Kamland, a culmination of half century of reactor neutrino studies


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KamLAND, a culmination of half century of reactor neutrino studies.

  • Petr Vogel, Caltech


Selected references to this lecture:

  • Kamland papers:

  • K.Eguchi et al., Phys. Rev. Lett.90, 021802 (2003),

  • K.Eguchi et al., Phys. Rev. Lett.92, 071301 (2004),

  • T. Araki et al., hep-ex/0406035 .

  • General review:

  • C. Bemporad, G. Gratta, and P. Vogel., Rev. Mod. Phys. 74, 297 (2002).



Pontecorvo already in 1946 suggested to

  • Pontecorvo already in 1946 suggested to

  • use nuclear reactors in order to perform

  • neutrino experiments.

  • Indeed, in 1953-1959 Reines and Cowan

  • showed that neutrinos are real particles

  • using nuclear reactors as a source.

  • Since then, reactors, powerful sources

  • with ~6x1020 /s electron antineutrinos

  • emitted by a modern ~3.8 GWthermal reactor,

  • have been used often in neutrino studies.

  • The spectrum is well understood….



Electron antineutrinos are produced by the  decay of fission fragments



Reactor spectrum:

  • Reactor spectrum:

  • 1) Fission yields Y(Z,A,t), essentially all known

  • 2) decay branching ratios bn,i(E0i) for decay branch i,

  • with endpoint E0i , some known but some (particularly

  • for the very short-lived and hence high Q-value)

  • unknown.

  • 3)  decay shape, assumed allowed shape, known

  • P(E,E0i,Z) or for electrons Ee= E0 – E

  • dN/dE = n Yn(Z,A,t) i bn,i(E0i) P(E,E0i,Z)

  • and a similar formula for electrons.

  • If the electron spectrum is known, it can be `converted’

  • into the antineutrino spectrum.



Spectrum Uncertainties



Reactor spectra



Detecting reactor antineutrinos; low detection threshold required





The survival probability of electron

  • The survival probability of electron

  • antineutrinos of energy E produced

  • at the distance L from the detector is

  • Pee(E,L) = 1 – sin2(2)sin2(m2L/4E

  • The experiment become sensitive to

  • oscillations if m2L/E ~ 1,

  • proof of oscillations is Pee(E,L) < 1.





Discovery of oscillations of atmospheric

  • Discovery of oscillations of atmospheric

  • neutrinos implies m2 ~ (2-3)x10-3 eV2,

  • thus indicating that reactor experiments

  • with L ~ (1-3) km should be performed

  • (Chooz and Palo Verde).

  • Also, the preferred `solution’ to the solar

  • neutrino deficit implies m2 ~ (5-10)x10-5 eV2,

  • thus indicating that reactor experiments

  • with L ~ 100 km should be performed

  • (KamLAND)

























Note: The best background in 76Ge  decay

  • Note: The best background in 76Ge  decay

  • detectors is at present ~0.2 counts/(keV kg y).

  • Expressing the background in the liquid scintillator

  • in KamLAND in the same units, and for

  • energies 2-3 MeV, one finds value ~10 times

  • smaller going out to 5.5 m radius and ~20 times

  • smaller for 5 m radius





















Decay chain leading to 210Po:

  • Decay chain leading to 210Po:

  • 222Rn (3.8d) 218Po (3.1m) 214Pb (27m) 214Bi,

  • 214Bi (20m) 214Po (164s) 210Pb (22.3y) 210Bi,

  • 210Bi (5d) 210Po (138d) 206Pb(stable)

  • The long lifetime of 210Pb causes its accumulation.

  • The from 210Po decay then interact with 13C in

  • the scintillator by 13C(,n)16O making unwanted

  • background. There is only ~10-11g of 210Pb in

  • fhe fiducial volume, enough however to cause

  • 1.7x109 decays in 514 days.















What’s next?



Future Reactor Measurements



A high sensitivity search for e from the Sun and other sources at KamLAND



Thanks to Atsuto Suzuki, Patrick Decowski,

  • Thanks to Atsuto Suzuki, Patrick Decowski,

  • Gianni Fiorentini, Andreas Piepke and

  • Giorgio Gratta who made some of the

  • figures used in this talk.



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