Search for muoproduction of the X(3872) at COMPASS

Alexey Guskov,Compass Collaboration

doi:10.1088/1742-6596/1137/1/012019

Alexey Guskov, Compass Collaboration

Open Access

https://doi.org/10.1088/1742-6596/1137/1/012019

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Abstract

Exotic charmonium-like states have been observed by various experiments over the last 15 years, but their nature is still under discussion. Photo-(muo)production is a new promising instrument to study them. COMPASS, a fixed target experiment at CERN, analyzed the full set of the data collected with a muon beam between 2002 and 2011, covering the range from 7 GeV to 19 GeV in the centre-of-mass energy of the virtual photon-nucleon system. A signal in the mass spectrum of J/ψπ+π− with the statistical significance of 4.1 σ was observed in the reaction µ+N → µ+(J/ψπ+π−)π±N′. Its mass and width are consistent with those of the X(3872). The shape of the π+π− mass distribution from the observed decay into J/ψπ+π−is different from previous observations for X(3872). The observed signal may be interpreted as possible evidence of a new charmonium state (3872). It could be associated with a neutral partner of X(3872) with C = −1 predicted by a tetraquark model.

Highlights

Over the last years a lot of new charmonium-like hadrons, so-called the XYZ states, at the mass range above 3.8 GeV/c2 were discovered
Searching for production of exotic charmonia that decay into final states with photons like Z0(3900) → J/ψπ0, X(3872) → J/ψω, X(3872) → J/ψη etc. will be possible with the upgraded setup
New results on photoproduction of exotic charmonia could be expected from the LHC experiments where sizeable statistics of J/ψ, comparable with one available at COMPASS, produced in ultra-peripheral hadronic collisions is collected [15, 16, 17, 18]

Summary

Introduction

Over the last years a lot of new charmonium-like hadrons, so-called the XYZ states, at the mass range above 3.8 GeV/c2 were discovered. Several interpretations of the new states do exist: pure quarkonia, tetraquarks, hadronic molecules, hybrid mesons with a gluon content, etc. New experimental input is required to distinguish between the models that provide different interpretations of the nature of exotic charmonia. The search for exotic charmonium-like states in exclusive photoproduction reactions was for the first time proposed in [1, 2, 3]. 2. Exclusive muoproduction of X(3872) The exotic hadron X(3872) was discovered by the Belle collaboration in 2003 [7]. The decay width of this state has not been determined yet, only an upper limit for the natural width ΓX(3872) of about 1.2 MeV/c2 (CL=90%) exists.

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Conclusions