Multiplicity dependence of light-flavor hadron production in p p collisions at √{s }=7 TeV

Comprehensive results on the production of unidentified charged particles, π^±, K^±, K_S⁰, K^*(892^{) 0} , p , p ¯, ϕ (1020), Λ , Λ ¯, Ξ^-, Ξ^¯+, Ω^-, and Ω^¯+ hadrons in proton-proton (p p ) collisions at √{s }=7 TeV at midrapidity (|y |<0.5 ) as a function of charged-particle multiplicity density are presented. In order to avoid autocorrelation biases, the actual transverse momentum (p_T) spectra of the particles under study and the event activity are measured in different rapidity windows. In the highest multiplicity class, the charged-particle density reaches about 3.5 times the value measured in inelastic collisions. While the yield of protons normalized to pions remains approximately constant as a function of multiplicity, the corresponding ratios of strange hadrons to pions show a significant enhancement that increases with increasing strangeness content. Furthermore, all identified particle-to-pion ratios are shown to depend solely on charged-particle multiplicity density, regardless of system type and collision energy. The evolution of the spectral shapes with multiplicity and hadron mass shows patterns that are similar to those observed in p -Pb and Pb-Pb collisions at Large Hadron Collider energies. The obtained p_T distributions and yields are compared to expectations from QCD-based p p event generators as well as to predictions from thermal and hydrodynamic models. These comparisons indicate that traces of a collective, equilibrated system are already present in high-multiplicity p p collisions.