Energiespektrum der Sonnenneutrinos

Transkript

1 Energiespektrum der Sonnenneutrinos

2 Summary Homestake experiment Detection of 37 Ar, decays via K-electon capture: 37 Ar + e - => 37 Cl + ν e Half live: t 1/2 = 35 d Decay products: (i) X-rays (Röntgenstrahlung)) (ii) Auger electrons Typical values: Threshold energy for ν- capture in 37 Cl: 814 kev => mainly 8 B neutrinos Final result after 20 years: Y = Ar atoms per day R = SNU Standard Sun Model SSM: ~ 8.0 SNU Solar neutrino deficit problem 100 days measurement 60 Ar-decays/10 31 Cl atoms

3 Summary GALLEX experiment Detection principal of radio chemical experiment: 71 Ga + ν e => 71 Ge + e t GaCl 3 Lower energy threshold: 244keV => flux of initial pp-neutrinos detected! Results are again below theoretical SSM expectation GALLEX /-8 SNU SSM /-6 SNU What about neutrino properties?

4 Neutrino quark reactions charged currents (CC) with proton, neutron ν e + p => e + + n ν e + n => e - + p ν µ + p => µ + + n ν µ + n => µ - + p ν e proton scattering Beta-decay of neutron

5 Cherenkov ligt: electron energy from opening cone Neutrino quark reactions Charged current (CC) and deuteron: ν e + d --> p + p + e - W- boson exchange: Neutron and neutrino -> proton and neutrino Detection scheme: Electron receives most of the energy from incoming neutrino. In case electron energy exceeds threshold energy for Cherenkov radiation -> Emission of visible Cherenkov light

6 Neutrino quark reactions Neutral current (NC) exchange of neutral Z-boson example: ν x + d --> p + n + ν x Deuteron breaks up All ν flavors have same cross section! neutron detection: - addition of 2 tons NaCl salt in water - neutron capture in 35 Cl - γ cascade ~8 MeV

7 Neutrino electron reaction Elastic scattering (ES) ν x +e - => ν x +e - - Neutral currents (NC) exchange of neutral Z-boson - Charged currents (CC) exchange of charged W-boson Elastic scattering with electron ν e differs from ES cross section with muon ν µ and tau ν τ ν e NC and CC contribute ν µ only NC contribute Cross section σ(es) with ν e is six times larger.

8 summary: neutrino reactions (CC) ν e + D => e p (1,442 MeV) -> ν e flux φ(ν e ) (NC) ν x + D => ν x + p + n (2,226 MeV) -> ν x flux φ(ν x ) - neutron detection via capture reaction n + 35 Cl => 36 Cl+ γ (ES) ν x + e - => ν x + e - (x for all neutrino flavors) Compare reactions and cross sections: - parts from different neutrino flavors φ(ν e ), φ(ν x ) - in case φ(ν e ) < φ(ν x ) -> information on disappearance and oscillations

9 High energy neutrino detectors Requirements large effectiv area large volume - N target combined detectors for - Cherenkov light - particle tracks - neutrons shielding: underground laboratory

10 Short intro: Cherenkov radiation In medium with diffraction index n is velocity of light c/n. Particle velocity can be higher than medium velocity of ligth c/n. Relativistic particles in medium with v > c/n radiate light in visible wavelength range: Cherenkov - radiation. Light cone with fixed θ c is emitted from every particle trajectory position. c / n cos θ = = c βc 1 β n in water ~ 40 Grad

11 Cherenkov radiation

12 Kamiokande, Super-Kamiokande Kamioka Nucleon Decay Experiment Kamioka mine 300km west of Tokyo, 1000m below ground level Data taking: (K: , SK:1996- ) 41,5m high, 39,3m diameter tons purified water (32.000t eff.) PMT (50cm) Photo multiplier tubes Energy threshold 5MeV

13 Super-Kamiokande

14 Super-Kamiokande Electron event, not neutrino! E = 492 MeV Muon event, not neutrino! E = 603 MeV

15 Kamiokande, Super-Kamiokande Water Cherenkov detector (real time) νe Elastic -scattering (ES): + e ν + e Real time detection: recoil electrons cause ν Cherenkov light Energy threshold at E S = 5MeV 8 only B ν s and higher energetic First time possible: angular distribution relativ to sun direct proof, measured neutrinos arrived from sun φ φ exp = 0.49 ± 0.03 ± ± SSM ( K ) ( SK )

16 Accident at within 10 sec PMT s destroyed in chain reaction damage millions $ seismograph in 8 km distant registered signal cause: one defect photo multiplier tube

17 Sudbury-Neutrino-Observatory SNO 2 km below ground in Sudbury mine (Canada) sine 1997 in operation spherical structure 12 m diameter 9600 PMT`s operated with heavy water [D 2 O] 1000 t energy threshold 1,42MeV

18 SNO results Energy threshold ES ES: CC: NC: 8 E S = 5MeV B ν s all ν x σ ν with : σ ( E S = 1. 4MeV ) ( E S 2. 2MeV ) n + d H 3 + γ ( ) µ, τ ( ν ) e = ε = only ν e all ν x γ + e γ + e neutron detection: n + Cl 35 => Cl 36 + γ e allows measurement of and µ, τ component of ν flux

19 SNO results Monte-Carlo method yields: (in units of 10 cm s ) SNO CC SNO NC SNO ES = 1.76 ± = 5.09 = ± 0.62 ± 0.26 analysis SNO CC SNO NC SNO ES = = = ( ν ) e ( ν ) + ( ν ) e µ, τ = ( ν ) + ε ( ν ) e µ, τ tot In case of pure ν e and no oscillations: CC = NC = ES

20 consistent results between experiment and SSM ( ν ) e ( ) ν µ SNO tot SSM tot = 1.76 ± 0.10, τ = 3.41± = 5.17 ± 0.66 = Consistent with SSM ( )! ν µ τ, 0

21 Zusammenfassung: Neutrinos von der Sonne Chlor-Experiment ist nur empfindlich für relativ energetische Neutrinos aus Nebenzweigen der p-p-kette: z.b.: 3 He+ 4 He 7 Be 7 Be+e - 7 Li + ν e Nicht empfindlich für Neutrinos aus Hauptreaktion: p + p 2 D + e + + ν e Ergebnis: Neutrinofluss war nur ca. 30% der erwarteten Rate! Solares Neutrino-Problem Ursache? Sonnenmodell falsch? 7 Be Reaktion ist temperaturabhängig. Fehler im Experiment? Neue Neutrino-Physik? z.b. Neutrino-Oszillationen, bei denen ν e teilweise in ν µ und ν τ umgewandelt werden.

22 Zusammenfassung: Neutrinos von der Sonne Lösung durch neue Experimente: GALLEX (Italien): ähnlich Chlor-Experiment, jedoch mit 30t Gallium. Empfindlich auf pp Neutrinos. Kamiokande (Japan): Cherenkov-Detektor, großer Wassertank umgeben von Photo-Multipliern: Detektiert Stöße zw. e- und ν e mittels Cherenkov-Licht vom relativistischen Elektron. Sudbury neutrino observatory (Kanada). Cherenkov-Detektor mit schwerem Wasser, detektiert auch ν τ und ν µ Kamiokande Detektor

23 Zusammenfassung: Neutrinos von der Sonne Ergebnisse von SK und SNO: Defizit von solaren ν e betätigt. Gilt auch für pp Neutrinos, deren theoretischer Fluss durch Sonnenleuchtkraft genau bestimmt ist. Bestätigung von Neutrino-Oszillationen ( Die Elektronneutrinos ändern flavor auf dem Weg von Sonnenkern und Erde. Bestätigung des Standard-Sonnenmodells. Theorie der Neutrino-Oszillationen beruht auf Ruhemasse der Neutrinos, die damit erstmals gefunden wurde experimenteller Nachweis für Physik jenseits des Standardmodells der Teilchenphysik ( Teilchenastrophysik)