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Measurement of the F2 structure function in deep inelastic scattering using 1994 data from the ZEUS detector at HERA

ZEUS Collaboration

TL;DR

This paper reports a high-precision measurement of the proton F2 structure function from 1994 ZEUS data in neutral-current deep inelastic e+p scattering, extending the kinematic reach via a novel PT kinematic reconstruction. By combining electron and hadronic information with data-driven energy calibrations and MC-guided corrections, the analysis achieves sub-5% systematics across much of the (x,Q^2) plane and reveals a pronounced rise of F2 at small x, with clear scaling violations described by NLO DGLAP evolution. The results, consistent with contemporary PDF parameterizations and with H1, solidify the applicability of perturbative QCD to a broad DIS range and provide stringent input for global parton-density fits. The methodology, including robust MC reweighting and the PT reconstruction, offers a template for precision structure-function extractions in complex detector environments.

Abstract

We present measurements of the structure function \Ft\ in $e^+p$ scattering at HERA in the range $3.5\;\Gevsq < \qsd < 5000\;\Gevsq$. A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At $ \qsd < 35 \;\Gevsq$ the range in $x$ now spans $6.3\cdot 10^{-5} < x < 0.08$ providing overlap with measurements from fixed target experiments. At values of $Q^2$ above 1000 GeV$^2$ the $x$ range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic region. The structure function rises as \x\ decreases; the rise becomes more pronounced as \qsd\ increases. The behaviour of the structure function data is well described by next-to-leading order perturbative QCD as implemented in the DGLAP evolution equations.

Measurement of the F2 structure function in deep inelastic scattering using 1994 data from the ZEUS detector at HERA

TL;DR

This paper reports a high-precision measurement of the proton F2 structure function from 1994 ZEUS data in neutral-current deep inelastic e+p scattering, extending the kinematic reach via a novel PT kinematic reconstruction. By combining electron and hadronic information with data-driven energy calibrations and MC-guided corrections, the analysis achieves sub-5% systematics across much of the (x,Q^2) plane and reveals a pronounced rise of F2 at small x, with clear scaling violations described by NLO DGLAP evolution. The results, consistent with contemporary PDF parameterizations and with H1, solidify the applicability of perturbative QCD to a broad DIS range and provide stringent input for global parton-density fits. The methodology, including robust MC reweighting and the PT reconstruction, offers a template for precision structure-function extractions in complex detector environments.

Abstract

We present measurements of the structure function \Ft\ in scattering at HERA in the range . A new reconstruction method has allowed a significant improvement in the resolution of the kinematic variables and an extension of the kinematic region covered by the experiment. At the range in now spans providing overlap with measurements from fixed target experiments. At values of above 1000 GeV the range extends to 0.5. Systematic errors below 5\perc\ have been achieved for most of the kinematic region. The structure function rises as \x\ decreases; the rise becomes more pronounced as \qsd\ increases. The behaviour of the structure function data is well described by next-to-leading order perturbative QCD as implemented in the DGLAP evolution equations.

Paper Structure

This paper contains 23 sections, 16 equations, 18 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Experimental conditions
  3. Triggering
  4. Monte Carlo simulation
  5. Energy and angle measurements
  6. Positron identification and efficiency
  7. Positron angle measurement
  8. Positron energy determination
  9. Hadronic energy determination
  10. Kinematic reconstruction
  11. Characteristics of standard reconstruction methods
  12. PT method
  13. The measurement of $y$ at low $y$
  14. Kinematic measurement in the full $y$ range
  15. Event selection
  16. ...and 8 more sections

Figures (18)

  • Figure 1: Distance (in cm) between track and RCAL position a) in X, b) and Y. Distance (in cm) between track and SRTD position c) in X, d) and Y. e) Vertex reconstruction efficiency as a function of $\hbox{$\gamma_{_{H}}$}$ (points: data; histogram: MC). f) Vertex resolution along the beam (in cm) as a function of $\hbox{$\gamma_{_{H}}$}$.
  • Figure 2: The ratio $\hbox{$\frac{y_{_{JB}}}{y_{gen}}$}$ averaged over $p_{Th}$ as a function of $\hbox{$\frac{p_{Th}}{p_{Te}}$}$ for several ranges of $\hbox{$\gamma_{_{H}}$}$. The curves show the correction function ${\cal C}(\hbox{$\frac{p_{Th}}{p_{Te}}$} ,p_{Th} ,\hbox{$\gamma_{_{H}}$})$, averaged over $p_{Th}$ as a function of $\frac{p_{Th}}{p_{Te}}$ for several ranges in $\hbox{$\gamma_{_{H}}$}$.
  • Figure 3: a) The distributions of $\hbox{$\frac{y_{_{JB}}}{y_{gen}}$}$ (dashed-dotted), $\hbox{$\frac{y_{(1)}}{y_{gen}}$}$ (dashed), $\hbox{$\frac{y_{(2)}}{y_{gen}}$}$ (dotted) and $\hbox{$\frac{y_{_{PT}}}{y_{gen}}$}$ (solid) for several ranges in $\gamma_{_{H}}$ as determined from the MC simulation. b) The distributions of $\hbox{$\frac{y_{e}}{y_{gen}}$}$ (dotted), $\hbox{$\frac{y_{_{DA}}}{y_{gen}}$}$ (dashed) and $\hbox{$\frac{y_{_{PT}}}{y_{gen}}$}$ (solid) for several ranges in $\gamma_{_{H}}$ as obtained from the MC simulation. c) The corresponding distributions of $\hbox{$\frac{Q^2_{PT}}{Q^2_{gen}}$}$ (solid), $\hbox{$\frac{Q^2_{DA}}{Q^2_{gen}}$}$ (dashed), $\hbox{$\frac{Q^2_{e}}{Q^2_{gen}}$}$ (dotted) and $\hbox{$\frac{Q^2_{(2)}}{Q^2_{gen}}$}$ (dashed-dotted).
  • Figure 4: The distributions of $\hbox{$\frac{y_{_{PT}}}{y_{gen}}$}$ for a) $140^\circ< \hbox{$\gamma_{_{H}}$} < 160^\circ$ and b) $160^\circ< \hbox{$\gamma_{_{H}}$} < 180^\circ$. The points show the data and the shaded histograms show the results from the MC simulation.
  • Figure 5: Distributions of a) positron energy, b) positron angle, c) $Z_{vertex}$, d)--f) $\frac{p_{Th}}{p_{Te}}$ for different ranges of $\gamma_{_{H}}$ . The vertical lines in c)--f) indicate the positions of the cuts used in the analysis. For d)-f) the cut values are shown for the central value of $\hbox{$\gamma_{_{H}}$}$ in each bin (see text). The MC distributions are normalised to the integrated luminosity of the data.
  • ...and 13 more figures