The Beta-Neutrino Correlation in Sodium-21 and Other Nuclei Page: 3 of 10
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January 28, 2008 12:17 WSPC - Proceedings Trim Size: 9in x 6in RIA INTproc abetanu
In the Standard Model (SM), CV and CA are almost purely reala CV CVz= 1,
and CA CA -1.27 (from experiments), and all other coupling constants are
zero. Experimental limits on scalar and tensor couplings predicted by some SM
extensions are model dependent, and not necessarily stringent . If present, these
couplings would alter ap, either through the quadratic dependence on Cs and CT
or through the helicity-sensitive Fierz interference terms. Searching for new tree-
level lepton-quark interactions in nuclear beta decay is tough because there are
many different couplings to measure: CV and CA, the opposite chirality (primed)
terms, and limits on Cs and CT. Absent a predicted symmetry group, we have
19 different couplings to measure. Naively, at tree-level, each coupling constant
would be related to a new boson like 1/M&,, so that measurements with a frac-
tional precision of 1% of Cv and CA constrain physics at an energy scale ten times
higher than the electroweak scale.
Interpreting measurements of beta-decay correlations to test the Standard
Model demands high precision auxiliary nuclear data. Several corrections alter
the allowed approximation prediction of aw and give Ee dependence to fi, ape,
and bFierz at the 1% level. The input data include ground and excited state de-
cay branching ratios, half-life, total decay energy, electron capture branching ra-
tio, radiative corrections to order a, isospin symmetry breaking corrections, and
magnetic moments of parent and daughter to estimate the weak magnetism con-
tribution. Measurements of decay correlations to better than 1% precision will be
limited by the precision of these auxiliary inputs. We should view these nuclear
beta decay systems as a significant frontier for testing Beyond Standard Model
physics, and advocate for new, high precision input data as a significant use of a
potential RIA/FRIB nuclear accelerator facility.
3. - v measurement technique
The experiment apparatus have been described in [7,8,11]. The measurement tech-
nique is at root a momentum spectrometer for the recoil nuclei. The magneto-
optic trap (MOT) is located between two microchannel plates (MCPs) and several
electrodes which form a focusing electric field in the region of the trap. The P
decay leaves 21Ne in a variety of charge states through shakeoff and Auger pro-
cesses . The electric field accelerates the ionized recoil nuclei to one MCP and
the low-energy electrons shaken off by the 21Ne towards the second MCP. A trig-
ger from the electron MCP starts a time to amplitude converter, with a stop signal
aCv and CA acquire a tiny imaginary part from the complex phase in the CKM matrix in heavy quark
flavor mixing. For the rest of this discussion, we assume they are purely real, and the non-Standard
Model couplings for which we derive limits are also real, i.e. time-reversal invariant.
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Vetter, Paul A.; Abo-Shaeer, Jamil; Freedman, Stuart J. & Maruyama, Reina. The Beta-Neutrino Correlation in Sodium-21 and Other Nuclei, article, January 16, 2008; (digital.library.unt.edu/ark:/67531/metadc895721/m1/3/: accessed January 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.