SFB 1044:  The Low-Energy Frontier of the Standard Model: From Quarks and Gluons to Hadrons and Nuclei

• Subject Area: Physics
• Term: from 2012 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 204404729

• Final Report Year: 2021

Final Report Abstract

The CRC 1044 studied the role of hadrons, which are subatomic particles built up from quarks and gluons, within the broader context of particle, atomic, and nuclear (astro-)physics. Hadron physics plays a central and connecting role in answering physics questions at both the highest and lowest energy scales. In nearly all questions at the forefront of the aforementioned research fields, the progress is limited by a missing quantitative knowledge of the strong interaction in the non-perturbative domain of Quantum Chromo Dynamics (QCD). Advancing this low-energy frontier of the Standard Model (SM) of particle physics has a direct impact on the most central questions in physics. In the CRC 1044, these research goals were pursued by a strategic cooperation between the Mainz Microtron (MAMI), the Beijing Spectrometer (BESIII), and the Mainz Energy Recovering Superconducting Accelerator MESA, which is presently being constructed as a main initiative within the PRISMA/PRISMA+ Excellence Cluster. Through a unique combination of measurements in electron scattering (MAMI and MESA), in electron-positron physics (BESIII), with state-of-the-art theoretical tools, such as lattice QCD, dispersion theory, and effective field theory, the CRC 1044 contributed to decisive advances in the low-energy frontier of the SM. The highlights of the CRC 1044 are firstly a new measurement at BESIII of the time-like pion form factor, reducing the dominant uncertainty, due to the hadronic vacuum polarization (HVP) contribution, in the SM prediction of the anomalous magnetic moment of the muon (g − 2)µ. The data-driven dispersive HVP determination has been complemented within the CRC 1044 with ab-initio lattice QCD calculations. An improvement of the SM prediction of (g − 2)µ is of utmost importance for a final interpretation of the experimental determination of (g − 2)µ, as obtained at Fermilab/USA and in the future at JPARC/Japan. Within the CRC 1044 the conceptual design of the parity violation experiment (P2) was completed at the MESA accelerator. In the next few years, this will make it possible to achieve the most precise measurement in the world of the weak mixing angle in electron-proton scattering and to test the SM to energy scales of around 50 TeV. A new measurement campaign of proton form factors and polarizabilities was performed at MAMI. This was complemented by refined theoretical analyses, which made it possible to significantly improve on the interpretation of high-precision tests of the Lamb shift in muonic Hydrogen as well as light muonic atoms. The activities were complemented by a new measurement of the time-like neutron form factor at BESIII. A photon-photon physics program at BESIII and A2/MAMI, aimed at extracting meson transition form factors, made it possible to derive more precise constraints on the hadronic light-by-light contribution (HLbL) to (g − 2)µ . These data were compared with a newly developed dispersive formalism, as well as a direct lattice calculation of the HLbL contribution. Furthermore, studies of spectroscopy with a polarized photon beam and polarized targets at A2/MAMI were successfully completed. The unique data sets for the photoproduction of pseudoscalar mesons on nucleons have allowed to clarify the role of several of the higher-lying resonances in the baryon spectrum. At BESIII the spectroscopy in the energy range at around 4 GeV has led to important observations of charmonium-like particles. High-precision measurements of the 4 He monopole transition form factor have been performed at A1/MAMI. A comparison with ab-initio chiral effective field theory calculations provided an important test of our understanding of few-body nuclear forces. Finally, an extended measurement campaign of beam-normal spin asymmetries in medium-heavy nuclei has been performed at MAMI, and has set the stage for the forthcoming parity-violation program at MESA, which will allow the nuclear equation of state to be studied.

Publications

• Light-by-light scattering sum rules constraining meson transition form factors. Phys. Rev. D 85 (2012) 116001
  V. Pascalutsa, V. Pauk and M. Vanderhaeghen
  
• Anomalous magnetic moment of the muon in a dispersive approach. Phys. Rev. D 90 (2014) 113012
  V. Pauk and M. Vanderhaeghen
  
• New determination of the η transition form factor in the Dalitz decay η → e+ e− γ with the Crystal Ball/TAPS detectors at the Mainz Microtron. Phys. Rev. C 89 no.4 (2014) 044608
  P. Aguar-Bartolome et al. [A2 Collaboration]
  
• The electric and magnetic form factors of the proton. Phys. Rev. C 90 (2014) 015206
  J. C. Bernauer et al. [A1 Collaboration]
  
• Measurement of the e+ e− → π + π − cross section between 600 and 900 MeV using initial state radiation. Phys. Lett. B 753 (2016) 629
  M. Ablikim et al. [BESIII Collaboration]
  
• Observation of 4Λ H Hyperhydrogen by Decay-Pion Spectroscopy in Electron Scattering. Phys. Rev. Lett., 114 (2015) 232501
  A. Esser, et al.
  
• Subtracted dispersion relation formalism for the two-photon exchange correction to elastic electron-proton scattering: Comparison with data. Eur. Phys. J. A 51 (2015) 2, 24
  O. Tomalak and M. Vanderhaeghen
  
• Lattice calculation of the pion transition form factor π 0 → γ ∗ γ ∗. Phys. Rev. D 94, no.7 (2016) 074507
  A. Gérardin, H. B. Meyer and A. Nyffeler
  
• Nucleon Polarizabilities: from Compton Scattering to Hydrogen Atom. Prog. Part. Nucl. Phys. 88 (2016) 29
  F. Hagelstein, R. Miskimen and V. Pascalutsa
  
• Dark Photon Search in the Mass Range Between 1.5 and 3.4 GeV/c2. Phys. Lett. B 774 (2017) 252
  M. Ablikim et al. [BESIII Collaboration]
  
• Determination of the scalar polarizabilities of the proton using beam asymmetry Σ3 in Compton scattering. Eur. Phys. J. A 53 (2017) 14
  V. Sokhoyan et al. [A2 Collaboration]
  
• First measurement of the polarization observable E and helicity-dependent cross sections in single π 0 photoproduction from quasi-free nucleons. Phys. Lett. B 770 (2017) 523
  M. Dieterle, F. Cividini et al. [A2 Collaboration]
  
• Measurement of the ω → π 0 e+ e− and η → e+ e− γ Dalitz decays with the A2 setup at MAMI. Phys. Rev. C 95 (2017) 035208
  P. Adlarson et al. [A2 collaboration]
  
• New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets. Phys. Rev. Lett. 119 (2017) 012501
  D. Balaguer Rios et al.
  
• Precise measurement of the e+ e− → π + π − J/ψ cross section at center-of-mass energies from 3.77 to 4.60 GeV. Phys. Rev. Lett. 118, no.9 (2017) 092001
  M. Ablikim et al. [BESIII Collaboration]
  
• Study of η and η’ Photoproduction at MAMI. Phys. Rev. Lett. 118, no.21 (2017) 212001
  V. L. Kashevarov et al. [A2 Collaboration]
  
• The hadronic vacuum polarization contribution to the muon g − 2 from lattice QCD. JHEP 1710 (2017) 020
  M. Della Morte, A. Francis, V. Gülpers, G. Herdoíza, G. von Hippel, H. Horch, B. Jäger, H. B. Meyer, A. Nyffeler and H. Wittig
  
• Two-photon exchange correction to 2S − 2P splitting in muonic 3 He ions. Phys. Rev. A 95, no. 1 (2017) 012506
  C. E. Carlson, M. Gorchtein and M. Vanderhaeghen
  
• η-η mixing in large-Nc chiral perturbation theory. Phys. Rev. D 95 (2017) 054023
  P. Bickert, P. Masjuan and S. Scherer
  
• Ab initio calculation of nuclear structure corrections in muonic atoms. J. Phys. G 45 (2018) 093002
  C. Ji, S. Bacca, N. Barnea, O. J. Hernandez and N. Nevo Dinur
  
• Dispersion Theory in Electromagnetic Interactions. Ann. Rev. Nucl. Part. Sci. 68 (2018) 75-103
  B. Pasquini and M. Vanderhaeghen
  
• Dissecting the hadronic contributions to (g − 2)µ by Schwinger’s sum rule. Phys. Rev. Lett. 120 (2018) 072002
  F. Hagelstein and V. Pascalutsa
  
• Efficiency and timing performance of the MuPix7 high-voltage monolithic active pixel sensor. Nucl. Instrum. Meth. A 902 (2018) 158
  H. Augustin et al.
  
• Eta and Etaprime Photoproduction on the Nucleon with the Isobar Model EtaMAID2018. Eur. Phys. J. A 54, no.12 (2018) 210
  L. Tiator et al.
  
• Experimental study of the γp → π 0 ηp reaction with the A2 setup at the Mainz Microtron. Phys. Rev. C 97, no.5 (2018) 055212
  V. Sokhoyan et al. [A2 Collaboration]
  
• First measurement of the Q2 dependence of the beam-normal single spin asymmetry for elastic scattering off Carbon. Phys. Rev. Lett., 121 (2018) 022503
  A. Esser et al.
  
• Measurement of the decay η → π 0 π 0 η at MAMI. Phys. Rev. D 98 (2018) 012001
  P. Adlarson et al. [A2 collaboration]
  
• Precision electron beam polarimetry for next generation nuclear physics experiments. Int. J. Mod. Phys. E 27 (2018) 1830004
  K. Aulenbacher, E. Chudakov, D. Gaskell, J. Grames and K. D. Paschke
  
• Precision Study of η → γπ + π − Decay Dynamics. Phys. Rev. Lett. 120 (2018) 242003
  M. Ablikim et al. [BESIII Collaboration]
  
• The P2 Experiment - A future high-precision measurement of the weak mixing angle at low momentum transfer. Eur. Phys. J. A 54 (2018) 208
  D. Becker et al.
  
• Deuteron photodisintegration by polarized photons in the region of the d∗ (2380). Phys. Lett. B 789 (2019) 7
  M. Bashkanov et al. [A2 Collaboration]
  
• Neutron skins of atomic nuclei: per aspera ad astra. J. Phys. G 46, no.9 (2019) 093003
  M. Thiel, C. Sfienti, J. Piekarewicz, C. J. Horowitz, M. Vanderhaeghen
  
• Second-order leptonic radiative corrections for lepton-proton scattering. Eur. Phys. J. A 55 (2019) 57
  R. D. Bucoveanu and H. Spiesberger
  
• The hadronic light-by-light contribution to the muon’s anomalous magnetic moment. Prog. Part. Nucl. Phys. 107 (2019) 20 - 68
  I. Danilkin, C. F. Redmer and M. Vanderhaeghen
  
• The leading hadronic contribution to (g − 2)µ from lattice QCD with Nf = 2 + 1 flavours of O(a) improved Wilson quarks. Phys. Rev. D 100, no.1 (2019) 014510
  A. Gérardin, Marco Cè, Georg von Hippel, et al.
  
• Extracting the spin polarizabilities of the proton by measurement of Compton doublepolarization observables. Phys. Rev. C 102, no.3 (2020) 035205
  D. Paudyal et al. [A2 Collaboration]
  
• Dispersive evaluation of the Lamb shift in muonic deuterium from chiral effective field theory. Phys. Rev. C 103, no.2 (2021) 024001
  B. Acharya, V. Lensky, S. Bacca, M. Gorchtein and M. Vanderhaeghen
  
• Isovector electromagnetic form factors of the nucleon from lattice QCD and the proton radius puzzle. Phys. Rev. D 103 (2021) 9, 094522
  D. Djukanovic, T. Harris, G. von Hippel, P. M. Junnarkar, H. B. Meyer, D. Mohler, K. Ottnad, T. Schulz, J. Wilhelm and H. Wittig
  
• Oscillating Features in the Electromagnetic Structure of the Neutron. Nature Physics (2021)
  M. Ablikim et al. [BES-III Collaboration]
  
• Search for the reaction channel e+ e− → ηc ηπ + π − at center-of-mass energies from 4.23 to 4.60 GeV. Phys. Rev. D 103 (2021) 032004
  M. Ablikim et al. [BESIII Collaboration]