/s • Rm(stop in target)6*107m+/s • Beam spot (target)s 10 mm • m/e separation (at collimator)7.5s(12 cm) 108m/s could be stopped in the target but only 3x107 are used because of accidental background

  14. Gradient field Uniform field Gradient field Uniform field 2) The positron spectrometer: COBRA spectrometer COnstantBendingRAdius(COBRA) spectrometer • High pT positrons quickly swept out • Constant bending radius independent of emission angles

  15. The magnet • 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)

  16. Gradient field

  17. The drift chambers • 16 chamber sectors aligned radially with 10°intervals • Two staggered arrays of drift cells • Chamber gas: He-C2H6 mixture • Vernier pattern to measure z-position made of 15 mm kapton foils goals (X,Y) ~200 mm (drift time) (Z) ~ 300 mm (charge division vernier strips)

  18. 2 10-3 X0 along positrons trajectory

  19. The Timing Counter BC404 • One (outer) layer of scintillator read by PMTs : timing • One inner layer of scintillating fibers read by APDs: trigger (the long. Position • is needed for a fast estimate of the positron direction) • Goal time~ 40 psec (100 ps FWHM) 5 x 5 mm2

  20. APD Cooled Support TC Final Design APD F.E. Board Fibers • A PLASTIC SUPPORT STRUCTURE ARRANGES THE SCINTILLATOR BARS AS REQUESTED • THE BARS ARE GLUED ONTO THE SUPPORT • INTERFACE ELEMENTS ARE GLUED ONTO THE BARS AND SUPPORT THE FIBRES • FIBRES ARE GLUED AS WELL • TEMPORARY ALUMINIUM BEAMS ARE USED TO HANDLE THE DETECTOR DURING INSTALLATION • PTFE SLIDERS WILL ENSURE A SMOOTH MOTION ALONG THE RAILS APD PM Divider Board Main Support Scintillator Slab Scintillator Housing PM-Scintillator Coupler

  21. 800 l of Liquid Xe 848 PMT immersed in LXe Only scintillation light High luminosity Unsegmented volume H.V. Refrigerator Signals Cooling pipe Vacuum for thermal insulation Al Honeycomb Liq. Xe window PMT filler Plastic 1.5m 3) The Liquid Xe calorimeter Experimental check In a Large Prototype

  22. The liquid xenon calorimeter

  23. PMT development OK!

  24. Xenon purification New (2009) liquid phase purification system completely made inside the collaboration (F. Sergiampietri)

  25. m radiative decay Laser 20 cm 3 cm LED Laser Lower beam intensity < 107 Is necessary to reduce pile-ups Better st, makes it possible to take data with higher beam intensity A few days ~ 1 week to get enough statistics g e m (rough) relative timing calib. < 2~3 nsec n n PMT Gain Higher V with light att. Can be repeated frequently p0 gg p- + p  p0 + n p0  gg (55MeV, 83MeV) p- + p  g + n (129MeV) 10 days to scan all volume precisely (faster scan possible with less points) LH2 target alpha Xenon Calibration PMT QE & Att. L Cold GXe LXe e+ g e- Nickel g Generator Proton Acc Li(p,)Be LiF target at COBRA center 17.6MeV g ~daily calib. Can be used also for initial setup 9 MeV Nickelγ-line on off quelle K Bi NaI Illuminate Xe from the back Source (Cf) transferred by comp air  on/off Tl Li(p, 1) at 14.6 MeV F Polyethylene 0.25 cm Nickel plate Li(p, 0) at 17.6 MeV

  26. Calorimeter energy Resolution and uniformity at 55 MeV by means of Energy resolution on the calorimer Entrance face sR = 1.5% FWHM = 4.6 %

  27. CW beam line

  28. LiF target LITHIUM  - spectrum + FLUORINE  - spectrum Automatic insertion/Extraction from the experiment center (target)

  29. 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 4) DAQ: trigger • Uses easily quantities: •  energy • Positron-  coincidence in time and direction • Built on a FADC-FPGA architecture • More complex algorithms implementable • Beam rate 108 s-1 • Fast LXe energy sum > 45MeV 2103 s-1 g interaction point (PMT of max charge) e+ hit point in timing counter • time correlation g – e+ 200 s-1 • angular correlation g – e+ 20 s-1  5 Hz in 2008 data taking

  30. On-line Eγresolution 55 MeVγ-line from π0-decay σ= 3.8% 45 MeV threshold (@4s from signal)

  31. DAQ: readout The Domino Principle 0.2-2 ns Inverter “Domino” ring chain IN Waveform stored Out FADC 33 MHz Clock Shift Register “Time stretcher” GHz  MHz Keep Domino wave running in a circular fashion and stop by trigger Domino Ring Sampler (DRS) Low cost One “oscilloscope” per channel

  32. Liquid xenon: waveforms: 2 digitizers Trigger@100 MHz DRS2 @ 500 MHz or 2 GHz

  33. 4) 2008 run • - First 3 months physics data taking (september-december 2008) • DCHs instability on part of the chambers after some months of operation: reduction of efficiency to 30% (now 2009 corrected: new HV distribution system ) • Xe LY increase (now 2009 at the nominal value) CW Calibration each three days during 2008 run

  34. 2008 2009

  35. In 2009 xenon scintillation waveforms have the right time decay constant: longer for gammas 2008 2009

  36. RD RD RD RD RD RD 2008 run : 1014 muons stopped in target We also took RMD data once/week at reduced beam intensity Programmed beam shutdowns Air test in COBRA Cooling system repair

  37. DCH resolutions from 2008 data Tracks with two turns in the spectrometer are used to detetrmine the Angular resolutions s(Df) =14 mrad s(f)=10 mrad The edge of Michel positrons used to determine momentum resolution score = 374 keV (60%) stail1 = 1.06 MeV (33%) stail2 = 2 MeV (7%) s(Dq) = 25 mrad s(q) = 18 mrad

  38. Timing resolutions from 2008 data Photon - positron timing resolution by using Radiative muon decay: physical background Intrinsic timing resolution by using positrons hitting several bars DT 80 ps Problems with DRS2 : will improve with DRS4

  39. Dedicated RMD runs at lower thresholds

  40. Blind analysis: Eg vs Dtge window

  41. Sidebands (|DTeg| > 1 ns ) are used to MEASURE accidental background distributions g Energy Radiative decay + In flight positron annihilation + resolution + pileup: in agreement with MCs

  42. Likelihood analysis: accidentals + radiative + signal PDFs to fit data + Feldman Cousins Best fit in the signal region Agreement of 3 different analyses

  43. Eg vs Ee+

  44. Normalization: measured Michel eventssimultaneous with the normal MEG trigger dove: pre-scaling 107 • Independent of instantaneous beam rate • Nearly insensitive to positron acceptance and efficiency factors associated with DCH and TC

  45. 90% CL limit • 90 % C.L. NSig 14.6 corresponds to BR(m→eg)  3.0 x 10-11 • Computed sensitivity1.3 x 10-11 • Statistical fluctuation 5% • From side bands analysis we expected 0.9 (left) and 2.1 (right) x 10-11 • Bad luck

  46. Future prospects • Re-start of data taking in september, until december (as in 2008) • Instabilities eliminated: DRS2DRS4 (timing improvement + noise reduction) • Data taking and trigger efficiencies: 3-5 factor improvement • Corresponding improvement in sensitivity: 2-4 * 10-12 for 2009 run • Continue running in 2010 + 2011 for the final (10-13) goal Proposal now LoI Planning R & D Assembly Data Taking 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 http://meg.psi.ch http://meg.pi.infn.it http://meg.icepp.s.u-tokyo.ac.jp More details at

  47. Pm (Y. Kuno et al., MEG TN1, 1997 and references) Det. 1 Det. 2 • For suitable geometry big  factors can be obtained • This is not the case for MEG (detailed calculations are necessary ) • In some theories (minimal SU(5) model) the positron has a definite helicity  Pm is less effective

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