Search

The isovector and isoscalar ND s-wave scattering lengths are extracted by fitting to the LHCb data of the p D 0 invariant-mass distribution in the decay Λ b → π − p D 0 , making use of the cusp effect at the n D + threshold. The analysis is based on a coupled-channel nonrelativistic effective field theory. We find that the real part of the isovector ND scattering length is unnaturally large due to the existence of a near-threshold state with a mass around 2.8 GeV. The state is consistent with the Σ c ( 2800 ) + resonance observed at Belle. Our results suggest that it couples strongly to the ND channel in an s-wave, and that its quantum numbers are J P = 1 / 2 − . The strong cusp behavior at the n D + threshold can be verified using updated LHCb data.

Whether the Y ( 4260 ) can couple to open charm channels has been a crucial issue for understanding its nature. The available experimental data suggest that the cross section line shapes of exclusive processes in e + e − annihilations have nontrivial structures around the mass region of the Y ( 4260 ) . As part of a series of studies of the Y ( 4260 ) as mainly a D ¯ D 1 ( 2420 ) + c . c . molecular state, we show that the partial widths of the Y ( 4260 ) to the two-body open charm channels of e + e − → D ⁎ D ¯ ⁎ and D s ⁎ D ¯ s ⁎ are much smaller than that to D ¯ D ⁎ π + c . c . . The line shapes measured by the Belle Collaboration for these two channels can be well described by the vector charmonium states ψ ( 4040 ) , ψ ( 4160 ) and ψ ( 4415 ) together with the Y ( 4260 ) . It turns out that the interference of the Y ( 4260 ) with the other charmonia produces a dip around 4.22 GeV in the e + e − → D ⁎ D ¯ ⁎ cross section line shape. The data also show an evidence for the strong coupling of the Y ( 4260 ) to the D D ¯ 1 ( 2420 ) , in line with the expectation in the hadronic molecular scenario for the Y ( 4260 ) .

We study the Λ c + → π 0 ϕ p decay by considering a triangle singularity mechanism. In this mechanism, the Λ + c decays into the K ⁎ Σ ⁎ ( 1385 ) , the Σ ⁎ ( 1385 ) decays into the π 0 Σ (or Λ), and then the K ⁎ Σ (or Λ) interact to produce the ϕp in the final state. This mechanism produces a peak structure around 2020 MeV. In addition, the possibility that there is a hidden-strange pentaquark-like state is also considered by taking into account the final state interactions of K ⁎ Λ , K ⁎ Σ , and ϕp. We conclude that it is difficult to search for the hidden-strange analogue of the P c states in this decay. However, we do expect nontrivial behavior in the ϕp invariant mass distribution. The predictions can be tested by experiments such as BESIII, LHCb and Belle-II.

The so far only known charmed non-strange scalar meson is dubbed as D 0 ⁎ ( 2400 ) in the Review of Particle Physics. We show, within the framework of unitarized chiral perturbation theory, that there are in fact two ( I = 1 / 2 , J P = 0 + ) poles in the region of the D 0 ⁎ ( 2400 ) in the coupled-channel Dπ, Dη and D s K ¯ scattering amplitudes. With all the parameters previously fixed, we predict the energy levels for the coupled-channel system in a finite volume, and find that they agree remarkably well with recent lattice QCD calculations. This successful description of the lattice data is regarded as a strong evidence for the two-pole structure of the D 0 ⁎ ( 2400 ) . With the physical quark masses, the poles are located at ( 2105 − 8 + 6 − i 102 − 12 + 10 ) MeV and ( 2451 − 26 + 36 − i 134 − 8 + 7 ) MeV , with the largest couplings to the Dπ and D s K ¯ channels, respectively. Since the higher pole is close to the D s K ¯ threshold, we expect it to show up as a threshold enhancement in the D s K ¯ invariant mass distribution. This could be checked by high-statistic data in future experiments. We also show that the lower pole belongs to the same SU(3) multiplet as the D s 0 ⁎ ( 2317 ) state. Predictions for partners in the bottom sector are also given.

In the hindered magnetic dipole transitions of heavy quarkonia, the coupled-channel effects originating from the coupling of quarkonia to a pair of heavy and anti-heavy mesons can play a dominant role. Here, we study the hindered magnetic dipole transitions between two $P$-wave bottomonia, $\chi_b(n P)$ and $h_b(n^\prime P)$, with $n\neq n^\prime$. In these processes the coupled-channel effects are expected to lead to partial widths much larger than the quark model predictions. We estimate these partial widths which, however, are very sensitive to unknown coupling constants related to the vertices $\chi_{b0}(nP)B\bar B$. A measurement of the hindered M1 transitions can shed light on the coupled-channel dynamics in these transitions and hence on the size of the coupling constants. We also suggest to check the coupled-channel effects by comparing results from quenched and fully dynamical lattice QCD calculations., Comment: 10 pages, 2 figures, version accepted for publication in Physics Letters B

The distribution of the QCD topological charge can be described by cumulants, with the lowest one being the topological susceptibility. The vacuum energy density in a theta-vacuum is the generating function for these cumulants. In this paper, we derive the vacuum energy density in SU(2) chiral perturbation theory up to next-to-leading order keeping different up and down quark masses, which can be used to calculate any cumulant of the topological charge distribution. We also give the expression for the case of SU(N) with degenerate quark masses. In this case, all cumulants depend on the same linear combination of low-energy constants and chiral logarithm, and thus there are sum rules between the N-flavor quark condensate and the cumulants free of next-to-leading order corrections., match the version published in PLB

We study the production of the spin partner of the X(3872), which is a D⁎D¯⁎ bound state with quantum numbers JPC=2++ and named X2(4012) here, with the associated emission of a photon in electron–positron collisions. The results show that the ideal energy region to observe the X2(4012) in e+e− annihilations is from 4.4 GeV to 4.5 GeV, due to the presence of the S-wave D¯⁎D1(2420) and D¯⁎D2(2460) thresholds, respectively. We also point out that it will be difficult to observe the γX(4012) at the e+e− center-of-mass energy around 4.26 GeV.

Heavy quark spin symmetry is useful to make predictions on ratios of decay or production rates of systems involving heavy quarks. The breaking of spin symmetry is generally of the order of $O({\Lambda_{\rm QCD}/m_Q})$, with $\Lambda_{\rm QCD}$ the scale of QCD and $m_Q$ the heavy quark mass. In this paper, we will show that a small $S$- and $D$-wave mixing in the wave function of the heavy quarkonium could induce a large breaking in the ratios of partial decay widths. As an example, we consider the decays of the $\Upsilon(10860)$ into the $\chi_{bJ}\omega\, (J=0,1,2)$, which were recently measured by the Belle Collaboration. These decays exhibit a huge breaking of the spin symmetry relation were the $\Upsilon(10860)$ a pure $5S$ bottomonium state. We propose that this could be a consequence of a mixing of the $S$-wave and $D$-wave components in the $\Upsilon(10860)$. Prediction on the ratio $\Gamma(\Upsilon(10860)\to\chi_{b0}\omega)/\Gamma(\Upsilon(10860)\to\chi_{b2}\omega)$ is presented assuming that the decay of the $D$-wave component is dominated by the coupled-channel effects., Comment: 13 pages, 5 figures. Discussion extended, version to appear in Phys.Lett.B

Direct production of the charmonium-like state X ( 3872 ) in e + e − collisions is considered in the framework of the vector meson dominance model. An order-of-magnitude estimate for the width Γ ( X → e + e − ) is found to be ≳0.03 eV. The same approach applied to the χ c 1 charmonium decay predicts the corresponding width of the order 0.1 eV in agreement with earlier estimates. Experimental perspectives for the direct production of the 1 + + charmonia in e + e − collisions are briefly discussed.

Nucleon electric dipole moments originating from strong CP-violation are being calculated by several groups using lattice QCD. We revisit the finite volume corrections to the CP-odd nucleon matrix elements of the electromagnetic current, which can be related to the electric dipole moments in the continuum, in the framework of chiral perturbation theory up to next-to-leading order taking into account the breaking of Lorentz symmetry. A chiral extrapolation of the recent lattice results of both the neutron and proton electric dipole moments is performed, which results in $d_n=(-2.7\pm1.2)\times10^{-16}e\theta_0$cm and $d_p=(2.1\pm1.2)\times10^{-16}e\theta_0$cm., Comment: 12 pages, 3 figures. A longer title, no change in the text. Accepted for publication in PLB

We discuss the possibilities of producing the X(3872), which is assumed to be a D (D) over bar* bound state, in radiative decays of charmonia. We argue that the ideal energy regions to observe the X(3872) associated with a photon in e(+)e(-)-annihilations are around the. Y(4260) mass and around 4.45 GeV, due to the presence of the S-wave D (D) over bar (1) (2420) and D*(D) over bar (1) (2420) threshold, respectively. Especially, if the Y(4260) is dominantly a D (D) over bar (1) molecule and the X(3872) a DD* molecule, the radiative transition strength will be quite large. (C) 2013 Elsevier B.V. All rights reserved.

The so far only known charmed non-strange scalar meson is dubbed as D0⁎(2400) in the Review of Particle Physics. We show, within the framework of unitarized chiral perturbation theory, that there are in fact two (I=1/2,JP=0+) poles in the region of the D0⁎(2400) in the coupled-channel Dπ , Dη and DsK¯ scattering amplitudes. With all the parameters previously fixed, we predict the energy levels for the coupled-channel system in a finite volume, and find that they agree remarkably well with recent lattice QCD calculations. This successful description of the lattice data is regarded as a strong evidence for the two-pole structure of the D0⁎(2400) . With the physical quark masses, the poles are located at (2105−8+6−i102−12+10) MeV and (2451−26+36−i134−8+7) MeV , with the largest couplings to the Dπ and DsK¯ channels, respectively. Since the higher pole is close to the DsK¯ threshold, we expect it to show up as a threshold enhancement in the DsK¯ invariant mass distribution. This could be checked by high-statistic data in future experiments. We also show that the lower pole belongs to the same SU(3) multiplet as the Ds0⁎(2317) state. Predictions for partners in the bottom sector are also given.

We construct the effective chiral Lagrangian involving the D-mesons and Goldstone bosons at next-to-leading order taking into account strong as well as electromagnetic interactions. This allows us to disentangle—to leading order in isospin violation—the electromagnetic and the strong contribution to the D-meson mass differences. In addition, we also apply the interaction to the decay D s 0 ∗ ( 2317 ) → D s π 0 under the assumption that the D s 0 ∗ ( 2317 ) is a hadronic molecule. We find ( 180 ± 110 ) keV for the decay width Γ ( D s 0 ∗ ( 2317 ) → D s π 0 ) —consistent with currently existing experimental constraints as well as previous theoretical investigations. The result provides further evidence that this decay width can serve as a criterion for testing the nature of the D s 0 ∗ ( 2317 ) .

We demonstrate that the experimental information currently available for the Y(4660) is consistent with its being an f0(980)ψ′ molecule. Possible experimental tests of our hypothesis are presented.

We calculate the mass shifts of heavy-light scalar mesons due to hadronic loops under the assumption that these vanish for the groundstate heavy-light mesons. The results show that the masses calculated in quark models can be reduced significantly. We stress that the mass alone is not a signal for a molecular interpretation. Both the resulting mass and the width suggest the observed $D_0^*$ state could be a dressed $c\bar q$ state. We give further predictions for the bottom scalar mesons which can be used to test the dressing mechanism., 14 pages, 2 figures. Version accepted for publication in Phys. Lett. B

We perform a model-independent analysis for recently reported data of the pi(+)pi(-) invariant mass spectra in the gamma (4S) -> gamma (1S, 2S)pi(+)pi(-) decays and point out that there does exist a broad peak below 0.6 GeV in the data of the gamma(4S) -> gamma(1S)pi(+)pi(-) decay, which is analogous to that in the gamma (3S) -> gamma(1S)pi(+)pi(-) decay. With the data of gamma(4S) decays, we further test our model developed for studying the puzzle in the gamma (3S) -> gamma (1S) pi(+)pi(-) decay. The result shows that with such a model, all the pi(+)pi(-) invariant mass spectra of gamma (4S) decays can be described. We also predict the cos theta(pi)* distributions of gamma (4S) -> gamma (1S, 2S)pi(+)pi(-) decays, which can be used to justify our model prediction. (c) 2007 Elsevier B.V. All rights reserved.

By using a heavy chiral unitary approach, we study the $S$ wave interactions between heavy vector meson and light pseudoscalar meson. By searching for poles of the unitary scattering amplitudes in the appropriate Riemann sheets, several $1^+$ heavy states are found. In particular, a $D^*K$ bound state with a mass of $2.462\pm0.010$ GeV which should be associated with the recently observed $D_{s1}(2460)$ state is obtained. In the same way, a $B^*{\bar K}$ bound state ($B_{s1}$) with mass of $5.778\pm0.007$ GeV in the bottom sector is predicted. The spectra of the dynamically generated $D_1$ and $B_1$ states in the $I=1/2$ channel are also calculated. One broad state and one narrow state are found in both the charmed and bottom sectors. The coupling constants and decay widths of the predicted states are further investigated., 17 pages, 3 figures. Version accepted for publication in Phys. Lett. B