Studies of final states in small x deep inelastic scattering

Abstract

We investigate the possibility of identifying In(l/x) dynamics from studies of the final state in electron - proton deep inelastic scattering (DIS) in the small x region of the HERA collider at DESY. Motivated by recent observations at HERA we consider again the measurement of DIS events containing an identified forward jet as proposed by Mueller. We find that the shape of the x distribution of the data is described well by a prediction based on In(l/x) dynamics. Since forward jets are difficult to identify and measure accurately in the experiments we suggest the study of deep inelastic events containing an energetic isolated photon. We quantify the enhancement arising from the leading In(l/x) gluon emissions with a view to using such events to identify the underlying dynamics in the small x regime at HERA. To overcome the small event rate of jet + γ we propose that the forward jet may alternatively be identified through a single energetic decay product, the π . We investigate the feasibility of utilizing these deep inelastic + forward π events as an indicator of the small x dynamics. Motivated by this study the HI collaboration recently performed a DIS + π measurement. Therefore we update our BFKL prediction imposing the HI cuts in the calculation. We fix the normalisation by comparing with HERA data for DIS + jet. Finally we study the transverse momentum (pr) spectrum of charged particles produced in DIS at small Bjorken x in the central region between the current jet and the proton remnants. Again we normalize the BFKL prediction by comparing with the H1 DIS + jet data. We calculate the spectrum at large pr with the BFKL ln(l/x) resummation included and then repeat the calculation with it omitted. We find that data favour the former.