nasim fatemi-ghomi

1 Nasim Fatemi-Ghomi, Manchester meeting 16 -18 July 2007

Nasim Fatemi-Ghomi

Update on 150Nd double beta decay results


Introduction

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

• Selection of the 2e events from Selection of the 2e events from 150150Nd foil• List of the backgrounds to List of the backgrounds to of of 150150NdNd• Extraction of half-life of 2Extraction of half-life of 2 for phaseI, phaseII and for phaseI, phaseII and

combined datacombined data• Systematic uncertainty of the half-life Systematic uncertainty of the half-life • Preliminary results of setting limits on half-lives of differentPreliminary results of setting limits on half-lives of different neutrinoless modesneutrinoless modes• Summary and future workSummary and future work


Pre-selection for Pre-selection for 150150Nd to 2Nd to 2 events: 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


NdNd22OO33 shifting problem shifting problem

Vertex position of the Vertex position of the selected MC events ofselected MC events of150150Nd, and its Nd, and its contaminants contaminants were shifted by 3.8 mm were shifted by 3.8 mm (2bin) to the left (as a (2bin) to the left (as a temporary solution)temporary solution)

Data seem to be Data seem to be shifted to the leftshifted to the left


Hot-spots in Hot-spots in 150150Nd foilNd foil

Hot-spots are observed by looking at the vertex Hot-spots are observed by looking at the vertex distribution of edistribution of e and 1e channel and 1e channel

The hot-spot regions are removed from The hot-spot regions are removed from analysis. analysis.

1e channel1e channel ee channel channel


Bg Act(mBq/kg) Number of

background events

Found from 1e channel

(see my technical note)

210Bi 177 29

40K 351.6 129

234mPa 49.8 176

Found from eChannel

207Bi 186 134

208Tl 7.95 42

228Ac 22.1 48

212Bi 22.1 29

152Eu 0.0521 17

From Vera’s Rn draft 214Bi 3.28 15

Summary table of the internal backgroundSummary table of the internal backgroundfor the combined (phaseI + phase2) datafor the combined (phaseI + phase2) data


External Background &External Background & Background on the SurfaceBackground on the Surface of the Wires and Foilsof the Wires and Foils

Bg Act(Bq) Number of background

SW 214Bi 0.690(phaseI), 0.123(phaseII)

20

SW 214Pb 0.690 (phaseI),

0.123 (phaseII)

11

Bg Act(Bg) Number of background

PM 214Bi 374 5

PM 214Pb 374 0

PM 228Ac 515 0

PM 60Co 50.7 2

PM208Tl 41.0 0

PM 40K 954 0

Air 214Pb 702 0

Air 214Bi 702 3

FromFromVladimir’sVladimir’smodelmodel

Vera’sVera’s draftdraft


Half-life resultsHalf-life results

PhaseI:PhaseI:Time= 404.079 daysTime= 404.079 daysefficiency= 0.0752efficiency= 0.0752Nexp= 1252Nexp= 1252Nbgr= 362Nbgr= 362

T12= 9.62 -0.36+0.4(stat) x 1018 y


PhaseII:PhaseII:Time=538.829 daysTime=538.829 daysefficiency=0.0729efficiency=0.0729Nexp=1575Nexp=1575Nbgr=431Nbgr=431

T12= 9.60 -0.32+0.35(stat) x 1018 y


Combined:Combined:Time=938.907 daysTime=938.907 days efficiency=0.0738efficiency=0.0738Nexp=2825Nexp=2825Nbgr=794Nbgr=794

T12= 9.613-0.24+0.26(stat) x 1018 y


Systematic uncertainty (so far)Systematic uncertainty (so far)

Origin of uncertainty Method of measurement Percentage

Internal TOF hypothesesHalf-life for internal TOF probability > 0.01 and >

0.04 0.8%

Geometry of the foilHalf-life before and after

shifting the MCs2%

Tracking efficiencyTaken from the collaboration

5.0%

235U daughter isotope activities Half-life in case of 211Pb

and 207Tl 01%

All other backgroundUncertainty in the

activities2.4%


Other sources of systematic uncertaintyOther sources of systematic uncertainty

Type of uncertainty Method of measurement Percentage

Efficiency of Energy calibration

From 100Mo excited paper 2%(?)

Simulation of energy losses inside the foil

? ?

Dead time ? ?

GEANT simulation ? 5%(?)

Others ? ?


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


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

Mode Limit (y) efficiency data

Mass mechanism

1.59 x 1022

(90% CL)0.19 0

Majoron M11.62 x 1021

(90% CL)0.14 0


(90% CL)0.13 0


(90 % CL)0.11 0

Majoron M7 ? 0.053 0


SummarySummary

• PhaseI and PhaseII data were combined and the half-life of 2PhaseI and PhaseII data were combined and the half-life of 2 was was measured for the combined data. measured for the combined data.

• Preliminary limits on different possible neutrino modes were presented. Preliminary limits on different possible neutrino modes were presented.

Future workFuture work • More accurate measurement of systematic uncertainty has to be doneMore accurate measurement of systematic uncertainty has to be done• The limits on different neutrino modes were presented without The limits on different neutrino modes were presented without

implementing the systematic uncertainty of the 2implementing the systematic uncertainty of the 2 half-life. This half-life. This needs to be doneneeds to be done


Background from neighboring isotopes Background from neighboring isotopes

Bg Act(Bq) Number of background

Composite 100Mo 0.082 96

96Zr 7.25 x 10-5 2

48Ca 4.28 x 10-5 1

90Y 0.0339 15


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

Mode Limit efficiency data

Mass mechanism

1.94 x 1021

(90% CL)0.11 0


(90% CL)0.069 0


(90% CL)0.069 0

Majoron M3 2.79 x 1020 0.014 0

Majoron M7 5.76 x 1018 0.0003 0

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