Jet and Di-Jet production in Photon-Photon collisions

During the past two years different analyses [1,2,3,4] of jet and di-jet production from real photons scattering at LEP have been presented. A unique computation it is available in the literature [5,6] at NLO for this process. This computation is based on the slicing method to cancel analytically virtual and infrared divergences. This technique relies on an approximate treatment of the phase space and of the matrix elements, which induces cancellations between large numbers. Hence in particular regions of the phase space it is possible that these cancellations are difficult to achieve numerically. To avoid this problem (it could be substantial for specific exclusive observables which have been measured [1]), it seems appropriate to use an exact technique to handle the infrared divergences. We use the subtraction method in the formulation of ref. [7,8]. This method treats exactly both the phase space and the matrix elements, thus ensuring a better behaved numerical result. We present a complete computation of jet and di-jet cross-sections and we compare our theoretical predictions with previous results and with experimental data.