Frixione isolation

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Frixione isolation[1] is a way of requiring prompt photons (i.e. not from fragmentation) in an infrared-safe way. Only such photons are accepted for which the total amount of hadronic (or partonic) transverse energy E_{T} in an angular cone of radius r is smaller than E_{T}^{\max }(r), defined as

E_{T}^{\max }(r) \equiv \epsilon_{\gamma} p_{T}^{\gamma}\left(\frac{1-\cos r}{1-\cos R}\right)^{n},

where p_{T}^{\gamma} is the photon transverse momentum. The isolation criterion E_{T}<E_{T}^{\max }(r) has to be fulfilled for all cones with r \leq R. Example values are \epsilon_{\gamma}=0.5, n=1 and R=0.4.


  1. Stefano Frixione: Isolated photons in perturbative QCD, Phys.Lett.B 429 (1998) 369-374, (inSPIRE:466689)