Neutrino at Daya Bay, 28 Nov 2003 KamLAND: Disappearance of Reactor Anti-neutrinos Kam-Biu Luk...

Neutrino at Daya Bay, 28 Nov 2003

KamLAND: Disappearance of Reactor Anti-neutrinos

Kam-Biu Luk

University of California, Berkeleyand

Lawrence Berkeley National Laboratory


Determination of m122 and 12

• LMA is favoured

• This region can be explored with reactor with a baseline of ~100 km

~ 100 km


The KamLAND Experiment


Nuclear Reactors in Japan

~80GW

~ 180 km

86% of eventsfrom ~180 km


Thermal Flux from Japanese Reactors


Present analysis

The KamLAND Detector

~22%

(3.2 kton)


Detecting Reactor e in Liquid Scintillator


68Ge : 1.012 MeV (+) 65Zn : 1.116 MeV ()60Co : 2.506 MeV ( +) AmBe : 2.20 , 4.40, 7.6 MeV

-5m 5m

Reconstructing Position

Position resolution ~ 25 cm


Energy Determination

E/E ~ 7.5% /√E , Light Yield ~ 300 p.e./MeVEnergy scale stable to 0.6% through out the period

Esyst = 1.91% at 2.6 MeV 2.13% for e


Prompt E ~ 3.2 MeV

t ~ 110 sec

Delayed E ~ 2.22 MeV

R ~ 0.35 m

An Anti-neutrino Candidate

timecharge


12B12N

L < 3m

-Induced Neutrons & Spallation-12B/12N


V/V = 4.06 %

Vfid/Vfid = 4.6 %

Neutron

R = 5m

R = 5m

R3 Vertex Distributions of Neutrons & 12B/12N


Radioactivity inside Liquid Scintillator


Energy Spectrum of Radioactivity inside Liquid Scintillator

×

×

×

Requirements for reactor e detection:

238U 232Th ~ 10-14 g/g 40K ~ 10-15 g/g


Estimated Systematic Uncertainties

For Eprompt > 2.6 MeV

4.60

%Total LS mass 2.13Fiducial mass ratio 4.06Energy threshold 2.13Tagging efficiency 2.06Live time 0.07Reactor power 2.05Fuel composition 1.00Time lag 0.28e spectra 2.48Cross section 0.2

Total Uncertainty 6.42 %


Data Sample Mar. 4 – Oct. 6, 2002 162 ton•yr (145.1 days)

Fiducial cut: • R < 5m Mass = 408 ton, yielding 3.46 x 1031 free protons Inverse -decay selection: • no OD signals • Eprompt > 2.6 MeV • 1.8 < Edelay < 2.6 MeV • R < 1.6m, 0.5 < T < 660 sec Using AmBe & LED, tag= (78.31.6)% Software cut on Spallation event: • T < 2sec

• E > 3 GeV or R< 3m

e Event Selection

Eprompt > 2.6 MeV

x2 + y2 (m2)

8

6

4

2

0

-2

-4

-6

-80 5 10 15 20 25 30 35 40 45 50

Z (m)


Correlation Between Prompt and Delayed Energies

from n12C


• Based on 162 ton•yr, with Eprompt > 2.6 MeV

Final sample, Nobs 54 events Expected, Nno 86.8 5.6(sys) events

Background, Nbg 0.95 0.99 event Accidental 0.0086 0.0005 event 9Li/8He (, n) 0.94 0.85 event fast neutron < 0.5 event

• Evidence for Reactor e Disappearance

First Results From KamLAND

= 0.611 0.085 (stat) 0.041 (sys)Nobs - Nbg

Nno


Perspective of Observed Rate Deficit

LMA: m12

2 = 5.5x10-5eV2

sin22 = 0.833G.Fogli et al., PR D66, 010001-406,(2002)

LMA flux predictionat 95% C.L.

Nob

s/N

no_

osc


Implication of Observed Rate Deficit

BeforeKamLAND


Energy Spectrum (Eprompt > 2.6 MeV)


Impact of KamLAND Results onm12

2 and 12

Best fit : m12

2 = 6.9 x 10-5 eV2

sin22= 1.0

95 % C.L.


Spring 2003 : Inspection 2006

2002

Operation of Reactors

Useful for distinguishingLMA-I from LMA-II

Reduce rate by 50%but good for studyingbackgrounds


Future Prospects

With 5 years of running

95 % C.L.


• Based on 162 ton•yr of data, KamLAND 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.

Conclusions


G.A.Horton-Smith, R.D.McKeown, J.Ritter, B.Tipton,

P.VogelCalifornia Institute of Technology

C.E.Lane, T.MileticDrexel University

Y-F.WangIHEP, Beijing

T.TaniguchiKEK

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.SvobodaLouisiana State University

J.Detwiler, G.Gratta, N.Tolich, Y.UchidaStanford University

K.Eguchi, S.Enomoto, K.Furuno, Y.Gando, H.Ikeda, K.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.WatanabeTohoku University

L.DeBraeckeleer, C.Gould, H.Karwowski, D.Markoff,

J.Messimore, K.Nakamura, R.Rohm, W.Tornow,

A.YoungTUNL

J.Busenitz, Z.Djurcic, K.McKinny, D-M.Mei, A.Piepke,

E.YakushevUniversity of Alabama

P.Gorham, J.Learned, J.Maricic, S.Matsuno,

S.PakvasaUniversity of Hawaii

B.D.Dieterle

University of New Mexico

M.Batygov, W.Bugg, H.Cohn, Y.Efremenko, Y.Kamyshkov, Y.NakamuraUniversity of Tennessee

The KamLAND Collaboration


• 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

Neutrino Mixing

e

Ue1 Ue2 Ue3U1 U2 U3

U1 U2 U 3

123

e Ue1e iE1t1 Ue2e

iE2t2 Ue3e iE 3t3

• The time evolution of the flavour eigenstate is then given by:


Evidence of Neutrino Oscillation

Accelerator (LSND)Solar (SNO)Atmospheric (SuperK)


• Parametrize the mixing matrix as:

• The probability of ee is:

Probability of Neutrino Mixing

U 1 0 0

0 cos23 sin230 sin23 cos23

cos13 0 e i sin130 1 0

e i sin13 0 cos13

cos12 sin12 0

sin12 cos12 0

0 0 1

atmospheric reactor @ short baseline solar

P e e 1 sin2 (212 )sin2m12

2 L

4E

at large L/E.

Neutrino at Daya Bay, 28 Nov 2003 KamLAND: Disappearance of Reactor Anti-neutrinos Kam-Biu Luk...

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