Matter-Antimatter Mass

Shailank

Does antimatter has more mass than matter?

Its not conclusively proven that they have the EXACT same mass. Also i read about an experiment being conducted. http://phys.org/news/2012-01-antimatter-lab.html
What happened to this experiment?

mfb

No experiment measured any difference.
A difference between the masses of particles and antiparticles would ruin significant parts of the Standard Model as it would violate CPT invariance.

That could take a while. Gravity is hard to see in particle physics as it is extremely weak.

Vanadium 50

One will never know that two particles (any two) will have the "EXACT same mass". We can only set limits on the difference.

Shailank

Yeah so it can be possible that that antimatter excerts a greater gravitational force on matter and vice versa?

And also that the difference may be significant? Like 10^-6 to 10^-9 gram.

mfb

You have to distinguish mass measurements from gravity measurements here.

Mass measurements are common in particle physics - it is a measurement of the rest energy of the particle. Those are very precise, especially for stable particles and antiparticles. Any difference would violate CPT invariance (quantum-mechanical statement)

Gravity measurements measure the influence of gravity. Those are tricky in particle physics. Any difference would be a different gravitational acceleration and violate the equivalence principle (from General Relativity).

If there is any difference at all, it has to be at the level of the particles itself, of the order of 10^-27 gram.

Shailank

Ok. S is there any difference? In the order of 10^-27?

mfb

To add some numbers:

The relative difference between electron and positron mass (if there is a difference at all) is smaller than 8*10^-9, or 8 parts in a billion (<10^-38g difference).
The relative difference between proton and antiproton mass (if there is a difference at all) is smaller than 2*10^-9, or 2 parts in a billion (<10^-32g difference).

The gravitational acceleration on objects of different composition differs by less than 10^-10, or 1 part in 100 billions (Eötvös experiment).

Shailank

Ok thank you.