Y(4260): Hadronic molecule versus hadro-charmonium interpretation

Abstract

In this paper we confront both the hadronic molecule and the hadro-charmonium interpretations of the Y (4260) with the experimental data currently available. We conclude that the data support the Y (4260) being dominantly a D1D + c.c. hadronic molecule while they challenge the hadrocharmonium interpretation. However, additional data is necessary to allow for stronger conclusions. The Z c (3900) was soon confirmed by the Belle Collaboration [6] and an analysis based on the CLEO-c data [7].In Ref.[8], it was argued that the strong signal of Z c (3900), being a DD * + c.c. molecular state [8][9][10], in the Y (4260) decays can be explained by a dominant D 1 D molecular component in the Y (4260) wave function [11,12] 1 . Related discussions can also be found in Refs. [13,14] emphasizing different aspects.Recently, the interpretation of the Y (4260) as a D 1 D molecular state was challenged in Ref. [15], where it is suggested that the Y (4260) is hadro-charmonium state (a compact quarkonium surounded by light quarks) [16,17]. The argument is based on the fact that the production of a pair of S P L = (1/2) − and S P L = (3/2) + heavy mesons, where S L is the sum of the spin of the light quark and the orbital angular momentum in the heavy meson, in electron-positron collisions is forbidden in the heavy quark limit-in the real world this should translate to a suppressed production of both the D 1 D continuum as well as D 1 D molecular states.In this paper we confront both interpretations of the Y (4260) the hadro-charmonium as well as the hadronic molecule with the data currently available. Especially, we argue that the D 1 D molecular interpretation of the Y (4260) does not contradict the current experimental facts despite the suppression of the production of the D andD 1 pair. It is shown that the heavy quark spin symmetry (HQSS) breaking due to a finite charm quark mass is important in this case [18]. We also discuss the challenges that both interpretations still face. In Ref.[15], Li and Voloshin stressed that in the heavy quark limit the production of a heavy state in e + e − -collisions proceeds via the electromagnetic currentcγ µ c leading to a cc pair in a 3 S 1 state with the spin of the heavy system S H = 1. At the same time the total angular momentum of the light degrees of freedom should be S L = 0. In the heavy quark limit both S H and S L are conserved. However, the light quark total angular momenta in the S-wave states D 1 D ( * ) and D 2 D * , S L = 3/2 and S L = 1/2, can not combine to S L = 0. Consequently, the S-wave production of D 1 D ( * ) and D 2 D * pairs with J P C = 1 −− in electron-positron collisions breaks the HQSS and thus would be forbidden, if the charm quark were infinitely heavy.This can also be understood using the angular momentum decomposition of the heavy and light degrees of freedom. The J P C = 1 −− states with (

Production ofY(4260)as a hadronic molecule state ofD¯DQin1, Xue2, Zhao3 2016Phys. Rev. DSelf Cite434570View full textAdd to dashboardCite

“…It should be addressed that the compact cc in an S wave should decouple to theDD 1 + c.c. molecular component in the HQSS limit [22,24,26,27]. However, since the charm quark is not heavy enough the HQSS breaking is anticipated and there will be several possible mechanisms leading to mixing between the compact cc and molecularDD 1 + c.c.…”

“…However, as shown by Refs. [26,27], the HQSS breaking in the charmonium mass region should be expected and it is sufficient to account for the cross sections observed for Y (4260). Our studies in this work will further clarify the HQSS breaking effects and make the molecular picture dynamically self-contained.…”

“…[22,24,26,27] and explore the Y (4260) production mechanism in e + e − annihilations. We will try to accommodate the short-distance production mechanism coherently in the molecular picture using Weinberg's compositeness theorem [28,29].…”

Threshold and Kinematic Effects for the Exotic Resonance-Like Structures

“…In a series of recent works it was shown that theDD 1 (2420) + c.c. molecular scenario is favored by the study of cross section lineshapes in those exclusive channels [27][28][29][30][31][32]36]. In particular, the nature of Y(4260) as theDD 1 (2420) + c.c.…”

Probing Y(4260) as the \(\bar{D}D_{1} + c.c.\) Hadronic Molecule State in e+e− Annihilations

“…However, as shown by Ref. [12], the heavy quark spin symmetry breaking in the charmonium mass region cannot be neglected and the production rate for D-wave charmonium vectors have been an indication of the heavy quark spin symmetry breaking strength. In the production of Y(4260) the presence of a small cc component is a natural measure of the heavy quark spin symmetry breaking scale, which can be extracted in our framework by implementing Weinberg's compositeness theorem [13,14].…”