[JProthero]

I've often heard it said that a particular prediction of Quantum Electrodynamics [1] may be the most precise experimentally confirmed value in physics [2], with an accuracy in the region of one part in a trillion (10^12).

I haven't heard the same claim made for the LIGO experiment yet, but I understand it is capable of detecting distance changes smaller than one part in a billion trillion (10^21) [3].

If this LHCb result is confirmed, given that it involves the detection of a mass difference of one part in a hundred million quadrillion quadrillion (10^38), would it qualify as a new precision record in physics? I'd be grateful if anyone familiar with the field could comment.

[1] https://en.wikipedia.org/wiki/Electron_magnetic_moment

[2] https://en.wikipedia.org/wiki/Precision_tests_of_QED

[3] https://en.wikipedia.org/wiki/LIGO#Observations

[dtgriscom]

This isn't a ratio of one part in 10^38; it's an absolute difference between the particles' masses of 1x10^-38 grams. The ratio implied depends on the mass of each particle. I presume this is far less than a gram, which means the radio is also far less.

[murkt]

From LHCb results summary https://lhcb-public.web.cern.ch/Welcome.html#Deltamc :

(m1-m2)/(D0mass) = 3x10^-15

10^-38 is an absolute measurement, not the ratio.

[JProthero]

Thanks for the replies. To clarify — is this not a measurement of the two particles' masses to ~38 significant figures?

[mkl]

None of those zeros are significant figures.

[JProthero]

I wondered from the announcement whether the other figures would be present somewhere in the paper.

[mkl]

Measured in grams like the 10^-38, there would still be lots of zeros first, so not 38 significant figures.

Besides, relative measurements are often easier than absolute ones, so even if you could determine that the masses of two objects of ~1g differed by 10^-38g, that wouldn't necessarily tell you the absolute masses to anywhere near that accuracy.