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\title{QCD Evolution of Jets in the Quark-Gluon Plasma}

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\author{S. Domdey}
\email[]{Domdey@tphys.uni-heidelberg.de} \affiliation{Institut
f\"ur Theoretische Physik, Universit\"at Heidelberg, Germany}

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Based on our recent paper \cite{DPZSIR} I briefly discuss the
effect of scattering for jet quenching of gluonic fragmentation
functions in the quark-gluon plasma. In contrast to the common
discussion \cite{BDPMS} which treats medium-induced gluon emission
as the main mechanism, we find that energy loss from scattering
will also contribute significantly.

The basic idea given in the talk is as follows: The DGLAP equation
is build from the probability for splitting due to change of
virtuality. The time scale for this process is
$\tau_{split}=E/Q^2$. We extend this equation to contain also
scatterings with gluons from the medium by constructing a
``scattering probability'' from the ratio of the time scale for
splitting and the scattering mean free path $\tau_{scat}=1/(\sigma
n_g)$, i.e. the number of scatterings which can happen between two
splittings. Similar to splitting the medium-modified evolution
equation contains a gain and a loss term.

We discuss two slightly different approaches: One is more suitable
for analytical calculations, the other one for implementation in a
Monte Carlo study. Both methods give very similar results.

Even with a perturbative cross section, we find a suppression of
the fragmentation function in medium relative to vacuum which is
increasing with energy fraction $x$. For $Q=100$ GeV and a plasma
temperature of $T=500$ MeV (which may be relevant for LHC) we find
a suppression of 10\% at $x\simeq 0.1$, but a suppression of
factor 2 and more for large $x$. For RHIC conditions, this
suppression is more moderate.

\begin{thebibliography}{9}
%\bibitem
\bibitem{DPZSIR}
S.~Domdey, G.~Ingelman, H.J.~Pirner, J.~Rathsman, K.~Zapp,
J.~Stachel, to be published [arXiv: hep-ph/08023282]

\bibitem{BDPMS} U.A. Wiedemann, Nucl. Phys. B 588 (2000), p. 303\\
C.A. Salgado and U.A. Wiedemann, Phys. Rev. D 68 (2003), p.
014008\\
  %M.~Gyulassy, I.~Vitev, X.~N.~Wang and B.~W.~Zhang,
  %``Jet quenching and radiative energy loss in dense nuclear matter,''
  arXiv:nucl-th/0302077.
\end{thebibliography}
\end{document}
