KamLAND: Reactor Neutrino Detection & Recent Results

1. KamLAND[Kamioka Liquid Scintillator Anti-Neutrino Detector]Reactor Neutrinos & Recent Results Junpei Shirai Research Center for Neutrino Science, Tohoku University (for the KamLAND Collaboration) Apr.17, 2004, Carolina Neutrino Workshop @University of South Carolina

2. K.Nakamura et al. 1012 Expected neutrino spectra from various sources The spectra steeply increases below ~10MeV and dominated by fluxes from reactors, earth, sun, etc. It is very important to measure low energy neutrinos. We can learn a lot not only on fundamental properties but on generating mechanism of the neutrino! 10MeV 10-20

3. Physics of KamLAND 1000ton liq. Scintillator to detect low energy n KamLAND Particle physics Geo-physics Solar physics Astrophysics Reactor n Supernova n Relic n Geo n Solar n

4. Long history ! Challenge to the Solar NP ‘60s Cl(Homestake): 37Cln37Ar e- 4p+2e-4He+2n+26.7MeV-En Significant deficit of n than expected! [SNP] ‘80s H2O(Kamiokande) [real time; 8B-n] Reactor experiments nxenxe [ES] ‘90s Ga(Gallex/Sage/Gno): for pp-n 71Gan71Ge e- ‘50~ *nm : Dm2≠0 H2O(SuperK) [real time; 8B-n] nxenxe [ES] ‘00s D2O(SNO) [real time; 8B-n] No evidence for n-disappearance Before KamLAND! Fne<FSSM], Fn-tot= FSSM], FS] consistent with FSSM] nde-pp [CC] nxdnxnp [NC] Conclusive evidence for flavor change; nnx. The results are well explained by oscillation with MSW-scheme, the LMA solution is the most promising one. KamLAND Other decisive experiment is needed!

5. P(nene) KamLAND makes a challenge to SNP by Reactor Neutrino Experiment Reactor: Pure ne source Detector: n+AX+Y+2n+Qth(~200MeV) P(nene)=1-sin22q b-decay n-rich ~6ne 2[DM2L/4E] *Commercial power reactor (3GWth): 5.61020ne/s! 235U,239Pu,238U,241Pu DM2 ~10-5eV2 [LMA] (L~100km) KamLAND 70GW; ~6% of world’s reactor power <L>=185km Event rate/yr/kt 1000ton LS target 100 200 900 Distant from Kamioka(km)

6. Dm2 sensitivity (eV2) Reactor power Target Mass (MW*ton) KamLAND Previous reactor results First to reach 10-5 eV2. Fit without oscillation Goesgen: Excellent agreement with expectation Derived independently from b-spectroscopy Events/MeV/hr No n-deficit up to 1km Positron Energy

7. KamLAND Collaboration

8. Location of KamLAND 400km Underground Lab.(KamLAND) Toyama 2.2km Kamioka Gifu

9. KamLAND area Mt.Ikenoyama 1km SuperK Detector 2.2km Control room Rn-free gas system Water purification system Oil purification system To the mine entrance

10. KamLAND Detector Calibration device 1000m rock (=2700m water equivalent) m rate:~0.34Hz, 10-earth level Stainless-steel spherical tank (18mf) Inner Detector LS: PC(20%)+n-dodecane(80%) +PPO(1.52g/l); 1000ton Plastic balloon (3nylon+2EVOH film, 135mm thick; Rn-barrier) Buffer oil (iso+n-dodecane, 2.5mthick) PMT: 1325(17”)+ 554(20”), 34%4p LS 13m Outer Detector Shield against fast n, g from rocks, Water Cherenkov detector to identify cosmic m’s Pure water(3.2kton) PMT: 20”(225) 20m

11. PMT assemble & installation Sendai (‘99~’00) Kamioka Completed! (Sep.’00) In the detector tank

12. Balloon development (‘97~’99) Proto-type 1/4-scale model 4 proto types, 3 1/4-scale and 1 real size models were tested before the final version! Real-size model Water test in KamLAND

13. Balloon installation Detector tank (Dec.’00-Mar.’01) Pulling up! Kamioka Final version Looking up the balloon.

14. Taking measure against Rn. 2000 Insert nylon pipes into the stainless steel pipes. Eval lining in the tanks. Cleaning the purification system 2000~2001 Cleaning every parts by water, detergent, chemical,…

15. Oil filling May.-Oct., ‘01. Mineral oil delivery Prepare and purify LS & MO Water extraction (K, U,Th) N2 purge (O2, H2O) To detector Simultaneous water filling in the anti-counter Monitor the balloon in the detector

16. First light of KamLAND ! Nov.26, 2001 Clipping m-on

17. nedetection Inverse b decay: Prompt =En-0.8MeV e+e- Te 2g(0.51MeV) ne + p  e+ + n [1.8MeV] Delayed neutron-ID t~210ms npd+g(2.2MeV) Only ne. Prompt-Delayed combination (D, DT) and delayed capture energy for neutron-ID significantly reduces backgrounds ! Cross section: large ~100(nene) and precisely known (0.1%).

18. Front Electronics

19. e flux calculation from reactor information Neutrino spectra of fuel elements/fission Thermal power Burnup Reactorn flux (1.8-8MeV) @KamLAND Fission rate Total 235U 239Pu Wakasa Bay F(En) Kashiwazaki 238U reactors Others 239Pu

20. Vertex distribution at different energy region. Balloon Balloon Stopping m Unstable nuclei produced by m’s 214Bi in the balloon Fid.vol(R<5m) Fid.vol(R<5m) External g  Radio-impurities in the liq. scintillator ’s from 40K in the balloon Fiducial volume cut rejects backgrounds near the balloon. Requiring delayed neutron rejects most of backgrounds in the fiducial volume except for neutron emitters (8He/9Li), fast neutrons and a part of events below 1 MeV which are carefully analyzed.

21. 214Bi 214Po 210Pb b Radio-impurity check by 214Bi-214Po chains Pob spectrum  bspectrum  t=237ms Fid.vol. cut Fid.vol. cut DT of delayed a’s t(Po)=237ms) Vertex position of delayed a Thermo- meter & a string Fid.volume

22. U/Th concentrations from Bi-Po decays (Mar.’02 -Oct.‘02) U; 214Bi 214Po 1mBq/m3 0.035mBq/m3 <<1mBq/m3 7 months (Mar.~Sep.,’02) 0.17mBq/m3 U: (3.5±0.5)10-18g/g Th; 212Bi 212Po Th: (5.2±0.8)10-17g/g (Assuming radio-equilibrium) Highest level of radio-purities in the world !! 1mBq/m3 U/Th series in KamLAND LS highly clears 1mBq/m3, which is required for planned 7Be solar neutrino detection !

23. Energy calibration gray sources68Ge(2.511), 65Zn(1.116), 60Co(1.173+1.332), Am/Be (7.652); along the central vertical axis (z axis). Time dependence: 0.6% Neutron captures after spallation events ; np (2.225), n12C13C (4.947); 4p position dependence: 1.4%, linearity: 1.1% Fractional difference of reconstructed and the known energies of g-ray sources Systematic error Sys. error DEsys=1.9% @2.6MeV 2.1% for DNev.

24. Position calibration [Nev,obs/Nev,calc] [NTot,obs/NTot,calc] 60Co g-ray sources along the Z-axis Position resolution s=25cm Non z-axis; by spallation neutrons Uncertainty of the event number in the fiducial volume; 1- =± DNev/Nev 

25. Energy spectrum of single ionization events 85Kr Observed spectrum is well understood by U/Th, spallation events and backgrounds.

26. Rejection of m-on induced backgrounds Study of fast neutron background m Most unstable products b-decays, and they are rejected by requiring delayed neutron. m n n Neutron emitters (8He&9Li) are rejected by time/space cuts. m m Fid. vol. veto Balloon R of the prompt events tagged by only the outer detector <0.5events “Showering m-on” (extra charge DQ>106 p.e .~3GeV): 2s veto of total volume. Non-showering m-on; Dead time; 11.4% Li/He: 0.94±0.85 events (in the sample of first Results, 0.162ktyear) Veto 2s & 3m within the m-on track.

27. Event selection for reactor ne events: [Before Eprompt cut] [Data sample:0.162ktonyr from 145.1d of Mar-Oct,’02] Edelay vs.DR Fiducial vol.; R<5m Delayed; ay=(1.8-2.6)MeV DR<160cm DT=(0.5-660)ms >1.2m from z-axis. Prompt; Eprompt>2.6MeV [remove geo-n] 160cm Eprompt vs. Edelay neutron-captured by 12C Edelay vs.DT 2.6MeV 660ms Observed: 54 events (~1 background from 9Li/ 8He and fast neutrons) Expected (with no-oscillation): (86.8±5.6) events

28. Positron spectra and rate R(obs/ no-oscill.)=0.611±0.085(stat)±0.041(sys)(Ee+>2.6MeV) KamLAND ~180km 1km 2.6MeV First observation of reactor ne deficit (99.95%CL). Assuming CPT invariance n-oscillation is the dominant process to SNP. (Other mechanisms like SFP(spin-flavor precession) due to mn and n-decay are not the leading mechanism to the SNP.)

29. Allowed & excluded oscillation regions by KamLAND and other experiments [Rate only] By assuming CPT invariance all solutions to the SNP other than LMA is excluded. A part of LMA is also excluded. [Rate+Shape] LMA is further restricted to two narrow regions in Dm2. Including Eprompt>0.9MeV data with a free parameter for geo-n does not change a lot. Geo-n events; 4(238U) and 5(232Th) are obtained (~40TW), while radio- genic power 0~110TW are allowed @95%CL.

30. KamLAND continues data taking ! Fraction of the physics run time/week 100% 80% 7 months Mar.’04 Aug.’03 Detector is quite stable; 2 years data have been accumulated since Mar.’02.

31. Prospects of KamLAND Higher statistics requires less systematic error (6.4% now). . It will be reduced by; studies on energy scale, improved vertex position 95%CL allowed by 5-year data 5% 4π calibration device 3% 2 bands in LMA can become narrower and discriminated by ~10s

32. Another oscillation search by a new reactor (Shika-2) joining in 2006 ! 3.926GWth at 88km from KamLAND(Oscill. Minimum). 25% increase of Fn at KamLAND. Expected contribution of Shika-2 by 3-year data sample No oscill. KamLAND 2.6MeV No of events (>2.6MeV) R(exptd/no osc.) 100km 1km LMA1: 45±37 .26±.21 LMA2: 121±36 .70±.21 No oscill. 173

33. Solar ne search by KamLAND Transition mn(0) BT(Solar Mag.Field): nenm + Flavor oscillation : nmne [PRL92,071301(2004)] Mn0 suggests possible magnetic moment and neutrino decay which may make a contribution to SNP. ne ne 1) Majorana (n=n) 2) n decay: |ne>=cosq|n1>+sinq|n2> n1+J[Majoron] cosq|ne>-sinq|nm> KamLANDhas a source-independent sensitivity to ne. If we take a search region, En=8.3-14.8MeV, dominant flux of 8B solar n can be used for the studies on nene transition. Reactor n, atmospheric n, WIMPs, relic n are expected to be small, <0.1 events/ktyear.

34. Data sample: 185.5 live-days in ’02, 0.28ktonyear (0.162ktonyear:first results) Correlated events (nepe+n) with Ee+=7.5-14.0MeV, Rfid.vol<550cm (500cm) *Bkg. .2 .2 (reactor) .001(atmosph.) .3 .2(fast n) .002 (accidental) .6 .2(8He/9Li) Sys. Error 6.3% e: 1.6% s: .2 npfv : 4.3 Eth: 4.5 livetime: .07 1.10.4 No ne signal ! Fn<370cm-2s-1 (90%CL) <2.8 10-4FSSM[(8.3-14.8)MeV] Search region for solar ne 30 times improves the previous best limit by SuperK[PRL90,171302(‘03)] [mn/10-10mB][BT/100kG]<1.3 (mn<110-10mB by MUNU,PLB553,7(2003)) t2/m2>0.067s/eV PromptEe+ Delayed E The results constrain models of mn and n lifetime.

35. Challenge to Geo-n detection Radiogenic heat generation: How much? It is the basic factor in the interior dynamics and evolution of the earth, but not well known. It is dominated by 238U and 232Th decays, and expected to ~16TW, but is model dependent and no direct measurement to date. KamLAND can measure the flux and spectrum (>1.8MeV) of geo-ne; 5 b-decays with Qb1.8MeV are observed; 238U:234PaU, 214BiPo, 232Th:228AcTh, 212BiPo, 208TlPb ~60 ne events/kt/yr (@16TW) U/Th ratio New approach to geo-physics will be opened by KamLAND !!

36. Challenge to 7Be solar n by KamLAND New real-time measurement of solar n other than 8B-n. HighIntensity; 109 (7.3% of the total) Next to the pp-n flux, ~940FB] Low Energy and monochromatic; 862keV(90%), 384keV(10%) from 7Be e-7Li n(g) KamLAND: recoil electron of nee (Te280keV; 14C bdecay) Spectrum: “Compton edge (665keV)” of 862keV Seasonal variation: ~7% (min./max.) High statistics : 9.6104 /ktonyear [LMA]

37. Direct check of LMA, Mixing parameter measurement, CPT check with reactor results Significance of the flux measurement is increased if uncertainty of the SSM prediction (±10%) is reduced by better understanding of the burning mechanism of the sun ! Sensitivity to m by 1.5ktyr Search for m LMA Backgr. subtracted f Sys.:3% EM: FSSM*0.99  (90%CL) ds/dT=(ds/dT)Weak +(ds/dT)EM m2(pa2/me2)(1/Te-1/En)  Lower En and Te makes sensitive to the contribution of EM term from m. trial study

38. 85Kr Present status Future goal !

39. Challenging 7Be solar n Goal: 1mBq/m3 New purification System to remove; 85Kr (t1/2; 10.8yr) ~1Bq/m3 210Pb (t1/2; 22.3yr) ~0.1Bq/m3 85Kr, 210Pb R&D’s are underway! New nitrogen purge, Filtration,adsorption,distillation,etc. [Present system] Water extraction N2 purge 85Kr 85Rb (687keV) 222Rn (t1/2; 3.8d) 218Po214PbBiPo210Pb 210Pb 210Bi 210Po 206Pb ~1hr b(1163) (5304)

40. KamLAND with a 1000ton ultra-pure liq.scintillator is challenging to low energy n physics; Conclusion First observationof reactor n disappearance (challenge to LMA); Strongly supports n oscillation, Excludes all solutions to SNP except for LMA (by rate), Restricts oscillation parameters (rate+shape). Higher statistics of reactor data is being analyzed to find spectrum distortion which will be another evidence for neutrino oscillation and further restrict the parameter region. New results on ne above the reactor energy region provides improved limits on [trans.-msolar BT] and n-lifetime. Detection of geo-n; first results will come out soon and it would open up a new field of “n-geophysics”.

41. 7Be solar n; KamLAND has made R&Ds to realize the challenging measurement. Direct confirmation of LMA and precise measurement of the flux could contribute a lot to determination of the oscillation parameters and better understanding of the burning mechanism of the sun.