Recent Results From GlueX 2019 April APS Meeting Colin Gleason Indiana University on Behalf of the GlueX Collaboration Work Supported by DE-FG02-05ER41374 April 10, 2019 Colin Gleason (IU) April 10, 2019 1 / 37
Overview 1. QCD and hybrid mesons 2. The GlueX experiment 3. Early Results • Beam Asymmetries • Spin Density Matrix Elements (SDMEs) • Cross sections and opportunistic measurements • Production of J /ψ at threshold 4. Laying the foundation for exotic searches in GlueX • Identifying known resonances • Beginning searches in hybrids channels Colin Gleason (IU) April 10, 2019 2 / 37
GlueX and QCD GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons Colin Gleason (IU) April 10, 2019 3 / 37
GlueX and QCD GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons • “Traditional” hadrons are well known q q • Bound states of quarks interacting via q q q gluons Colin Gleason (IU) April 10, 2019 3 / 37
GlueX and QCD GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons • “Traditional” hadrons are well known q q • Bound states of quarks interacting via q q q gluons • Nothing in quark models forbidding q q q q tetra and pentaquarks q q • Still in color singlet state q q q Colin Gleason (IU) April 10, 2019 3 / 37
GlueX and QCD GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons • “Traditional” hadrons are well known q q • Bound states of quarks interacting via q q q gluons • Nothing in quark models forbidding q q q q tetra and pentaquarks q q • Still in color singlet state q q q • Λ 0 b → J /ψ K − p by LHCb (PRL 115, 072001 (2015)) • P c (4450) accessible at JLab energies via J /ψ production Colin Gleason (IU) April 10, 2019 3 / 37
GlueX and QCD GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons • “Traditional” hadrons are well known q q • Bound states of quarks interacting via q q q gluons • Nothing in quark models forbidding q q q q tetra and pentaquarks q q • Still in color singlet state q q q • Λ 0 b → J /ψ K − p by LHCb (PRL 115, 072001 (2015)) • 3 narrow states reported at Moriond QCD, Mar 26, 2019 Colin Gleason (IU) April 10, 2019 4 / 37
Bound States in QCD • “Traditional” hadrons are well known q q • Bound states of quarks interacting via q q q gluons • Nothing in QCD forbidding tetra and q q q q pentaquarks q q • Still in color singlet state q q q q • Do gluonic degrees of freedom exist? g q • Can/how do we observe them? g g Colin Gleason (IU) April 10, 2019 5 / 37
Constructing Mesons Conventional Meson q q • Classify as J PC • J = L + S • P = ( − 1) L +1 • C = ( − 1) L + S • Allowed: 0 − + , 0 ++ , 1 −− , 1 − + , 2 ++ , ... • Forbidden: 0 −− , 0 + − , 1 − + , 2 + − , ... Colin Gleason (IU) April 10, 2019 6 / 37
Constructing Mesons Conventional Meson Hybrid Meson q q q q g • Classify as J PC • Excited gluon field coupled to q ¯ q • J = L + S • P = ( − 1) L +1 • Rich spectrum predicted by lattice • C = ( − 1) L + S QCD • Allowed: 0 − + , 0 ++ , 1 −− , 1 − + , 2 ++ , ... • Forbidden: 0 −− , 0 + − , 1 − + , 2 + − , ... Colin Gleason (IU) April 10, 2019 6 / 37
Constructing Mesons Conventional Meson Hybrid Meson q q q q g • Classify as J PC • Excited gluon field coupled to q ¯ q • J = L + S • P = ( − 1) L +1 • Rich spectrum predicted by lattice • C = ( − 1) L + S QCD • Detection of forbidden J PC → non • Allowed: 0 − + , 0 ++ , 1 −− , 1 − + , 2 ++ , ... q ¯ q structure • Forbidden: 0 −− , 0 + − , 1 − + , 2 + − , ... Colin Gleason (IU) April 10, 2019 6 / 37
Lattice QCD Negative Parity Positive Parity Exotics 3000 2500 2000 1500 1000 500 Dudek, PRD 88 (2013) no.9, 094505 Colin Gleason (IU) April 10, 2019 7 / 37
Lattice QCD Negative Parity Positive Parity Exotics 3000 2500 2000 1500 1000 Lightest hybrid q q mesons g 500 Dudek, PRD 88 (2013) no.9, 094505 Colin Gleason (IU) April 10, 2019 8 / 37
Lattice QCD Exotics 3000 2500 η 0 1 2000 η 1 1500 π 1 1000 Lightest hybrid Observation of exotic mesons J PC would be signal 500 for non qq The goal of GlueX is to study the spectrum hybrid mesons Colin Gleason (IU) April 10, 2019 9 / 37
Global Spectroscopy Program hadron probes electromagnetic probes colliding beam completed/analysis ongoing/future ongoing/future completed/analysis fixed target Colin Gleason (IU) April 10, 2019 10 / 37
The GlueX Experiment Colin Gleason (IU) April 10, 2019 11 / 37
The GlueX Experiment G lue X forward calorimeter barrel time-of DIRC calorimeter -flight start counter target Linearly polarized photon beam Large acceptance photon beam diamond forward drift wafer chambers central drift chamber electron superconducting tagger magnet beam electron magnet tagger to detector distance beam is not to scale Colin Gleason (IU) April 10, 2019 12 / 37
The GlueX Experiment Hall D Photon Tagger Pair Spectrometer Triplet Polarimeter North LINAC 75 m Photon Beam Dump Collimator Diamond Radiator Electron GlueX East ARC "↑ − " % → &"↑ − % Beam Dump select � < 25 � r Spectrometer polarized photons Tagger Area Hall-D Colin Gleason (IU) April 10, 2019 13 / 37
The GlueX Experiment Hall D Photon Tagger Pair Spectrometer Triplet Polarimeter North LINAC 75 m Photon Beam Dump Collimator Diamond Radiator Electron GlueX East ARC "↑ − " % → &"↑ − % Beam Dump select � < 25 � r Spectrometer polarized photons Tagger Area Hall-D Measured Flux Photon Flux (Arb. Units) 7000 (a) Diamond: PARA Diamond: PERP 6000 Aluminum 5000 4000 3000 2000 1000 0 7.5 Polarization 7.5 8 8 8.5 8.5 9 9 9.5 9.5 10 10 10.5 10.5 11 11 11.5 11.5 Photon Beam Energy (GeV) Colin Gleason (IU) April 10, 2019 13 / 37
The GlueX Experiment Hall D Photon Tagger Pair Spectrometer Triplet Polarimeter North LINAC 75 m Photon Beam Dump Collimator Diamond Radiator Electron GlueX East ARC "↑ − " % → &"↑ − % Beam Dump select � < 25 � r Spectrometer polarized photons Tagger Area Hall-D Measured Flux Polarization Photon Flux (Arb. Units) 7000 (a) Diamond: PARA Polarization 7.5 8 8.5 9 9.5 10 10.5 11 11.5 Diamond: PERP 6000 (b) 0.5 PARA Aluminum 5000 0.4 PERP 0.3 4000 0.2 3000 0.1 2000 0 1000 3% Syst. Uncert. 7.5 8 8.5 9 9.5 10 10.5 11 11.5 0 7.5 Photon Beam Energy (GeV) Polarization 7.5 8 8 8.5 8.5 9 9 9.5 9.5 10 10 10.5 10.5 11 11 11.5 11.5 Photon Beam Energy (GeV) Colin Gleason (IU) April 10, 2019 13 / 37
First Physics: Beam Asymmetries • First priority is to understand how known mesons ( π, η, ρ, φ, ) are produced Colin Gleason (IU) April 10, 2019 14 / 37
First Physics: Beam Asymmetries • First priority is to understand how known mesons ( π, η, ρ, φ, ) are produced • Beam asymmetry Σ is sensitive to the production mechanisms • Want to understand how known mesons are produced and use this information in our search for hybrids Colin Gleason (IU) April 10, 2019 14 / 37
First Physics: Beam Asymmetries • First priority is to understand how known mesons ( π, η, ρ, φ, ) are produced • Beam asymmetry Σ is sensitive to the production mechanisms • Want to understand how known mesons are produced and use this information in our search for hybrids Σ = | ω + ρ | 2 −| h + b | 2 Exchange J PC 1 −− : ! , ρ | ω + ρ | 2 + | h + b | 2 1 + − : b, h JPAC, PRD 92, 074013 Colin Gleason (IU) April 10, 2019 14 / 37
First Physics: Beam Asymmetries • First priority is to understand how known mesons ( π, η, ρ, φ, ) are produced • Beam asymmetry Σ is sensitive to the production mechanisms • Want to understand how known mesons are produced and use this information in our search for hybrids Y ⊥ − F R Y || σ pol ( φ ) = σ unpol (1 − P γ Σ cos 2 φ ) = σ unpol (1 − Y ⊥ + F R Y || ) • P γ = beam polarization • Σ= beam asymmetry • φ = azimuthal angle of scattered meson w.r.t polarization plane • Y ⊥ , || are yields at different polarizations • F R is the photon flux ratio between ⊥ and || Colin Gleason (IU) April 10, 2019 15 / 37
π 0 and η Beam Asymmetries 1.4 Σ (a) γ p → p π 0 1.2 1 2.6% Norm. Uncert. 0.8 • First results from GlueX: Σ vs. − t for 0.6 π 0 and η production (PRC 95, 042201 (2017)) 0.4 GlueX 8.4<E <9.0 GeV γ 0.2 SLAC E =10 GeV γ 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -t (GeV/ c ) 2 1.4 Σ (b) γ p → p η 1.2 1 Laget [5,6] 0.8 JPAC [7,8] 0.6 Donnachie [9] Goldstein [4] 0.4 0.2 0 -0.2 -0.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 -t (GeV/ c ) 2 Colin Gleason (IU) April 10, 2019 16 / 37
Recommend
More recommend
