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How do we know that the process of accelerating a particle in a circle at a circular collider (such as the LHC) doesn't create particle spin?

If it does, then how do we know that a particle's scattering and behavior doesn't change when it is accelerated without circular methods?

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    $\begingroup$ I think you are conflating spin the quantum property with spin in the sense of circular macroscopic motion. They aren't the same thing. $\endgroup$
    – paisanco
    Commented Oct 18, 2016 at 2:57
  • $\begingroup$ Yes I know they arent, i was wondering have they proven that the accelerators don't give the particles spin $\endgroup$ Commented Oct 18, 2016 at 3:17
  • $\begingroup$ By spin you mean intrinsic angular momentum? as opposed to e.g. orbital angular momentum? or do you mean any form of angular momentum? $\endgroup$
    – innisfree
    Commented Oct 18, 2016 at 3:29
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    $\begingroup$ Spin really means intrinsic angular momentum, but I'm struggling to understand your question, so wondering if you mean any kind of angular momentum. $\endgroup$
    – innisfree
    Commented Oct 18, 2016 at 3:29
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    $\begingroup$ One could always look for differences in scattering between SLAC (a linear accelerator) and other facilities. (None have been seen). $\endgroup$
    – Jon Custer
    Commented Oct 18, 2016 at 13:52

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Particles in linear accelerators have the same intrinsic spin as the same particles in ring accelerators. (The same is true for those particles when they're in bound systems, for what it's worth. The discovery of the spins of the proton, neutron, and electron were based on statistical arguments. But that's something to discuss in another question.)

An interesting facility where spin physics plays an important role is the Continuous Electron Beam Accelerator Facility at Jefferson Lab:

How CEBAF Works
[n.b. this image doesn't show the new hall]

One of CEBAF's strengths is that it can produce strongly polarized beams, and this polarization is produced, and can be measured, entirely in the injector: a pure linear accelerator about thirty meters long. Oscillating magnetic fields in the injector can be used to re-orient the electron spin so that electron's north poles point in essentially any direction when the enter the main accelerator.

The electron's spin is related to its magnetic moment, and its direction precesses in a magnetic field, like the bending magnets in the arcs that connect the two linear accelerators. This means that the orientation of the spin of the electron beams that enter experimental halls is different from the orientation of the spin at the injector, and is different for a beam that's gone around the accelerator once versus for beams that have gone once or more through the recirculation arcs. This is something that the accelerator engineers have to compute for each configuration of beams to the experimental halls. After the calculations are done, the spins are measured at the experimental halls as well; the behavior of the entire system is quite well-understood.

The LHC, unlike CEBAF, is a storage ring where the particle acceleration happens elsewhere. Another storage ring, where the evolution of the particle spin is well-tracked and essentially independent of the particles' linear momentum, is the muon $g-2$ ("gee minus two") experiment. In the results paper from the previous iteration of the $g-2$ experiment, the second figure shows that the muon spin precesses about 130 times over about a half-millisecond --- much, much slower than time for muons to orbit the ring, about 150 ns.

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  • $\begingroup$ 1. Does the increased mass from its speed amplify its fundamental forces? $\endgroup$ Commented Oct 19, 2016 at 1:19
  • $\begingroup$ 2. Is it possible that its behavior might only be straightened out in wave phase, but not absolute? $\endgroup$ Commented Oct 19, 2016 at 1:20
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    $\begingroup$ @JGQuestions 1. The behavior of intrinsic spin is well-described for particle energies ranging from ultra-cold neutrons (50 nano-eV) to LHC energies (tera-eV). 2. I don't understand this question. $\endgroup$
    – rob
    Commented Oct 19, 2016 at 1:51
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In particle physics, which is very well modeled by the standard model, spin is an intrinsic property of the elementary particles which are at the foundations of the standard model .

elempart

Note that this finite number of particles have a lot of quantum numbers which are conserved , like charge for example. Spin comes in angular momentum units and is conserved in all interactions in combinations of angular momentum.

These attributes and the standard model itself are an encapsulation of a large number of measurements/data, not guesses, and the model is predictive and has not been falsified up to now by any higher energy experiments. The particles in the table cannot acquire a spin different than what we have measured and classified . It is an observational fact.

Now if you are asking whether the electrons and positrons at LEP acquire an angular momentum and whether this makes any difference with interactions that happened in linear colliders, the answer is that the collisions in circular colliders are done is straight sections, head on, by design, so that only the linear momenta enter the collisions , and of course the intrinsic spins.

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  • $\begingroup$ The spin quantum number $s$ is fixed, but the spin measured along a given axis could take one of many permitted values $-s$ to $s$ in integer steps... $\endgroup$
    – innisfree
    Commented Oct 18, 2016 at 7:06
  • $\begingroup$ @innisfree when you say "spin" you are using the classical definition synonymous with angular momentum? $\endgroup$
    – anna v
    Commented Oct 18, 2016 at 11:14
  • $\begingroup$ no, spin quantum number $s $... $\endgroup$
    – innisfree
    Commented Oct 18, 2016 at 11:15
  • $\begingroup$ @innisfree all angular momentum in a quantized setting is in units of h_bar en.wikipedia.org/wiki/Angular_momentum#Quantization . It is J that is the vector sum of angular momentum and spin. A rotating in LEP electron will have an angular momentum added to its spin except that the experiments are not interested in that, and design straight sections for the collisions . $\endgroup$
    – anna v
    Commented Oct 18, 2016 at 11:46
  • $\begingroup$ I really mean that since the study of them always has them travelling so rapidly in circular direction that maybe it affects certain aspects of its behavior as it is smashed and studied $\endgroup$ Commented Oct 18, 2016 at 13:52

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