GRSV parton densities revisited

An updated next-to-leading order (NLO) QCD analysis of all presently available longitudinally polarized deep-inelastic scattering (DIS) data is presented in the framework of the radiative parton model.Comment: 3 pages, LaTeX, 2 eps figures, uses amssymb, npb (included), and epsfig styles; Contribution to the Proceedings of the 7th International Workshop on `Deep Inelastic Scattering and QCD (DIS99)' [Nucl. Phys. B (Proc. Suppl.)], Zeuthen, Germany, April 199

A new approach to calculate the gluon polarization

We derive the Leading-Order master equation to extract the polarized gluon distribution G(x;Q^2) = x \deltag(x;Q^2) from polarized proton structure function, g1p(x;Q^2). By using a Laplace-transform technique, we solve the master equation and derive the polarized gluon distribution inside the proton. The test of accuracy which are based on our calculations with two different methods confirms that we achieve to the correct solution for the polarized gluon distribution. We show that accurate experimental knowledge of g1p(x;Q^2) in a region of Bjorken x and Q^2, is all that is needed to determine the polarized gluon distribution in that region. Therefore, to determine the gluon polarization \deltag /g,we only need to have accurate experimental data on un-polarized and polarized structure functions (F2p (x;Q^2) and g1p(x;Q^2)).Comment: 12 pages, 5 figure

Non-perturbative structure of the polarized nucleon sea

We investigate the flavour and quark-antiquark structure of the polarized nucleon by calculating the parton distribution functions of the nucleon sea using the meson cloud model. We find that the SU(2) flavor symmetry in the light antiquark sea and quark-antiquark symmetry in the strange quark sea are broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar. The polarization of the strange sea is found to be positive, which is in contradiction to previous analyses. We predict a much larger quark-antiquark asymmetry in the polarized strange quark sea than that in the unpolarized strange quark sea. Our results for both polarized light quark sea and polarized strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure

Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data

We present a combined next-to-leading order QCD analysis to data on both inclusive and semi-inclusive polarized deep inelastic scattering asymmetries. Performing NLO QCD global fits with different sets of observables, we evaluate the impact of the very recent semi-inclusive results presented by SMC in the extraction of NLO polarized parton distributions.Comment: 22 pages, 4 figures include

Determination of gluon polarization from deep inelastic scattering and collider data

We investigate impact of $\pi^0$-production data at Relativistic Heavy Ion Collider (RHIC) and future E07-011 experiment for the structure function $g_1$ of the deuteron at the Thomas Jefferson National Accelerator Facility (JLab) on studies of nucleonic spin structure, especially on the polarized gluon distribution function. By global analyses of polarized lepton-nucleon scattering and the $\pi^0$-production data, polarized parton distribution functions are determined and their uncertainties are estimated by the Hessian method. Two types of the gluon distribution function are investigated. One is a positive distribution and the other is a node-type distribution which changes sign at $x \sim 0.1$. Although the RHIC $\pi^0$ data seem to favor the node type for $\Delta g(x)$, it is difficult to determine a precise functional form from the current data. However, it is interesting to find that the gluon distribution $\Delta g(x)$ is positive at large $x$ ($>0.2$) due to constraints from the scaling violation in $g_1$ and RHIC $\pi^0$ data. The JLab-E07-011 measurements for $g_1^d$ should be also able to reduce the gluon uncertainty, and the reduction is comparable to the one by RUN-5 $\pi^0$-production data at RHIC. The reduction is caused by the error correlation between polarized antiquark and gluon distributions and by a next-to-leading-order (NLO) gluonic effect in the structure function $g_1^d$. We find that the JLab-E07-011 data are accurate enough to probe the NLO gluonic term in $g_1$. Both RHIC and JLab data contribute to better determination of the polarized gluon distribution in addition to improvement on polarized quark and antiquark distributions.Comment: 11 pages, 9 eps figures, To be published in Nuclear Physics B. AAC08 FORTRAN package is available at the web site http://spin.riken.bnl.gov/aac

Proton Structure Functions from Chiral Dynamics and QCD Constraints

The spin fractions and deep inelastic structure functions of the proton are analyzed using chiral field theory involving Goldstone bosons. A detailed comparison with recent chiral models sheds light on their successful description of the spin fractions of the proton as being due to neglecting helicity non-flip chiral transitions. This approximation is valid for zero mass quarks but not for constituent quarks. Since the chiral spin fraction models with the pure spin-flip approximation reproduce the measured spin fractions of the proton, axialvector constituent-quark-Goldstone boson coupling is found to be inconsistent with the proton spin data. Initial quark valence distributions are then constructed using quark counting constraints at Bjorken $x \to 1$ and Regge behavior at $x \to 0$. Sea quark distributions predicted by chiral field theory on this basis have correct order of magnitude and shape. The spin fractions agree with the data.Comment: 30 pages, 2 tables, 10 figure-ps files, LaTex. Accepted by Int. J. Mod. Phys. A. More details added on polarized chiral splitting function

Can the polarization of the strange quarks in the proton be positive ?

Recently, the HERMES Collaboration at DESY, using a leading order QCD analysis of their data on semi-inclusive deep inelastic production of charged hadrons, reported a marginally positive polarization for the strange quarks in the proton. We argue that a non-negative polarization is almost impossible.Comment: 6 pages, latex, minor changes in the discussion after Eq. (9

Intrinsic susceptibility and bond defects in the novel 2D frustrated antiferromagnet Ba2_{2}Sn2_{2}ZnCr7p_{7p}Ga10−7p_{10-7p}O22_{22}

We present microscopic and macroscopic magnetic properties of the highly frustrated antiferromagnet Ba$_{2}$Sn$_{2}$ZnCr$_{7p}$Ga$_{10-7p}$O$_{22}$, respectively probed with NMR and SQUID experiments. The $T$-variation of the intrinsic susceptibility of the Cr$^{3+}$ frustrated kagom\'{e} bilayer, $\chi_{kag}$, displays a maximum around 45 K. The dilution of the magnetic lattice has been studied in detail for $0.29 \leq p \leq0.97$. Novel dilution independent defects, likely related with magnetic bond disorder, are evidenced and discussed. We compare our results to SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$. Both bond defects and spin vacancies do not affect the average susceptibility of the kagom\'{e} bilayers.Comment: Published in Phys. Rev. Lett. 92, 217202 (2004). Only minor changes as compared to previous version. 4 pages, 4 figure

Critical behavior of 2 and 3 dimensional ferro- and antiferromagnetic spin ice systems in the framework of the Effective Field Renormalization Group technique

In this work we generalize and subsequently apply the Effective Field Renormalization Group technique to the problem of ferro- and antiferromagnetically coupled Ising spins with local anisotropy axes in geometrically frustrated geometries (kagome and pyrochlore lattices). In this framework, we calculate the various ground states of these systems and the corresponding critical points. Excellent agreement is found with exact and Monte Carlo results. The effects of frustration are discussed. As pointed out by other authors, it turns out that the spin ice model can be exactly mapped to the standard Ising model but with effective interactions of the opposite sign to those in the original Hamiltonian. Therefore, the ferromagnetic spin ice is frustrated, and does not order. Antiferromagnetic spin ice (in both 2 and 3 dimensions), is found to undergo a transition to a long range ordered state. The thermal and magnetic critical exponents for this transition are calculated. It is found that the thermal exponent is that of the Ising universality class, whereas the magnetic critical exponent is different, as expected from the fact that the Zeeman term has a different symmetry in these systems. In addition, the recently introduced Generalized Constant Coupling method is also applied to the calculation of the critical points and ground state configurations. Again, a very good agreement is found with both exact, Monte Carlo, and renormalization group calculations for the critical points. Incidentally, we show that the generalized constant coupling approach can be regarded as the lowest order limit of the EFRG technique, in which correlations outside a frustrated unit are neglected, and scaling is substituted by strict equality of the thermodynamic quantities.Comment: 28 pages, 9 figures, RevTeX 4 Some minor changes in the conclussions. One reference adde

Production of J/ψJ/\psi-pairs at HERA-N⃗\vec{{\rm N}}

The production of $J/\psi$-pairs as a possible measure of the polarized gluon distribution $\Delta G(x)$ is studied for proton--nucleon collisions at \sqrt{s} =40\;\mbox{GeV}^2 (HERA-$\vec{{\rm N}}$). Possibilities of reconstructing the helicity state of at least one of the $J/\psi$'s are critically reviewed. The observation of production asymmetries in the single polarized mode of HERA-$\vec{{\rm N}}$ is found to be not feasible.Comment: 8 pages, LATeX, 3 figures availabe as .uu-fil