Is X(3872) a bound state? * * This work is partly supported by the Spanish Ministerio de Economía y Competitividad and European FEDER funds (FPA2016-77177-C2-2-P, FIS2017-85053-C2-1-P) and Junta de Andalucía (FQM-225)

Pablo G Ortega,Enrique Ruiz Arriola

doi:10.1088/1674-1137/43/12/124107

Pablo G Ortega, Enrique Ruiz Arriola

Open Access

https://doi.org/10.1088/1674-1137/43/12/124107

Copy DOI

Abstract

All existing experimental evidence for the bound state nature of relies on observing its decay products, which are measured with a finite experimental mass resolution that is typically MeV , and much larger than its alleged binding energy, MeV. On the other hand, we have found recently that there is a clear cancellation in the channel of the invariant mass around the threshold between continuum and the bound state. This is very much like a similar cancellation in the proton-neutron continuum with the deuteron in the channel. Based on comparative fits with a common Tsallis distribution of the experimental cross-sections for prompt production of deuterons and in pp collisions with a finite , we find a strong argument for questioning the bound state nature of this state, which also suggests that the large observed production rate could be consistent with a half-bound state.

Highlights

The existence of loosely bound states near the charm threshold, first envisaged in Ref. [1], seems to be confirmed by the wealth of evidence concerning the X(3782) state with a binding energy BX = MD + MD ∗ − MX = 0.00(18) MeV [2], which has triggered a proliferation of the so-called X, Y, Z states
We have found recently that there is a clear cancellation in the 1++ channel of the invariant DD ∗ mass around the threshold between continuum and the bound state
Based on comparative fits with a common Tsallis distribution of the experimental cross-sections for prompt production of deuterons and X(3872) in pp collisions with a finite pT, we find a strong argument for questioning the bound state nature of this state, which suggests that the large observed production rate could be consistent with a half-bound state

Summary

Introduction

In the absence of electroweak interactions, this state has the smallest known hadronic binding energy Since it is unstable, all detection methods of X(3872) are based on looking at the decay channel spectra, such as X → J/ψπ+π− , where the mass resolution does not exceed ∆m ∼ 1 − 2 MeV [5,6,7,8] We have noticed recently a clear and accurate cancellation between the would-be X(3872) bound state and the DD ∗ continuum, which has a sizable impact on the occupation number at finite temperature [12, 13] This reduction stems from a cancellation of the density of states in the 1++ channel, and potentially blurs any detected signal where a superposition of 1++ states is at work.

The Dashen-Kane cancellation mechanism

Conclusions