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Parton
About: Parton is a research topic. Over the lifetime, 13484 publications have been published within this topic receiving 368877 citations.
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TL;DR: New positivity constraints on the spin-dependent structure functions of the nucleon are derived and their domain of allowed values are reduced, in particular, for the chiral-odd parton distribution.
Abstract: We derive new positivity constraints on the spin-dependent structure functions of the nucleon These model-independent results reduce considerably their domain of allowed values, in particular, for the chiral-odd parton distribution [ital h][sub 1]([ital x])
237 citations
TL;DR: In this article, a partial review of QCD at high energies is given Factorization and the use of the renormalization group equation are emphasized Topics discussed are the parton model, cut vertices in covariant and axial gauges, μ-pair production, jets, form factors, x → 1 limit of structure fu nctions, wide angle elastic scattering and heavy quarkonium exclusive decays.
237 citations
TL;DR: In this article, a covariant coalescence model was proposed to describe the hadron production in relativistic heavy ion collisions from both soft partons in the quark-gluon plasma and hard partons of minijets.
Abstract: Using a covariant coalescence model, we study hadron production in relativistic heavy ion collisions from both soft partons in the quark-gluon plasma and hard partons in minijets. Including transverse flow of soft partons and independent fragmentation of minijet partons, the model is able to describe available experimental data on pion, kaon, and antiproton spectra. The resulting antiproton to pion ratio is seen to increase at low transverse momenta and reaches a value of about one at intermediate transverse momenta, as observed in experimental data at RHIC. A similar dependence of the antikaon to pion ratio on transverse momentum is obtained, but it reaches a smaller value at intermediate transverse momenta. At high transverse momenta, the model predicts that both the antiproton to pion and the antikaon to pion ratio decrease and approach those given by the perturbative QCD. Both collective flow effect and coalescence of minijet partons with partons in the quark-gluon plasma affect significantly the spectra of hadrons with intermediate transverse momenta. Elliptic flows of protons, Lambdas, and Omegas have also been evaluated from partons with elliptic flows extracted from fitting measured pion and kaon elliptic flows, and they are found to be consistent with available experimental data.
237 citations
TL;DR: In this paper, the problem of going from one description to the other can be solved in a satisfactory manner to all orders, where the key ingredient is the constraint of matching the evolution of the physical structure function F_2 order by order in alpha-s(Q^2) in addition to the matching of the value of Fǫ itself.
Abstract: At low Q^2, charm production in deep-inelastic scattering is adequately described by assuming generation in electroweak boson-light parton scattering (dominantly boson-gluon fusion) which naturally incorporates the correct threshold behaviour. At high Q^2 this description is inadequate, since it does not sum logs in Q^2/m_c^2, and is replaced by the treatment of the charm quark as a light parton. We show how the problem of going from one description to the other can be solved in a satisfactory manner to all orders. The key ingredient is the constraint of matching the evolution of the physical structure function F_2 order by order in alpha_s(Q^2) in addition to the matching of the value of F_2 itself. This leads to new expressions for the coefficient functions associated with the charm parton which are unique in incorporating both the correct threshold and asymptotic behaviours at each order in perturbation theory. The use of these improved coefficients lead to an improvement in global fits and an excellent description of the observed F_2,charm.
236 citations
TL;DR: In this paper, the authors derived a parton model from canonical field theory for deep-inelastic lepton processes and derived a transverse momentum cutoff so that there exists an asymptotic region in which q2 and Mν can be made larger than the transverse momenta of all the partons involved.
Abstract: The structure functions for deep-inelastic lepton processes including (along with other hadron charges and SU3 quantum numbers) e−+p→e−+anything," e−+e+→p+anything," ν+p→e−+anything," ν¯+p→e++anything" are studied in the Bjorken limit of asymptotically large momentum and energy transfers, q2 and Mν, with a finite ratio w≡2Mνq2. A "parton" model is derived from canonical field theory for all these processes. It follows from this result that all the structure functions depend only on w, as conjectured by Bjorken for the deep-inelastic scattering. To accomplish this derivation it is necessary to introduce a transverse momentum cutoff so that there exists an asymptotic region in which q2 and Mν can be made larger than the transverse momenta of all the partons that are involved. Upon crossing to the e+e− annihilation channel and deriving a parton model for this process, we arrive at the important result that the deep-inelastic annihilation cross section to a hadron plus "anything" is very large, varying with colliding e+e− beam energy at fixed w in the same way as do point-lepton cross sections. General implications for colliding-ring experiments and ratios of annihilation to scattering cross sections and of neutrino to electron inelastic scattering cross sections are computed and presented. Finally, we discuss the origin of our transverse momentum cutoff and the compatibility of rapidly decreasing elastic electromagnetic form factors with the parton model constructed in this work.
235 citations