Measurements are presented of the production of primary $K_S^0$ and $\Lambda$ particles in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of $K_S^0$ and $\Lambda$ particles measured at pseudorapidities $|\eta |<2$ rise with increasing charged-particle jet $p_{\mathrm{T}}$ in the range $1–10\mathrm{GeV}/c$ and saturate in the region $10–50\mathrm{GeV}/c$. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the pythia Monte Carlo event generator. The pythia simulations underestimate the data by 15%–30% for $K_S^0$ mesons and by about 50% for $\Lambda$ baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet $p_{\mathrm{T}}$ and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.

• Received 26 May 2013

DOI:https://doi.org/10.1103/PhysRevD.88.052001

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© 2013 CERN, for the CMS Collaboration