The differential cross section for the quasi-free photoproduction reaction $$\gamma n\rightarrow K^0\Sigma ^0$$ γ n → K 0 Σ 0 was measured at BGOOD at ELSA from threshold to a centre-of-mass energy of $$2400\,\hbox {MeV}$$ 2400 MeV . Close to threshold the results are consistent with existing data and are in agreement with partial wave analysis solutions over the full measured energy range, with a large coupling to the $$\Delta (1900)1/2^-$$ Δ ( 1900 ) 1 / 2 - evident. This is the first dataset covering the $$K^*$$ K ∗ threshold region, where there are model predictions of dynamically generated vector meson-baryon resonance contributions.

PANDA (anti-Proton ANnihiliation at DArmstadt) is planned to be one of the four main experiments at the future international accelerator complex FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. It is going to address fundamental questions of hadron physics and quantum chromodynamics using cooled antiproton beams with a high intensity and and momenta between 1.5 and 15 GeV/c. PANDA is designed to reach a maximum luminosity of 2x10^32 cm^2 s. Most of the physics programs require an excellent particle identification (PID). The PID of hadronic states at the forward endcap of the target spectrometer will be done by a fast and compact Cherenkov detector that uses the detection of internally reflected Cherenkov light (DIRC) principle. It is designed to cover the polar angle range from 5{\deg} to 22{\deg} and to provide a separation power for the separation of charged pions and kaons up to 3 standard deviations (s.d.) for particle momenta up to 4 GeV/c in order to cover the important particle phase space. This document describes the technical design and the expected performance of the novel PANDA Disc DIRC detector that has not been used in any other high energy physics experiment (HEP) before. The performance has been studied with Monte-Carlo simulations and various beam tests at DESY and CERN. The final design meets all PANDA requirements and guarantees suffcient safety margins.

A measurement of the double-polarization observable $E$ for the reaction $\gamma p\to \pi^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_\gamma =600$~MeV to $E_\gamma =2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.

A measurement of the double-polarization observable E for the reaction $$\gamma p\rightarrow \pi ^0 p$$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C $$_4$$ H $$_9$$ OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $$E_\gamma =600$$ to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.

The polarization observables T, E, P, H, and G in photoproduction of η mesons off protons are measured for photon energies from threshold to W=2400MeV (T), 2280 MeV (E), 1620 MeV (P, H), or 1820 MeV (G), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JüBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the Nη decay of nucleon resonances. A Nη-branching ratio of 0.33± 0.04 for N(1650)1/2^- is found, which reduces the large and controversially discussed Nη-branching ratio difference of the two lowest mass J^P=1/2^--resonances significantly.

The polarization observables T, E, P, H, and G in photoproduction of eta mesons off protons are measured for photon energies from threshold to W = 2400 MeV (T), 2280 MeV (E), 1620 MeV (P, H), or 1820 MeV (G), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, JuBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the N eta decay of nucleon resonances. A N eta-branching ratio of 0.33 +/- 0.04 for N(1650)1/2(-) is found, which reduces the large and controversially discussed N eta-branching ratio difference of the two lowest mass J(P) = 1/2(-) -resonances significantly. (C) 2020 The Authors. Published by Elsevier B.V.

Data on the beam asymmetry Σ in the photoproduction of η mesons off protons are reported for tagged photon energies from 1130 to 1790 MeV (mass range from W=1748  MeV to W=2045  MeV). The data cover the full solid angle that allows for a precise moment analysis. For the first time, a strong cusp effect in a polarization observable has been observed that is an effect of a branch-point singularity at the pη^{'} threshold [E_{γ}=1447  MeV (W=1896  MeV)]. The latest BnGa partial wave analysis includes the new beam asymmetry data and yields a strong indication for the N(1895)1/2^{-} nucleon resonance, demonstrating the importance of including all singularities for a correct determination of partial waves and resonance parameters.

This documents describes the technical design and the expected performance of the Barrel DIRC detector for the PANDA experiment. The Barrel DIRC will provide hadronic charged particle identification in the polar angle range of $22^\circ$ to $140^\circ$ for particle momenta between 0.5 GeV/c and 3.5 GeV/c. The design is based on the successful BaBar DIRC with several key improvements. The performance and system cost were optimized in detailed detector simulations and validated with full system prototypes using particle beams at GSI and CERN. The final design meets or exceeds the PID goal of clean $π/K$ separation with at least 3 standard deviations over the entire phase space of charged kaons in the Barrel DIRC.

The (P) over bar ANDA (anti-Proton ANnihiliation at DArmstadt) experiment will be one of the four flagship experiments at the new international accelerator complex FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. (P) over bar ANDA will address fundamental questions of hadron physics and quantum chromodynamics using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c and a design luminosity of up to 2 x 10(32) cm(-2) S-1. Excellent particle identification (PID) is crucial to the success of the (P) over bar ANDA physics program. Hadronic PID in the barrel region of the target spectrometer will be performed by a fast and compact Cherenkov counter using the detection of internally reflected Cherenkov light (DIRC) technology. It is designed to cover the polar angle range from 22 degrees to 140 degrees and will provide at least 3 standard deviations (s.d.) pi/K separation up to 3.5 GeV/c, matching the expected upper limit of the final state kaon momentum distribution from simulation. This documents describes the technical design and the expected performance of the (P) over bar ANDA Barrel DIRC detector. The design is based on the successful BaBar DIRC with several key improvements. The performance and system cost were optimized in detailed detector simulations and validated with full system prototypes using particle beams at GSI and CERN. The final design meets or exceeds the PID goal of clean pi/K separation with at least 3 s.d. over the entire phase space of charged kaons in the Barrel DIRC.

This paper summarises a comprehensive Monte Carlo simulation study for precision resonance energy scan measurements. Apart from the proof of principle for natural width and line shape measurements of very narrow resonances with PANDA, the achievable sensitivities are quantified for the concrete example of the charmonium-like X(3872) state discussed to be exotic, and for a larger parameter space of various assumed signal cross-sections, input widths and luminosity combinations. PANDA is the only experiment that will be able to perform precision resonance energy scans of such narrow states with quantum numbers of spin and parities that differ from $ J^{PC} = 1^{--}$.

This paper summarises a comprehensive Monte Carlo simulation study for precision resonance energy scan measurements. Apart from the proof of principle for natural width and line shape measurements of very narrow resonances with PANDA, the achievable sensitivities are quantified for the concrete example of the charmonium-like X(3872) state discussed to be exotic, and for a larger parameter space of various assumed signal cross-sections, input widths and luminosity combinations. PANDA is the only experiment that will be able to perform precision resonance energy scans of such narrow states with quantum numbers of spin and parities that differ from J = 1−−.

T. C. Jude1, S. Alef1, D. Bayadilov2, R. Beck2, M. Becker2, A. Bella1, P. Bielefeldt 1, S. Boese2, A. Braghieri 3, K. Brinkmann4, P. Cole1, F. Curciarello6,7, V. De Leo6,7, R. Di Salvo8, H. Dutz1, D. Elsner 1, A. Fantini8,9, O. Freyermuth 1, S. Friedrich4, F. Frommberger 1, V. Ganenko5, G. Gervino10,11, F. Ghio12,13, G. Giardina6,7, S. Goertz1, A. Gridnev15, E. Gutz4, D. Hammann1, J. Hannappel 1, P. Hartmann 1, W. Hillert1, A. Ignatov16, R. Jahn2, R. Joosten 2, F. Klein1, K. Koop2, B. Krusche17, A. Lapik16, P. Levi Sandri 18, I. V. Lopatin15, G. Mandaglio6,7, F. Messi 1, R. Messi 8,9, V. Metag4, D. Moricciani8, A. Mushkarenkov 16, M. Nanova4, V. Nedorezov16, D. Novinskiy15, P. Pedroni 3, B. Reitz1, M. Romaniuk8, T. Rostomyan 17, N. Rudnev16, G. Scheluchin 1, H. Schmieden 1, A. Stugelev15, V. Sumachev 15, V. Tarakanov15, V. Vegna1, D. Walther2, D. Watts14, H. Zaunick2,4 and T. Zimmermann 1

. The production of η^' mesons in coincidence with forward-going protons has been studied in photon-induced reactions on 12 C and on a liquid hydrogen (LH 2 ) target for incoming photon energies of 1.3-2.6 GeV at the electron accelerator ELSA. The η^' mesons have been identified via the η^'→π^0π^0η→ 6 γ decay registered with the CBELSA/TAPS detector system. Coincident protons have been identified in the MiniTAPS BaF 2 array at polar angles of 2^∘≤θ_p≤ 11^∘ . Under these kinematic constraints the η^' mesons are produced with relatively low kinetic energy ( ≈ 150 MeV) since the coincident protons take over most of the momentum of the incident-photon beam. For the C-target this allows the determination of the real part of the η^' -carbon potential at low meson momenta by comparing with collision model calculations of the η^' kinetic energy distribution and excitation function. Fitting the latter data for η^' mesons going backwards in the center-of-mass system yields a potential depth of V = -(44 ± 16(stat) ± 15(syst)) MeV, consistent with earlier determinations of the potential depth in inclusive measurements for average η^' momenta of ≈ 1.1 GeV/ c . Within the experimental uncertainties, there is no indication of a momentum dependence of the η^' -carbon potential. The LH 2 data, taken as a reference to check the data analysis and the model calculations, provide differential and integral cross sections in good agreement with previous results for η^' photoproduction off the free proton.

Excitation-energy spectra of C-11 nuclei near the eta'-meson production threshold have been measured by missing-mass spectroscopy using the C-12(p,d) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce eta'-meson bound states in C-11 nuclei. Deuterons emitted at 0 degrees in the reaction have been momentum analyzed by the fragment separator (FRS), used as a high-resolution spectrometer. No distinct structure due to the formation of eta'-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of eta'-mesic states are determined, and thereby a constraint imposed on the eta'-nucleus interaction is discussed.

Y.K. Tanakaa, Y. Ayyadb, J. Benlliurec, K.-T. Brinkmannd S. Friedrichd, H. Fujiokae, H. Geissela,d, J. Gellankif , C. Guog E. Gutzd, E. Haettnera, M.N. Harakehf , R.S. Hayanoh Y. Higashii, S. Hirenzakii, C. Hornungd, Y. Igarashij, N. Ikenok K. Itahashil, M. Iwasakil, D. Jidom, N. Kalantar-Nayestanakif R. Kanungon, R. Knöbeld,e, N. Kurza, V. Metagd, I. Mukhaa T. Nagaee, H. Nagahiroi, M. Nanovad, T. Nishil, H.J. Ongb S. Pietria, A. Prochazkaa, C. Rappolda, M.P. Reitera J.L. Rodríguez-Sánchezc, C. Scheidenbergera,d, H. Simona B. Sitaro, P. Strmeno, B. Sung, K. Suzukip, I. Szarkao, M. Takechiq, I. Tanihatab,g, S. Terashimag, Y.N. Watanabeh H. Weicka, E. Widmannp, J.S. Winfielda, X. Xua, H. Yamakamie J. Zhaog

T.C. Jude∗1, S. Alef1, P. Bauer1, D. Bayadilov2, R. Beck2, J. Bieling1, A. Bella1, S. Boese2, A. Braghieri3, K. Brinkmann4, D. Burdeynyi5, P. Cole1, R. Di Salvo7, D. Elsner1, A. Fantini7,9, O. Freyermuth1, S. Friedrich4, F. Frommberger1, G. Gervino8,9, F. Ghio10,11, A. Gridnev12, E. Gutz4, D. Hammann1, J. Hannappel1, W. Hillert1, R. Jahn2, R. Joosten2, F. Klein1, K. Kohl1, B. Krusche14, A.M. Lapik13, P. Levi Sandri15, V.P. Lisin13, I. V. Lopatin12, G. Mandaglio5,6, F. Messi1, R. Messi7,9, V. Metag4, D. Moricciani7, A.N. Mushkarenkov13, M. Nanova4, V.G. Nedorezov13, D. Novinskiy12, P. Pedroni3, A.S. Polonski13, B. Reitz1, M. Romaniuk8, G. Scheluchin1, H. Schmieden1, A. Stugelev12, V. Sumachev12, V. Tarakanov12, V. Vegna1, D. Walther2, H. Zaunick2,4 T. Zimmermann1 1 Physikalisches Institut, Universität Bonn, Germany,2 Helmholtz-Institut für Strahlenund Kernphysik, Universität Bonn, Germany,3 INFN sezione di Pavia, Via Agostino Bassi, Pavia, Italy,4 II. Physikalisches Institut, Universität Gießen, Germany,5 INFN sezione Catania, Italy,6 Università degli Studi di Messina, Italy,7 INFN Roma Tor Vergata, Italy,8 INFN sezione di Torino, Italy,9 Dipartimento di Fisica, Università di Torino, Italy, 10 INFN sezione di Roma, Italy, 11 Istituto

This paper reports on a measurement of the double-polarization observable G in \( \pi^0\) photoproduction off the proton using the CBELSA/TAPS experiment at the ELSA accelerator in Bonn. The observable G is determined from reactions of linearly polarized photons with longitudinally polarized protons. The polarized photons are produced by bremsstrahlung off a diamond radiator of well-defined orientation. A frozen spin butanol target provides the polarized protons. The data cover the photon energy range from 617 to 1325 MeV and a wide angular range. The experimental results for G are compared to predictions by the Bonn-Gatchina (BnGa), Jülich-Bonn (JüBo), MAID and SAID partial wave analyses. Implications of the new data for the pion photoproduction multipoles are discussed.