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

2 Most recent  +  e +  Experiments Lab.YearUpper limitExperiment or Auth. PSI1977 < 1.0  A. Van der Schaaf et al. TRIUMF1977 < 3.6  P. Depommier et al. LANL1979 < 1.7  W.W. Kinnison et al. LANL1986 < 4.9  Crystal Box LANL1999 < 1.2  MEGA PSI~2011~ MEG 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-GUT (SUGRA) First contribution: V CKM  cLFV SUSY SU(5) predictions BR (  e  )   SUSY SO(10) predictions BR SO(10)  100 BR SU(5) R. Barbieri et al., Phys. Lett. B338(1994) 212 R. Barbieri et al., Nucl. Phys. B445(1995) 215 LFV induced by slepton mixing Our goal Experimental limit combined LEP results favour tan  >10

4 SO10

5 Our goal Experimental limit V PMNS ( oscillations    cLFV J. Hisano, N. Nomura, Phys. Rev. D59 (1999) Independent contribution to slepton mixing from masses (see-saw model): V less known tan(  )=30 tan(  )=1 After SNO After Kamland in the Standard Model !! If it is seen it is not SM!

6 Signal and background e+ +  e+ +   e  = 180° Ee = E  = 52.8 MeV Te = T  signal   e  background physical   e  e+ +  e+ +  accidental   e    e  ee   eZ  eZ  e+ + e+ + 

7 The sensitivity is limited by the accidental background Integral on the detector resolutions of the Michel and radiative decay spectra Effective BRback (n back /R  ) The n. of acc. backg events (n acc.b. ) depends quadratically on the muon rateand on how well we measure the experimental quantities: e-  relative timing and angle, positron and photon energy

8 Required Performances Exp./LabYear  E e /E e (%)  E  /E  (%)  t e  (ns)  e  (mrad) Stop rate (s -1 ) Duty cyc.(%) BR (90% CL) SIN x x TRIUMF x x LANL x x Crystal Box x 10 5 (6..9)4.9 x MEGA x 10 8 (6..7)1.2 x MEG x x FWHM BRacc.b.  and BRphys.b.  0.1 BRacc.b. with the following resolutions Need of a DC muon beam BR (  e  )  reachable

9 Experimental method Detector outline 1.Stopped beam of  /sec in a 150  m target 2.Solenoid spectrometer & drift chambers for e + momentum 3.Scintillation counters for e + timing 4.Liquid Xenon calorimeter for  detection (scintillation) Method proposed in 1998: PSI-RR-99-05: possibility MEG proposal: september 2002: goal: A. Baldini and T. Mori spokespersons: Italy, Japan, Switzerland, Russia

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

11 Next slides... 1.The PSI  E5 beamline 2.The Positron spectrometer 3.The Liquid Xenon calorimeter 4.DAQ 5.The 2008 run 6.Future

12 1) The PSI  E5 DC beam Primary proton beam 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 ++ Particles intensity as a function of the selected momentum

13 Beam studies Optimization of the beam elements: Wien filter for  /e separation Degrader to reduce the momentum stopping in a 150  m CH 2 target Solenoid to couple beam with COBRA spectrometer Results (4 cm target): Z-version R  (total) 1.3*10 8  + /s R  (after W.filter & Coll.)1.1*10 8  + /s R  (stop in target) 6*10 7  + /s Beam spot (target)   10 mm  /e separation (at collimator) 7.5  (12 cm) 10 8  /s could be stopped in the target but only 3x10 7 are used because of accidental background

14 2) The positron spectrometer: COBRA spectrometer Gradient field Uniform field COnstant Bending RAdius (COBRA) spectrometer Constant bending radius independent of emission angles High p T positrons quickly swept out Gradient field Uniform field

15 The magnet B c = 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 X 0 )

16 Gradient field

17 The drift chambers 16 chamber sectors aligned radially with 10°intervals Two staggered arrays of drift cells Chamber gas: He-C 2 H 6 mixture Vernier pattern to measure z-position made of 15  m kapton foils  (X,Y) ~200  m (drift time)  (Z) ~ 300  m (charge division vernier strips) goals

X 0 along positrons trajectory

19 The Timing Counter 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) BC404 5 x 5 mm 2

20 TC Final Design 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 PM-Scintillator Coupler Scintillator Housing Scintillator Slab Main Support Divider Board PM APD APD F.E. Board Fibers APD Cooled Support

21

l of Liquid Xe 848 PMT immersed in LXe Only scintillation light High luminosity Unsegmented volume 3) The Liquid Xe calorimeter Experimental check In a Large Prototype

23 The liquid xenon calorimeter

24 1 st generation R6041Q2 nd generation R9288TB3 rd generation R9288ZA 228 in the LP (2003 CEX and TERAS) 127 in the LP (2004 CEX) 111 In the LP (2004 CEX)Not used yet in the LP Rb-Sc-Sb Mn layer to keep surface resistance at low temp. K-Sc-Sb Al strip to fit with the dynode pattern to keep surface resistance at low temp. K-Sc-Sb Al strip density is doubled. 4% loss of the effective area. 1 st compact version QE~4-6% Under high rate background, PMT output reduced by % with a time constant of order of 10min. Higher QE ~12-14% Good performance in high rate BG Still slight reduction of output in very high BG Higher QE~12-14% Much better performance in very high BG PMT development OK!

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

LED PMT Gain Higher V with light att. Can be repeated frequently alpha PMT QE & Att. L Cold GXe LXe Laser (rough) relative timing calib. < 2~3 nsec Nickel  Generator 9 MeV Nickel γ-line NaI Polyethylene 0.25 cm Nickel plate 3 cm 20 cm quelle on off Illuminate Xe from the back Source (Cf) transferred by comp air  on/off Proton Acc Li(p,  )Be LiF target at COBRA center 17.6MeV  ~daily calib. Can be used also for initial setup  K Bi Tl F Li(p,  0) at 17.6 MeV Li(p,  1) at 14.6 MeV  radiative decay  0    - + p   0 + n  0   (55MeV, 83MeV)  - + p   + n (129MeV) 10 days to scan all volume precisely (faster scan possible with less points) LH 2 target  e+e+ e-e- e e     Lower beam intensity < 10 7 Is necessary to reduce pile- ups Better  t, makes it possible to take data with higher beam intensity A few days ~ 1 week to get enough statistics Xenon Calibration

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

29 CW beam line

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

31 4) DAQ: trigger  Beam rate10 8 s -1  Fast LXe energy sum > 45MeV2  10 3 s -1 g interaction point (PMT of max charge) e + hit point in timing counter  time correlation  – e s -1  angular correlation  – e + 20 s -1 Uses easily quantities:  energy Positron-  coincidence in time and direction Built on a FADC-FPGA architecture More complex algorithms implementable 1 board 2 VME 6U 1 VME 9U Type2 LXe inner face (312 PMT) boards 20 x 48 Type Type2 2 boards boards 10 x 48 Type LXe lateral faces (488 PMT: 4 to 1 fan-in) Type2 1 board boards 12 x 48 Type Timing counters (160 PMT) Type2 2 boards 2 x 48 4 x 48 2 x 48  5 Hz in 2008 data taking

On-line E γ resolution σ = 3.8% 45 MeV threshold  from signal) 55 MeV γ -line from π 0 -decay

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

34 Liquid xenon: waveforms: 2 digitizers MHz 500 MHz or 2 GHz

35 4) 2008 run CW Calibration each three days during 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)

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

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

DCH resolutions from 2008 data Tracks with two turns in the spectrometer are used to detetrmine the Angular resolutions  =14 mrad   =10 mrad  = 25 mrad   = 18 mrad The edge of Michel positrons used to determine momentum resolution  core = 374 keV (60%)  tail1 = 1.06 MeV (33%)  tail2 = 2 MeV (7%)

Timing resolutions from 2008 data Intrinsic timing resolution by using positrons hitting several bars Photon - positron timing resolution by using Radiative muon decay: physical background Problems with DRS2 : will improve with DRS4  T  ps

Dedicated RMD runs at lower thresholds

Blind analysis: E  vs  t  e window

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

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

E  vs E e+

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

90% CL limit 90 % C.L. N Sig  14.6 corresponds to BR(  →e  )  3.0 x Computed sensitivityComputed sensitivity 1.3 x Statistical fluctuation 5%Statistical fluctuation 5% From side bands analysis we expected 0.9 (left) and 2.1 (right) x From side bands analysis we expected 0.9 (left) and 2.1 (right) x Bad luckBad luck

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 * for 2009 run Continue running in for the final ( ) goal More details at Planning R & D Assembly Data Taking now LoI Proposal

50 PP (Y. Kuno et al., MEG TN1, 1997 and references) Det. 2Det. 1 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  P  is less effective

51 DRS charge vs Trigger WFM Charge (TC)