GlueX: Search for Gluonic Excitations at JLab

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GlueX Search for Gluonic Excitations at JLab

• Dr. David Lawrence
• Jefferson Lab

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Motivation

Simplest quark-structure is a meson
Meson Wave Function
Confinement Quarks cannot exist alone
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Hybrid Models

• Bag Model
• Flux Tube Model
• Constituent Gluon Model
• QCD Sum Rules
• Lattice Gauge Theory (model indep.)

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The Flux Tube Model
G. Bali
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Hybrid Mesons
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Hybrid Mesons
L 1 JPC 1- , 1-
JPC 1-- , 1
Hybrid Meson or ?, ?, ?, ?
P (-1)L1 C (-1)LS
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Hybrid Mesons
L 1 JPC 1- , 1-
JPC 0-, 1-, 2- 0-, 1-, 2-
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Hybrids Should Appear as a Nonet

9 hybrid particles Should exist for each
JPC combination
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1- Hybrid Mass spectrumFrom LQCD calculations.
All masses in GeV/c2

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Collaboration
UKQCD(97) 1.87 0.2 2.0 0.2
MILC(97) 1.97 0.09 0.30
2.1700.0800.30
MILC(99) 2.11 0.10 (sys)
SESAM(98) 1.9 0.20
Mei Luo(03) 2.013 0.026 0.071
Bernard et al.(04) 1.792 0.139 2.100
0.120
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Light Meson Spectrum
Exotic quantum numbers imply deeper structure
than simple (No mixing with those states!)
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Why Are Hybrids Hard To See?

• Most searches involve looking at twobody final
  states. Coupling of hybrids totwo body final
  states is almost nonexistent

• Large masses (2GeV/c2)

• About 1/3 of the (exotic) states havebroad widths

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Hybrid Decays
Hybrids preferentially couple to states with Both
an S-wave and P-wave meson

X? ? b1
? ? ? ? ? ? ? ? ? ?
X? ? f1
? ? ? ? ? ? ? ? ? ? ? ?
X? ? a2
X? ? a1
? ? ? ? ? ? ? ? ?
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Hybrid Candidates(?)

?1(1400) 1- E852,Crys. Barrel,VES
?1(1600) 1- E852,Crys. Barrel,VES
?1(2000) 1- E852
?2(1880) 2- E852
a1(2096) 1 E852
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?1(1400) JPC 1-
(Looks like a meson-meson molecule!)
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?1(1600) JPC 1-
E852 PRL 86, 3977 (2001)
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?1(2000) JPC 1-

f1(1285)
E852 hep-ex/0405044 v1 (2004) E852 Phys.
Lett. B595(2004) 109-117
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Hadroproduction vs. Photoproduction
Non-Exotic
Exotic
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Incident Photon Energy
Need at least E? 8.4GeV - 9GeV to access
masses upto 2.8GeV/c2
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Linearly Polarized ?s(produced by coherent
bremsstrahlung)
Having the angle between the photon polarization
vector and reaction plane ? provides an
additional handle in the analysis that can
simplify the PWA.
The angle ? is related to naturality of exchange
particle e.
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Location of Jefferson Lab
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Jlab Upgrade

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The GlueX Detector 1
Hermetic Design
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The GlueX Detector(all aboard!)
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Acceptance of GlueX detector

? p ? ?1 p ? ??-4? p
Good acceptance of both charged and neutral
particles
?GJ
cos?GJ
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PWA Double Blind Monte Carlo Study of 3? Final
states

? p ? ?1n ? ???-n ? ??0?0n
Background waves included a1(1260), a2(1320) and
?2 (1670)
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Protoyping and Testing
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Beam Flux and Event Rate
Eelectron 12GeV
Coherent Peak E? 9GeV
In the first year, GlueX will exceed existing
photoproduction data by a couple of orders of
magnitude. It will also exceed existing
hadroproduction data.
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Status of Upgrade

DOE Order 413.3 Project Management Manual
CD-0 Approve Mission Need
FY2004
CD-1 Approve Preliminary Baseline Range
FY2005
CD-2 Approve Performance Baseline Range
FY2007
CD-3 Approve Start of Construction
FY2008
Start of Data Taking
FY2011
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Summary

• Understanding confinement means understanding
  the glue which binds quarks. Hybrid mesons are
  perhaps the most promising subject for studying
  the nature of the glue

• A rich spectrum of hybrid mesons is predicted.
  Models agree the masses of hybrid states should
  be around 2GeV, some with exotic JPC.

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Summary

• GlueX is being constructed to map out the
  spectrum of Exotic Hybrid Mesons with
  unprecedented statistics.

• GlueX will begin taking data in 2011