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Energy and momentum units in particle physics

Learn about the use of "GeV-type" units rather than SI in particle physics, how to measure mass using E^2 = p^2c^2 + m^2c^4, and what highly relativistic particles are.

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Energy and momentum units in particle physics

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  1. Energy and momentum units in particle physics CERN HST2014 Gron Tudor Jones UNIVERSITY OF BIRMINGHAM

  2. Use of ‘GeV-type’ units rather than SI in Particle Physics In ordinary Newtonian physics, given the kinetic energy Ek of a particle (4 Joules, say) and its momentump (4 kg m/s), one can calculate m = p2/2Ek = 2 kg In highly relativistic collisions at the LHC, the total energy E of a particle is measured by detectors quaintly called ‘calorimeters’, and the momentum pby determining the curvature of charged tracks moving in a magnetic field. Then, using E2 = p2c2 + m2c4, we can calculate the mass m:

  3. Given Ein Joules, p in kg m/s, and c= 3 x 108 m/s, this yields m in kg. However:

  4. For the units in each term of E2 = p2c2 +m2c4 to be the same, p must be in GeV/c and m must be in GeV/c2. Then E2(in GeV2) = p2(in GeV2/c2) c2+ m2 (in GeV2/c4) c4 Physicists ‘simplify’ this by writing it as E2(in GeV2) = p2 (in GeV2) + m2 (in GeV2) So when you see E2 = p2 + m2 think of Particle physicists measure energies in GeV, where 1 GeV = 109 eV = energy gained by an electron or proton accelerated through 109 volts. How does one use E2 = p2c2 + m2c4 to measure mass using particle physicists’ units?

  5. What is a highly relativistic particle? E2 = p2c2 + m2c4 p2c2 >> m2c4 E ~ pc * Examples/discussion

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