Measurement and Phenomenology of the Proton Structure Function $F_2$ from ZEUS at HERA

Abstract

Measurements of the proton structure function $F_2$ in the $Q^2$ range $0.6-17\mathrm{Ge}{\mathrm{V}}^2$ from ZEUS 1995 shifted vertex data and $Q^2\simeq 1.5-20000\mathrm{Ge}{\mathrm{V}}^2$ from 1996 and 1997 ZEUS data are presented. From the former and other ZEUS $F_2$ data the slopes $d{F}_2/d\ln Q^2$ at fixed $x$ and $d{F}_2/d\ln (1/x)$ at fixed $Q^2$ are derived. $F_2$ data at $Q^2$ below $0.9\mathrm{Ge}{\mathrm{V}}^2$ are described successfully by a combination of generalised vector meson dominance and Regge theory. Using a NLO QCD fit the gluon density in the proton is extracted in the range $3\times 10^{-5}<x<0.7$ from ZEUS 1994 and 1995 data. For $Q^2\sim 1\mathrm{Ge}{\mathrm{V}}^2$ it is found that the $q\bar{q}$ sea distribution is still rising at small $x$ whereas the gluon distribution id strongly suppressed. It is shown that these observations may be understood from the behaviour of the $F_2$ and $d{F}_2/d\ln Q^2$ data themselves.

Comments: 5 pages, 9 figures, to appear in the proceedings of the 29th International Conference on High Energy Physics (ICHEP'98), Vancouver, Canada, 1998