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Antineutrino science by KamLAND.

Suzuki A - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2007)

Bottom Line: KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.).The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models.This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget.

View Article: PubMed Central - PubMed

Affiliation: Director General, High Energy Accelerator Research Organization, Ibaraki, Japan . ; Director General, High Energy Accelerator Research Organization, Ibaraki, Japan .

ABSTRACT
KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.). The observed energy spectrum disagrees with the expected spectral shape at 99.6% C.L., and prefers the distortion from neutrino oscillation effects. A two-flavor oscillation analysis of the data from KamLAND and solar neutrino experiments with CPT invariance, yields [Formula: see text] eV(2) and [Formula: see text]. All solutions to the solar neutrino problem except for the large mixing angle (LMA) region are excluded. KamLAND succeeded in detecting geoneutrinos produced by the decays of (238)U and (232)Th within the Earth. The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models. This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget.

No MeSH data available.


Related in: MedlinePlus

Scatter plot of Eprompt and Edelayed for the ν̄e candidate events.
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Related In: Results  -  Collection


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f4-83_027: Scatter plot of Eprompt and Edelayed for the ν̄e candidate events.

Mentions: So far KamLAND demonstrated “First Results from KamLAND: Evidence for Reactor Antineutrino Disappearance”, using the first period data sample taken in 4 March 2002 to 6 October 2002 (ANA-I), 6) and “Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion”, using the second period data sample taken in 9 March 2002 to 11 January 2004 (ANA-II).7) These data samples correspond to a total exposure time of 162.2 ton-yr for ANA-I and 766.3 ton-yr for ANA-II, respectively. The selection cuts for ν̄e events in ANA-I are in the following: (i) fiducial volume (R < 5 m), (ii) time correlation (0.5 μsec < ΔT < 660 μsec), (iii) vertex correlation (ΔR < 1.6 m), (iv) delayed energy (1.8 MeV < Edelayed< 2.6 MeV), and (v) a requirement from the delayed vertex position to be more than 1.2 m from the central vertical axis to eliminate background from LS monitoring thermometers. Antineutrinos emitted through the 238U and 232Th decays in the Earth, geoneutrinos contribute lowenergy events with Eprompt< 2.49 MeV. To avoid ambiguities from geoneutrinos (vi) a prompt energy cut of Eprompt> 2.6 MeV is applied. In ANA-II more elaborate selection cuts are used: R < 5.5 m corresponding to the fiducial mass of 543.7 ton and the target-free protons of 4.61 × 1031, 0.5 μsec < ΔT < 1000 μsec, ΔR < 2 m and 2.6 < Eprompt< 8.5 MeV. The efficiency of ν̄e event selection is improved from (78.3±1.6)% for ANA-I to (89.8±1.5)% for ANA-II. The overall systematic error is 6.5% for Eprompt>2.6 MeV. The cosmic μ-induced spallation events are eliminated, using the time and space correlations between μ’s with the energy deposit of Eμ> 3 GeV and prompt events. The correlation of prompt and delayed energies for the ANA-II ν̄e candidates before applying Edelayed cut is plotted in Fig. 4. A clear event-isolation in the delayed energy window can be seen. Events concentrated in Edelayed ∼ 1 MeV are expected to be accidental backgrounds. The event rate of Edelayed ∼ 5 MeV is consistent with the expected neutron radiative capture rate on 12C. These events are not used at present due to very low statistics.


Antineutrino science by KamLAND.

Suzuki A - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2007)

Scatter plot of Eprompt and Edelayed for the ν̄e candidate events.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756737&req=5

f4-83_027: Scatter plot of Eprompt and Edelayed for the ν̄e candidate events.
Mentions: So far KamLAND demonstrated “First Results from KamLAND: Evidence for Reactor Antineutrino Disappearance”, using the first period data sample taken in 4 March 2002 to 6 October 2002 (ANA-I), 6) and “Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion”, using the second period data sample taken in 9 March 2002 to 11 January 2004 (ANA-II).7) These data samples correspond to a total exposure time of 162.2 ton-yr for ANA-I and 766.3 ton-yr for ANA-II, respectively. The selection cuts for ν̄e events in ANA-I are in the following: (i) fiducial volume (R < 5 m), (ii) time correlation (0.5 μsec < ΔT < 660 μsec), (iii) vertex correlation (ΔR < 1.6 m), (iv) delayed energy (1.8 MeV < Edelayed< 2.6 MeV), and (v) a requirement from the delayed vertex position to be more than 1.2 m from the central vertical axis to eliminate background from LS monitoring thermometers. Antineutrinos emitted through the 238U and 232Th decays in the Earth, geoneutrinos contribute lowenergy events with Eprompt< 2.49 MeV. To avoid ambiguities from geoneutrinos (vi) a prompt energy cut of Eprompt> 2.6 MeV is applied. In ANA-II more elaborate selection cuts are used: R < 5.5 m corresponding to the fiducial mass of 543.7 ton and the target-free protons of 4.61 × 1031, 0.5 μsec < ΔT < 1000 μsec, ΔR < 2 m and 2.6 < Eprompt< 8.5 MeV. The efficiency of ν̄e event selection is improved from (78.3±1.6)% for ANA-I to (89.8±1.5)% for ANA-II. The overall systematic error is 6.5% for Eprompt>2.6 MeV. The cosmic μ-induced spallation events are eliminated, using the time and space correlations between μ’s with the energy deposit of Eμ> 3 GeV and prompt events. The correlation of prompt and delayed energies for the ANA-II ν̄e candidates before applying Edelayed cut is plotted in Fig. 4. A clear event-isolation in the delayed energy window can be seen. Events concentrated in Edelayed ∼ 1 MeV are expected to be accidental backgrounds. The event rate of Edelayed ∼ 5 MeV is consistent with the expected neutron radiative capture rate on 12C. These events are not used at present due to very low statistics.

Bottom Line: KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.).The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models.This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget.

View Article: PubMed Central - PubMed

Affiliation: Director General, High Energy Accelerator Research Organization, Ibaraki, Japan . ; Director General, High Energy Accelerator Research Organization, Ibaraki, Japan .

ABSTRACT
KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.). The observed energy spectrum disagrees with the expected spectral shape at 99.6% C.L., and prefers the distortion from neutrino oscillation effects. A two-flavor oscillation analysis of the data from KamLAND and solar neutrino experiments with CPT invariance, yields [Formula: see text] eV(2) and [Formula: see text]. All solutions to the solar neutrino problem except for the large mixing angle (LMA) region are excluded. KamLAND succeeded in detecting geoneutrinos produced by the decays of (238)U and (232)Th within the Earth. The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models. This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget.

No MeSH data available.


Related in: MedlinePlus