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Revelations of the neutrino :

Revelations of the neutrino :. Weak interaction ( beta decay , double beta decay ). Sebastian Liebschner 15.11.2012. Outline. Beta decay – experimental results Neutrino hypothesis Detection Properties of neutrinos Weak interaction Double beta decay.

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Revelations of the neutrino :

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  1. Revelationsoftheneutrino: Weakinteraction(betadecay, double beta decay) Sebastian Liebschner 15.11.2012

  2. Outline Beta decay – experimental results Neutrino hypothesis Detection Properties ofneutrinos Weakinteraction Double betadecay

  3. 1. Beta decay – experimental results - radioactivedecay - nucleusemitselectronor positron (β-orβ+particle) - massofnucleusnearly constant nucleonreaction: - β-decay: - (β+decay: ) 1/23

  4. 1. Beta decay – experimental results - betadecay was observedcloser - cloud chambers showed curious results - - anticipated: - but both objects in the same half room disagreement with conservation of momentum 2/23

  5. 1. Beta decay – experimental results - measurementofelectron/positronenergyprovidednextunexpectedresult  - insteadofdiscrete  continuousspectrum 3/23

  6. 1. Beta decay – experimental results - investigationofspin example: nucleushalf-integer spin nucleushalf-integer spin+ electronhalf-integer spin  disagreementwithconservationof angular momentum 4/23

  7. 2. Neutrino hypothesis Wolfgang Pauli (1900-1958) - insteadofgivinguptheconservationsofenergy, momentumand angular momentum, Wolfgang Pauli theorized a new particle, calledneutrino (1930) 5/23

  8. 2. Neutrinohypothesis - accordingtotheexp. results, theneutrinohas: ○ half-integer spin ○ noelectriccharge ○ verysmallmass( nextweek) - newequation: β- decay: β+decay: - determinationofandnecessary, becauseofconservationofleptonnumber(lepton L=1, antilepton L=-1) 6/23

  9. 2. Neutrinohypothesis • withquark model: Charge ofquarks: cut down toquarkreaction: β-decay: β+decay: 7/23

  10. 3. Detection Pb - Detectionofparticles: ○ proton, electron:electromagneticinteraction ○ neutron:collisonwithprotons ○ photon:photoeffect, comptoneffect - neutrinosdon‘tinteract with strong orelectro- magneticforce nearlygothrougheverything (like a bulletthroughfog) 8/23

  11. 3. Detection Enrico Fermi (1901-1954) Hans Bethe (1906-2005) -Fermi calculatedcrosssectionfrom neutrinoswith matter: (neutrinoswith 10 MeV) (forneutronswith same energie: ) -Bethe: „Nobodycan everdetect thisparticle.“ 9/23

  12. 3.Detection Project Poltergeist 10/23

  13. 3.Detection β-decay:β+decay: inverse β-decay: inverse β+decay: - used in the inverse β+decaytocreateneutron andpositron  "trigger“ forreaction 11/23

  14. 3.Detection -measurement: ○ first E(e+e)=1,02MeV, ○ later E(n)=9,1MeV 12/23

  15. 3.Detection 200l reservoir • The neutrino • detector • „Herr Auge“: 90 photomultiplier 13/23

  16. 4.Properties - 3 families/flavours: ○ electronneutrinosνe ○ muonneutrinoνμ ○ tau neutrinoντ - theleptonfamilynumberisconservedin reactions - Neutrino oscillationisthetheorizedtransformation ofneutrinos in anotherflavour conflictwithconservation ofleptonfamilynumber 14/23

  17. 4.Properties - transformationisperiodic oscillation • theory: ifoscillation  neutrinosnonzeromass - neutrinooscillations observedfrom manysourceswith different detector technologies (e.g. Kamioka, Japan)  nonzeromass 15/23

  18. 5. Weakinteraction - radioactivityat all iseffectedby a „newforce“: the weakinteraction - oneofthefour fundamental forcesofnature - originally formulated, in the 1930s, by Fermi - weakforceisdescribedwithgaugebosons: W+,W- (charged)andZ0(uncharged) - ratioofthe power of all fourforces: 16/23

  19. 5. Weakinteraction final state initialstate - threetypesofweakinteraction: ○ elasticscattering: onlyenergyand momentumexchange, e. g. ○ chargedcurrent:particlescouple via W+,W- particle- transformation, e. g. piondecay 17/23

  20. 5. Weakinteraction - beta-decay: ○ firstreaction: ○ secondreaction: 18/23

  21. 5. Weakinteraction ○ neutral current:particlescouple via Z0and thereis a particle-transformation, e. g. - processalsopossiblewithγ-quant - in naturethereisoverlap ofweakandelectromagnetic force 19/23

  22. 6. Double β-decay - double-betadecay (ββ-decay) allowed, ifthe final stateof a nucleushas a larger bindingenergythan before, e. g. - Germanium-76: ○ hassmallerbindingenery than , preventingββ-decay ○ has a larger bindingenergy  ββ-decayallowed - in generalarenucleiwithevenproton-number andevenneutron-numberableforββ-decay 20/23

  23. 6. Double β-decay 21/23

  24. 6. Double β-decay 22/23 - ββ-decayisvery rare - twoneutrino double-betadecay(2νββ-decay) ○ twoβ-decaysatthe same time ○ processisallowedwithinthe standard model (double β+ decayis also possible)

  25. 6. Double β-decay 23/23 - neutrinoless double-betadecay (0νββ-decay) ○ neutrinosannihilateeachother ○ neutrionsarethereown anti-particles (Majorana-fermion) ○ accordingtotheory: at least one neutrinohastohave a nonzeromass  physicsbeyondthestandard model ifthisdecaycanbedetected

  26. 7. References andacknowledgements - Demtröder: Experimentalphysik 4 - Prof. Dr. K. Zuber - Povh, Rith, Scholz, Zetsche: Teilchen und Kerne - KEK News: Neutrino oscillationexperiment - Carsten Hof: Neutrino-Seminar, RWTH Aachen

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