Two-Nucleon Higher Partial-Wave Scattering from Lattice QCD

04 Aug 2015

Physics Letters B, Volume 765, 10 February 2017, Pages 285 to 292 [arXiv:1508.00886]

We present a determination of nucleon-nucleon scattering phase shifts for $l \geq 0$. The S, P, D and F phase shifts for both the spin-triplet and spin-singlet channels are computed with lattice Quantum ChromoDynamics. For $l > 0$, this is the first lattice QCD calculation using the Luscher finite-volume formalism. This required the design and implementation of novel lattice methods involving displaced sources and momentum-space cubic sinks. To demonstrate the utility of our approach, the calculations were performed in the SU(3)-flavor limit where the light quark masses have been tuned to the physical strange quark mass, corresponding to $m_\pi = m_K \sim 800$ MeV. In this work, we have assumed that only the lowest partial waves contribute to each channel, ignoring the unphysical partial wave mixing that arises within the finite-volume formalism. This assumption is only valid for sufficiently low energies; we present evidence that it holds for our study using two different channels. Two spatial volumes of $V \sim (3.5\ {\rm fm})^3$ and $V \sim (4.6\ {\rm fm})^3$ were used. The finite-volume spectrum is extracted from the exponential falloff of the correlation functions. Said spectrum is mapped onto the infinite volume phase shifts using the generalization of the Luscher formalism for two-nucleon systems.