KamLAND Neutrino Oscillation Results and Solar Future Patrick - PowerPoint PPT Presentation

KamLAND Neutrino Oscillation Results and Solar Future Patrick Decowski (UC Berkeley) for the KamLAND Collaboration Neutrino 2008, Christchurch, NZ 1

KamLAND Collaboration Patrick Decowski / UC Berkeley 2

Reactors for Oscillation Studies ν e ν e Simulation 10 No oscillation 8 Δ m 2 =7x10 -5 eV 2 Δ m 2 =2x10 -5 eV 2 Rate [au] 6 (sin 2 2 θ =0.8) L 4 P ( ν e → ν e ) = 1 − sin 2 2 θ sin 2 1 . 27∆ m 2 L 2 E 0 0 2 4 6 8 10 E [MeV] � e Neutrino oscillation changes the overall normalization and shape of the spectrum Patrick Decowski / UC Berkeley 3

Anti-Neutrino Detection Method Inverse beta decay ν e + p → e + + n γ Liquid γ 207 μ s Scintillator n + p → d + γ e+ Scintillator is both target and detector  e n γ 2.2MeV • Distinct two step process: • prompt event: positron E ν e � E prompt + 0 . 8 MeV • delayed event: neutron capture after ~207 μ s • 2.2 MeV gamma Delayed coincidence: good background rejection Patrick Decowski / UC Berkeley 4

Detected Reactor Spectrum Zacek G. et al., Phys. Rev. D34, 2621 (1986). Reactor ν e ν e + p → e + + n from neutron rich Cross section fission fragments Detected Gösgen Spectrum Counts [MeV -1 h -1 ] 1.8MeV threshold in Inverse Beta Decay • In practice, only 1.5 neutrinos/fission detectable • Calculated spectrum has been verified to 2% accuracy in past reactor experiments No near detector necessary! E e+ (MeV) Patrick Decowski / UC Berkeley 5

from 55 Reactor Cores in Japan ν e 70 GW (7% of world total) is generated at 130-220 km distance from Kamioka 500 Events/ year / kton 450 400 Effective baseline ~180km 350 300 250 200 150 100 50 0 0 100 200 300 400 500 600 700 800 900 1000 Distance [km] Reactor neutrino flux: KL Mt. Ikenoyama 1000m rock ~6x10 6 cm -2 s -1 = 2700 mwe Japan Korean long. 137 ◦ 18 � 43 . 495 �� World lat. 36 ◦ 25 � 35 . 562 �� alt. 358 m Patrick Decowski / UC Berkeley 6

KamLAND detector • 1 kton Scintillation Detector • 6.5m radius balloon filled with: } • 20% Pseudocumene (scintillator) • 80% Dodecane (oil) • PPO • 34% PMT coverage 20 m • ~1300 17” fast PMTs • ~550 20” large PMTs • Multi-hit electronics 1800 m 3 Buffer Oil • Water Cherenkov veto counter Water Cherenkov 3200 m 3 Outer Detector Patrick Decowski / UC Berkeley 7

KamLAND Physics Capabilities 0.4 1.0 2.6 8.5 Energy [MeV] neutrino electron elastic scattering ν e + p → e + + n ¯ ν + e − → ν + e − inverse beta decay supernova, relic neutrino, geo-neutrino reactor neutrino solar neutrino solar anti-neutrinos etc. Neutrino Astrophysics Neutrino Geophysics Neutrino Physics Neutrino Cosmology Verification of SSM Study of earth heat Precision measurement Verification of universe model of oscillation parameters evolution, SSM Geoneutrinos Solar KL2002 reactor result ν e Nature 436, 499 (2005). PRL 92 071301 (2004). PRL 90 021802 (2003). KL2004 reactor result Future PRL 94 081802 (2005). Low background Recent Results phase Accepted by PRL Patrick Decowski / UC Berkeley 8

Analysis Improvements Max Radius(m) Lifetime(days) Exposure(ton-yr) Exposure Increase KL2002 5 145 162 1x KL2004 5.5 515 766 4.7x Latest 6 1491 2881 17.8x S/B 6m Energy threshold from 2.6MeV → 1.0MeV (Inverse Beta Decay threshold) accidentals “Fuzzy” cut using event characteristics to distinguish signal from accidentals Patrick Decowski / UC Berkeley 9

Full Volume Calibration System Deployed in 2005-2006 z-axis Range of radioactive sources (250keV to 6MeV): 203 Hg, 137 Cs, 68 Ge , 65 Zn, 60 Co, 241 Am 9 Be, 210 Po 13 C Reconstructed Position Deviation [cm] 68 60 Ge - Configuration 4+1 Co 6 68 60 Ge - Configuration 5+1 Co 68 60 Ge - Configuration 5+1w Co Reconstructed Energy Deviation [%] 68 60 4 Ge - Configuration 6+1w Co 68 60 Ge - Configuration 4+1 Co 68 60 Ge - Configuration 5+1 Co 4 68 60 2 Ge - Configuration 5+1w Co 68 60 Ge - Configuration 6+1w Co 0 2 -2 0 Position uncert. R<5.5m 3cm -4 -2 FV uncert. ~1.6% -6 Energy deviation <2% -4 0 100 200 300 400 500 600 R [cm] 0 100 200 300 400 500 600 Use 12 B/ 12 N spallation uniformity for 5.5m<R<6m R [cm] → Total FV uncert R<6m: 1.8% Patrick Decowski / UC Berkeley 10

Systematic Uncertainties Systematic uncertainties between Δ m 212 and θ 12 decouple to a large degree Sum: 2.0% } Primarily affecting θ 12 Sum: 4.1% Patrick Decowski / UC Berkeley 11

Event Selection Prompt • Inverse beta-decay selection: • Rprompt, delayed < 6 m Z p [m] • 0.9 MeV < Eprompt < 8.5 MeV • 1.8 MeV < Edelayed < 2.6 MeV • Δ R < 2m • 0.5 μ s < Δ T < 1000 μ s • L-selector: Use event characteristics ρ 2 [m] to limit effect of accidental Delayed backgrounds at high R • Muon-induced spallation event cuts: Z d [m] • 2 ms veto after every μ • 2 s veto for showering/bad μ • 2 s veto in a R = 3m tube along track Balloon ρ 2 [m] Patrick Decowski / UC Berkeley 12

L-selector: Signal/Accidentals Discrimination Use prompt-delayed event characteristics to distinguish Accidental BG from Signal Generate Accidentals PDF from DATA (random pairs): f acc ( E p , E d , ∆ R, ∆ T, R p , R d ) 100 80 Generate Signal PDF from MC (no-osc spectrum): Efficiency (%) Efficiency f ν e ( E p , E d , ∆ R, ∆ T, R p , R d ) 60 L-selector (calculated EbE): 40 f ν e L = f ν e + f acc 0 1 2 3 4 5 6 7 8 E (MeV) prompt Establish L-selector cuts for different E p bins, where FOM is maximal S L cut (E p bins of 0.1MeV) FOM = √ S + B acc If for candidate event pair L > L cut → anti-neutrino Efficiency for E p >~3MeV as expected from spatial cuts alone Patrick Decowski / UC Berkeley 13

Dominant BG: 13 C( α ,n) 16 O 6.130 MeV From T 1/2 =22yr 5d 138d 3 - 6.049 MeV 0 + 222 Rn chain: 210 Pb 210 Bi 210 Po 206 Pb α , E=5.3MeV e+e- γ 0 + 1.1% abundance of 13 C in LS → 13 C( α ,n) 16 O 16 O Cross sections tuned using detector MC 4 4 -decay -decay 210 Po 13 C source deployed KamLAND PoC calib. source DATA into the detector S.Harissopulos et al., 3 3 Ground state (MC) � � PRC 72, 062801 (2005) } events/50keV/ events/50keV/ st 1 exc. state (MC) JENDL nd 2 exc. state (MC) 2 2 Total (MC) Good match after 210 Po/ 13 C 1 1 scaling C.S. mixture -7 -7 10 10 0 0 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 D.McKee et al., NIM A527, 272 (2008) E E (MeV) (MeV) visible visible Patrick Decowski / UC Berkeley 14

Backgrounds Accidental Coincidences } Cosmogenic } Background from 222 Rn chain Total excluding geo-neutrino Geo-neutrinos are a background to the neutrino oscillation measurement → Talk by John Learned Using one geological model, which assumes 16TW of radiogenic heat from U+Th geo-neutrinos, expect 69.7 events However, analysis is done by simultaneously fitting geo- and reactor neutrinos ! Patrick Decowski / UC Berkeley 15

Energy Spectrum From Mar 9, 2002 to May 12, 2007 1491 live days, 2881 ton-year exposure (3.8x KL2004) arXiv:0801.4589 / Accepted by PRL KamLAND data no oscillation 250 best-fit osci. Events / 0.425 MeV accidental 16 13 C( ,n) O � 200 best-fit Geo � e best-fit osci. + BG 150 + best-fit Geo � e 100 50 0 0 1 2 3 4 5 6 7 8 E (MeV) p Fit to scaled no-oscillation spectrum excluded at 5.1 σ Patrick Decowski / UC Berkeley 16

Neutrino Oscillation Parameters Solar Global KamLAND 20 4 σ 15 2 χ Best-fit light side: Δ 3 σ 10 2 σ ∆ m 2 = 7 . 58 +0 . 21 − 0 . 20 × 10 − 5 eV 2 5 1 σ tan 2 θ = 0 . 56 +0 . 14 1 2 3 4 5 6 LMA-2 LMA-1 KamLAND σ σ σ σ σ σ − 0 . 09 95% C.L. 99% C.L. 99.73% C.L. ) 2 best fit (eV -4 10 21 Best-fit dark side: 2 m Δ ∆ m 2 = 7 . 64 × 10 − 5 eV 2 Solar 95% C.L. tan 2 θ = 1 . 84 99% C.L. LMA-0 99.73% C.L. best fit -1 10 1 10 20 30 40 2 2 tan θ Δ χ 12 Patrick Decowski / UC Berkeley 17

Neutrino Oscillation Parameters Solar Global KamLAND 20 4 σ 15 2 χ Best-fit light side: Δ 3 σ 10 2 σ ∆ m 2 = 7 . 58 +0 . 21 − 0 . 20 × 10 − 5 eV 2 5 1 σ tan 2 θ = 0 . 56 +0 . 14 1 2 3 4 5 6 LMA-2 LMA-1 KamLAND σ σ σ σ σ σ − 0 . 09 95% C.L. 99% C.L. 99.73% C.L. ) 2 best fit (eV -4 10 21 Best-fit dark side: 2 m Δ ∆ m 2 = 7 . 64 × 10 − 5 eV 2 Solar 95% C.L. tan 2 θ = 1 . 84 99% C.L. LMA-0 99.73% C.L. best fit -1 10 1 10 20 30 40 2 2 tan θ Δ χ 12 Patrick Decowski / UC Berkeley 17

Global Analysis 8 ) 2 eV -5 7 (10 21 KamLAND + Solar 2 m 95% C.L. " 6 99% C.L. 99.73% C.L. best fit 5 0.2 0.3 0.4 0.5 0.6 0.7 0.8 2 tan ! 12 Solar Experiments + KamLAND: ∆ m 2 = 7 . 59 +0 . 21 − 0 . 21 × 10 − 5 eV 2 tan 2 θ = 0 . 47 +0 . 06 − 0 . 05 Patrick Decowski / UC Berkeley 18