Showing papers by "W. Meyer published in 2022"

Polarization observables in double neutral pion photoproduction

Abstract: . Measurements of target asymmetries and double-polarization observables for the reaction γ p → p π 0 π 0 are reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facil-ity (Bonn University) using the Bonn frozen-spin butanol (C 4 H 9 OH) target, which provided transversely polarized protons. Linearly polarized photons were produced via bremsstrahlung off a diamond crystal. The data cover the photon energy range from E γ = 650 MeV to E γ = 2600 MeV and nearly the complete angular range. The results have been included in the BnGa partial wave analysis. Experimental results and the fit agree very well. Observed systematic differences in the branching ratios for decays of N ∗ and ∆ ∗ resonances are attributed to the internal structure of these excited nucleon states. Resonances which can be assigned to SU(6) × O(3) two-oscillator configurations show larger branching ratios to intermediate states with non-zero intrinsic orbital angular momenta than resonances assigned to one-oscillator configurations.

Exotic meson π1(1600) with JPC=1-+ and its decay into ρ(770)π

Abstract: G. D. Alexeev, M. G. Alexeev, A. Amoroso, V. Andrieux, V. Anosov, K. Augsten, W. Augustyniak, C. D. R. Azevedo, B. Badełek, F. Balestra, M. Ball, J. Barth, R. Beck, Y. Bedfer, J. Berenguer Antequera, J. Bernhard, M. Bodlak, F. Bradamante, A. Bressan, V. E. Burtsev, W.-C. Chang, C. Chatterjee, M. Chiosso, A. G. Chumakov, S.-U. Chung, A. Cicuttin, P. M. M. Correia, M. L. Crespo, D. D’Ago, S. Dalla Torre, S. S. Dasgupta, S. Dasgupta, I. Denisenko, O. Yu. Denisov, S. V. Donskov, N. Doshita, Ch. Dreisbach, W. Dünnweber, R. R. Dusaev, A. Efremov, D. Eremeev, P. D. Eversheim, P. Faccioli, M. Faessler, M. Finger, M. Finger, Jr., H. Fischer, K. Floethner, C. Franco, J. M. Friedrich, V. Frolov, L. Garcia Ordonez, F. Gautheron, O. P. Gavrichtchouk, S. Gerassimov, J. Giarra, D. Giordano, M. Gorzellik, A. Grasso, A. Gridin, M. Grosse Perdekamp, B. Grube, M. Grüner, A. Guskov, F. Haas, D. von Harrach, R. Heitz, M. Hoffmann, N. Horikawa, N. d’Hose, C.-Y. Hsieh, S. Huber, S. Ishimoto, A. Ivanov, T. Iwata, M. Jandek, V. Jary, R. Joosten, E. Kabuß, F. Kaspar, A. Kerbizi, B. Ketzer, G. V. Khaustov, Yu. A. Khokhlov, Yu. Kisselev, F. Klein, J. H. Koivuniemi, V. N. Kolosov, I. Konorov, V. F. Konstantinov, A. M. Kotzinian, O. M. Kouznetsov, A. Koval, Z. Kral, F. Krinner, F. Kunne, K. Kurek, R. P. Kurjata, A. Kveton, K. Lavickova, S. Levorato, Y.-S. Lian, J. Lichtenstadt, P.-J. Lin, R. Longo, V. E. Lyubovitskij, A. Maggiora, A. Magnon, N. Makins, N. Makke, G. K. Mallot, A. Maltsev, S. A. Mamon, B. Marianski, A. Martin, J. Marzec, J. Matoušek, T. Matsuda, G. Mattson, F. Metzger, M. Meyer, W. Meyer, Yu. V. Mikhailov, M. Mikhasenko, E. Mitrofanov, Y. Miyachi, A. Moretti, A. Nagaytsev, C. Naim, D. Neyret, J. Nový, W.-D. Nowak, G. Nukazuka, A. G. Olshevsky, M. Ostrick, D. Panzieri, B. Parsamyan , S. Paul, H. Pekeler, J.-C. Peng, M. Pešek, D. V. Peshekhonov, M. Pešková, N. Pierre, S. Platchkov, J. Pochodzalla, V. A. Polyakov, J. Pretz, M. Quaresma, C. Quintans, G. Reicherz, C. Riedl, T. Rudnicki, D. I. Ryabchikov, A. Rychter, A. Rymbekova, V. D. Samoylenko, A. Sandacz, S. Sarkar, I. A. Savin, G. Sbrizzai, S. Schmeing, H. Schmieden, A. Selyunin, K. Sharko, L. Sinha, M. Slunecka, D. Spülbeck, A. Srnka, D. Steffen, M. Stolarski, O. Subrt, M. Sulc, H. Suzuki, S. Tessaro, F. Tessarotto, A. Thiel, J. Tomsa, F. Tosello, A. Townsend, T. Triloki, V. Tskhay, S. Uhl, B. Valinoti, A. Vauth, B. M. Veit, J. Veloso, B. Ventura, A. Vidon, M. Virius, M. Wagner, S. Wallner, K. Zaremba, M. Zavertyaev, M. Zemko, E. Zemlyanichkina, Y. Zhao, and M. Ziembicki University of Aveiro, I3N, Department of Physics, 3810-193 Aveiro, Portugal Universität Bochum, Institut für Experimentalphysik, 44780 Bochum, Germany Universität Bonn, Helmholtz-Institut für Strahlenund Kernphysik, 53115 Bonn, Germany Universität Bonn, Physikalisches Institut, 53115 Bonn, Germany Institute of Scientific Instruments of the CAS, 61264 Brno, Czech Republic Matrivani Institute of Experimental Research & Education, Calcutta-700 030, India Joint Institute for Nuclear Research, 141980 Dubna, Moscow region, Russia Universität Freiburg, Physikalisches Institut, 79104 Freiburg, Germany CERN, 1211 Geneva 23, Switzerland Technical University in Liberec, 46117 Liberec, Czech Republic LIP, 1649-003 Lisbon, Portugal Universität Mainz, Institut für Kernphysik, 55099 Mainz, Germany University of Miyazaki, Miyazaki 889-2192, Japan Lebedev Physical Institute, 119991 Moscow, Russia Technische Universität München, Physik-Department, 85748 Garching, Germany Nagoya University, 464 Nagoya, Japan Charles University, Faculty of Mathematics and Physics, 18000 Prague, Czech Republic Czech Technical University in Prague, 16636 Prague, Czech Republic State Scientific Center Institute for High Energy Physics of National Research Center “Kurchatov

The new APD-Based Readout of the Crystal Barrel Calorimeter -- An Overview

Abstract: The Crystal Barrel is an electromagnetic calorimeter consisting of 1380 CsI(Tl) scintillators, and is currently installed at the CBELSA/TAPS experiment where it is used to detect decay products from photoproduction of mesons. The readout of the Crystal Barrel has been upgraded in order to integrate the detector into the first level of the trigger and to increase its sensitivity for neutral final states. The new readout uses avalanche photodiodes in the front-end and a dual back-end with branches optimized for energy and time measurement, respectively. An FPGA-based cluster finder processes the whole hit pattern within less than 100 ns. The important downside of APDs – the temperature dependence of their gain – is handled with a temperature stabilization and a compensating bias voltage supply. Additionally, a light pulser system allows the APDs’ gains to be measured during beamtimes.

he large COMPASS polarized solid ammonia target for Drell–Yan easurements with a pion beam

Abstract: The transversely polarized target (PT) of the COMPASS (NA58) collaboration at CERN has been used for Drell– Yan measurements in 2015 and 2018. The transverse spin structure of the proton has been studied using a negative pion beam and a solid ammonia target. Employing the dynamic nuclear polarization (DNP) method, proton polarization values of more than 80% have been routinely achieved after one day, at a homogeneous magnetic field of 2.5 T and using a 3He/4He dilution refrigerator. During the data-taking the target operates in a transversely oriented magnetic dipole field at 0.6 T. This so-called frozen spin operation mode without the DNP pumping process leads to a slow depolarization of the target material, which is further accelerated by the heat input of the pion beam, produced secondary particles and radiation damage effects to the target material. Ammonia has the highest resistance against radiation-induced depolarization among known solid target materials. The proton polarization has been measured by the nuclear magnetic resonance (NMR). Relaxation times of about 1100 h have been observed for the proton polarization resulting in an average polarization between 68% and 76% during about two weeks long data-taking periods. To achieve a systematic uncertainty of the polarization ΔP∕P as low as 3.2% and a statistical one of less than 1.8% two large target cells with appropriate positioning of the NMR-coils have been built.