Bounds on sterile neutrino using full kinematic reconstruction of radioactive decays

Transcription

1 Bounds on sterile neutrino using full kinematic reconstruction of radioactive decays F. Bezrukov MPI für Kernphysik, Heidelberg, Germany Kaffeepalaver

2 Outline Outline 1 Implications for light sterile neutrino 2 Full kinematic reconstruction experiment General consideration Required precision and backgrounds 3 Existing experiments 38m K β decay 37 Ar EC decay 4 Conclusions Reading: Behr, Gwinner, arxiv: [nucl-ex] FB, Shaposhnikov, PRD,75,053005(2007) F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 2 / 24

3 Outline Implications for light sterile neutrino 1 Implications for light sterile neutrino 2 Full kinematic reconstruction experiment General consideration Required precision and backgrounds 3 Existing experiments 38m K β decay 37 Ar EC decay 4 Conclusions F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 3 / 24

4 Implications for light sterile neutrino Standard Model and neutrino masses SM: gauge bosons: γ, W ±, Z, g; Higgs boson H; three matter generations: L = ( ν L e L ), er ; Q = ( ul d L ), d R, u R Describes all experiments dealing with electroweak and strong interactions Does not describe Neutrino oscillations Dark matter (Ω DM ) Dark energy (Ω Λ ) Baryon asymmetry Gravity A lot can be explained by just adding three singlet neutrinos νmsm Asaka, Shaposhnikov, 05 Inflation F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 4 / 24

5 Implications for light sterile neutrino Standard Model and neutrino masses SM: gauge bosons: γ, W ±, Z, g; Higgs boson H; three matter generations: L = ( ν L e L ), er ; Q = ( ul d L ), d R, u R Describes all experiments dealing with electroweak and strong interactions Does not describe Neutrino oscillations Dark matter (Ω DM ) Dark energy (Ω Λ ) Baryon asymmetry Gravity A lot can be explained by just adding three singlet neutrinos νmsm Asaka, Shaposhnikov, 05 Inflation F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 4 / 24

6 Implications for light sterile neutrino The scales for see-saw (νmsm) The active neutrino masses m ν are expressed from the Dirac masses m D and singlet neutrino Majorana masses M by see-saw formula Two natural options: m ν = m D M 2 All the Yukawa couplings are of the same order. Then the new energy scale is introduced for the singlet neutrinos, M GeV. M SM scale, but the Yukawa couplings (or m D ) are very small F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 5 / 24

7 Implications for light sterile neutrino Sterile neutrino Dark Matter 2-50 kev sterile neutrino is a natural Warm Dark Matter candidate The evolution of the particle distributions in phase space. A small halo of mass h 1 M has been selected for comparative study in (left to right) ΛCDM, ΛWDM, and ΛWDM power spectrum but without thermal velocities. From bottom to top: Z = 8, 1, and 0. Bode, Ostriker, Turok 01 F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 6 / 24

8 Implications for light sterile neutrino Sterile neutrino Dark Matter 2-50 kev sterile neutrino is a natural Warm Dark Matter candidate Asaka, Shapohnikov 05; Laine, Shaposhnikov 08 F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 6 / 24

9 Implications for light sterile neutrino Existing sterile ν bounds 0.1 Full reconstruction 38m K trap, Ar EC ion recoil, 98 U ex Kink search 187 Re, S, Pu, Ni, 99 3 H, 95 3 H, S, Ni, Ni, F, Cu, m N [kev] F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 7 / 24

10 Outline Full kinematic reconstruction experiment 1 Implications for light sterile neutrino 2 Full kinematic reconstruction experiment General consideration Required precision and backgrounds 3 Existing experiments 38m K β decay 37 Ar EC decay 4 Conclusions F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 8 / 24

11 Full kinematic reconstruction experiment General consideration Possibilities of (light) sterile neutrino search Creation and detection in the lab Creation somewhere and detection in the lab Creation in the lab without subsequent detection F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 9 / 24

12 Full kinematic reconstruction experiment General consideration Possibilities of (light) sterile neutrino search Creation and detection in the lab Creation and detection Suppressed by mixing angle θ 4 Creation somewhere and detection in the lab Creation in the lab without subsequent detection F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 9 / 24

13 Full kinematic reconstruction experiment General consideration Possibilities of (light) sterile neutrino search Creation and detection in the lab Creation somewhere and detection in the lab X-ray experiments Sterile N in the DM clouds decay by the channel N νγ providing the X-ray line with E γ = M/2. Limit on θ 2 can be deduced as far as Ω DM is known Creation in the lab without subsequent detection F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 9 / 24

14 Full kinematic reconstruction experiment General consideration Possibilities of (light) sterile neutrino search Creation and detection in the lab Creation somewhere and detection in the lab Creation in the lab without subsequent detection Forbidden decays Decay kinematics Partial kinematics kink search in electron beta decay spectrum. Large statistics to see the effect ( N statistical error) Excellent theoretical knowledge of the decay spectrum is needed (c.f. 17 kev neutrino discovery ) Full kinematics event-by-event mass measurement! F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 9 / 24

15 Full kinematic reconstruction experiment Beta decay kinematics General consideration 3 H p = 0 3 He, p ν, q e, k Neutrino mass is reconstructed from observed momenta For 3 H: Q = kev mν 2 = (Q Ep kin Ee kin ) 2 (p + k) 2 Typical ion energy Ep kin 1 ev or p 100 kev Typical electron energy Ee kin 10 kev F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 10 / 24

16 Full kinematic reconstruction experiment Possible experimental setup General consideration Cold and compact 3 H source Time of flight measurement of the recoil 3 He ion, using position sensitive detector for 3d momentum reconstruction Electron momentum measurement Time of flight Needs decay moment trigger Lyman photon from the excited 3 He ion ( 25% of the decays)? Spectrometer for the electron energy measurement Electron itself can be used to determine the decay moment. F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 11 / 24

17 Full kinematic reconstruction experiment Required precision and backgrounds Required precision of momentum measurement To measure m ν kev one needs precision in momentum p, k kev. For 3 H decay this means precision p p 1% For other isotopes p p p me Q Isotopes with higher energy release Q require better momentum measurement F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 12 / 24

18 Thermal noise Full kinematic reconstruction experiment Required precision and backgrounds Nonzero thermal velocity v 2 = 3T /M of the decaying atom imitates some nonzero neutrino mass in usual beta decays mν eff 2 m 2 ν + M 2 v 2 2Mv(p + k) Temperature constraint 0.7 ( 10 3 ms ) 4 ( )( ) 6 GeV 18.6 kev 2 T log(1/θ 2 (1 K) ) 1 kev M Q slow neutrino cut (p + k) 2 3MT reduces the constraint ) T (1 K) 1 ( ms log(1/θ 2 ) 1 kev ) 2 ( 6 GeV M and luminosity... T 1K T 0.01K Br(p + k < 1keV) Br(p + k < 0.1keV) F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 13 / 24

19 Full kinematic reconstruction experiment Required precision and backgrounds Optimistic prospects (zero background) β decay kink searches T=0.1 mk T=10 mk T=1 K N tot =10 6 sin 2 (2θ) 1e-05 1e-06 N tot =10 8 1e-07 1e-08 N tot = e M s, kev F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 14 / 24

20 Full kinematic reconstruction experiment Required precision and backgrounds Background from radiative decay 3 H 3 He + e + ν e + γ dγ/dm * kev/γ 0 1e-05 1e-06 1e m ν [kev] N(E γ > 1keV)/N total F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 15 / 24

21 Full kinematic reconstruction experiment Required precision and backgrounds Ideal requirements for the experiment Momentum measurement with precision δ p/p 1% Source Temperature mK Size 1 mm (depends on the momentum measurement device) Quantity > H (in case no background, 100% efficiency, 1 year of observation) F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 16 / 24

22 Full kinematic reconstruction experiment Existing cooling techniques Required precision and backgrounds Supersonic jets T 0.1K, density cm 3 (10 15 cm 3?) Magnetic trapping of decelerated supersonic jet of H atoms, T 0.1K Hogan et al., PRL101,143001(2008) Single-photon atomic cooling Price et al., PRL100,093004(2008) of 87 Rb atoms in an optical trap 100 µm 100 µm 130 µm at 7 µk Cooling of H is promised F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 17 / 24

23 Full kinematic reconstruction experiment Other backgrounds Required precision and backgrounds Tritium molecule dissociation Should not be a major problem very large momentum distortion Scattering/interactions in the source Possible variations of the experimental setup: Other isotopes Easier to capture, shorter lifetime Electron capture instead of beta decay 2-body kinematics F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 18 / 24

24 Full kinematic reconstruction experiment Other backgrounds Required precision and backgrounds Tritium molecule dissociation Should not be a major problem very large momentum distortion Scattering/interactions in the source Possible variations of the experimental setup: Other isotopes Easier to capture, shorter lifetime Electron capture instead of beta decay 2-body kinematics F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 18 / 24

25 Outline Existing experiments 1 Implications for light sterile neutrino 2 Full kinematic reconstruction experiment General consideration Required precision and backgrounds 3 Existing experiments 38m K β decay 37 Ar EC decay 4 Conclusions F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 19 / 24

26 Existing experiments Existing sterile ν bounds 0.1 Full reconstruction 38m K trap, Ar EC ion recoil, 98 U ex Kink search 187 Re, S, Pu, Ni, 99 3 H, 95 3 H, S, Ni, Ni, F, Cu, m N [kev] F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 20 / 24

27 38m K β decay Existing experiments 38m K β decay TRIUMF, Canada 38m K t 1/2 = s Q β + = MeV trap lifetime 45 s Trinczek et al., PRL90(2003) F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 21 / 24

28 38m K β decay Existing experiments 38m K β decay TRIUMF, Canada Trinczek et al., PRL90(2003) F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 21 / 24

29 37 Ar EC decay Existing experiments 37 Ar EC decay 37 Ar t 1/2 = days Q = kev 37 Ar on the layer of Au or 40 Ar Hindi et al., PRC58(1998)2512 F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 22 / 24

30 37 Ar EC decay Existing experiments 37 Ar EC decay Hindi et al., PRC58(1998)2512 F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 22 / 24

31 Outline Conclusions 1 Implications for light sterile neutrino 2 Full kinematic reconstruction experiment General consideration Required precision and backgrounds 3 Existing experiments 38m K β decay 37 Ar EC decay 4 Conclusions F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 23 / 24

32 Conclusions Conclusions Search for the relatively light kev scale sterile neutrino is an interesting experimental task Improvement of existing bounds U ex can be possible by experiments with event-by-event measurement of the neutrino mass by full kinematic reconstruction For light sterile neutrino isotopes with small decay energy and small mass are good 3 H Detailed study of these type of experiments is needed! Excellent experimental techniques exist and are constantly improving! F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 24 / 24

33 Conclusions Conclusions Search for the relatively light kev scale sterile neutrino is an interesting experimental task Improvement of existing bounds U ex can be possible by experiments with event-by-event measurement of the neutrino mass by full kinematic reconstruction For light sterile neutrino isotopes with small decay energy and small mass are good 3 H Detailed study of these type of experiments is needed! Excellent experimental techniques exist and are constantly improving! F. Bezrukov (MPI) Full kinematic reconstruction Kaffeepalaver 24 / 24