D. Frekers. Putting together the pieces of the puzzle in bb-decay n. TRIUMF May Gentle Touch: q tr = 0 l = 0.

Transcription

1 D. Frekers Putting together the pieces of the puzzle in bb-decay n b TRIUMF May-2016 n b GT? Gentle Touch: q tr = 0 l = 0 dσ dσ hω excitation σ n n

2 The pieces of the puzzle Chargex-reactions ( 3 He,t) & (d, 2 He) 2nbb nuclear matrix elements Q: is it relevant for 0nbb decay? A: yes! (i.e. nucl. shape) Chargex-reactions 0nbb nuclear matrix element Q: is it possible? A: yes! (NME s & 2 - states, occupation # s) Mass measurements 0nbb nuclear matrix element Q: what is the connection? A: 96 Zr is a golden case 96 Zr (b ) 96 Nb, and g A 4u (PRL116, Feb-2016)

3 Nucl.MatrixElements 2nb b decay q-transfer like in ordinary β-decay (q ~ 0.01 fm -1 ~ 2 MeV/c) i.e. only allowed transitions possible

4 4 2 2 C GF ga ( 2 ) 2 ( ) 7 C DGT ( ) 8 G 2 2 (Q,Z)! cos( ) M f( Q ) M ( 2 ) DGT 2 Q 11 Z 2 exp 10 3 MeV extracted from half-life -2 favorable: 1. high Q-value 2. large Z unfavorable (but cannot be changed): 1. large neutron excess (Pauli-blocking) p n p n

5 M ( 2 ) DGT (f) (i) 0g.s k k k m m k k k g.s. 1 (f) m 2 Q (0 g.s.) E(1 m ) E0 m m + - m M GT M GT E m to remember: 1. 2 sequential & allowed b -decays of Gamow-Teller type 2. 1, 2, 3,... forbidden decays negligible 3. Fermi transitions do no contribute (because of different isospin-multiplets) Can be determined via chargeexchange reactions in the (n,p) and (p,n) direction ( e.g. (d, 2 He) or ( 3 He,t) )

6 Nucl.MatrixElements 0nb b decay neutrino is a virtual particle q~0.5fm -1 (~ 100 MeV/c) (due to Heisenberg q x~ 1 ) degree of forbiddenness is lifted

7 !! (Q,Z) ( ) A 2 ( 0 ) gv ( 0 ) DGT DF ga G g M M m 2 e 2 Q 5 Z 4 10!! to remember: 1. higher-fold forbidden transitions possible 2. Fermi transitions important 3. Pauli-blocking largely lifted 4. large Q-value, high Z important NOT (easily) accessible via charge-exchange reactions theory largely independent of (A,Z) (except near magic nuclei) mass of Majorana-n!

8 1 st piece of puzzle

9 GT + GT - (n,p) type (p,n) type - Q: what is the connection between weak st operator and the hadronic reaction A: dominance of the Vst effective interaction at medium energies (n,p), q 0!!

10 GT + GT - (n,p) type (p,n) type - (n,p), q 0!!

11 Charge-exchange reactions DE/E ~ 5 x10-5 ~ 25 kev at 420 MeV ( 3 He)

12

13 76 Ge N-Z=10 Resolution is the key!!!

14 almost 70!! resolved single states up to 5 MeV identified as GT 1+ transitions!!!

15 ~ 70!! single states up to 5 MeV!!!???? anti-correlation???? the other leg (BGT + ): 76 Se(d, 2 He) 76 As MeV (DE = 120 kev) is the anti-correlation a property of deformation?? 76Ge moderately oblate/ prolate (b 2 ~ 0.1) 76Se oblate (b 2 ~ 0.2)

16 Nuclear matrix elements and deformation 76 Ge: b ~ Se : b ~ 0.2 reduction of the NME due to deformation is theoretically confirmed but expm lly it seems to manifests itself (in 2nbb decay) by a lack of correlation between the two different B(GT) legs, rather than a reduction of individual strength From: T. R. Rodriguez, et al, PRL105 (2010)

17 another surprise: low-e part of NME makes up ~100% of total 2nbb-ME no need for GT giant resonance contribution

18 100 Mo N-Z=16 also useful as SN neutrino detector (sensitive to n temperature in SN)

19 HERE: almost the entire low-e GT strength is concentrated in the g.s. 100 Mo entire low-energy GT strength is concentrated in a SINGLE STATE and with b logft known M n (g.s.) M (total) 2n 2 DGT DGT No need for GT giant resonance

20 136 Xe N-Z=28 question: why so stable!!!

21 136Xe

22 What s the size of the NME? T yr ( 2 ) -1 DGT MeV M. all signs positive > B GT 10 B m 2 m GT Bm GT 10!!!! 3

23 A. Poves (simultaneous to our publication): NO CANCELLATION!! there is no B(GT + ) strength, except for lowest 1 + state Recall: 136 Xe is almost doubly magic!! 3x10-3 Shell model provides conclusive explanation for the deemed pathologically long half-life of 136 Xe. Expt l test: 136 Ba(d, 2 He) 136 Cs

24 136 Xe b b 136 Ba expmt: question: 2nbb NME is exceptionally small how does the ME scale in the case of 0nbb decay? could it be that: 2nbb ME is suppressed AND 0nbb ME is enhanced???

25 2 nd piece of puzzle Charge-exchange reaction towards the 0nbb NMEs??? Here: 2 - states and occupation vacancy numbers via chargex reactions

26 40.0 Decomposition of M GT Xe g pp = 0.89 g pp = 0.96 g pp = 1.00 g pp = ! 100 Mo Theory: The 2 strength makes up relative 2 strength to ~ 5 MeV ~ 20-30% of the 0nbb ME!! Expmt: J. Suhonen, Phys. Lett B607, 87 (2005) 136Xe exhibits largest 2 strength 0nbb ME enhanced?!?!

27 Poves (Poves)

28

29 3 rd piece of puzzle The A=96 system and the 0n/2n bb NMEs

30 Single b & bb decay in 96 Zr NEMO-3: geo-chem: two conflicting half-lives: 2 19 T nbb 1/2 ( ) 10 y 19 T ( ) 10 y 1/2 Q: can this difference be reconciled? A: yes, if single b competes with bb decay 2nbb b T1/2 T1/2 T1/ expected 1/2 experiment T b 1/2 19 pred. (QRPA) T b y T b y 1/ y ( ) ( ) b u T Q M 2 1/2 0 b b T1/2 162(4) kev fold non-unique (unobservably long) fold unique (possible) fold non-unique (no phase space) T 1/2 =23h 2 T nbb 5 + 1/2 Q bb =3356 kev h h Q-value u M 4 0nbb 1 5 0n 2 2 ( T Q M m b 1/2 ) bb bb Wieser, PRC64,2001, Barabash, JPG-NPP22, 1996 Heiskanen, JPG3,

31 Suhonen PLB Idea (i) measure Q-value for 96 Zr 96 Nb single b-decay by precision mass measurement and (ii) measure the single b-decay rate (iii) ft-value determine the 96 Zr 4-fold forbidden b-decay NME and confront with theory natural p unnatural p confront with same theories aimed at calculating 0nbb-decay NME for the same nucleus!!

32 7-T magnet TOF ms Eronen PhD Thesis 2008 IGISOL/JYFLTRAP mass measm nts HELIUM FLOW CYCLOTRON BEAM target A FC +HV B 57% enriched 96 Zr performing accurate mass measurements via cyclotron frequency Si C FC FC+MCP+Si dipole magnet n c 1 2p q m B n +HV D n n n c RFQ cooler/buncher frequency determination n } } FC E F purification trap done by TOF-ICR technique precision trap G H FC+MCP+Si MCP detector n rf n /Hz c 33

33 7-T magnet end cap z 0 ion motion in a Penning Trap a superposition of 3 harmonic motions: 1) axial motion (n z ) 2) magnetron motion (n ) 3) reduced cyclotron motion (n + ) r0 +HV HELIUM FLOW A ring electrode CYCLOTRON BEAM FC n typical freq s: n 1 khz, n + 1 MHz cycl. freq.: n c = n + n + B n Si C FC FC+MCP+Si principle of isobar separation in purification trap +HV D G } } FC purification trap E F precision trap FC+MCP+Si RFQ cooler/buncher MCP detector excitation of ion of interest with cyc. freq. causes collisional cooling of this species (purification: > 500/1 ) H

34 Results Q bb kev 7.1 kev higher than AME2012 Q b kev

35 Next: need T 1/2 of single b decay 19 T1/2 (QRPA) yr ( g A 1) T1/2 (SM) 10 yr (g ) 2 A g A T 19 1/2 (exp) yr Important side effect: single b decay depends on 2n/0nbb decay depends on 2 g A4 g A A measurements of single b decay would give for the first time an expmtl handle on the 36 quenching of the axial vector coupling constant

36 T 1/2 of 96 Zr decay Geochemical method (zircon sample) accumulation of decay daughter over geological time Pros: can provide longer T 1/2 Cons: - measure only total decay - systematics from 95 Mo (n,g) reaction n-sources: 238 U sf, cosmics BUT: zircon contains Gd (i.e. 157 Gd(n,g)) - needs chemical isobar separation (A=96) age of sample: origin: advantage: 1.822(±0.003) 10 9 y dated by U-Pb technique Capel Australia Mo is embedded in zircon attice with infinite retention time geo. T 1/2 calculation # of 96 Mo excess atoms in sample # of 96 Zr atoms in sample age of the sample Counting-rates method measures the decay rate Pros: measure partial decays Cons: - extremely low counting rates - background and time limited T 1/2 =23h h h 7

37 Isobar separation method (U of Calgary) 10 ml Zr silicate mg + + HF acid 48% 250 C & 3200 kpa dissolved Zr Zr & Mo ion-exchange chemistry re-dissolved in acid with 4 M HCl ZrCl 4 separate Zr from Mo D 96 Mo/ 95 Mo)=0.01% Zr purified Mo>10 ng plasma mass spectrometer measurable limit b T 1/2 < y ~ 8

38 These and more pieces to the puzzle chargex-reactions for 2nbb decay Hadronic chargex and weak-interaction x-sections are fortuitously connected -- exploit this!! 0nbb-decay and chargex-reaction useful but limited e.g. 2 states (resol n is key) mass measurements for bb-decay NME the potential still needs to be exploited single b decay half-life for 96 Zr (and 48 Ca) ground-state properties of intermediate odd-odd nuclei (TRIUMF, TITAN-EC) need to address quenching issue urgently!! need relevant spectroscopic information (but theory needs to tell what is relevant) theory needs to converge!!