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

qq

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