928 resultados para baryon asymmetry


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The first experimental evidence for one of the six predicted baryon states which contain two valence charmed quarks-the doubly charmed baryons. As such, there were many predictions of the masses and other properties of these states. The properties of doubly charmed baryons provide a new window into the structure of baryonic matter.

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We perform a careful study on the effect of the Pauli blocking to the light polarized antiquark structure of the proton sea. We develop the formal expressions for the polarized antiquark distributions, highlighting the role played by quark statistics and the vacuum structure. The ratio involving the polarized antiquarks is calculated. In particular, it is found that Δd̄(x)/Δū(x) should be negative and x independent.

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We present general explicit expressions for a shell-model calculation of the vector hypernuclear parameter in nonmesonic weak decay. We use a widely accepted effective coupling Hamiltonian involving the exchange of the complete pseudoscalar and vector meson octets (π, η, K, ρ, ω, K*). In contrast to the approximated formula widely used in the literature, we correctly treat the contribution of transitions originated from single-proton states beyond the s-shell. Exact and simple analytical expressions are obtained for the particular cases of Λ 5He and Λ 12C, within the one-pion-exchange model. Numerical computations of the asymmetry parameter, aΛ, are presented. Our results show a qualitative agreement with other theoretical estimates but also a contradiction with recent experimental determinations. Our simple analytical formulas provide a guide in searching the origin of such discrepancies, and they will be useful for helping to solve the hypernuclear weak decay puzzle.

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We propose a phenomenological approach based in the meson cloud model to obtain the strange quark structure function inside a kaon, considering the strange quark asymmetry inside the nucleon. © 2009 American Institute of Physics.

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A measurement of the lepton charge asymmetry in inclusive pp → WX production at √s = 7TeV is presented based on data recorded by the CMS detector at the LHC and corresponding to an integrated luminosity of 36 pb -1. This high precision measurement of the lepton charge asymmetry, performed in both the W → eν and W → μν channels, provides new insights into parton distribution functions. Copyright CERN.

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We present a measurement of the semileptonic mixing asymmetry for B0 mesons, asld, using two independent decay channels: B0→μ +D -X, with D -→K +π -π -; and B0→μ +D *-X, with D * -→D ̄0π -, D ̄0→ K +π - (and charge conjugate processes). We use a data sample corresponding to 10.4fb -1 of pp̄ collisions at √s=1.96TeV, collected with the D0 experiment at the Fermilab Tevatron collider. We extract the charge asymmetries in these two channels as a function of the visible proper decay length of the B0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final measurement combines four signal visible proper decay length regions for each channel, yielding asld=[0.68±0.45(stat)±0.14(syst)]%. This is the single most precise measurement of this parameter, with uncertainties smaller than the current world average of B factory measurements. © 2012 American Physical Society.

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A measurement of the forward-backward asymmetry (AFB) of Drell-Yan lepton pairs in pp collisions at s=7TeV is presented. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 5fb-1. The asymmetry is measured as a function of dilepton mass and rapidity in the dielectron and dimuon channels. Combined results from the two channels are presented, and are compared with the standard model predictions. The AFB measurement in the dimuon channel and the combination of the two channels are the first such results obtained at a hadron collider. The measured asymmetries are consistent with the standard model predictions. © 2012 CERN.

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This study aimed to determine whether: i) tethered-swimming can be used to identify the asymmetry during front crawl swimming style; ii) swimmers that perform unilateral breathing present greater asymmetry in comparison to others that use bilateral breathing; iii) swimmers of best performance present smaller asymmetry than their counterparts; iv) repeated front crawl swimming movements influence body asymmetry. 18 swimmers were assessed for propulsive force parameters (peak force, mean force, impulse and rate of force development) during a maximal front crawl tethered-swimming test lasting 2 min. A factorial analysis showed that propulsive forces decreased at the beginning, intermediate and end of the test (p<0.05), but the asymmetries were not changed at different instants of the test. When breathing preference (uni- or bilateral) was analyzed, asymmetry remained unchanged in all force parameters (p>0.05). When performance was considered (below or above mean group time), a larger asymmetry was found in the sub-group of lower performance in comparison to those of best performance (p<0.05). Therefore, the asymmetries of the propulsive forces can be detected using tethered-swimming. The propulsive forces decreased during the test but asymmetries did not change under testing conditions. Although breathing preference did not influence asymmetry, swimmers with best performance were less asymmetric than their counterparts. © Georg Thieme Verlag KG Stuttgart New York.

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PURPOSE

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Epidermoid cysts are rare benign tumors that are derived from the development of abnormally situated ectodermal tissue and are often an incidental finding. They are usually diagnosed between 15 and 50 years of age, with both sexes equally affected. In epidermoid cyst management, complete excision is the therapy of choice. The authors reported a case of a 24-year-old man with an epidermoid cyst located on the left side of the face, on the region of mandibular body, which was treated by complete surgical excision. The patient has been followed up for 2 years without signs of recurrence. Copyright © 2013 by Mutaz B. Habal, MD.

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Sanitary and phytosanitary matters have acquired greater significance in the region's trade, as reflected in the significant number of complaints brought before the various dispute settlement mechanisms pertaining to the regional integration schemes. This may be attributed to the importance of the Latin American countries in world agricultural trade and to different phytosanitary and zoosanitary standards required by each. Given the multiplication of bilateral and plurilateral agreements in Latin America and the Caribbean, convergence on the sanitary standards required under such accords is crucial for the trade integration of a region that is an agro-exporter par excellence. Convergence is essential to facilitate market access and expedite trade flows. This bulletin assesses convergence of standards in the bilateral and plurilateral trade agreements signed by the countries of the region, the treatment afforded to the principles contained in the World Trade Organization (WTO) Agreement on the Application of Sanitary and Phytosanitary Measures (SPS Agreement) and the progress the region has made relative to that Agreement.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)