arXiv subjects

Feng-Kun Guo

Publications and source records attributed to Feng-Kun Guo.

At least 217 records · Page 12Linked to original sources

arXiv2013

Hadron physics potential of future high-luminosity B-factories at the Upsilon(5S) and above

We point out the physics opportunities of future high-luminosity B-factories at the Upsilon(5S) resonance and above. In this paper we discuss numerous interesting investigations, which can be performed in the e+e- centre-of-mass energy region from the Upsilon(5S) and up to 11.5 GeV, where an efficient data taking operation should be possible with the planned B-factories. These studies include abundant Bs production and decay properties; independent confirmation and if found, exhaustive exploration of Belle's claimed charged bottomonia; clarification of puzzles of interquarkonium dipion transitions; extraction of the light quark mass ratio from hadronic Upsilon(5S) decays; analysis of quarkonium and exotic internal structure from open flavour decays, leading to severe SU(3) symmetry violations; clarification of whether a hybrid state has similar mass to the Upsilon(5S) bottomonium, making it a double state; searches for molecular/tetraquark states that should be more stable with heavy quarks; completion of the table of positive-parity B_J mesons and study of their basic properties; production of Lambda_b\bar{Lambda}_b heavy baryon pairs, that, following weak decay, open vistas on the charmed baryon spectrum and new channels to study CP violation; confirmation or refutation of the deviation from pQCD of the pion transition form factor, by extending the Q^2 reach of current analysis; and possibly reaching the threshold for the production of triply-charmed baryons. If, in addition, the future colliders can be later upgraded to 12.5 GeV, then the possibility of copious production of B_c\bar{B}_c pairs opens, entailing new studies of CP violation and improved, independent tests of the CKM picture (through determination of V_{bc}), and of effective theories for heavy quarks.

hep-ph↗

arXiv2012

Extracting $ππ$ $S$-wave scattering lengths from cusp effect in heavy quarkonium dipion transitions

Charge-exchange rescattering $π^+π^-\to π^0π^0$ leads to a cusp effect in the $π^0π^0$ invariant mass spectrum of processes with $π^0π^0$ in the final state which can be used to measure $ππ$ $S$-wave scattering lengths. Employing a non-relativistic effective field theory, we discuss the possibility of extracting the scattering lengths in heavy quarkonium $π^0π^0$ transitions. The transition $Υ(3S)\toΥ(2S)π^0π^0$ is studied in details. We discuss the precision that can be reached in such an extraction for a certain number of events.

hep-ph↗

arXiv2012

Baryon electric dipole moments from strong CP violation

The electric dipole form factors and moments of the ground state baryons are calculated in chiral perturbation theory at next-to-leading order. We show that the baryon electric dipole form factors at this order depend only on two combinations of low-energy constants. We also derive various relations that are free of unknown low-energy constants. We use recent lattice QCD data to calculate all baryon EDMs. In particular, we find d_n = -2.9\pm 0.9 and d_p = 1.1\pm 1.1 in units of 10^{-16} e θ_0 cm. Finite volume corrections to the moments are also worked out. We show that for a precision extraction from lattice QCD data, the next-to-leading order terms have to be accounted for.

hep-ph↗

arXiv2012

Where is the χ_{c0}(2P)?

Although the analysis of the BaBar Collaboration prefers J^P=0^+ for the X(3915), it is difficult to assign the X(3915) to the χ_{c0}(2P). We show that there is an indication of the χ_{c0}(2P) with a mass around 3840 MeV and width of about 200 MeV in the Belle and BaBar data for γγ--> D\bar D.

hep-ph↗

arXiv2012

Light quark mass dependence in heavy quarkonium physics

The issue of chiral extrapolations in heavy quarkonium systems is discussed. We show that the light quark mass dependence of the properties of heavy quarkonia is not always suppressed. For quarkonia close to an open flavor threshold, even a nonanalytic chiral extrapolation is needed. Both these nontrivial facts are demonstrated to appear in the decay widths of the hindered M1 transitions between the first radially excited and ground state P-wave charmonia. The results at a pion mass of about 500 MeV could deviate from the value at the physical pion mass by a factor of two. Our findings show the necessity of performing chiral extrapolations for lattice simulations of heavy quarkonium systems.

hep-ph↗

arXiv2012

Examining coupled-channel effects in radiative charmonium transitions

Coupled-channel effects due to coupling of charmonia to the charmed and anticharmed mesons are of current interest in heavy quarkonium physics. However, the effects have not been unambiguously established. In this paper, a clean method is proposed in order to examine the coupled-channel effects in charmonium transitions. We show that the hindered M1 radiative transitions from the 2P to 1P charmonia are suitable for this purpose. We suggest to measure one or more of the ratios Gamma(h_c'-->chi_{cJ} gamma)/Gamma(chi_{cJ}'-->chi_{cJ} pi^0) and Gamma(chi_{cJ}'-->h_c gamma)/Gamma(chi_{cJ}'-->chi_{cJ} pi^0), for which highly nontrivial and parameter-free predictions are given. The picture can also be tested using both unquenched and quenched lattice calculations.

hep-ph↗

arXiv2012

Anomalous decays of eta' and eta into four pions

We calculate the branching ratios of the yet unmeasured eta' decays into four pions, based on a combination of chiral perturbation theory and vector-meson dominance. The decays eta' --> 2(pi+ pi-) and eta' --> pi+ pi- 2pi0 are P-wave dominated and can largely be thought to proceed via two rho resonances; we predict branching fractions of (1.0+-0.3)*10^-4 and (2.4+-0.7)*10^-4, respectively, not much lower than the current experimental upper limits. The decays eta' --> 4pi0 and eta --> 4pi0, in contrast, are D-wave driven as long as conservation of CP symmetry is assumed, and are significantly further suppressed; any experimental evidence for the decay eta --> 4pi0 could almost certainly be interpreted as a signal of CP violation. We also calculate the CP-violating amplitudes for eta' --> 4pi0 and eta --> 4pi0 induced by the QCD theta-term.

hep-ph↗

arXiv2011

Skyrmion properties from holographic instantons of large size

Based on the intanton approximation of Skyrmion and recent progresses on the holographic approach, we study baryon properties using Skyrmions generated from holographic instantons. First we employ Atiyah and Manton's early observation to show that the instanton approximation gives the correct infrared behavior for the Skyrmion solution, and thus those of the electromagnetic form factors of the nucleon. We then use Skyrmions generated from flat-space instanton solutions to study various baryon properties, treating the instanton size as an arbitrary variable. It is found that, a large instanton size is required to reproduce the physical axial coupling. From such an instanton configuration, the predictions for other baryon quantities in the Skyrme model improve the original results quite a lot. Some of the results reproduce those by quantizing the full instanton solution, while no fine-tuning of the mesonic parameters are needed. From these we conclude that the baryons in the low energy region can be effectively described by large instantons.

hep-ph↗

arXiv2011

Bound state nature of the exotic Z_b states

The assumption that the newly observed charged bottomonia states Z_b(10610) and Z_b(10650) are of molecular nature is confronted with the measured invariant mass distributions for the transitions of the Upsilon(5S) to the final states h_b pi^+ pi^- and h_b(2P) pi^+ pi^-. It is shown that the assumption that the Z_b(10610) and Z_b(10650) are B\bar B^*+{\rm c.c.} and B^*\bar B^* bound states, respectively, with very small binding energies is consistent with the data. The calculation is based on a power counting for bottom meson loops, which is explicitly given up to two-loop in the framework of a nonrelativistic effective field theory. We also show that if the Z_b states are of molecular nature, then the data should not be analyzed by using a Breit-Wigner parametrization.

hep-ph↗

arXiv2011

More kaonic bound states and a comprehensive interpretation of the D_{sJ} states

The leading order interaction between a Goldstone boson and a matter field is universally dominated by the Weinberg-Tomozawa term. Based on this observation, we predict a rich spectrum of bound states of a kaon and a heavy meson. We argue that if the lifetime of an excited heavy meson is significantly longer than the range of forces, then the finite width of that state can be neglected in a first approximation. Then, the D_{s0}^*(2317), D_{s1}(2460), D_{sJ}(2860) and D_{sJ}(3040) are generated as DK, D^*K, D_1(2420)K and D^*(2600)K bound states, respectively. In addition to the remarkable agreement with the measured masses, the decay patterns of the D_{sJ}(2860) and D_{sJ}(3040) can also be understood. Two more D_{sJ} states, and kaonic bound states with the bottom mesons as well as the doubly charmed baryon are also predicted.

hep-ph↗

arXiv2011

Effect of charmed meson loops on charmonium transitions

The effects of intermediate charmed mesons on charmonium transitions with the emission of one pion or eta are studied systematically. Based on a non-relativistic effective field theory we show that charmed meson loops are enhanced compared to the corresponding tree-level contributions for transitions between two S-wave charmonia as well as for transitions between two P-wave charmonia. On the contrary, for the transitions between one S-wave and one P-wave charmonium state, the loops need to be analyzed case by case and often appear to be suppressed. The relation to and possible implications for an effective Lagrangian approach are also discussed. This study at the same time provides a cross check for the numerical evaluations.

hep-ph↗

arXiv2011

Isospin splittings of doubly heavy baryons

The SELEX Collaboration has reported a very large isospin splitting of doubly charmed baryons. We show that this effect would imply that the doubly charmed baryons are very compact. One intriguing possibility is that such baryons have a linear geometry Q-q-Q where the light quark q oscillates between the two heavy quarks Q, analogous to a linear molecule such as carbon dioxide. However, using conventional arguments, the size of a heavy-light hadron is expected to be around 0.5 fm, much larger than the size needed to explain the observed large isospin splitting. Assuming the distance between two heavy quarks is much smaller than that between the light quark and a heavy one, the doubly heavy baryons are related to the heavy mesons via heavy quark-diquark symmetry. Based on this symmetry, we predict the isospin splittings for doubly heavy baryons including Xi_{cc}, Xi_{bb} and Xi_{bc}. The prediction for the Xi_{cc} is much smaller than the SELEX value. On the other hand, the Xi_{bb} baryons are predicted to have an isospin splitting as large as (6.3\pm1.7) MeV. An experimental study of doubly bottomed baryons is therefore very important to better understand the structure of baryons with heavy quarks.

hep-ph↗

arXiv2010

Extracting the light quark mass ratio m_u/m_d from bottomonia transitions

We propose a new method to extract the light quark mass ratio $m_u/m_d$ using the $Υ(4S)\to h_bπ^0(η)$ bottomonia transitions. The decay amplitudes are dominated by the light quark mass differences, and the corrections from other effects are rather small, allowing for a precise extraction. We also discuss how to reduce the theoretical uncertainty with the help of future experiments. As a by-product, we show that the decay $Υ(4S)\to h_bη$ is expected to be a nice channel for searching for the $h_b$ state.

hep-ph↗

arXiv2010

Light meson mass dependence of the positive parity heavy-strange mesons

We calculate the masses of the resonances D_{s0}^*(2317) and D_{s1}(2460) as well as their bottom partners as bound states of a kaon and a D^*- and B^*-meson, respectively, in unitarized chiral perturbation theory at next-to-leading order. After fixing the parameters in the D_{s0}^*(2317) channel, the calculated mass for the D_{s1}(2460) is found in excellent agreement with experiment. The masses for the analogous states with a bottom quark are predicted to be M_{B^*_{s0}}=(5696\pm 40) MeV and M_{B_{s1}}=(5742\pm 40) MeV in reasonable agreement with previous analyses. In particular, we predict M_{B_{s1}}-M_{B_{s0}^*}=46\pm 1 MeV. We also explore the dependence of the states on the pion and kaon masses. We argue that the kaon mass dependence of a kaonic bound state should be almost linear with slope about unity. Such a dependence is specific to the assumed molecular nature of the states. We suggest to extract the kaon mass dependence of these states from lattice QCD calculations.

hep-ph↗

arXiv2010

Novel analysis of the decays psi' -> h_c pi^0 and eta_c'-> chi_{c0} pi^0

We show that in the transitions psi' -> h_c π^0 and eta_c' -> chi_{c0} pi^0 the contributions from charmed meson loops are highly suppressed, in contrast to various other charmonium decays. We calculate the width of the psi' -> h_c pi^0, which agrees with the recent BES-III data, and predict the width of the eta_c' -> chi_{c0} pi^0, Γ(eta_c' -> chi_{c0} pi^0) = 1.5\pm0.4 keV. A confirmation of this prediction would also provide additional support for a recent analysis of psi' -> J/psi pi^0 (eta), where loops are claimed to play a prominent role.

hep-ph↗

arXiv2010

Reconciling the X(4630) with the Y(4660)

The Belle Collaboration observed an enhancement called X(4630) in the Lambda_c^+ Lambda_c^- mass distribution using initial state radiation. We demonstrate that the enhancement could be consistent with the psi'f_0(980) molecular picture of the Y(4660) taking into account the Lambda_c^+ Lambda_c^- final state interaction. To test the hypothesis that the X(4630) and Y(4660) are the same molecular state, we give predictions for its spin partner, the eta_c'f_0(980) molecule. High statistic measurements of the B decays into the K Lambda_c^+ Lambda_c^- and K eta_c' pi^+ pi^- are strongly recommended.

hep-ph↗

arXiv2010

Extraction of the light quark mass ratio from the decays psi' --> J/psi pi^0 (eta)

Light quark masses are important fundamental parameters of the Standard Model. The decays psi'-->J/psi pi^0 (eta) were widely used in determining the light quark mass ratio m_u/m_d. However, there is a large discrepancy between the resulting value of m_u/m_d and the one determined from the light pseudoscalar meson masses. Using the technique of non-relativistic effective field theory, we show that intermediate charmed meson loops lead to a sizeable contribution to the decays and hence make the psi'-->J/psi pi^0 (eta) decays not suitable for a precise extraction of the light quark mass ratio.

hep-ph↗

arXiv2009

Exotic open and hidden charm states

We discuss recent theoretical developments in the context of charmed exotics with special emphasis on hadronic molecules. Especially we discuss, how these could be identified from experimental as well as lattice QCD observables.

hep-ph↗