Measurement of high-Q2 charged current cross sections in e-p deep inelastic scattering at HERA

TL;DR

This study measures high-Q^2 charged-current deep inelastic scattering in e−p collisions at HERA with the ZEUS detector, using Jacquet-Blondel kinematic reconstruction to obtain single- and double-differential cross sections. The results are compared to Standard Model predictions based on the ZEUS NLO QCD fit and various PDFs, showing good agreement and enabling a space-like W-boson mass determination. From the Q^2 dependence of the cross section, the analysis yields M_W = 80.3 ± 2.1 (stat) ± 1.2 (syst) ± 1.0 (PDF) GeV, consistent with time-like measurements and with reduced PDF-induced uncertainties due to u-quark dominance in e−p CC DIS. The work also explores the helicity structure via reduced cross sections and confirms the SM chiral structure in the space-like regime, strengthening the understanding of electroweak interactions in the proton.

Abstract

Cross sections for e-p charged current deep inelastic scattering have been measured at a centre-of-mass energy of 318 GeV with an integrated luminosity of 16.4 pb-1 using the ZEUS detector at HERA. Differential cross-sections dσ/dQ2, dσ/dx and dσ/dy are presented for Q2>200 GeV2. In addition, d2σ/dxdQ2 was measured in the kinematic range 280 GeV2 < Q2 < 30000 GeV2 and 0.015 < x < 0.42. The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson, determined from a fit to dσ/dQ2, is MW=80.3 \pm 2.1 (stat.) \pm 1.2 (syst.) \pm 1.0 (PDF) GeV.

Figures (5)

• Figure 1: Comparison of the final $e^- p$ CC data sample (solid points) with the expectations of the sum of the signal and $ep$ background Monte Carlo simulations (light shaded histogram). The $ep$ background Monte Carlo is shown as the dark shaded histogram. (a) the missing transverse momentum, $P_{T,{\rm miss}}$, (b) $P_{T,{\rm miss}}$ excluding the very forward cells, $P_{T,{\rm miss}}'$, (c) the variable $\delta$, defined in the text, (d) the ratio of missing transverse momentum to total transverse energy, $P_{T,{\rm miss}}/E_T$, (e) $\gamma_h$, (f) the number of good tracks, (g) the $Z$ position of the CTD vertex for the high-$\gamma_0$ sample and (h) the $Z$ position of the timing vertex for the low-$\gamma_0$ sample.
• Figure 2: The $e^-p$ CC DIS cross-sections (a) $d\sigma/dQ^2$, (b) $d\sigma/dx$ and (c) $d\sigma/dy$ for data (solid points) and the SM expectation evaluated using the ZEUS NLO QCD fit, CTEQ5D and MRST(99) PDFs. The insets show the ratios of the measured cross sections to the SM expectations evaluated using the ZEUS NLO QCD fit. The statistical errors are indicated by the inner error bars (delimited by horizontal lines), while the full error bars show the total uncertainty obtained by adding the statistical and systematic contributions in quadrature. The shaded band shows the uncertainties associated with the PDFs estimated using the ZEUS NLO QCD fit.
• Figure 3: The reduced cross section, $\tilde{\sigma}$, as a function of $Q^2$, for different fixed values of $x$. The points represent the data, while the expectation of the Standard Model evaluated using the ZEUS NLO QCD fit is shown as a line.
• Figure 4: The reduced cross section, $\tilde{\sigma}$, as a function of $x$, for different values of $Q^2$. The points represent the data, while the expectation of the Standard Model evaluated using the ZEUS NLO QCD fit is shown as a solid line. The separate contributions of the PDF combinations $x (u+c)$ and $(1-y)^2 x (\bar{d}+\bar{s})$ are shown by the dashed and dotted lines, respectively.
• Figure 5: The reduced cross section, $\tilde{\sigma}$, as a function of $(1-y)^2$, for different fixed values of $x$, for $e^- p$ (solid points) and $e^+ p$ (open circles) CC DIS. The expectation of the Standard Model evaluated using the ZEUS NLO QCD fit is shown as a solid line. The contributions of the PDF combinations $x (u+c)$ and $x (\bar{u}+\bar{c})$ are shown by the dashed and dotted lines, respectively.