The Previous Results and Future Possibilities of Kamland kazumi Tolich

The Previous Results and Future Possibilities of KamLAND

• Kazumi Tolich

• Stanford University

• 2/6/2007

Outline

• KamLAND

• Previous Reactor Neutrino Result

• Previous Geoneutrino Result

• Future Possibilities

• Full Energy Analysis
• Solar Neutrinos
• Supernova

KamLAND

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

L0/E

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.

Conclusions

• 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.

Questions?

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.