Measurement of Neutral and Charged Current Cross Sections in Electron-Proton Collisions at High Q^2

TL;DR

This paper reports high-$Q^2$ measurements of neutral- and charged-current cross sections in electron-proton DIS using the H1 detector at HERA, spanning $Q^2$ from 150 to 30,000 GeV^2 and $x$ from 0.002 to 0.65. The analysis employs $e^-$p data from 1998–1999 at $\sqrt{s}\approx320$ GeV with 16.4 pb$^{-1}$, comparing to $e^+$p data to observe the NC asymmetry driven by $Z^0$ exchange and to extract the generalized structure function $x\tilde{F}_3$, including the first high-$Q^2$ measurement of $x\tilde{F}_3$ and the derived $xF_3^{\gamma Z}$. The charged-current sector yields a precise determination of the $W$ propagator mass, $M_W = 79.9$ GeV with competitive uncertainties, and the results are in good agreement with the Standard Model, supporting its universality in deep inelastic scattering. The work provides stringent tests of PDFs (via the H1 97 fit) and sets constraints on EW effects at high $Q^2$, with implications for valence-quark structure and photon–Z interference.

Abstract

The inclusive e^-p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA, in the range of four-momentum transfer squared Q^2 between 150 and 30000 GeV^2, and Bjorken x between 0.002 and 0.65. The data were taken in 1998 and 1999 with a centre-of-mass energy of 320 GeV and correspond to an integrated luminosity of 16.4 pb^(-1). The data are compared with recent measurements of the inclusive neutral and charged current e^+p cross sections. For Q^2>1000 GeV^2 clear evidence is observed for an asymmetry between e^+p and e^-p neutral current scattering and the generalised structure function xF_3 is extracted for the first time at HERA. A fit to the charged current data is used to extract a value for the W boson propagator mass. The data are found to be in good agreement with Standard Model predictions.

Figures (10)

• Figure 1: Distributions of (a) $E_e^{\prime} {\rm~for}~Q^2 > 150 \rm~GeV^2$, (b) $E_e^{\prime} {\rm~for}~Q^2 > 1\,000 \rm~GeV^2$ and (c) $\theta_e$ for NC data (solid points) and simulation (solid line). The filled histograms show the photoproduction contribution.
• Figure 2: Distributions of (a) $P_{T,h}$ and (b) $y_h$ for CC data (solid points) and simulation (solid line). The filled histograms show the photoproduction contribution.
• Figure 3: The NC cross sections ${\rm d} \sigma_{\rm NC}/{\rm d} x$ for the $e^-p$ data are shown in (a) for $Q^2>1\,000$${\rm GeV}^2$ and in (c) for $Q^2>10\,000$${\rm GeV}^2$. The H1 $e^+p$ cross sections h1hiq2 are shown in (b) and (d) for $Q^2>1\,000$${\rm GeV}^2$ and $10\,000$${\rm GeV}^2$ respectively. In addition the ZEUS $e^+p$ data zeushiq2 are shown for $Q^2>10\,000$${\rm GeV}^2$. The solid curves show the Standard Model expectation based on the H1 97 PDF Fit. The dashed curves show the contribution of photon exchange only. All cross sections are shown for $y<0.9$. The inner error bars represent the statistical error, and the outer error bars show the total error. The normalisation uncertainties are not included in the error bars.
• Figure 4: The CC cross section ${\rm d} \sigma_{\rm CC}/{\rm d} x$ for $Q^2>1\,000$${\rm GeV}^2$ and $y<0.9$ is shown for the H1 $e^-p$ data (solid points) and the H1 $e^+p$ data h1hiq2(open points). The solid curves show the Standard Model expectation based on the H1 97 PDF Fit. The dashed curve shows the $e^+p$ cross section for an increased centre-of-mass energy. The inner error bars represent the statistical error, and the outer error bars show the total error. The normalisation uncertainties are not included in the error bars.
• Figure 5: The $Q^2$ dependence of the NC cross section ${\rm d} \sigma_{\rm NC}/{\rm d} Q^2$ is shown for the H1 $e^-p$ data (solid points) and $e^+p$ measurements (open points) from H1 h1hiq2 and ZEUS zeushiq2. The data are compared with the Standard Model expectation determined from the H1 97 PDF Fit including the H1 $e^+p$ data. The dashed curve shows the influence of an increased centre-of-mass energy on the $e^+p$ cross section. The ratio of the $e^-p$ data to the Standard Model expectation is shown in the lower figure. The Standard Model uncertainty is shown as the shaded band. The inner error bars represent the statistical error, and the outer error bars show the total error. The normalisation uncertainties are not included in the error bars.