99 research outputs found

    [Cahier 0199]

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    Do we understand the single-spin asymmetry for pi0pi^0 inclusive production in pp collisions?

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    The cross section data for π0\pi^0 inclusive production in pppp collisions is considered in a rather broad kinematic region in energy s\sqrt{s}, Feynman variable xFx_F and transverse momentum pTp_T. The analysis of these data is done in the perturbative QCD framework at the next-to-leading order. We find that they cannot be correctly described in the entire kinematic domain and this leads us to conclude that the single-spin asymmetry, ANA_N for this process, observed several years ago at FNAL by the experiment E704 and the recent result obtained at BNL-RHIC by STAR, are two different phenomena. This suggests that STAR data probes a genuine leading-twist QCD single-spin asymmetry for the first time and finds a large effect.Comment: text modified, version to be published in Eur. Phys. J. C, 6 pages, 5 figure

    Electromagnetic form factors of the baryon octet in the perturbative chiral quark model

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    We apply the perturbative chiral quark model at one loop to analyze the electromagnetic form factors of the baryon octet. The analytic expressions for baryon form factors, which are given in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling, strong pion-nucleon form factor), and the numerical results for baryon magnetic moments, charge and magnetic radii are presented. Our results are in good agreement with experimental data.Comment: 15 pages, 6 figures, to be published in Eur. Phys. J.

    The statistical parton distributions: status and prospects

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    New experimental results on polarized structure functions, cross sections for e±pe^{\pm}p neutral and charge current reactions and ν\nu (νˉ\bar{\nu}) charge current on isoscalar targets are compared with predictions using the statistical parton distributions, which were previously determined. New data on cross sections for Drell-Yan processes, single jet in ppˉp\bar{p} collisions and inclusive π0\pi^0 production in pppp collisions are also compared with predictions from this theoretical approach. The good agreement which we find with all these tests against experiment, strenghtens our opinion on the relevance of the role of quantum statistics for parton distributions. We will also discuss the prospects of this physical framework.Comment: 34 pages, 23 figures, references and figures adde

    Reconclining phi radiative decays with other data for a0(980), fo(980), pi-pi -> KK and pi-pi -> eta-eta

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    Data for phi -> gamma (eta-pizero) are analysed using the KK loop model and compared with parameters of a0(980) derived from Crystal Barrel data. The eta-pi mass spectrum agrees closely and the absolute normalisation lies just within errors. However, BES parameters for fo(980) predict a normalisation for phi -> gamma (pizero-pizero) at least a factor 2 lower than is observed. This discrepancy may be eliminated by including constructive interference between fo(980) and sigma. The magnitude required for sigma -> KK is consistent with data on pi-pi -> KK. A dispersion relation analysis by Buttiker, Descotes-Genon and Moussallam of pi-pi -> KK leads to a similar conclusion. Data on pi-pi -> eta-eta also require decays of sigma to eta-eta. Four sets of pi-pi -> KK data all require a small but definite fo(1370) signal.Comment: 21 pages, 11 figures, Small rearrangement of reference

    Probing the QCD equation of state with thermal photons in nucleus-nucleus collisions at RHIC

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    Thermal photon production at mid-rapidity in Au+Au reactions at sNN\sqrt{s_{NN}} = 200 GeV is studied in the framework of a 2D+1 hydrodynamical model that describes efficiently the bulk identified hadron spectra at RHIC. The combined thermal plus NLO pQCD photon spectrum is in good agreement with the yields measured by the PHENIX experiment for all Au+Au centralities. Within our model, we demonstrate that the correlation of the thermal photon slopes with the charged hadron multiplicity in each centrality bin provides direct empirical information on the underlying degrees of freedom and on the equation of state, s(T)/T3s(T)/T^3, of the strongly interacting matter.Comment: Version to appear in EPJ-C (extended discussion and refs. and a few corrections

    Pensions to Indian fighters

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    25-2Select Committee on Extending the Provisions of the Pension Law of 1832 to Troops Employed Against the Indians.Report on Pensions to Indian Fighters. [333] Recommends extension of laws to the period 1783 to 1795.1838-1
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