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Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan Unsegmented detector featuring 300 tons of ultra-pure liquid scintillator viewed by 2200 photomultipliers PC + PPO (1,5 g/l) r = 0.88 g cm-3 n = 1.505 Threshold: 250 keV (due to 14C) Energy Resolution: FWHM 12% @ 1 MeV Spatial Resolution: 10 cm @ 1 MeV Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan In 100 tons of fiducial volume we expect ~ 30 events per day (for LMA) via the ES on e- : νe + e- → νe + e- Requirements for a 7Be solar νe detector: Ultra-low radioactivity in the detector : 10-16 g/g level for U and Th. 10-14 g/g level for K Shielding from environmental γ rays Muon veto and underground location Low energy threshold Large fiducial mass Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan By far the best method to detect antineutrino is the classic Cowan Reines reaction of capture by proton in a liquid scintillator: e p n e Threshold Thee signal energy: E(MeV) E(νe ) Q 2mec2 (Q 1.8MeV) The entire scintillator mass of 300 tons may be utilized The electron antineutrino tag is made possible by a delayed coincidence of the e+ and by a 2.2 MeV γ-ray emitted by capture of the neutron on a proton after a delay of ~ 200 µs One of the few sources of correlated background is muon induced activities that emit β-neutron cascade. 6 However, all such cases have lifetimes τ < 1 s. Thus they can be vetoed by the muon signal. At LNGS µ reducing factor ~ 10 Borexino µ veto ~ 1/5000 Sensitivity : Lino Miramonti 1 ν e event (in 300 tons) yr 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan Supernova neutrinos Geo-neutrinos Long-Baseline Reactor Neutrinos from artificial sources 51Cr Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics & 90Sr June 9-14, 2003, Nara Japan NEUTRINO PHYSICS ν absolute mass from time of flight delay ν oscillations from spectra (flavor conversion in SN core, in Earth) CORE COLLAPSE PHYSICS explosion mechanism proto nstar cooling, quark matter black hole formation ASTRONOMY FROM EARLY ALERT some hours of warning before visible supernova Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan In a liquid scintillator detector, the electron antineutrino on proton reactions constitute the majority of the detected Supernova neutrino events. C9H12 Nevertheless The abundance of carbon in PC provides an additional interesting target for neutrino interactions. Pseudocumene [PC] (1,2,4-trimethylbenzene) Neutrino reactions on 12C nucleus include transition to: gs e 12C12B e Threshold = 14.4 MeV 12N gs e 12C12N e Threshold = 17.3 MeV 12C* 12C12C Threshold = 15.1 MeV 12B Lino Miramonti All of the reactions on tagged in Borexino: 12C can be • The CC events have the delayed coincidence of a β decay following the interaction (τ ~ qq 10 ms). • The NC events have a monoenergetic γ ray of 15.1 MeV 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan We consider 300 tons of PC and a Type II Supernova at 10 kpc (galactic center) 1) Essentially all gravitational energy (Eb = 3 1053 ergs) is emitted in neutrinos. 2) The characteristic neutrino emission time is about 10 s. 3) The total emitted energy is equally shared by all 6 neutrino flavors. L νe L ν L ν e 4) μ, ν τ , νμ , ν τ Energy hierarchy rule: E νe 11 MeV Eν 16 MeV e E νx 25 MeV (ν x ν μ , ν τ , ν μ , ν τ ) Supernova neutrino energy spectra Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan Measurements of cross-sections for 12C(ν ,e-)12N and 12C(ν,ν’)12C* have been e performed at KARMEN, at LAMPF and by LSND. Since 12N and 12B are mirror nuclei, the matrix elements and energy-independent terms in the cross-section are essentially identical. Only the Coulomb correction differs when calculating the capture rates of the anti-νe. Cross sections for CC on p, ES, CC and NC on 12C. Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan SN ν events in Borexino from a SN at 10kpc (Eb = 3 1053 ergs) νμ and ντ dominate the neutralcurrent reactions 12C(ν,ν’)12C with an estimated contribution of around 90 %. In order to exploit these aspects, a liquid scintillator SN neutrino detector needs to be able to cleanly detect the 15.1 MeV γ ray. This implies that the detector require a 4.82 events e p n e β-inv. Reactions on 12C The νμ and the ντ are more energetic than νe. e e e e ES CC NC 79 events e 12C12N e 0.65 events e 12C12B e 3.8 events e 12C12C e' 0.4 events e 12C 12C e' 1.5 events x 12C12C x' 20.6 events large volume to contain this energetic γ ray. Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Total ~ 110 events June 9-14, 2003, Nara Japan 2.2 MeV γ rays By studying the arrival time of neutrinos of different flavors from a SN, mass limit on νµ and ντ down to some 10 of eV level can be explored 15.1 MeV γ rays The time delay, in Borexino, is obtained by measuring the time delay between NC events and CC events Continuum of e+ from inverse β decay Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan Earth emits a tiny heat flux with an average value ΦH ~ 80 mW/m2. Integrating over the Earth surface: HE ~ 40 TW (about 20000 nuclear plants) It is possible to study the radiochemical composition of the Earth by detecting antineutrino emitted by the decay of radioactive isotopes. Confirming the abundance of certain radioelements gives constrain on the heat generation within the Earth. Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan 238 U 12300 232 T h 4020 40 Bq g Bq g Bq K 29.8 ( K 0.0118 % of 40 238 232 40 40 g nat K) U206 Pb 8α 6e- 6νe 51.7MeV ε(U) 9.510-8 W g (U ) 7.4 104 Th208 Pb 4α 4e- 4νe 42.8MeV ε(T h) 2.710-8 W g (Th) 1.6 104 K Ca e νe 1.32MeV (89%) 40 12 ε(K) 3.610 K e 40 Ar νe 1.51MeV (11%) W g e e ( K ) 27 e ( K ) 3.3 e e gs e gs e gs e g s (ε is the present natural isotopic abundance) Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan The energy threshold of the reaction e p n e There are 4 β in the 238U and 232Th chains with energy > 1.8 MeV : Signal energy: is 1.8 MeV [U] 214Bi < 3.27 MeV [U] 234Pa < 2.29 MeV [Th] 228Ac < 2.08 MeV [Th] 212Bi < 2.25 MeV E(MeV) E(νe ) 1.8 2mec2 The terrestrial antineutrino spectrum above 1.8 MeV has a “2-component” shape. The high energy component coming solely from U chain and The low energy component coming with contributions from U and Th chains. This signature allows individual assay of U and Th abundance in the Earth Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan Each element has a fixed ratio Heat H = 9.5 10-8 · M(U) + 2.7 10-8 · M(Th) + 3.6 · 10-12 M(K) [W] LAnti-ν = 7.4·104 · M(U) + 1.6·104 · M(Th) + 27 · M(K) Lν = 3.3 · M(K) [ν/s] Everything is fixed in term of 3 numbers: M(U) Lino Miramonti [anti-ν/s] 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Th U K U June 9-14, 2003, Nara Japan The radiogenic contribution to the terrestrial heat is not quantitatively understood. Models have been considered: Primitive Mantle The starting point for determining the distribution of U, Th and K in the present CRUST and MANTLE is understanding the composition of the “Bulk Silicate Earth” (BSE), which is the model representing the primordial mantle prior to crust formation consistent with observation and geochemistry (equivalent in composition to the modern mantle plus crust). BSE concentrations of: U ~ 20 ppb (±20%), have been suggested Th 3.8 U K 10000 U M Mantle= 68% M Earth M(U) = 20 ppb · 0.68 · 6·1027g = 8.5·1019g In the BSE model: •The radiogenic heat production H rate is ~ 20 TW (~ 8 TW from U, ~ 8.6 TW from Th, ~ 3 TW from K) •The antineutrino production L is dominated by K. Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan During the formation of the Earth’s crust: the primitive mantle was depleted of U, Th and K, while the crust was enriched. Continental Crust: average thickness ~ 40 km Oceanic Crust: average thickness ~ 6 km CC is about 10 times richer in U and Th than OC Measurements of the crust provide isotopic abundance information: 238U Primitive Mantle (BSE) With these measurement, it is possible to deduce the average U and Th concentrations in the present depleted mantle. 232Th 20 ppb 76 ppb Continental Crust 910 ppb 3500 ppb Oceanic Crust 100 ppb 360 ppb 15 ppb 60 ppb Present depleted Mantle Crust type and thickness data in the form of a global crust map: A Global Crustal Model at 5° x 5° (http://quake.wr.usgs.gov/study/CrustalStructure/) Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan Borexino is homed in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E LNGS Data from the International Nuclear Safety Center (http://www.insc.anl.gov) Calculated anti-νe flux at the Gran Sasso Laboratory (106 cm-2 s-1) U Crust Th Mantle 1.8 Lino Miramonti 1.4 Crust Total (U+Th) Reactor BKG 5.9 0.65 Mantle 1.5 1.2 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan In Borexino are expected: 7.8 events yr The background will be: 29 events yr (7.6 of them in the same spectral region as the terrestrial anti-ν) The characteristic 2-component shape of the terrestrial anti-neutrino energy spectrum make it possible to identify these events above the reactor anti-neutrino background. The reactor anti-neutrino background has a well-known shape it can be easily subtracted allowing the discrimination of the U contribution from the Th contribution. Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan The very effective ability to detect the high energy gamma peak (15.1 MeV) from NC reactions on 12C thanks to the unsegmented large volume detector. The absence of nuclear plants in Italy gives a very low contribution to the geo antineutrino background. Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan NC reactions on 12C have no spectral information In a low threshold detector like Borexino the ES on proton (NC reaction): p ' p' can be observed measuring the recoiling protons. In principle, it can furnish spectroscopic information. Furthermore: the total neutrino flux from a SN is 6 times greater than the flux from just anti-νe. The νµ and ντ flavors are more energetic, increasing the total event rate. This provide Borexino with several hundred supernova neutrino interactions Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan