Radio-chemical method

Transcription

1 Neutrino Detectors

2 Radio-chemical method Neutrino reactions: n+ν e => p+e - p+ν e => n+e + Radio chemical reaction in nuclei: A N Z+ν e => A-1 N(Z+1)+e - (Electron anti-neutrino, right) (Z+1) will be extracted, decay products are detected (charged particles, γ-transitions, x-rays, 511 kev annihilation radiation) Reaction rates are tiny: ~ atoms are needed for one reaction per day The very low reaction rate caused a new term: 1 SNU = reactions per second and per atom

3 General demands on detector properties Measurement of neutrino reactions require: very large detector mass (caused by very small cross sections) Very high shielding against direct and indirect particles from cosmic radiation, especially muons suppression of natural radio-activity

4 Homestake experiment I First experiment which detected solar neutrinos, R. Davis (1968) 380m 3 := 615t C 2 Cl 4 Detection is based on neutrino capture in 37 Cl: 37 Cl + ν e => 37 Ar + e - Chemical separation of 37 Ar atoms after Tagen

5 Homestake experiment II 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 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

6 GALLEX experiment I 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 What about neutrino properties? GALLEX /-8 SNU SSM /-6 SNU

7 GALLEX experiment II

8 Radio chemical - vs. real time experiment Radio chemical experiments (Homestake, GALLEX) no information about direction of incoming neutrinos (are they solar?) information about the energy only limited and indirect due to the energy threshold of capture reaction long time averages Real time experiments New, additional information from detected neutrinos: direction -> origin from sun Energy -> from which fraction of spectrum time -> time dependent effects (day/night...) All neutrino flavors are measurable Back ground reduction with electronic, coincidences,

9 Beta decay incoming neutron: two d-quarks, one u-quark. Concentrate on one d-quark, other quarks are tightly bound by gluons to this quark. Do not contribute to decay in first order. d-quark emitts virtual W Boson and transforms into one u-quark. W - -Boson couples to an electron and an electron-antineutrino.

10 Neutrino 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

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

12 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! => deutron detection: - Addition of 2 tons NaCl salt in water - neutron capture in 35 Cl - γ cascade ~8 MeV

13 Neutrino electron reaction Neutral currents (NC) Charged currents (CC) ν e NC and CC contribute ν µ NC contribute Elastic scattering (ES) ν x +e - => ν x +e - Elastic scattering with electron ν e differs from ES with ν µ, ν τ Cross section σ(es) with ν e is six times larger.

14 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 + Cl 35 => Cl 36 + 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

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

16 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

17 Principal ideas

18 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

19 Super-Kamiokande

20 Super-Kamiokande Electron event E = 492 MeV Muon event E = 603 MeV

21 Kamiokande, Super-Kamiokande Water Cherenkov detector (real time) νe Elastic -scattering(es): Real time detection: recoil electrons cause 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 ν + e + e ν φ φ 0.49 ± 0.03 exp ± 0.06 = SSM 0.46 ± ( K ) ( SK )

22 Accident at Within 10 sec PMT s destroyed in chain reaction Damage Millionen $ seismograph in 8 km distant registered signal cause: one defect photo multiplier tube

23 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

24 SNO results Energy threshold ES ES: CC: NC: E S = 5MeV 8 B ν s all ν α 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 γ + e γ + ν α e neutron detection: n + Cl 35 => Cl 36 + γ allows measurement of and µ, τ component of ν flux Deficit of solaren neutrino flux is caused by no deficit in comparison with SSM e ν e ν µ, τ

25 SNO results Monte-Carlo method yields: (in units of 10 cm s ) Φ Φ Φ SNO CC SNO NC SNO ES = 1.76 ± 0.10 = 5.09 ± 0.62 = 2.39 ± 0.26 analysis Φ Φ Φ SNO CC SNO NC SNO ES = Φ = Φ = Φ ( ν ) e ( ν ) ( ) e + Φ ν µ, τ ( ν ) + ε Φ( ν ) e µ, τ = Φ tot In case of pure ν e and no oscillations: Φ CC = Φ NC = Φ ES

26 consistent results between experiment and SSM Φ Φ Φ Φ ( ν ) e ( ) ν µ, τ SNO tot SSM tot = 1.76 ± 0.10 = 3.41± 0.65 = 5.17 ± 0.66 = Consistent with SSM Φ ( )! ν µ, τ 0

27 AMANDA (Antarctic Myon And Neutrino Detection Array) Southpole effective area ( m 2 ) threshold: ca. 20GeV

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31 ICE-CUBE ( future project) 1 km 2 effective area 80 chains with 4800 PMT s 1 GT mass

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