RESUMO
High precision measurements of the differential cross sections for π0 photoproduction at forward angles for two nuclei, 12C and 208Pb, have been performed for incident photon energies of 4.9-5.5 GeV to extract the π0âγγ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0âγγ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0âγγ)=7.82±0.14(stat)±0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.
RESUMO
In 27 of 47 patients with Sneddon's syndrome (33 females, 14 males age 40 years) enzyme immunoassay has detected IgG-antibodies to prothrombin (aPT)--one of cofactor proteins responsible for binding of antiphospholipid antibodies (aPL) to phospholipids. Other aPL were also found: antibodies to cardiolipin (aCL), lupus anticoagulant (LA) in 14 and 27 patients, respectively. 37 (79%) patients had at least one of the studied aPL suggesting that such patients belong to patients with primary antiphospholipid syndrome. A correlation exists between aPT and LA: LA is detectable in 67% of aPT-positive patients compared to 45% of aPT-negative patients (p < 0.05). This is in agreement with the fact that prothrombin is a cofactor for most aPL registered as LA. Comparison of two subgroups of aPL patients different by dominant antigenic specificity (18 patients with aPT but free of ACL and 6 patients with aCP but free of aPT) demonstrated that the latter developed disorders of cerebral circulation, head ache, dementia and renal syndrome less frequently. aPT in Sneddon's syndrome seems to be a marker of comparatively low risk of thrombosis and less severe course of the disease.
