The ME-PS matching problem ­ Matrix Element calculations: ✓ Describe well separated jets configurations ✓ Are exact at a given order ✕ Run into troubles in the soft and collinear regions ✕ Can't describe the internal structure of jets - Parton Shower calculations: ✓ PS is universal, given the basic hard process the PS recipe will produce reasonable parton configurations ✓ The use of Sudakov form factors ensures controlled behavior in the soft and collinear region, so jet evolution is well described ✕ Cannot steer the shower evolution too much, some regions of the phase space are not efficiently filled, e.g.
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