Double beta decay and neutrino physics

1. Double beta decay and neutrino physics Osaka University M. Nomachi

2. Outline Weak interaction and neutrino property Exercise: Helicity Exercise: parity violation Neutrino mass Exercise: Seesaw mechanism Neutrino oscillation Exercise; Neutrino oscillation Oscillation experiments Neutrino mass measurement Beta decay Exercise: Beta ray energy spectrum Double beat decay

3. Beta decay In the modern view Weak interaction

4. Neutrino Lepton Spin ½ No charge Three generations Mass ?? http://particleadventure.org/particleadventure/index.html

5. Helicity spin Helicity = +1 Helicity = -1 spin Helicity = +1 spin Helicity is not Lorentz invariant

6. Free Dirac equation are 4x4 matrix Special relativity

7. Pseudo Scalar operator Chirality operator Diagonal representation In usual representation, βis diagonal

8. The solution of the Dirac equation is Helicity operator and its eigen states

9. Is zero for mass-less particle Chirality +1: Right handed -1: Left handed Helicity eigenstate = chirality eigenstate for mass-less particle Wrong helicity

10. Weak interaction Weak current Projection operator of negative (left handed) chirality In Weak interaction Electron and neutrino are always left handed While Positron and anti-neutrino are always right handed

11. Parity violation In Weak interaction Electron and neutrino are always left handed While Positron and anti-neutrino are always right handed electron anti-neutrino anti-neutrino electron spin spin We can know which is our world! mirror

12. Beta decay of 60Co Z Z electron Z Electron should be left handed Electron must have Electron and anti-neutron spin

13. Angular distribution Z Z Rotation of spin 1/2 For angular momentum conservation, spin must be down. Angular distribution will be

14. Dirac particle and Majorana particle • Dirac particle • Particle and anti-particle can be distinguished • Majorana particle • Particle and anti-particle can not be distinguished

15. Mass Dirac mass Majorana mass Charge conjugate Charged particle cannot have Majorana mass.

16. Neutrino mass Neutrino may have both Dirac mass and Majorana mass. Dirac mass breaks chiral symmetry.

17. Mass eigenvalue

18. Seesaw mechanism Dirac mass will be the same order as the others. (0.1~10 GeV) Right handed Majorana mass will be at GUT scale 1015 GeV

20. Mixing and oscillation Time evolution Mixing

21. Mixing and oscillation Assuming Probability to be at t is

23. For non relativistic limit For small mass particle ⊿m2 Mixing angle

24. 0.2 GeV fm or 0.2x10-6 eVm The value you have to remember

25. Atmospheric Neutrinos Super Kamiokande DATA μ neutrino disappearance Figures from Prof. Y. Suzuki at TAUP 2005

26. Solar neutrino Electron neutrino disappearance Nuclear fusion reaction in the sun is WEAK interaction.

28. MNS matrix By Minakata

29. Mass hierarchy Mass hierarchy is not derived from the oscillation measurements. Normal hierarchy Inverted hierarchy Δm2 (atmospheric) Δm2 (solar) m=0

30. Beta ray spectrum The transition rate is the density of final states the matrix element Assuming plane wave

31. Phase space volume The number of state in momentum p in the volume V The transition rate will be

32. gives The transition rate will be Assuming neutrino mass is zero,

33. Because of the coulomb potential, the electron wave function is not plane wave. It causes the modification of the result Fermi-function consequently

34. Neutrino mass in beta decay The end point of beta-ray depends on neutrino mass.

35. Beta decay experiments 3H beta decay, end point energy KATRIN experiment http://www-ik.fzk.de/~katrin/

36. Figure from http://www-ik.fzk.de/~katrin/overview/index.html

37. FINAL RESULTS FROM PHASE II OF THE MAINZ NEUTRINO MASS SEARCH IN TRITIUM BETA DECAY.Ch. Kraus et al.. Dec 2004. 22pp. Published in Eur.Phys.J.C40:447-468,2005e-Print Archive: hep-ex/0412056

38. Double beta decay

39. Double beta decay u(p) d(n) e W ν e ν W d(n) u(p) ν T1/2 (2nbb): ~ 1.15 x 1019year d(n) u(p) W ν e e W d(n) u(p) T1/2 (0nbb): > 1023year 1) 2 neutrino double beta decay. • 2) 0 neutrino double beta decay • Neutrino has mass • Neutrino is Majorana particle

40. Lepton number non-conservation u(p) d(n) e W ν e ν W d(n) u(p) ν T1/2 (2nbb): ~ 1.15 x 1019year d(n) u(p) W ν e e W d(n) u(p) T1/2 (0nbb): > 1023year Lepton number 2 electron +2 2 anti neutrino -2 = Lepton number is conserved. (Baryon number is conserved.) Lepton number 2 electron +2 = Lepton number is NOT conserved. (Baryon number is conserved)

41. Mass measurement electron electron W W Mass term Probability of helicity flip (wrong helicity) is proportional to m.

42. Beta decay observable It should be larger than that of double beta decay measurements. Double beta decay observable It depends on the phase. Could be zero.

43. νe 50meV νe 5meV Next generation experiments are aiming to explore 50meV region From NOON2004 summary by A. Yu. Smirnov

44. Mass hierarchy 0.1 eV 10 meV

45. Double beta decay 100Mo S.Elliott, Annu.Rev.Nucl.Part.Sci. 52, 115(2002) • Background • Natural radio activities • Cosmogenic background • 2 neutrino double beta decay

46. NEMO3

47. Transverse view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Longitudinal view Vertex emission Vertex emission Drift distance Deposited energy: E1+E2= 2088 keV Internal hypothesis: (Dt)mes –(Dt)theo = 0.22 ns Common vertex: (Dvertex) = 2.1 mm (Dvertex)// = 5.7 mm • Trigger: 1 PMT > 150 keV • 3 Geiger hits (2 neighbour layers + 1) • Trigger rate = 7 Hz • bb events: 1 event every 1.5 minutes Criteria to select bb events: • 2 tracks with charge < 0 • 2 PMT, each > 200 keV • PMT-Track association • Common vertex • Internal hypothesis (external event rejection) • No other isolated PMT (g rejection) • No delayed track (214Bi rejection) bb events selection in NEMO-3 Typical bb2n event observed from 100Mo Transverse view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Longitudinal view 100Mo foil 100Mo foil Geiger plasma longitudinal propagation Scintillator + PMT Hideaki OHSUMI for the NEMO-3 Collaboration APN04 Osaka 12-14 July 2004

48. Data • Data 100Mo 22 preliminary results (Data 14 Feb. 2003 – 22 Mar. 2004) Sum Energy Spectrum Angular Distribution 145 245 events 6914 g 241.5 days S/B = 45.8 145 245 events 6914 g 241.5 days S/B = 45.8 NEMO-3 NEMO-3 100Mo 100Mo 22 Monte Carlo Background subtracted 22 Monte Carlo Background subtracted Cos() E1 + E2 (keV) T1/2 = 7.72 ± 0.02 (stat) ± 0.54 (syst)  1018 y 4.57 kg.y Hideaki OHSUMI for the NEMO-3 Collaboration APN04 Paris 12-14 July 2004

49. PRELIMINARY 6914 g 265 days 100Mo 265 days Cu + natTe + 130Te Data E1+E2 (MeV) Data bb2n Monte-Carlo Cu + natTe + 130Te Radon Monte-Carlo Radon Monte-Carlo 2.6<E1+E2<3.2 2.8<E1+E2<3.2 ____ ____ bb0n arbitrary unit 11.4  3.4 2.6  0.7 11.4  3.4 2.6  0.7 8 2 E1+E2 (MeV) bb0n Analysis with 100Mo 100Mo 2.6<E1+E2<3.2 2.8<E1+E2<3.2 100Mo 2b2n M-C 32.3  1.9 1.4  0.2 Radon M-C 23.5  6.7 5.6  1.7 55.8  7.0 7.0  1.7 TOTAL Monte-Carlo DATA 50 8 V-A: T1/2(bb0n) > 3 1023 y V+A: T1/2 > 1.8 1023 y with E1- E2> 800 keV Majoron: T1/2 > 1.4 1022 ywith Esingle > 700 keV Hideaki OHSUMI for the NEMO-3 Collaboration APN04 Osaka 12-14 July 2004

50. MOON Osaka U. , U. of Washington etc. 100Mo + Plastic scintillator