The onset on the ridge structure in AA, pA and pp collisions

Abstract

It is shown that the anomalous sharp increasing of the strength of the near-side ridge structures observed in Au-Au collisions at √ s = 62 GeV and √ s = 200 GeV and the onset of the ridge structure in pPb and in pp collisions can be naturally explained in the framework of string percolation. In all the cases the near-side strength reflects the collision area covered by the strings stretched between the colliding objects and therefore it is related to the shape of their profile functions. The dependence of the pseudorapidty and azimuthal widths on multiplicty and energy is qualitatively explained.

De-confinement and clustering of color sources in nuclear collisions

“…On the other hand, the RHIC data on Au-Au indicate a change in the strength of the near side ridge structure at a given multiplicity [166]. All these facts can be naturally explained in string percolation [165]. In fact, the ridge structure in pp at high multiplicity was anticipated by string percolation [167].…”

“…Au-Au collisions at two RHIC energies. (b) pp collisions at 7 TeV and p-Pb collisions at 5.02 TeV[165].…”

Several Effects Unexplained by QCD

“…The balancing particles appear as an opposite side ridge plateau at ∆φ ≈ π. The near side plateau at small ∆φ looks as if the strings stretched between protons percolate [35] and break up into the oldfashioned clusters [36] moving fast along the string direction according to the multiperipheral kinematics [37]. Other interpretations of this effect have been proposed but no complete agreement is yet achieved.…”

String percolation in AA and p+p collisions

“…The same occurs at pPb although in this case is flattened at higher multiplicity. This behavior is understood as a consequence of Eq (63). In fact, the factor 1/F (ρ) is responsible of the rise of p T with multiplicity because grows with multiplicity.…”

“…where ρ c = 1.5 and the parameters a and b depend on the profile function, b that controls the ratio between the width of the border of the profile (2πR) and the total area (πR2), and therefore is proportional to 1/R [63]. In the collisions of two hadrons or two nuclei, the surface where the discs are distributed is rather an ellipse or a circle, what gives rise to smaller values of the critical density [64].…”