Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Threshold: 250 keV (due to 14 C) Energy Resolution: FWHM  1 MeV Spatial Resolution:  10 1 MeV PC + PPO (1,5 g/l)  = 0.88 g cm -3 n = Unsegmented detector featuring 300 tons of ultra-pure liquid scintillator viewed by 2200 photomultipliers

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Requirements for a 7 Be solar ν e detector: Ultra-low radioactivity in the detector : g/g level for U and Th g/g level for K Shielding from environmental γ rays Muon veto and underground location Low energy threshold Large fiducial mass In 100 tons of fiducial volume we expect ~ 30 events per day (for LMA) via the ES on e - : ν e + e - → ν e + e -

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics By far the best method to detect antineutrino is the classic Cowan Reines reaction of capture by proton in a liquid scintillator: The entire scintillator mass of 300 tons may be utilized One of the few sources of correlated background is muon induced activities that emit β-neutron cascade. However, all such cases have lifetimes τ < 1 s. Thus they can be vetoed by the muon signal. 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 Threshold At LNGS µ reducing factor ~ 10 6 Borexino µ veto ~ 1/5000

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Long-Baseline Reactor Geo-neutrinos Supernova neutrinos Neutrinos from artificial sources 51 Cr & 90 Sr

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics 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 MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics In a liquid scintillator detector, the electron antineutrino on proton reactions constitute the majority of the detected Supernova neutrino events. Nevertheless The abundance of carbon in PC provides an additional interesting target for neutrino interactions. In a liquid scintillator detector, the electron antineutrino on proton reactions constitute the majority of the detected Supernova neutrino events. Nevertheless The abundance of carbon in PC provides an additional interesting target for neutrino interactions. Pseudocumene [PC] (1,2,4-trimethylbenzene) C 9 H 12 Neutrino reactions on 12 C nucleus include transition to: 12 B gs Threshold = 14.4 MeV 12 N gs Threshold = 17.3 MeV 12 C*Threshold = 15.1 MeV All of the reactions on 12 C can be tagged in Borexino: 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

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics We consider 300 tons of PC and a Type II Supernova at 10 kpc (galactic center) 1)Essentially all gravitational energy (E b = 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. 4)Energy hierarchy rule: Supernova neutrino energy spectra

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Measurements of cross-sections for 12 C(ν e,e - ) 12 N and 12 C(ν,ν’) 12 C* have been performed at KARMEN, at LAMPF and by LSND. Since 12 N and 12 B 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-ν e. Cross sections for CC on p, ES, CC and NC on 12 C.

Lino MiramontiJune 9-14, 2003, Nara Japan The ν μ and the ν τ are more energetic than ν e. ν μ and ν τ dominate the neutral- current reactions 12 C(ν,ν’) 12 C with an estimated contribution of around 90 %. 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics ES β-inv. Reactions on 12 C CC NC 4.82 events 79 events 0.65 events 3.8 events 0.4 events 20.6 events 1.5 events SN ν events in Borexino from a SN at 10kpc (E b = ergs) Total ~ 110 events 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 large volume to contain this energetic γ ray.

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics 2.2 MeV γ rays 15.1 MeV γ rays By studying the arrival time of neutrinos of different flavors from a SN, mass limit on ν µ and ν τ down to some 10 of eV level can be explored 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 MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Earth emits a tiny heat flux with an average value Φ H ~ 80 mW/m 2. Integrating over the Earth surface: H E ~ 40 TW (about 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 MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics (ε is the present natural isotopic abundance)

The energy threshold of the reaction is 1.8 MeV Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics There are 4 β in the 238 U and 232 Th chains with energy > 1.8 MeV : [U] 214 Bi< 3.27 MeV [U] 234 Pa< 2.29 MeV [Th] 228 Ac< 2.08 MeV [Th] 212 Bi< 2.25 MeV 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 MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Each element has a fixed ratio H = · M(U) · M(Th) · M(K) [W] L Anti-ν = 7.4·10 4 · M(U) + 1.6·10 4 · M(Th) + 27 · M(K) [anti-ν/s] L ν = 3.3 · M(K) [ν/s] Everything is fixed in term of 3 numbers:

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics radiogenic contribution The radiogenic contribution to the terrestrial heat is not quantitatively understood. Models have been considered: 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). 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. Primitive Mantle BSE concentrations of: U ~ 20 ppb (±20%), have been suggested M Mantle = 68% M Earth M(U) = 20 ppb · 0.68 · 6·10 27 g = 8.5·10 19 g

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics During the formation of the Earth’s crust: the primitive mantle was depleted of U, Th and K, while the crust was enriched. Measurements of the crust provide isotopic abundance information: 238 U 232 Th Primitive Mantle (BSE)20 ppb76 ppb Continental Crust910 ppb3500 ppb Oceanic Crust100 ppb360 ppb Present depleted Mantle15 ppb60 ppb With these measurement, it is possible to deduce the average U and Th concentrations in the present depleted mantle. Global Crustal Model Crust type and thickness data in the form of a global crust map: A Global Crustal Model at 5° x 5° ( Continental Crust: average thickness ~ 40 km Oceanic Crust: average thickness ~ 6 km CC is about 10 times richer in U and Th than OC

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics Borexino is homed in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E Calculated anti-ν e flux at the Gran Sasso Laboratory (10 6 cm -2 s -1 ) UThTotal (U+Th)Reactor BKG CrustMantleCrustMantle Data from the International Nuclear Safety Center ( LNGS

Lino MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics 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. In Borexino are expected: The background will be: (7.6 of them in the same spectral region as the terrestrial anti-ν) 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 MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics The very effective ability to detect the high energy gamma peak (15.1 MeV) from NC reactions on 12 C 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 MiramontiJune 9-14, 2003, Nara Japan 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics NC reactions on 12 C have no spectral information In a low threshold detector like Borexino the ES on proton (NC reaction): 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-ν e. The ν µ and ν τ flavors are more energetic, increasing the total event rate. This provide Borexino with several hundred supernova neutrino interactions