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Register a new userIn-beam tests of scintillating fibre detectors at MAMI and at GSI
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The performance of scintillating fibre detectors was studied with electrons at the spectrometer facility of the Mainz microtron MAMI, as well as in a C-12 beam of 2 AGeV energy and in a beam of different particle species at GSI. Multi-anode photomultipliers were used to read out one or more bundles of 128 fibres each in different geometries. For electrons a time resolution of FWHM = 1 ns was measured in a single detector plane with a detection efficiency epsilon > 99%. A time resolution of 310 ps (FWHM) between two planes of fibres was achieved for carbon ions, leading to a FWHM = 220 ps for a single detector. The hit position residual was measured with a width of FWHM = 0.27 mm. The variation in the measured energy deposition was Delta E/E= 15-20% (FWHM) for carbon ions. In addition, the energy response to p/pi/d particles was studied. Based on the good detector performance fibre hodoscopes will be constructed for the KAOS/A1 spectrometer at MAMI and for the HypHI experiment at GSI.
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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.
We present new data for the transverse target asymmetry T and the very first data for the beam-target asymmetry F in the $vec gamma vec ptoeta p$ reaction up to a center-of-mass energy of W=1.9 GeV. The data were obtained with the Crystal-Ball/TAPS detector setup at the Glasgow tagged photon facility of the Mainz Microtron MAMI. All existing model predictions fail to reproduce the new data indicating a significant impact on our understanding of the underlying dynamics of $eta$ meson photoproduction. The peculiar nodal structure observed in existing T data close to threshold is not confirmed.
For the first time a vertically polarized electron beam has been used for physics experiments at MAMI in the energy range between 180 and 855 MeV. The beam-normal single-spin asymmetry $A_{mathrm{n}}$, which is a direct probe of higher-order photon exchange beyond the first Born approximation, has been measured in the reaction $^{12}mathrm C(vec e,e)^{12}mathrm C$. Vertical polarization orientation was necessary to measure this asymmetry with the existing experimental setup. In this paper we describe the procedure to orient the electron polarization vector vertically, and the concept of determining both its magnitude and orientation with the available setup. A sophisticated method has been developed to overcome the lack of a polarimeter setup sensitive to the vertical polarization component.
The reactions $gamma pto eta p$ and $gamma pto eta p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. A strong cusp is observed in the total cross section and excitation functions for $eta$ photoproduction at the energies in vicinity of the $eta$ threshold, $W=1896$MeV ($E_gamma=1447$MeV). This behavior is explained in a revised $eta$MAID isobar model by a significant branching of the $N(1895)1/2^-$ nucleon resonance to both, $eta p$ and $eta p$, confirming the existence and constraining the properties of this poorly known state.
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.
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