Abstract
We report on our progress in studying exotic, heavy tetraquark states, qq′ Q̅Q̅′. Using publicly available dynamical nf = 2 + 1 Wilson-Clover gauge configurations, generated by the PACS-CS collaboration, with pion masses ≃ 164, 299 and 415 MeV, we extend our previous analysis to heavy quark components containing heavier than physical bottom quarks Q̅Q̅′ = b̅′b̅′ or Q̅Q̅′ = b̅b̅′, charm and bottom quarks c̅b̅ and also only charm quarks c̅ c̅. Throughout we employ NRQCD and relativistic heavy quarks for the heavier than bottom, bottom and charm quarks. Using our previously established diquark-antidiquark and meson-meson operator basis we comment in particular on the dependence of the binding energy on the mass of the heavy quark component Q̅Q̅, with heavy quarks ranging from mQ = 0:85… 6.3 · mb. In the heavy flavor non-degenerate case, Q̅Q̅′, and especially for the tetraquark channel udc̅d̅, we extend our work to utilize a 3 × 3 GEVP to study the ground and threshold states thereby enabling a clear identification of possible binding. Finally, we present initial work on the Q̅Q̅′ = c̅c̅ system where a much larger operator basis is available in comparison to flavor combinations with NRQCD quarks.
Highlights
The study of exotic states in QCD can provide insights into the mechanisms behind the binding of quarks into hadrons
A benefit of the former is that arbitrary quark masses can be used as input into simulations to probe important features of composite states of quarks, such as the constituent quark mass dependencies, which will help us to understand why some configurations of quarks are bound while others are not
Prior to our studies [1,2,3] the question of whether bound heavy tetraquark states exist in nature had been tackled in lattice QCD mainly with heavy quarks in the static approximation and/or with very heavy light sea-quarks [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]
Summary
The study of exotic states in QCD can provide insights into the mechanisms behind the binding of quarks into hadrons. The binding energies obtained from a chiral extrapolation to the physical pion mass were ∆Eudbb = 189(10)(3) MeV and ∆Elsbb = 98(7)(3) MeV Since this prediction and the results from the static approximation, compounded by the discovery of the doubly charmed Ξcc baryon at LHCb [24], there has been a renewed interest to explore this type of tetraquark configuration We study the heavy quark mass dependence of the binding ∆Eqq bb (mb, mb ) for unphysical bottom quark masses and present first results for channels with the flavor configurations udQ Q = udcband udQ Q = udcc The latter has been investigated at mπ = 391 MeV in [28] since this conference
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