Self energies of the pion and the delta isobar from the ^3He(e,e'pi^+)^3H reaction
| Autor: | M. Kohl, P. Bartsch, D. Baumann, J. Bermuth, R. Böhm, K. Bohinc, S. Derber, M. Ding, M.O. Distler, I. Ewald, J. Friedrich, J.M. Friedrich, P. Jennewein, M. Kahrau, S.S. Kamalov, A. Kozlov, K.W. Krygier, M. Kuss, A. Liesenfeld, H. Merkel, P. Merle, U. Müller, R. Neuhausen, Th. Pospischil, M. Potokar, C. Rangacharyulu, A. Richter, D. Rohe, G. Rosner, H. Schmieden, G. Schrieder, M. Seimetz, S. Širca, T. Suda, L. Tiator, M. Urban, A. Wagner, Th. Walcher, J. Wambach, M. Weis, A. Wirzba |
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| Jazyk: | angličtina |
| Rok vydání: | 2001 |
| Předmět: | |
| Popis: | In a kinematically complete experiment at the Mainz microtron MAMI, pion angular distributions of the $^3$He(e,e'$\pi^+)^3$H reaction have been measured in the excitation region of the $\Delta$ resonance to determine the longitudinal ($L$), transverse ($T$), and the $LT$ interference part of the differential cross section. The data are described only after introducing self-energy modifications of the pion and $\Delta$-isobar propagators. Using Chiral Perturbation Theory (ChPT) to extrapolate the pion self energy as inferred from the measurement on the mass shell, we deduce a reduction of the $\pi^+$ mass of $\Delta m_{\pi^+} = (-1.7^{+ 1.7}_{- 2.1})$ MeV/c$^2$ in the neutron-rich nuclear medium at a density of $\rho = (0.057^{+ 0.085}_{- 0.057})$ fm$^{-3}$. Our data are consistent with the $\Delta$ self energy determined from measurements of $\pi^0$ photoproduction from $^4$He and heavier nuclei. Comment: Elsart, 12 pages and 4 figures, Correspondent: Professor Dr. Dr. h.c. mult. Achim Richter, richter@ikp.tu-darmstadt.de, submitted to Phys. Rev. Lett |
| Databáze: | OpenAIRE |
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