Present Status of the DCBA Experiment H. Iwase (KEK) on behalf of - PowerPoint PPT Presentation

"Double Beta Decay and Neutrinos" (DBD11), Osaka Japan Present Status of the DCBA Experiment H. Iwase (KEK) on behalf of the DCBA collaboration 1

Double beta decay experiments Scintillation/Cal n/Calorimetry (source = dete = detector) ionization scintillation bolometry COBRA ( 130 Te, 116 Cd, etc.) CANDLES( 48 Ca) CUORE( 130 Te) Majorana( 76 Ge) XMASS( 136 Xe) GERDA( 76 Ge) GERDA( 76 Ge) KamLAND-Zen( 136 Xe) KamLAND-Zen( 136 Xe) ionization+scintillation SNO+( 150 Nd) EXO( 136 Xe) Combination (source ≠ detector) Tracking (source ≠ detector) NEMO3 ( 100 Mo, 82 Se, 150 Nd, etc.) DCBA ( 100 Mo, 150 Nd, etc.) Super NEMO ( 100 Mo, 82 Se, 150 Nd, etc.) 2

DCBA method X-Y surface y anode cathod anode cathod x pickup → circle y → B → y-z 投影 pickup Y-Z surface cosine curve p (MeV/c) momentum, T (MeV) k. energy, r (cm) radius, m e (MeV/c 2 ) rest mass of e - B (kG) magnetic flux density, λ pitch angle 3

DCBA experiment • charge dividing 2005 DCBA • 6 mm pitch wires (xy + xz) 2007 DCBA-T2 • 100 Mo source (natural Mo 30g) • 0.6 - 0.8 kG magnetic field • conducting magnet: 9h/day (Mo. - Fr.) 2011 present DCBA-T2.5 24h operation DCBA-T3 • 6 mm pitch wires (xy + xz) • 100 Mo source (natural Mo 30g) • 0.8 kG magnetic field • super-conducting magnet : 24h nonstop operation 2013 DCBA-T3 higher resolution • 3 mm pitch wires (xy + xz)x6 • 150 Nd (natural Nd 2 O 3 ) • maximum 3 kG 2017 MTD higher event rates DCBA-T2-detector (tentative name) • 150 Nd (condensed, several 10 kg) in T3 (=T2.5) 4 5

DCBA T-2 results 5

Energy resolution of DCBA T-2 Energy spectra of internal conversion electrons 0.48 (1.5%), 0.56 (0.6%), 0.98 (7.0%) and 1.05 MeV (2.4%) from 207 Bi MC Measurement chamber conditions - He (90%) + CO 2 (10%) 1 atm - B = 0.8 kG - wire pitch = 6 mm 6

214 Po half-life measurement by T-2 214 Bi β -decay → 214 Po α -decay detection and the 214 Po half-life 214 Bi β -decay 214 Po α -decay e - e - vertex point vertex point 214 Po 半減期評価 214 Po half-life T 1/2 = 144 ± 46 μ s (ref. 164.3 μ s) 7

DCBA T-2 result 8

DCBA T-3 9

Super conducting magnet for T-3 - coolant-less - GM refrigerator for DCBA T-3 - B = 0.2 T ± 0.5% ( Δ E ~ 80 keV ) - φ 600mm x L600mm 10

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Magnetic field uniformity of DCBA-T3 center 2000 G 12

DCBA T-2.5 DCBA-T2 T3 superconducting magnet 13

present result of DCBA T-2.5 14

DCBA T-2.5 events 15

against noise events > additional veto counter whole veto counter inside the magnet > move to underground 16

recent DCBA time table & ββ events × ββ event × ββ event (not included in analysed not analysed 24 the final graph) × 18 × × × × hour × 12 6 β 1 = 0.82 MeV β 2 = 0.67 MeV × × × 0 2011/07/02 2011/08/01 2011/08/31 2011/09/30 2011/10/30 day 17

DCBA data analysis - raw data X-Y surface X-Z surface 18

DCBA data analysis 19

DCBA data analysis 20

DCBA (T-2 + T-2.5) 100 Mo ββ results β 1 + β 2 single β 21

MTD - the next DCBA 27 source plates 22

Summary • DCBA ββ -decay data taking was started by T-2 • 21 2 νββ candidate events found by T-2 • DCBA-T3 super conducting magnet was finished • T-2 chamber in T-3 s.c. magnet (T-2.5) is in operation • 24h data taking • T-3 is under development for higher energy resolution and source amount 23

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recent DCBA time table & ββ events × ββ event analyzed not analyzed 24 × β 1 = 1.07 MeV β 2 = 0.50 MeV 18 × β 1 = 0.45 MeV β 2 = 0.43 MeV hour 12 6 β 1 = 0.82 MeV β 2 = 0.67 MeV × 0 7/2 7/5 7/8 7/11 7/14 7/17 7/20 7/23 7/26 7/29 8/1 8/4 8/7 8/10 8/13 8/16 day 1week 25