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How to express particle momentum in [rad]

  1. Oct 7, 2013 #1
    Hi all,

    I need to use the output of a simulation code in another code who accepts totally different format for data.
    Now, the file I have has 5 column with positions and momenta of a certain number of particles (momenta are dimensionless - normalized to electron mass times c (light speed) )
    The other code wants momenta expressed in [rad] but I don't know how to convert them...
    COuld you help me?

    Thanks a lot
  2. jcsd
  3. Oct 8, 2013 #2


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    What is a momentum expressed in rad? Is that some angle of the flight direction?
    You'll have to check the documentation how that angle and other parameters are defined.
  4. Oct 9, 2013 #3
    Documentation is very poor.
    Anyway I think I have to evaluate it in this way:

    arcosin (ModulusP/py)
  5. Oct 9, 2013 #4


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    There's not enough information here to be sure, but rad might mean radians, which are used as units of rapidity. http://en.wikipedia.org/wiki/Rapidity

    Are you working with highly relativistic particles?
  6. Oct 9, 2013 #5

    Vanadium 50

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    This is not rapidity.

    cos-1(|p|/py) is already in rads/ That is, |p|/py is already dimensionless.
  7. Oct 10, 2013 #6
    Yes, I think this is the way.
    But now I have another problem: 3rd component of momenta is defined as Dp/pn (n = particle numeber).
    But it is not very clear in the documentation how Dp is defined.
    I think it is the average momentum - pn, but in this way I have an error message saying gamma < 1...

    This is making me crazy...
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