Beta-decay Correlations in the LHC Era

K Bodek

doi:10.5506/aphyspolb.47.349

Abstract

Neutron and nuclear beta decay correlation coefficients are linearly sensitive to the exotic scalar and tensor interactions that are not included in the Standard Model. The proposed experiment will measure simultaneously 11 neutron correlation coefficients ($a$, $A$, $B$, $D$, $H$, $L$, $N$, $R$, $S$, $U$, $V$) where 5 of them ($H$, $L$, $S$, $U$, $V$) were never addressed before. Silicon pixel detectors are considered as promising alternative to multi-wire gas chambers devoted for electron tracking in the original setup. The expected sensitivity limits for $\epsilon_S$ and $\epsilon_T$ -- EFT parameters describing the scalar and tensor contributions to be extracted from the transverse electron polarization related coefficients $H$, $L$, $N$, $R$, $S$, $U$, $V$ are discussed.

Highlights

The observed excess of matter over antimatter in the Universe remains one of the most important puzzles in physics and unknown sources of fundamental CP symmetry violation are its necessary preconditions
The effective field theory (EFT) parametrization of measured observables in nuclear, neutron and pion decay and of the cross section for pp → eν + . . . process at high transverse mass led to the combined limits for exotic scalar and tensor interactions showing that, presently, the constraints obtained from both approaches are on a comparable accuracy level
The key ideas of the originally proposed setup were: (i) efficient cylindrical detector geometry, (ii) electron tracking in a multi-wire drift chamber (MWDC) with both wire ends readout, (iii) detection of both direct and Mott-scattered electrons in a plastic scintillator hodoscope, (iv) conversion of protons into bunches of electrons ejected from a thin LiF layer, and (v) acceleration and subsequent detection of ejected electrons in a multi-wire proportional chamber (MWPC) with both wire ends readout

Summary

Introduction

The observed excess of matter over antimatter in the Universe remains one of the most important puzzles in physics and unknown sources of fundamental CP symmetry violation are its necessary preconditions. Process at high transverse mass led to the combined limits for exotic scalar and tensor interactions showing that, presently, the constraints obtained from both approaches are on a comparable accuracy level. The EFT analysis describes prospects and defines challenges for future experiments in the lowand high-energy searches for BSM physics. We recall the idea of an entirely new experiment devoted to a simultaneous measurement of 11 correlation coefficients in the neutron decay where 5 of them were never attempted before [7]. Seven of these correlation coefficients are related to the transverse polarization component of the electrons emitted in the decay. As compared to Ref. [7], new experimental options are discussed

Neutron β-decay correlation coefficients

Scalar and tensor contributions to weak interaction in EFT approach

Transverse electron polarization in neutron β-decay

Experiment: the BRAND project

Conclusions