Measurement of charm and beauty production at central rapidity versus charged-particle multiplicity in proton–proton collisions at √s = 7 TeV

Adam, J. and Adamova, D. and Aggarwal, M. M. and Rinella, G. A. and Agnello, M. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Kiss, Gábor and Varga-Kőfaragó, Mónika and Lévai, Péter and Oláh, László and Pochybova, Sona (2015) Measurement of charm and beauty production at central rapidity versus charged-particle multiplicity in proton–proton collisions at √s = 7 TeV. JOURNAL OF HIGH ENERGY PHYSICS (9). ISSN 1126-6708

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Abstract

Prompt D meson and non-prompt J/ ψ yields are studied as a function of the multiplicity of charged particles produced in inelastic proton–proton collisions at a centre-of-mass energy of √s = 7 TeV. The results are reported as a ratio between yields in a given multiplicity interval normalised to the multiplicity-integrated ones (relative yields). They are shown as a function of the multiplicity of charged particles normalised to the average value for inelastic collisions (relative charged-particle multiplicity). D0, D+ and D∗+ mesons are measured in five pT intervals from 1 GeV/c to 20 GeV/c and for |y| < 0.5 via their hadronic decays. The D-meson relative yield is found to increase with increasing charged-particle multiplicity. For events with multiplicity six times higher than the av- erage multiplicity of inelastic collisions, a yield enhancement of a factor about 15 relative to the multiplicity-integrated yield in inelastic collisions is observed. The yield enhancement is indepen- dent of transverse momentum within the uncertainties of the measurement. The D0-meson relative yield is also measured as a function of the relative multiplicity at forward pseudo-rapidity. The non-prompt J/ ψ, i.e. the B hadron, contribution to the inclusive J/ ψ production is measured in the di-electron decay channel at central rapidity. It is evaluated for pT > 1.3 GeV/c and |y| < 0.9, and extrapolated to pT > 0. The fraction of non-prompt J/ ψ in the inclusive J/ ψ yields shows no de- pendence on the charged-particle multiplicity at central rapidity. Charm and beauty hadron relative yields exhibit a similar increase with increasing charged-particle multiplicity. The measurements are compared to PYTHIA 8, EPOS 3 and percolation calculations.

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