1,459 research outputs found

    Axial resonances a1(1260), b1(1235) and their decays from the lattice

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    The light axial-vector resonances a1(1260)a_1(1260) and b1(1235)b_1(1235) are explored in Nf=2 lattice QCD by simulating the corresponding scattering channels ρπ\rho\pi and ωπ\omega\pi. Interpolating fields qΛ‰q\bar{q} q and ρπ\rho\pi or ωπ\omega\pi are used to extract the s-wave phase shifts for the first time. The ρ\rho and Ο‰\omega are treated as stable and we argue that this is justified in the considered energy range and for our parameters mπ≃266Β m_\pi\simeq 266~MeV and L≃2Β 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 a1(1260)a_1(1260) resonance mass ma1res=1.435(53)(βˆ’109+0)m_{a1}^{res}=1.435(53)(^{+0}_{-109}) GeV compared to ma1exp=1.230(40)m_{a1}^{exp}=1.230(40) GeV. The a1a_1 width Ξ“a1(s)=g2p/s\Gamma_{a1}(s)=g^2 p/s is parametrized in terms of the coupling and we obtain ga1ρπ=1.71(39)g_{a_1\rho\pi}=1.71(39) GeV compared to ga1ρπexp=1.35(30)g_{a_1\rho\pi}^{exp}=1.35(30) GeV derived from Ξ“a1exp=425(175)\Gamma_{a1}^{exp}=425(175) MeV. In the b1b_1 channel, we find energy levels related to Ο€(0)Ο‰(0)\pi(0)\omega(0) and b1(1235)b_1(1235), and the lowest level is found at E1≳mΟ‰+mΟ€E_1 \gtrsim m_\omega+m_\pi but is within uncertainty also compatible with an attractive interaction. Assuming the coupling gb1ωπg_{b_1\omega\pi} extracted from the experimental width we estimate mb1res=1.414(36)(βˆ’83+0)m_{b_1}^{res}=1.414(36)(^{+0}_{-83}).Comment: 15 pages, 4 figures, updated to match published versio

    Vector and scalar charmonium resonances with lattice QCD

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    We perform an exploratory lattice QCD simulation of DDΛ‰D \bar D scattering, aimed at determining the masses as well as the decay widths of charmonium resonances above open charm threshold. Neglecting coupling to other channels, the resulting phase shift for DDΛ‰D \bar D scattering in p-wave yields the well-known vector resonance ψ(3770)\psi(3770). For mΟ€=156m_\pi = 156 MeV, the extracted resonance mass and the decay width agree with experiment within large statistical uncertainty. The scalar charmonium resonances present a puzzle, since only the ground state Ο‡c0(1P)\chi_{c0}(1P) is well understood, while there is no commonly accepted candidate for its first excitation. We simulate DDΛ‰D \bar D scattering in s-wave in order to shed light on this puzzle. The resulting phase shift supports the existence of a yet-unobserved narrow resonance with a mass slightly below 4 GeV. A scenario with this narrow resonance and a pole at Ο‡c0(1P)\chi_{c0}(1P) agrees with the energy-dependence of our phase shift. Further lattice QCD simulations and experimental efforts are needed to resolve the puzzle of the excited scalar charmonia.Comment: 24 pages, 8 figures, updated to match published versio

    Excited light and strange hadrons from the lattice with two Chirally Improved quarks

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    Results for excited light and strange hadrons from the lattice with two flavors of Chirally Improved sea quarks are presented. We perform simulations at several values of the pion mass ranging from 250 to 600 MeV and extrapolate to the physical pion mass. The variational method is applied to extract excited energy levels but also to discuss the content of the states. Among others, we explore the flavor singlet/octet content of Lambda states. In general, our results agree well with experiment, in particular we confirm the Lambda(1405) and its dominant flavor singlet structure.Comment: Contribution to the XV International Conference on Hadron Spectroscopy "Hadron 2013", 4-8 November 2013, Nara, Japa

    Predicting positive parity BsB_{s} mesons from lattice QCD

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    We determine the spectrum of BsB_s 1P states using lattice QCD. For the Bs1(5830)B_{s1}(5830) and Bs2βˆ—(5840)B_{s2}^*(5840) mesons, the results are in good agreement with the experimental values. Two further mesons are expected in the quantum channels JP=0+J^P=0^+ and 1+1^+ near the BKBK and Bβˆ—KB^{*}K thresholds. A combination of quark-antiquark and B(βˆ—)B^{(*)} meson-Kaon interpolating fields are used to determine the mass of two QCD bound states below the B(βˆ—)KB^{(*)}K threshold, with the assumption that mixing with Bs(βˆ—)Ξ·B_s^{(*)}\eta and isospin-violating decays to Bs(βˆ—)Ο€B_s^{(*)}\pi are negligible. We predict a JP=0+J^P=0^+ bound state Bs0B_{s0} with mass mBs0=5.711(13)(19)m_{B_{s0}}=5.711(13)(19) GeV. With further assumptions motivated theoretically by the heavy quark limit, a bound state with mBs1=5.750(17)(19)m_{B_{s1}}= 5.750(17)(19) GeV is predicted in the JP=1+J^P=1^+ channel. The results from our first principles calculation are compared to previous model-based estimates.Comment: 5 pages, 2 figures; Final versio
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