1. Prediction of Reactor Neutrino Spectra David Lhuillier CEA Saclay - France

2. General Considerations Honolulu - AAP 2012D. Lhuillier - CEA Saclay2

3. Origin of Reactor Antineutrinos Honolulu - AAP 2012D. Lhuillier - CEA Saclay3  -decay of the fission products of U and Pu isotopes Ab initio approach: build up the total spectrum with individual contribution of ~800 nuclei. Reference spectra approach: measure the mean fission  spectrum of U an Pu isotopes and weight them by the predicted fission rates. e-e- e-e- All predictions require a reactor simulation with core geometry, initial fuel composition and power history.

4. Energy Spectrum Honolulu - AAP 2012D. Lhuillier - CEA Saclay4 Exponential decrease of emitted spectrum  inverse detection reaction Detected Spectrum Relevant E range [1.8 – 8] MeV

5. Contributing Nuclei Honolulu - AAP 2012D. Lhuillier - CEA Saclay5 Detection reaction enhances the contribution of high energy  -transitions: - Lot of very unstable nuclei, high above valley of stability - Short lived, reach equilibrium fast w.r.t. experiment time scale  Reference fission spectra approach favored w.r.t. ab initio approach. © F. Durillon, animea

6. Evolution Along a Reactor Cycle Honolulu - AAP 2012D. Lhuillier - CEA Saclay6 Typical evolution of the isotopic composition of a commercial rector At P th = constant, 239 Pu fission leads to 60% less detected neutrinos than 235 U fission. Monitoring of reactor flux with sensitivity to plutonium content. ON 239 Pu 235 U 238 U 241 Pu Refueling with fresh 235U Total Spectrum:

7. Fission Spectra uncertainties & Non-proliferation Honolulu - AAP 2012D. Lhuillier - CEA Saclay7 V. Bulaevskaya and A. Bernstein, nucl-ex/1009.2123 73 kg of 239 Pu removed Non proliferation relies on evolution of the neutrino rate along a reactor cycle; Relative variations and/or reference anchor point. In the case of converted spectra, the normalization and shape uncertainties are mostly correlated for all fissioning isotopes  their impact is suppressed.

8. Re-evaluation of Reference Spectra Honolulu - AAP 2012D. Lhuillier - CEA Saclay8

9. ILL data: reference  - Spectra Honolulu - AAP 2012D. Lhuillier - CEA Saclay9 Target foil ( 235 U, 239 Pu, 241 Pu) in thermal n flux Magnetic BILL spectrometer ILL research reactor (Grenoble, France) e-e- Emitted  spectra per fission A. A. Hahn, K. Schreckenbach et al., Phys. Let. B218,365 (1989)+ refs therein

10.  -   Conversion Honolulu - AAP 2012D. Lhuillier - CEA Saclay10 1- Need to break down the total e - spectrum into single  -branches  fit the data with 30 virtual branches: 2- Convert each virtual e - branches to branches 3- Sum all converted branches to get total spectrum

11. Theory of  -decay Honolulu - AAP 2012D. Lhuillier - CEA Saclay11 W = total energy W 0 = end-point p = momentum Z = Nuclear charge Fermi theory: Corrections: Fermi function Phase space Shape factor of forbidden Finite size of nuclear electric charge Finite size distrib. of decaying neutron Screening of Atomic e- QED radiative correction Weak magnetism branch obtained by replacing: W  W 0 -W, G   G

12. Corrections to Fermi theory Honolulu - AAP 2012D. Lhuillier - CEA Saclay12 Example of a single branch with Z=46 A=117 E 0 =10 MeV Total fission spectra is a sum over a quasi continuous end-point distribution  +/- cancellation at low E, adds up at high E. P. Huber  spectrum corrections spectrum corrections

13. Re-evaluation of Converted Spectra Honolulu - AAP 2012D. Lhuillier - CEA Saclay13 Maximize the use of nuclear data: 90% of the total  spectrum is described by the sum of measured  -decays * Fission yields. Use virtual branches only to fill the remaining 10% gap. Nuclear Data T. A. Mueller et al., Phys. Rev. C83,054615 (2011) Initiated by the need of accurate prediction for the far detector of Double Chooz

14. Re-evaluation of Converted Spectra Honolulu - AAP 2012D. Lhuillier - CEA Saclay14 T. A. Mueller et al., Phys. Rev. C83,054615 (2011) True distribution of Z from all  -decays of databases. Apply all corrections at the branch level instead of an effective global slope. Old effective correction Corrections applied at branch level “true” Z distribution from nuclear databases Combined effect at low and high energy leading to a global +3% shift

15. Reactor Anomaly Honolulu - AAP 2012D. Lhuillier - CEA Saclay15 Atmospheric Oscilation Solar Oscilation New Oscilation to sterile ? G. Mention et al., Phys. Rev. D83, 073006, 2011

16. Confirmed by Complementary Work Honolulu - AAP 2012D. Lhuillier - CEA Saclay16 P. Huber, Phys. Rev. C84, 024617(2011) Confirms global increase of predicted spectrum Fixes remaining oscillations of first re-evaluation Extra slope correction New conv. with “extra correction” New conv. P. Huber New conv. T.A. Mueller et al. ILL conversion Revisit conversion procedure of ILL data with minimal use of nuclear data.

17. Two Predictions in Agreement Honolulu - AAP 2012D. Lhuillier - CEA Saclay17 L0 correction not properly implemented in Mueller et al. re-evaluation. Different expressions of C(Z,W) term. The two published predictions contain the same physics. Difference in global slope is now understood: T.A. Mueller, D. Lhuillier

18. Updated Reactor Anomaly Honolulu - AAP 2012D. Lhuillier - CEA Saclay18 White paper: K. N. Abazajian et al., hep-ph/1204.5379 7% deficit ~4% from reactors 1% from  n, 1% from off-eq 1% from previous deficit Reactor + Gallium anomaly

19. Normalization Uncertainty Honolulu - AAP 2012D. Lhuillier - CEA Saclay19

20. Normalization of ILL data Honolulu - AAP 2012D. Lhuillier - CEA Saclay20 207 Pb(n,  ) 208 Pb 115 In(n,  ) 116m In 113 Cd(n,  ) 114 Cd Dominant systematic error : 1.8 % (1  ) Absolute calibration via internal conversion electron lines of known partial cross section per neutron capture Correlated across all energy bins of all isotopes directly propagates into the converted antineutrino spectra. &: absolute normalization : relative normalization

21. Independent Norm. at 2% level? Honolulu - AAP 2012D. Lhuillier - CEA Saclay21 2. 10 -2  /fission in 250keV bin centered on 6 MeV: The required few 10 6 fissions could be recorded with less intense neutron source (away from reactor  background reduction). Same calibration using internal conversion line + Precise counting with evt by evt fission tagging? Magnetic design for e - detection in large solid angle, and well controlled energy resolution. No off-equilibrium corrections Potential large impact on reactor anomaly…

22. Shape Uncertainty Honolulu - AAP 2012D. Lhuillier - CEA Saclay22

23. Weak Magnetism Honolulu - AAP 2012D. Lhuillier - CEA Saclay23 Measurement of  WM through transitions in isobaric analog states: Approximate expression neglecting nuclear structure: CVC symmetry Magnetic dipole M1  decay width  WM

24. Weak Magnetism Honolulu - AAP 2012D. Lhuillier - CEA Saclay24 Contribution of large ft’s in fission neutrino spectra? Experimental slope in good agreement for transitions with low ft values, assume 100% error P. Huber, Phys. Rev. C84, 024617(2011)

25. Weak Magnetism Honolulu - AAP 2012D. Lhuillier - CEA Saclay25 High log(ft) values have a sizeable contribution to fission spectra across all E range (reflects the large contribution of forbidden decays) CVC still valid for very large ft transition which have tiny overlap of wave functions in  -decay? Relative contribution

26. Weak Magnetism Honolulu - AAP 2012D. Lhuillier - CEA Saclay26  A factor 4 increase of  WM would compensate the +4% deviation from ILL spectra, but also induce a large negative tilt.  Reanalysis of Bugey3 data may already constrain the weak magn slope at this level.  Upcoming data from DayBay, Reno and Double Chooz near detectors have the potential to confirm the current shape uncertainty! Estimated shape uncertainty with ~3.5 10 5 accumulated neutrinos,  Escale = 0.5% and ~4% 9 Li background.

27. Shape Uncertainty Honolulu - AAP 2012D. Lhuillier - CEA Saclay27 Correlated across all energy bins and isotopes  favorable to non-proliferation and oscillation search

28. New Data Honolulu - AAP 2012D. Lhuillier - CEA Saclay28

29. Updated Ab Initio Predictions Honolulu - AAP 2012D. Lhuillier - CEA Saclay29 Correct for Pandemonium effect by using Total Absorption  -ray Spectrometry (TAS) Short list of fission products contributing by more than 4% to 2-6MeV bins. A. Algora et al., Phys. Rev. Lett. 105, 202501 (2010)

30. Updated Ab Initio Predictions Honolulu - AAP 2012D. Lhuillier - CEA Saclay30 M. Fallot et al., nucl-ex/1208.3877 Inclusion of 7 new Tc, Mo and Nb isotopes. Sizeable correction of predicted spectra  within ±10% of new converted spectra. Analysis and new measurements on-going. Same uncertainties on slope factors beyond databases systematics. Toward a competitive prediction of absolute normalization?

31. New 238 U data Honolulu - AAP 2012D. Lhuillier - CEA Saclay31 Anchor point of 235U measurement: - Background well understood. - Comparison to ILL spectrum cancels most uncertainties. N. Haag, K. Schrekenbach et al. New 238 U data @ FRMII reactor, Munich n flux Natural U foil  MWC Plastic Scintillator

32. New 238 U Data Honolulu - AAP 2012D. Lhuillier - CEA Saclay32 Spread of ab Initio flux predictions in the ±10% range  Possible update of the reactor anomaly at 1% level with sligthly improved total uncertainty N. Haag Ph.D. thesis to be published by end of this year. Final measurement of 238 U ranges from 2.0 MeV to 6.5 MeV with relative errors of 5% - 15%

33. Conclusions Honolulu - AAP 2012D. Lhuillier - CEA Saclay33  Demonstrated bias in the conversion procedure of the ILL data.  +4% increase of detected rate is confirmed by two independent works.  +1% off-equilibrium correction of reactor simulation + 1% updated neutron life-time + 1% previous mean shift with old spectra  ~7% deficit of the reactor anomaly

34. Conclusions Honolulu - AAP 2012D. Lhuillier - CEA Saclay34  Application to reactor surveillance: - Main uncertainties are common to all isotopes suppressing their impact on relative monitoring - Short baseline oscillations to be tested soon. rate at one location is affected through U-Pu shape difference only.  Challenging independent Xcheck of spectra normalization  New data coming soon to consolidate the current error budget: - 238 U Spectrum from FRM II - New shape envelope to be measured by near detectors of currently running reactor experiments.

35. Back Up Slides Honolulu - AAP 2012D. Lhuillier - CEA Saclay35

36. Complementary Approaches Honolulu - AAP 2012D. Lhuillier - CEA Saclay36 Ab initio calculations Conversion of total  spectra Complete simulation of core evolution - Fuel loading, geometry, n-capture and fission physics  Fission product inventory Description of all  -decays - Nuclear databases - Fermi theory + corrections - Nuclear models   and total spectra from some 10 4  -branches. Total  spectra of fissile isotopes measured at ILL in the 80’s  Accurate reference electron spectra Conversion to antineutrinos - Use of “virtual”  -branches - Fermi theory + corrections - Control of approximations  Reference spectra per isotope to be combined with prediction of fissions rates.

37. Ingredients Honolulu - AAP 2012D. Lhuillier - CEA Saclay37 Sum of all fission products’ activities Sum of all β-branches of each fission product Theory of β- decay

38. Status of Spectra Rate Honolulu - AAP 2012D. Lhuillier - CEA Saclay38  Linear trend with slope ≤1%/MeV enhances this increase in detected rate Emitted FluxDetected Rate Shift (%) Signif. (  ) Shift (%) Signif. (  ) 235 U2.43.7 2.4 239 Pu2.93.94.22.8 241 Pu3.24.04.73.0 Final difference with respect to ILL spectra :  Global rate increase

39. Finite Size Correction of Weak Interaction Honolulu - AAP 2012D. Lhuillier - CEA Saclay39 Include the envelope of various calculations as extra uncertainty? Would reach ~2% at 7 MeV. D. Wilkinson, Nucl. Phys. Inst. and Meth. A 290, 509 (1990) Different expressions of C(Z,W) term: P. Vogel, Phys. Rev. D29, 1918 (1984).

40. Uncertainties Honolulu - AAP 2012D. Lhuillier - CEA Saclay40  Finite size corrections could be further studies by combining nuclear model and lepton scattering data. Not dominant uncertainty. Conversion of  spectra  Current treatment of weak magnetism neglect the nuclear structure. -Dominant shape uncertainty, 100% error assumed. -Underestimated uncertainty?  Normalization: - Common to all predictions. - Currently 1.8% at 1  - A new measurement should target 1%. Not likely to happen. Quadratically stacked errors

41. Shape Evolution Along a Reactor Cycle Honolulu - AAP 2012D. Lhuillier - CEA Saclay41 Expected shape rotation on top of flux reduction But significant measurement requires very large statistics on month time scale.

42. Total Reactor Spectrum Honolulu - AAP 2012D. Lhuillier - CEA Saclay42  k = fission fraction, S k (W)=Reference spectrum Prediction of  k (t) 238 U couldn’t be measured at ILL because it undergoes fission in fast neutron flux. Extrapolation of the ILL spectra to commercial reactors? Half way through:  Ab initio approach addresses it all

43. Ab initio Honolulu - AAP 2012D. Lhuillier - CEA Saclay43 Total error in the 10-20% range. Dominated by systematics of nuclear databases. Build as complete as possible nuclear database coupled to MCNP Utility for Reactor Evolution (*)  full core inventory 235 U spectrum matches the ILL data at ~10% level Deviation from Vogel et al., Phys. Rev. C24, 1543 (1981) 238 U prediction 10% higher than previous estimate ENSDF only Pandemonium corr. Add gross theory Phys. Rev. C83,054615 (2011) (*) http://www.nea.fr/tools/abstract/detail/nea-1845.

44. Ab initio Honolulu - AAP 2012D. Lhuillier - CEA Saclay44  ILL reference data are photos of  decays after 12-36h irradiation time.  Long-lived isotopes, dominant at low energy, keep accumulating over several weeks.  Sizeable correction to ILL data in below 3 MeV; +1% total detected flux ILL conditions See poster 146, A., Reactor and antineutrino spectrum calculation for the Double Chooz first phase result Off-eq. correction as computed by the MURE C. Jones et al. arXiv:nucl-ex/1109.5379v1 ILL conditions Study of relative spectrum variations to reach equilibrium [53] = Chooz paper

45. Error Budget Honolulu - AAP 2012D. Lhuillier - CEA Saclay45 235 U 239 Pu 241 Pu Phys. Rev. C83,054615 (2011)

46. Honolulu - AAP 2012D. Lhuillier - CEA Saclay46 Error Budget Phys. Rev. C84, 024617(2011)

47. Bugey Honolulu - AAP 2012D. Lhuillier - CEA Saclay47