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Inclusive Strangeness Photoproduction on the Neutron (Lima, Berman) We have determined the inclusive K+ photoproduction cross section on deuterium (from the g2 data) as a function of incident photon energy and the polar angle of the kaon. From the missing mass, we can resolve the associated L from the S produced in the reaction process, as shown in Fig. 9, for four photon-energy intervals: 1.0 to 1.3 GeV, 1.3 to 1.6 GeV, 1.6 to 1.9 GeV, and 1.9 to 2.2 GeV. We see from Fig. 9 how the L cross section, indicated by the brightly colored region at the left of each plot, decreases strongly with photon energy, while the S cross section, to the right of the L , first increases with photon energy and then decreases.
Figure 9. Missing mass as a function of qK for four different intervals of incident photon energy: upper left—1.0-1.3 GeV; upper right—1.3-1.6 GeV; lower left—1.6-1.9 GeV; and lower right—1.9-2.2 GeV.The L peak must come from the proton in the deuteron if it is in coincidence with a K+, but the S can come from either the proton (if it is a S 0) or the neutron (if it is a S - ). Therefore, we can use our L data and the S 0-to-L ratio for the proton from the g1 data to subtract the S 0 cross section from the total S peak to obtain the S - cross section from the neutron. The resulting cross section as a function of photon energy is shown in Fig. 10, together with the scaled (by a factor of 2) predictions of two theoretical models [Mar95]. Neither shape is consistent with the data, and both models predict a cross section about twice too large.
Figure 10. The integrated-over-angle cross section for S - photoproduction on the neutron (solid squares) as a function of photon energy, compared with the results of calculations (black and red curves) based on two different theoretical models [Mar95]. Note that the calculations have been scaled down by a factor of 2. Finally, for certain bins in energy and angle, the kinematics allow us to observe the S (1385) in our data set, as can be seen in Fig. 11, where it rises clearly above the underlying background.
Figure 11. A peak in the data histogram corresponding to the S (1385) can be seen clearly in this kinematics. These data are under further study, pending internal review by the CLAS Collaboration. Details can be found in the Ph.D. thesis (in Portuguese) of Ana Lima [Lim02], who completed her degree in Fall, 2002. B.L. Berman was her co-advisor with J.D.T. Arruda Neto of the Universidade de São Paulo. |
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