Introduction
November 2002
Good News
House
Senate
References
All of the above can be downloaded from our websiteGo to “Documents” - top of left frame:
n n
pp
Periodic Table
Spectroscopy of the Atom
Discovery of the Hadrons
In the 50’s and 60’s physicists discovered over 100 elementary particles incosmic ray showers and accelerators. Almost all of these were short-livedand 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
neutronproton π meson
MesonsBaryons
Electromagnetic forceexplains atoms
Electroweak forceexplains radioactivity
Strong Forcebinds quarks
Ordinary Matter
Standard Model
Subatomic Sizes
Color
Color Field: Because of self interaction, confining flux tubes form between static color charges
No Free Quarks
Lattice Calculations and Flux Tubes
Flux
tube
forms
between
From G. Bali: quenched QCD with heavy quarks
Flux Tube Breaking
Exciting the Flux Tube
q
q
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
JPC = 1– + or JPC=1+ – for the excited flux-tube
q q
q q
Excitedfluxtube
The Light Quarks and Light Mesons
JPC = 0– – 0+ – 1– + 2+ – …
Not-allowed: exotic
JPC = 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
S=0
L =0
J PC =0−+
S=1
L =0
J PC =1−−
Excited Flux Tube
J PC =1+−
1−+
⎧ ⎨ ⎪
⎩ ⎪
J PC =1+−
1−+
⎧ ⎨ ⎪
⎩ ⎪
Hybrid Meson
J PC =1−−
1++
⎧ ⎨ ⎪
⎩ ⎪
⊕
J PC =0−+ 1−+ 2−+
0+− 1+− 2+−
⎧ ⎨ ⎪
⎩ ⎪
Exotic
π, Klike
like γ,ρ
So only parallel quark spins lead to exotic JPC
QCD and Spectroscopy
Exotic Hybrids Will Be Found More Easily in Photoproduction
Production of exotichybrids favored.
Almost no data available
There are strong indications from
theory that photons will produceexotic hybrid mesons with
relatively large cross sections.
Quark spins already aligned
flu
x
photon energy (GeV)
12 GeV electronsCoherent 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 polarizedphotons out
spectrometer
diamondcrystal
Tagger Magnet
Aerial View of Jefferson Lab
Linac
Cryomodule
Arcs
Helium Factory
Upgrade Plan
Detector
Magnet arrives in Bloomington
Lead GlassCalorimeter &Magnet
Electronics assemblyrobotics facility to be installed at IU in June
PMT Bases:
FADCs:
Electronics
TOF Prototype
$70K from JLab
Magnetic Shielding
Helmholtz coils built by undergrads lastyear - upgraded this year new power supplies
Collaboration
Founded in 1998 Workshops (latest in May 2003) 4th Design Report Collaboration meetings Regular conference calls Management plano 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 makingimportant contributions to answering a fundamental question:
What is the nature of confinement in QCD?
We welcome additional collaborators - theory and experimentand bright, enthusiastic undergrads
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