Kam LAND Disappearance of Reactor Antineutrinos KamBiu Luk

Kam. LAND: Disappearance of Reactor Anti-neutrinos Kam-Biu Luk University of California, Berkeley and Lawrence Berkeley National Laboratory Neutrino at Daya Bay, 28 Nov 2003

Determination of Dm 122 and 12 • LMA is favoured • This region can be explored with reactor with a baseline of ~100 km ~ 100 km Neutrino at Daya Bay, 28 Nov 2003

The Kam. LAND Experiment Neutrino at Daya Bay, 28 Nov 2003

Nuclear Reactors in Japan ~80 GW 86% of events from ~180 km ~ 180 km Neutrino at Daya Bay, 28 Nov 2003

Thermal Flux from Japanese Reactors Neutrino at Daya Bay, 28 Nov 2003

The Kam. LAND Detector r m Dr ~22% (3. 2 kton) Present analysis Neutrino at Daya Bay, 28 Nov 2003

Detecting Reactor e in Liquid Scintillator Neutrino at Daya Bay, 28 Nov 2003

Reconstructing Position 68 Ge : 1. 012 Me. V (g + g) 60 Co : 2. 506 Me. V (g +g) -5 m 65 Zn : 1. 116 Me. V (g) Am. Be : 2. 20 , 4. 40, 7. 6 Me. V (g) Position resolution ~ 25 cm Neutrino at Daya Bay, 28 Nov 2003 5 m

Energy Determination DEsyst = 1. 91% at 2. 6 Me. V 2. 13% for e DE/E ~ 7. 5% /√E , Light Yield ~ 300 p. e. /Me. V Energy scale stable to 0. 6% through out the period Neutrino at Daya Bay, 28 Nov 2003

An Anti-neutrino Candidate Delayed E ~ 2. 22 Me. V Prompt E ~ 3. 2 Me. V m charge time Dt ~ 110 msec DR ~ 0. 35 m Neutrino at Daya Bay, 28 Nov 2003

m-Induced Neutrons & Spallation-12 B/12 N DL < 3 m 12 N 12 B Neutrino at Daya Bay, 28 Nov 2003

R 3 Vertex Distributions of Neutrons & DVfid/Vfid = 4. 6 % DV/V Neutron = 4. 06 % R = 5 m Neutrino at Daya Bay, 28 Nov 2003 R = 5 m 12 B/12 N

Radioactivity inside Liquid Scintillator Neutrino at Daya Bay, 28 Nov 2003

Energy Spectrum of Radioactivity inside Liquid Scintillator Requirements for reactor e detection: 238 U 232 Th ~ 10 -14 g/g 40 K ~ 10 -15 g/g × × × Neutrino at Daya Bay, 28 Nov 2003

Estimated Systematic Uncertainties For Eprompt > 2. 6 Me. V Total LS mass Fiducial mass ratio Energy threshold Tagging efficiency Live time Reactor power Fuel composition Time lag e spectra Cross section 2. 13 2. 05 0. 2 Total Uncertainty Neutrino at Daya Bay, 28 Nov 2003 % 4. 06 2. 13 2. 06 0. 07 1. 00 0. 28 2. 48 6. 42 % 4. 60

e Event Selection Data Sample Mar. 4 – Oct. 6, 2002 162 ton • yr (145. 1 days) · Fiducial cut: • R < 5 m 8 Mass = 408 ton, yielding 3. 46 x 1031 free protons 6 · Inverse b-decay selection: 4 • no OD signals 2 • Eprompt > 2. 6 Me. V Z (m) 0 • 1. 8 < Edelay < 2. 6 Me. V • DR < 1. 6 m, 0. 5 < DT < 660 msec -2 Using Am. Be & LED, tag= (78. 3 1. 6)% · Software cut on Spallation event: • DTm < 2 sec • DEm > 3 Ge. V or DRm < 3 m Eprompt > 2. 6 Me. V -4 -6 -8 0 5 10 Neutrino at Daya Bay, 28 Nov 2003 15 20 25 30 35 x 2 + y 2 (m 2) 40 45 50

Correlation Between Prompt and Delayed Energies g from n 12 C Neutrino at Daya Bay, 28 Nov 2003

First Results From Kam. LAND • Based on 162 ton • yr, with Eprompt > 2. 6 Me. V Final sample, Nobs Expected, Nno 54 events 86. 8 5. 6(sys) events Background, Nbg 0. 95 0. 99 event Accidental 9 Li/8 He (b, n) fast neutron 0. 0086 0. 0005 event 0. 94 0. 85 event < 0. 5 event • Evidence for Reactor e Disappearance Nobs - Nbg Nno = 0. 611 0. 085 (stat) 0. 041 (sys) Neutrino at Daya Bay, 28 Nov 2003

Perspective of Observed Rate Deficit G. Fogli et al. , PR D 66, 010001 -406, (2002) Nobs/N no_osc LMA: Dm 122 = 5. 5 x 10 -5 e. V 2 sin 22 12 = 0. 833 LMA flux prediction at 95% C. L. Neutrino at Daya Bay, 28 Nov 2003

Implication of Observed Rate Deficit Before Kam. LAND Neutrino at Daya Bay, 28 Nov 2003

Energy Spectrum (Eprompt > 2. 6 Me. V) Neutrino at Daya Bay, 28 Nov 2003

Impact of Kam. LAND Results on Dm 122 and 12 95 % C. L. Best fit : Dm 122 = 6. 9 x 10 -5 e. V 2 sin 22 12 = 1. 0 Neutrino at Daya Bay, 28 Nov 2003

Operation of Reactors 2002 Spring 2003 : Inspection Reduce rate by 50% but good for studying backgrounds Neutrino at Daya Bay, 28 Nov 2003 2006 Useful for distinguishing LMA-I from LMA-II

Future Prospects 95 % C. L. With 5 years of running Neutrino at Daya Bay, 28 Nov 2003

Conclusions • Based on 162 ton • yr of data, Kam. LAND observed a deficit in the number of e events. • Interpreting this observation as evidence of neutrino oscillation, it implies the LMA solution as the most viable explanation of the solar-neutrino problem. • With higher statistics, we will look for spectral distortion, and measure neutrino mixing parameters with better precision. Neutrino at Daya Bay, 28 Nov 2003

The Kam. LAND Collaboration G. A. Horton-Smith, R. D. Mc. Keown, J. Ritter, B. Tipton, P. Vogel California Institute of Technology C. E. Lane, T. Miletic Drexel University L. De. Braeckeleer, C. Gould, H. Karwowski, D. Markoff, J. Messimore, K. Nakamura, R. Rohm, W. Tornow, A. Young TUNL Y-F. Wang IHEP, Beijing T. Taniguchi KEK B. E. Berger, Y-D. Chan, M. P. Decowski, D. A. Dwyer, S. J. Freedman, Y. Fu, B. K. Fujikawa, J. Goldman, K. M. Heeger, K. T. Lesko, K-B. Luk, H. Murayama, D. R. Nygren, C. E. Okada, A. W. Poon, H. M. Steiner, L. A. Winslow UC Berkeley/LBNL S. Dazeley, S. Hatakeyama, R. C. Svoboda Louisiana State University J. Detwiler, G. Gratta, N. Tolich, Y. Uchida Stanford University K. Eguchi, S. Enomoto, K. Furuno, Y. Gando, H. Ikeda, K. Inoue, K. Ishihara, T. Iwamoto, T. Kawashima, Y. Kishimoto, M. Koga, Y. Koseki, T. Maeda, T. Mitsui, M. Motoki, K. Nakajima, H. Ogawa, K. Oki, K. Owada, I. Shimizu, J. Shirai, F. Suekane, A. Suzuki, K. Tada, O. Tajima, K. Tamae, H. Watanabe Tohoku University J. Busenitz, Z. Djurcic, K. Mc. Kinny, D-M. Mei, A. Piepke, E. Yakushev University of Alabama P. Gorham, J. Learned, J. Maricic, S. Matsuno, S. Pakvasa University of Hawaii B. D. Dieterle University of New Mexico M. Batygov, W. Bugg, H. Cohn, Y. Efremenko, Y. Kamyshkov, Y. Nakamura University of Tennessee Neutrino at Daya Bay, 28 Nov 2003

Neutrino Mixing • If neutrinos have mass, it is possible that the weak eigenstates are not the same as the mass eigenstates: PMNS (Pontecorvo-Maki-Nakagawa-Sakata) matrix • The time evolution of the flavour eigenstate is then given by: Neutrino at Daya Bay, 28 Nov 2003

Evidence of Neutrino Oscillation Atmospheric (Super. K) Solar (SNO) Neutrino at Daya Bay, 28 Nov 2003 Accelerator (LSND)

Probability of Neutrino Mixing • Parametrize the mixing matrix as: atmospheric n • reactor n @ short baseline The probability of ne is: at large L/En. Neutrino at Daya Bay, 28 Nov 2003 solar n