/ hep-ex CMS-QCD-11-010

Measurement of neutral strange particle production in the underlying event in proton-proton collisions at $\sqrt{s}$ = 7 TeV

Abstract: Measurements are presented of the production of primary $K_S^0$ and $\Lambda$ particles in proton-proton collisions at $\sqrt{s}$ = 7 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 abs(eta) < 2 rise with increasing charged-particle jet pt in the range 1-10 GeV and saturate in the region 10-50 GeV. 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 and the similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.

Note: Submitted to Phys. Rev. D

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