How to understand the $X(2900)$?

Abstract

In this work, the Sand P -wave D * K * interactions are studied in a coupled-channel formalism to understand the recently observed X0(2900) and X1(2900) at LHCb. The experimental event distributions can be well described, and two states with I(J P ) = 0(0 + ) and 0(1 − ) are yielded in an unified framework with the same set of parameters. Their masses and widths are determined to be [m, Γ] −10.7 , 52.5 +9.5 −1.3 ] MeV from the pole analyses, respectively. The masses of the 0 + and 1 − states are consistent with the experimental data, but the width of the 0 + state is larger than that of the 1 − one. The X1(2900) can be interpreted as the P -wave excitation of the ground-state X0(2900) in the hadronic molecular picture. The Sand P -wave multiplets in the D * K * system have many members, so the present peak in the D − K + invariant mass distributions might contain multi subpeaks. In order to probe the fine structures behind the single whole peak now, more refined measurements in the B + → D + D − K + decay channel are necessary.

The $\bar{B}^0 \to D^{*+} \bar{D}^{*0} K^- $ reaction to detect the $I=0, J^P=1^+$ partner of the $X_0(2866)$

“…Its structure as a compact tetraquark state is discussed in [5][6][7][8]. The sum rules technique is used in [9][10][11][12][13] and the molecular picture as an I = 0, J P = 1 + D * K * molecular state is pursued in [14][15][16][17][18][19]. Some of the sum rule studies go deeper into details and conclude that the state is of D * K * molecular nature [11][12][13].…”

X_1(2900) as a D_1 K molecule

“…Although data can be fit well in the Ref. [30], it should be noteworthy that almost all heavy exotic hadrons that have been observed so far locate near the threshold of two hadrons and can be attributed to the S-wave hadronic molecules (except for Z c (4430) which is recognized as a P -wave molecule [31]). To a large extend, an S-wave D1 K molecule picture in this paper is more acceptable for X 1 (2900).…”

“…It is noticed that in Ref. [30], X 0 (2900) and X 1 (2900) are interpreted as S-wave and P -wave D * K * molecules, respectively. Although data can be fit well in the Ref.…”

Heavy Flavour Physics and CP Violation at LHCb: a Ten-Year Review

“…A final state rescattering effect is considered to explain such a large branching fraction [420]. The observation of X states in the B + → D + D − K + decay opens a new avenue for studies of exotic hadrons composed of four different quark flavours [421][422][423][424][425][426][427][428][429][430][431][432][433][434]. Actually there are more than two dozens of B → DDK(π) decays, and also a few similar decays for b-baryons, and it is promising that more X states will be observed in these decays.…”