John Behr
TRIUMF
addendum Dec 6:
There is an issue with the "naive dimensional analysis" for that 2-loop diagram. Momentum ranges must stay below the EFT scale, or large overestimates can result. (see e.g. "Uses and abuses of effective Lagrangians" C. P. Burgess and David London Phys. Rev. D 48, 4337 (1993)). Better estimates are possible for that m_N**5 in the numerator (which was merely 'the only scale in the problem')... simple ones were done that include the M of the EFT and have many orders smaller results for the naive dimensional analysis.
Updated Dec 5. Planning nuclear beta decay TRV experiments is challenging, given neutron null results and given indirect constraints from other experiments.
The organizers asked me to review TRV experiments in nuclear beta decay. I will cover:
a) The R coefficient (tranverse polarization of the beta emitted from polarized decay) measurement by Jiro Murata's Rikkyo University group using TRIUMF's 8Li polarized beam, which has likely completed final data-taking and is under analysis. They will show an upside final error estimate (machines must still learn to reject background while maintaining efficiency), which can be compared to the PSI result from the early 90's. but of course the results will be blinded. The final state effects in R scale with Abeta/momentum_beta, and end up somewhat smaller in 8Li than in the neutron (depending on energy threshold).
b) The seminal 19Ne Princeton result for D (nuclear spin dotted into cross product of lepton momenta), while Pierre Delahaye has provided slides of the LPCTrap plans (optically pumping ions in a Paul trap) based on their TCP conference arXiv 1810.09246, with a goal of 10**-5 statistics possible.
The organizers ask me to contrast atom and ion traps with neutron decay, which for "D" effectively contrasts systematics of a point-source experiment with useful symmetries of the cold beam. Tim Chupp is one expert on the latter with whom I've discussed these issues before. At the least, high accuracy is required of the point source location. (I was overly ambitious and will not do this.)
c) Albert Young's 36K proposed nuclear spin-beta-gamma 5-fold correlation PRL 1995 (reference in talk), with its built-in comparison of GT and GT/Fermi decays, and K. Minamisono's long-term interest in pursuing this with FRIB yields.
d) Our own proposal and progress for radiative beta decay 3-momenta (beta, nu, gamma) TRV in TRIUMF's neutral atom trap with 37K or 38mK, strongly influenced by Gardner and He theory papers that amony other things worked out final-state corrections in decays with similar Z.
e) I will mention Ted Clifford's old Chalk River proposal (PRL ref. in slides) for 20Na beta-delayed alpha decay, which cleverly converts TRV asymmetries into energy shifts of alpha peaks.
Theory papers on D and EDM's include El-Menoufi, Ramsey-Musolf, and Seng, Phys Lett B 765 (2017) 62, which along with Ng and Tulin Phys Rev D 85 033001 (2012) suggest one needs approximately 10**-N [N is in slides] sensitivity to complement other experiments (TRV EDM's; LHC non-TRV p+p -> e + Etransverse missing; atomic PNC constraints on leptoquarks...).
Variations on "sole-source" constraints from EDM's include "Linear programming analysis of the R-parity violation within EDM-constraints" Yamanaka, Sato, and Kubota, 1406.3713 JHEP12(2014)110, which identifies one SUSY term to which R is particularly sensitive, with an eye towards constraining/discovering that term with "R," leaving combinations of other terms for EDM's.
That LHC p+p -> e + Etransverse constrains a sum of absolute squares of coupling coefficients, so there is no cancellation of new terms there.
I'm looking for motivation to pursue a "D" measurement in the GT/Fermi decay of 37K with our atom trap.
Our own plans in radiative beta decay are largely inspired by Gardner and He's careful workup of final state effects and contributing phenomenology, and are very much in the spirit of the late 1950's-- a new observable that could still at lowest order have large asymmetries. Whether or not this remains symbiotic or justifies a dedicated geometry design is my other goal for this workshop. Coincidence of 3 particles is statistically problematic, particularly when one branch is small. We've done a test experiment in 92Rb 0- to 0+ decay, which might provide sensitivity to TRV in pseudoscalar interactions.
LGRT 419B
