Discovery of the Hadrons In the 50s and 60s physicists discovered over 100 elementary particles in cosmic ray showers and accelerators. Almost all of these were short-lived and were classified as mesons or baryons. Typical lifetime: 10 -23 s Bubble chamber photo Baryons have half-integer spin and obey Pauli Exclusion Principle (PEP). They are fermions. Mesons have integer spin and do not obey the PEP. They are bosons.
Discovery of Elementary Particles in showers of Cosmic Rays
Spectroscopy of Hadrons neutronprotonπ meson MesonsBaryons
Electromagnetic force explains atoms Electroweak force explains radioactivity Strong Force binds quarks Ordinary Matter Standard Model
Exciting the Flux Tube Normal meson: flux tube in ground state There are two degenerate first-excited transverse modes with J=1 – clockwise and counter-clockwise – and their linear combinations lead to J PC = 1 – + or J PC =1 + – for the excited flux-tube Excited flux tube
The Light Quarks and Light Mesons J PC = 0 – – 0 + – 1 – + 2 + – … Not-allowed: exotic J PC = 0 – + 0 ++ 1 – – 1 + – 2 ++ … Allowed combinations Expect to find nine mesons with the same J, P, C - a nonet
Quantum Numbers for Hybrid Mesons Quarks Excited Flux Tube Hybrid Meson Exotic like So only parallel quark spins lead to exotic J PC
Exotic Hybrids Will Be Found More Easily in Photoproduction Production of exotic hybrids favored. Almost no data available There are strong indications from theory that photons will produce exotic hybrid mesons with relatively large cross sections. Quark spins already aligned
flux photon energy (GeV) 12 GeV electrons Coherent Bremsstrahlung This technique provides requisite energy, flux and polarization collimated Incoherent & coherent spectrum tagged with 0.1% resolution 40% polarization in peak electrons in Linearly polarized photons out spectrometer diamond crystal
Magnetic Shielding Helmholtz coils built by undergrads last year - upgraded this year new power supplies
Collaboration Founded in 1998 Workshops (latest in May 2003) 4th Design Report Collaboration meetings Regular conference calls Management plan o Collaboration Board PAC12 Cassel Review APS/DNP Town Meeting NSAC LRP PAC23 Reviews History
Computational Challenge GlueX will collect data at 100 MB/sec or 1 Petabyte/year - comparable to LHC-type experiments. Close collaboration with computer scientists has started and the collaboration is gaining experience with processor farms.
Conclusions The spectroscopy of light quark mesons is on the verge of making important contributions to answering a fundamental question: What is the nature of confinement in QCD? We welcome additional collaborators - theory and experiment and bright, enthusiastic undergrads