Measurement of Strange Particle Production in Underlying Events in proton-proton collisions at $\sqrt{s

Measurements of the production of $K^0_S$, $\Lambda$ and $\overline{\Lambda}$ particles in the underlying activity of events with a $p_T$ scale ranging from 1 to 50 GeV$/c$ are made in proton-proton collisions at $\sqrt{s} = 7$ TeV, using data collected by the CMS experiment at the LHC. Particle production is studied with reference to the azimuthal direction of the leading set of charged particles forming a ``track-jet". A growth in the average multiplicity and average scalar $p_T$ sum of $K^0_S$ and $\Lambda+\overline{\Lambda}$, with $p_{T}^{K^0_S} > 0.6$ GeV$/c$ and $p_{T}^{\Lambda,\overline{\Lambda}} > 1.5$ GeV$/c$, within $|\eta| < 2$ and azimuthal direction transverse to that of the leading track-jet, is observed with increasing scale given by the leading track-jet $p_T$. This growth is followed by a saturation at large values of the scale. The growth and saturation are very similar to what is observed for charged primary particles. The average activity of the underlying event in primary $K^0_S$ mesons and $\Lambda$ baryons is compared to recent tunes of the PYTHIA Monte Carlo generator. The PYTHIA simulations underestimate the activity by 15-30 percent for $K^0_S$ mesons and by about 50 percent for $\Lambda+\overline{\Lambda}$ baryons.