Determination of the Strange Quark Content of the Nucleon from a Next-to-Leading-Order QCD Analysis of Neutrino Charm Production

Abstract

We present the first next-to-leading-order QCD analysis of neutrino charm production, using a sample of 6090 $ν_μ$- and $\barν_μ$-induced opposite-sign dimuon events observed in the CCFR detector at the Fermilab Tevatron. We find that the nucleon strange quark content is suppressed with respect to the non-strange sea quarks by a factor $κ= 0.477 \: ^{+\:0.063}_{-\:0.053}$, where the error includes statistical, systematic and QCD scale uncertainties. In contrast to previous leading order analyses, we find that the strange sea $x$-dependence is similar to that of the non-strange sea, and that the measured charm quark mass, $m_c = 1.70 \pm 0.19 \:{\rm GeV/c}^2$, is larger and consistent with that determined in other processes. Further analysis finds that the difference in $x$-distributions between $xs(x)$ and $x\bar s(x)$ is small. A measurement of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|=0.232 ^{+\:0.018}_{-\:0.020}$ is also presented. uufile containing compressed postscript files of five Figures is appended at the end of the LaTeX source.

Figures (5)

• Figure 1: Mechanisms that contribute to neutrino production of charm up to ${\cal O}(\alpha_S)$. a) The dominant diagrams: the leading-order quark-initiated diagram, and the t channel and u channel gluon-initiated diagrams, respectively. b) The radiative-gluon and self-energy diagrams.
• Figure 2: $x_{\rm vis}$, $E_{\rm vis}$ and $z_{\rm vis}$ distributions for $\nu$- and $\overline\nu$-induced dimuon events. Data are given by the points and the solid histogram is the result of fitting the dimuon event simulation. The dotted histogram is the background contribution to the former from pion and kaon decay.
• Figure 3: The quark sea distribution $x\overline q(x,\mu^2=4.0\: {\rm GeV^2/c^2})$ determined at next-to-leading order and leading order.
• Figure 4: The strange quark distribution $x s(x,\mu^2=4.0\: {\rm GeV^2/c^2})$ determined at next-to-leading order (described in section 4.1) and leading order. The band around the NLO curve indicates the $\pm 1\sigma$ uncertainty in the distribution.
• Figure 5: The $\mu^2$ scale dependence of the differential cross section for neutrino and antineutrino production of charm, where $\mu^2$ identifies the factorization and renormalization scales. The scale $\mu$ on the abscissa is in units of $p_\perp^{\rm max}$. For $E=200$ GeV and $y=0.5$, the $x=0.05$, 0.15, 0.25 lines correspond to $p_\perp^{\rm max}=6.6$, 6.2, 5.8 GeV/c, respectively.