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NEUTRINOLESS DOUBLE BETA DECAY ANGULAR

CORRELATION AND NEW PHYSICS

Dmitry Zhuridov Particles and Fields Journal

club Department of Physics National Tsing Hua

University

The talk is based mostly on the paper Probing

new physics in the neutrinoless double beta

decay using electron angular correlation. A. Ali

(DESY) , A.V. Borisov, D.V. Zhuridov (Moscow

State U.) . DESY-07-097, Jun 2007. 36pp.

e-Print arXiv0706.4165 hep-ph (to appear in

Phyical Review D)

Popularity of the theme

- M. Doi, T. Kotani, E. Takasugi,

Prog.Theor.Phys.Suppl.83 (1985) 329 - T. Tomoda, Rep.Prog.Phys.54 (1991) 133
- S.L. Adler et al., Phys.Rev.D11 (1975)

74 - H. Pas, M. Hirsch, H.V. Klapdor-Kleingrothaus,

S.G. Kovalenko, Phys.Lett.B453 (1999)

26

- SPIRES-HEP
- FIND TITLE NEUTRINOLESS DOUBLE BETA DECAY

470 - FIND K NEUTRINOLESS DOUBLE BETA DECAY 476

- E-print arXiv Abstract NEUTRINOLESS DOUBLE

BETA DECAY - 1991-1995 29
- 1996-2000 139
- 2001-2005 251
- 2006-p.t. 87

Contents

- Introduction
- Neutrinoless Double Beta Decay
- Angular Correlation in Long-Range Mechanism
- Analysis of the Angular Correlation
- Conclusion

Introduction

SNO, Super-Kamiokande, KamLAND ? oscillations

Neutrinos have non-zero masses and they mix with

each other

Bounds on the neutrino masses

It is largely anticipated that the neutrinos are

Majorana particles

Correspondence between Dirac and Majoana fields

Dirac field can be constructed from two Majorana

fields

Dirac field has additional freedom of phase

trasformation

How to induce small neutrino masses?

Other possible mechanisms

- Model with scalar triplet
- Model with right-handed neutrino and scalar

singlet - In Zee model (with charged scalar singlet and

additional scalar doublets) Majorana neutrino

masses arise at one loop level - In models with doubly charged scalar singlet

Majorana neutrino masses arise at two loop level - Models with effective nonrenormalizable term in

Lagrangian

See-saw mechanism

Neutrinoless Double Beta Decay

n

n

Lepton number is changed by 2 units. 0?2? decay

is forbidden in the SM. Extended version of the

SM could contain tiny nonrenormalizable terms

that violate LN and allow 0?2? decay.

- Probable mechanisms of LN violation may include

exchanges by - Majorana neutrinos
- Scalar bilinears, e.g. doubly charged dileptons
- SUSY particles
- Leptoquarks
- Right-handed W_R bosons etc.

- Two possible classes of mechanisms for the 0?2?

decay - Long range

Short range - (with the light ?s in the intermediate state)

According to the Schechter-Valle theorem, any

mechanism inducing the 0?2? decay produces an

effective Majorana mass for the neutrino, which

must therefore contribute to this decay.

e

e

u

u

d

d

Purpose to examine the possibility to

discriminate among the various possible

mechanisms contributing to the 0?2? decays using

the information on the angular correlation

of the final electrons.

Angular Distribution in Long-Range Mechanism

Most general Lorentz invariant effective

Lagrangian for the long-range mechanism of 0?2ß

decay is

- Approximations
- leading order in the Fermi constant
- leading contribution of the parameters \epsilon
- relativistic electrons and non-relativistic

nucleons - S_1/2 and P_1/2 waves for the outgoing

electrons

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Expressions for A for one ?, considered at a time

Expressions for B for one ? at a time

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Analysis of the Electron Angular Correlation

If the nonstandard" effects, are zero then K

B01/A01. Its values are given in the Table for

various decaying nuclei of current experimental

interest

The angular correlation coefficient K for various

SM extensions for decays of

Particular cases for the parameter space

Constraints on the couplings of the effective

LQ-quark-lepton interactions

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1a 1b 2a 2b

Angular correlation in left-right symmetric models

103?

103?

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Conclusion

- We have presented a detailed study of the

electron angular correlation for the long range

mechanism of 0?2? decays in a general theoretical

context. This information, together with the

ability of observing these decays in several

nuclei, would help greatly in identifying the

dominant mechanism underlying these decays. - The running experimental facility that in

principle can measure the electron angular

correlation in the 0?2? decay NEMO3 possibly has

no the sufficient sensitivity. The proposed

facilities are SuperNEMO, MOON and EXO. We have

argued that there is a strong case in building at

least one of them.