نتایج جستجو برای: pion production
تعداد نتایج: 610393 فیلتر نتایج به سال:
It is shown how the single spin asymmetry observed in inclusive pion production is related, in the helicity basis, to the imaginary part of the product of two different distribution amplitudes, rather than to the usual quark and gluon distribution functions; there is then no reason why it should be zero even in massless perturbative QCD, provided the quark intrinsic motion is taken into account...
We consider threshold pion electroproduction on a proton target for photon virtualities in the region 1 − 10 GeV. The S-wave multipoles at threshold, E0+ and L0+, are calculated using light-cone sum rules.
We propose an intensity-dependent pion-nucleon coupling Hamiltonian within a unitary multiparticle-production model of the Auerbach-Avin-Blankenbecler-Sugar (AABS) type in which the pion field is represented by the thermal-density matrix. Using this Hamiltonian, we explain the appearance of the negative-binomial (NB) distribution for pions and the well-known empirical relation, the so-called Wr...
The STAR experiment at the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program colliding transverse or longitudinal polarized proton beams at √ s = 200−500GeV to gain a deeper insight into the spin structure and dynamics of the proton. These studies provide fundamental tests of Quantum Chromodynamics (QCD). One of the main object...
The observation of the quark transversity distribution requires another soft object sensitive to the quark's transverse spin. Dihadron fragmentation functions represent a convenient tool to analyze partonic spin, which can influence the angular distribution of the two hadrons. In particular, the so-called interference fragmentation functions can be used to probe transversity both in semi-inclus...
m+ photoproduction. If this resonant behavior is to be assigned to a definite state of isotopic spin, then the fact that the peak is more prominent in w+ than m production indicates a T = ~ resonance as suggested by Wilson. ~ However, no very simple explanation of the pion-nucleon interaction in this energy region appears likely in view of -the rather different behavior observed in the three re...
A model for dihadron fragmentation functions is briefly outlined, that describes the fragmentation of a quark in two unpolarized hadrons. The parameters are tuned to the output of the PYTHIA event generator for two-hadron semi-inclusive production in deep inelastic scattering at HERMES. Then predictions are made for the unknown polarized fragmentation function and the related single-spin asymme...
In this talk it is reported on analyses of p → lπn and πp → lln within the handbag approach. It is argued that recent measurements of hard pion production performed by HERMES and CLAS clearly indicate the occurrence of strong contributions from transversely polarized photons. The γ ∗ T → π transitions are described by the transversity GPDs accompanied by twist-3 pion wave functions. The experim...
Separated longitudinal and transverse cross sections for charged pion electroproduction from (1)H, (2)H, and (3)He were measured at Q(2) = 0.4 (GeV/c)(2) for two values of the invariant mass, W = 1.15 GeV and W = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surf...
In this article, we investigate the contribution of the high twist Feynman diagrams to the large-pT pion production cross section in proton-proton collisions and we present the general formulae for the high and leading twist differential cross sections. The pion wave function where two non-trivial Gegenbauer coefficients a2 and a4 have been extracted from the CLEO data, two other pion model wav...
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