Is X ( 3915 ) accessible at meson photoproduction experiment ?

In this paper, we introduce our study on the discovery potential of charmoniumlike state X(3915) via meson photoproduction. By considering the signal and background contribution to γp → J/ψωp process, we obtain the total cross sections for γp → J/ψωp, which provide important information to further experimental exploration of X(3915). Especially, we also emphasize that the discovery potential of charmonium-like state X(3915) is determined by the coupling constant of X(3915) → J/ψω, which is a crucial parameter of reflecting the inner structure of X(3915). Thus, studying X(3915) via meson photoproduction is helpful in revealing the underlying property of X(3915).


Introduction
In the past decade, more and more charmonium-like states, which are also named as XYZ states, were announced by experiment.At present, the observed XYZ are from B meson decays, e + e − annihilation, the double charm production, γγ fusion process, and the hidden-charm/bottom dipion and open-charm/bottom decays of higher charmonia/bottomonia and charmonium-like/bottomonium-like states.The study of XYZ states is helpful to improve our understanding of the non-perturbative behavior of QCD [1].
Among these studies of XYZ states, exploring XYZ states via other production processes different from observed processes mentioned above is an interesting research topic.In this paper, we introduce our progress on the investigation of charmonium-like state X(3915) [2] via meson photoproduction.
a. e-mail: x.yuan@impcas.ac.cnDue to the vector meson dominance (VMD), we give the signal contribution depicting the γp → X(3915)p → J/ψωp (see Fig. 1), while the background contribution is from the Pomeron exchange.We obtain the square of the total invariant transition amplitude the total cross section of the process γp → J/ψωp reads as where is the 3-body phase space.Adopting the effective Lagrangian approach, we write out the transition amplitudes and (see Ref. [5] for more details of the deduction of amplitudes).For numerically obtaining the total cross section including both signal and background contributions, we adopt the FOWL code.
In Fig. 2, we show the total cross section of γp → J/ψωp, where we consider the signal and background contributions.The comparison of the typical σ ω , σ T and σ Pom indicates: 1) When Γ(X(3915) → J/ψω) = 0.15 MeV, the corresponding σ ω is rather small.However, σ ω is larger than σ Pom around √ s = 5 GeV, which is close to the threshold of √ s of the γp → J/ψωp reaction.Since the decay width of X(3915) → J/ψω determines whether the X(3915) signal is buried by the background, the above analysis makes us obtain the lower limit of Γ(X(3915) → J/ψω) if distinguishing the X(3915) signal from the background.2) When Γ(X(3915) → J/ψω) = 1.7 MeV and 5.1 MeV, the corresponding σ T is dominated by the X(3915) signal contribution at √ s ≤ 8 and √ s ≤ 15 GeV, respectively (see Fig. 2 for the detail).It means that the X(3915) signal can be easily observed if taking suitable √ s range.

Summary
In this paper, we introduce our result of studying charmonium-like state X(3915) via meson photoproduction.X(3915) is a good candidate of χ c0 (2P) [4], where X(3915) was only reported in the γγ fusion process [2,3].This study can further shed light on the properties of X(3915).We notice that the final state of the observed X(3915) decay contain two vector mesons.Thus, meson photoproduction process is suitable to study X(3915).For quantitatively answering whether X(3915) can be observed in meson photoproduction process, we study the γp → J/ψωp process by including the X(3915) signal and background contributions, where the corresponding cross section is obtained, which provide valuable information to the experimental study of X(3915) by meson photoproduction.
Our calculation shows that the experimental measurement of the decay width of X(3915) → J/ψω is a crucial input in studying the meson photoprodution of X(3915).At present, this value is still missing in experiments.In our work, we have to consider several typical values of Γ(X(3915) → J/ψω) to discuss the discovery potential of X(3915) by meson photoproduction.
Among these running and forthcoming experiments, the COMPASS experiment is a good platform to perform the search for X(3915) via meson photoproduction.We also expect further experimental progresses on X(3915).
DOI: 10.1051/ C Owned by the authors, published by EDP Sciences,

Figure 1 .
Figure 1.The signal (left panel) and background contributions to γp → J/ψωp.Here, there are two typical diagrams describing the background contribution, which are marked by (a) and (b).