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## Scientists Calculate Most Precise Measurement of Electron's Mass59

sciencehabit writes "A team of physicists has produced the most precise electron mass measurement ever made. Instead of trying to measure the mass directly, the researchers bound a single electron to a bare carbon nucleus and placed the resulting atom in a uniform electromagnetic field called a Penning trap. The team's new measurement is 13 times more precise than previous efforts, with an uncertainty of just 0.03 parts per billion. The group's precise result will help physicists more accurately calculate the fine-structure constant, an important value in tests of the standard model of particle physics, which shapes our understanding of the basic building blocks of the universe."
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## Scientists Calculate Most Precise Measurement of Electron's Mass

• #### Re:So what's the mass then? (Score:5, Informative)

by Anonymous Coward on Wednesday February 19, 2014 @09:27PM (#46292137)
They determined the electron mass compared to that of a proton, so it depends on how accurate the proton mass has been determined.

on Wednesday February 19, 2014 @09:50PM (#46292247)

DOIs can take a few hours/days or so to start working in some cases, if the results were recently announced. While Slashdot covering recent news would be surprising, it's not totally unheard of.

• #### Re:So what's the mass then? (Score:5, Informative)

on Thursday February 20, 2014 @12:51AM (#46292821) Homepage

Actually, the mass of a hydrogen atom isn't equal to the sum mass of the proton and that of the electron. There's a 13.6 eV binding energy (good 'ol E-mc^2) that needs to be taken into account. Considering that the 511 eV rest mass of the electron and the fact that we're taking about measurements that are supposed to be accurate to less than 1 part per billion, then the binding energy is pretty significant. I suspect there are other effects that also need to be taken into account.

• #### Re:So what's the mass then? (Score:4, Informative)

on Thursday February 20, 2014 @12:53AM (#46292827) Homepage

Sorry, I meant to say 511 *keV* for the rest mass of the electron.

• #### Re:So what's the mass then? (Score:3, Informative)

by Anonymous Coward on Thursday February 20, 2014 @10:48AM (#46294993)
I don't know where the parent poster got that number, but that is way too many digits, even considering the new precision the recent experiment added. As in, that is nearly 3 times as many digits as the error bars in the paper would suggest. They gave the measurement in two forms, the mass of the electron in atomic mass units: m_e = 0.000548579909067(14)(9)(2), and as the ratio of the proton mass to electron mass: m_p/m_e = 1836.15267377(17).

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