Accessing glue through photoproduction measurements at GlueX


  • Peter Pauli University of Glasgow



GlueX, SDME, hybrid mesons, pentaquark


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.


D. Alde et al, Evidence for a 1−+ Exotic Meson, Phys. Lett. B, 205 (1988) 397, 2693(88) 91686- 3

H. Aoyagi et al, Study of the ηπ− system in the π−p re- action at 6.3 GeV/c. Phys. Lett. B, 314 (1993) 246, https: //

G. M. Beladidze et al, Study of π−N → ηπ−N and π−N → η′π−N reactions at 37 GeV/c, Phys. Lett. B, 313 (1993) 276,

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.


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.

D. R. Thompson et al, Evidence for exotic meson production in the reaction π−p → ηπ−p at 18GeV/c, Phys. Rev. Lett., 79 (1997) 1630,

A. Abele et al, Exotic ηπ state in p ̄d annihilation at rest into π−π0ηpspectator, Phys. Lett. B, 423 (1998) 175, https: //

A. Abele et al, Evidence for a πη-P-wave in p ̄p-annihilations at rest into π0π0η, Phys. Lett. B, 446 (1999) 349, https: //

C. Adolph et al, Odd and even partial waves of ηπ− and η′π− in π−p → η(′)π−p at 191GeV/c, Phys. Lett. B, 740 (2015) 303 [Erratum: Phys. Lett. B 811 (2020) 135913,]

Yu. P. Gouz et al, Study of the wave with JPC = 1−+ in the partial wave analysis of η′π−, ηπ−, f1π− and ρ0π− systems produced in π−N interactions at pπ− = 37 GeV/c, AIP Conf. Proc., 272 (2008) 572,

V. Dorofeev. New results from VES, Frascati Phys. Ser. 15 (1999) 3

G. S. Adams et al, Observation of a New JPC = 1−+ Ex- otic State in the Reaction π−p → π+π−π−p at 18GeV/c, Phys. Rev. Lett., 81 (1998) 5760, PhysRevLett.81.5760

S. U. Chung et al, Exotic and qq ̄ resonances in the π+π−π− system produced in π−p collisions at 18GeV/c, Phys. Rev. D, 65 (2002) 072001, 072001

E. I. Ivanov et al, Observation of Exotic Meson Production in the Reaction π−p → η′π−p at 18 GeV/c, Phys. Rev. Lett., 86 (2001) 3977,

M. Alekseev et al, Observation of a JPC = 1−+ Exotic Resonance in Diffractive Dissociation of 190 GeV/c π− into π−π−π+, Phys. Rev. Lett., 104 (2010) 241803, 10.1103/PhysRevLett.104.241803

A.Rodasetal,Determinationofthepolepositionofthelightest hybrid meson candidate, Phys. Rev. Lett., 122 (2019) 042002,

S. Adhikari et al, The GLUEX beamline and detector, Nucl. Instrum. Meth. A, 987 (2021) 164807, j.nima.2020.164807

U. Timm, Coherent bremsstrahlung of electrons in crystals, Fortsch. Phys., 17 (1969) 765

B.-G. Yu and K.-J. Kong, Photoproduction of γp → K+Λ∗(1520) and decay of Λ∗(1520) → K−p in the Reggeized framework, Phys. Rev. C, 96 (2017) 025208,

K. Gottfried and J.D. Jackson, On the connection between production mechanism and decay of resonances at high en- ergies, Nuovo Cim, 33 (1964) 309, BF02750195

S. Adhikari et al, Measurement of Spin Density Matrix El- ements in Λ(1520) Photoproduction at 8.2 GeV to 8.8 GeV, arXiv:2107.12314 (submitted to Phys. Rev. C) (2021)

S. Agostinelli et al, Geant4 - a simulation toolkit, Nucl. In- strum. and Methods Sect. A, 506(3) (2003) 250, 10.1016/S0168-9002(03)01368-8

C. Gleason. elsewhere in these proceedings

V. Mathieu, M. Albaladejo, C. Ferna ́ndez-Ram ́ırez, A. W. Jackura, M. Mikhasenko, A. Pilloni, and A. P. Szczepaniak, Moments of angular distribution and beam asymmetries in ηπ0 photoproduction at GlueX, Phys. Rev. D, 100 (2019) 054017,

V. Mathieu, A. Pilloni, M. Albaladejo, Ł. Bibrzycki, A. Celen- tano, C. Ferna ́ndez-Ram ́ırez, and A. P. Szczepaniak, Exclu- sive tensor meson photoproduction, Phys. Rev. D, 102 (2020) 014003,

S. Uehara et al, High-statistics study of ηπ0 production in two-photon collisions, Phys. Rev. D, 80 (2009) 032001, https: //

B. Gittelman, K. M. Hanson, D. Larson, E. Loh, A. Silver- man, and G. Theodosiou, Photoproduction of the ψ(3100) Meson at 11 GeV, Phys. Rev. Lett., 35 (1975) 1616, https: //

U. Camerini, J. G. Learned, R. Prepost, Cherrill M. Spencer, D. E. Wiser, W. Ash, Robert L. Anderson, D. Ritson, D. Sher- den, and Charles K. Sinclair, Photoproduction of the ψ Parti- cles, Phys. Rev. Lett., 35 (1975) 483, PhysRevLett.35.483

R. Aaij et al, Observation of J/ψp Resonances Consistent with Pentaquark States in Λ0b → J/ψK−p Decays, Phys. Rev. Lett., 115 (2015) 072001, 072001

R. Aaij et al, Observation of a narrow pentaquark state, Pc (4312)+ , and of two-peak structure of the Pc (4450)+ , Phys. Rev. Lett., 122 (2019) 222001, PhysRevLett.122.222001

L. Maiani, A. D. Polosa, and V. Riquer, The New Pentaquarks in the Diquark Model, Phys. Lett. B, 749 (2015) 289, https: //

R. Zhu and C.-F. Qiao, Pentaquark states in a diquark–triquark model, Phys. Lett. B, 756 (2016) 259, j.physletb.2016.03.022

R. Chen, X. Liu, X.-Q. Li, and S.-L. Zhu, Identifying ex- otic hidden-charm pentaquarks, Phys. Rev. Lett., 115 (2015) 132002,

L. Roca, J. Nieves, and E. Oset, LHCb pentaquark as a D ̄ ∗ Σc − D ̄ ∗ Σ∗c molecular state, Phys. Rev. D, 92 (2015) 094003,

M. Mikhasenko, A triangle singularity and the LHCb pen- taquarks, arXiv:1507.06552 (2015)

F.-K. Guo, U.-G. Meißner, W. Wang, and Z. Yang, How to re- veal the exotic nature of the Pc(4450), Phys. Rev. D, 92 (2015) 071502,

A. Ali et al, First Measurement of Near-Threshold J/ψ Ex- clusive Photoproduction off the Proton, Phys. Rev. Lett., 123 (2019) 072001, 072001

D. Kharzeev, H. Satz, A. Syamtomov, and G. Zinovev, J/ψ photoproduction and the gluon structure of the nucleon, Nucl. Phys. A, 661 (1999) 568, S0375-9474(99)85090-8

S. J. Brodsky, E. Chudakov, P. Hoyer, and J. M. Laget, Photo- production of charm near threshold, Phys. Lett. B, 498 (2001) 23,

A.N.HillerBlin,C.Ferna ́ndez-Ram ́ırez,A.Jackura,V.Math- ieu, V. I. Mokeev, A. Pilloni, and A. P. Szczepaniak, Study- ing the Pc(4450) resonance in J/ψ photoproduction off pro- tons, Phys. Rev. D, 94 (2016) 034002, PhysRevD.94.034002




How to Cite

Pauli P. Accessing glue through photoproduction measurements at GlueX. Supl. Rev. Mex. Fis. [Internet]. 2022 Jul. 8 [cited 2024 May 22];3(3):0308002 1-6. Available from: