Accessing glue through photoproduction measurements at GlueX
DOI:
https://doi.org/10.31349/SuplRevMexFis.3.0308002Keywords:
GlueX, SDME, hybrid mesons, pentaquarkAbstract
Photoproduction experiments are a key tool in the investigation of the spectrum of hadronic states and the way gluons contribute to this spectrum. The GlueX experiment, located at Jefferson Lab, features a linearly polarized tagged photon beam and its detector system is optimized to measure a wide range of neutral and charged final states. GlueX offers unique capabilities to study the spectrum of hadrons and is dedicated to the search for hybrid mesons, states with gluonic degrees of freedom. This talk presents first results from our initial campaign of data taking which finished in 2018.
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Summary and Outlook
In this talk we have presented the latest results from GlueX, showing that we are making good progress towards our main goal of studying exotic hybrid mesons. We presented the nec- essary steps taken on the way to a successful partial-wave analysis that can identify exotic waves in the η(′)π channel. We measure polarization observables such as spin-density matrix elements for a variety of different reactions to deter- mine the dominant production processes at GlueX photon en- ergies. In the case of Λ(1520) production, the SDMEs point towards a dominance of natural amplitudes - a result we also see in other reactions. Our preliminary partial-wave analysis in the ηπ channel also shows this dominance of natural ampli- tudes. We can identify S- and D-waves in positive reflectivity corresponding to the known states a0(980) and a2(1320).
Beyond our ongoing search for exotic hybrid mesons, we presented results for J/ψ photoproduction near threshold. These results inform our understanding of the gluonic con- tent of the proton but also provide us with a way to search for the pentaquark candidates reported by LHCb. Using about 25% of the data, no signal was observed in the total cross- section and model-dependent upper limits were set. The re- maining data are currently under analysis and results are ex- pected soon.
Since 2019, GlueX has been taking data with an addi- tional detector. The DIRC (detection of internally reflected Cherenkov light), which is installed in the forward direction between the solenoid and the TOF wall, will greatly enhance GlueX’s pion-kaon separation. This will enable us to extend our search for exotic mesons to the strangeness sector.
GlueX is underway to deliver on its scientific goals and many analyses are currently being carried out. Exciting re- sults can be expected in the near future.
Acknowledgments
This material is based upon work supported by the U.S. De- partment of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 1. This work was supported by the UK Science and Technology Facilities Council.
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