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MIT bag model inspired partonic transverse momentum distribution for prompt photon production in pp collisions

We consider the prompt photon production in pp collisions using, within the framework of perturbative QCD, a non-Gaussian distribution for the transverse momentum distribution of the partons inside the proton. Our description adopts the widely used in the literature factorization of the partonic momentum distribution into longitudinal and transverse components. It is argued that the non-Gaussian distribution of the intrinsic transverse momenta of the partons is dictated by the asymptotic freedom as well as the 3D confinement of the partons in the proton. To make this association more transparent we use the MIT bag model, which plainly incorporates both properties (asymptotic freedom, confinement), in order to determine in a simplified way the partonic transverse momentum distribution. A large set of data from six different experiments have been fitted with this simple description using as a single free parameter the mean partonic transverse momentum <kT>. Surprisingly enough, a perfect fit of the experimental data turns out to require <kT> values which are compatible with Heisenberg's uncertainty relation for the proton and decrease almost smoothly as a function of the scaled variable z=pT/\sqrt{s}, where pT is the transverse momentum of the final photon and \sqrt{s} is the beam energy in the center of mass frame. Our analysis indicates that asymptotic freedom and 3D confinement may influence significantly the form of the partonic transverse momentum distribution leaving an imprint on the pp\toγ+X cross section.