Quark fragmentation and trigger side momentum distributions in high-p T processes

Abstract

It has been widely argued that the experimental evidence concerning the momentum accompanying highpT triggers is a grave problem for models which take the trigger hadron to be a quark fragment. It is claimed that the trigger hadron takes much too large a fraction (z c ) of the jet momentum for the trigger side jet to be a quark. The jet momentum is not directly measured, but deduced from the derivative of the momentum (p x ) accompanying the trigger with respect to the trigger transverse momentum-p T t . This argument is shown to be unsafe. Using both an approximate analytic approach to illustrate the physics and subsequently a full numerical computation it is proved that the deduction of the fractional momentum accompanying the trigger, 1/z c −1, fromdp x /dp T t is not correct. Further we show that models—specifically that of Feynman and Field—which do take the trigger to be a quark fragment are essentially in agreement with the data on trigger side momentum distributions. A surprising prediction of our analysis is thatp x should be approximately constant forp T t ≧6GeV/c.