Known and Unknown for Neutrinos. Kim Siyeon Chung-Ang g University Lecture at Yonsei Univ.

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1 Known and Unknown for Neutrinos Kim Siyeon Chung-Ang g University Lecture at Yonsei Univ.

2 Known and Unknown for Neutrinos Dirac vs. Majorana 3 generation vs. 4 generation (neutrino vs. antineutrino) (terrestrial vs. cosmological)

3 Majorana Neutrinos

4 Handedness(Chirality) d LH (left handedness) RH(right handedness) handedness) For an electron, e = e L + e R e + = e L+ + e + R combination of two handedness Discrete transformation of fields C: charge conjugation P: space inversion T: time reversal P is said to be mirror transform, such that P (LH) > RH

5 Handedness d of Dirac particles (1) Electron: If neutrinos are Dirac e = e L + e R particles like charged leptons, there are 4 Anti electron: CPT distinct states such that e + = e R+ + e + L ν = ν L + ν R (e + L,e R+ ) CAN couple ν = ν with W boson, while (e + R + ν L L, e R ) CANNOT. Neutrinos are LH, while In Weak interaction basis, antineutrinos are RH. electronsare LH, antielectrons are RH.

6 Handedness d of Dirac particles (2) e (e L ) e (e L ) W W ν (ν L ) ν ( ν R )

7 Hliit Helicityof massive particles Projection of spin ( s ) along the direction of motion ( p ): ~s ~p <0 : left(negative) helicity ~s ~p >0 : right(positive) helicity Helicity eigenstate is a combination of handedness states The helicity of a massive particle can be flipped depending on the motion of observer (Lorentzboost) Massless particles are either pure LH or RH: helicity handedness (chirality)

8 C, P, T, and CPT t e p s x momentum: P(odd), T(odd) Spin:P(even) P(even), T(odd) CPT(e L ) > e + R CPT invariant i ttheory P t p t p t p e + e+ e s s C T s x x x

9 Hliit Helicityof Mj Majorana neutrinos ti CPT µ νl ν R µ νl ν R 4 different states for Dirac neutrinos Lorentz If ν = ν, CPT µ νl ν R boost There are 2 distinct states for Majorana neutrinos. Anti neutrino is obtained simply by flipping. 180 degree rotation

10 Dirac vs. Mj Majorana Neutrinos and antineutrinos are distinct particles. Neutrinos and antineutrinos are the same. Lepton number is conserved. Couple with : neutrino Couple with + : anti neutrino Lepton number is NOT conserved. Couple with : neutrino Couple with + : neutrino Dirac mass term needs a RH neutrino. m D ( ν L ν R + ν R ν L ) Majorana mass term with lepton number violation. i 1 2 m L ( ν L νl c + ν L c ν L ) 2 L

11 See saw mechanism If both L and R exist, and they are Majorana particles, then both Majorana mass and Dirac mass can exist. 1 µ T ν c 2 L νr c m L m D m D M R If m L =0,andm D m R, the LH neutrino can obtain very light mass, µ νl ν R m ν m2 D ν m R SEE SAW Mechanism

12 Handedness d of Dirac particles (2) Recall! e (e L ) e (e L ) W W ν (ν L ) ν ( ν R ) What if Majorana neutrino?

13 Handedness d of Mj Majorana neutrino(1) ti e (e L ) e (e L ) W W ν (ν L ) ν (ν R + M E ν L) The amplitude for the neutrino to be emitted with the wrong(lh) helicity is of order M/E.

14 Handedness d of Mj Majorana neutrino(2) ti e (e L ) e (e L ) W W ν (ν L ) ν L C b d Can be connected, but suppressed by O(M/E)!

15 Neutrinoless double bt beta decay Emitting can be Majorana neutrinos with RH and O(m/E)LH. Amp [ contribution] is proportional p to m.

16 Some Remarks The CPT partner of ν L is ν R for a Dirac neutrino, or ν R for a Majorana neutrino. It is impossible to tell experimentally whether the partner of ν L is ν R or ν R. If m ν = 0, ther is no distinction between Dirac and Majorana neutrinos. No helicity flip can occur by Lorentz boost. Even the existence of ν R and ν L is not needed. Although m ν 6= 0, the distinction between Dirac and Majorana is very difficult to observe. The processes including Z 0 > νν do not tell if the neutrino is a Majorana or a Dirac. The feasible expetiment is neutrinoless double-betabeta decay.

17 Antineutrino flux from a reactor

18 Measurement of antineutrinos from reactors N ν = N p² P th 2 hσ 4πR f i he f i N p : No. of protons in target = size of the detector : Detection efficiency R: baseline, the distance from the reactor core to the detector dt t < f >: P th : Average Thermal power cross <E f >: section Average energy per per fission fission P th / <E f >: Fission rate, # of fissions per unit time

19 Fission i rate inside id a reactor Isotope evolution of a typical PWR Fission rates at Palo Verde reactor cores. LWR (Light Water Reactor) > BWR (Boiling WR) > PWR (Pressurized WR) Corethermal power = reactor thermal power small heat fromreactor reactor coolantpumps In a PWR, 235 U (enrichment) is 3~4% 238 U is 95%. decay dominant 4 isotopes are 235 U, 239 Pu, 241 Pu and 238 U.

20 Fission i rate inside id a reactor Fission fraction of 4 isotopes, 235 U, 239 Pu, 241 Pu and 238 U. U 235 (Blue) Hanbit Reactor 1 E i (MeV): energy release per fission Isotope James Kopeikin (1969) (2004) 235 U 201.7± ± U 205.0± ±0.96 Pu 239 (Red) U 238 (P urple) P u 241 (Green) 239 Pu 210.0± ± Pu 212.4± ±0.65 i : averaged fraction quoted he f i = P i α i iee i ( 235 U : 238 U : 239 Pu : 241 Pu) = i : the relative fraction of i th (0.574 : 0.081: : 0.052) isotope

21 Fission i rate inside id a reactor Fission fraction of 4 isotopes, 235 U, 239 Pu, 241 Pu and 238 U. Hanbit Reactor 1 U 235 (Blue) Pu 239 (Red) U 238 (P urple) P u 241 (Green) he f i = P i α i iee i i : the relative fraction of i th isotope

22 Measurement of antineutrinos from reactors N ν = N p² P th 2 hσ 4πR f i he f i N p : No. of protons in target = size of the detector : Detection efficiency R: baseline, the distance from the reactor core to the detector dt t < f >: P th : Average Thermal power cross <E f >: section Average energy per per fission fission P th / <E f >: Fission rate, # of fissions per unit time

23 Average cross section per fissioni hσ f i = P i α R i φi σde For each isotope, Y = R φ i σde is the V A cross section of weak interaction, energy dependent IBD rate in the detector. is the spectral flux. Neutrinos produced in beta decays decrease depending di on energy. [reactor]

24 Average cross section per fissioni hσ f i = P i α R i φi σde For each isotope, Y = R φ i σde is the V A cross section of weak interaction, energy dependent IBD rate in the detector. is the spectral flux. Neutrinos produced in beta decays decrease depending di on energy. [reactor]

25 Average cross section per fissioni IBD cross section

26 Average cross section per fissioni IBD cross section

27 Average cross section per fissioni Spectrum of neutrinos from decays of fission fragments: In 1985, ILL measurements of spectrum for 235 U, 239 Pu and 241 Pu. Conversion to spectrum is trivial. E ν Q E β There is no relevant measurement for 238 U. Only theoretical method was relied on. Summation method Add upall possible hypothetical beta branches. ~10% uncertainty unavoidable. K. Schreckenbach et al., A. A. Hahn et al. (1985)

28 Average cross section per fissioni E ν Q E β

29 Measurement of antineutrinos from reactors N ν = N p² P th 2 hσ 4πR f i he f i N p : No. of protons in target = size of the detector : Detection efficiency R: baseline, the distance from the reactor core to the detector dt t < f >: P th : Average Thermal power cross <E f >: section Average energy per per fission fission P th / <E f >: Fission rate, # of fissions per unit time

30 Measurement of antineutrinos N ν = N p² from reactors P th he i 2 hσ 4πR f i he f i

31 Uncertainties ti By Jun Cao, 2010

32 Uncertainties ti RENO, 2012

33 Uncertainties ti

Uncertainties ti Thermal power uncertainty: The best

$IBD rate uncertainty Fission fraction: Mostly$ uncertainty of core simulation code. KME, SAPEC.

34 Uncertainties ti Thermal power uncertainty: The best accuracy is obtained by secondary heat balance method. Chooz 0.6%, Palo Verde 0.7% Most US reactors 1.4%. 0.7% 7%is obtainable if properly calibrated. IBD rate uncertainty Fission fraction: Mostly uncertainty of core simulation code. KME, SAPEC..(US, Japan) Uncertainties of the simulated concentration of isotope: 235 U : ~4%, 238 U : ~0.1% 239 Pu : ~5%, 241 Pu: ~6%

35 S. G. Ji, 2005

36 Mention et al, 2011 Reactor Antineutrino t i Anomaly Observed to expected ratio based on old & new spectra. Neutron life time: 885.7s (PDG2012)

37 PROSPECT Toy analysis by Y. Ko distance probability curve SRP II Goesgen II Goesgen I Krasnoyarsk III P 1 Bugey 3,4 Bugey 3 ROVNO88 2S Krasnoyarsk I ROVNO88, 91 Goesgen III SRP I Krasnoyarsk II ILL Bugey 3 gy RENO ND RENO FD P 0.9 P m 350m 500m 1400m

38 Analysis of Reactor antineutrino oscillation Absolute flux estimation Physical meaning of this gap? Reactor neutrino anomaly Far to near ratio does depend don not the normalization of the expected flux, but the slope of the curve. Multi detector observations, RENO and Daya Bay, determined the definite value of angle 13. Short baseline oscillation

39 Search for Sterile Neutrinos

40 Search for Sterile Neutrinos Outline 1. Active vs. Sterile neutrinos 2. 3 vs. 4 oscillation 3. LSND and MiniBooNE 4. Reactor antineutrino anomaly decay with sterile neutrinos 6. * Four neutrino analysis of RENO result. 7. Conclusion

41 Ati Active Neutrinos ti vs. Sterile Neutrinos ti Only 3 neutrinos are active in weak interaction. Massive but very light, with mixed flavor: sin 2 12 ~ 0.3, sin 2 23 ~ 0.5, sin 2 13 ~ Mass Hierarchy: Normal or Inverted Mass driven oscillation: sin 2 (1.27 m 2 L/E) NOT active in the Standard Model interaction. Oscillation observables: Too much disappearance of active neutrinos Too much appearance of active neutrinos Indirect evidence by combined fit of data If m21 2 << m31 2 << m41 2 : Short baseline anomaly

42 No. of neutrinos in Cosmology Before BICEP2 Cosmological l Hints (maybe model dependent): dld d Ns = number of thermalized sterile neutrinos CMB and LSS : Ns = 1.3 +/ 0.9, ms < 0.66 ev (95% C.L.) BBN : Ns < 1, (95% C.L.) CMB + LSS + BBN: Ns = ( 0.56) (95% C.L.) Standard CDM: 3+1 allowed, 3+2 disfavored Unidentified X ray emission from galaxies (Bulbul et al. 2014) E = (3.55~3.57) 57) +/ 003kV 0.03 kev Ms =2E=7.1 kev, and sin2(2 ) 7ⅹ10-11

43 No. of neutrinos in Cosmology After BICEP2 Light sterile neutrinos ( Archidiacono et al. 2014) WP: Wilkinson Microwave Anisotropy Probe High l: Atacama CosmologyTelescope + South Pole Telescope (Temp fluctuation power, 500<l<3500, 650<l<3000, respectively ), compared to Planck ( l upto 2479)

44 No. of neutrinos in Cosmology After BICEP2 Light sterile neutrinos ( Archidiacono et al. 2014) LSS: frin WiggleZ Dark Energy Survey H0: Cepheid distance with Hubble Space Telescope CFHTLenS: Canada France Hawaii Telescope Lensing Survey PSZ : Planck Sunayev Zel Dovich l D catalogue of galuxy clusters

45 No. of neutrinos in Cosmology After BICEP2 Including terrestrial t neutrino oscillation Model dependency: Thermalizedsterilene neutrinos conflict with terrestrialne neutrino oscillations.

46 Sterile neutrinos in our planet Appearance at LSND and MiniBooNE LSND: The first evidence in favor of oscillations i beyond d3 flavor framework.

47 Sterile neutrinos in our planet Appearance at LSND and MiniBooNE MiniBooNE: i designed dto test LSND, in both neutrino mode and antineutrino mode. In neutrino mode: Disfavor most of the parameter space preferred by LSND. In anti neutrino mode: partially consistent with oscillations at m 2 ~1eV^2. An excess of events at low energy, outside the LSND type oscillation energy range, was reported.

48 Sterile neutrinos in our planet Appearance at LSND and MiniBooNE MiniBooNE: i designed dto test LSND, in both neutrino mode and antineutrino mode. In neutrino mode: Disfavor most of the parameter space preferred by LSND. In anti neutrino mode: partially consistent with oscillations at m 2 ~1eV^2. An excess of events at low energy, outside the LSND type oscillation energy range, was reported.

49 Sterile neutrinos in our planet Reactor Antineutrino Anomaly Observed to expected ratio based on old & new spectra. (Mention et al., Phys.Rev.D ) Neutron life time: 885.7s (PDG2012)

50 Average cross section per fissioni IBD cross section

51 Prospect Absolute flux estimation Physical meaning of this gap? Reactor neutrino anomaly Far to near ratio does depend don not the normalization of the expected flux, but the slope of the curve. Multi detector observations, RENO and Daya Bay, determined e ed the definite e value aueof angle ge 13. Short baseline oscillation

52 Prospect Absolute flux estimation Toy analysis by Y. Ko distance probability curve Bugey 3,4 SRP II Goesgen II Goesgen I Krasnoya rsk III Bugey 3 ROVNO88 2S Krasnoyarsk I ROVNO88, 91 Goesgen SRP I III ILL Krasnoyars k II Bugey 3 RENO ND P 1 P 0.9 RENO P 0.8 FD 100m 350m 500m 1400m

53 Concluding remarks Issues for sterile neutrinos 1. Three anomalies: LSND(MiniBooNE), Reactor Antineutrino Anomaly, Gallium Anomaly. 2. Although we have several hints for sterile neutrinos, there is no fully consistent picture so far. Neutrino mode vs. anti neutrino mode Disappearancevs vs. appearanceoscillation Terrestrial experiment vs. cosmology observation h f dd l ff h 3. The presence of additional neutrino mass states can affect the interpretation of neutrino less double beta decay experiments.

54 Neutrinoless double bt beta decay 3+1 or 1+3?

Status of Light Sterile Neutrinos Carlo Giunti

Status of Light Sterile Neutrinos Carlo Giunti INFN, Torino, Italy EPS-HEP 07 07 European Physical Society Conference on High Energy Physics Venezia, Italy, 5- July 07 C. Giunti Status of Light Sterile