Speaker
Description
We compute the in-medium jet broadening $\langle p^2_\perp\rangle$ to leading order in energy in the opacity expansion. At leading order in $\alpha_s$ the elastic energy loss gives a jet broadening that grows with $\ln{E}$. The next-to-leading order in $\alpha_s$ result is a jet narrowing, due to destructive LPM interference effects, that grows with $\ln^2{E}$. We find that in the opacity expansion the jet broadening asymptotics are - unlike for the mean energy loss - extremely sensitive to the correct treatment of the finite kinematics of the problem; integrating over all emitted gluon transverse momenta leads to a prediction of jet broadening rather than narrowing. We compare the asymptotics from the opacity expansion to a recent twist-4 derivation of $\langle p^2_\perp\rangle$ and find a qualitative disagreement: the twist-4 derivation predicts a jet broadening while the opacity expansion method predicts a narrowing. Comparison with current jet measurements cannot distinguish between the broadening or narrowing predictions. We comment on the origin of the difference between the opacity expansion and twist-4 results.
| Submitted on behalf of a Collaboration? | No |
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