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Nasim Fatemi-Ghomi

Update on 150 Nd double beta decay results. Nasim Fatemi-Ghomi. Introduction. Selection of the 2e events from 150 Nd foil List of the backgrounds to  of 150 Nd Extraction of half-life of 2  for phaseI, phaseII and combined data Systematic uncertainty of the half-life

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Nasim Fatemi-Ghomi

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  1. Update on 150Nd double beta decay results Nasim Fatemi-Ghomi

  2. Introduction • Selection of the 2e events from 150Ndfoil • List of the backgrounds to  of 150Nd • Extraction of half-life of 2 for phaseI, phaseII and combined data • Systematic uncertainty of the half-life • Preliminary results of setting limits on half-lives of different neutrinoless modes • Summary and future work Data Selection • The standard runs with LTC is analysed • Phase I : run number 1869 - run number 3395 (404.079 days) • Phase II: run number 3396 - run number 5468 (534.829 days) • Events should come from Nd2O3

  3. Pre-selection for 150Nd to 2 events: • Two reconstructed tracks, each track: • - has negative curvature • - is associated with one isolated PMT with energy > 0.2 MeV • - hits face of the scintilator • - has a Geiger cell hit in one of the two closest to the foil Geiger layers • Both electrons originate from a common vertex with |∆r| < 2 cm & |∆z| < 4 cm • Event vertex located inside source foil • There are less than 3 fast Geiger hits (not associated with any track) with distance to event vertex in XY plane < 15 cm • If both tracks belong to one part of the tracker (inner or outer), • there is no fast Geiger hits on the other part with distance to event • vertex in XY plane <15cm • Internal TOF hypothesis > 4% & external TOF hypothesis < 1% • Sum of electron track lengths > 60 cm

  4. Nd2O3 shifting problem Data seem to be shifted to the left Vertex position of the selected MC events of 150Nd, and its contaminants were shifted by 3.8 mm (2bin) to the left (as a temporary solution)

  5. Hot-spots in 150Nd foil Hot-spots are observed by looking at the vertex distribution of e and 1e channel e channel 1e channel The hot-spot regions are removed from  analysis.

  6. Summary table of the internal background for the combined (phaseI + phase2) data

  7. External Background & Background on the Surface of the Wires and Foils Vera’s draft From Vladimir’s model

  8. Half-life results PhaseI: Time= 404.079 days efficiency= 0.0752 Nexp= 1252 Nbgr= 362 T12= 9.62 -0.36+0.4(stat) x 1018 y

  9. PhaseII: Time=538.829 days efficiency=0.0729 Nexp=1575 Nbgr=431 T12= 9.60 -0.32+0.35(stat) x 1018 y

  10. Combined: Time=938.907 days efficiency=0.0738 Nexp=2825 Nbgr=794 T12= 9.613-0.24+0.26(stat) x 1018 y

  11. Systematic uncertainty (so far)

  12. Other sources of systematic uncertainty

  13. T12= 9.61 -0.24+0.26(stat) ± 0.78 (syst) year

  14. Limit on half-lives of different Neutrinoless modes using MCLimit

  15. Summary • PhaseI and PhaseII data were combined and the half-life of 2 was measured for the combined data. • Preliminary limits on different possible neutrino modes were presented. • Future work • More accurate measurement of systematic uncertainty has to be done • The limits on different neutrino modes were presented without implementing the systematic uncertainty of the 2 half-life. This needs to be done

  16. Background from neighboring isotopes

  17. Limit on different neutrino modes using Helen formula (Energy window 2.310 -3.192 MeV)

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