Baryon stopping at HERA: evidence for gluonic mechanism

Recent results from the H1 experiment [The H1 Collaboration, C. Adloff et al., Measurement of the Baryon-Antibaryon Asymmetry in Photoproduction at HERA, Submitted to the 29th Int. Conf. on High-Energy Phys. ICHEP98, Vancouver, Canada, July 1998. Abstract 556. http://ichep98.triumf.ca/private/convenors/body.asp?abstractID=556] have confirmed the existence of a substantial baryon asymmetry of the proton sea at small x with magnitude predicted in [B.Z. Kopeliovich, B. Povh, Z. Phys. C 75 (1997) 693]. This is strong support for the idea [B.Z. Kopeliovich, B.G. Zakharov, Z. Phys. C 43 (1989) 241] that baryon number can be transferred by gluons through a large rapidity interval without attenuation. In this paper we calculate the dependence of baryon asymmetry on associated multiplicity of produced hadrons which turns out to be very sensitive to the underlying dynamics. Comparison with data [The H1 Collaboration, C. Adloff et al., Measurement of the Baryon-Antibaryon Asymmetry in Photoproduction at HERA, Submitted to the 29th Int. Conf. on High-Energy Phys. ICHEP98, Vancouver, Canada, July 1998. Abstract 556. http://ichep98.triumf.ca/private/convenors/body.asp?abstractID=556] confirms the dominance of the gluonic mechanism of baryon number transfer and excludes any substantial contribution of valence quark exchange.