/ Experiment-Nucl nucl-ex/0104004


Selfenergies of the pion and the Delta isobar from the He-3(e, e' pi+) H-3 reaction


Kohl, M. (Darmstadt, Tech. Hochsch.) ; Bartsch, P. ; Baumann, D. ; Bermuth, J. ; Bohm, R. ; Bohinc, K. ; Derber, S. ; Ding, M. ; Distler, M.O. ; Ewald, I. ; Friedrich, J. ; Friedrich, J.M. ; Jennewein, P. ; Kahrau, M. ; Kamalov, S.S. ; Kozlov, A. ; Krygier, K.W. ; Kuss, M. ; Liesenfeld, A. ; Merkel, H. ; Merle, P. ; Muller, U. ; Neuhausen, R. ; Pospischil, T. ; Potokar, M. ; Rangacharyulu, C. ; Richter, A. ; Rohe, D. ; Rosner, G. ; Schmieden, H. ; Schrieder, G. ; Seimetz, M. ; Sirca, S. ; Suda, T. ; Tiator, L. ; Urban, M. ; Wagner, A. ; Walcher, T. ; Wambach, J. ; Weis, M. ; Wirzba, A.

Published in: Phys.Lett.
Year: 2002
Vol.: B530
Page No: 67-73
Pages: 4

Abstract: 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.

Web-Page: http://www.adsabs.harvard.edu/abs/2002PhLB..530...67S; http://alice.cern.ch/format/showfull?sysnb=2248362; http://www.sciencedirect.com/science?_ob=GatewayURL&_origin=SPIRES&_method=citationSearch&_volkey=03702693%23530%2367&_version=1&md5=bf047b0f2a1f80e61c8dacb46123f17d; http://www.sciencedirect.com/web-editions?_ob=GatewayURL&_origin=SPIRES&_method=citationSearch&_volkey=03702693%23530%2367&_version=1&md5=bf047b0f2a1f80e61c8dacb46123f17d

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