We consider the possibility of a direct determination of the polarized gluon density in the proton using charm production with polarized beams at HERA. We study total cross sections and distributions at leading order using different parametrizations of the polarized gluon density. We conclude that charm photoproduction data can be used to constrain the polarized gluon density in the proton if a...

We show that measurements of semi-inclusive π asymmetries on p and n with polarized and unpolarized target and beams allow, without any knowledge of the polarized parton densities 1) to test independent fragmentation and SU(2) symmetry for the polarized sea, and 2) to determine separately the polarized strange and valence quarks densities, and the ratio of the fragmentation functions D +π s /D ...

We review the nucleon's polarized structure functions from the viewpoint of gauge invariant, nonlocal light-cone operators in QCD. We discuss a systematic treatment of the polarized structure functions and the corresponding parton distribution functions. We also address a question of what information on the structure of Nature will be obtained from the future polarized experiments. From this po...

We study photoproduction of jets and single-inclusive hadrons in a polarized ep collider mode of HERA at √ s ≈ 300 GeV, examining the sensitivity of the cross sections and their asymmetries to the proton’s polarized gluon distribution and to the completely unknown parton distributions of polarized photons. We also present for the first time the NLO corrections to the direct part of polarized si...

We present estimates of possible data on spin-dependent asymmetries in inclusive scattering of high energy polarized electrons by high energy polarized protons at HERA, including statistical errors, and discuss systematic uncertainties. We show that these data would shed light on the small x behaviour of the polarized structure function g 1 , and would reduce substantially the uncertainty on th...

We report global analysis results for polarized parton distribution functions in the nucleon. The optimum distributions are determined by using spin asymmetry data on polarized lepton scattering on proton, neutron, and deuteron. Their uncertainties are estimated by the Hessian method. As a result, polarized quark distributions are relatively well determined, whereas the polarized gluon distribu...

Recent developments of the two MC-generators Sphinx and Pepsi are discussed. In Sphinx the process of polarized photo production was included to simulate the potential of a polarized HERA to measure the photon structure function. In Pepsi the CC polarized cross sections on tree level have been added together with the electroweak corrections to simulate their effect on CC signals proposed for a ...

We show that measurements of semi-inclusive π asymmetries on p and n with polarized and unpolarized target and beams allow, without any knowledge of the polarized parton densities 1) to test independent fragmentation and SU(2) symmetry for the polarized sea, and 2) to determine separately the polarized strange and valence quarks densities, and the ratio of the fragmentation functions D +π s /D ...

The recent high precision SMC data on polarized μp scatterings have again confirmed that very little of the proton spin is carried by quarks. To unravel the mystery of the proton spin structure, it is quite important to know the behavior of the polarized gluon distribution. By using the positivity condition of distribution functions together with the unpolarized and polarized experimental data,...

The noncanonical wnt/planar cell polarity (PCP) pathway [1] regulates the mediolaterally (planarly) polarized cell protrusive activity and intercalation that drives the convergent extension movements of vertebrate gastrulation [2], yet the underlying mechanism is unknown. We report that perturbing expression of Xenopus PCP genes, Strabismus (Xstbm), Frizzled (Xfz7), and Prickle (Xpk), disrupts ...