Observation of scattering and absorption centers in lead fluoride crystals

For the first time, lead fluoride is used as a fast and compact material in electromagnetic calorimetry. Excellent optical and mechanical properties of the pure Cherenkov crystals are necessary for the A4 collaboration to perform a measurement of the nucleon's strange form factors. Visible scattering and absorption centers as well as surface damages have been investigated to characterize the quality of more than one thousand crystals. Besides, transmittance measurements have been performed on all crystals to reveal absorption bands produced by intrinsic or impurity related point-structure defects. As a consequence, 89 crystals had to be replaced by the Chinese manufacturer SICCAS.Comment: LaTeX, 6 pages, 6 figure

Fizika stranosti u MAMI: prvi ishodi i izgledi

(for the A1 Collaboration) During the last two years, several experimental approaches to strange systems have been realized at the spectrometer facility of the Mainz Microtron MAMI. An instrument of central importance for the strangeness electro-production program is the magnetic spectrometer Kaos that was installed during 2003-8, and is now operated by the A1 collaboration in (e,e′K) reactions on the proton or light nuclei. Since 2008, kaon production at low four-momentum transfers off a liquid hydrogen target was studied. The measurements are sensitive to details of the phenomenological models describing the reaction. Two very prominent isobar models, Kaon-Maid and Saclay-Lyon A, differ in the number of contributing nucleon resonances and their longitudinal couplings at the kinematics measured at MAMI. In order to use Kaos as a zero-degree double-arm spectrometer, a magnetic chicane comprising two compensating sector magnets was constructed and a new electron-arm focal-plane detector system was built.Tijekom posljednje dvije godine ostvarene su mnoge nove mogućnosti istraživanja stranih sustava pri spektrometarskom postrojenju mikrotrona u Mainzu. Od središnje važnosti za program elektrotvorbe stranosti je magnetski spektrometar Kaos koji je stavljen u rad tijekom 2003. – 2008., i sada njime upravlja grupa A1 u istraživanjima (e, e′K) reakcija na protonima i lakim jezgrama. Tvorba kaona na niskim prijenosima četiri-impulsa u meti tekućeg vodika proučava se od 2008. Mjerenja omogućuju jasnije probire fenomenoloških modela koji opisuju reakcije. Dva se istaknuta izobarna modela, Kaon-Maid i Saclay-Lyon A, razlikuju u broju nukleonskih rezonancija koje daju doprinose u uvjetima mjerenja u MAMI i njihovih uzdužnih vezanja. Radi upotrebe Kaosa kao spektrometra s dvije grane, sagrađena je magnetska brana koja se sastoji od dva sektorska magneta za izjednačenje te nov detektor u žarišnoj ravnini grane za elektrone

Associated Lambda/Sigma electroproduction with the Kaos spectrometer at MAMI

An instrument of central importance for the strangeness photo- and electroproduction at the 1.5-GeV electron beam of the MAMI accelerator at the Institut f\"ur Kernphysik in Mainz, Germany, is the newly installed magnetic spectrometer Kaos that is operated by the A1 collaboration in $(e,e'K)$ reactions on the proton or light nuclei. Its compact design and its capability to detect negative and positive charged particles simultaneously complements the existing spectrometers. The strangeness program performed with Kaos in 2008-9 is addressing some important issues in the field of elementary kaon photo- and electroproduction reactions. Although recent measurements have been performed at Jefferson Lab, there are still a number of open problems in the interpretation of the data and the description of the elementary process using phenomenological models. With the identification of $\Lambda$ and $\Sigma^0$ hyperons in the missing mass spectra from kaon production off a liquid hydrogen target it is demonstrated that the extended facility at MAMI is capable to perform strangeness electroproduction spectroscopy at low momentum transfers $Q^2$ < 0.5 (GeV/c)$^2$. The covered kinematics and systematic uncertainties in the cross-section extraction from the data are discussed.Comment: 19th International IUPAP Conference on Few-Body Problems in Physic

Fizika stranosti u MAMI: prvi ishodi i izgledi

(for the A1 Collaboration) During the last two years, several experimental approaches to strange systems have been realized at the spectrometer facility of the Mainz Microtron MAMI. An instrument of central importance for the strangeness electro-production program is the magnetic spectrometer Kaos that was installed during 2003-8, and is now operated by the A1 collaboration in (e,e′K) reactions on the proton or light nuclei. Since 2008, kaon production at low four-momentum transfers off a liquid hydrogen target was studied. The measurements are sensitive to details of the phenomenological models describing the reaction. Two very prominent isobar models, Kaon-Maid and Saclay-Lyon A, differ in the number of contributing nucleon resonances and their longitudinal couplings at the kinematics measured at MAMI. In order to use Kaos as a zero-degree double-arm spectrometer, a magnetic chicane comprising two compensating sector magnets was constructed and a new electron-arm focal-plane detector system was built.Tijekom posljednje dvije godine ostvarene su mnoge nove mogućnosti istraživanja stranih sustava pri spektrometarskom postrojenju mikrotrona u Mainzu. Od središnje važnosti za program elektrotvorbe stranosti je magnetski spektrometar Kaos koji je stavljen u rad tijekom 2003. – 2008., i sada njime upravlja grupa A1 u istraživanjima (e, e′K) reakcija na protonima i lakim jezgrama. Tvorba kaona na niskim prijenosima četiri-impulsa u meti tekućeg vodika proučava se od 2008. Mjerenja omogućuju jasnije probire fenomenoloških modela koji opisuju reakcije. Dva se istaknuta izobarna modela, Kaon-Maid i Saclay-Lyon A, razlikuju u broju nukleonskih rezonancija koje daju doprinose u uvjetima mjerenja u MAMI i njihovih uzdužnih vezanja. Radi upotrebe Kaosa kao spektrometra s dvije grane, sagrađena je magnetska brana koja se sastoji od dva sektorska magneta za izjednačenje te nov detektor u žarišnoj ravnini grane za elektrone