Precision Tests of Standard Model at Low Energies with Atoms, Hadrons and Neutrinos
Final Report Abstract
The dispersive formulation of the γW -box correction to the Fermi part of the neutron and nuclear β decays introduced is a major improvement in this field since over a decade. The use of the new method allowed for a direct use of experimental data in the uncertainty estimate. This led to an almost factor of 2 reduction in the hadronic structure-dependent uncertainty in the value of Vud extracted from the superallowed decays. Because the uncertainty estimate is data driven, it is systematically improvable if new, more precise data will become available. In view of the upcoming neutrino and antineutrino scattering experiment DUNE at Fermilab, the hadronic uncertainty in Vud can be confirmed and further reduced in the near future. The new dispersive formalism also provided a natural unification of the hadronic and nuclear structure corrections within the same framework, and led to the observation that the nuclear structure affects the shape of the β spectrum. These results already stimulated a renewed scrutiny of nuclear structure corrections in nuclear beta decays within the nuclear theory community where new, more advanced techniques have become available in the recent years. The indications that the nuclear uncertainties are likely to have been underestimated shift the emphasis onto more precise measurements of the neutron decay since the analysis of the latter is free from nuclear uncertainties. The state-of-the-art theory calculations that are needed to interpret high-precision parity-violating electron scattering (PVES) experiments in terms of the weak charge of the proton and the weak mixing angle have been performed, and their uncertainties critically assessed. A novel effect, an exchange of two photons accompanied by parity violation in the hadronic system gives rise to long-range parity-violating (LRPV) interaction. We showed that an exact sum rule protects the definition of the weak charge of these LRPV effects, and provided a formal proof of this sum rule in relativistic chiral perturbation theory. An estimate of the LRPV corrections to Q-Weak and P2 experiments in a hadronic model was provided. All theoretical uncertainties are under control, and once the experimental situation changes (e.g., an improved accuracy of the proton anapole moment) this information will easily be translated into improved theoretical uncertainty estimates. In the process of working on the radiative corrections to PVES, and to more efficiently interact with the local experimental group, I officially joined the P2 collaboration. As part of Mainz-Tuzla-Zagreb collaboration that I joined during this project, I contributed to the new analysis of η, η -photoproduction. This analysis includes all recent data on photoproduction of η and η on the proton and neutron target inthe resonance region and beyond, and is available on the MAID website. I considered unitarity and analyticity constraints on π, η-photoproduction with dispersion relations and showed that the matching of the parametrization of the amplitude in the resonance region to the Regge model valid at high energies can be done on the level of multipoles, rather than invariant amplitudes. This will serve as the basis for the further development of MAID in the electromagnetic and weak sectors. The new dispersion formalism can be further exploited for more precise theory calculations of the nuclear structure corrections ∆^V E , δNS and δ^E NS ; to evaluate the γW-box for kaon semileptonic β decay to resolve the discrepancy in Vus with the purely leptonic channel; to compute radiative corrections to the Gamow-Teller transition, important for relating the measured value of gA to lattice QCD calculations. The closely related correction to PVES, γZ-box should be updated accordingly. The impact of the LRPV interaction in nuclear systems needs to be assessed, in the context of plans to measure nuclear weak charges and neutron skins with PVES. The parametrization of the inclusive neutrino and antineutrino data entering the calculation of the γW-box can be constrained by the upcoming DUNE data. The Regge contribution to the PV structure function F^γW,γZ 3 can be used to estimate real γ production in neutrino scattering, possible cause for the MiniBooNE and LSND event excess. Once the high energy part of inclusive neutrino scattering amplitudes is fixed, it can be used for matching the partial wave analysis for neutrinoproduction of pions and etas.
Publications
- γW-box inside-out: nuclear polarizabilities distort the nuclear β-decay spectrum
M. Gorchtein
(See online at https://doi.org/10.1103/PhysRevLett.123.042503) - “Hadronic weak charges and parity-violating forward Compton scattering”, Phys. Rev. C 94, no. 5, 055502 (2016)
M. Gorchtein and H. Spiesberger
(See online at https://doi.org/10.1103/PhysRevC.94.055502) - “Precision Measurement of sin2 θw at MESA”, PoS LL 2016 (2016) 061
R. Bucoveanu, M. Gorchtein and H. Spiesberger
(See online at https://doi.org/10.22323/1.260.0061) - “Eta and Etaprime Photoproduction on the Nucleon with the Isobar Model EtaMAID2018”, Eur. Phys. J. A54 (2018) no. 12, 210
L. Tiator et al.
(See online at https://doi.org/10.1140/epja/i2018-12643-x) - “Reduced hadronic uncertainty in the determination of Vud ”, Phys. Rev. Lett. 121 (2018) no.24, 241804
C. Y. Seng, M. Gorchtein, H. H. Patel and M. J. Ramsey-Musolf
(See online at https://doi.org/10.1103/PhysRevLett.121.241804) - “The P2 Experiment - A future high-precision measurement of the electroweak mixing angle at low momentum transfer”, Eur. Phys. J. A54 (2018) no. 11, 208
D. Becker et al.
(See online at https://doi.org/10.1140/epja/i2018-12611-6) - Dispersive evaluation of the inner radiative correction in neutron and nuclear β decay
C. Y. Seng, M. Gorchtein and M. J. Ramsey-Musolf
(See online at https://doi.org/10.1103/PhysRevD.100.013001) - “Unitarity, analyticity and duality constraints in η and π photoproduction”, EPJ Web of Conf. 199, 02002 (2019)
M. Gorchtein
(See online at https://doi.org/10.1051/epjconf/201919902002)
