Physics of fundamental Symmetries and Interactions - PSI2013

The limits on tensor-type weak currents and the beta-neutrino correlation of 6He

11 Sept 2013, 16:50

20m

Oral Low energy precision tests of the Standard Model We - 4

Speaker

Dr Frederik Wauters (Center for Experimental Nuclear Physics and Astrophysics)

Description

Precision measurements in nuclear and neutron beta decays are a powerful tool in search for non V-A components in the weak interaction. Such a chirality-violating scalar or tensor interaction is predicted by several theories beyond Standard Model (e.g. [1][2]). We will present a new evaluation of the limits on time-reversal invariant tensor-type weak currents [3], taking into account most recent experimental data in nuclear and neutron beta decays (e.g. [4][5]), including the 5 sigma shift in the PDG2012 recommended value for the neutron lifetime. The effective field theory framework of ref [6] enables a comparison with the limits from pion decay. In addition, the sensitivity of a future 0.1% measurement of a correlation coefficient in beta decays is investigated. Such precision is currently pursued at the University of Washington on the beta-neutrino correlation in the pure Gamow-Teller decay of 6He. The high-intensity 6He source at the local accelerator [7] makes it possible to simultaneously trap several thousand 6He atoms in a magneto-optical trap (MOT). These atoms are then transferred to a second, back-ground free, MOT. The beta-neutrino correlation is derived from the time-of-flight spectrum of the recoil 6Li ions. The beta particle which serves as a trigger is detected by a position sensitive hodoscope, the recoil ions are guided by an electrostatic field towards a multi-channel plate detector. All detector systems and both atom traps have been successfully commissioned. A first physics run is planned for this summer, aiming for a precision of 1% on the beta-neutrino correlation. [1] P. Herczeg, Progress in Particle and Nuclear Physics 46, 413 (2001). [2] S. Profumo, M. J. Ramsey-Musolf, and S. Tulin, Phys. Rev. D 75, 075017 (2007). [3] F. Wauters, A. Garcia, and R. Hong, arXiv:1306.2608 [nucl-ex] (2013). [4] M.P. Medenhall et al. (UCNA Collaboration), Phys. Rev. C 87, 032501 (2013). [5] F. Wauters et al., Phys. Rev. C 82, 055502 (2010). [6] T. Bhattacharya et al., Phys. Rev. D 85, 054512 (2012). [7] A. Knecht et al., Nucl. Instrum. Methods Phys. Res. Sect. A 660, 43-47 (2011).

Summary

Precision data in nuclear and neutron beta decays provide strong limits on tensor-type weak currents. To further increase the discovery potential of such experiments, a precision of 0.1% has to be reached. The ongoing experiment at the University of Washington to measure the beta-neutrino correlation in the decay 6He is pursuing such accuracy.

Presentation materials

Slides

PSI2013.pdf