Shrunken proton leaves scientists stunned

[Analog]

PARIS: Scientists lobbed a bombshell into the world of sub-atomic theory by reporting that a primary building block of the visible universe, the proton, is smaller than previously thought.

More precisely, revised measurements shave 4% off the particle's radius, according to a study in Nature. That may not seem like much, especially given the proton's infinitesimally tiny size.

But if borne out in further experiments, the findings could challenge fundamental precepts of quantum electrodynamics, the theory of how quantum light and matter interact, said its authors.

Either the previously accepted measures upon which hundreds of calculations have been based are wrong, or there is a problem with the theory of quantum electrodynamics itself.

The new experiment - at least 10 times more accurate than any performed to date - was envisioned by physicists 40 years ago, but only recent developments in technology made it feasible.
The trick was to replace the electron in the hydrogen atom with a negative muon, a particle with the same electric charge but more than 200 times heavier and unstable to boot.


The muon's larger mass gives muonic hydrogen a smaller atomic size and allows a much larger interaction with the proton. As a result, the proton's structure can be probed more accurately than by using hydrogen.

http://www.cosmosmagazine.com/news/3548/proton-bombshell-leaves-scientists-stunned

 

[SagaLore]

The trick was to replace the electron in the hydrogen atom with a negative muon, a particle with the same electric charge but more than 200 times heavier and unstable to boot.

The muon's larger mass gives muonic hydrogen a smaller atomic size and allows a much larger interaction with the proton. As a result, the proton's structure can be probed more accurately than by using hydrogen.

Muonic hydrogen? That's a neat trick. Completely off on a tangent, but is it possible to create molecules with that?

 

[BrunoPuntzJones]

My proton didnt shrink, it's just cold!

 

[SunnyD]

Muonic hydrogen? That's a neat trick. Completely off on a tangent, but is it possible to create molecules with that?

Given the fact that they say it's extremely unstable, I doubt it.

What confuses me is how a particle with 200x more mass could equate to a smaller atom. I assume it pulls the electron orbit in some, but you've still got to physically put all the mass somewhere (hence much bigger than the proton it replaced).

 

[joesmoke]

that wasnt a proton


edit:damn you BPJ

 

[rcpratt]

Given the fact that they say it's extremely unstable, I doubt it.

What confuses me is how a particle with 200x more mass could equate to a smaller atom. I assume it pulls the electron orbit in some, but you've still got to physically put all the mass somewhere (hence much bigger than the proton it replaced).

The size of an atom has almost nothing to do with the size of the electron (or muon, in this case), but rather the size of the orbital. Higher mass means a stronger gravitational force and thus a smaller orbital, I assume.

 

[SunnyD]

The size of an atom has almost nothing to do with the size of the electron (or muon, in this case), but rather the size of the orbital. Higher mass means a stronger gravitational force and thus a smaller orbital, I assume.

I agree, but which force is going to make the difference here? Gravitation or electromagnetic? I'm probably wrong but I would thing the electromagnetic forces due to the radius of the muon being larger would equate to a larger orbit riding the electromagnetic forces (the charges) further out. Dunno though, I'm not a particle scientist, hence why I ask.

 

[sandorski]

My proton didnt shrink, it's just cold!

It was in the Pool!!!

 

[Analog]

The size of an atom has almost nothing to do with the size of the electron (or muon, in this case), but rather the size of the orbital. Higher mass means a stronger gravitational force and thus a smaller orbital, I assume.

The muon was the first elementary particle discovered that does not appear in ordinary atoms. Negative muons can, however, form muonic atoms (also called mu-mesic atoms), by replacing an electron in ordinary atoms. Muonic hydrogen atoms are much smaller than typical hydrogen atoms because the much larger mass of the muon gives it a much smaller ground-state wavefunction than is observed for the electron. In multi-electron atoms, when only one of the electrons is replaced by a muon, the size of the atom continues to be determined by the other electrons, and the atomic size is nearly unchanged. However, in such cases the orbital of the muon continues to be smaller and far closer to the nucleus than the atomic orbitals of the electrons.
A positive muon, when stopped in ordinary matter, can also bind an electron and form an exotic atom known as muonium (Mu) atom, in which the muon acts as the nucleus. The positive muon, in this context, can be considered a pseudo-isotope of hydrogen with one ninth of the mass of the proton. Because the reduced mass of muonium, and hence its Bohr radius, is very close to that of hydrogen, this short-lived "atom" behaves chemically — to a first approximation — like hydrogen, deuterium and tritium.

 

[rcpratt]

The muon was the first elementary particle discovered that does not appear in ordinary atoms. Negative muons can, however, form muonic atoms (also called mu-mesic atoms), by replacing an electron in ordinary atoms. Muonic hydrogen atoms are much smaller than typical hydrogen atoms because the much larger mass of the muon gives it a much smaller ground-state wavefunction than is observed for the electron. In multi-electron atoms, when only one of the electrons is replaced by a muon, the size of the atom continues to be determined by the other electrons, and the atomic size is nearly unchanged. However, in such cases the orbital of the muon continues to be smaller and far closer to the nucleus than the atomic orbitals of the electrons.
A positive muon, when stopped in ordinary matter, can also bind an electron and form an exotic atom known as muonium (Mu) atom, in which the muon acts as the nucleus. The positive muon, in this context, can be considered a pseudo-isotope of hydrogen with one ninth of the mass of the proton. Because the reduced mass of muonium, and hence its Bohr radius, is very close to that of hydrogen, this short-lived "atom" behaves chemically — to a first approximation — like hydrogen, deuterium and tritium.

Nice, thanks.

TLDR - It's more a quantum mechanics issue than a gravitational or electromagnetic force issue.

 

[logo908]

damn. wonder how they got the muon on there

 

[Crono]

Does that mean we can now cross proton streams without it being gay?

 

[Jeff7]

Damn. I hope they contribute 4% towards the cost of new physics books.

 

[GodlessAstronomer]

Quantum electrodynamics was never a fundamental theory, it's more of a calculational framework.

 

[silverpig]

Nice, thanks.

TLDR - It's more a quantum mechanics issue than a gravitational or electromagnetic force issue.

Well, it's an electromagnetics issue for sure. The schroedinger equation for muonic hydrogen is very dependent on EM. Gravity means nothing at these scales.

 

[MarkXIX]

They changed the size of it by measuring it!

 

[rcpratt]

Well, it's an electromagnetics issue for sure. The schroedinger equation for muonic hydrogen is very dependent on EM. Gravity means nothing at these scales.

Of course, just meant in the classical EM sense, should have clarified.

 

[silverpig]

They changed the size of it by measuring it!

:thumbsup;