1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Tau lepton decay problem - weird answer?

  1. Nov 23, 2009 #1
    I've got a tauon weak-decaying into a charged pion and a neutrino. The tauon has total energy [tex]\ E_{\tau} = 2.5GeV[/tex], rest mass [tex]\ m_{\tau} = 1.777GeV/c^2[/tex], and the pion has rest mass [tex]\ m_{\pi} = 0.1396GeV/c^2[/tex].
    This is everything I am told.
    I have to find the maximum energy the pion can have after the decay.

    So, what I said was that the pion will get the most energy by retaining all of the tauon's momentum, ie.

    [tex]\ p_{\tau} = \sqrt{E_{\tau}^2 - m_{\tau}^2} = p_{\pi} = 1.758GeV/c[/tex]

    and so [tex]\ E_{\pi} = \sqrt{p_{\pi}^2 + m_{\pi}^2} [/tex]

    This gives me the result that [tex]\ E_{\pi} = 1.764GeV [/tex].
    However, the neutrino that is also produced has a tiny mass and I have assumed it to have zero momentum, so where has most of the 2.5GeV tauon energy gone?

    I had 2.5GeV before the decay, but now I have not much more than 1.764GeV after the decay, so where has the rest of this energy magically disappeared to?

  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted