Two-spin Asymmetry Research Articles

Two-spin asymmetry forψ′photoproduction with the color-octet mechanism

We study the photoproduction of ${\ensuremath{\psi}}^{\ensuremath{'}}$ in the forward regions in polarized $\ensuremath{\gamma}p$ collisions at relevant (DESY) HERA energies. We find that this reaction is very effective to test the color-octet mechanism which is based on the NRQCD factorization formalism. Furthermore we find that the value of the NRQCD matrix elements can be severely constrained by measuring the two-spin asymmetry, though the process depends on the polarized gluon distribution $\ensuremath{\Delta}g(x).$

Contribution of Sea Quarks and Gluons to the Proton Spin

Contributions of sea quark and gluon spins to the proton spin in Drell-Jahn processes and direct production of photons in proton-proton and proton-antiproton collisions are studied in the present work. Analytical expressions for two-spin asymmetries \(A_{LL}^{DY}\) and \(A_{LL}^{\gamma }\) are derived. In both processes, these asymmetries are studied and analyzed as functions of the kinematic variables τ, xT, and xF. Measurements of two-spin asymmetries \(A_{LL}^{DY}\) and \(A_{LL}^{\gamma }\) make it possible to determine the individual contributions of sea quark and gluon spins to the proton spin.

Spin Effects in a Collision of Polarized Protons

The one- and two-spin asymmetries in a collision of polarized protons pp → (γ*,z) + X are studied in the present work within the framework of the quantum chromodynamics and the electroweak interaction. We use the method of helical amplitudes. Analytical expressions for one-spin A L and two-spin A LL asymmetries are derived and their dependences on the transverse momentum of the lepton pair are investigated for three values of invariant mass of the lepton pair. The results obtained allow the spin structure of the proton to be investigated.

Two-spin asymmetries for χ productions at RHIC

Hadroproductions of charmonium and bottomonium χ J in polarized pp collisions at RHIC energies are studied. Two-spin asymmetries A LL χ J ( pp) for these reactions allow one to determine polarized gluon distributions in a proton.

NN scattering amplitudes from 90 degrees c.m. into the Landshoff region.

It is likely that nucleon-nucleon elastic scattering at large, fixed {vert_bar}{ital t}{vert_bar} can be described by the Landshoff three-gluon exchange mechanism. However, a phenomenological normalization rules out the possibility that the Landshoff mechanism is involved in producing the sharp structure of the two-spin asymmetry {ital A}{sub {ital N}{ital N}}, observed experimentally at {ital p}{sub lab}{approx}13 GeV/{ital c}, or that it is involved in producing the oscillations observed in {ital d}{sigma}/{ital dt} at 90{degree} in the c.m. frame. A simplified analysis of the 90{degree} amplitudes shows that it is likely that some subasymptotic mechanism interfering with the dominant quark-interchange amplitudes is responsible for both these intriguing phenomena. While the large-angle data show evidence for amplitudes approaching those of exclusive QCD, the Landshoff region in {ital pp}{r_arrow}{ital pp} shows no evidence for Sudhakov suppression nor evidence for effects associated with the running of the QCD coupling. We suggest that a measurement of the energy depenence of the polarization asymmetry at large {vert_bar}{minus}{ital t}{vert_bar} can greatly enlarge the understanding of exclusive QCD.

Quantum-chromodynamic investigation of polarization effects in inclusive photoproduction of supersymmetric particles

A quantum-chromodynamic study of polarization effects in inclusive photoproduction of supersymmetric particles is reported. The two-spin asymmetries are investigated in detail as functions of transverse momentum PT, effective scalar-pair mass Q2, and scattering angle. It is shown that study of spin asymmetry can yield information on the masses of scalar quarks.

Effects of the large gluon polarization on xg1d( x) and [formula omitted] productions at polarized ep and pp collisions

The recent SMC data of xg 1 d ( x) are reproduced with the large polarized gluons. To study further the polarized gluon distribution in a proton, we calculate the spin-dependent differential cross section for J ψ leptoproductions and the two-spin asymmetry for J ψ hadroproductions. Its experimental implication is discussed.

Two-spin asymmetry in $$\mathop p\limits^{( - )} p$$ reactions and spin-dependent parton distributions

The two-spin asymmetries\(A_{LL}^{\pi ^0 } (\mathop p\limits^{( - )} p)\) and\(A_{LL}^\gamma (\mathop p\limits^{( - )} p)\) are calculated in a new model incorporating the nonrelativistic quark model and the parton model which interprets well EMCg1p(x) data. The model can reproduce the experimental data for inclusive π0 rather well.

Tests and signatures of polarized structure functions

We study various processes in polarized ep and pp experiments which might serve to delineate the polarized parton distributions of the proton, especially the polarized gluon distribution ΔG. Among these we take a closer look at the two-spin asymmetry in inclusive hadronic π 0 production and at the production of polarized prompt photons in collisions of unpolarized high energy protons with polarized target protons. Finally we show how it might be possible to uncover the polarized parton distributions of the photon.

Do present data on the two-spin asymmetry ALL pi 0(p(-)p) exclude a large gluon polarization in the proton?

We study carefully the two-spin asymmetry ${A}_{\mathrm{LL}}^{{\ensuremath{\pi}}^{0}}({(\ensuremath{-})}{p}p)$ for inclusive ${\ensuremath{\pi}}^{0}$ production in collisions of longitudinally polarized (anti)protons with longitudinally polarized protons. It is shown that the recent Fermilab data for ${A}_{\mathrm{LL}}^{{\ensuremath{\pi}}^{0}}({(\ensuremath{-})}{p}p)$ do not exclude a large polarization of gluons in the proton and are consistent with most proton spin scenarios suggested up to now. In order to study the reliability of perturbative QCD predictions for ${A}_{\mathrm{LL}}^{{\ensuremath{\pi}}^{0}}({(\ensuremath{-})}{p}p)$ we investigate the influence of intrinsic ${k}_{T}$ smearing on the asymmetry.