In the laboratory frame

PHYSICS · Multi-part · Fermi University Physics · Relativity & Gravitation · Relativistic dynamics and fields in flat spacetime · Relativistic dynamics and fields in flat spacetime

Relativity and Gravitation, Ch Relativistic momentum, energy and collisions

Problem

In the laboratory frame, one photon of energy

700\ \mathrm{keV}

travels along the

+x

axis and a second photon of energy

300\ \mathrm{keV}

travels along the

-x

axis. A photon is massless, so its momentum has magnitude

E/c

. ((a)) Find the invariant mass of this two-photon system, in

\mathrm{keV}/c^2

. ((b)) Find the invariant mass of the same two photons if instead both travel along the

+x

axis with the same energies. ((c)) A particle whose mass equals the answer to (a) sits at rest and decays into two photons. Find the energy of each photon in the frame in which that particle is at rest.

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