Exploring the Geo-reactor Hypothesis with Neutrinos Jelena Maričić KamLAND Collaboration March 24 th 2007 DOANOW Workshop University of Hawai’i

Outline The geo-reactor hypothesis Limits on the geo-reactor hypothesis with KamLAND experiment Prospects of verifying the geo- reactor hypothesis with future Hanohano experiment Summary and conclusion

Uranium in the Core? Radical hypothesisRadical hypothesis If it is there, it may undergo fission. Natural nuclear reactor with power up to 10 TW operating in the center of the Earth, proposed by M. Herndon as the energy source of geo-magnetic field (geo-magnetic field reversals and higher ratios of 3 He/ 4 He observed in volcanic plumes in some places). Although not a mainstream theory, not ruled out by any evidence. If the geo-reactor exists, its anti- neutrino flux is visible in KamLAND and Hanohano in future!

Why do we Care about Verifying a Radical Hypothesis such as Geo-reactor Sitting in the Earth ’ s Core? It is a freebie. It can be verified with existing experiments and future planned experiments Geo-reactor Discovered: Does not exist or/and too small: - revolutionize geology - independent check that there are no surprises in the energy region where we do not expect them

Differentiating between Geo-neutrinos and Geo-reactor Neutrinos -Geo-neutrinos emitted in the decay chains of 40 K, 232 Th, 238 U and can have energies up to 3.4 MeV -Geo-reactor neutrino’s energy spectrum approximately resembles the spectrum of a typical commercial nuclear reactor and these neutrinos may have energies that extend all the way to 9 MeV -Any positive signal above 3.4 MeV limit for geo-neutrinos must be attributed to reactor like neutrinos Inverse β-decay energy threshold 1.8 MeV.  e  p +  e + + n Inv.  reaction: No geo-neutrinos above 3.4 MeV

Geo-reactor Search with KL KamLAND detects reactor anti- neutrinos The possible surplus of detected events implies that there may be another source of anti-neutrinos that have not been accounted for. Proposed 3-10 TW georeactor if exists would produce anti- neutrino signal of 4-14% of the KamLAND signal. The goal is to set an upper limit on the power of the hypothetical geo-reactor. Is it there and if so, how large is it?

Motivation for Geo-reactor Search Incoming daily flux varies due to nuclear reactors varying work regime. Rate from the putative geo-reactor very small! It is assumed that geo-reactor power is constant on the data taking time scale. Small positive offset of 0.03e/day with VERY LARGE ERROR may be present, for 0 ev/day expected! Phys.Rev.Lett.94:081801,2005 Time integrated plot Survival probability Large error! 90% C.L. KamLAND

Confidence Levels on the Geo-reactor Power Very wide minimum Comparison of the Best Fit Result with Geological Data The best fit value is 6 TW and 90% C.L. limit is 19 TW Based on 515 days of livetime events/TW·day

Simulation of the Improving Limits on the Geo-reactor Power with 2.5 more data Simulations with 2.5 more data! Value of the geo-reactor power treated as a free parameter. 68% 90% 68% 90% 68% Rate only No parameter constraints Rate only + parameter constraints Rate + shape + parameter constraints TightestlimitTightestlimit R 0 = (-6  10) TW R 0 = 14 TW at 90%C.L. R 0 = (-4  5) TW R 0 = 9 TW (90%C.L.) R 0 = (0  4) TW R 0 = 7 TW (90%C.L.) R 0 = (0  4) TW R 0 = 7 TW (90%C.L.) Expectation With 2.5 more data

Geo-reactor Search with KamLAND Summary 90% C.L. is 19 TW.90% C.L. is 19 TW. Simulations with 2.5 times more data shows that there will be improvement in the limits, but it is still insufficient to give any final say about the geo-reactor. Based on the simulation:Simulations with 2.5 times more data shows that there will be improvement in the limits, but it is still insufficient to give any final say about the geo-reactor. Based on the simulation: –90 % C.L. limit will be lowered to 7 TW. –The best fit will be lowered: (0  4) TW Final result is greatly influenced by:Final result is greatly influenced by: –Error on the input neutrino mixing parameters that will not improve greatly in near future –Background from man-made nuclear reactors that is times larger than geo-reactor signal –Detector backgrounds will be decreased by a new radioactive source calibration measurement at KamLAND KamLAND size detector far away from nuclear reactorsKamLAND size detector far away from nuclear reactors needed for high confidence (>99.99%) measurement. needed for high confidence (>99.99%) measurement. Hawaii presents an excellent choice for a definite geo-reactor measurement ( ).

Making a more decisive measurement of geo-neutrinos with future Hanohano experiment

Hano Hano - KamLAND in Ocean Hano Hano = Hawaii Antineutrino Detector - Hanohano = Hawaiian for “ glorious, Distinctive ” Basic Idea: - KamLAND-style anti-neutrino detector in the 4km depth - Design: measurement of 238 U and 232 Th in the mantle - 25% measurement of mantle geo- neutrinos (U/Th) - Will be able to distinguish between different geological models of the Earth. -Will be able to detect geo-reactor neutrinos from the 1 TW or larger geo-reactor if one exists with > 4  C.L.

Planned Detector Design and Location Big Island Hanohano Oahu - Designed as 10 kton liquid scintillator detector. - Detection reaction: 4 km depth Pier construction constraint!

Why Hawaii Represents Such a Good Location for Geo-reactor Detection Japan presents one of the worst locations for the geo-reactor detection while Hawaii presents one of the best locations for geo-reactor detection. Japan Hawaii Commercial nuclear reactor background

Significance and Signals for the Geo-reactor Detection Signal significance: σ = S / √(S+B) Background rate: 30 events per 10 kT-y (3.4 < Eν(MeV) < 9.3) 1 TW geo-reactor signal 38 events per 10 kT-y (3.4 < E ν (MeV) < 9.3) If the goals for backgrounds are achieved:  = 4.6 C.L. for 1 TW geo-reactor discovery

Summary and Conclusion Current upper limit on the power on the hypothetical geo-reactor has been set at 19 TW at 90% C.L. Simulations with larger data set show improvements but insufficient to give any final say about the existence of geo-reactor. Destiny of the geo-reactor will be far better resolved with Hanohano detector.

Geo-reactor Pros and Cons …can explain the following unresolved question: - provide the energy source for driving the Earth’s magnetic field ( TW of power running for more than 3 billion years!!!). - perhaps explains reversals of the geo-magnetic field (171 reversals recorded in the last 70 million years). - provide explanation for the up to 40 times higher measured ratios (comparing to average atmospheric ratio) of 3 He/ 4 He observed in volcanic plumes in Hawaii, Iceland some other places. …requires substationally different inner core content: Traditional Model (BSE): content of the inner core based on meteorites called carbonaceous chondrites. As a result, U and Th are in the form of oxides, act as lithophiles and can exist in the crust and mantle only. Nuclear Earth Model (by M. Herndon): content of the inner core based on rare type of meteorites called enstatite chondrites. U and Th are alloyed with Fe or S, act as siderophiles and due to high density can exist in the inner core and particularly the Earth’s center.