1 / 43

Selected references to this lecture:

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).

conan
Download Presentation

Selected references to this lecture:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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).

  2. 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….

  3. Electron antineutrinos are produced bythe b decay of fission fragments

  4. Reactor spectrum: 1) Fission yields Y(Z,A,t), essentially all known 2) bdecay 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) b decay shape, assumed allowed shape, known P(En,E0i,Z) or for electrons Ee= E0 – En. dN/dE = Sn Yn(Z,A,t) Sibn,i(E0i) P(En,E0i,Z) and a similar formula for electrons. If the electron spectrum is known, it can be `converted’ into the antineutrino spectrum.

  5. Spectrum Uncertainties Theory only Klapdor and Metzinger, 1982 Beta calibrated Schreckenbach, 1985 Hahn, 1989 Bemporad, Gratta, and Vogel, RMP 74, 297 (2002) Results of Bugey experiment (1996)

  6. Reactor spectra

  7. Detecting reactor antineutrinos;low detection threshold required

  8. Detector reaction ne + p -> e+ + n, positron spectrum measured Cross section known to ~0.2%, see Vogel & Beacom, Phys. Rev. D60,053003

  9. To study oscillations, use the disappearance test: The survival probability of electron antineutrinos of energy En produced at the distance L from the detector is Pee(En,L) = 1 – sin2(2q)sin2(Dm2L/4En) The experiment become sensitive to oscillations if Dm2L/En ~ 1, proof of oscillations is Pee(En,L) < 1.

  10. History of reactor neutrino oscillation search: Probability of oscillations is proportional to sin2(Dm2L/4E). Since for the reactors E~4MeV, the sensitivity to Dm2 is inversely proportional to the distance L.

  11. Discovery of oscillations of atmospheric neutrinos implies Dm2 ~ (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 Dm2 ~ (5-10)x10-5 eV2, thus indicating that reactor experiments with L ~ 100 km should be performed (KamLAND)

  12. ~180 km

  13. ~80 GW : 6% of world nuclear power ~25GW : most powerful station in the world

  14. KamLAND Collaboration 13 institutions & 93 members Ｃｏｌｌａｂｏｒａｔｏｒ

  15. KamLAND Experiment 180 km 300 antineutrinos from the Sun . . .

  16. A brief history of KamLAND *Was 145.1 with old analysis † T.Araki et al,arXiv:hep-ex/0406035 Jun 13, 04 submitted to Phys Rev Lett

  17. A limited range of baselines contribute to the flux of reactor antineutrinos at Kamioka Over the data period Reported here Korean reactors 3.4±0.3% Rest of the world +JP research reactors 1.1±0.5% Japanese spent fuel 0.04±0.02%

  18. m- Induced Neutrons & Spallation-12B/12N DL < 3m 12B 12N DT (T-Tm ), DL

  19. Tagged cosmogenics can be used for calibration τ=29.1ms Q=13.4MeV 12B 12N τ=15.9ms Q=17.3MeV μ Fit to data shows that 12B:12N ~ 100:1

  20. Radioactivity in liquid scintillator 238U: 214Bi →214Po →210Pb β+γα τ=28.7 mτ=237 μs E=3.27 MeV E=7.69 MeV 232Th: 212Bi →212Po →208Pb β+γα τ=87.4 mτ=440 ns E=2.25 MeVE=8.79 MeV

  21. 238U: (3.5±0.5)∙10-18 g/g needed 10-14 g/g 232Th: (5.2±0.8)∙10-17 g/g τ=(219±29) μs Expected: 237 μs

  22. Note: The best background in 76Ge bb 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

  23. Systematic Uncertainties 4. 6 5 % : goal % Total LS mass 2.1 Fiducial mass ratio 4.1 Energy threshold 2.1 Tagging efficiency 2.1 Live time 0.07 Reactor power 2.1 Fuel composition 1.0 Time lag 0.28 ne spectra 2.5 Cross section 0.2 # of target protons < 0.1 Total Error6.4 % E > 2.6 MeV

  24. Expect 1.5 n-12C captures Very clean measurement Accidental background Second KamLAND paper

  25. 2003 saw a substantial dip in reactor antineutrino flux

  26. Good correlation with reactor flux Fit constrained through known background χ2=2.1/4 Expected for no oscillations 90% CL ~0.03 for 3TW hypothetical Earth core reactor (But a horizontal line still gives a decent fit with χ2=5.4/4)

  27. In CHOOZ it was possible to determine background by this effect.

  28. (766.3 ton·yr, ~4.7 the statistics of the first paper) Results Observed events 258 No osc. expected 365±24(syst) Background 7.5±1.3 Inconsistent with simple 1/R2 propagation at 99.995% CL (Observed-Background)/Expected = 0.686±0.044(stat)±0.045(syst) Caveat: this specific number does not have an absolute meaning in KamLAND, since, with oscillations, it depends on which reactors are on/off Second paper

  29. Decay chain leading to 210Po: 222Rn a(3.8d) 218Po a(3.1m) 214Pb b(27m) 214Bi, 214Bi b(20m) 214Po a(164ms) 210Pb b(22.3y) 210Bi, 210Bi b(5d) 210Po a(138d) 206Pb(stable) The long lifetime of 210Pb causes its accumulation. The a from 210Po decay then interact with 13C in the scintillator by 13C(a,n)16O making unwanted background. There is only ~10-11g of 210Pb in fhe fiducial volume, enough however to cause 1.7x109a decays in 514 days.

  30. Ratio of Measured to Expected ne Flux from Reactor Neutrino Experiments LMA: Dm2 = 5.5x10-5 eV2 sin2 2Q = 0.833 G.Fogli et al., PR D66, 010001-406, (2002)

  31. Energy spectrum now adds substantial information Best fit to oscillations: Δm2=8.3·10-5 eV2 sin22θ=0.83 Straightforward χ2 on the histo is 19.6/11 Using equal probability bins χ2/dof=18.3/18 (goodness of fit is 42%) A fit to a simple rescaled reactor spectrum is excluded at 99.89% CL (χ2=43.4/19) Second paper

  32. This result Δm2=8.3·10-5 eV2 sin22θ=0.83 First KamLAND result Dm2 = 6.9 x 10-5 eV2 sin2 2 q = 1.0

  33. Combined solar ν – KamLAND 2-flavor analysis Includes (small) matter effects

  34. KamLAND uses a range of L and it cannot assign a specific L to each event Nevertheless the ratio of detected/expected for L0/E (or 1/E) is an interesting quantity, as it decouples the oscillation pattern from the reactor energy spectrum no oscillation expectation p/2 Hypothetical single 180km baseline experiment p

  35. Conclusions KamLAND reactor exposure: 766.3 ton·yr (470% increase) Data consistent with large flux swings in 2003 Spectrum distortions now quite significant, shape-only very powerful Best KamLAND fit to oscillations Δm=8.3·10-5 eV2, sin22θ=0.83 LMA2 is now excluded Together with solar ν Welcome to precision neutrino physics !

  36. What next in reactor neutrino studies? What’s next? • Purification of liquid scintillator; remove 85Kr • and 210Pb (low energy background) and • attempt to observe solar 7Be ne • (feasibility studies under way). • Determine or constrain the flux of solar • antineutrinos and of the geoneutrinos. Study • the neutron production by muons. • In a different reactor experiment (two detectors, • one close and another at ~1-2 km) determine or • constrain the unknown mixing angle q13. That • is a whole different story.

  37. Future Reactor Measurements Chooz reached at ~1 km 2.8% statistical error 2.7% systematic error Next generation search for Theta-13 needs to achieve ~1% errors Apollonio et al., EPJ C27, 331 (2003)

  38. A high sensitivity search for ne from the Sun and other sources at KamLAND hep-ex/0310047, Phys. Rev. Lett. 92, 071301 (2004) No events found between 8.3-14.8 MeV for 0.28kt-y exposure. Assuming the 8B spectrum shape, this limits the antineutrino flux to 2.8x10-4 of the SSM 8B flux. This represents a factor of 30 improvement over the best previous limit.

  39. Thanks to Atsuto Suzuki, Patrick Decowski, Gianni Fiorentini, Andreas Piepke and Giorgio Gratta who made some of the figures used in this talk.

More Related