# The charged $Z_c$ and $Z_b$ structures in a constituent quark model approach

### Submission summary

 As Contributors: Pablo G. Ortega Preprint link: scipost_201910_00022v1 Date submitted: 2019-10-15 Submitted by: G. Ortega, Pablo Submitted to: SciPost Physics Proceedings Proceedings issue: 24th European Few Body Conference (University of Surrey, U.K.) Discipline: Physics Subject area: High-Energy Physics - Phenomenology Approach: Theoretical

### Abstract

The nature of the recently discovered $Z_c$ and $Z_b$ structures is intriguing. Their charge forces its minimal quark content to be $Q\bar Q q\bar q$ (where $Q=\{c,b\}$ and $q=\{u,d\}$). In this work we perform a molecular coupled-channels calculation of the $I^G(J^{PC})=1^+(1^{+-})$ charm and bottom sectors in the framework of a constituent quark model which satisfactorily describes a wide range of properties of (non-)conventional hadrons containing heavy quarks. All the relevant channels are included for each sector, i.e.: The $D^{(\ast)}\bar D^{\ast}+h.c.$, $\pi J/\psi$ and $\rho\eta_c$ channels for the $Z_c$ and $B^{(\ast)}B^{\ast}$ and $\Upsilon(nS)\pi$ ($n=1,2,3$) channels for the $Z_b$ analysis. Possible structures of these resonances will be discussed

###### Current status:
Editor-in-charge assigned

### Submission & Refereeing History

Submission scipost_201910_00022v1 on 15 October 2019

## Reports on this Submission

1. Timely
2. Well written
3. Good results

### Weaknesses

1. Some confusing statements that can be amended

### Report

Report SciPost Physics Proceedings
The charged Zc and Zb structures in a constituent quark model approach
by: P.G. Ortega, J. Segovia, D. Entem, F. Fernandez)

This work analyzes the nature of some charged structures in the chamonium and bottomonium sectors within a constituent quark model. The paper is well presented, sufficient details of the theoretical model are given and the results are clearly presented and discussed.
I have only a few minor comments or typos that, when addressed properly, will leave the manuscript ready for publication:
1. Please, comment in the text (second paragraph in page 5) and in the caption of Fig. 1 the reactions to which the invariant mass distributions of the figure correspond.
2. I find strange that the widths extracted from the poles of the Zb’s are relatively narrow (2.8 and 8.9 MeV, according to Table 2), while these states seem to leave a much wider signature (20 MeV, 30 MeV) in the invariant mass distributions shown in Figure 3. Please comment.
3. Page 8, line 4: what does “point-wise” behaviour mean?
4. The authors mention in page 5, paragraph 3: “while the opening of the D*Dbar* threshold appears as a slight step down in the number of events”. The errors prevent one to see a step down in the data... Do you mean that the model shows a step down? Please clarify.
Some typos:
After Eq. 81): The Goldstone-boson field matrix
9 lines after eq. (4): and an effective cluster-cluster interaction emerges
1st line in page 4: two types of diagrams appear
Page 5 paragraph 3, line 6: only one enhancement appears

### Requested changes

See report above

• validity: high
• significance: high
• originality: high
• clarity: high
• formatting: excellent
• grammar: good