Saturation momentum scale extracted from semi-inclusive transverse spectra in high-energy collisions
Takeshi Osada (Department of Physics, Faculty of Liberal Arts and Sciences, and Tokyo City University, Tamazutsumi 1-28-1, Setagaya-ku, Tokyo 158-8557, Japan); Takuya Kumaoka (Department of Physics, Shinshu University, Matsumoto 390-8621, Japan)
Geometric scaling is well confirmed for transverse-momentum distributions observed in proton-proton collisions at Large Hadron Collider (LHC) energies. We introduced multiplicity dependence on a saturation momentum of the geometrical scaling, assuming the scaling holds for semi-inclusive distributions as well as for inclusive distributions. The saturation momentum is usually given by Bjorken's variable, but redefinition of the scaling variable can make the saturation momentum a function of collision energy . We treat the energy as a free parameter (denoted to distinguish it from ) and associate the energy-dependent saturation momentum with particle number density. By using for a scaling variable , we show semi-inclusive distributions can be geometrically scaled, i.e., all semi-inclusive spectra observed at , 2.76, and 7.00 TeV overlap one universal function. The particle density dependencies of mean transverse momentum for LHC energies scales in terms of . Furthermore, our model explains a scaling property of event-by-event fluctuation measure at LHC energies for collisions, where is a two-particle transverse-momentum correlator. Our analysis of the fluctuation makes possible to evaluate a nonperturbative coefficient of the gluon correlation function.