Protons and Special Relativity

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marco85
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Protons and Special Relativity

Post by marco85 » Wed May 02, 2012 1:32 am

I was curious as to what happens to particles in the LHC? As everyone know Special Relativity states that as velocity increases so does mass. Now does this apply with a particle such as a proton or would a strange property of quantum physics prevent this? Also how big would a proton get if travelling at 99% the speed of light?


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tswsl1989
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Re: Protons and Special Relativity

Post by tswsl1989 » Sat May 05, 2012 10:17 am

It certainly does apply to protons - the operation of the LHC depends on this fact.
When talking about objects travelling at relativistic velocities, it's pretty common to consider the rest mass - m0 - and the relativistic mass, m. It's the latter that gets bigger in the lab frame.

As far as physical size is concerned, without doing the calculations I can't say whether or not the protons would be appear to be bigger or not from the lab frame. Gut instinct says that they will, but instinct and physics don't always line up.

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chriwi
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Re: Protons and Special Relativity

Post by chriwi » Sun May 06, 2012 2:53 pm

In Wikipedia they state the mass of a proton as 938MeV this must be the restmass according to E0mC^2 sin the the protons in the LHC have a an energy of 4TeV = 4,000,000MeV so you can see that most of this mass must be due to the relavistic effect.
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adam_jeff
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Re: Protons and Special Relativity

Post by adam_jeff » Mon May 07, 2012 12:05 pm

Yes, the mass of the protons certainly increases according to Einstein's equations, and that's why the protons don't speed up very much in the LHC - most of the added energy goes into extra mass, not extra speed.
But that is mass not size. According to Special Relativity, a moving object will appear shorter than it really is (the size in directions perpendicular to the direction of motion, i.e. the cross-section, are unchanged). I believe this happens, but I don't think it can be measured - I'm not sure it's possible to measure the physical size of a proton even at rest, let alone while it's flying round in an accelerator.

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Re: Protons and Special Relativity

Post by Kasuha » Mon May 07, 2012 11:18 pm

With added energy, the proton cross-section for various rare interaction increases. Even the Totem experiment reports increase in proton elastic collision diameter. This does not mean its physical dimensions are changing - in fact it is very tricky to consider anything like physical dimensions for elementary particles - it only means the way its interactions happen are changing.

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chriwi
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Re: Protons and Special Relativity

Post by chriwi » Tue May 08, 2012 5:24 am

Thanks Kasuha for this contribution about this new confirmed effect.

I wonder if this is connected to the relativistic mass-gain of the proton or if it is just a totaly different effect.
Evenso macroscopic considerations will never tell the whole truth about particlepysics, but i try tu enpicture this effact in the following way:
asuming the proton as a structure of 2 quarks bound together by 3 springs, now comparing it to a carussell with the seats hanging on strings, the faster it turns the further the seats will swing out giving it a biger diameter, if we had now many of theese carussels mooving around the chance of the same number of fast turning carussels with high diameter to collide would be higher than for slow turning carussels.
Maybe also in the protons the quarks ar just pulled apart motre and more as the proton reaches higher energy levels, giving the proton a bigger crosssection.
If this picture would carry somewhat further I wonder if hter is an energylevel at wich the protons would be pulled apart so much that the proton would just split up into the 3 single quarks just by this effect without even colliding with another particle. this could be an interesting effect, but dont take me wrong, I wouldnt be scared that this would end up in a big explosion of all protons, since splitting protons into quarks rather consumes energy than to release more energy to trigger even more protons to desintigrate and start a chainreaction, I just find this idea interesting but not dangerous.
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Kasuha
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Re: Protons and Special Relativity

Post by Kasuha » Tue May 08, 2012 11:28 pm

The idea of proton consisting of quarks connected by springs is about as realistic as the classic planetary model of atom. It just does not work that way.

I believe the effect may be rather related to relativistic aberration. There's a video on youtube where you can see aberration (and other effects) applied on light but it works similar way with any forces. You may notice that when passing an object at speed close to speed of light, the object may appear to be turned inside out or you see its backside ahead of you because of how photons from different (and differently distant) parts of the object arrive at the same time differently than how we are used to. The bigger portion of the object's surface you see at the same time, the stronger interaction you have with it. Well, maybe ... it's just a guess.

sciing
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Re: Protons and Special Relativity

Post by sciing » Sun Jun 17, 2012 11:32 am

Hi all,

I just wondering. An increase of the crossection (also the for elastic scattering) is something absolutely unexpected for me. If I take electrons and increase the energy the cross section gets smaller. Otherwise no one would do transmission elctron microscopy at higher energies like 300kV instead the 5-30kV used in scanning EM. So could someone explain the effect. Is it related that the proton is not just a "single particle" but consits of many quarks (BTW not only 3, but much more quark,- antiquark pairs)?

Sci

sciing
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Re: Protons and Special Relativity

Post by sciing » Sun Jun 17, 2012 11:54 am

According to this site, this effect could even not explained by the standard model, e.g. the QCD.
http://nohiggs.wordpress.com/2010/06/28 ... he-proton/

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