Radiative energy loss of high-energy quarks in finite-size nuclear matter and quark-gluon plasma

The induced gluon radiation of a high-energy quark in a finite-size QCD medium is studied. For a sufficiently energetic quark produced inside a medium we find the radiative energy loss Delta E-q proportional to L-2, where L is the distance traveled by quark in the medium. It has a weak dependence on the initial quark energy E-q. The L-2 dependence turns to L-1 as the quark energy decreases. Numerical calculations are pet-formed for a cold nuclear matter and a hot quark-gluon plasma. For a quark incident on a nucleus we predict Delta E-q approximate to 0.1 E-q(L/10 fm)(beta), with beta close to unity. (C) 1997 American Institute of Physics.