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Title: Axial resonances a$$_{1}$$(1260), b$$_{1}$$(1235) and their decays from the lattice

The light axial-vector resonances $a_1(1260)$ and $b_1(1235)$ are explored in Nf=2 lattice QCD by simulating the corresponding scattering channels $$\rho\pi$$ and $$\omega\pi$$. Interpolating fields $$\bar{q} q$$ and $$\rho\pi$$ or $$\omega\pi$$ are used to extract the s-wave phase shifts for the first time. The $$\rho$$ and $$\omega$$ are treated as stable and we argue that this is justified in the considered energy range and for our parameters $$m_\pi\simeq 266~$$MeV and $$L\simeq 2~$$fm. We neglect other channels that would be open when using physical masses in continuum. Assuming a resonance interpretation a Breit-Wigner fit to the phase shift gives the $a_1(1260)$ resonance mass $$m_{a1}^{res}=1.435(53)(^{+0}_{-109})$$ GeV compared to $$m_{a1}^{exp}=1.230(40)$$ GeV. The $a_1$ width $$\Gamma_{a1}(s)=g^2 p/s$$ is parametrized in terms of the coupling and we obtain $$g_{a_1\rho\pi}=1.71(39)$$ GeV compared to $$g_{a_1\rho\pi}^{exp}=1.35(30)$$ GeV derived from $$\Gamma_{a1}^{exp}=425(175)$$ MeV. In the $b_1$ channel, we find energy levels related to $$\pi(0)\omega(0)$$ and $b_1(1235)$, and the lowest level is found at $$E_1 \gtrsim m_\omega+m_\pi$$ but is within uncertainty also compatible with an attractive interaction. Lastly, assuming the coupling $$g_{b_1\omega\pi}$$ extracted from the experimental width we estimate $$m_{b_1}^{res}=1.414(36)(^{+0}_{-83})$$.
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Univ. of Graz, Graz (Austria)
  2. Jozef Stefan Institute, Ljubljana (Slovenia)
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  4. Jozef Stefan Institute, Ljubljana (Slovenia); Univ. of Ljubljana, Ljubljana (Slovenia)
Publication Date:
OSTI Identifier:
1128720
Report Number(s):
FERMILAB-PUB--14-002-T
Journal ID: ISSN 1029-8479; arXiv eprint number arXiv:1401.2088
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
Journal of High Energy Physics (Online)
Additional Journal Information:
Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2014; Journal Issue: 4; Journal ID: ISSN 1029-8479
Publisher:
Springer Berlin
Research Org:
Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS lattice QCD; QCD