The Previous Results and Future Possibilities of KamLAND Kazumi Tolich Stanford University 2/6/2007

2 Outline KamLAND Previous Reactor Neutrino Result Previous Geoneutrino Result Future Possibilities 1.Full Energy Analysis 2.Solar Neutrinos 3.Supernova

2/6/20073 KamLAND Introduction to the KamLAND experiment

2/6/20074 KamLAND Collaboration T. Ebihara, 1 S. Enomoto, 1 K. Furuno, 1 Y. Gando, 1 K. Ichimura, 1 H. Ikeda, 1 K. Inoue, 1 Y. Kibe, 1 Y. Kishimoto, 1 M. Koga, 1 Y. Konno, 1 Y. Minekawa, 1 T. Mitsui, 1 K. Nakajima, 1 K. Nakajima, 1 K. Nakamura, 1 K. Owada, 1 I. Shimizu, 1 J. Shirai, 1 F. Suekane, 1 A. Suzuki, 1 K. Tamae, 1 S.Yoshida, 1 J. Busenitz, 2 T.Classen, 2 C. Grant, 2 G. Keefer, 2 D.S.Leonard, 2 D. McKee, 2 A. Piepke, 2 B.E. Berger, 3 M.P. Decowski, 3 D.A. Dwyer, 3 S.J. Freedman, 3 B.K. Fujikawa, 3 F. Gray, 3 L. Hsu, 3 R.W. Kadel, 3 C. Lendvai, 3 K.-B. Luk, 3 H. Murayama, 3 T. O’Donnell, 3 H.M. Steiner, 3 L.A. Winslow, 3 C. Jillings, 4 C. Mauger, 4 R.D. McKeown, 4 C. Zhang, 4 C.E. Lane, 5 J. Maricic, 5 T. Miletic, 5 J.G. Learned, 6 S. Matsuno, 6 S. Pakvasa, 6 G.A. Horton-Smith, 7 A. Tang, 7 K. Downum, 8 G. Gratta, 8 K. Tolich, 8 M.Batygov, 9 W. Bugg, 9 Y. Efremenko, 9 Y. Kamyshkov, 9 A.Kozlov, 9 O. Perevozchikov, 9 H.J. Karwowski, 10 D.M.Markoff, 10 W. Tornow, 10 J.S. Ricol, 11 F. Piquemal, 11 and K.M. Heeger, Research Center for Neutrino Science, Tohoku University, Sendai , Japan 2. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA 3. Physics Department, University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 4. W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA 5. Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA 6. Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA 7. Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA 8. Physics Department, Stanford University, Stanford, California 94305, USA 9. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA 10. Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA and Physics Departments at Duke University, North Carolina State University, and the University of North Carolina at Chapel Hill 11. CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F Gradignan Cedex, France 12. Department of Physics, University of Wisconsin at Madison, Madison, Wisconsin, USA

2/6/20075 KamLAND Location KamLAND was designed to measure reactor anti-neutrinos. KamLAND is surrounded by nuclear reactors in Japan. KamLAND

2/6/20076 KamLAND Detector Electronics Hut Steel Sphere of 8.5m radius Water Cherenkov outer detector ” PMT’s 1 kton liquid- scintillator Inner detector ” PMT’s ” PMT’s 34% coverage 1km (2700 m.w.e) Overburden Buffer oil Transparent balloon of 6.5m radius

2/6/20077 Detecting Anti-neutrinos with KamLAND KamLAND (Kamioka Liquid scintillator Anti- Neutrino Detector) d p e+e+ 0.5 MeV  2.2 MeV  n p 0.5 MeV  e e-e- Inverse beta decay e + p → e + + n The positron loses its energy then annihilates with an electron. The neutron first thermalizes then gets captured on a proton with a mean capture time of ~200  s. Prompt Delayed Neutrino energy can be estimated by the kinetic energy of the positron plus 1.8MeV.

2/6/20078 Major Background Events for Antineutrino Detection Accidentals: uncorrelated events due to the radioactivity in the detector mimicking the inverse beta decay signature. 1 H(n,n) 1 H: the neutron collides with protons (prompt) and later captures on a proton (delayed). 12 C(n,n  ) 12 C: the neutron excites a 12 C producing a 4.4 MeV  (prompt), and later captures on a proton (delayed). 13 C( ,n  ) 16 O: the 16 O* de-excites with a 6 MeV  (prompt), and the neutron later captures on a proton (delayed). 13 C( ,n): 210 Po (introduced as 222 Rn) emits an  particle, which reacts with naturally occurring 13 C (~1.1% of C).

2/6/20079 Neutrino Oscillation Results Phys. Rev. Lett. 90, (2003) “First Results from KamLAND: Evidence for Reactor Anti- Neutrino Disappearance” 1269 citations as of last week! The most cited paper in physics in 2003 The 2nd most cited paper in all sciences in 2003 Phys. Rev. Lett. 94, (2005) “Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion” 425 citation as of last week!

2/6/ Neutrino Oscillations in Vacuum The weak interaction neutrino eigenstates may be expressed as superpositions of definite mass eigenstates The electron neutrino survival probability can be estimated as a two flavor oscillations:

2/6/ Selecting Reactor Anti-neutrino Events Δr < 2m 0.5μs < ΔT < 1000μs 2.6MeV < E e +, p < 8.5MeV 1.8MeV < E , d < 2.6MeV Veto after muons R p, R d < 5.5m e+e+ 0.5 MeV  2.2 MeV  0.5 MeV  Prompt Delayed

2/6/ Dataset and Rate Analysis From March to January ± 23.7 expected reactor antineutrinos with no oscillation ± 7.3 expected background events. 258 candidate events. The average survival probability is ± 0.044(stat) ± 0.047(syst). We confirmed antineutrino disappearance at % C.L. (~4  ).

2/6/ Prompt Energy Distribution KamLAND saw an antineutrino energy spectral distortion at 99.6% significance.

2/6/ Oscillation Analysis Shape distortion is the key factor in determining  m 2. Shape Only Shape + Rate

2/6/ Average Distance, L 0 L 0 = 180 km 80% of total flux comes from reactors 140 to 210km away. KamLAND

2/6/ L 0 /E Would the data come back up again??? Observed/No Oscillation Expected

2/6/ Geoneutrino Result Nature 436, (28 July 2005) “Experimental investigation of geologically produced antineutrinos with KamLAND”

2/6/ Convection in the Earth The mantle convection is responsible for the plate tectonics and earthquakes. The mantle convection is driven by the heat production in the Earth. Image:

2/6/ Heat from the Earth Heat production rate from U, Th, and K decays is estimated from chondritic meteorites to be 19TW. Heat flow is estimated from bore-hole measurements to be 44 or 31TW. Models of mantle convection suggest that the radiogenic heat production rate should be a large fraction of the total heat flow. Problem with –Mantle convection model? –Total heat flow measured? –Estimated radiogenic heat production rate?

2/6/ Geoneutrino Signal Inverse Beta Decay Threshold  decays in U and Th decay chains produce antineutrinos. Geoneutrinos can serve as a cross-check of the radiogenic heat production rate. KamLAND is only sensitive to antineutrinos above 1.8MeV Geoneutrinos from K decay cannot be detected with KamLAND.

2/6/ Selecting Geoneutrino Events Δr < 1m* 0.5μs < ΔT < 500μs* 1.7MeV < E,p < 3.4MeV 1.8MeV < E ,d < 2.6MeV Veto after muons R p, R d < 5m* ρ d >1.2m* e+e+ 0.5 MeV  2.2 MeV  0.5 MeV  Prompt Delayed *These cuts are tighter compared to the reactor antineutrino event selection cuts because of the excess background events for lower geoneutrino energies.

2/6/ Geoneutrino Candidate Energy Distribution Expected total Expected reactor 80.4 ± 7.2 Expected total background 127 ± 13 Expected U 14.8 ± 0.7 Expected ( ,n) 42 ± 11 Measured Accidental 2.38 ± 0.01 Expected Th 3.9 ± 0.2 Candidate data 152 events Data from March, 2002 to October, 2004.

2/6/ How Many Geoneutrinos? Expected chondritic meteorites 3 U geoneutrinos 18 Th geoneutrinos 28 U + Th geoneutrinos

Future Possibility I Full Energy Analysis My Thesis in Progress Reactor neutrinos Geoneutrinos

2/6/ Combined Analysis Combined analysis probes lower energy reactor anti- neutrinos and should improve  m 2 measurement. We will possibly observe the re-reappearance of reactor antineutrinos. Better understanding of reactor spectrum might improve the geoneutrino measurement. Re-reappearance?

2/6/ Previous and Planned Cuts Geoneutrino event selection cuts are tighter due to the low energy accidental background. Combined analysis requires consolidation of the difference in the event selection cuts.

2/6/ Real and Visible Energies E real is the particle’s real energy. E visible is determined from the amount of optical photons detected, including quenching and Cerenkov radiation effects. The model of E visible /E real as a function of E real fits calibration data very well. Previous analyses were done in positron real energy, having to convert background energies (such as  ’s) into effective positron real energies. Fit to our model 203 Hg 68 Ge 65 Zn 60 Co 1 H(n,  ) 2 H 12 C(n,  ) 13 C

2/6/ Expected Prompt Energy Spectra *Scaled approximately to the number of events expected. Reactor neutrinos Accidentals U geoneutrinos Th geoneutrinos ( ,n)

2/6/ Expected Delayed Energy Spectra *Scaled approximately to number of events expected n-capture on p Accidentals

2/6/ Expected  t Spectra *Scaled approximately to number of events expected n-capture on p Accidentals Previous Geoneutrino Analysis Cut

2/6/ Time Variation of Reactor Neutrino Flux Shika reactor ~90km (half of L 0 ) away turned on from May to July Shika contributed 14% of total flux. May help distinguish LMA I and LMA II.

2/6/ Probability Density Functions Expected prompt energy spectra and time variation of reactor neutrino flux were used in the previous analyses. Expected delayed energy and  t spectra will be added to distinguish accidental background. Prompt EnergyDelayed Energy tt Time

2/6/ Future Possibility II 7 Be Solar Neutrino Detection

2/6/ Solar Neutrinos from the p-p Chain Reactions p + p  2 H + e + + e p + e - + p  2 H + e 99.75% 0.25% 2 H + p  3 He 86% 14% 3 He + 3 He   + 2p 3 He +   7 Be 99.89% 0.11% 7 Be + e -  7 Li + e 862keV & 383keV 7 Be + p  8 B 7 Li + p   +  8 B  8 Be + e + + e 8 Be   +  7 Be e flux is much greater than 8 B e flux!

2/6/ Solar Neutrino Spectrum Solar Neutrino Flux at the surface of the Earth with no neutrino oscillations. Uses the solar model, BS05(OP). We expect to see a few hundred events per day.

2/6/ Be Solar Neutrino Detection Solar scatters off e -. The electron recoil energy is From e From  &  *Detection resolution is not included.

2/6/ Current Radioactivity in KamLAND After fiducial volume cut is applied

2/6/ Test Removal of Reducible Background Distillation removed 222 Rn by a factor of 10 4 to Heating and distillation reduced the 212 Pb activity by a factor of 10 4 to Distillation reduced the 40 K concentration in PPO by a factor of Distillation reduced nat Kr by a factor of 10 5 to 10 6.

2/6/ Expected Energy Spectra after the Purification 85 Kr Total BG 40 K 14 C

2/6/ From October 2006 Purification System Constructed The purification system is being commissioned right now. We have done some testing and are fixing bugs. We should be able to start the full purification operations soon.

2/6/ Future Possibility III Supernova Detection

42 Expected Signals For a “standard supernova” (d = 10 kpc, E=3x10 53 ergs, equal luminosity in all neutrino flavors), we expect to see (no neutrino oscillations): –~310 events –~20 events –~60 events –~45 events –~20 events –~10 events –~300 events (0.2 MeV threshold) There should be 300 e + events above 10 MeV, with an initial rate of 100 Hz (exponential decay with ~3s time constant). The proton scattering events (low visible energy) provide a determination of both luminosity of all neutrino flavors and temperature. * J. F. Beacom et al.

2/6/ Expected Proton Scattering Events * J. F. Beacom et al. E visible [MeV] dN/dE visible [1/MeV] Realistic energy threshold after purification of scintillator

2/6/ Supernova Trigger 8 high energy inverse beta decay events (>~9MeV) within ~0.8s causes a supernova trigger. With the supernova trigger, the trigger switches to a pre-determined supernova mode. The supernova mode has a lower energy threshold (~0.6MeV) in order to detect low energy events (especially ν + p → ν + p.) The energy threshold could be lowered after the purification.

2/6/ Conclusions KamLAND has been producing some impressive results. I am analyzing the full energy range, reactor neutrinos and geoneutrinos simultaneously, to improve sensitivity. The planned purification of scintillator will be followed by the solar neutrino phase. If there is a supernova explosion, KamLAND is the only detector that can possibly detect the proton scattering events.

2/6/ Questions?

2/6/ Total Heat Flow from the Earth Conductive heat flow measured from bore-hole temperature gradient and conductivity Deepest bore-hole (12km) is only ~1/500 of the Earth’s radius. Total heat flow 44.2  1.0TW (87mW/m 2 ), or 31  1TW (61mW/m 2 ) according to more recent evaluation of same data despite the small quoted errors. Image: Pollack et. al Bore-hole Measurements

2/6/ Radiogenic Heat U, Th, and K concentrations in the Earth are based on measurement of chondritic meteorites. Chondritic meteorites consist of elements similar to those in the solar photosphere. The predicted radiogenic total heat production is 19TW. Th/U ratio of 3.9 is known better than the absolute concentrations of Th and U.

2/6/ Reference Earth Model Flux ~20% from nearby crust (within ~30km). ~20% from outside of a ~4000km radius. ~25% from the mantle.

2/6/ MSW Effect in the Sun  e ’s experience MSW effect in the Sun. For 7 Be e ’s, For E = 862keV &  m 2 =7.9x10 -5 eV 2 Possible sin 2 2 

2/6/ Irreducible Radioactivity  ’s (1.46MeV) and  ’s from 40 K in the balloon  ’s (2.6MeV) from 208 Tl decay in the surrounding rocks 14 C throughout the detector (less than ~200keV) 11 C from cosmic muons (more than 700keV) Most of the 40 K and 208 Tl background is removed with fiducial volume cut. Most of the 14 C and 11 C background is removed with energy cut.

2/6/ Detector Capability The electronics’ buffers can hold ~10k high energy events (all PMTs hit). KamLAND handled a simulated supernova with 400 Hz high energy events (all PMTs hit) for 10 seconds with ~0.6MeV detector threshold.