Group 3 – Cheryl, Wojtek, and SandyGroup 3 – Cheryl, Wojtek, and Sandy

Question 14: Question 14:

Reactor Neutrino Experiments Reactor Neutrino Experiments

and the 3% flux shiftand the 3% flux shift

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What is the influence of 3% shift in flux What is the influence of 3% shift in flux on reactor neutrino experiments?on reactor neutrino experiments?

Double Chooz re-evaluated reactor antineutrino Double Chooz re-evaluated reactor antineutrino flux (arXiv 1101.2663)flux (arXiv 1101.2663)• previous procedure used a phenomenological previous procedure used a phenomenological

model based on 30 effective beta branchesmodel based on 30 effective beta branches• new analysis used detailed knowledge of the new analysis used detailed knowledge of the

decays of 10,000+ fission productsdecays of 10,000+ fission products New calculation results in overall flux increase of New calculation results in overall flux increase of

3.5% in reactor anti-neutrinos 3.5% in reactor anti-neutrinos

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Compare old to new flux resultsCompare old to new flux results

The old data used to be up here with the old flux calculation (clustered around 1.0)

Purple line: ratio neutrinos Nobs/Nexpected = 1.0

T. LasserreINSS 2011

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Compare old to new flux resultsCompare old to new flux results

This is the set of corrected data

Purple line: ratio neutrinos Nobs/Nexpected = 1.0

T. LasserreINSS 2011

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Compare old to new flux resultsCompare old to new flux results

Purple line: ratio neutrinos Nobs/Nexpected = 1.0

T. LasserreINSS 2011

However, these analyses were NOT blind… EXCEPT Bugey-3 and Bugey-4 (mostly)

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"Reactor Antineutrino Anomaly""Reactor Antineutrino Anomaly"

Common bias in systemsCommon bias in systems• Scintillator countersScintillator counters• Integral detectorsIntegral detectors

Neutrons capturedNeutrons captured• Metal loaded scintillatorsMetal loaded scintillators• Proportional countersProportional counters

Isotope composition (mostly the same)Isotope composition (mostly the same) Other systematics?Other systematics? Other physics reasons?Other physics reasons?

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Effects on experimentsEffects on experiments

Daya Bay & RENO:Daya Bay & RENO:• Uses near and far detector to calculate ratiosUses near and far detector to calculate ratios• Both detectors are affected by 3% flux changeBoth detectors are affected by 3% flux change• Flux effect is mostly canceled Flux effect is mostly canceled

Double Chooz:Double Chooz:• Single detector experiment = affectedSingle detector experiment = affected• Can "normalize" to another experiment (such Can "normalize" to another experiment (such

as Chooz using Bugey-4 results)as Chooz using Bugey-4 results)• Minimally affected if far detector combined Minimally affected if far detector combined

with near detector (in progress) to create ratiowith near detector (in progress) to create ratio

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What is effect of flux on Chooz?What is effect of flux on Chooz? Result of experiment (Result of experiment (1313) depends upon ratio of ) depends upon ratio of

actual/expected eventsactual/expected events• Expected flux is higher -> ratio is lowerExpected flux is higher -> ratio is lower• Expected flux affects cross section Expected flux affects cross section

measurements from low-energy experimentsmeasurements from low-energy experiments

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Effect on Chooz (cont)Effect on Chooz (cont) Chooz had to choose which cross section to use Chooz had to choose which cross section to use

because it didn't have a near/far detectorbecause it didn't have a near/far detector• They originally decided to use Bugey-4 cross They originally decided to use Bugey-4 cross

section (smallest error, most blind result)section (smallest error, most blind result)• This also agreed with the "averaged" cross This also agreed with the "averaged" cross

section from the short baseline experimentssection from the short baseline experiments• However, new flux caused 5% change in However, new flux caused 5% change in

Bugey-4 cross section valueBugey-4 cross section value• Thus, Chooz decided to use Thus, Chooz decided to use predictedpredicted cross cross

section with bigger errorssection with bigger errors Chooz result of ratio actual/expected events Chooz result of ratio actual/expected events

changes from 0.98 to 0.96 with reevaluationchanges from 0.98 to 0.96 with reevaluation

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Effect on Chooz (cont)Effect on Chooz (cont)

RedRed = using cross section expected from new fluxBlueBlue = using cross section from measurements

T. LasserreINSS 2011

NEAR blind analysis?

FAR 13

Daya Bay, RENO, Double Chooz

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Effect on Chooz (cont)Effect on Chooz (cont) Reevaluation of low-energy experiments indicates Reevaluation of low-energy experiments indicates

something might be going onsomething might be going on One possibility is there is one (or more?) "sterile" One possibility is there is one (or more?) "sterile"

neutrino(s) involvedneutrino(s) involved ButBut, the required |, the required |mm22| for one sterile neutrino is | for one sterile neutrino is

significantly larger than those required by solar significantly larger than those required by solar and atmospheric experiments and atmospheric experiments • ||mm22| > 1 eV| > 1 eV22

New terms

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Effect on Chooz (cont)Effect on Chooz (cont)

T. LasserreINSS 2011

Kamland

Dotted line = 3 neutrinos with mixing

Solid line = 3+1 sterile with mixing

Need more (blind) analyses to determine what is going on

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Effect on Chooz (cont)Effect on Chooz (cont)BlueBlue = Recalc with 3 neutrinos->higher upper bound on sin2(213)

GreenGreen = Recalc with 3+1 sterile neutrinos->more in agreement with the experimental results

T. LasserreINSS 2011

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Sterile Neutrino HypothesisSterile Neutrino Hypothesis

Best X2 fit (95%): sin2(2new) ~ 0.14

mnew2 > 1.5 eV2

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Give arguments for/against Give arguments for/against reevaluating Chooz limitsreevaluating Chooz limits

Chooz and Double Chooz are (currently) single Chooz and Double Chooz are (currently) single detector systems (not using near/far ratio)detector systems (not using near/far ratio)• More affected by flux differenceMore affected by flux difference

Chooz used previous experiment result as their Chooz used previous experiment result as their baseline for the ratio baseline for the ratio • Both are affected roughly the same, effect Both are affected roughly the same, effect

cancelscancels Chooz experiment already reevaluated their Chooz experiment already reevaluated their

results (thus it must have been a good idea)results (thus it must have been a good idea)

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Give arguments for/against Give arguments for/against reevaluating Chooz limitsreevaluating Chooz limits

Chooz and Double Chooz are (currently) single Chooz and Double Chooz are (currently) single detector systems (not using near/far ratio)detector systems (not using near/far ratio)• More affected by flux differenceMore affected by flux difference

Chooz used previous experiment result as their Chooz used previous experiment result as their baseline for the ratio baseline for the ratio • Both are affected roughly the same, effect Both are affected roughly the same, effect

cancelscancels Chooz experiment already reevaluated their Chooz experiment already reevaluated their

results (thus it must have been a good idea)results (thus it must have been a good idea)

We students agree with the expertsWe students agree with the experts

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ReferencesReferences

"The Reactor Antineutrino Anomaly", arXiv "The Reactor Antineutrino Anomaly", arXiv 1101.2755, March 20111101.2755, March 2011

"Improved Predictions of Reactor Antineutrino "Improved Predictions of Reactor Antineutrino Spectra", arXiv 1101.2663, March 2011Spectra", arXiv 1101.2663, March 2011

"Double Chooz: Searching For "Double Chooz: Searching For 1313 With Reactor With Reactor Neutrinos", arXiv 1105.6079, March 2011Neutrinos", arXiv 1105.6079, March 2011

"Evidence of "Evidence of 1313 > 0 from Global Neutrino Data > 0 from Global Neutrino Data Analysis", arXiv 1106.6028, June 2011Analysis", arXiv 1106.6028, June 2011

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Questions?Questions?