modern physics question..

https://i46.tinypic.com/r9ha92.jpg

it looks like a coordinate

i dont know what is the meaning of this thing
?

Hard to say for sure, not knowing the problem or having read your text and its notation, but it looks like the energy and momemtum (magnitude) parts of the relativistic energy-momentum four-vector. It seems to be a calculation involving (decay of?) a pion (pi meson) and a muon (mu meson) and a neutrino.

Agreed with skyhawk.