the role of atom and ion traps

Transcription

1 Beyond Standard Model physics with nuclei V ud from mirror transitions and the role of atom and ion traps Oscar Naviliat-Cuncic LPC-Caen, ENSI CNRS/IN2P3 and Université de Caen Basse-Normandie Caen, France

2 Outline 1. Context - Quark mixing, CKM unitarity 2. Determinations of V ud - Super-allowed pure Fermi transitions - Neutron decay - Pion beta decay - Mirror transitions in nuclei 3. The role of atom and ion traps - Correlation measurements in beta decay 2

3 1. Context 3

4 1.1 Weak universality and quark mixing The strength of the weak interaction ν e e ν e e ν e e g W W W µ g ν µ d u d u u d s u d u u d Pure leptonic n Semi-leptonic (non strange) p Semi-leptonic (strange) Quark mixing with 2 generations one parameter: θ C (Cabibbo angle) Λ p G µ = G F g 2 G β = G F cosθ C G Λ = G F sinθ C 4

5 1.2 Quark mixing and CKM unitarity Quark mixing with 3 generations : Cabibbo-Kobayashi-Maskawa matrix Weak states Mass states (definite flavor) & d' # & d # $! $! 1,0 $ s'! = VCKM $ s! 0,8 $! $! 0,6 % b' " % b " & V V V # $ ud us ub 0,4! V CKM = 0,2 $ V cd V cs V cb! $! 0,0 % V td V ts V tb " Flavor (mass) content of weak states down' strange' bottom' bottom strange down Within the SM, the CKM matrix is unitary From 1st raw: The most stringent unitarity test Deviations from unitarity provide signatures of physics beyond SM 5

6 1.3 CKM unitarity and V ud The V ud element dominates the most stringent test of CKM unitarity. Is obtained by comparing the Vector weak coupling (from semi-leptonic processes involving the lightest quarks) with the Fermi coupling (from muon decay). V ud = G V /G F Three sources considered so far to determine V ud from experiments: - Nuclear super-allowed pure Fermi ( ) transitions (Vector) - Neutron decay (Vector and Axial) - Pion beta decay (Vector) # n " p + e +! " # " + e +! e e 6

7 2. Determinations of V ud 7

8 2.1 Super-allowed pure Fermi transitions Isobaric analogue transitions 0 + Br 0 + T 1/2 Q EC Ft " 1! G 2 V 2 F ud Corrected decay rates Measurements - half-lives - branching ratios - masses Theory - isospin corrections - radiative corrections Is the strength of the vector coupling the same in all transitions? [J.C. Hardy and I.S. Towner arxiv:nucl-ex/ ] Test of the Conserved Vector Current (CVC) hypothesis at the level V ud = (22) Contributions to EuNPC-DPG HK A. Jokinen (Tu) 8

9 2.2 Neutron decay # Neutron lifetime " 1 n! G 2 F V 2 ud ( Beta asymmetry A! g " / A g V g 2 V + 3g 2 A ) (No nuclear structure, no branching to measure but ) since the Axial current is NOT conserved, it is necessary to measure another decay property (correlation) to deduce the Vector coupling. (Particle Data Group 2008) τ n g A /g V g A transitions Beta asymmetry V ud = (19) g V Neutron lifetime Contributions to EuNPC-DPG HK R. Picker et al. (Mo) C. Tietze et al. (Mo) M. Simson et al. (Th) 9

10 2.3 Pion beta decay " # " + e +! e PIBETA@PSI Pi-beta decay rate " 1 % #$! G 2 V 2 F ud Measurements - half-life - branching ratio!!! masses Reconstruction of π 0 mass [D. Pocanic et al., PRL 93 (2008) ] V ud = (30) 10

11 2.4 Nuclear mirror transitions (T=1/2) Consider nuclear mirror transitions within T=1/2 isospin doublets There are 35 candidates between 3 H and 83 Mo, near N=Z They are driven by the Vector and Axial interactions (like neutron decay) Correlation measurements have been carried out in: 17 F, 19 Ne, 21 Na, 29 P, 35 Ar and 37 K Mixing ratio:! = C A M GT / C V M F J p e A " #! J p v pe Beta asymmetry Neutrino asymmetry βν angular correlation B " #! a "# $! p v 11

12 2.5 New test of CVC and new value of V ud Is the strength of the vector coupling the same in all T=1/2 transitions? (O. N-C and N. Severijns, to appear in Phys. Rev. Lett. 2009) Ft 0 = 2Ft( ) 21 Na 37 K 29 P 19 Ne 35 Ar First consistent test of CVC from a set of nuclear transitions other than super-allowed pure Fermi New value of V ud V ud = (17) pion Not a revolution but remarkable! neutron mirrors 12

13 2.6 Error budget and outlook Contributions to the relative error on V ud 6 Relative error (%) Ft-value GT/F mixing ratio fa/fv ratio Mass number A Errors are dominated by those on GT/F mixing ratio, ρ Correlation measurements with improved precision are required. 13

14 3. Atom and ion traps 14

15 3.1 Traps for correlation measurements Offer an ideal (matter free) environment - small sample size - atoms/ions at very low energies - enable detection of recoiling ions following beta-decay - reduce effects of electron scattering in matter MOTs are mainly limited to alkalis (e.g. present efficiencies of MOTs for radioactive He elements are still too low for competitive decay correlation measurements) Experimental developments were motivated so far by searches for exotic (Scalar or Tensor) contributions to the weak interaction but can also provide inputs to determine GT/F mixing ratios. 15

16 3.2 Trap 1: TRINAT, K MOT at TRIUMF Pioneering work on K atom trapping Measured the βν angular correlation in 38m K Extended setup to polarize 37 K Measurement of the neutrino asymmetry [D.Melconian et al., PLB 649 (2007) 370] B ν = 0.755(24) (value included in our set BUT ) The neutrino asymmetry is not very sensitive to ρ. A measurement of the βν angular correlation with a precision of 0.5% (like in 38m K) would provide a huge improvement to determine ρ. 16

17 3.3 Trap 2: Na MOT at Berkeley Measurement of the βν angular correlation [P.A.Vetter et al., PRC 77 (2008) ] a βν = (60) Solved standing puzzle since 2003 (molecular recoil scattering) Result consistent with SM; interpreted in terms of exotic (S, T) couplings. (value included in our set) Can likely be improved to the 0.1% level!!! 17

18 3.4 Trap 3: LPC-Caen Paul trap at GANIL ideal 3D Paul trap First transparent prototype Fully transparent trap (rings) U RF hat ring RFQ cooler buncher 18

19 3.5 LPCTrap status GOAL: Measure the βν angular correlation in 6 He decay with (Δa/a) stat < 0.5% Proof of principle demonstrated [X. Fléchard et al., PRL101 (2008) ] All position sensitive detectors; complete kinematics neutrino mass TOF 3rd shot (2008): collected (for stat) and (for sys studies) events. Statistical precision reached, analysis under way. 19

20 3.6 LPCTrap outlook In contrast to MOTs, ion traps are not limited to an element. Cooling and trapping of 19 Ne or 35 Ar (mirror candidates abundantly produced at SPIRAL) is easier than for 6 He 20

21 3.7 Trap 4: WITCH Penning trap at ISOLDE K.U.Leuven, Uni. Munster, ISOLDE, GSI, NPI Rez-Prague (N.Severijns et al.) Detect recoiling ions in singles for βν angular correlation Select ion energies sequentially: retardation potential First recoil ion spectrum 124 Sn recoils Preliminary 35 Ar considered as candidate but can also trap 19 Ne Retardation potential (V) Contributions to EuNPC-DPG HK J. Mader et al. (Th) P. Friedag et al. (Th) 21

22 3.8 Trap 5: TRImP, Na MOT at KVI (H. Wilschut) (same remarks as Berkeley s MOT) Signals of trapping radioactive 21 Na observed. Contributions to EuNPC-DPG HK P.D. Shidling et al. (Tu) P.D. Shidling et al. (We) D.J. v d Hoek et al. (Th) 22

23 Summary The first consistent test of CVC in a set of transitions other than the (historical) super-allowed pure Fermi ones has been carried out. An new independent value of V ud was extracted from the Ft values and correlation coefficients in the mirror transitions of 19 Ne, 21 Na, 29 P, 35 Ar and 37 K. The result is more precise than the pion result, comparable with the neutron, and consistent at 1.2 combined σ with the value from transitions. Possible improvements call in priority for new precision measurements of correlation coefficients (βν angular correlation and decay asymmetries). Atom and ion traps will likely continue to play a crucial role. 23