S=0 pseudoscalar meson photoproduction from the proton

Many measurements of pseudoscalar mesons with S = 0 photoproduced on the proton have been made recently. These new data are particularly useful in theoretical investigations of nucleon resonances. How the new data from various labs complement each other and help fill in the gaps in the world data set is disscussed, with a glance at measurements to be made in the near future. Some theoretical techniques used to explain the data are briefly described.Comment: 6 pages, 3 figures, Nstar workshop proceeding to be published with World Scientifi

CLAS+FROST: new generation of photoproduction experiments at Jefferson Lab

A large part of the experimental program in Hall B of the Jefferson Lab is dedicated to baryon spectroscopy. Photoproduction experiments are essential part of this program. CEBAF Large Acceptance Spectrometer (CLAS) and availability of circularly and linearly polarized tagged photon beams provide unique conditions for this type of experiments. Recent addition of the Frozen Spin Target (FROST) gives a remarkable opportunity to measure double and triple polarization observables for different pseudo-scalar meson photoproduction processes. For the first time, a complete or nearly complete experiment becomes possible and will allow model independent extraction of the reaction amplitude. An overview of the experiment and its current status is presented.Comment: 6 pages, 7 figures. Invited paper NSTAR 2009 conferenc

Lewis and Clarke in the Caves: Art and Platonic Worlds in \u3ci\u3ePiranesi\u3c/i\u3e

Susanna Clarke’s 2020 novel Piranesi openly acknowledges its debt to C.S. Lewis’s Chronicles of Narnia. Piranesi’s imagined world, the House, is modeled after Charn from The Magician’s Nephew in the Chronicles: both feature uninhabited and apparently endless series of halls. Clarke’s world is not Lewis’s, however. As she puts it, “I always liked Charn better than Lewis liked Charn,” and the House in Piranesi is not a cold, dead shell, but the beloved home of the novel’s eponymous narrator. Piranesi’s handling of the relationship between models (like Charn) and their differing imitations (like Piranesi\u27s House) is important because a theme both Lewis and Clarke explore is the relationship between Platonic ideals and their imperfect copies. Following Plato’s Republic, with its hierarchy of intelligible, physical, and mimetic-artistic worlds, both Piranesi and the Chronicles of Narnia are multi-world stories in which one world echoes another. But just as Clarke adapts Charn into the more positively-connotated House, she also adapts Lewis’s Platonism. Unlike the Chronicles, which feature a Neoplatonic heaven influenced by Plato’s description of the intelligible world, Clarke’s novel features a narrator who questions the existence of any higher knowledge at all, and focuses instead on a critique of the relationship between Plato’s physical and artistic worlds. In contrast to Plato, Clarke presents artistic work not as an inferior imitation of the physical world, but as an interpenetrating influence on it. By exploring art’s influence as it pays fond but dissenting homage to the inspiration of Lewis’s work, Piranesi encourages us to reflect on what, during a time of critical reassessment and canon revision, we owe to the stories that have made us. While Piranesi is far from a morally-relative novel, in the absence of an ethos of perfection, it fixes meaning neither in the works of a nostalgic past nor in those of a progressive present. Past and present, art and society, fantasy and realism are all reciprocally constructive. Understood in static isolation, the worlds of the mind are troubling and perilous. But in our connections to them, they matter, becoming a comfort and light in our own rough times

π0 photoproduction on the proton for photon energies from 0.675 to 2.875 GeV

Differential cross sections for the reaction γp→pπ0 have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.675 to 2.875 GeV. The results reported here possess greater accuracy in the absolute normalization than previous measurements. They disagree with recent CB-ELSA measurements for the process at forward scattering angles. Agreement with the SAID and MAID fits is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been extended to 3 GeV. Resonance couplings have been extracted and compared to previous determination

π+ photoproduction on the proton for photon energies from 0.725 to 2.875 GeV

Differential cross sections for the reaction γp→nπ+ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID and MAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes

η Photoproduction on the Proton for Photon Energies from 0.75 to 1.95 GeV

Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W=1.75  GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass ~1.8  GeV couples to the ηN channel

\u3ci\u3eπ\u3c/i\u3e\u3csup\u3e+\u3c/sup\u3e Photoproduction on the Proton for Photon Energies from 0.725 to 2.875 GeV

Differential cross sections for the reaction γp → nπ+ have been measured with the CEBAF Large Acceptance Spectrometer (CLAS) and a tagged photon beam with energies from 0.725 to 2.875 GeV. Where available, the results obtained here compare well with previously published results for the reaction. Agreement with the SAID andMAID analyses is found below 1 GeV. The present set of cross sections has been incorporated into the SAID database, and exploratory fits have been made up to 2.7 GeV. Resonance couplings have been extracted and compared to previous determinations. With the addition of these cross sections to the world data set, significant changes have occurred in the high-energy behavior of the SAID cross-section predictions and amplitudes

Prediction of flame velocities of hydrocarbon flames

The laminar-flame-velocity data previously reported by the Lewis Laboratory are surveyed with respect to the correspondence between experimental flame velocities and values predicted by semitheoretical and empirical methods. The combustible mixture variables covered are hydrocarbon structure (56 hydrocarbons), equivalence ratio of fuel-air mixture, mole fraction of oxygen in the primary oxygen-nitrogen mixture (0.17 to 0.50), and initial mixture temperature (200 degrees to 615 degrees k). The semitheoretical method of prediction considered are based on three approximate theoretical equations for flame velocity: the Semenov equation, the Tanford-Pease equation, and the Manson equation

N∗→Nη′N^*\to N \eta^\prime decays from photoproduction of η′\eta^\prime-mesons off protons

A study of the partial-wave content of the $\gamma p\to \eta^\prime p$ reaction in the fourth resonance region is presented, which has been prompted by new measurements of polarization observables for that process. Using the Bonn-Gatchina partial-wave formalism, the incorporation of new data indicates that the $N(1895)1/2^-$, $N(1900)3/2^+$, $N(2100)1/2^+$, and $N(2120)3/2^-$ are the most significant contributors to the photoproduction process. New results for the branching ratios of the decays of these more prominent resonances to $N\eta^\prime$ final states are provided; such branches have not been indicated in the most recent edition of the Review of Particle Properties. Based on the analysis performed here, predictions for the helicity asymmetry $E$ for the $\gamma p\to \eta^\prime p$ reaction are presented.Comment: 7 pages, 5 figures, 3 table