Strong decays of $${\bar{D}}^{*}K^{*}$$ D
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Regular Article - Theoretical Physics
¯ ∗ K ∗ molecules and the newly observed X 0,1 Strong decays of D states Yin Huang1, Jun-Xu Lu2,a , Ju-Jun Xie3,4,5,b , Li-Sheng Geng2,5,6,c 1
School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China School of Physics and Beijing Key Laboratory of Advanced Nuclear Materials and Physics, Beihang University, Beijing 100191, China 3 Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China 4 School of Nuclear Sciences and Technology, University of Chinese Academy of Sciences, Beijing 101408, China 5 School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450001, Henan, China 6 Beijing Advanced Innovation Center for Big Data-based Precision Medicine, Beihang University, Beijing 100191, China
2
Received: 20 August 2020 / Accepted: 2 October 2020 © The Author(s) 2020
Abstract Lately, the LHCb Collaboration reported the discovery of two new states in the B + → D + D − K + decay, i.e., X 0 (2866) and X 1 (2904). In the present work, we study whether these states can be understood as D¯ ∗ K ∗ molecules from the perspective of their two-body strong decays into D − K + via triangle diagrams and three-body decays into D¯ ∗ K π . The coupling of the two states to D¯ ∗ K ∗ are determined from the Weinberg compositeness condition, while the other relevant couplings are well known. The obtained strong decay width for the X 0 (2866) state, in marginal agreement with the experimental value within the uncertainty of the model, hints at a large D¯ ∗ K ∗ component in its wave function. On the other hand, the strong decay width for the X 1 (2904) state, much smaller than its experimental counterpart, effectively rules out its assignment as a D¯ ∗ K ∗ molecule.
1 Introduction Ever since the experimental discovery of X (3872) and ∗ (2317), many hadrons that cannot be simply classified Ds0 into conventional mesons of q q¯ and baryons of qqq have been discovered, with the latest addition being the ccc¯c¯ states discovered by the LHCb Collaboration [1]. See, e.g., Refs. [2–5] for recent reviews. It should be noted that most of the so-called exotic hadrons mix with conventional hadrons or can be understood as hadron–hadron molecules or threshold effects such that they are not that “exotic”. Curiously, two of the truly exotic candidates, θ + (1540) [6] and X (5568) [7] seem to fade away with time. In such a context, the lata e-mail:
est LHCb announcement of two structures observed in the D − K + invariant mass of the B + → D + D − K + decay points to the likely existence of genuinely exotic mesonic states with a minimum quark content of c¯ ¯s ud [8,9]. Their spin-parities, masses, and widths (in units of MeV) are, respectively1 X 0 (2866) :
0+ ,
M = 2866 ± 7 ± 2,
and = 57 ± 12 ± 4, X 1 (2904) :
−
1 ,
(1)
M = 2904 ± 5 ± 1,
and = 110 ± 11 ± 4.
(2)
The existence of compact tetraquark states in this energy region has been predicted in either quark models [10–13], or QCD sum rules [14,15]. However, the lattice QCD
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