ZEUS results on the measurement and phenomenology of $F_2$ at low $x$ and low $Q^2$

The ZEUS Collaboration J. Breitweg; et al

doi:doi:10.1007/s100529901084

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2019 Impact factor 4.389

Particles and Fields

Eur. Phys. J. C 7, 609-630
DOI 10.1007/s100529901084

ZEUS results on the measurement and phenomenology of F₂ at low x and low Q²

The ZEUS Collaboration

J. Breitweg - et al

Argonne National Laboratory, Argonne, IL, USA

Received: 7 September 1998 / Published online: 19 February 1999

Abstract
Measurements of the proton structure function F₂ for $0.6<Q^2<17 \mbox{\hspace{0.3em}\rm GeV}^2$ and $1.2\times 10^{-5} <x<1.9\times 10^{-3}$ from ZEUS 1995 shifted vertex data are presented. From ZEUS F₂ data the slopes $dF_2/d\ln Q^2$ at fixed x and $d\ln F_2/d\ln(1/x)$ for x<0.01 at fixed Q² are derived. For the latter, E665 data are also used. The transition region in Q² is explored using the simplest non-perturbative models and NLO QCD. The data at very low Q² $\leq 0.65\mbox{\hspace{0.3em}\rm GeV}^2$ are described successfully by a combination of generalised vector meson dominance and Regge theory. From a NLO QCD fit to ZEUS data the gluon density in the proton is extracted in the range $3\times 10^{-5}<x<0.7$ .Data from NMC and BCDMS constrain the fit at large x. Assuming the NLO QCD description to be valid down to $Q^2\sim 1\mbox{\hspace{0.3em}\rm GeV}^2$ ,it is found that the $q\bar{q}$ sea distribution is still rising at small x and the lowest Q² values whereas the gluon distribution is strongly suppressed.