Choose timezone
Your profile timezone:
2010
The search for missing resonances and new forms of nuclear matter
by
→
Pacific/Honolulu
Rm. 417 (UHM - Watanabe Hall)
Rm. 417
UHM - Watanabe Hall
2505 Correa Road
Honolulu, HI 96822
Description
Special Seminar
For the CBELSA/TAPS and A2 Collaborations
Photoproduction of mesons from light nuclei is important for two different aspects of hadron physics. Electromagnetic excitations of the free proton have been (and are still) under intensive investigation, but so far much less attention has been paid to their neutron counter parts. However, due to SU(3) selection rules, some states are predicted to be much stronger excited electromagnetically in the neutron case. Investigation of the isospin composition of the electro magnetic excitations always requires measurements of the neutron. Quasifree photoproduction of mesons of neutrons bound in light nuclei, in particular in the deuteron, is so far the only experimental possibility to investigate this topic. Coherent photoproduction of mesons of light nuclei can be explored as an additional spin/isospin filter for the elementary excitations. The other aspect is the interaction of mesons with nucleons and nuclei. For short lived mesons like the # o , #, # # ... the only access is via final state interaction (FSI), when the meson is produced in some nucleus and subsequently interacts with it. Topics like the search for mesic nuclei may be addressed. In a series of experiments at the ELSA accelerator in Bonn with the Crystal Barrel/TAPS setup and at the MAMI accelerator in Mainz with the Crystal Ball/TAPS setup, photoproduction of mesons o# the deuteron, o# 3 He has been studied in detail. A completely unexpected finding is the pronounced structure in the excitation function of the #n # #n reaction around 1 GeV, which has no counterpart for the proton. The statistical significance of this structure is large and it has been seen not only for neutrons bound in the deuteron but also for 3 He target nuclei. Recent measurements at ELSA, GRAAL, MAMI, and in Sendai estimate its width below 50 MeV, which would be extremely narrow for a nucleon res onance at this excitation energy. Many different suggestions of its nature have been discussed, ranging from intricate interference structures between the lowlying S 11 resonances, threshold efects in coupled channel dynamics, over contributions of the D 15 (1670) resonance (suppressed for the proton), to a narrow P 11 state. The production of #-mesons in the ## final state with very small momenta relative to the final state nucleus may be furthermore explored as a new tool for the possible formation of #mesic states. Finally, first results for the measurement of polarization observables for quasifree neutrons, which will be explored intensively during the next few years, will be discussed.
For the CBELSA/TAPS and A2 Collaborations
Photoproduction of mesons from light nuclei is important for two different aspects of hadron physics. Electromagnetic excitations of the free proton have been (and are still) under intensive investigation, but so far much less attention has been paid to their neutron counter parts. However, due to SU(3) selection rules, some states are predicted to be much stronger excited electromagnetically in the neutron case. Investigation of the isospin composition of the electro magnetic excitations always requires measurements of the neutron. Quasifree photoproduction of mesons of neutrons bound in light nuclei, in particular in the deuteron, is so far the only experimental possibility to investigate this topic. Coherent photoproduction of mesons of light nuclei can be explored as an additional spin/isospin filter for the elementary excitations. The other aspect is the interaction of mesons with nucleons and nuclei. For short lived mesons like the # o , #, # # ... the only access is via final state interaction (FSI), when the meson is produced in some nucleus and subsequently interacts with it. Topics like the search for mesic nuclei may be addressed. In a series of experiments at the ELSA accelerator in Bonn with the Crystal Barrel/TAPS setup and at the MAMI accelerator in Mainz with the Crystal Ball/TAPS setup, photoproduction of mesons o# the deuteron, o# 3 He has been studied in detail. A completely unexpected finding is the pronounced structure in the excitation function of the #n # #n reaction around 1 GeV, which has no counterpart for the proton. The statistical significance of this structure is large and it has been seen not only for neutrons bound in the deuteron but also for 3 He target nuclei. Recent measurements at ELSA, GRAAL, MAMI, and in Sendai estimate its width below 50 MeV, which would be extremely narrow for a nucleon res onance at this excitation energy. Many different suggestions of its nature have been discussed, ranging from intricate interference structures between the lowlying S 11 resonances, threshold efects in coupled channel dynamics, over contributions of the D 15 (1670) resonance (suppressed for the proton), to a narrow P 11 state. The production of #-mesons in the ## final state with very small momenta relative to the final state nucleus may be furthermore explored as a new tool for the possible formation of #mesic states. Finally, first results for the measurement of polarization observables for quasifree neutrons, which will be explored intensively during the next few years, will be discussed.
