The Previous Results and Future Possibilities of Kamland kazumi Tolich

Download 495 b.
Hajmi495 b.

The Previous Results and Future Possibilities of KamLAND

  • Kazumi Tolich

  • Stanford University

  • 2/6/2007


  • KamLAND

  • Previous Reactor Neutrino Result

  • Previous Geoneutrino Result

  • Future Possibilities

    • Full Energy Analysis
    • Solar Neutrinos
    • Supernova


KamLAND Collaboration

KamLAND Location

  • KamLAND was designed to measure reactor anti-neutrinos.

  • KamLAND is surrounded by nuclear reactors in Japan.

KamLAND Detector

Detecting Anti-neutrinos with KamLAND

  • KamLAND (Kamioka Liquid scintillator Anti-Neutrino Detector)

Major Background Events for Antineutrino Detection

  • Accidentals: uncorrelated events due to the radioactivity in the detector mimicking the inverse beta decay signature.

Neutrino Oscillation Results

  • Phys. Rev. Lett. 90, 021802 (2003)

  • “First Results from KamLAND:

  • Evidence for Reactor Anti-Neutrino Disappearance”

  • 1269 citations as of last week!

  • The most cited paper in physics in 2003

  • The 2nd most cited paper in all sciences in 2003

Neutrino Oscillations in Vacuum

  • The weak interaction neutrino eigenstates may be expressed as superpositions of definite mass eigenstates

  • The electron neutrino survival probability can be estimated as a two flavor oscillations:

Selecting Reactor Anti-neutrino Events

  • Δr < 2m

  • 0.5μs < ΔT < 1000μs

  • 2.6MeV < Ee+, p < 8.5MeV

  • 1.8MeV < E, d < 2.6MeV

  • Veto after muons

  • Rp, Rd < 5.5m

Dataset and Rate Analysis

  • From March 9 2002 to January 11 2004.

  • 365.2 ± 23.7 expected reactor antineutrinos with no oscillation.

  • 17.8 ± 7.3 expected background events.

  • 258 candidate events.

  • The average survival probability is 0.658 ± 0.044(stat) ± 0.047(syst).

  • We confirmed antineutrino disappearance at 99.998% C.L. (~4).

Prompt Energy Distribution

  • KamLAND saw an antineutrino energy spectral distortion at 99.6% significance.

Oscillation Analysis

  • Shape distortion is the key factor in determining m2.

Average Distance, L0


Geoneutrino Result

  • Nature 436, 499-503 (28 July 2005)

  • “Experimental investigation of

  • geologically produced antineutrinos

  • with KamLAND”

Convection in the Earth

  • The mantle convection is responsible for the plate tectonics and earthquakes.

  • The mantle convection is driven by the heat production in the Earth.

Heat from the Earth

  • Heat production rate from U, Th, and K decays is estimated from chondritic meteorites to be 19TW.

  • Heat flow is estimated from bore-hole measurements to be 44 or 31TW.

  • Models of mantle convection suggest that the radiogenic heat production rate should be a large fraction of the total heat flow.

  • Problem with

    • Mantle convection model?
    • Total heat flow measured?
    • Estimated radiogenic heat production rate?

Geoneutrino Signal

  •  decays in U and Th decay chains produce antineutrinos.

  • Geoneutrinos can serve as a cross-check of the radiogenic heat production rate.

  • KamLAND is only sensitive to antineutrinos above 1.8MeV

  • Geoneutrinos from K decay cannot be detected with KamLAND.

Selecting Geoneutrino Events

  • Δr < 1m*

  • 0.5μs < ΔT < 500μs*

  • 1.7MeV < E,p< 3.4MeV

  • 1.8MeV < E,d< 2.6MeV

  • Veto after muons

  • Rp, Rd < 5m*

  • ρd>1.2m*

Geoneutrino Candidate Energy Distribution

How Many Geoneutrinos?

Future Possibility I Full Energy Analysis

Combined Analysis

  • Combined analysis probes lower energy reactor anti-neutrinos and should improve m2 measurement.

  • We will possibly observe the re-reappearance of reactor antineutrinos.

  • Better understanding of reactor spectrum might improve the geoneutrino measurement.

Previous and Planned Cuts

  • Geoneutrino event selection cuts are tighter due to the low energy accidental background.

  • Combined analysis requires consolidation of the difference in the event selection cuts.

Real and Visible Energies

  • Ereal is the particle’s real energy.

  • Evisible is determined from the amount of optical photons detected, including quenching and Cerenkov radiation effects.

  • The model of Evisible/Ereal as a function of Ereal fits calibration data very well.

  • Previous analyses were done in positron real energy, having to convert background energies (such as ’s) into effective positron real energies.

Expected Prompt Energy Spectra

Expected Delayed Energy Spectra

Expected t Spectra

Time Variation of Reactor Neutrino Flux

  • Shika reactor ~90km (half of L0) away turned on from May 26 2005 to July 4 2006.

  • Shika contributed 14% of total flux.

  • May help distinguish LMA I and LMA II.

Probability Density Functions

  • Expected prompt energy spectra and time variation of reactor neutrino flux were used in the previous analyses.

  • Expected delayed energy and t spectra will be added to distinguish accidental background.

Future Possibility II 7Be Solar Neutrino Detection

Solar Neutrinos from the p-p Chain Reactions

Solar Neutrino Spectrum

7Be Solar Neutrino Detection

  • Solar  scatters off e-.

  • The electron recoil energy is

Current Radioactivity in KamLAND

Test Removal of Reducible Background

  • Distillation removed 222Rn by a factor of 104 to 105.

  • Heating and distillation reduced the 212Pb activity by a factor of 104 to 105.

  • Distillation reduced the 40K concentration in PPO by a factor of 102.

  • Distillation reduced natKr by a factor of 105 to 106.

Expected Energy Spectra after the Purification

Purification System Constructed

  • The purification system is being commissioned right now.

  • We have done some testing and are fixing bugs.

  • We should be able to start the full purification operations soon.

Future Possibility III Supernova Detection

Expected Signals

  • For a “standard supernova” (d = 10 kpc, E=3x1053 ergs, equal luminosity in all neutrino flavors), we expect to see (no neutrino oscillations):

    • ~310 events
    • ~20 events
    • ~60 events
    • ~45 events
    • ~20 events
    • ~10 events
    • ~300 events
    • (0.2 MeV threshold)
  • There should be 300 e+ events above 10 MeV, with an initial rate of 100 Hz (exponential decay with ~3s time constant).

  • The proton scattering events (low visible energy) provide a determination of both luminosity of all neutrino flavors and temperature.

Expected Proton Scattering Events

Supernova Trigger

  • 8 high energy inverse beta decay events (>~9MeV) within ~0.8s causes a supernova trigger.

  • With the supernova trigger, the trigger switches to a pre-determined supernova mode.

  • The supernova mode has a lower energy threshold (~0.6MeV) in order to detect low energy events (especially ν + p → ν + p.)

  • The energy threshold could be lowered after the purification.


  • KamLAND has been producing some impressive results.

  • I am analyzing the full energy range, reactor neutrinos and geoneutrinos simultaneously, to improve sensitivity.

  • The planned purification of scintillator will be followed by the solar neutrino phase.

  • If there is a supernova explosion, KamLAND is the only detector that can possibly detect the proton scattering events.


Total Heat Flow from the Earth

  • Conductive heat flow measured from bore-hole temperature gradient and conductivity

  • Deepest bore-hole (12km) is only ~1/500 of the Earth’s radius.

  • Total heat flow 44.21.0TW (87mW/m2), or 311TW (61mW/m2) according to more recent evaluation of same data despite the small quoted errors.

Radiogenic Heat

  • U, Th, and K concentrations in the

  • Earth are based on measurement

  • of chondritic meteorites.

  • Chondritic meteorites consist of

  • elements similar to those in the

  • solar photosphere.

  • The predicted radiogenic total heat production is 19TW.

  • Th/U ratio of 3.9 is known better than the absolute concentrations of Th and U.

Reference Earth Model Flux

  • ~20% from nearby crust (within ~30km).

  • ~20% from outside of a ~4000km radius.

  • ~25% from the mantle.

MSW Effect in the Sun

  • e’s experience MSW effect in the Sun.

Irreducible Radioactivity

  • ’s (1.46MeV) and ’s from 40K in the balloon

  • ’s (2.6MeV) from 208Tl decay in the surrounding rocks

  • 14C throughout the detector (less than ~200keV)

  • 11C from cosmic muons (more than 700keV)

  • Most of the 40K and 208Tl background is removed with fiducial volume cut.

  • Most of the 14C and 11C background is removed with energy cut.

Detector Capability

  • The electronics’ buffers can hold ~10k high energy events (all PMTs hit).

  • KamLAND handled a simulated supernova with 400 Hz high energy events (all PMTs hit) for 10 seconds with ~0.6MeV detector threshold.

Do'stlaringiz bilan baham:

Ma'lumotlar bazasi mualliflik huquqi bilan himoyalangan © 2017
ma'muriyatiga murojaat qiling