Ridge correlation structure in high multiplicity pp collisions with CMS

Understand

Results on two-particle angular correlations are presented in proton-proton collisions at center of mass energies of 7 TeV, over a broad range of pseudorapidity and azimuthal angle.

• In very high multiplicity events at 7 TeV, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate $p_{\mathrm{T}}$ of 1--3 GeV/c, in the kinematic region $2.0 < |\Delta\eta| < 4.8$ and small $\Delta\phi$.
• This structure, which has not been observed in pp collisions before, is similar to what is known as the &#34;ridge&#34; in heavy ion collisions.
• It is not predicted by commonly used proton-proton Monte Carlo models and is not seen in lower multiplicity pp collisions.