55 research outputs found

    The Spin-Dependent Structure Functions of Nuclei in the Meson-Nucleon Theory

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    A theoretical approach to the investigation of spin-dependent structure functions in deep inelastic scattering of polarized leptons off polarized nuclei, based on the effective meson-nucleon theory and operator product expansion method, is proposed and applied to deuteron and 3He^3He. The explicit forms of the moments of the deuteron and 3He^3He spin-dependent structure functions are found and numerical estimates of the influence of nuclear structure effects are presented.Comment: 42 pages revtex, 7 postscript figures available from above e-mail upon request. Perugia preprint DFUPG 92/9

    Study of the Process e+ e- --> omega pi0 --> pi0 pi0 gamma in c.m. Energy Range 920--1380 MeV at CMD-2

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    The cross section of the process e+ e- --> omega pi0 --> pi0 pi0 gamma has been measured in the c.m. energy range 920-1380 MeV with the CMD-2 detector. Its energy dependence is well described by the interference of the rho(770) and rho'(1450) mesons decaying to omega pi0. Upper limits for the cross sections of the direct processes e+ e- --> pi0 pi0 gamma, eta pi0 gamma have been set.Comment: Accepted for publication in PL

    Light-flavor sea-quark distributions in the nucleon in the SU(3) chiral quark soliton model (I) -- phenomenological predictions --

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    Theoretical predictions are given for the light-flavor sea-quark distributions including the strange quark ones on the basis of the flavor SU(3) version of the chiral quark soliton model. Careful account is taken here of the SU(3) symmetry breaking effects due to the mass difference between the strange and nonstrange quarks. This effective mass difference Δms\Delta m_s between the strange and nonstrange quarks is the only one parameter necessary for the flavor SU(3) generalization of the model. A particular emphasis of study is put on the {\it light-flavor sea-quark asymmetry} as exemplified by the observables dˉ(x)uˉ(x),dˉ(x)/uˉ(x),Δuˉ(x)Δdˉ(x)\bar{d} (x) - \bar{u} (x), \bar{d} (x) / \bar{u} (x), \Delta \bar{u} (x) - \Delta \bar{d} (x) as well as on the {\it particle-antiparticle asymmetry} of the strange quark distributions represented by s(x)sˉ(x),s(x)/sˉ(x),Δs(x)Δsˉ(x)s (x) - \bar{s} (x), s (x) / \bar{s} (x), \Delta s (x) - \Delta \bar{s} (x) etc. As for the unpolarized sea-quark distributions, the predictions of the model seem qualitatively consistent with the available phenomenological information provided by the NMC data for dˉ(x)uˉ(x)\bar{d} (x) - \bar{u} (x), the E866 data for dˉ(x)/uˉ(x)\bar{d} (x) / \bar{u} (x), the CCFR data and Barone et al.'s fit for s(x)/sˉ(x)s (x) / \bar{s} (x) etc. The model is shown to give several unique predictions also for the spin-dependent sea-quark distribution, such that Δs(x)Δsˉ(x)0\Delta s (x) \ll \Delta \bar{s}(x) \lesssim 0 and Δdˉ(x)<0<Δuˉ(x)\Delta \bar{d}(x) < 0 < \Delta \bar{u}(x), although the verification of these predictions must await more elaborate experimental investigations in the near future.Comment: 36 pages, 20 EPS figures. The revised version accepted for publication in Phys. Rev. D. The title has been changed, and the body of the paper has been divided into two pieces, i.e.. the present one which discusses the main phenomenological predictions of the model and the other one which describes the detailed formulation of the flavor SU(3) chiral quark soliton model to predict light-flavor quark and antiquark distribution functions in the nucleo

    Search for CP violation in D0 and D+ decays

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    A high statistics sample of photoproduced charm particles from the FOCUS (E831) experiment at Fermilab has been used to search for CP violation in the Cabibbo suppressed decay modes D+ to K-K+pi+, D0 to K-K+ and D0 to pi-pi+. We have measured the following CP asymmetry parameters: A_CP(K-K+pi+) = +0.006 +/- 0.011 +/- 0.005, A_CP(K-K+) = -0.001 +/- 0.022 +/- 0.015 and A_CP(pi-pi+) = +0.048 +/- 0.039 +/- 0.025 where the first error is statistical and the second error is systematic. These asymmetries are consistent with zero with smaller errors than previous measurements.Comment: 12 pages, 4 figure

    Light flavor asymmetry of nucleon sea

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    The light flavor antiquark distributions of the nucleon sea are calculated in the effective chiral quark model and compared with experimental results. The contributions of the flavor-symmetric sea-quark distributions and the nuclear EMC effect are taken into account to obtain the ratio of Drell-Yan cross sections σpD/2σpp\sigma^{\mathrm{pD}}/2\sigma^{\mathrm{pp}}, which can match well with the results measured in the FermiLab E866/NuSea experiment. The calculated results also match the measured dˉ(x)uˉ(x)\bar{d}(x)-\bar{u}(x) from different experiments, but unmatch the behavior of dˉ(x)/uˉ(x)\bar{d}(x)/\bar{u}(x) derived indirectly from the measurable quantity σpD/2σpp\sigma^{\mathrm{pD}}/2\sigma^{\mathrm{pp}} by the FermiLab E866/NuSea Collaboration at large xx. We suggest to measure again dˉ(x)/uˉ(x)\bar{d}(x)/\bar{u}(x) at large xx from precision experiments with careful experimental data treatment. We also propose an alternative procedure for experimental data treatment.Comment: 10 pages, 8 figures, final version to appear in EPJ

    Heavy quarkonium: progress, puzzles, and opportunities

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    A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the BB-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newly-found quarkonium-like states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K. Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D. Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A. Petrov, P. Robbe, A. Vair

    First observation of the ϕπ+πγ\phi\to\pi^+\pi^-\gamma decay

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    Radiative decays of the ϕ\phi meson have been studied using a data sample of about 20 million ϕ\phi decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From selected e+eπ+πγe^+e^-\to\pi^{+}\pi^{-}\gamma events the ϕπ+πγ\phi\to\pi^{+}\pi^{-}\gamma decay has been observed for the first time. \par Under the assumption that the intermediate f0(980)γf_{0}(980)\gamma state dominates in the ϕπ+πγ\phi \to \pi^+\pi^-\gamma decay, the corresponding branching ratio is Br(ϕf0(980)γ)=(1.93±0.46±0.50)×104Br(\phi\to f_{0}(980)\gamma)=(1.93\pm 0.46\pm 0.50)\times10^{-4}. \par Selected e+eμ+μγe^+e^-\to\mu^+\mu^-\gamma events were used to obtain Br(ϕμ+μγ)=(1.43±0.45±0.14)×105Br(\phi\to\mu^+\mu^-\gamma) =(1.43\pm 0.45\pm 0.14)\times10^{-5} for Eγ>20E_{\gamma}>20 MeV. \par Using the same data sample, upper limits at 90% CL have been obtained for the C-violating decay of the ϕ\phi: Br(ϕργ)<1.2×105Br(\phi\to\rho\gamma) < 1.2\times10^{-5}; and for the P- and CP-violating decay of the η\eta: \par Br(ηπ+π)<3.3×104Br(\eta\to\pi^+\pi^-) < 3.3\times10^{-4}.Comment: 16 pages, 10 figures, Submitted to Phys. Lett.

    Quark Model and multiquark system

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    The discovery of many particles, especially in the 50's, when the firsts accelerators appeared, caused the searching for a model that would describe in a simple form the whole of known particles. The Quark Model, based in the mathematical structures of group theory, provided in the beginning of the 60's a simplified description of hadronic matter already known, proposing that three particles, called quarks, would originate all the observed hadrons. This model was able to preview the existence of particles that were later detected, confirming its consistency. Extensions of the Quark Model were made in the beginning of the 70's, focusing in describing observed particles that were excited states of the fundamental particles and others that presented new quantum numbers (flavors). Recently, exotic states as tetraquarks and pentaquarks types, also called multiquarks systems, previewed by the model, were observed, what renewed the interest in the way as quarks are confined inside the hadrons. In this article we present a review of the Quark Model and a discussion on the new exotic states.Comment: In Portugues

    New insights into the genetic etiology of Alzheimer's disease and related dementias

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    Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele
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