TRR 16:  Subnuclear Structure of Matter

• Subject Area: Physics
• Term: from 2004 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5486044

• Final Report Year: 2017

Final Report Abstract

The main theme of this CRC was the investigation of the formation and decay of baryon resonances made of the light quarks up, down and strange. While the underlying gauge theory, Quantum Chromodynamics (QCD), is well established, understanding the non-perturbative phenomenon of structure formation – the fundamental fields (the quarks and gluons) only appear within bound states (mesons and baryons) and their excitations – is notoriously difficult and extremely challenging. Progress can only be made through a strong interplay of experiment and theory, as it was the case in the CRC/TR16. The experimental activities centered around photo-nucleon experiments to measure the production and decay of resonances utilizing the electron stretcher accelerator ELSA and the two detector systems CBELSA/TAPS and BGO-OD, while theory made use of effective field theories, lattice simulations, functional methods and modeling. A bridge between experiment and theory was given by partial-wave analysis, that was also successfully pursued within this CRC. In an extension of this research it was investigated whether the properties of hadrons, established in vacuum, are modified when embedded in a strongly interacting environment such as nuclei. Substantial progress has been made within the CRC in its different areas. Experiments with unpolarized and polarized beams and targets have been performed. The measurement of polarization observables is of crucial importance to establish baryon resonances and their properties. The precise data obtained at ELSA provide an important part of the significantly extended data base now available for multi-channel partial wave analyses. Within the CRC new resonances have been established for the first time and the properties of known or less well known baryon resonances have been determined with increasing precision. These results entering also the Review of Particle properties have led to a significantly better understanding of the baryon spectrum. Theory played an important role in not only supporting the various experimental activities, but also further reaching important developments were made. Just as a few examples we mention the systematic studies of baryon resonances from meson-baryon interactions, the dispersion-theoretical analysis of the nucleon electromagnetic form factors, NREFT and dispersion-theoretical investigations of three-flavor meson decays and their impact on the muon (g − 2), the Roy-Steiner equation analysis of pion-nucleon scattering including a high-precision determination of the elusive πN σ-term, the systematic development of finite volume methods for lattice QCD, the lattice studies of light pseudoscalar mesons and the QCD vacuum topology, functional methods applied to the baryon spectrum and, last but not least, ground-breaking developments in chiral nuclear effective field theory for nuclear forces and currents. Instrumentation was vital for the CRC. Steady research and developments on the accelerator and polarized target side did not only lead to interesting results but did also result in the high quality beam and the polarized target needed for the experiments. The BGO-OD-experiment has been build up within the CRC and the Crystal Barrel calorimeter was upgraded for better trigger and timing capabilities.

Publications

• “A Coupled-channel analysis of KΛ production in the nucleon resonance region,” Phys. Rev. C 72 (2005) 015210
  V. Shklyar, H. Lenske and U. Mosel
  
• “Infrared regularization for spin-1 fields,” Eur. Phys. J. C 40 (2005) 97
  P. C. Bruns and U.-G. Meißner
  
• “Photoproduction of eta mesons off protons for 0.75-GeV < E(gamma) < 3-GeV,” Phys. Rev. Lett. 94 (2005) 012004
  V. Crede et al. [CB-ELSA Collaboration]
  
• “Cusps in K → 3π decays,” Phys. Lett. B 638 (2006) 187
  G. Colangelo, J. Gasser, B. Kubis, A. Rusetsky
  
• “Electron spin resonance and its implication on the maximum nuclear polarization of deuterated solid target materials”, Phys. Rev. B 74 (2006) 134418
  J. Heckmann, W. Meyer, E. Radtke, G. Reicherz, S. Goertz
  
• “K−p scattering length from scattering experiments,” Phys. Rev. C 74 (2006) 055201
  B. Borasoy, U.-G. Meißner and R. Nißler
  
• “Dispersion analysis of the nucleon form-factors including meson continua,” Phys. Rev. C 75 (2007) 035202
  M. A. Belushkin, H.-W. Hammer and U.-G. Meißner
  
• “eta-photoproduction in the resonance energy region,” Phys. Lett. B 650 (2007) 172
  V. Shklyar, H. Lenske and U. Mosel
  
• “Measurement of the beam asymmetry in η-photoproduction off the proton,” Eur. Phys. J. A 33 (2007) 147
  D. Elsner et al. [CBELSA/TAPS Collaboration]
  
• “Further evidence for N(1900) P13 from photoproduction of hyperons,” Phys. Lett. B 662 (2008) 245
  V. A. Nikonov, A. V. Anisovich, E. Klempt, A. V. Sarantsev and U. Thoma
  
• “Modification of the ω-Meson Lifetime in Nuclear Matter,” Phys. Rev. Lett. 100 (2008) 192302. Erratum: Phys. Rev. Lett. 114 (2015) 199903
  M. Kotulla et al. [CBELSA/TAPS Collaboration]
  
• “Quasi-free photoproduction of eta-mesons of the neutron,” Phys. Rev. Lett. 100 (2008) 252002
  I. Jaegle et al. [CBELSA and TAPS Collaborations]
  
• “Determination of the Dalitz plot parameter alpha for the decay η → 3π0 with the Crystal Ball at MAMI-B,” Eur. Phys. J. A 39 (2009) 169
  M. Unverzagt et al. [Crystal Ball at MAMI, TAPS and A2 Collaborations]
  
• “Linearly polarised photon beams at ELSA and measurement of the beam asymmetry in π0 photoproduction off the proton”, Eur. Phys. J. A 39 (2009) 373
  D. Elsner et al.
  
• “Modern Theory of Nuclear Forces,” Rev. Mod. Phys. 81 (2009) 1773
  E. Epelbaum, H. W. Hammer and U.-G. Meißner
  
• “Hadrons in strongly interacting matter,” Int. J. Mod. Phys. E 19 (2010) 147
  S. Leupold, V. Metag, U. Mosel
  
• “Chiral dynamics of the S11(1535) and S11(1650) resonances revisited,” Phys. Lett. B 697 (2011) 254
  P. C. Bruns, M. Mai and U.-G. Meißner
  
• “Scalar mesons in a finite volume,” JHEP 1101 (2011) 019
  V. Bernard, M. Lage, U.-G. Meißner and A. Rusetsky
  
• “Anomaly in the Ks0Σ+ photoproduction cross section off the proton at the K∗ threshold,” Phys. Lett. B 713 (2012) 180
  R. Ewald et al. [CBELSA/TAPS Collaboration]
  
• “Measuring the intensity and position of a pA electron beam with resonant cavities”, Phys. Rec. ST Accel. Beams 15 (2012) 112801
  T. Pusch et al.
  
• “Properties of baryon resonances from a multichannel partial wave analysis,” Eur. Phys. J. A 48 (2012) 15
  A. V. Anisovich, R. Beck, E. Klempt, V. A. Nikonov, A. V. Sarantsev and U. Thoma
  
• “Transparency ratio in γA → η′A′ and the in-medium η′ width,” Phys. Lett. B 710 (2012) 600
  M. Nanova et al. [CBELSA/TAPS Collaboration]
  
• “Well-established nucleon resonances revisited by doublepolarization measurements,” Phys. Rev. Lett. 109 (2012) 102001
  A. Thiel et al. [CBELSA/TAPS Collaboration]
  
• “η and η′ mixing from Lattice QCD,” Phys. Rev. Lett. 111 (2013) 181602
  C. Michael et al. [ETM Collaboration]
  
• “A framework for the calculation of the ΔNγ⋆ transition form factors on the lattice,” Nucl. Phys. B 886 (2014) 1199
  A. Agadjanov, V. Bernard, U.-G. Meißner and A. Rusetsky
  
• “First measurement of the helicity asymmetry for γp → pπ0 in the resonance region,” Phys. Rev. Lett. 112 (2014) 012003
  M. Gottschall et al. [CBELSA/TAPS Collaboration]
  
• “Measurement of polarisation observables in Ks0Σ+ photoproduction off the proton,” Phys. Lett. B 738 (2014) 268
  R. Ewald et al. [CBELSA/TAPS Collaboration]
  
• “Pion cloud effects on baryon masses,” Phys. Lett. B 733 (2014) 151
  H. Sanchis-Alepuz, C. S. Fischer and S. Kubrak
  
• “The N(1520) 3/2- helicity amplitudes from an energy-independent multipole analysis based on new polarization data on photoproduction of neutral pions,” Phys. Rev. Lett. 113 (2014) 062001
  J. Hartmann, H. Dutz et al. [CBELSA/TAPS Collaboration]
  
• “Baryon chiral perturbation theory extended beyond the low-energy region,” Eur. Phys. J. C 75 (2015) 499
  E. Epelbaum, J. Gegelia, U.-G. Meißner and D. L. Yao
  
• “Measurement of double polarisation asymmetries in ω-photoproduction,” Phys. Lett. B 750 (2015) 453
  H. Eberhardt et al. [CBELSA/TAPS Collaboration]
  
• “Non-perturbative Test of the Witten-Veneziano Formula from Lattice QCD,” JHEP 1509 (2015) 020
  K. Cichy et al. [ETM Collaboration]
  
• “Precision nucleon-nucleon potential at fifth order in the chiral expansion,” Phys. Rev. Lett. 115 (2015) 122301
  E. Epelbaum, H. Krebs and U.-G. Meißner
  
• “Spectrum of three-body bound states in a finite volume,” Phys. Rev. Lett. 114 (2015) 091602
  U.-G. Meißner, G. Rios and A. Rusetsky
  
• “The polarization observables T, P, and H and their impact on γp → pπ0 multipoles,” Phys. Lett. B 748 (2015) 212
  J. Hartmann, H. Dutz et al. [CBELSA/TAPS Collaboration]
  
• “Three-body nature of N∗ and Δ∗ resonances from sequential decay chains,” Phys. Rev. Lett. 114 (2015) 091803
  A. Thiel et al. [CBELSA/TAPS Collaboration]
  
• “Upgrade of the inverted source of polarized electrons at ELSA”, J. Phys. Conf. Series 298 (2011) 012003
  D. Heiliger et al.
  
• “Baryons as relativistic threequark bound states,” Prog. Part. Nucl. Phys. 91 (2016) 1
  G. Eichmann, H. Sanchis-Alepuz, R. Williams, R. Alkofer and C. S. Fischer
  
• “Elastic pion-nucleon scattering in chiral perturbation theory: A fresh look,” Phys. Rev. C 94 (2016) 014620
  D. Siemens, V. Bernard, E. Epelbaum, A. Gasparyan, H. Krebs and U.-G. Meißner
  
• “Roy-Steiner-equation analysis of pionnucleon scattering,” Phys. Rept. 625 (2016) 1
  M. Hoferichter, J. Ruiz de Elvira, B. Kubis and U.-G. Meißner