Anna Maria Rotunno Dip. Di Fisica, Univ. degli Studi di Bari annamaria.rotunno@bafn.it

1. INCONTRO NAZIONALE INIZIATIVE DI FISICA ASTROPARTICELLAREINFN - Laboratori Nazionali di Frascati, 22-23 June 2010 Geo-Neutrino: combined analysis of KamLAND and Borexino results Anna Maria Rotunno Dip. Di Fisica, Univ. degli Studi di Bari annamaria.rotunno@ba.infn.it Based on: G.L. Fogli, E. Lisi, A. Palazzo, A.M. Rotunno, Combined analysis of KamLAND and Borexino Signals from Th and U decays in the Earth’s interior; e-print arXiv: 1006.1113

2. Purpose of this Work U, Th, K decay chains KamLAND (KL) and Borexino (BX) (currently running) experiments for the first time Geo-Neutrinos data and energy spectra probe with solar and l.b.l. reactor Our approach: Earth interior 1) free Th, U event rates in KL and BX; 2)common Th/U abundance ratio; 3)common scaling of Th+U event rates; 4) fixed (chondritic) Th/U abund.ratio. Our results: • - KL  BXreject the null hypothesis (no geo-ν signal) at 5; • indicationson the Th+U geo-ν rates and on the Th/U ratio, in agreement with typical Earth model; • the hypothesis of a georeactor in the Earth’s core is disfavored (Pgeo > few TW) .

3. Contents • Introduction to Geo-Neutrinos • KamLAND and Borexino data • - Analyses with 4, 3, 2 and 1 d.o.f. • - Additional degree of freedom: the georeactor • Results for the above steps • Conclusions and Prospects

4. What do we know about Earth Interior? - The mantle convects even though it is “solid”. - Oceanic crust is being renewed at mid-ocean ridges and recycled at trenches. - Main issue today: Whole or layeredmantle convection? • Seismology:based on sound velocity measurement from seismic data • reconstructs density profilethroughout the Earth • - infers crust-mantle-core layer structure • GeoChemistry:based • on direct sampling • - gives direct info on chemical composition of crust and upper mantle • - does not reach deep Earth

5. - Earth’s Global Heat: ·~ 45 TW(~ 30 TW in some unorthodox models): not well constrained due to scarce oceanic sampling and model dependence ·probably 40 – 60% has radiogenic origin: mainly from decays of 238U, 232Th, 40K (trace elements)inside crust and mantle Geo-Neutrinos from radioactive decays of 238U, 232Th, 40K trace elements in crust and mantle of Earth • bring to surface information about: • the whole planet • its radioactive contents • energetics and thermal history Where are radioactive elements located?

6. Earth Global Composition in Trace Elements U, Th, K volatile refractory: expect Th/U as in meteorites (Th/U ~ 3.9) incompatible: prefer liquid phase (= crust during its formation) lithophile: prefer rock to metals Abundances: [Th]crust >> [Th]mantle , [Th]core~ 0 [U]crust >> [U]mantle , [U]core~ 0 Constraints: Direct sampling (crust & upper mantle) & Neutrino Geophysics (in the future)

7. A recent new field in Neutrino Physics: Geo-n detection by Liquid Scintillator. Experiments with Liquid Scintillator observe: - Geo–ne - reactor events(mostly at higher energies) - backgrounds • KamLAND: • huge reactor flux • - large background • Borexino: • small reactor flux • tiny background

8. 2005:first geo–ne observation at KamLAND KamLAND Coll., Nature 436, 499 (2005) 2008:next geo–ne KamLAND results KamLAND Coll., Phys. Rev. Lett. 100, 221803 (2008) 2010:first Geo–ne observation at Borexino Borexino Coll., Phys. Lett. B 687, 299 (2010) @ KL: - geo-n signal pronounced at lower energy - relatively large contribution from Th decay (Ep≤ 1.7 MeV) @ BX: - leading contribution from U decay

9. Analyses with 4, 3, 2, and 1 degree of freedom KL and BX statistical analysis (Poisson 2function): 7-dimensional manifold geo-n reactor Parameters: (dm2, q12, q13 ; R(Th)KL, R(U)KL, R(Th)BX, R(U)BX ) Equivalent parameters: R(Th+U) = R(Th) + R(U) (Th/U) = [R(Th)/ R(U)]/ 6.96 ·10-2 3n oscillation parameters: - constrained by solar-n data - marginalized away KamLAND Borexino abundance ratio TABLE I: Summary of adopted degrees of freedom and constraints ND Constraints R(Th + U)KL (Th/U)KLR(Th + U)BX (Th/U)BX 4 None free free free free 3 (Th/U)BX = (Th/U)KL free free free - 2 (Th/U)BX = (Th/U)KL and RBX = 1.15 RKL free free - - 1 (Th/U)BX = (Th/U)KL = 3.9 and RBX = 1.15 RKL free - - - approximate scaling law, coming from comparison of KL and BX event rate estimates for a wide range of admissible Earth models

10. Th/U vs R(Th+U) joint 1s (Dc2 = 1) regions 4 dof:both KL and BX - placeupper and lower bounds on R(Th+U) - consistency with typical Earth model expectations: 29-41 TNU for KL 34-48 TNU for BX at 1s - can not currently determine Th and U separately. In fact: KL compatible with all events from Th (Th/U → ∞) BX compatible with all events from U (Th/U → 0) A broad range compatible with KL and BX results at 1s: we impose the same Th/U ratio 3 dof: - total rate estimates not significantly altered with respect to 4 dof case - KL  BX data sensitive to the global Th/U ratio of Earth (although only at ~ 1s level) 1 TNU = 1032 events/proton yr

11. 1 TNU = 1032 events/proton yr 2 dof: - approximate scaling law: RBX = 1.15 RKL - KL parameters free, BX derived (dotted curve) - Th/U best fit not significantly altered with respect to 3 dof case 1 dof: - chondritic assumption: Th/U = 3.9 KL, BX - preference for Earth models with relatively high expectations in Th and U contents 2 dof 1 dof

12. Bounds on Th/U ratio 4 dof: - KL data placelower 1s limit on Th/U - BX data placeupper 1s limit on Th/U - no significant sensitivity in opposite directions - weak bounds: they vanish at ~ 1.3s in KL and at ~ 1.6s in BX 3 dof, 2dof: - joint limit on Th/U at the 1s level, with no significant variation between 3dof and 2dof cases 1 dof: - Dirac delta at Th/U = 3.9

13. Bounds on R(Th+U) 4 dof, 3 dof: - the null hypothesis (no geo-n) rejected at: 2.9s in KamLAND and 4.1s in Borexino - independently of the Th/U constraint 2 dof, 1dof: - significant error reduction, induced by scaling law assumption - null hypothesis rejection at 5s - the chondritic assumpion (Th/U= 3.9) has a minor impact on combined rate constraints

14. Additional degree of freedom: the georeactor Georeactor hypothesis: enough uranium in the Earth’s core to naturally start a nuclear fission chain over geological timescale typical power (at current epoch) Pgeo≈ 3-10 TW independent probe disfavoredby geochemical & geophysical arguments Particle Physics confirms • 6 dof:2s upper limit: Pgeo≤ 4.1 TW BX Pgeo≤ 6.7 TW KL • < 6 dof: joint KL + BX limit: Pgeo≤ 3.9 TW at 2s (Pgeo≤ 5.2 TW at 3s ) • - independent of the chosen geo-n degree of freedom

15. Conclusions • We have performed a detailed analysisofcurrent geoneutrino eventsfrom Th and U decay chains as detected in KamLAND and Borexino • The relevant parameter space is spanned by the total Th+U event rates and the Th/U ratio in the two experiments, while te oscillation parameters (dm2, q12, q13) aremarginalized away • - constrained analyses with fewer dof are obtained by successively assuming for both KL and BX a common Th/U ratio, a common scaling of Th+U event rates, and a fixed (chondritic) Th/U ratio • we have also considered the case of an hypothetical georeactor • Results: • agreement with typical Earth model expectations, although within still large uncertainties • global Th+U signal emerges at 2.9s in KL and at 4.1s in BX, reaching 5s in combination • preferred Th/U values in broad agreement with chondritic expectations • slight preference for relatively high Th and U contents in the Earth • data disfavor the hypothesis of a georeactor, and limit its power to Pgeo≤ 3.9 TW at 2s (Pgeo≤ 5.2 TW at 3s )

16. Prospects Significantly higher statistics, possibly from new large volume detector, with somedirectional sensitivity will be needed to improveour understanding of the Earth’s interior. Even a minimal directional information would help the source discrimination: reactor & crust anti-n → horizontal mantle anti-n→ vertical NEW EXPERIMENTS in sites with both LOWER FLUX (mantle) & HIGHER FLUX (thick crust) - LENA - Sudbury - Hawaii - Baksan

17. Backup

18. Radiogenic Heat A correlation is expected between: H = radiogenic heat production rate R = geo-n event rate from the same Th + U sources. The results for KL can be approximated as: H(Th+U)~ (1.11±0.14) · R(Th+U) - 25.0 TW TNU KL, 6 TW ≤ H ≤ 40 TW fully radiogenic limit provides a total KL signal in excess of the “garanteed” min contribution from Earth’s crust R(Th+U) ≥ 24 TNU. From: G. Fiorentini, M. Lissia and F. Mantovani, Phys. Rept. 453, 117 (2007)

19. Implications of our results From: G. Fiorentini, M. Lissia and F. Mantovani, Phys. Rept. 453, 117 (2007) In the most constrained case (ND=1): at fixed R(Th+U)KL = 47.7 TNU (central value) we obtain the allowed range H(Th+U) ~ 21 – 35 TW somewhat above typical expectation 14-18 TW. Including the 1s rate, the allowed range is enlarged: H(Th+U) ~ 10 – 49 TW Lower value exceeds the “guaranteed” contribution from Th and U in the crust ~ 6 TW and suggest (indirectly) the presence of an additional contribution from a different reservoir – which can be naturally identified with the mantle.