Introduction
Alex R. DzierbaIndiana University
Spokesman Hall D Collaboration
Searching for Gluonic Excitations
and the JLab 12 GeV Upgrade
A FluxTube
BetweenTwo
Quarks
The Hall D Project
Outline
Confinement - flux tubes - gluonic excitations& QCD exotics
The experimental evidence for gluonic excitations
Looking for gluonic excitations in the light-quarksector with linearly polarized photons
The technique
Conclusions
QCD and confinement
Large DistanceLow Energy
Small DistanceHigh Energy
PerturbativeQCD
StrongQCD
High EnergyScattering
GluonJets
Observed
Spectroscopy
GluonicDegrees of Freedom
Missing
Flux Tubes andConfinement
Color Field: Because of self interaction, confining flux tubes form between static color charges
Notion of flux tubes comes about from model-independentgeneral considerations. Idea originated with Nambu in the ‘70s
π/rground statetransverse phonon modes
Lattice QCD Flux tubes realized Flux
tube
forms
between
Confinement arises from flux tubes and
their excitation leads to a new
spectrum of mesons
Hybrid mesons
Normal mesons
1 GeV mass difference
linear potential
From G. Bali
Normal Mesons Normal mesons occur when theflux tube is in its ground state
LSS12S = S + S12J = L + SC = (-1)L + SP = (-1)L + 1
Spin/angular momentum configurations& radial excitations generate our knownspectrum of light quark mesons
Nonets characterized by given JPC
Not allowed: exoticcombinations:
JPC = 0-- 0+- 1-+ 2+- …
q
q
q
q
Excited Flux TubesHow do we look for gluonic
degrees of freedom in spectroscopy?
First excited state of flux tube has J=1 andwhen combined with S=1 for quarksgenerate:
JPC = 0-+ 0+- 1+- 1-+ 2-+ 2+-
exotic
q
q
Exotic mesons are not generated when S=0
Mas
s (G
eV)
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
Each box correspondsto 4 nonets (2 for L=0)
Radial excitations
(L = qq angular momentum)
exoticnonets
0 – +
0 + –
1 + +
1 + –
1– +
1 – –
2 – +
2 + –2 + +
0 – +
2 – +
0 + +
Glueballs
Hybrids
Meson Map
Current Evidence
Glueballs Hybrids
Overpopulation of thescalar nonet and LGT
predictions suggest thatthe f0(1500) is a glueball
See results fromCrystal Barrel
JPC = 1-+ states reported
1(1400)
1(1600)
by BNL E852 &others
Complication ismixing with conventional qq
states
Not withoutcontroversy
Have gluonic excitations been observed ?
Crystal BarrelResult
0
1
2
3
0 1 2 3m2(00)[GeV2]
500,000Events Evidence for fo(1500)
-Scalar
Glueball
m2 (0
0 )
[GeV
2 ]
p p→ π0π0π0
E852 Results −p → π +π−π −p
+− At 18 GeV/c
suggests π−p→ ρ0π−p
→ π+π−π−p
to partial wave analysis
π+π−π−
M(π+π−π−) GeV/ c2[ ] M(π+π−) GeV/ c2
[ ]
Results of Partial Wave Analysis
a1
a2
Benchmarkresonances
π2
An Exotic Signal in E852
LeakageFrom
Non-exotic Wavedue to imperfectly
understood acceptance
ExoticSignal
1−+
Correlation ofPhase
&Intensity
M(π+π−π−) GeV/ c2[ ]
Why Photoproduction ?
A pion or kaon beam, when scattering occurs,
can have its flux tube excited
beam
Quark spins anti-aligned
Much data in hand but littleevidence for gluonic excitations
(and not expected)
q
q
befo
req
qaft
er
q
q
aft
er
q
q
befo
re
beamAlmost no data in hand
in the mass regionwhere we expect to find exotic hybrids
when flux tube is excited
Quark spins aligned
Compare p and p Data
−p → π +π−π −p
BNL
@ 18 GeV
Compare statistics and shapes
ca. 1998
28
4
Eve
nts
/50
MeV
/c2
SLAC
p → π +π +π −n
@ 19 GeV
SLAC
1.0 2.52.01.5
ca. 1993
M(3π) GeV/ c2[ ]
Hybrid Decays
Hall D will be sensitive to a wide variety of decay modes - the measurements of which will be compared against theory predictions.
To certify PWA - consistency checks will be made among different final states for the same decay mode, for example:
b1 → ωπω→ π0γ → 3γ
ω→ π0π+π−→ 2γπ+π−
⎧ ⎨ ⎪
⎩ ⎪ Should givesame results
Gluonic excitations transfer angular momentum in their decays tothe internal angular momentum of quark pairs not to the relative angularmomentum of daughter meson pairs - this needs testing.
X → π+b1For example, for hybrids:favored
not-favoredX → π+η
What is Needed?
PWA requires that the entire event be identified - all particles detected, measured and identified.
• The detector should be hermetic for neutral and charged particles, with excellent resolution and particle ID capability.
The beam energy should be sufficiently high to produce mesons in the desired mass range with excellent acceptance.
• Too high an energy will introduce backgrounds, reduce cross-sections of interest and make it difficult to achieve above experimental goals.
PWA also requires high statistics and linearly polarized photons.
• Linear polarization will be discussed. At 108 photons/sec and a 30-cm LH2 target a 1 µb cross-section will yield 600M events/yr. We want sensitivity to sub-nanobarn production cross-sections.
Review
David Cassel Cornell (chair)Frank Close RutherfordJohn Domingo JLabBill Dunwoodie SLACDon Geesaman ArgonneDavid Hitlin CaltechMartin Olsson WisconsinGlenn Young ORNL
The Committee
Executive Summary Highlights:
The experimental program proposed in the Hall D Project is well-suited for definitive searches of exotic states that are required according to our current understanding of QCD
JLab is uniquely suited to carry out this program of searching for exotic states
The basic approach advocated by the Hall D Collaboration is sound
Linear Polarization
Linear polarization is:
Essential to isolate the production mechanism (M) if X is known
A JPC filter if M is known (via a kinematic cut)
Related to the fact that states of linear polarization are eigenstates ofparity. States of circular polarization are not.
M
X
N N
Linear polarization is important inPWA - loss in degree of linear polarization can be compensated forby increase in statistics.
Optimal Photon Energy
Figure of merit based on:
1. Beam flux and polarization2. Production yields3. Separation of meson/baryon production
Electron endpointenergy of 12 GeV
producedmeson mass
rela
tive y
ield
Staying below 10 GeV allows usto use an all-solenoidal detector.
Optimum photon energyis about 9 GeV
flu
x
photon energy (GeV)
12 GeV electronsCoherent Bremsstrahlung
This technique provides requisite energy, flux
and polarization
collimated
Incoherent &coherent spectrum
tagged
0.1% resolution
40%polarization
in peak
electrons in
photons out
spectrometer
diamondcrystal
DetectorLead GlassDetector
Solenoid
Electron Beam from CEBAF
Coherent BremsstrahlungPhoton Beam
Tracking
Target
CerenkovCounter
Time ofFlight
BarrelCalorimeter
Note that tagger is80 m upstream of
detector
Event rate to processor farm:10 kHz and later 180 kHz correspondingto data rates of 50 and 900 Mbytes/sec
respectively
Solenoid & Lead Glass Array
At SLAC
At LANL
Now at JLab
Acceptance-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
Cos(θGJ )
5GeV
( )=1.4Mass X GeV
( )=1.7Mass X GeV
( )=2.0Mass X GeV
-3 -2 -1 0 1 2 30
0.2
0.4
0.6
0.8
1
φGJ
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
(Cos θGJ )
8GeV
( )=1.4Mass X GeV
( )=1.7Mass X GeV
( )=2.0Mass X GeV
-3 -2 -1 0 1 2 30
0.2
0.4
0.6
0.8
1
φGJ
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
(Cos θGJ )
12GeV
( )=1.4Mass X GeV
( )=1.7Mass X GeV
( )=2.0Mass X GeV
-3 -2 -1 0 1 2 30
0.2
0.4
0.6
0.8
1
φGJ
-> p n++−
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
Cos(θGJ )
5GeV
( )=1.4Mass X GeV
( )=1.7Mass X GeV
( )=2.0Mass X GeV
-3 -2 -1 0 1 2 30
0.2
0.4
0.6
0.8
1
φGJ
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
(Cos θGJ )
8GeV
( )=1.4Mass X GeV
( )=1.7Mass X GeV
( )=2.0Mass X GeV
-3 -2 -1 0 1 2 30
0.2
0.4
0.6
0.8
1
φGJ
-1 -0.8 -0.6 -0.4 -0.2 -0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
(Cos θGJ )
12GeV
( )=1.4Mass X GeV
( )=1.7Mass X GeV
( )=2.0Mass X GeV
-3 -2 -1 0 1 2 30
0.2
0.4
0.6
0.8
1
φGJ
-> p p00p → Xn → π +π +π −n
p → Xn → ηπ 0π 0n
Acceptance in
Decay Angles
Gottfried-Jackson frame:
In the rest frame of Xthe decay angles aretheta, phi
assuming 9 GeVphoton beam
Mass [X] = 1.4 GeV
Mass [X] = 1.7 GeV
Mass [X] = 2.0 GeV
Acceptance is high and uniform
500
400
300
200
100
0
1.81.61.41.2
PWA fit
500
400
300
200
100
0
1.81.61.41.2
Mass (3 pions) (GeV)
events/20 MeV generated
Finding the Exotic Wave
Mass
Input: 1600 MeV
Width
Input: 170 MeV
Output: 1598 +/- 3 MeV
Output: 173 +/- 11 MeV
Double-blind M. C. exercise
An exotic wave (JPC = 1-+) was generated at level of 2.5 % with 7 other waves. Events were smeared, accepted, passed to PWA fitter.
Statistics shown here correspondto a few days of running.
X(exotic)→ ρπ→ 3π
CollaborationUS Experimental Groups
A. Dzierba (Spokesperson) - IUC. Meyer (Deputy Spokesperson) - CMUE. Smith (JLab Hall D Group Leader)
L. Dennis (FSU) R. Jones (U Conn)J. Kellie (Glasgow) A. Klein (ODU)G. Lolos (Regina) (chair) A. Szczepaniak (IU)
Collaboration Board
Carnegie Mellon University
Catholic University of America
Christopher Newport University
University of Connecticut
Florida International University
Florida State University
Indiana University
Jefferson Lab
Los Alamos National Lab
Norfolk State University
Old Dominion University
Ohio University
University of Pittsburgh
Renssalaer Polytechnic Institute
University of Glasgow
Institute for HEP - Protvino
Moscow State University
Budker Institute - Novosibirsk
University of Regina
CSSM & University of Adelaide
Carleton University
Carnegie Mellon University
Insitute of Nuclear Physics - Cracow
Hampton University
Indiana University
Los Alamos
North Carolina Central University
University of Pittsburgh
University of Tennessee/Oak Ridge
Other Experimental Groups
Theory Group
90 collaborators25 institutions
Conclusion
In the last decade we have seen much theoretical progress in using lattice gauge theory techniques in the confinement region of QCD. Low energy data on gluonic excitations are needed to understand the nature of confinement in QCD.
Recent data in hand provide hints of these excitations - but a detailed map of the hybrid spectrum is essential.
Photoproduction promises to be rich in hybrids - starting with those possessing exotic quantum numbers - little or no data exist.
We are now in a position to use the energy-upgraded JLab to provide photon beams of the needed flux, duty factor, polarization along with a state-of-the-art detector to collect high-quality data of unprecedented statistics and precision.
