Measurement and QCD Analysis of Neutral and Charged Current Cross Sections at HERA

TL;DR

This work presents high-precision measurements of neutral- and charged-current deep inelastic scattering at HERA with the H1 detector, extending kinematic coverage to high y to determine the longitudinal structure function FL and the generalised function x tilde F3. A comprehensive NLO QCD analysis is performed to extract flavor-separated proton PDFs directly from H1 data, subsequently validated against BCDMS data. The results yield detailed up- and down-quark distributions at large x and provide a consistent description of F2, FL, and xF3 across four orders of magnitude in x and Q^2, confirming the Standard Model and offering precise inputs for LHC phenomenology. The study demonstrates the unification of electromagnetic and weak interactions in DIS and establishes a foundation for future, higher-luminosity measurements to further constrain parton dynamics and heavy-flavor contributions.

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. The data were taken in 1999 and 2000 at a centre-of-mass energy of \sqrt{s} = 319 GeV and correspond to an integrated luminosity of 65.2 pb^-1. The cross sections are measured in the range of four-momentum transfer squared Q^2 between 100 and 30000 GeV^2 and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e^+ p data and the earlier e^- p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function F_L at high Q^2 (110 - 700 GeV^2). A new measurement of the structure function x F_3 is obtained using the new e^+ p and previously published e^\pm p neutral current cross section data at high Q^2. These data together with H1 low Q^2 precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.

Figures (16)

• Figure 1: Mean values of (a) $P_{T,h}/P_{T,e}$ as a function of $P_{T,e}$ and (b) $y_{h}/y_{DA}$ as a function of $\gamma_{h}$ for neutral current data (solid points) and Monte Carlo (MC) simulation (open points) for $\gamma_h>15^{\circ}$ and $12{\rm\,GeV}<P_{T,h}<50{\rm\,GeV}$. The curves correspond to a $\pm 1\%$ variation around the simulation.
• Figure 2: Distributions of $E_e^{\prime}$ for (a) $Q^2>150{\rm\,GeV}^2$ and (b) $Q^2>5\,000{\rm\,GeV}^2$, (c) $\theta_e$ and (d) $E-P_z$ for $e^+p$ data (solid points) and Monte Carlo (MC) simulation (open histograms) in the nominal analysis. The shaded histograms show the simulated background (bg) contribution, dominated by photoproduction.
• Figure 3: Distributions of (a) $E_e^{\prime}$, (b) $\theta_e$ and (c) $E-P_z$ for $e^+p$ data (solid points), $e^-p$ data (open points) and Monte Carlo (MC) simulation (histograms) in the high-$y$ analysis after background subtraction (see text). In (c) the $E-P_z$ cut is not applied, but is indicated by the dashed vertical line. Shown in (d) is the energy distribution of wrongly charged lepton candidates in background events. In (d) the $e^+p$ data have been normalised to the luminosity of the $e^-p$ data set.
• Figure 4: Distributions of (a) $P_{T,h}$ and (b) $E_h-P_{z,h}$ for CC data (solid points) and Monte Carlo (MC) simulation (open histograms). The shaded histograms show the simulated background (bg) contribution, dominated by photoproduction.
• Figure 5: (a) The $Q^2$ dependence of the NC cross section ${\rm d}\sigma/{\rm d}Q^2$, shown for the new $e^+p$ (solid points) and previously published $94-97$$e^+p$ (open points) data. The error band and full curve represent the Standard Model expectations determined from the H1 PDF $2000$ fit at $\sqrt{s}= 319{\rm\,GeV}$ and $\sqrt{s}= 301{\rm\,GeV}$, respectively. (b) The ratios of the $94-97$ and $99-00$ data to their corresponding Standard Model expectations, where the normalisation shifts as determined from the fit are applied to the data (see table \ref{['tab:h1fit']}). The error band shows the Standard Model uncertainty for $\sqrt{s}= 319{\rm\,GeV}$ by adding in quadrature the experimental uncertainty as derived from the fit and the model uncertainty (see section \ref{['h1fit']}). In (a) and (b), the inner and outer error bars represent respectively the statistical and total errors. The luminosity uncertainty is not included in the error bars.