Various ways of determining particles rest mass

[xyzt]

In a recent thread (now rightfully deposited in "Trash"), a member was disputing the idea that mainstream science can measure particles rest mass. Contrary to those crank claims, the measurement can and IS done, there are multiple methods (you can google "rest mass measurement"). I will present a method that, though quite routine, doesn't show up in the search (not clear why).

In a cyclotron, a particle of charge [math]q[/math] and rest mass [math]m_0[/math] will describe a circular trajectory of radius [math]R=\frac{\gamma m_0 v}{qB}[/math] when subjected to a transverse Lorentz force due to a magnetic induction [math]B[/math]. [math]v[/math] is the measured speed of the particle and [math]\gamma=\frac{1}{\sqrt{1-v^2/c^2}}[/math]

From the above, the rest mass is calculated easily as [math]m_0=\frac{RqB}{\gamma v}[/math].

Since [math]v[/math] is difficult to measure accurately, we tend to use the fact that [math]v=\frac{2\pi R}{T}[/math] where [math]T[/math] is the period of rotation (that can be measured very precisely).

Edited October 14, 2014 by xyzt

[fiveworlds]

mainstream science can measure particles rest mass

 

 

No what I said was that you could not measure the invariant mass independent of velocity. http://www.phys.ncku.edu.tw/mirrors/physicsfaq_old/Relativity/SR/mass.html

The invariant mass of a particle is independent of its velocity v

 

[xyzt]

 

No what I said was that you could not measure the invariant mass independent of velocity. http://www.phys.ncku.edu.tw/mirrors/physicsfaq_old/Relativity/SR/mass.html

What do you think [math]m_0[/math] is?

I anticipated that you were going to argue that [math]v[/math] appears in the formula but I already preempted that by replacing [math]v[/math] as a function of [math]T[/math].

Edited October 14, 2014 by xyzt

[fiveworlds]

Not the invariant mass.

[Strange]

No what I said was that you could not measure the invariant mass independent of velocity.

 

I'm curious why you think that. If, for example, the particles is stationary relative to you when you measure its mass, then you are measuring its rest mass. No?

Not the invariant mass.

 

Then what do you think it is?

[fiveworlds]

I'm curious why you think that. If, for example, the particles is stationary relative to you when you measure its mass, then you are measuring its rest mass. No?

 

Correct but it is in motion relative to me.

[Strange]

Correct but it is in motion relative to me.

 

What is?

[fiveworlds]

What is?

Everything. It all moves.

[xyzt]

Everything. It all moves.

So, I showed that despite the particle being in (circular) motion, mainstream physicists can measure its rest mass, despite claims to the contrary from cranks.

Edited October 14, 2014 by xyzt

[Strange]

Everything. It all moves.

 

I can assure you that my chair is not moving relative to me.

[fiveworlds]

I can assure you that my chair is not moving relative to me.

 

It is because you don't occupy the same space as your chair. You have a unique velocity based on your position in space.

Edited October 14, 2014 by fiveworlds

[Strange]

It is because you don't occupy the same space as your chair. You have a unique velocity based on your position in space.

 

If that were the case, then I would soon find myself on the floor as my chair moved from under me.

[ajb]

You have a unique velocity based on your position in space.

No, velocities are relative.

 

The only sensible way to interpret what you have said is that he as a unique velocity relative to his chair and that this velocity is zero. This means that they are co-moving.

 

Anyway, whatever the method used to measure m0, indirectly maybe, then you have the rest mass by definition. This actually does not require you to be in the same frame. But if you were in the same inertial frame then m0 is the mass you would 'see'.

 

The method suggested by xyzt is a variant of mass spectrometry. You see how charged massive particles are deflected in magnetic fields. This will give you the mass to charge ratio. Then if you know the charge, say via theological means, then you can deduce the mass.

Edited October 15, 2014 by ajb

[imatfaal]

!

Moderator Note

 

I have removed Fiveworlds' misguided digression into the nature of velocity and vectors and placed it in a new thread in speculations

 

http://www.scienceforums.net/topic/86106-split-from-various-ways-of-determining-particles-rest-mass/

 

do not respond to this moderation within the thread - report this post if you have a problem.

 

 

Thanks to xyzt for the nice explanation up top. Do we have any other way of performing the same measurement other than a method that boils down to mass/charge ratio?

[xyzt]

!

Moderator Note

 

I have removed Fiveworlds' misguided digression into the nature of velocity and vectors and placed it in a new thread in speculations

 

http://www.scienceforums.net/topic/86106-split-from-various-ways-of-determining-particles-rest-mass/

 

do not respond to this moderation within the thread - report this post if you have a problem.

 

 

Thanks to xyzt for the nice explanation up top. Do we have any other way of performing the same measurement other than a method that boils down to mass/charge ratio?

Thank you, most methods for charged particles involve controlled collisions of particles accelerated in an electrostatic field, by observing the angle of recoil.

By far, the most complicated methods are reserved for particles that have no charge, like the neutrino. Here is a synopsis of the methods. Here is the complete list of references.

My favorite is the case of the photon. We all know that the photon has zero rest mass. In order to constrain the rest mass of the photon we need a theory that assumes, by absurd, that the rest mass of the photon is non-zero. Using the equations of this theory, we can set up experiments that constrain the deviation from zero of the photon rest mass. This is a wonderful theory, that parallels Maxwell's theory, we owe it to N. Proca.

Edited October 17, 2014 by xyzt