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Register a new userProbing hypernuclei at PANDA and at MAMI-C
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Patrick Achenbach
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Spectroscopy of Lambda hypernuclei has recently become one of the most valuable tools for the experimental investigation of strangeness nuclear physics. Several new approached are being pursued currently: In Mainz, the Microtron MAMI has been upgraded to 1.5 GeV electron beam energy and will be used to produce strange hadronic systems in the near future. The KaoS spectrometer is being installed for large acceptance, high resolution strangeness reaction spectroscopy at the existing spectrometer facility. The Mainz hypernuclei research programme will be complemented by experiments on multi-strange systems at the planned FAIR facility at GSI. The gamma-ray spectroscopy of double Lambda hypernuclei produced via Xi-bar Xi pair production is one of the four main topics which will be addressed by the PANDA Collaboration. In this paper the status of the planned experiments and the future prospects are presented.
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In February 2007, the fourth stage of the Mainz Microtron, MAMI-C, started operations with a first experiment. The new Harmonic Double-Sided Microtron delivers an electron beam with energies up to 1.5 GeV while preserving the excellent beam quality of the previous stages. The experimental program at MAMI is focused on studies of the hadron structure in the domain of non-perturbative QCD. In this paper, a few prominent selections of the extensive physics program at MAMI-C will be presented.
Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Anti-proton and Ion Research FAIR at Darmstadt, Germany. A copious production of Xi-hyperons at a dedicated internal target in the stored anti-proton beam is expected, which will enable the high-precision gamma-spectroscopy of double strange systems for the first time. In addition to the general purpose PANDA setup, the hypernuclear experiments require an active secondary target of silicon layers and absorber material as well as high purity germanium (HPGe) crystals as gamma-detectors. The design of the setup and the development of these detectors is progressing: a first HPGe crystal with a new electromechanical cooling system was prepared and the properties of a silicon strip detector as a prototype to be used in the secondary target were studied. Simultaneously to the hardware projects, detailed Monte Carlo simulations were performed to predict the yield of particle stable hypernuclei. With the help of the Monte Carlo a procedure for Lambda-Lambda-hypernuclei identification by the detection and correlation of the weak decay pions was developed.
A characterisation of scintillating fibres with silicon photomultiplier read-out was performed in view of their possible application in fibre tracking detector systems. Such a concept is being considered for the Kaos spectrometer at the Mainz Microtron MAMI and as a time-of-flight start detector for the hypernuclear physics programme at the PANDA experiment of the FAIR project. Results on particle detection effciency and time resolution are discussed. In summary, the silicon devices are very suitable for the detection of the low light yield from scintillating fibres insofar a trigger scheme is found to cope with the noise rate characteristics.
At the Institut fur Kernphysik in Mainz, Germany, the microtron MAMI has been upgraded to 1.5-GeV electron beam energy. The magnetic spectrometer Kaos is now operated by the A1 collaboration to study strangeness electro-production. Its compact design and its capability to detect negative and positive charged particles simultaneously under forward scattering angles complements the existing spectrometers. In 2008 kaon production off a liquid hydrogen target was measured at <Q^2> = 0.050 (GeV/c)^2 and 0.036 (GeV/c)^2. Associated Lambda and Sigma hyperons were identified in the missing mass spectra. Major modifications to the beam-line are under construction and a new electron arm focal-surface detector system was built in order to use Kaos as a double-arm spectrometer under zero degree scattering angle.
Measurements of the electric and the magnetic neutron form factors have been performed at the Mainz Microtron for more than 20 years. These MAMI experiments are reviewed in the context of measurements from other groups, and future measurements at MAMI are outlined.
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