Measurement of the neutral current cross section and F2 structure function for deep inelastic e+p scattering at HERA

TL;DR

The ZEUS Collaboration presents a high-precision measurement of the neutral current e+p cross section and the electromagnetic structure function F2^{em} over a wide kinematic range, using 1996–1997 HERA data. By leveraging a large dataset and refined detector understanding, the analysis delivers significantly reduced statistical and systematic uncertainties and demonstrates scaling violations predicted by NLO QCD through DGLAP evolution. An inclusive NLO QCD fit, incorporating world data, yields an excellent description of the measurements and reinforces the reliability of proton PDFs in the explored x–Q^2 domain. The results provide stringent tests of perturbative QCD and contribute valuable constraints to parton distributions in the proton.

Abstract

The cross section and the proton structure function F2 for neutral current deep inelastic e+p scattering have been measured with the ZEUS detector at HERA using an integrated luminosity of 30 pb-1. The data were collected in 1996 and 1997 at a centre-of-mass energy of 300 GeV. They cover the kinematic range 2.7 < Q^2 < 30000 GeV2 and 6.10^-5 < x < 0.65. The variation of F2 with x and Q2 is well described by next-to-leading-order perturbative QCD as implemented in the DGLAP evolution equations.

Figures (14)

• Figure 1: Schematic view of the ZEUS detector showing those components important for this analysis.
• Figure 2: Vertex finding efficiency as a function of the hadronic angle $\hbox{$\gamma_{\textrm{PT}}$}$, defined in Eq. (\ref{['eq:gammapt']}).
• Figure 3: a) The purity. b) The acceptance. The analysis binning is shown, together with the limits of the ZEUS acceptance. At the edges of the kinematic plane, the acceptance is lower due to the various selection criteria. The rear beamhole limits the acceptance of events with small angles of the scattered positron to $Q^2\gtrsim 2$ GeV$^2$. For $y\gtrsim 0.7$, the positron energy cut and for $Q^2\gtrsim 1000$ GeV$^2$ and $y=1$ the kinematic limit of HERA constrains the measurements. The forward beamhole limits the acceptance to $y\gtrsim 0.004$ for events with small angles of the hadronic system; this limit is shown by the line $W=20$ GeV.
• Figure 4: a) Distribution of $\delta$, see Eq. (\ref{['eq:delta']}), for the low-$Q^2$ sample (filled circles), for that subset of the data tagged by the positron tagger (stars) and for these tagged data corrected for the acceptance of the positron tagger (open circles). The lines show MC distributions after reweighting as discussed in the text. b) The photoproduction MC (PHP) and the scaled tagged data are shown on a linear scale. The shaded area shows the uncertainty assigned to the photoproduction background, see Section \ref{['SYSUNC']}.
• Figure 5: Distributions of measured quantities, as discussed in the text, are shown for the low-$Q^2$ sample and the high-$Q^2$ sample. The MC histograms are based on the NLO QCD fit to the data and are normalised according to the luminosity. The diffractive component and the photoproduction background contributions are separately shown. The inserts show details of the corresponding distributions.