Seminars IFIC

IFIC SEMINAR: Baryon-baryon interactions and the axial charge of the triton at $m_\pi \sim$ 450 MeV

by Prof. Assumpta Parreño (Universidad de Barcelona)


Building upon our previous works at heavier quark masses, we present our studies on the low-energy finite-volume spectra of two- and three-baryon systems using the numerical technique of lattice QCD. The study includes the spin-singlet and triplet $NN$, $\Sigma N$ ($I=3/2$), and $\Xi\Xi$ states, the spin-singlet $\Sigma \Sigma$ ($I=2$) and $\Xi \Sigma$ ($I=3/2$) states, the spin-triplet $\Xi N$ ($I=0$) state, and the triton channel. 
The calculations have been performed in three ensembles of gauge field configurations generated with quark masses corresponding to a pion mass of 450 MeV. While the results are consistent with most of the baryon-baryon (BB) systems being bound at this pion mass, the interactions in the spin-triplet $\Sigma N$ and $\Xi \Xi$ channels are found to be repulsive and do not support bound states.  Using results from previous studies of these systems at a larger pion mass, an extrapolation of the BB binding energies to the physical point is performed and is compared with available experimental values and phenomenological predictions. For the three-body system, a compact bound state with the quantum numbers of the triton at the studied quark masses is found. Additionally, we compute the axial current matrix elements using background field techniques on one of the ensembles, and use finite-volume pionless effective field theory to determine the axial charge of the proton and triton. A simple quark mass extrapolation of these results leads to a value of the ratio of the triton to proton axial charges at the physical quark masses consistent with the experimental determination, showing that the modification of the axial charge of the triton can be reproduced directly from QCD.

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