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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

Revelationsoftheneutrino:

Weakinteraction(betadecay,

double beta

decay)

Sebastian Liebschner 15.11.2012


Outline

Outline

Beta decay – experimental results

Neutrino hypothesis

Detection

Properties ofneutrinos

Weakinteraction

Double betadecay


1 beta decay experimental results

1. Beta decay – experimental results

- radioactivedecay

- nucleusemitselectronor

positron (β-orβ+particle)

- massofnucleusnearly

constant

nucleonreaction:

- β-decay:

- (β+decay: )

1/23


1 beta decay experimental results1

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


1 beta decay experimental results2

1. Beta decay – experimental results

- measurementofelectron/positronenergyprovidednextunexpectedresult

- insteadofdiscrete 

continuousspectrum

3/23


1 beta decay experimental results3

1. Beta decay – experimental results

- investigationofspin example:

nucleushalf-integer spin nucleushalf-integer spin+ electronhalf-integer spin

 disagreementwithconservationof angular momentum

4/23


2 neutrino hypothesis

2. Neutrino hypothesis

Wolfgang Pauli (1900-1958)

- insteadofgivinguptheconservationsofenergy,

momentumand angular momentum,

Wolfgang Pauli theorized a new

particle, calledneutrino (1930)

5/23


2 neutrino hypothesis1

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


2 neutrino hypothesis2

2. Neutrinohypothesis

  • withquark model:

Charge ofquarks:

cut down toquarkreaction:

β-decay:

β+decay:

7/23


3 detection

3. Detection

Pb

- Detectionofparticles:

○ proton, electron:electromagneticinteraction

○ neutron:collisonwithprotons

○ photon:photoeffect, comptoneffect

- neutrinosdon‘tinteract

with strong orelectro-

magneticforce

nearlygothrougheverything (like a bulletthroughfog)

8/23


3 detection1

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


3 detection2

3.Detection

Project Poltergeist

10/23


3 detection3

3.Detection

β-decay:β+decay:

inverse β-decay: inverse β+decay:

- used in the inverse

β+decaytocreateneutron

andpositron

 "trigger“ forreaction

11/23


3 detection4

3.Detection

-measurement: ○ first E(e+e)=1,02MeV,

○ later E(n)=9,1MeV

12/23


3 detection5

3.Detection

200l reservoir

  • The neutrino

  • detector

  • „Herr Auge“:

90

photomultiplier

13/23


4 properties

4.Properties

- 3 families/flavours:○ electronneutrinosνe ○ muonneutrinoνμ

○ tau neutrinoντ

- theleptonfamilynumberisconservedin

reactions

- Neutrino oscillationisthetheorizedtransformation

ofneutrinos in anotherflavour

conflictwithconservation

ofleptonfamilynumber

14/23


4 properties1

4.Properties

- transformationisperiodic oscillation

  • theory: ifoscillation  neutrinosnonzeromass

    - neutrinooscillations

    observedfrom

    manysourceswith

    different detector

    technologies

    (e.g. Kamioka, Japan)

     nonzeromass

15/23


5 weak interaction

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


5 weak interaction1

5. Weakinteraction

final state

initialstate

- threetypesofweakinteraction:

○ elasticscattering: onlyenergyand

momentumexchange, e. g.

○ chargedcurrent:particlescouple via W+,W-

particle-

transformation,

e. g. piondecay

17/23


5 weak interaction2

5. Weakinteraction

- beta-decay: ○ firstreaction:

○ secondreaction:

18/23


5 weak interaction3

5. Weakinteraction

○ neutral current:particlescouple via Z0and

thereis a particle-transformation, e. g.

- processalsopossiblewithγ-quant

- in naturethereisoverlap

ofweakandelectromagnetic

force

19/23


6 double decay

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


6 double decay1

6. Double β-decay

21/23


6 double decay2

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)


6 double decay3

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


7 references and acknowledgements

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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