Single particle spectra in deep inelastic scattering as a probe of small x dynamics

We study the transverse momentum () spectrum of charged particles produced in deep inelastic scattering (DIS) at small Bjorken x in the central region between the current jet and the proton remnants. We calculate the spectrum at large with the BFKL ln (1/x) resummation included and then repeat the calculation with it omitted. We find that data favour the former. We normalize our BFKL predictions by comparing with HERA data for DIS containing a forward jet. The shape of the x distribution of DIS + jet data is also well described by BFKL dynamics. Received: 4 May 1998 / Published online: 21 August 1998