Elementary Particle Questions...fundamentals of Higgs Boson Theory

[Christenson]

Re-post:

Let's have an educational/historical diversion:
Does anyone remember the "ultraviolet catastrophe" of Raleigh-Jeans fame, proving that quantisation was necessary? I want to review the fundamental experimental evidence that anything other than a proton, neutron, electron, and photon actually exist...let's start with anti-matter.

@davieddy: I'm not a physicist! I'm an engineer!
*********

That is, we know photons exist and are quantised because of the photoelectric effect. The black body radiation curve is also helped by quantising the photon energy, as shown by Max Planck.

Charge is clearly quantised as shown by both cathode rays, photomultipliers, thermionic vacuum tubes, and by Millikan's oil drop experiment.

Polonium was produced during WWII by transmutation. I have neutron-activated nickel in a lab before.

*******
So how do I prove that anti-electrons exist? How about the other leptons? Neutrinos? Baryons?

All respondents please note that I am aware that this is probably undergraduate physics material...I want to review and understand the fundamental evidence here. It recalls some lectures I had in physics a very long time ago.

[xilman]

Originally Posted by Christenson

Re-post:

Let's have an educational/historical diversion:
Does anyone remember the "ultraviolet catastrophe" of Raleigh-Jeans fame, proving that quantisation was necessary? I want to review the fundamental experimental evidence that anything other than a proton, neutron, electron, and photon actually exist...let's start with anti-matter.

@davieddy: I'm not a physicist! I'm an engineer!
*********

That is, we know photons exist and are quantised because of the photoelectric effect. The black body radiation curve is also helped by quantising the photon energy, as shown by Max Planck.

Charge is clearly quantised as shown by both cathode rays, photomultipliers, thermionic vacuum tubes, and by Millikan's oil drop experiment.

Polonium was produced during WWII by transmutation. I have neutron-activated nickel in a lab before.

*******
So how do I prove that anti-electrons exist? How about the other leptons? Neutrinos? Baryons?

All respondents please note that I am aware that this is probably undergraduate physics material...I want to review and understand the fundamental evidence here. It recalls some lectures I had in physics a very long time ago.

Positrons are fairly easily shown to exist. Here is just one line of evidence.

Some nuclei, such as Na-22, emit a positively charge particle with the same charge to mass ratio as an electron, as shown by its behaviour in a magnetic field. These particles ultimately disappear and at that instant two or three photons are produced for each particle. In the case of the 2-photon process each of their energies are exactly those predicted by plugging the mass of the electron into E=mc^2. In the three particle case, the sum of the photon energies is also 2mc^2 where, again, m is the mass of the electron. This behaviour very strongly suggests that the positively charged particle is an anti-electron.

[fivemack]

I have the vague memory, from reading histories of early particle physics, that if you watch a reasonable elevated cloud chamber set between strong magnets for a while you will see muons in vast abundance and the occasional lambda-particle (which decays to two trails going off and looking like an upper-case lambda). But I don't know how you determine that the muons are leptons and that the lambda-particle contains a strange quark.

[davieddy]

Originally Posted by Christenson

@davieddy: I'm not a physicist! I'm an engineer!

Well that explains it.
Paul is a chemist and Tom a number-theorist.

"Science is either physics or stamp-collecting"
(Ernest Rutherford).
Discuss.

(Question on the "General Paper" of the Oxford entrance exam, my answer to which I attribute my Scholarship to Exeter. My father attributed his to a discussion of the merits of "Punch" as a satirical magazine.)

David

[xilman]

Originally Posted by fivemack

I have the vague memory, from reading histories of early particle physics, that if you watch a reasonable elevated cloud chamber set between strong magnets for a while you will see muons in vast abundance and the occasional lambda-particle (which decays to two trails going off and looking like an upper-case lambda). But I don't know how you determine that the muons are leptons and that the lambda-particle contains a strange quark.

There's no need to go up particularly high to detect muons. Neutrino telescopes are buried under at least a kilometre of rock specifically to screen out cosmic-ray generated muons. Back when I was working at the Unclear Physics Dept at Oxford, a (roughly 1 metre cube) spark detector was set up in the foyer when prospective students and the relatives of staff were invited to learn about the department's activities. A muon would generate a roughly vertical line of sparks about once a second.

Demonstrating that they are leptons (as distinct from mesons, with which they were confused for quite some time) is a bit trickier. What is easy is to show that they have a rest mass of roughly 200 times the mass of an electron and equal charge. The equality of charge is proved by the observed decay of a muon into an electron and no other charged particle. The mass/charge ratio is determined by their behaviour in a magnetic field.


The lambda particles can wait for a subsequent post.

[davieddy]

Can either of you suggest a time/venue we might meet in Cambridge?

I ride the X5 for free, although no alcohol is allowed on the bus these days:(

David

PS There is talk of reuniting Bletchley with Oxon and/or Cantab by rail.

[Dubslow]

I can make a comment as to the theoretical prediction of the positron, though it's off the top of my head from a lecture in January that I was only sort of paying attention to.

This gets into quantum mechanics and the Lagrangian of whichever groups describe the EM force. A rough search makes out:

Mathematically, QED is an abelian gauge theory with the symmetry group U(1).

from here.
Edit: Went and looked at the positron article -- I now remember hearing about the 'Dirac sea', though I still can't remember what it means. However the paragraph does mention the Dirac equation, which shows up in the previous link.

Wikipedia says that a L-naught decays to pions + pro/neu/tron, which themselves decay to leptons. Assuming you know the structure of the proton, it shouldn't be too hard to reverse engineer those decays. (It's a bit harder for L-+/-, but I'm sure it's analogous.)

Edit2: I believe the neutrino was first used to explain neutron decay, n = udd --> udu W^- --> uud e^- v_e = p⁺ e^- v_e (where the v is actually a greek nu). They observed the p⁺ and e^-, but their combined energy subtracted from the neutron's energy was greater than zero, though admittedly very tiny. A quick Wiki sojourn confirms this and reminds me it needs to be an anti-neutrino -- I forgot my Feynman rules. In fact, the beta decay (neutron decay) article has a nice picture of the Feynman diagram to which I am referring.

[davieddy]

Originally Posted by Dubslow

I can make a comment as to the theoretical prediction of the positron, though it's off the top of my head from a lecture in January that I was only sort of paying attention to.

You were probably on acid.
Dirac retired just before I went to do Part III of the maths tripe at Cambridge.

Feed your head

David

BTW Much as I love drug-inspired(?) music,
I can strongly recommend you don't take this route. At least 3 of my very best friends used to, and would tell you the same thing about flashbacks...

Stick to beer and fags.

Never done me any harm:)

[Christenson]

How do I make the Na-22? What's the half-life? Is this how they get positrons for accelerators and antimatter experiments?

What happens if those electrons have many kEV of energy when annihilated?

I'm pleased with the help I'm getting so far....it's precisely what I was looking for.

As for flashbacks, you don't need drugs to induce them...just enough of the wrong kind of stress will do it...it's a survival reflex. Think "The last time I was in this situation, my life was in danger, so I want out, now, BEFORE the trap springs...." but operating below conscious awareness.

[Dubslow]

Originally Posted by Christenson

How do I make the Na-22? What's the half-life? Is this how they get positrons for accelerators and antimatter experiments?

Na-22 info
The wiki article for beta decay (above) mentions Beta+, which is analogous and opposite to the beta- decay I metioned above -- a proton converts to a neutron, and instead of an anti-neutrino and electron, we get an anti-electron and neutrino. I can't say much about positron production; as for anti-protons as used at Fermilab, I got this:

However, at CERN, protons are accelerated in the Proton Synchrotron to an energy of 26 GeV, and then smashed into an iridium rod. The protons bounce off the iridium nuclei with enough energy for matter to be created. A range of particles and antiparticles are formed, and the antiprotons are separated off using magnets in vacuum.

from here. I can't guarantee anything, but I believe Fermilab production fired proton beams at some sort of stationary nickel-cadium alloy. Very possibly wrong though.

[Dubslow]

Originally Posted by Christenson

What happens if those electrons have many kEV of energy when annihilated?

You mean e^-e⁺ annihilation? All you get is a lot of energy in a concentrated place, i.e. explosion. Keep in mind that 1 MeV is still on the order of 10^-13 J, a paltry amount. Also keep in mind that over the 40 year history of Fermilab, they produced about enough antimatter to make a dollar bill -- which dubious internet searching weighs 1 g, or 1/454 lbs. That's ~90 billion Joules, or ~25GWhrs. That sounds like a lot, and all at once it is, but (I can't find figures to back this up) it wouldn't power Chicago for a month. (And it took 40 years to make it all.)