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

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Eroe, J. and Fabjan, C. and Friedl, M. and Fruehwirth, R. and Ghete, V. M. and Hoermann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knuenz, V. and Krammer, M. and Kraeschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schoefbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Molnár, József and Pálinkás, József and Karancsi, János and Trócsányi, Zoltán and Ujvári, Balázs and Krajczár, Krisztián and Veres, Gábor (2013) Measurement of neutral strange particle production in the underlying event in proton-proton collisions at √s = 7 TeV. PHYSICAL REVIEW D, 88 (5). ISSN 2470-0010

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Abstract

Measurements are presented of the production of primary K0 S and Λ particles in proton-proton collisions at √s = 7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar trans- verse momentum sum of K0 S and Λ particles measured at pseudorapidities |η| < 2 rise with increasing charged-particle jet pT in the range 1–10 GeV/c and saturate in the re- gion 10–50 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 K0 S mesons and by about 50% for Λ baryons, a deficit similar to that observed for the in- clusive strange particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet pT 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.

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