Azimuthal anisotropy harmonics from long-range correlations in high multiplicity pp collisions at sqrt{s} = 7 TeV

Measurements of two- and four-particle angular correlations in pp collisions at $\sqrt{s_{_{NN}}}$ = 7 TeV are presented as a function of charged-particle multiplicities. The data, corresponding to an integrated luminosity of about 6.2 pb$^{-1}$, were collected during the 2010 LHC pp run using the CMS detector. In high-multiplicity events, a long-range ($|\Delta\eta|>2$), near-side ($\Delta\phi \approx 0$) structure is found in the two-particle $\Delta\eta$-$\Delta\phi$ correlation functions. The second-order ($v_2$) and third-order ($v_3$) azimuthal anisotropy harmonics of charged particles, $\text{K}_{\text{S}}^{0}$ and $\Lambda$/$\overline{\Lambda}$ particles are extracted from long-range two-particle correlations as a function of particle multiplicity and transverse momentum, after correcting for the contribution of back-to-back jet correlations. A $v_2$ and $v_3$ value of about 4$\%$ and 1$\%$, averaging over $0.3 < p_\mathrm{T} < 3$ GeV$/$c, are observed in the high-multiplicity region, and are found to be smaller than values obtained in pPb and PbPb collisions at similar multiplicities. A measurement of four-particle azimuthal correlations is also presented as a function of multiplicity.