# Are there any regulating condition on the spin of particle?

ndung200790
Are there any regulating limit on spin of particle?.E.g why spin of electron is 1/2 but not 3/2,spin of photon is 1 but not 2 e.t.c
Thank you very much in advance.

gluefish
Currently, what is assumed is that an electron's spin is an intrinsic property. That it originates from the angular momentum of the particle.

In quantum mechanics, angular momentum is quantized (meaning that it is not only comprised of energy but also of particles). Since physical particles are enabling this spin to occur, there should be a countable, finite number of them. Perhaps that explains why the numbers are finite ratios of integers, and not weird repeating decimals.

I cannot answer WHY every particle has some intrinsic angular momentum (probably due to the conditions under which it was formed).

One of the "regulating conditions" you ask about is most likely the quantization of angular momentum. Generally when you think of angular momentum, you think of some kind of energetic value, not chunks of matter that are rotating the object in question around.
If you want to know why angular momentum is quantized, you can refer to this thread: https://www.physicsforums.com/showthread.php?t=194897

This is a good source to read further: http://www.electronspin.org/
Also, this Wikipedia page explains how in relatively simple terms (but not why): http://en.wikipedia.org/wiki/Spin_(physics [Broken])

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ndung200790
So,are there any relations between symmetry(e.g Lorentz symmetry) and quantization of energy(because we think of angular momentum as some kind of energy)?

ndung200790
Are there any general transformation of spinor(or field operator of high spin particles) under Lorentz symmetry?