Partons and their applications at high energies (original) (raw)

The parton model and its applications

International Journal of Modern Physics A, 2014

This is a review of the program we started in 1968 to understand and generalize Bjorken scaling and Feynman's parton model in a canonical quantum field theory. It is shown that the parton model proposed for deep inelastic electron scatterings can be derived if a transverse momentum cutoff is imposed on all particles in the theory so that the impulse approximation holds. The deep inelastic electron-positron annihilation into a nucleon plus anything else is related by the crossing symmetry of quantum field theory to the deep inelastic electron-nucleon scattering. We have investigated the implication of crossing symmetry and found that the structure functions satisfy a scaling behavior analogous to the Bjorken limit for deep inelastic electron scattering. We then find that massive lepton pair production in collisions of two high energy hadrons can be treated by the parton model with an interesting scaling behavior for the differential cross sections. This turns out to be the first example of a class of hard processes involving two initial hadrons.

A New Qualitative Prediction of the Parton Model for High-Energy Hadron Collisions

Foundations of Physics, 2000

Inclusive single jet production in hadron collisions is considered. It is shown that the QCD parton model predicts a nonmonotonic dependence of the inclusive cross section on the fraction of the energy deposited in the jet registered, if it is normalized on the same cross section measured at another collision energy. Specifically, if the cross section is normalized by the one measured at a higher collision energy, it possesses a minimum which depends on jet rapidity. This prediction can be tested at the Fermilab Tevatron, at the CERN LHC, and at the Very Large Hadron Collider under discussion.

Nuclear Physics A Dynamics of strongly interacting parton-hadron matter

2016

In this study we investigate the dynamics of strongly interacting parton-hadron matter by calculating the centrality dependence of direct photons produced in Au+Au collisions at √ s NN = 200 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach. As sources for 'direct' photons, we incorporate the interactions of quarks and gluons as well as hadronic interactions (π+ π → ρ+ γ, ρ+ π → π+ γ, meson-meson bremsstrahlung m+ m → m+ m+ γ, meson-baryon bremsstrahlung m+ B → m+ B+ γ), the decays of φ and a 1 mesons and the photons produced in the initial hard collisions ('pQCD'). Our calculations suggest that the channel decomposition of the observed spectrum changes with centrality with an increasing (dominant) contribution of hadronic sources for more peripheral reactions. Furthermore, the 'thermal' photon yield is found to scale roughly with the number of participant nucleons as N α part with α ≈ 1.5, whereas the partonic contribution scales with an exponent α p ≈ 1.75. Additionally, we provide predictions for the centrality dependence of the direct photon elliptic flow v 2 (p T). The direct photon v 2 is seen to be larger in peripheral collisions compared to the most central ones since the photons from the hot deconfined matter in the early stages of the collision carry a much smaller elliptic flow than those from the final hadronic interactions.

A parton-hadron cascade approach in high-energy nuclear collisions

Nuclear Physics A, 1998

A parton-hadron cascade model which is the extension of hadronic cascade model incorporating hard partonic scattering based on HIJING is presented to describe the spacetime evolution of parton/hadron system produced by ultra-relativistic nuclear collisions. Hadron yield, baryon stopping and transverse momentum distribution are calculated and compared with HIJING and VNI.

A Short Review of Some Double-parton Scattering Processes

Acta Physica Polonica B Proceedings Supplement, 2015

A few examples of quickly developing field of double parton scattering are discussed. We present arguments that the production of two pairs of charm quark-antiquark is the golden reaction to study the double parton scattering effects. We discuss briefly also mechanism of single parton scattering and show that it gives much smaller contribution to the cccc final state. In this context we discuss also the contribution of perturbative parton-splitting mechanism which should also be added to the conventional DPS mechanism. The presence of the letter leads to collision energy and other kinematical variables dependence of so-called σ ef f. We briefly discuss production of four jets. We concentrate on estimation of the contribution of DPS for jets widely separated in rapidity. Finally we briefly mention about DPS effects in production of W + W − .

Dilepton Production from Parton Interactions in the Early Stage of Relativistic Heavy-Ion Collisions

Journal of Physics: Conference Series, 2011

We address the dilepton production from the parton interactions in the early stage of relativistic heavy-ion collisions within the parton-hadron-string dynamics (PHSD) offshell transport approach. The description of partons in PHSD is based on the dynamical quasiparticle model (DQPM) matched to reproduce lattice QCD results in thermodynamic equilibrium. According to the DQPM the constituents of the strongly interacting quark-gluon plasma (sQGP) are massive and off-shell quasi-particles (quarks and gluons) with broad spectral functions. In order to address the electromagnetic radiation of the sQGP, we derive off-shell cross sections of qq → γ * , qq → γ * + g and qg → γ * q (qg → γ * q ) reactions taking into account the effective propagators for quarks and gluons from the DQPM. Dilepton production in In+In collisions at 158 AGeV and in Au+Au at √ s = 200 GeV is calculated by implementing these off-shell processes into the PHSD transport approach. By comparing to the data of the NA60 and PHENIX Collaborations, we study the relative importance of different dilepton production mechanisms and point out the regions in phase space where partonic channels are dominant.

Deep-inelastic scattering, partons and strong interactin ideas

The quark-parton model as applied to deep-inelastic lepton-hadron scattering is used as a laboratory model for the study of ideas encountered in strong interaction physics. First, two-component duality constraints are imposed on single-particle inclusive deep-inelastic distributions. In the target fragmentation region this involves a modification of the def'mition of the E functions introduced by Feynman. A duality relation connecting neutrino and electroproduction singie-particle inclusive distributions is obtained. For to ~ 1 and w --* ** we predict in the target fragmentation region an excess of ~r + over ~-production for proton targets and an excess of~r-over ~r + for neutron targets. For deuteron targets we f'md an excess of lr-over Ir + for to --, 1.

Parton-hadron dynamics in heavy-ion collisions

Astronomische Nachrichten

The dynamics of partons and hadrons in relativistic nucleus-nucleus collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for the partonic phase (DQPM) including a dynamical hadronization scheme. The PHSD approach is applied to nucleus-nucleus collisions from low SPS to LHC energies. The traces of partonic interactions are found in particular in the elliptic flow of hadrons and in their transverse mass spectra. We investigate also the equilibrium properties of strongly-interacting infinite parton-hadron matter characterized by transport coefficients such as shear and bulk viscosities and the electric conductivity in comparison to lattice QCD results.