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Wang Q.,Julich Research Center | Hanhart C.,Julich Research Center | Zhao Q.,CAS Institute of High Energy Physics
Physical Review Letters | Year: 2013

The observation of Zc(3900) by the BESIII Collaboration in the invariant mass spectrum of J/ψπ± in e+e -→J/ψπ+π- at the center of mass 4.260 GeV suggests the existence of a charged D̄D*+DD ̄* molecular state with I(JP)=1(1+), which could be an isovector brother of the famous X(3872) and an analogue of Zb(10610) claimed by the Belle Collaboration. We demonstrate that this observation provides strong evidence that the mysterious Y(4260) is a D̄D1(2420)+DD̄1(2420) molecular state. Especially, we show that the decay of this molecule naturally populates low momentum D̄D* pairs and leads unavoidably to a cusp at the D̄D* threshold. We discuss the signatures that distinguish such a D̄D* cusp from the presence of a true resonance. © 2013 American Physical Society. Source


Yuan C.-Z.,CAS Institute of High Energy Physics
International Journal of Modern Physics A | Year: 2014

In this article, we review the recent experimental studies on the charmoniumlike states, mainly from the e+e- annihilation experiments BESIII, Belle, BaBar, and CLEO-c, and the hadron collider experiment LHCb. We discuss the results on the X(3872), the vector Y states [Y(4008), Y(4660), and those in e+e- → π+π -hc], and the charged charmoniumlike Z- c states. © 2014 World Scientific Publishing Company. Source


Xing Z.-Z.,CAS Institute of High Energy Physics
Chinese Physics C | Year: 2012

The Daya Bay collaboration has recently reported its first e e oscillation result which points to θ 13 8.8 ± 0.8 (best-fit ±1σ range) or θ 13 0 at the 5.2σ level. The fact that this smallest neutrino mixing angle is not strongly suppressed motivates us to look into the underlying structure of lepton flavor mixing and CP violation. Two phenomenological strategies are outlined: (1) the lepton flavor mixing matrix U consists of a constant leading term U 0 and a small perturbation term ΔU; and (2) the mixing angles of U are associated with the lepton mass ratios. Some typical patterns of U 0 are reexamined by constraining their respective perturbations with current experimental data. We illustrate a few possible ways to minimally correct U 0 in order to fit the observed values of three mixing angles. We point out that the structure of U may exhibit an approximate μ-τ permutation symmetry in modulus, and reiterate the geometrical description of CP violation in terms of the leptonic unitarity triangles. The salient features of nine distinct parametrizations of U are summarized, and its Wolfenstein-like expansion is presented by taking U 0 to be the democratic mixing pattern. © 2012 Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd. Source


Gu J.,CAS Institute of High Energy Physics | Liu Z.,Fermi National Accelerator Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2016

A very plausible explanation for the recently observed diphoton excess at the 13 TeV LHC is a (pseudo)scalar with mass around 750 GeV, which couples to a gluon pair and to a photon pair through loops involving vectorlike quarks (VLQs). To accommodate the observed rate, the required Yukawa couplings tend to be large. A large Yukawa coupling would rapidly run up with the scale and quickly reach the perturbativity bound, indicating that new physics, possibly with a strong dynamics origin, is nearby. The case becomes stronger especially if the ATLAS observation of a large width persists. In this paper we study the implication on the scale of new physics from the 750 GeV diphoton excess using the method of renormalization group running with careful treatment of different contributions and perturbativity criterion. Our results suggest that the scale of new physics is generically not much larger than the TeV scale, in particular if the width of the hinted (pseudo)scalar is large. Introducing multiple copies of VLQs, lowering the VLQ masses, and enlarging VLQ electric charges help reduce the required Yukawa couplings and can push the cutoff scale to higher values. Nevertheless, if the width of the 750 GeV resonance turns out to be larger than about 1 GeV, it is very hard to increase the cutoff scale beyond a few TeVs. This is a strong hint that new particles in addition to the 750 GeV resonance and the vectorlike quarks should be around the TeV scale. © 2016 American Physical Society. Source


Yuan C.-Z.,CAS Institute of High Energy Physics
Chinese Physics C | Year: 2014

The cross sections of e+e -→π+π-hc at center-of-mass energies from 3.90 to 4.42 GeV were measured by the BESIII and the CLEO-c experiments. Resonant structures are evident in the e +e-→π+π-hc line shape. The fit to the line shape results in a narrow structure at a mass of (4216±18) MeV/c2 and a width of (39±32) MeV, and a possible wide structure of mass (4293±9) MeV/c2 and width (222±67) MeV. Here, the errors are combined statistical and systematic errors. This may indicate that the Y(4260) state observed in e+e -→π+π-J/ψ has a fine structure in it. © 2014 Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Sciences and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd. Source

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