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Event Shapes

In this section we study general event shape variables: sphericity, thrust, Fox-Wolfram moments, and jet masses. These measures are implemented in the routines PYSPHE, PYTHRU, PYFOWO and PYJMAS, respectively. While possible to calculate for any event, their largest use is in $\mathrm{e}^+\mathrm{e}^-\to \gamma^* / \mathrm{Z}^0\to \mathrm{q}\overline{\mathrm{q}}$ annihilation events, where the (unknown) $\mathrm{q}\overline{\mathrm{q}}$ axis largely regulates the particle flow.

Each event is assumed characterized by the particle four-momentum vectors $p_i = (\mathbf{p}_i, E_i)$, with $i = 1, 2, \cdots , n$ an index running over the particles of the event.


Stephen Mrenna 2007-10-30