Infrared renormalons and power suppressed effects in e+e− jet events

Abstract

We study the effect of infrared renormalons upon shape variables that are commonly used to determine the strong coupling constant in e + e − annihilation into hadronic jets. We consider the model of QCD in the limit of large n f . We find a wide variety of different behaviours of shape variables with respect to power suppressed effects induced by infrared renormalons. In particular, we find that oblateness is affected by 1/ Q non-perturbative effects even away from the two jet region, and the energy-energy correlation is affected by 1/ Q non-perturbative effects for all values of the angle. On the contrary, variables like thrust, the c parameter, the heavy jet mass, and others, do not develop any I/ Q correction away from the two jet region at the leading n f level. We argue that 1/ Q corrections will eventually arise at subleading n f level, but that they could maintain an extra α s ( Q) suppression. We conjecture therefore that the leading power correction to shape variables will have in general the form as α S n ( Q)/ Q, and it may therefore be possible to classify shape variables according to the value of n.