Task 2.1 - Hadron resonances, form factors, LECs, fundamental parameters of QCD and light nuclei spectroscopy

 

Coordinators: A. Lovato, A. Parreño

Contributors: M. Bertani, D. Boito, N. Brambilla, R. Escribano, E. Hernández, A. Lovato, V. Magas, A. Mangoni, V. Mateu, J. Menéndez, J. Nieves, S. Pacetti, J. R. Peláez, N. Penalva, À. Ramos, D. Rodríguez Entem, E. Santopinto, J. Soto, and A. Vairo.

 

 

 

General description:

 

We aim at studying Lattice-QCD (LQCD) simulations in finite volumes. Methods will be developed to deal with the extraction of the properties of hadrons from the simulations. Lattice and Green's function MC simulations, combining chiral NN and 3N forces, will be also performed to study light and medium-heavy nuclei.

 

 

Progress [1-18 months]:

 

List of achievements:

 

1. Determination of the strong coupling constant  α_s:

 

Using a combination of lattice data at unprecedented small qq distance and EFTs, we have obtained two competitive determinations of the strong coupling α_s [Ba19]. The first one is from the static energy at three-loop accuracy. In this new analysis we included new lattice data at smaller lattice spacings, and reached distances as short as 0.0237 fm. We present a comprehensive and detailed estimate of the error sources that contribute to the uncertainty of the final result, α_s(M_Z)=0.11660^+0.00110_-0.00056 . The second determination is based on lattice data for the singlet free energy at finite temperature up to distances as small as 0.0081 fm, from which we obtain α_s(M_Z)=0.11638^+0.00095_-0.00087. In addition, employing experimental and LQCD data, we have also performed a precise extraction of α_s from dimensionless ratios of roots of the moments of the charm- and bottom-quark vector correlators and the charm pseudo-scalar correlator [Bo20].

 

 

2. New physics (NP). Test of lepton flavor universality (LFU)

 

2.1  We carried out tests of LFU from the charged lepton energy distribution in b→c semileptonic decays [Pe19]. We studied the Λ_b → Λ_c l ν_l , with l=τ or e,μ  (massless charged leptons), decay using LQCD form-factors and study effects of NP beyond the Standard Model, affecting only the third generation of quarks and leptons. We provided a general framework for semileptonic decays with all NP effective Hamiltonians, which are considered in LFU violation studies, included.

 

2.2 A model-independent global fit to b → s l⁺l^- observables to confirm existing NP patterns and to identify new ones emerging from the inclusion of the updated LHCb and Belle measurements  of R_K  and R_K*, respectively, was performed in [Al19]. The analysis suggests the presence of right-handed couplings encoded in some of the Wilson coefficients. It is discussed a scenario that provides a simple and model-independent connection to the b→cτν_τ anomalies, which provides a preference of ∼7σ with respect to the Standard Model.

 

 

3. Nuclear structure with chiral forces

 

3.1 We carried out a comprehensive set of neutron matter calculations using as input nucleon-nucleon chiral-EFT interactions that explicitly include the excitation of the Delta resonance [Pi20]. We benchmarked the predictions of the auxiliary-field diffusion Monte Carlo (AFDMC), the Fermi-hypernetted chain (FHNC), and the Brueckner-Hartree-Fock (BHF) many-body methods. We removed the bias affecting previous AFDMC calculations by performing unconstrained-path imaginary-time propagations, finding a much better agreement with FHNC and BHF. We are now carrying out calculations of the energy per particle of infinite neutron matter using consistent two- and three-body forces.

 

3.2 In a synergistic effort with experimentalists, we study nuclear electromagnetic transitions [He20, Ci20] and the evolution of magic numbers in neutron-rich nuclei [Ma20c, Co20].

 

3.3 An accurate understanding of neutrino interactions with nuclei is fundamental for the success of the world-wide neutrino-oscillation program. Within our effective model of nuclear dynamics, we study exclusive final state hadron observables from neutrino-nucleus multi-nucleon knockout [So20b] and the polarization of τ in quasielastic (anti-)neutrino scattering [So19].

 

 

References:

 

• [Ba19] TUMQCD Collaboration: A. Bazavov et al., Phys. Rev. D 100 (2019) 11, 114511; e-Print: 1907.11747 [hep-lat]; N. Brambilla, A. Bazavov, X. Garcia i Tormo, P. Petreczky, J. Soto, et al., PoS ALPHAS2019 (2019) 024.

• [Bo20] D. Boito and V. Mateu, Phys. Lett. B 806 (2020), 135482; JHEP 03 (2020), 094.

• [Pe19] N. Penalva, E. Hernández and J. Nieves, Phys.Rev.D 100 (2019) 113007; Phys. Rev. D 101, 113004 (2020).

• [Al19] M. Algueró, B. Capdevila, A. Crivellin, S. Descotes-Genon, P. Masjuan. Eur. Phys. J. C 79 (2019) 8, 714, Eur. Phys. J. C 80 (2020) 6, 511 (addendum).

• [Pi20] M. Piarulli, I. Bombaci, D. Logoteta, A. Lovato and R.B. Wiringa, Phys. Rev. C 101 045801 (2020)

• [He20] S. Heil et al., Phys. Lett. B 809 135378 (2020)

• [Ci20] M. Ciemala et al., Phys. Rev. C 101 021303 (2020)

• [Ma20c[ V. Manea et al., Phys. Rev. Lett. 124, 092502 (2020)

• [Co20] M. L. Cortés et al, Phys. Lett. B 800 135071(2020).

• [So20b] J.E. Sobczyk, J. Nieves and F. Sánchez, Phys. Rev. C 102 (2020) 024601

• [So19] J.E. Sobczyk, N. Rocco and J. Nieves, Phys. Rev. C 100 (2019) 035501