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Nasim Fatemi-Ghomi

Double Beta Decay Study of 150 Nd. Nasim Fatemi-Ghomi. Introduction. Data Selection. Data taking time =422.665 days = 1.16 yr - 348.036 days=0.95 yr (status=1) Dubna-2006 - 74.629 days=0.21 yr (status!=1)

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Nasim Fatemi-Ghomi

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  1. Double Beta Decay Study of 150Nd Nasim Fatemi-Ghomi

  2. Introduction Data Selection • Data taking time =422.665 days = 1.16 yr • - 348.036 days=0.95 yr (status=1) Dubna-2006 • - 74.629 days=0.21 yr (status!=1) • Events should come from Nd2O3. The foil has 57g mass (37g pure 150Nd). Analysis tool Used UCL OO framework written by V.Vasiliev.

  3. External Background & Background on the Surface of the Wires and Foils. Internal Background Found by V.Vasilev checked with Cu foil

  4. Pre-selection for 150Nd to 2 events: • Two negatively charged tracks associated with isolated PMTs and • E1 ,E2 > 0.2 MeV. • Both electrons originate from a common vertex • with |∆r| < 2 cm & |∆z| < 4 cm. • Internal TOF hypothesis > 4% & external TOF hypothesis < 1%. • Track starts from layers 1 & 2 of GG. • No delayed alpha decay with refiring time > 70 s. • No single or group delayed hit(s).

  5. 150Nd Half-life (with Status ==1) 1.11e-19 0.030 0.01988 9.22e-4

  6. 150Nd Half-life (status !=1) • Problems with PMs during runs (status 2 &10). 83 events • Problems with Geigers during run (status 3 &100). 12 events • Less than ~24 hours after absolute calibration (status 4 & 1000). 27 events • Less than ~24 hours after general HV shutdown (status 5 &10000) / less than ~24 hours after HV shutdown of 1HV board (status 20000). 51 events • Problems with ventilation, high radon rate (status 6&100000). 15 events • No laser run for day correction (status 1000000) 28 events

  7. Combined good and bad runs

  8. Half-life result for good and bad data. Good data: Number of data events: 1055 Number of total background: 315 Efficiency: 6.75% T12= 9.23 -0.40+0.43(stat)  0.82(syst) x 1018 y Bad data: Number of data events: 216 Number of total background: 78 Efficiency: 6.70% T12= 10.5 -1.0+1.3(stat)  0.96(syst) x 1018 y The results are consistent  Can combine the data

  9. Half-life result for the combined data Number of data events: 1271 Number of total background: 412 Efficiency 6.74% T12= 9.46 -0.37+0.41(stat)  0.85(syst) x 1018 y

  10. Preliminary 0 result using MCLIMIT Number of generated 0 = 50000 Number of accepted events = 3943 Using 1-dim histogram: Esum for all energy regions (E1+E2>0.4 MeV) Limit on half-life with 90% CL: T120 >2.73 x 1020 y

  11. Summary • Half-life was extracted for good data and bad data separately and the result for the half-life was consistent. • The half-life was extracted for the combined data. • Avery preliminary result on limit on T120 was presented. • Have to start working with Phase II Data!! • + • The first draft of a technical note on 150Nd2 (phaseI) analysis is written!

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