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Neutrinoless Double Beta Decay Student: Alina Hriscu Supervisors: Olaf Scholten Gerco Onderwater 30 November 2005

Neutrinoless Double Beta Decay

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Neutrinoless Double Beta Decay. Student : Alina Hriscu Supervisors : Olaf Scholten Gerco Onderwater 30 November 2005. Summary. - Beta decay(-review-) -Two neutrinos double beta decay (2 ν 2 β ) -Zero neutrinos double beta decay(0 ν 2 β ) -Majorana particles - PowerPoint PPT Presentation

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Page 1: Neutrinoless Double Beta Decay

Neutrinoless Double Beta Decay

Student: Alina HriscuSupervisors: Olaf Scholten

Gerco Onderwater

30 November 2005

Page 2: Neutrinoless Double Beta Decay

Summary

-Beta decay(-review-) -Two neutrinos double beta decay (2ν2β) -Zero neutrinos double beta decay(0ν2β) -Majorana particles -Calculus of half-life time

-elementary particle problem -nuclear structure point of view

-Experiments on neutrinoless double beta decay -Conclusions -References

Page 3: Neutrinoless Double Beta Decay

Beta decay-Decay of a neutron in a nucleus, into a proton

-Theory of β decay -parity is violated

-neutrinos exist in nature only as “left-handed ” particles (antineutrinos “right-handed”)and only these can interact

eeZAZA ~)1,(),(

Page 4: Neutrinoless Double Beta Decay

Fermi theory -analogy with electromagnetic interaction

-Dirac-Pauli representation with γ matrixes

-Matrix elements are calculated

0

0

nosantineutri handed-rightfor )1(

neutrinos handed-leftfor )1(

5

5

5

I

I

u

u

Page 5: Neutrinoless Double Beta Decay

Other possible decays

n p

e-W-

β- decay

p n

e+W+

+ decay

(A,Z+1) (A,Z)

W+

e-

EC

p n

e+

W+

e~

neutrino conversion

-In nature-only in supernovae-

e~

Page 6: Neutrinoless Double Beta Decay

(A,Z)

(A,Z+1)

Q

β decay(A,Z)

(A,Z+2)

Q

sequential β decay

(A,Z+1)

(2ν)ββ decay

Page 7: Neutrinoless Double Beta Decay

2νββ decay-Simultaneous transmutation of two neutrons in two protons inside a nucleus

thanks to β-decay

ex: 54Xe136 -> 56Ba136 + 2e-

-It is possible whenever beta decay is forbidden by energy conservation or by angular momentum mismatch

-Conserves the lepton number-Allowed in SM

Page 8: Neutrinoless Double Beta Decay

2νββ decay

-Very rare process -It is possible only for heavy nuclei (nuclei which can

ββ decay have complicated nuclear structure) -It has been observed experimentally -Half-life time of order of y241810

Page 9: Neutrinoless Double Beta Decay

The ββ emitting isotopes

Isotope Half-time T1/ 2,2ν (y) exp.

48Ca ~ 4.0 1019

76Ge ~ 1.4 1021

82Se ~ 0.9 1020

96Zr ~ 2.1 1019

100Mo ~ 8.0 1018

116Cd ~ 3.3 1019

128Te ~ 2.5 1024

136Xe not observed yet

150Nd ~ 7.0 1018

Page 10: Neutrinoless Double Beta Decay

0νββ decay If the two neutrinos are missing…

Violates the lepton conservation rule (left side has lepton nb=0,right side equal to 2)=>beyond SM

Possible only if neutrinos are Majorana particles neutrinos have non-zero mass

Existence of right-handed currents in weak interaction Has not been (yet) observed experimentally

Page 11: Neutrinoless Double Beta Decay

Feynman diagram for 0νββ decay

~

ν

e-

e-

p

p

n

n

W+

W+

ν->e-

eν~ (in SM)

Page 12: Neutrinoless Double Beta Decay

Calculating the half-life time Two aspects:

Elementary particle Nuclear structure

Half-life time (for Majorana neutrinos)

So,if we know the half-life time and the matrix elements=> we can obtain the NEUTRINO MASS

Elem. particle properties: neutrino masses and mixing Nuclear strucure calculations: the matrix elements

mass neutrino effective

elementsmatrix nuclear -M

charge)nuclear on the depends(which integral space-phase theis g where

22)(

12/1

m

moMZgoT

Page 13: Neutrinoless Double Beta Decay

Majorana Particles Majorana particles –the particle is the same as the antiparticle, opposite as

the Dirac particles Ex: Dirac particles: electron,proton Majorana particles: photon,*all particles with spin ½ known (fermions) are Dirac particles

We define left- and right-handed components of Dirac 4-spinor by:

Construct left-handed neutrinos - charge conjugate field, which for neutrinos is also neutral

00 ,

2

1 5,

RL

Rc

L

c

i

i

C

)()(

0

0 where,

0

0 where,iC

operator charge the-C *,

c

22

222

Page 14: Neutrinoless Double Beta Decay

Neutrino-fields-can be linear combination of ,since

We define independent Majorana neutrino fields that are their own charge conjugate (antiparticles)

-Since the helicity flips,Majorana particles have nonzero mass

handed-right iscLhanded-left is and c

R

c,

Page 15: Neutrinoless Double Beta Decay

Neutrinos masses and mixing-the See-saw mechansim

If neutrinos have masses,flavour is mixed, and a leptonic mixing matrix will appear

-Since we can write the neutrino fields as linear combination of

Mass term in Lagrangian can couple these two kinds of fields

themselves and to eachother:

c,

2

)(,

2

)( cRR

R

cLL

L

two thecouples that mass Dirac is and masses Majorana are , where

)(

DRL

LRRLDRRRLLLm

MMM

MMML

Page 16: Neutrinoless Double Beta Decay

If ML and MR are zero, the Majorana ν-left pair with ν-right to form N Dirac neutrinos

The Seesaw mechanism: assuming a hierarchy in the values of elements of with μ negligible or zero,one (set)of particle(s)become

heavy,while another becomes light In the simple seesaw model, there are as many right- as left-handed

neutrinos such that we have three light and three heavy neutrinos, the lightest of which has mass

LD MMMM RM :~

N*N now are ~

,~

,~

matrices thewhere

~~

~~M~

,~

)(L

:matrix Seesaw the-

matrix ain arranged becan masses theseneutrinos of flavours NFor

M

DRL

RD

DL

R

LRL

MMM

MM

MMM

RD MM /2

Page 17: Neutrinoless Double Beta Decay

Neutrino mixing Mixes of light neutrinos: For three active neutrinos,the mixing matrix can be written:

The effective neutrino mass:

mass definite with where, m, statesU mmll

particles Majoranaonly affect phases other two theandmatrix, CKM in the

phase the toanalogus phase Dirac is , angles mixing the,cosc,sins where

1,,

ijij

2

2

2

132313231223121323122312

132313231223121323122312

13131213121

ijijij

ii

ii

ii

i

eediag

ccescsscesccss

csesssccessccs

escscc

U

ej

j

)2(2

33

)(2

22

2

112

Uamplitudewith

absorbed and emitted,m mass of neutrino Majorana exchanged and outgoing

112

ie

i

eeejj eUmeUmUmUmm

Page 18: Neutrinoless Double Beta Decay

Calculating the nuclear matrix elements

If the 0νββ decay will be observed,it is important to have accurate values of nuclear matrix elements in order to obtain quantitative results

The hadronic part contributing to the half time must be evaluated between initial and final states in the intermediate nucleus summed over

Many body techniques which lead to such results are: QRPA (neutron-proton Quasiparticle Random Phase Approximation)

-treats a large fraction of nucleons as active and allows these a large single-particle space to move in-suitable for collective motion

SHELL MODEL-Treats a small fraction of the nucleons in a limited single-particle space, but allows nucleons to corrrelate in arbritary ways

These methods have been applied to 2νββ decay(which was observed)->result: RPA model gave the most precise n.m.e –same order of magnitude-it is expected to give better results for 0νββ, too –one order of magnitude difference

Page 19: Neutrinoless Double Beta Decay

Why is that so difficult?

Theorists are making real efforts to reduce the uncertainty in calculated n.m.e

Matrix elements: <Z+2| Oβ Oβ|Z>= <Z+2| Oβ |Z+1> <Z+1| Oβ|Z>

ββdecay sequential β decay Graphical representation

|Z>0

|Z+1>0 sequential β decay

|Z+2>0

n

nn

E

ZZ1

11

Page 20: Neutrinoless Double Beta Decay

Values of the calculated n.m.e for 2νββ decay and experimental ones

Predicted n.m.e. and half-times vs. experimental ones for decay

; WS=Wood-Saxon basis for calculated n.m.e(still QRPA); calculated for decay in ground and excited states of daughter nucleus

KrSe 8282

Page 21: Neutrinoless Double Beta Decay

…and calculated ones for 0νββ

In one of the most recent QRPA model: Rodin(2003)

Compared with the SM results;except of Mo similar results

Page 22: Neutrinoless Double Beta Decay

Predicted life-time for some calculated n.m.e (2ν)

The outliers predict wrong life-time; the n.m.e of Rodin and SM are quite close

Page 23: Neutrinoless Double Beta Decay

Experimental 0νββ?

If an experiment observes 0νββ it will have profound physics implications

=>extraordinary evidence is required Difficulties:

Very slow process(one of the most slowest in nature)=>requires a lot of material(500 kg to 1 tone)

Extremely high energy resolution is required Only very pure material is used (contaminations may give background

signals) The material is difficult to obtain - experimentalists have to enrich

nuclei;also,very expensive The experiment must take place in underground-mines or like others,under

a mountain Even in the best conditions, false peaks may appear(cosmic rays,walls)

-Since enormous blocks of material are used,how can they determine the energy of only one decay

A lot of experiments are running to date,and others are being prepared

One of the most advanced : Heidelberg-Moscow

Page 24: Neutrinoless Double Beta Decay

Energetic resolution 0νββ decay being a 2 body decay, experimentally,only the energy of the two

outgoing electrons needs to be measured Ideal case-infinite resolution Real case-finite resolution

N

E

2νββ0νββ

EN

0νββ2νββ

Page 25: Neutrinoless Double Beta Decay

Importance of energy resolution

Page 26: Neutrinoless Double Beta Decay

Heidelberg-Moscow experiment

German-Russian experiment In Gran Sasso Underground Laboratory in Italy Operating with 76Ge(the sample and the detector)

-experiment is possible due to simultaneous use of large source strengths with high resolution detectors

In the underground lab the flux of cosmic muon is reduced by 6 orders of magnitude

They claim to have “seen” 0νββ decay

Page 27: Neutrinoless Double Beta Decay

H-M experimental setup

Page 28: Neutrinoless Double Beta Decay

What do they have?Peak expected

here

Page 29: Neutrinoless Double Beta Decay

Their results

eVm

yT

39.0

105.1 2502/1

with 50% uncertainty in n.m.e

Their best values

Page 30: Neutrinoless Double Beta Decay

Conclusions If 0νββ decay will be observed, it will reveal the

identity of neutrino,so a fundamental issue will be answered If a nonzero rate is seen=> ν=Majorana particle If no signal is seen=> ν=Dirac particle

Experimental proposal are promising To obtain quantitative results (neutrino masses

and hierarchy) from the experiment, good theoretical results are required uncertainties in calculus of n.m.e must be reduced

Page 31: Neutrinoless Double Beta Decay

References Neutrinoless double beta decay from a modern perspective, J.D.

Vergados (Phys. Rep 361(2002) 1-56) Weak interaction and nuclear-structure aspects of nuclear double beta

decay-Jouni Suhonen,Osvaldo Civitarese (Phys. Rep 300(1998)123-214) Double beta decay –Topical review, S.R. Elliot,J. Engel(Jour. Of Phys G.

30(2004)183-215) Renormalized proton-neutron QRPA and double beta decay of 82Se to

excited states in 82Kr, J. Suhonen, J. Toivanen, A.S. Barabash, I.A. Vanushin, V.I. Umatov, R. Gurriar´an, F. Hubert, Ph. Hubert(Z. Phys. A 358, 297–301 (1997))

Evidence for neutrinoless double beta decay, Klapdor-Kleingrothaus, Modern Physics Letters A [Particles and Fields; Gravitation; Cosmology and Nuclear Physics], Vol. 16, No. 37 (2001) 2409-2420