The Previous Results and Future Possibilities of KamLAND

Kazumi Tolich

Stanford University

2/6/2007

2/6/2007 2

Outline

• KamLAND

• Previous Reactor Neutrino Result

• Previous Geoneutrino Result

• Future Possibilities1. Full Energy Analysis

2. Solar Neutrinos

3. Supernova

2/6/2007 3

KamLANDIntroduction to the KamLAND experiment

2/6/2007 4

KamLAND CollaborationT. Ebihara,1 S. Enomoto,1 K. Furuno,1 Y. Gando,1 K. Ichimura,1 H. Ikeda,1 K. Inoue,1 Y. Kibe,1 Y. Kishimoto,1 M. Koga,1 Y. Konno,1 Y. Minekawa,1 T. Mitsui,1 K. Nakajima,1 K. Nakajima,1 K. Nakamura,1 K. Owada,1 I. Shimizu,1 J. Shirai,1 F. Suekane,1 A. Suzuki,1 K. Tamae,1 S.Yoshida,1 J. Busenitz,2 T.Classen,2 C. Grant,2 G. Keefer,2 D.S.Leonard,2 D. McKee,2 A. Piepke,2 B.E. Berger,3 M.P. Decowski,3 D.A. Dwyer,3 S.J. Freedman,3 B.K. Fujikawa,3 F. Gray,3 L. Hsu,3 R.W. Kadel,3

C. Lendvai,3 K.-B. Luk,3 H. Murayama,3 T. O’Donnell,3 H.M. Steiner,3 L.A. Winslow,3 C. Jillings,4 C. Mauger,4 R.D. McKeown,4 C. Zhang,4 C.E. Lane,5 J. Maricic,5 T. Miletic,5 J.G. Learned,6 S. Matsuno,6 S. Pakvasa,6 G.A. Horton-Smith,7

A. Tang,7 K. Downum,8 G. Gratta,8 K. Tolich,8 M.Batygov,9 W. Bugg,9 Y. Efremenko,9 Y. Kamyshkov,9 A.Kozlov,9 O. Perevozchikov,9 H.J. Karwowski,10 D.M.Markoff,10 W. Tornow,10 J.S. Ricol,11 F. Piquemal,11 and K.M. Heeger,12

1. Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan

2. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA

3. Physics Department, University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

4. W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA

5. Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA

6. Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA

7. Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA

8. Physics Department, Stanford University, Stanford, California 94305, USA

9. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA

10. Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA and Physics Departments at Duke University, North Carolina State University, and the University of North Carolina at Chapel Hill

11. CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F-33175 Gradignan Cedex, France

12. Department of Physics, University of Wisconsin at Madison, Madison, Wisconsin, USA

2/6/2007 5

KamLAND Location• KamLAND was

designed to measure reactor anti-neutrinos.

• KamLAND is surrounded by nuclear reactors in Japan.

KamLAND

2/6/2007 6

KamLAND Detector

Electronics Hut

Steel Sphere of 8.5m radius

Water Cherenkov outer detector225 20” PMT’s

1 kton liquid-scintillator

Inner detector1325 17” PMT’s554 20” PMT’s34% coverage

1km (2700 m.w.e) Overburden

Buffer oil

Transparent balloon of 6.5m radius

2/6/2007 7

Detecting Anti-neutrinos with KamLAND

• KamLAND (Kamioka Liquid scintillator Anti-Neutrino Detector)

dp

e+

0.5 MeV 2.2 MeV

np

0.5 MeV

e

e-

• Inverse beta decay

e + p → e+ + n

• The positron loses its energy then annihilates with an electron.

• The neutron first thermalizes then gets captured on a proton with a mean capture time of ~200s.

PromptDelayed

• Neutrino energy can be estimated by the kinetic energy of the positron plus 1.8MeV.

2/6/2007 8

Major Background Events for Antineutrino Detection

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

1H(n,n)1H: the neutron collides with protons (prompt) and later captures on a proton (delayed).

12C(n,n)12C: the neutron excites a 12C producing a 4.4 MeV (prompt), and later captures on a proton (delayed).

13C(,n)16O: the 16O* de-excites with a 6 MeV (prompt), and the neutron later captures on a proton (delayed).

• 13C(,n): 210Po (introduced as 222Rn) emits an particle, which reacts with naturally occurring 13C (~1.1% of C).

2/6/2007 9

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

Phys. Rev. Lett. 94, 081801 (2005)

“Measurement of Neutrino Oscillation with

KamLAND:

Evidence of Spectral Distortion”

425 citation as of last week!

2/6/2007 10

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:

3

1l li i

i

U =

=∑

Pe→ eL( ) =1−sin2 2θ12 sin

2 πLLosc

⎛

⎝⎜⎞

⎠⎟, Losc =

4πEe

Δm122

2/6/2007 11

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

e+

0.5 MeV 2.2 MeV

0.5 MeV

PromptDelayed

2/6/2007 12

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).

2/6/2007 13

Prompt Energy Distribution

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

2/6/2007 14

Oscillation Analysis

• Shape distortion is the key factor in determining Δm2.

Δm122 =8.0 ±0.5×10−5eV 2

tan2θ12 =0.76

Shape Only Shape + Rate

tan2θ12 =0.46 Δm12

2 =7.9−0.5+0.6 ×10−5eV 2

2/6/2007 15

Average Distance, L0

L0 = 180 km

80% of total flux comes from reactors 140 to 210km away.

KamLAND

Pe→ eL( ) =1−sin2 2θ12 sin

2 Δm122 L

4Ee

⎛

⎝⎜⎜

⎞

⎠⎟⎟

2/6/2007 16

L0/E

Would the data come back up again???

Obs

erve

d/N

o O

scil

lati

on

Exp

ecte

d

Pe→ eL( ) =1−sin2 2θ12 sin

2 Δm122 L

4Ee

⎛

⎝⎜⎜

⎞

⎠⎟⎟

2/6/2007 17

Geoneutrino Result

Nature 436, 499-503 (28 July 2005)

“Experimental investigation of geologically produced antineutrinos

with KamLAND”

2/6/2007 18

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.

Image: http://www.dstu.univ-montp2.fr/PERSO/bokelmann/convection.gif

2/6/2007 19

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?

2/6/2007 20

Geoneutrino Signal

Inverse Beta Decay Threshold 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.

2/6/2007 21

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*

e+

0.5 MeV 2.2 MeV

0.5 MeV

PromptDelayed

*These cuts are tighter compared to the reactor antineutrino event selection cuts because of the excess background events for lower geoneutrino energies.

2/6/2007 22

Geoneutrino Candidate Energy Distribution

Expected total

Expected reactor80.4 ± 7.2

Expected total background127 ± 13

Expected U 14.8 ± 0.7

Expected (,n)42 ± 11

MeasuredAccidental2.38 ± 0.01

Expected Th3.9 ± 0.2

Candidate data152 events

Data from March, 2002 to October, 2004.

2/6/2007 23

How Many Geoneutrinos?

Expected

chondritic meteorites

3 U geoneutrinos18 Th geoneutrinos

28 U + Th geoneutrinos

Future Possibility IFull Energy Analysis

My Thesis in Progress

Reactor neutrinos

Geoneutrinos

QuickTime™ and aGIF decompressorare needed to see this picture.

2/6/2007 25

Combined Analysis

• Combined analysis probes lower energy reactor anti-neutrinos and should improve Δm2 measurement.

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

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

Re-reappearance?

2/6/2007 26

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.

2/6/2007 27

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.

Fit to our model

203Hg

68Ge

65Zn

60Co

1H(n,)2H

12C(n,)13C

2/6/2007 28

Expected Prompt Energy Spectra

*Scaled approximately to the number of events expected.

Reactor neutrinos

Accidentals

U geoneutrinosTh geoneutrinos

(,n)

2/6/2007 29

Expected Delayed Energy Spectra

*Scaled approximately to number of events expected

n-capture on p

Accidentals

2/6/2007 30

Expected Δt Spectra

*Scaled approximately to number of events expected

n-capture on p

Accidentals

Previous Geoneutrino Analysis Cut

2/6/2007 31

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.

2/6/2007 32

Probability Density Functions

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

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

Prompt Energy Delayed Energy Δt Time

2/6/2007 33

Future Possibility II7Be Solar Neutrino Detection

http://www.noaanews.noaa.gov/stories2005/images/sun-soho011905-1919z.jpg

2/6/2007 34

Solar Neutrinos from the p-p Chain Reactions

p + p 2H + e+ + e p + e- + p 2H + e 99.75% 0.25%

2H + p 3He

86% 14%3He + 3He + 2p 3He + 7Be

99.89% 0.11%

7Be + e- 7Li + e 862keV & 383keV 7Be + p 8B

7Li + p + 8B 8Be + e+ + e

8Be +

7Be e flux is much greater than 8B e flux!

2/6/2007 35

Solar Neutrino Spectrum

Solar Neutrino Flux at the surface of the Earth with no neutrino oscillations.Uses the solar model, BS05(OP).

We expect to see a few hundred events per day.

2/6/2007 36

7Be Solar Neutrino Detection

• Solar scatters off e-.

• The electron recoil energy is

E

e≤

2E2

2E +me

From e

From &

*Detection resolution is not included.

2/6/2007 37

Current Radioactivity in KamLAND

After fiducial volume cut is applied

2/6/2007 38

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.

Current Goal238U 3.5x10-18g/g OK

232Th 5.2x10-17g/g OK40K 2.7x10-16g/g 10-18g/g

85Kr 0.7Bq/m3 10-6Bq/m3

210Pb 10-20g/g 5x10-25g/g

2/6/2007 39

Expected Energy Spectra after the Purification

85KrTotal BG

40K

14C

2/6/2007 40From October 2006

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.

2/6/2007 41

Future Possibility IIISupernova Detection

http://upload.wikimedia.org/wikipedia/commons/4/43/Supernova-1987a.jpg

42

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.

e + p → e+ + n

+ 12C → ν + 12C*(15.11MeV )

e + 12C → e+ + 12B e + 12C → e− + 12N + p → ν + p

+ e− → ν + e−

+ 12C → ν + 11B + p

+ 12C → ν + 11C + n

* J. F. Beacom et al.

2/6/2007 43

Expected Proton Scattering Events

ee

+ + +

* J. F. Beacom et al.

Evisible [MeV]

dN/d

Evi

sibl

e [1/

MeV

]Realistic energy threshold after purification of scintillator

2/6/2007 44

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.

2/6/2007 45

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.

2/6/2007 46

Questions?

2/6/2007 47

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 44.21.0TW (87mW/m2), or 311TW (61mW/m2) according to more recent evaluation of same data despite the small quoted errors.

Image: Pollack et. al

Bore-hole Measurements

2/6/2007 48

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.

2/6/2007 49

Reference Earth Model Flux

• ~20% from nearby crust (within ~30km).• ~20% from outside of a ~4000km radius.• ~25% from the mantle.

2/6/2007 50

MSW Effect in the Sun e’s experience MSW effect in the Sun.

Pe→ e

L( ) : 1−12sin2 2θ12• For 7Be e’s,

For E = 862keV & Δm2=7.9x10-5eV2

Possible sin22θ

2/6/2007 51

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.

2/6/2007 52

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.