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 6 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 = p T √ s , where pT is the transverse momentum of the final photon and √ 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 → γ + X cross section.PACS numbers: 13.60. Le,13.85.Ni,12.38.Qk The production of photons with large transverse momentum is an excellent probe of the dynamics in hard scattering processes [1,2]. In particular, the study of direct photon production possesses numerous and well known advantages, both theoretical and experimental [2][3][4][5][6][7][8][9]. In the latter case the main advantage is that photons are easier to detect than jets. From the theoretical point of view the main advantage is the simplicity of the process allowing for an accurate determination of the gluon distribution within the proton. In the lowest order (O(αα s )) only two subprocesses, gq → γq (Compton) and qq → γg (annihilation), contribute to high p T photons. Their characteristic signature is the production of a photon isolated from the hadrons in the event, accompanied by a kinematically balancing high-p T jet appearing on the opposite site. In the next-to-leading order (NLO) the process associated with the production of a photon coming from the collinear fragmentation of a hard parton produced in a short-distance subprocess, constitutes a background to the direct photon production of the same order in α s as the corresponding Born level terms [10] provided that the fragmentation scale is large enough. However, the contribution from fragmentation remains small (less than 10%) for fixed target experiments and becomes significant only in inclusive prompt photon production at higher collider energies [10]. Recently there has been observed a systematic disagreeme...
We use a non-gaussian intrinsic transverse momentum distribution, associated with the wavefunction of the partonic ground state inside the proton, to calculate the production of π0 with intermediate transverse momentum values in p − p collisions at high energies. It is shown that a perfect description of the experimental data for different experiments is achieved using an almost constant value for the mean transverse momentum of the initial partons, compatible with Heisenberg’s uncertainty relation (⟨kT ⟩ ≈ 0.3 GeV ). Our analysis suggests the presence of a non-vanishing, non-perturbative contribution from partonic bound states to the pp → πo(γ) + X and pp → p + X cross section.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.