Measurement of high-Q^2 charged current cross sections in e^+p deep inelastic scattering at HERA

TL;DR

This paper reports a comprehensive measurement of high-Q^2 charged-current deep inelastic scattering in e^+ p collisions at HERA using the ZEUS detector, covering single- and double-differential cross sections and extending to Q^2 up to 17000 GeV^2. It tests the Standard Model's electroweak and QCD structure by examining the W propagator behavior, the chiral nature of CC interactions via (1−y)^2, and the flavor decomposition through F_2^{CC}. The W-mass is extracted from the Q^2 spectrum and the quark singlet structure function F_2^{CC} is obtained by combining with prior e^- p results, with all measurements in good agreement with SM predictions and various PDF sets. Overall, the results validate the SM description of CC DIS at unprecedented Q^2 and provide constraints on PDFs in a high-Q^2 regime relevant for precision electroweak tests at ep colliders.

Abstract

Cross sections for e^+p charged current deep inelastic scattering at a centre-of-mass energy of 318 GeV have been determined with an integrated luminosity of 60.9pb^-1 collected with the ZEUS detector at HERA. The differential cross sections dsigma/dQ^2, dsigma/dx and dsigma/dy for Q^2>200 GeV^2 are presented. In addition, d^2sigma/dxdQ^2 has been measured in the kinematic range 280 GeV^2 < Q^2 < 17000 GeV^2 and 0.008 < x < 0.42. The predictions of the Standard Model agree well with the measured cross sections. The mass of the W boson propagator is determined to be M_W=78.9 +/- 2.0 (stat.) +/- 1.8 (syst.) +2.0 -1.8 (PDF) GeV from a fit to dsigma/dQ^2. The chiral structure of the Standard Model is also investigated in terms of the (1-y)^2 dependence of the the double-differential cross section. The structure-function F_2^CC has been extracted by combining the measurements presented here with previous ZEUS results from e^-p scattering, extending the measurement obtained in a neutrino-nucleus scattering experiment to a significantly higher Q^2 region.

Figures (8)

• Figure 1: Comparison of the final $e^+ p$ CC data sample (solid points) with the sums of the signal and $ep$-background Monte Carlo simulations (light shaded histograms). The simulated $ep$-background events are shown as the dark shaded histograms. Shown are the distributions of (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 Section \ref{['s:reconstruction']}, (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 large-$\gamma_0$ sample and (h) the $Z$ position of the timing vertex for the small-$\gamma_0$ sample.
• Figure 2: (a) The $e^+p$ CC DIS Born cross section $d\sigma/dQ^2$ for data and the Standard Model expectation evaluated using the ZEUS-S, the CTEQ6D and the MRST (2001) PDFs. The data are shown as the filled points, the statistical uncertanties are indicated by the inner error bars (delimited by horizontal lines) and the full error bars show the total uncertainty obtained by adding the statistical and systematic contributions in quadrature. (b) The ratio of the measured cross section, $d\sigma/dQ^2$, to the Standard Model expectation evaluated using the ZEUS-S fit. The shaded band shows the uncertainties from the ZEUS-S fit.
• Figure 3: (a) The $e^+p$ CC DIS Born cross section $d\sigma/dx$ for data and the Standard Model expectation evaluated using the ZEUS-S, the CTEQ6D and the MRST (2001) PDFs. The data are shown as the filled points, the statistical uncertanties are indicated by the inner error bars (delimited by horizontal lines) and the full error bars show the total uncertainty obtained by adding the statistical and systematic contributions in quadrature. (b) The ratio of the measured cross section, $d\sigma/dx$, to the Standard Model expectation evaluated using the ZEUS-S fit. The shaded band shows the uncertainties from the ZEUS-S fit.
• Figure 4: (a) The $e^+p$ CC DIS Born cross section $d\sigma/dy$ for data and the Standard Model expectation evaluated using the ZEUS-S, the CTEQ6D and the MRST (2001) PDFs. The data are shown as the filled points, the statistical uncertanties are indicated by the inner error bars (delimited by horizontal lines) and the full error bars show the total uncertainty obtained by adding the statistical and systematic contributions in quadrature. (b) The ratio of the measured cross section, $d\sigma/dy$, to the Standard Model expectation evaluated using the ZEUS-S fit. The shaded band shows the uncertainties from the ZEUS-S fit.
• Figure 5: The reduced cross section, $\tilde{\sigma}$, as a function of $Q^2$, for different fixed values of $x$. The data are shown as the filled points, the statistical uncertanties are indicated by the inner error bars (delimited by horizontal lines) and the full error bars show the total uncertainty obtained by adding the statistical and systematic contributions in quadrature. The expectation of the Standard Model evaluated using the ZEUS-S, the CTEQ6D and the MRST(2001) PDFs is shown by the solid, dashed and dotted lines, respectively. The shaded band shows the uncertainties from the ZEUS-S fit.