Neutrino Dimuon Production and the Strangeness Asymmetry of the Nucleon

TL;DR

This paper performs the first global QCD analysis that includes CCFR and NuTeV neutrino dimuon data to directly constrain strange and anti-strange PDFs, employing a flexible parametrization for $s^{+}$ and $s^{-}$ and using the Lagrange Multiplier method to study the integrated strangeness asymmetry $[S^-]$. The results indicate a positive, but small, preferred range for $[S^-]$ with $-0.001 < [S^-] < 0.004$, and demonstrate that dimuon data provide stronger constraints on strangeness than inclusive DIS data. The analysis systematically examines uncertainties from LO vs NLO treatment, charm mass, and fragmentation/decay modeling, and compares with prior work (notably BPZ), underscoring the pivotal role of direct dimuon measurements for nucleon strangeness and their potential impact on precision electroweak observables like sin^2 theta_W. Overall, the work establishes a framework for robust exploration of $s(x)$ and $\bar{s}(x)$, highlighting how dimuon data shape the strangeness sector within PQCD.

Abstract

We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and anti-strange parton distributions, $s(x)$ and $\bar{s}(x)$. To explore the strangeness sector, we adopt a general parametrization of the non-perturbative $s(x), \bar{s}(x)$ functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral $[S^{-}]\equiv \int_0^1 x [s(x)-\bar{s}(x)] dx$, is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange Multiplier method to probe the quality of the global fit as a function of $[S^-]$ and find $-0.001 < [S^-] < 0.004$. Representative parton distribution sets spanning this range are given. Comparisons with previous work are made.

Figures (4)

• Figure 1: Different functional behaviors of the strangeness number asymmetry function $s^-(x)$ and momentum asymmetry function $S^-(x)$: comparison of our central fit "B" (solid, discussed in detail later in the text) with those of BPZ (dashed) and CCFR-NuTeV (dot-dashed). The horizontal axis is linear in $z\equiv x^{1/3}$ so that both large and small $x$ regions are adequately represented; the functions are multiplied by a Jacobian factor $dx/dz$ so that the area under the curve is the corresponding integral over $x$.
• Figure 2: Typical strangeness asymmetry $s^-(x)$ and the associated momentum asymmetry $S^-(x)$, as obtained in our global analysis. The axes are the same as in Fig. \ref{['fig:A']}.
• Figure 3: Comparison of data to fit B. The data points are sorted in $x$-bins, and within each $x$-bin, by $y$ value.
• Figure 4: Values of $\chi^2/\chi^2_B$ versus $[S^-]$ by the Lagrange multiplier method in global analysis. Figure (a) show the dimuon data sets ($\blacksquare$) and the "Inclusive I" data sets ($\blacktriangle$) separately, and figure (b) shows these data sets combined ($\blacksquare$). (Cf. text and Table 1)