Triangle singularities and XYZ quarkonium peaks
We discuss analytical properties of partial waves derived from projection of a 4-legged amplitude with crossed-channel exchanges in the kinematic region of the direct channel that corresponds to the XYZ peaks in charmonium and bottomonium. We show that in general partial waves can develop anomalous branch points in the vicinity of the direct channel physical region. In a specific case, when these branch points lie on the opposite side of the unitary cut they pinch the integration contour in a dispersion relation and if the pinch happens close to threshold, the normal threshold cusp is enhanced. We show that this effect only occurs if masses of resonances in the crossed channel are in a specific, narrow range. We estimate the size of threshold enhancements originating from these anomalous singularities in reactions where the $$Z_c(3900)$$ and the $$Z_b(10610)$$ peaks have been observed.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- Grant/Contract Number:
- AC05-06OR23177; FG0287ER40365
- OSTI ID:
- 1198551
- Alternate ID(s):
- OSTI ID: 1184622
- Report Number(s):
- JLAB-THY-15-1999; DOE/OR/23177-3264; arXiv:1501.01691; S0370269315004517; PII: S0370269315004517
- Journal Information:
- Physics Letters B, Journal Name: Physics Letters B Vol. 747 Journal Issue: C; ISSN 0370-2693
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- Netherlands
- Language:
- English
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