QCD Axial Anomaly Enhances the ηη′ Decay of the Hybrid Candidate η<sub>1</sub>(1855)
Hua-Xing Chen, Niu Su, Shi-Lin Zhu
Abstract
We study the hybrid mesons with the exotic quantum number I G J PC = 0 + 1 −+ and investigate their decays into the η η ′, a 1 (1260) π , f 1 (1285) η , f 1 (1420) η , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mrow><mml:msup><mml:mi>K</mml:mi><mml:mo>*</mml:mo></mml:msup><mml:mo stretchy="false">(</mml:mo><mml:mn>892</mml:mn><mml:mo stretchy="false">)</mml:mo><mml:mover accent="true"><mml:mi>K</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mrow><mml:msub><mml:mi>K</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>1270</mml:mn><mml:mo stretchy="false">)</mml:mo><mml:mover accent="true"><mml:mi>K</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mrow><mml:msub><mml:mi>K</mml:mi><mml:mn>1</mml:mn></mml:msub><mml:mo stretchy="false">(</mml:mo><mml:mn>1400</mml:mn><mml:mo stretchy="false">)</mml:mo><mml:mover accent="true"><mml:mi>K</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math> channels. It is found that the QCD axial anomaly enhances the decay width of the η η ′ channel although this mode is strongly suppressed by the small p-wave phase space. Our results support the interpretation of the η 1 (1855) recently observed by BESIII as the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mrow><mml:mover accent="true"><mml:mi>s</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mi>s</mml:mi><mml:mi>g</mml:mi></mml:mrow></mml:math> hybrid meson of I G J PC = 0 + 1 −+ . The QCD axial anomaly ensures the η η ′ decay mode to be a characteristic signal of the hybrid nature of the η 1 (1855).