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

by P. G. Ortega, J. Segovia, D. R. Entem and F. Fernández

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

Anonymous Report 1 on 2019-10-28 Invited Report

Strengths

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

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