Lepton Flavor Violation: present and future experiments - 1 LNF- May, 11ht 2008 F.Gatti University and INFN of Genoa
First experiment: E.P.Hincks and B. Pontecorvo (1948) At that time the motivation for a such searches was motivated by the general study of m decay Lead Degrader n e, n m and e spectrum not discoverd m was supposed to decay in e + n e (Yukawa) target PR 73 (1948)
History and future of FLV m decay searches MEG (2010) Cosmic m Mu2e PRIME stopped p m beams
background signal m e g accidental m e n n physical m e g n n m e g n n ee g g e + m + g (radiative decay) eZ eZ g n n e + m + g q e g = 180° n n e + m + E e = E g = 52.8 MeV T e = T g g
The last of a series Exp./Lab Year D E e /E D E g D t eg Dq eg Stop rate Duty BR /E g (ns) cyc.(% (s -1 ) (mrad (90% CL) e ) (%) (%) ) 197 5 x 10 5 3.6 x 10 -9 SIN 8.7 9.3 1.4 - 100 7 197 2 x 10 5 1 x 10 -9 TRIUMF 10 8.7 6.7 - 100 7 197 LANL 8.8 8 1.9 37 2.4 x 10 5 6.4 1.7 x 10 -10 9 198 4 x 10 5 4.9 x 10 -11 Crystal Box 8 8 1.3 87 (6..9) 6 199 2.5 x 10 8 1.2 x 10 -11 MEGA 1.2 4.5 1.6 17 (6..7) 9 201 0.1 MEG 0.8 4 19 2.5 x 10 7 100 1 x 10 -13 0 5
Conceptual design of MEG Liq. Xe Scintillation Liq. Xe Scintillation Detector Detector Thin Superconducting Coil g Stopping Target g Muon Beam + e + Timing Counter e Drift Chamber Drift Chamber 1m
Actual MEG configuration Liquid Xenon Calorimeter Drift Chambers Timing counters COBRA Magnet
PSI-beam The most powerful continuous machine in the world; Proton energy 590 MeV ; Power 1.1 MW ;n ominal operational current 2.0 mA. 27.7 MeV/c muons from p stop at rest ( surface muons ); Provides a DC beam of 10 8 m/s . Primary proton beam
PSI-Beam The beam elements: Wien filter for m /e separation Degrader to reduce the momentum stopping in a 150 m m CH2 target Transport Solenoid to couple beam with COBRA spectrometer R m (total) 1.3*108 m + /s R m (after W.filter & Coll.) 1.1*10 8 m + /s 6*10 7 m + /s R m (stop in target) s 10 mm Beam spot (target) m /e separation 7.5 s (12 cm) Maximum beam stop rate 10 8 m /s, • but we will use only 3 x 10 7 because of accidental background (proportional to (muon rate) 2 )
COnstant Bending RAdius- COBRA- magnet COBRA spectrometer was designed to provide a graded magnetic field whose flux lines have large divergence also in the center (1.27 T at the center and 0.49 T at both ends). Positrons with the same absolute momentum follow trajectories with a constant projected bending radius, independent on the emission angles over a wide angular range.
COBRA-magnet Constant bending radius independent of emission angles Gradient field Uniform field High p T positrons quickly swept out Gradient field Uniform field
Target and positron tracking
Positron Tracking Sixteen drift chambers (ten degrees interval), each one equipped with 18 staggered wires and cathodic kapton foils. Wires: r , f coordinates Cathode: z coordinate s (X,Y) ~ 200 m m Chamber gas: He-C 2 H 6 mixture Vernier pattern to measure z- position made of 15 m m kapton foils(charge division) s (Z) ~ 300 m m
Positron timing- Timing Counter APD Cooled Support TC Final Design APD F.E. Board Scintillating Fibers • A PLASTIC SUPPORT APD STRUCTURE ARRANGES THE SCINTILLATOR BARS AS REQUESTED PM • THE BARS ARE GLUED ONTOTHE SUPPORT • INTERFACE ELEMENTS ARE GLUED ONTO THE Ladder Board BARS AND SUPPORT THE FIBRES & cabling • FIBRES ARE GLUED AS WELL Main Support • TEMPORARY ALUMINIUM BEAMS ARE USED TO HANDLE THE DETECTOR DURING INSTALLATION BC404-Scintillator slab • PTFE SLIDERS WILL ENSUREA SMOOTH MOTION ALONG THE RAILS Scintillator Housing PM-Scintillator Coupling
Positron timing- Timing Counter Two layers of scintillation counters placed at right angles with each other. Outer layer: scintillator bars, mainly devoted to timing measurement. Two sections of 15 bars each, read by PMTs, before and after DCH system. Inner layer: scintillating fibres, devoted to provide trigger and z information. 5 x 5 mm2 fibres, read by APDs. Measurements of TC bars timing resolution in dedicated test beams at several positions and impact angles at BTF in Frascati
Limitations due to the B field PMT TTS, gain as a function of magnetic field and orientation angles Scintillation time, attenuation length, PMT-bar coupling Fine-mesh PMTs show good timing properties even in magnetic field up to 1 Tesla Gain behaviour is related to the orientation angle – best for q = 20-30° A high number of photoelectrons is necessary to be in a 100 ps resolution range 200 200 4.0 1100 photoelectrons 1100 photoelectrons q =0° 180 180 300 photoelectrons 300 photoelectrons 60 photoelectrons 60 photoelectrons q =20° 3.5 160 160 q =30° 3.0 140 140 time resolution 25 ps 120 120 2.5 s (ps) 100 100 2.0 80 80 1.5 60 60 1.0 40 40 0.5 20 20 Inner position PMT Outer position PMT 0 0 0.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 0 5 10 15 20 0 5 10 15 20 geometric angle (degrees) magnetic field (T)
B field and He atmosphere Optimization of angular position of PMs Protecting Bag with thin low diffusivity plastics (EVAL T) COBRA BORE 1 atm He4 N2Bag Gas Flushing
Experimental constraints: re- shaping the TC elements Scintillator Cross 5mm 5mm Section Sectional view PM active diameter: 39 mm PM outer Diameter :52 mm From 105 cm 25 cm COBRA center 8.5º 19º 22º 11º B 0.75 T B Long. view 1.05 T
Testing single element at Beam Test Facility (LNF) Apparatus for 2-axis + longitidinal Typical BTF beam performance sample movements
Single element timing resolution BC 404 110 2160 2180 2200 2220 2240 100 100 80 time resolution @ FWHM (ps) 90 90.0° 60 65.0° 80 53.5° 40 40.0° 70 79.1 ps @ FWHM 20 counts/6.33 ps 130 0 100 120 75 110 50 100 25 BC 408 108.3 ps @ FWHM 90 -40 -30 -20 -10 0 0 3345 3360 3375 3390 3405 3420 distance from the MCA channel number
Timing performance with some other ToF 1. B. Adeva et al. , Nucl. Instr. and s Scintil. PMT LxWxT Ref Meth A 491 (2002) 41. type (cm) (ps) . 2. G. Palla et al. , Nucl. Instr. and Meth. A 451 (2000) 406. BC420 R1828-01 40x7x2.2 123 1 3. V. Sum et al. , Nucl. Instr. and Meth. A 326 (1993) 489. BC408 R3478 12-48x1-1.25x1.5-2.4 80 2 4. M. Baldo-Ceolin et al., Nucl. Instr. and Meth. A 532 (2004) BC408 H1949 200x8.5x5 110 3 548. 5. Y. Kubota et al. , Nucl. Instr. BC408 XP2020 180-250x21x2.5 160 4 and Meth. A 320 (1992) 66. 6. M. Baldo Ceolin et al. , Nuovo BC408 XP2020 280x10x5 139 5 Cimento 105A (1992) 1679. 7. G.C. Bonazzola et al. , Nucl. NE110 † XP2020 210-300x21x2 300 6 Instr. and Meth. A 356 (1995) 270. NE110 † XP2020 300x9.3x4 170 7 8. S. Benerjee et al. , Nucl. Instr. and Meth. A 269 (1988) 121. BC408 XP2020 305x10x5 110 8 9. E.S. Smith et al. , Nucl. Instr. and Meth A 432 (1999) 265 NE Pilot F ‡ XP2020 317.5x15.6x5.1 170 9 10 J.S. Brown et al. , Nucl. Instr. and Meth. 221 (1984) 503. BC408 XP43132B/D1 32-450x15-22x5.1 163 10 BC404 R5924 80x4x4 40 our
Final detector, test at BTF (LNF) and run performance DTD Time resolution s = 52 ps (with low z-cuts) Run Conditions
APD readout of scintillating fibers detectors New solution with APD and scintillating fibers: 1. High QE of APD 2. Good performances, not influenced by magnetic field 3. Optimum matching APD-fiber 4. Better spatial resolution (5mm) 5. Lower cost per channel (total 512 channels) 6. Fast - Low noise electronics for analog signals (ENC = 1500e) custom made 7. Digital output with hitmap encoding R1 10 0k R8 33 0 V3 400 V2 5 R2 10 0k R5 33 0 R7 13k T1 2N3955 C1 10n C2 80 p - R3 10 C3 10 0p IG1 - VF3 + + R4 10 DIS T2 2N3955 + 145000 e- + DIS 1ns U2 OPA847 U1 OPA847 2 x MMBF4392 V1 5 2 x OPA847 R6 100k C4 1p ----- V4 5 DIS
Avalanche Photo-Diodes (APD) Dark noise Total noise of illuminated APD including Shot niose, excess noise, photon noise Excess noise factor at M=500 x= 0.5
APDs production I dark vs H.V. Temperature 20°C 1.00E+01 APDJA0304_20ID_M APDJA0316_20ID_M APDJA0305_20ID_M I=50 nA APDJA0288_20ID_M APDJA0296_20ID_M APDJA0302_20ID_M 1.00E+00 APDJA0307_20ID_M I dark@ 10Mohm (Volts) APDJA0312_20ID_M I dark vs H.V. Temperature 20°C APDJA0308_20ID_M Selected samples APDJA0309_20ID_M 1.00E+01 APDJA0311_20ID_M 1.00E-01 from Hamamatsu Irradiatted samples of CMS APDJA0295_20ID_M APDJA0289_20ID_M APDJa0290_20ID_M APDJA0292_20ID_M APDJA0294_20ID_M 1.00E-02 1.00E+00 APDJA0307_20ID_M I Dark @ 10Mohm (Volts) 1.00E-03 2.50E+02 3.00E+02 3.50E+02 4.00E+02 4.50E+02 5.00E+02 1.00E-01 H.V. (Volts) 1.00E-02 MEG APD s 1.00E-03 2.50E+02 3.00E+02 3.50E+02 4.00E+02 4.50E+02 5.00E+02 H.V. (Volts)
Fiber detector under run consitions 8 Channels analog sum 8 Channels 8 Channels analog sum analog sum Signal of 8+8 Interleaved fibers
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