Neutrino mass hierarchy Neutrino mass hierarchy and and 1313 Determination by Determination by

Remote Detection of Remote Detection of Reactor AntineutrinosReactor Antineutrinos

Mikhail Batygov,Mikhail Batygov,On behalf of UH Hanohano group,On behalf of UH Hanohano group,September 14, Sendai TAUP 2007September 14, Sendai TAUP 2007

OutlineOutline

Neutrino oscillation parametersNeutrino oscillation parameters• Current knowledgeCurrent knowledge• Parameters to be estimated at higher Parameters to be estimated at higher

accuracyaccuracy• MethodsMethods• Requirements and the Hanohano projectRequirements and the Hanohano project

Other physics goalsOther physics goals Current status and conclusionCurrent status and conclusion

Oscillation Parameters: presentOscillation Parameters: present KamLAND (with SNO) KamLAND (with SNO)

analysis:analysis:tantan22((θθ1212))==0.40(0.40(++0.10/0.10/––0.07)0.07)

ΔΔmm222121=(7.9+0.4/-0.35)=(7.9+0.4/-0.35)××1010-5-5 eV eV22

Araki et al., Araki et al., Phys. Rev. Lett. Phys. Rev. Lett. 9494 (2005) 081801. (2005) 081801. (UPDATED: talk by I. Shimizu at this (UPDATED: talk by I. Shimizu at this conference)conference)

SuperK and K2K:SuperK and K2K: ΔΔmm22

3131=(2.5=(2.5±±0.5)0.5)××1010-3-3 eV eV22

Ashie et al., Ashie et al., Phys. Rev. Phys. Rev. D64D64 (2005) (2005) 112005112005Aliu et al., Aliu et al., Phys. Rev. Lett. Phys. Rev. Lett. 9494 (2005) (2005) 081802081802

CHOOZ limit: CHOOZ limit: sinsin22(2(2θθ1313) ) ≤ ≤ 0.200.20Apollonio et al., Apollonio et al., Eur. Phys. J. Eur. Phys. J. C27C27 (2003) (2003) 331-374.331-374.

Oscillation parameters to be measuredOscillation parameters to be measured

Precision measurement Precision measurement of mixing parameters neededof mixing parameters needed

World effort to determine World effort to determine θθ13 13 (=(= θθ3131))

Determination of mass hierarchyDetermination of mass hierarchy

2 mass diffs, 3 angles, 1 CP phase2 mass diffs, 3 angles, 1 CP phase

3-3- mixing mixing

PPeeee==1-{ cos1-{ cos44((θθ1313) sin) sin22(2(2θθ1212) [1-cos() [1-cos(ΔΔmm221212L/2E)]L/2E)]

+ + coscos22((θθ1212) sin) sin22(2(2θθ1313) [1-cos() [1-cos(ΔΔmm221313L/2E)]L/2E)]

+ + sinsin22((θθ1212) sin) sin22(2(2θθ1313) [1-cos() [1-cos(ΔΔmm222323L/2E)]}/2L/2E)]}/2

Survival probability: 3 oscillating terms each cycling in L/E space Survival probability: 3 oscillating terms each cycling in L/E space (~t) with own “periodicity” ((~t) with own “periodicity” (ΔΔmm22~~ωω))• Amplitude ratios ~13.5 : 2.5 : 1.0Amplitude ratios ~13.5 : 2.5 : 1.0• Oscillation lengths ~110 km (Oscillation lengths ~110 km (ΔΔmm22

1212) and ~4 km () and ~4 km (ΔΔmm221313 ~~ ΔΔmm22

2323) at ) at reactor peak ~3.5 MeVreactor peak ~3.5 MeV

Two possible approaches:Two possible approaches: ½-cycle measurements can yield½-cycle measurements can yield

• Mixing angles, mass-squared differencesMixing angles, mass-squared differences• Less statistical uncertainty for same parameter and detectorLess statistical uncertainty for same parameter and detector

Multi-cycle measurements can yieldMulti-cycle measurements can yield• Mixing angles, precise mass-squared differencesMixing angles, precise mass-squared differences• Mass hierarchyMass hierarchy• Less sensitivity to systematic errorsLess sensitivity to systematic errors

1212 precise measurement precise measurement Reactor experiment- Reactor experiment- νν ee

point sourcepoint source P(P(ννee→→ννee))≈≈1-1-

sinsin22(2(2θθ1212)sin)sin22((ΔΔmm222121LL/4/4EE))

60 GW·kt·y exposure at 60 GW·kt·y exposure at 50-70 km50-70 km• ~4% systematic error ~4% systematic error

from near detectorfrom near detector• sinsin22((θθ1212) measured with ) measured with

~2% uncertainty~2% uncertainty

Bandyopadhyay et al., Phys. Rev. D67 (2003) 113011.Minakata et al., hep-ph/0407326Bandyopadhyay et al., hep-ph/0410283

Ideal spot

3-flavor oscillations3-flavor oscillations

““High-frequency” amplitude is High-frequency” amplitude is 1313 In L/E plot, a purely sinusoidal factorIn L/E plot, a purely sinusoidal factor Invites the use of Fourier Transform for analysisInvites the use of Fourier Transform for analysis

Fourier Transformed SpectrumFourier Transformed Spectrum The size of the peak The size of the peak

proportional to proportional to 1313.. The peak’s The peak’s

asymmetry tells asymmetry tells about hierarchyabout hierarchy

Method developed at Method developed at UHUH

Δm232 < Δm2

31 normal hierarchy

0.0025 eV2 peak due to nonzero θ13

Preliminary-50 kt-y exposure at 50 km range

sin2(2θ13)≥0.02 Δm2

31=0.0025 eV2 to 1% level

Learned, Dye,Pakvasa, Svoboda hep-ex/0612022

Includes energy smearing

Hierarchy DiscriminationHierarchy Discrimination

Uses the difference in spectraUses the difference in spectra Efficiency depends heavily on energy Efficiency depends heavily on energy

resolutionresolution

Perfect E resolution E = 6%*sqrt(Evis)

E, MeV E, MeV

Estimation of the statistical significanceEstimation of the statistical significance

Thousands of events necessary for reliable discrimination, even at 1 Thousands of events necessary for reliable discrimination, even at 1 CL CL Longer baselines more sensitive to energy resolution; may be beneficial to Longer baselines more sensitive to energy resolution; may be beneficial to

adjust for actual detector performanceadjust for actual detector performance

Detector energy resolution, MeV0.5

Neu

trin

o ev

ents

to

1

CL

KamLAND: 0.065 MeV0.5

< 3%: desirable but maybe unrealistic E resolution

Additional goal: neutrino Additional goal: neutrino geophysicsgeophysics

Antineutrinos produced in Antineutrinos produced in -decays of -decays of 232232Th and Th and 238238U U decay series isotopesdecay series isotopes

A substantial (but not A substantial (but not known precisely) part of known precisely) part of Earth heat flux of 40 (31) Earth heat flux of 40 (31) TWTW

In continent-based In continent-based detectors, flux dominated detectors, flux dominated by continental crustby continental crust

Ocean-based detectors Ocean-based detectors allow to measure geo-allow to measure geo-neutrino flux from mantleneutrino flux from mantle

RequirementsRequirements

Baseline on the order of 50 km; better Baseline on the order of 50 km; better variable for different studiesvariable for different studies

Big number of events (large detector)Big number of events (large detector) For Hierarchy:For Hierarchy:

• Good to excellent energy resolutionGood to excellent energy resolution• sinsin22(2(21313) ) 0 0• No full or nearly full mixing in No full or nearly full mixing in 12 12 (almost (almost

assured by SNO and KamLAND)assured by SNO and KamLAND) For Geo-neutrinos: ability to “switch off” For Geo-neutrinos: ability to “switch off”

reactor backgroundreactor background

MeV-Scale Electron Anti-Neutrino DetectionMeV-Scale Electron Anti-Neutrino Detection

Evis=Eν-0.8 MeVprompt

delayedEvis=2.2 MeV

• Standard inverse β-decay coincidence

• Eν > 1.8 MeV

• Rate and precise spectrum but no direction

Production in reactorsand natural decays

Detection

Key: 2 flashes, close in space and time, 2 flashes, close in space and time, 22ndnd of known energy, of known energy, eliminate backgroundeliminate background

Reines & Cowan

Hanohano detectorHanohano detector 10-kt LS detector10-kt LS detector Primary detection method: Primary detection method:

inverse-beta decayinverse-beta decay Ocean-based, with 2 key Ocean-based, with 2 key

advantages:advantages:• Adjustable baselineAdjustable baseline• Ability to avoid reactor Ability to avoid reactor

background in the geo-background in the geo-neutrino studiesneutrino studies

Barge 112 m long x 23.3 wide

Additional Physics/AstrophysicsAdditional Physics/AstrophysicsHanohano will be biggest low energy neutrino detectorHanohano will be biggest low energy neutrino detector

Nucleon Decay: Nucleon Decay: (SUSY-favored kaon (SUSY-favored kaon modes may be also modes may be also possible)possible)

Supernova Detection: Supernova Detection: special special ννe e abilityability

Relic SN NeutrinosRelic SN Neutrinos GRBs and other rare GRBs and other rare

impulsive sourcesimpulsive sources Long list of Long list of

ancillary, non-ancillary, non-interfering science, interfering science, with strong with strong discovery potentialdiscovery potential

Current statusCurrent status Several workshops held (’04, ’05, ’06) and ideas Several workshops held (’04, ’05, ’06) and ideas

developeddeveloped Study funds provided preliminary engineering and Study funds provided preliminary engineering and

physics feasibility report (11/06)physics feasibility report (11/06) Strongly growing interest in geology communityStrongly growing interest in geology community Work proceeding and collaboration in formationWork proceeding and collaboration in formation Upcoming workshops in Washington DC (10/07) Upcoming workshops in Washington DC (10/07)

and Paris (12/07) for reactor monitoringand Paris (12/07) for reactor monitoring Funding request for next stage (’06) in motionFunding request for next stage (’06) in motion Ancillary proposals and computer studies Ancillary proposals and computer studies

continuecontinue

SummarySummary Better precision for sinBetter precision for sin22(2(21212) and sin) and sin22(2(21313) along with the ) along with the

determination of hierarchy possible for reactor-based determination of hierarchy possible for reactor-based antineutrino experimentantineutrino experiment

Variable baseline desirableVariable baseline desirable• particular measurements require individual tuningparticular measurements require individual tuning• optimal placement dependent on unknown parametersoptimal placement dependent on unknown parameters• minimize systematic errors (esp. in energy scale) minimize systematic errors (esp. in energy scale)

Needs large statistics Needs large statistics → big detector→ big detector Requires precise Requires precise ee energy measurement energy measurement

Hanohano designed to meet those goals and also provides:Hanohano designed to meet those goals and also provides:

Unique sensitivity to mantle geo-neutrinosUnique sensitivity to mantle geo-neutrinos Ability to avoid reactor background when neededAbility to avoid reactor background when needed Additional physics measurements achievable to higher Additional physics measurements achievable to higher

precisionprecision