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Group 3 – Cheryl, Wojtek, and Sandy

Group 3 – Cheryl, Wojtek, and Sandy. Question 14: Reactor Neutrino Experiments and the 3% flux shift. What is the influence of 3% shift in flux on reactor neutrino experiments?. Double Chooz re-evaluated reactor antineutrino flux (arXiv 1101.2663)

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Group 3 – Cheryl, Wojtek, and Sandy

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  1. Group 3 – Cheryl, Wojtek, and Sandy Question 14: Reactor Neutrino Experiments and the 3% flux shift

  2. What is the influence of 3% shift in flux on reactor neutrino experiments? • Double Chooz re-evaluated reactor antineutrino flux (arXiv 1101.2663) • previous procedure used a phenomenological model based on 30 effective beta branches • new analysis used detailed knowledge of the decays of 10,000+ fission products • New calculation results in overall flux increase of 3.5% in reactor anti-neutrinos

  3. Compare old to new flux results The old data used to be up here with the old flux calculation (clustered around 1.0) T. Lasserre INSS 2011 Purple line: ratio neutrinos Nobs/Nexpected = 1.0

  4. Compare old to new flux results This is the set of corrected data T. Lasserre INSS 2011 Purple line: ratio neutrinos Nobs/Nexpected = 1.0

  5. Compare old to new flux results T. Lasserre INSS 2011 Purple line: ratio neutrinos Nobs/Nexpected = 1.0 However, these analyses were NOT blind… EXCEPT Bugey-3 and Bugey-4 (mostly)

  6. "Reactor Antineutrino Anomaly" • Common bias in systems • Scintillator counters • Integral detectors • Neutrons captured • Metal loaded scintillators • Proportional counters • Isotope composition (mostly the same) • Other systematics? • Other physics reasons?

  7. Effects on experiments • Daya Bay & RENO: • Uses near and far detector to calculate ratios • Both detectors are affected by 3% flux change • Flux effect is mostly canceled • Double Chooz: • Single detector experiment = affected • Can "normalize" to another experiment (such as Chooz using Bugey-4 results) • Minimally affected if far detector combined with near detector (in progress) to create ratio

  8. What is effect of flux on Chooz? • Result of experiment (q13) depends upon ratio of actual/expected events • Expected flux is higher -> ratio is lower • Expected flux affects cross section measurements from low-energy experiments

  9. Effect on Chooz (cont) • Chooz had to choose which cross section to use because it didn't have a near/far detector • They originally decided to use Bugey-4 cross section (smallest error, most blind result) • This also agreed with the "averaged" cross section from the short baseline experiments • However, new flux caused 5% change in Bugey-4 cross section value • Thus, Chooz decided to use predicted cross section with bigger errors • Chooz result of ratio actual/expected events changes from 0.98 to 0.96 with reevaluation

  10. Effect on Chooz (cont) NEAR blind analysis? FAR q13 Daya Bay, RENO, Double Chooz T. Lasserre INSS 2011 Red = using cross section expected from new flux Blue = using cross section from measurements

  11. Effect on Chooz (cont) • Reevaluation of low-energy experiments indicates something might be going on • One possibility is there is one (or more?) "sterile" neutrino(s) involved • But, the required |Dm2| for one sterile neutrino is significantly larger than those required by solar and atmospheric experiments • |Dm2| > 1 eV2 New terms

  12. Effect on Chooz (cont) Dotted line = 3 neutrinos with mixing Solid line = 3+1 sterile n with mixing Need more (blind) analyses to determine what is going on Kamland T. Lasserre INSS 2011

  13. Effect on Chooz (cont) Blue = Recalc with 3 neutrinos ->higher upper bound on sin2(2q13) Green = Recalc with 3+1 sterile neutrinos ->more in agreement with the experimental results T. Lasserre INSS 2011

  14. Sterile Neutrino Hypothesis Best X2 fit (95%): sin2(2qnew) ~ 0.14 Dmnew2 > 1.5 eV2

  15. Give arguments for/against reevaluating Chooz limits • Chooz and Double Chooz are (currently) single detector systems (not using near/far ratio) • More affected by flux difference • Chooz used previous experiment result as their baseline for the ratio • Both are affected roughly the same, effect cancels • Chooz experiment already reevaluated their results (thus it must have been a good idea)

  16. Give arguments for/against reevaluating Chooz limits • Chooz and Double Chooz are (currently) single detector systems (not using near/far ratio) • More affected by flux difference • Chooz used previous experiment result as their baseline for the ratio • Both are affected roughly the same, effect cancels • Chooz experiment already reevaluated their results (thus it must have been a good idea) • We students agree with the experts

  17. References • "The Reactor Antineutrino Anomaly", arXiv 1101.2755, March 2011 • "Improved Predictions of Reactor Antineutrino Spectra", arXiv 1101.2663, March 2011 • "Double Chooz: Searching For q13 With Reactor Neutrinos", arXiv 1105.6079, March 2011 • "Evidence of q13 > 0 from Global Neutrino Data Analysis", arXiv 1106.6028, June 2011

  18. Questions?

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