Perspectives for geoneutrinos after KamLAND results

Transcription

1 Neutrino Geophysics Honolulu December 14-16, 2005 Fabio Mantovani Sienna University - Italy Perspectives for geoneutrinos after KamLAND results Predictions of of the Reference Model and its uncertainties How much Uranium is is in in the Earth? Beyond the Reference Model KamLAND results and improvements Who is is the enemy of ofgeoneutrinos? The goals of of future experiments based on work with L. Carmignani, G. Fiorentini, T. Lasserre, M. Lissia, B. Ricci, S. Schoenert, R. Vannucci

2 The Reference Model Event yields from U and Th over the globe have been calculated by using: Observational data for Crust and Upper Mantle The BSE (Bulk Silicate Earth) Model constraint for Lower Mantle Th/U consistent with with chondritic prediction Best fit ν-oscillation parameters Predicted events are: about 30 per kiloton.yr, depending on location ¾ originate from U, ¼ from Th decay chains

3 The Reference Model for KamLAND We predict * the produced antineutrino flux For Uranium: ( ) U ν cm s Φ = For Thorium: ( ) For Thorium: Φ ν Th = cm s From the fluxes to the signals 1 TNU = Terrestrial Neutrino Units: one event per protons per year Average survival probability <P ee > = 0.59 Detector efficiency 100% S( U) = 29 TNU STh ( ) = 7TNU * F. Mantovani et al. Phys. Rev. D hep-ph/

4 Φ 4 ν 10 cm s The origin of the flux at KamLAND Sediments Contribute to the Φ [U] in percentage Contribute to the Φ [Th] in percentage 3.2 % 3.3 % 3 Upper Crust 41.6 % 40.4 % 2 Middle and Lower Crust 28.8 % 32.4 % Upper Mantle 5.2 % 3.4 % 1 Lower Mantle 20.8% 20.3% 0 Uranium Thorium Oceanic Crust 0.4 % 0.2 %

5 The region near KamLAND We use a 2 x 2 degrees crust map, which distinguishes several components (OC and CC, sediments, upper, middle, lower) 6tiles ( ) S U = 13 TNU 45 % of S(U) is produced by 6 tiles* The better you know the geochemical the better you will be and geophysics properties of the able to understand the region around the detector interior of the Earth! * G. Fiorentini et al. - Phys.Rev. D hep-ph/ / S. Enomoto PhD Thesis

6 Refining the Reference Model We use A geochemical study of the Japan upper crust Detailed measurements of crust depth KamLAND Selected values for Lower Crust Taking into account (3σ) errors on sample activity measurements Finite resolution of geochemical study Uncertainty from the Japan sea crust characterization Uncertainty from subducting plates below Japan Uncertainty of seismic measurements

7 Refining the Reference Model KamLAND Regional uncertainties* Composition of the upper-crust sample Upper-crust discretization ΔS [TNU] Lower-crust composition 0.8 Crustal depths 0.7 Subducting slab 2.1 Japan Sea 0.3 S U = 15.4 ± 3.1 TNU regional ( ) What about the contribution from the rest of the world S RW? It depends RW? * G. Fiorentini et al. - Phys.Rev. D hep-ph/ / S. Enomoto PhD Thesis

8 How much Uranium is in the Earth? And where is it? The contribution from the rest of the world depends on the total mass of Uranium m as well as on its distribution inside the Earth Crust : kg < m U < kg crust Crust : ( ) Mantle: Uniform abundance man ( ) = ( ) ( ) m U m U m U crust [Based on geochemical data] ( ) = ( ) S U 17.4 m U high man m man (U) man Homogeneous m crust (U) Rich The proximity argument Signal High Thin layer at the bottom low man Retreated Poor ( ) = ( ) S U 12.1 m U man Low Note: Uranium mass in unit of kg ; signal in unit of TNU

9 The uncertainties* of the Reference Model at KamLAND uncertainty from the global Earth's structure and composition 17 mbse ( U) = kg SRW ( U) = 14.1± 1.5 TNU uncertainty of the regional contribution regional ( ) S U = 15.4 ± 3.1 TNU For the central value of the BSE model we predict at KamLAND: KamLAND: ( ) S U = 29.5± 3.4 TNU uncertainty from oscillation parameters [ 0.52 < P < 0.67 ] ee ΔS/S 12% * G. Fiorentini et al. - Phys.Rev. D hep-ph/

10 U and Th measured in the crust implies a signal at least of 24 TNU Earth energetics implies the signal does not exceed 62 TNU Beyond the Reference Model*: Signal and Heat at KamLAND high S low S ± 3σ BSE prediction is a signal between 31 and 43 TNU mman ( U) = m( U) mcrust ( U) H( U+ Th) = 9.5m( U) + 2.7m ( Th ) Th 3.9 U = * G. Fiorentini et al. - Phys.Rev. D hep-ph/

11 In this scenario where are KamLAND results? The KamLAND signal is: + 33 ( + ) = SU Th 57 TNU 31 From the geoneutrino signal to power relationship we get: + 35 ( + ) = H U Th 38 TW 33 Consistent within 1σ1 with: BSE model Fully radiogenic model The 99% CL upper bound on geo-signal translates into*: H( U + Th) < 160TW * G. Fiorentini et al. - Phys.Lett. B hep-ph/

12 How to make the most of KamLAND signal* In 749 days 152 counts in the geoneutrino energy range Reactor events N event 80.4 ± 7.2 The 13 C(α,n) cross section is based on relatively old data [JENDL]: 20% overall uncertainty Fake geo-neutrinos from 13 C(α,n) Minor background Geoneutrino* * With anti-ν spectrum analysis 42 ± ± = 14 geoν 13 N 31 + Recent** high precision measurments confirm JENDL data with 4% accuracy: N = 40.0 ± C α,n ( ) Evidence for geoneutrinos: near to 2.5 σ * G. Fiorentini et al. - Phys.Lett. B hep-ph/ / **S. Harissopulos et al

13 Who is the enemy of geoneutrinos? The nuclear reactors! r = Events Events reactor geo ν In the geo-neutrino energy window KamLAND Sudbury Borexino LENA Baksan Homestake Hawaii Curacao r All reactors at full power Based on International Atomic Energy Agency Database (2000)

14 The goals of future experiments Definite evidence of geoneutrinos (3σ at least) How much Uranium and Thorium in the crust? How much Uranium and Thorium in the mantle?..

15 The relation between signal [TNU] and heat [TW] ( ) a ( ) S U + Th = H U + Th + b Sudbury Homestake Baksan LENA S (U+Th) [TNU] BSE Fully Radiogenic Borexino KamLAND Curacao (EARTH) Hawaii b depends on: U and Th mass in the crust location of the detector H (U+Th) [TW] a is the universal slope: ( ) ( ) Δ S U+ Th 1[TNU] = Δ H U+ Th 1[TW]

16 Measuring radioactivity from the crust * Based on the Reference Model constraints Signal (U+Th) expected from the crust* [TNU] Signal (U+Th) expected from the mantle* [TNU] Signal (U+Th) total [TNU] r = Events Events reactor geo ν LENA Homestake Sudbury Baksan for each detector, almost 80% of the signal is expected from the crust these detectors will have excellent opportunities to determine the Uranium and Thorium abundance in the crust the uncertainties can be minimized studying the geochemical and geophysics properties of the region around the detector Homestake and Baksan have a better r factor (E reactor /E geo ν )

17 Measuring radioactivity from the mantle * Based on the Reference Model constraints Signal (U+Th) expected from the crust* [TNU] Signal (U+Th) expected from the mantle* [TNU] Signal (U+Th) total [TNU] r = Events Events reactor geo ν Borexino KamLAND Curacao Hawaii Borexino: good for U and Th signal from the crust. It has a low r factor, but it has a small mass KamLAND: it has a high r factor (E reactor /E geo ν ). It will be the first experiment which provide a definite evidence of geoneutrinos (3σ) Curacao: almost 25% of the signal is expected from the mantle and it has a low r factor (E reactor /E geo ν ) Hawaii: almost 70% of the signal is expected from the mantle and it has a low r factor (E reactor /E geo ν )

18

19 Can geoneutrinos measure the plume s depth? h p r p Detector Computer simulation of a mantle plume by Hawaii Scientific Drilling Project web site A mantle plume is an upwelling of anomalously hot rock in the Earth's mantle. Mantle plumes are thought to be the cause of volcanic centers known as hotspots: Hawaii island is the most famous hotspot We assumed* cylindrical plume with uniform density and Uranium abundance a p (U) With h p >>r p the geoneutrinos flux depends on the asymptotic value Φ as proportional to a p and r p * Fiorentini et all. - Earth and Planetary Science Letters, Volume 238, physics/ The U-neutrino flux from a plume with r p = 350 km, h p = 2800 km and a p (U) = 40 ppb is about 20% of that from the whole mantle.

20 The lesson of solar neutrinos The study of solar neutrinos started as an investigation of the solar interior. Homestake experiment (Raymond Davis and colleagues) see the first solar neutrinos A long and fruitful detour lead to the discovery of oscillations. Through several steps, we have now a direct proof of the solar energy source, we are making solar neutrino spectroscopy, we have neutrino telescopes.

21 Follow this lesson! The study of geoneutrinos started as an investigation of the interior of the Earth [Eder 1966 Marks 1969] KamLAND experiment found the first evidence of geoneutrinos. The technique for identifying geo-neutrinos is now available. What s the next?

22 geoneutrinos is a baby instrument that permit us to look the Earth with new eyes Let it grow!

23 Extra slides

24 Predictions of the Reference Model at KamLAND 100 Percentage of total flux from the crust [%] KamLAND: Ref. Model Kamland: Phys. Rev. D 2004 Reference Model KamLAND: Kamland: Ref. Model Nature KamLAND: Araki et al. Phys. Rev. KamLAND: Paper D 2004 Nature Reference Model Distance from detector [km]

25 The Reference Model r r A ρ Φ ( ) = dr π ( r ) a ( r ) X X X 2 4 r r V r THE CRUST A X depends on the life time, atom mass and number of antineutrinos per decay chains U [ppm] Th [ppm] Water 0, Sediments 1,68 6,9 Upper crust * 2,5 9,8 Middle crust 1,6 6,1 Lower crust ** 0,62 3,7 Oceanic Crust 0,1 0,22 * Average of: U = 2,2 ; 2,4 ; 2,5; 2,8 Th/U = 3,8 ; 3,8 ; 3,9 ; 4,1 ** Average of: U = 0,2 ; 0,28 ; 0,93 ; 1,1 Th/U = 3,8 ; 6,0 ; 7,0 ; 7,1

26 The Reference Model THE MANTLE Assumptions Spherical symmetry Two reservoirs (geochemistry s model) : discontinuity line at ~ 600 km under the earth surface 17 ( ) = M U kg BSE Uranium abundance in the Upper Mantle 6,5 ppb (the average of 5 ; 8 ppb) The amount of Uranium mass in the Lower Mantle is obtained by the equation: M LM (U) = M BSE (U) [ M CC (U) + M OC (U) + M UM (U) ] Uranium Mass [10 17 kg] Abundance [ppb] Upper Mantle 0,062 6,5 Lower Mantle 0,389 13,2

27 Predictions of the Reference Model at KamLAND U [ppm] Th [ppm] Φ [U] Φ [Th] Water 0, Sediments 1,68 6,9 0,117 0,108 Upper crust * 2,5 9,8 1,518 1,309 Middle crust 1,6 6,1 0,773 0,684 Lower crust ** 0,62 3,7 0,279 0,366 Oceanic Crust 0,1 0,22 0,017 0,008 Upper Mantle 0,0065 0,0173 0,189 0,111 Lower Mantle 0,0132 0,052 0,760 0,658 Tot 3,653 3,244

28 The uncertainties of the Reference Model at KamLAND The crust Using a 2 x 2 Crustal Model, for each of the six components we have fixed: Thickness [Km] Density [g/cm3] We obtained: 17 ( ) = m U kg cc Abundance of Uranium [ppm] cc ( ) a U = 1.54 ppm ( 1) ( 2) ( ) 0.91 ppm < a U < 1.8 ppm cc The abundance ratios look relatively well determined: we concentrate on the uncertainties of the uranium abundances in the different layers and propagate them to the other elements. (1) S. R. Taylor and S.M. McLennan 1985 (2) D. M. Shaw et al. 1986

29 A few words on directionality Bin cos max (α)

30 Directionality at KamLAND Flux(U) 10 cm s 2, Mantle 2 Crust 1,5 1 0, Bin < Horizontal Vertical >

31 Directionality at Hawaii Flux(U) 0,45 10 cm s ,4 0,35 0,3 Mantle Crust 0,25 0,2 0,15 0,1 0, Bin Bin < Horizontal Vertical >