Phys.Rev.Lett.106:162303,2011 High precision measurements of the differential cross sections for $\pi^0$
photoproduction at forward angles for two nuclei, $^{12}$C and $^{208}$Pb, have
been performed ...for incident photon energies of 4.9 - 5.5 GeV to extract the
${\pi^0 \to \gamma\gamma}$ decay width. The experiment was done at Jefferson
Lab using the Hall B photon tagger and a high-resolution multichannel
calorimeter. The ${\pi^0 \to \gamma\gamma}$ 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 $\Gamma{(\pi^0 \to
\gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm
eV}$. With the 2.8% total uncertainty, this result is a factor of 2.5 more
precise than the current PDG average of this fundamental quantity and it is
consistent with current theoretical predictions.
A technique is presented for precision measurements of the area densities, density * T, of approximately 5% radiation length carbon and 208Pb targets used in an experiment at Jefferson Laboratory to ...measure the neutral pion radiative width. The precision obtained in the area density for the carbon target is +/- 0.050%, and that obtained for the lead target through an x-ray attenuation technique is +/- 0.43%.
High precision measurements of the differential cross sections for \(\pi^0\) photoproduction at forward angles for two nuclei, \(^{12}\)C and \(^{208}\)Pb, have been performed for incident photon ...energies of 4.9 - 5.5 GeV to extract the \({\pi^0 \to \gamma\gamma}\) decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The \({\pi^0 \to \gamma\gamma}\) 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 \(\Gamma{(\pi^0 \to \gamma\gamma)} = 7.82 \pm 0.14 ~({\rm stat.}) \pm 0.17 ~({\rm syst.}) ~{\rm eV}\). With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current PDG average of this fundamental quantity and it is consistent with current theoretical predictions.
An update on Argonne's AWA Rosing, M.; Chojnacki, E.; Gai, W. ...
Conference Record of the 1991 IEEE Particle Accelerator Conference,
1991
Conference Proceeding
The Argonne Wakefield Accelerator (AWA) is a research facility which should possess unprecedented research capabilities for the study of wake fields and related areas requiring short, intense ...electron bunches. The AWA is designed to produce 100-nC, 14-ps (full width) electron bunches at rep rates up to 30 Hz. Phase-I of the AWA, now under construction, will provide these pulses at 20 MeV for various experiments. Current designs, related research and development, and construction status are presented in this general overview and project update.< >
The principles of wakefield acceleration employing structures (cavity, dielectric) and plasmas as wakefield devices have been successfully demonstrated using the AATF at Argonne National Laboratory. ...Due to the limited driver electron pulse intensity and relatively long pulse length, only modest accelerating gradients were observed. In order to study the wakefield effects in much greater detail and demonstrate the feasibility of a wakefield accelerator for high energy physics, construction of a laser photocathode injector on the existing 20-MeV Chem-Linac to produce very intense and short electron pulses is being considered. The laser photocathode design and computer simulation of its performance are described. The experiments performed using the upgraded facility are discussed.< >
The theory of the anisotropic ferrite wake-field accelerator is solved for the case of any general angular mode {ital m}. The ferrite is driven into saturation by a static magnetic field, resulting ...in the permeability tensor having off-diagonal elements. Expressions for the radial and angular transverse forces are obtained. Finally, we give numerical examples showing that the transverse forces in the anisotropic ferrite wake-field accelerator are reduced as the static saturated magnetization is increased.
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