Magnitude of the proton strangeness asymmetry

Determine the magnitude and momentum-fraction dependence of the proton strangeness asymmetry, defined by a nonzero difference between the strange- and antistrange-quark parton distribution functions, subject to a vanishing integral over the momentum fraction.

Background

The strange-quark parton distribution is more difficult to constrain than many light-quark distributions. The paper defines strangeness asymmetry as s(x)−s̄(x) being nonzero at some momentum fractions while integrating to zero overall. Different global PDF analyses treat this asymmetry differently: CT18 imposes s=s̄, whereas MSHT20 and NNPDF4.0 allow the asymmetry to vary. The associated W-plus-charm charge ratios studied in the paper are proposed as observables sensitive to this unresolved property.

References

An open question is the size of strangeness asymmetry, which refers to $s-\Bar{s}$ PDF not being zero for all values of the momentum fraction $x$ while still yielding zero when integrated over $x$.

— Simultaneous production of a $W$ boson and a charmed hadron at the LHC in general-mass variable-flavour-number scheme  (2608.14268 - Alanko et al., 14 Aug 2026) in Section 1, Introduction

However, the required changes in NNPDF4.0 would be rather significant which could potentially lead to conflicts with other data included in these global fits. Whether there is a compromise remains to be seen.

— Simultaneous production of a $W$ boson and a charmed hadron at the LHC in general-mass variable-flavour-number scheme  (2608.14268 - Alanko et al., 14 Aug 2026) in Section 5, Conclusions