Measurement of neutral strange particle production in the underlying event in proton-proton collisions at sqrt(s) = 7 TeV

TL;DR

This study measures the production of strange particles in proton-proton collisions at 7 TeV, revealing how their yields and momentum sums depend on jet activity and comparing results to Monte Carlo simulations.

Contribution

It provides the first detailed measurement of primary K(S)0 and Lambda production in the underlying event at 7 TeV, highlighting discrepancies with PYTHIA predictions.

Findings

Strange particle yields increase with jet pt and saturate at higher values.

PYTHIA underestimates strange particle production by 15-50%.

Strange-to-charged particle ratios remain constant across jet activities.

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.