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Transcript of Introduction 2
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Introduction 2
Alex R. DzierbaIndiana University
Spokesman Hall D Collaboration
Searching for QCD Exotics
with Photon Beams
LSS12S = S + S12J = L + SC = (-1)L + SP = (-1)L + 1
A FluxTube
BetweenTwo
Quarks
p p
Mγ
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References
The Hall D ProjectDesign ReportVer 3
November, 2000
Mapping quarkconfinement byexotic particles
The search forQCD exotics
Sept, 2000 Sept/Oct, 2000
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Outline
Why photoproduction?
The experimental evidence for gluonic excitations
QCD exotics, gluonic excitations & confinement
Experimental technique
Collaboration and project status
Conclusion
How to identify exoticsPartial Wave Analysis (PWA)What is needed
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QCD and confinement
Large DistanceLow Energy
Small DistanceHigh Energy
PerturbativeRegime
Non-PerturbativeRegime
High EnergyScattering
GluonJets
Observed
Spectroscopy
GluonicDegrees of Freedom
Missing
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Flux Tubes
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
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Early Flux Tubes
6
4
2
0
6420
m2 (GeV2)
I = 0 I = 1
ro
v
c=
rro
E =mc2 =2k⋅dr
1−v2 / c20
ro
∫ =kroπ
J ∝m2
k = constant energy density per lengthimplies a linear potential: V = kr
angular momentum:
energy:
In the 1970’s Nambu points out that linearRegge trajectories imply that quarks insideare tied by strings.
mesons
J =2
hc2kvr⋅dr
1−v2 / c20
ro
∫ =kro
2π2hc
k = 1 GeV/fermior about 16 Tons
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Lattice QCDFlux tubes realized
Flux
tube
forms
between
π/rground statetransverse phonon modes
Confinement arises from flux tubesand their excitation leads to a newspectrum of mesons
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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 knowspectrum of light quark mesons
Nonets characterized by given JPC
Not allowed: exoticcombinations:
JPC = 0+- 1-+ 2+- …
q
q
q
q
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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
q
q
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Meson Map
Glueballs
Hybrids
Mas
s (G
eV)
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
LSS12S = S + S12J = L + SC = (-1)L + SP = (-1)L + 1
Each box correspondsto 4 nonets (2 for L=0)
Radial excitations
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Meson Map 1
Glueballs
Hybrids
Mas
s (G
eV)
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
S
I3
K
+
π+
π–
πo
K
o
K
o
K–
η
′η
Pseudoscalar
S
I3
K *
o
K *
+
K *o
K *–
ρ–
ρo ρ
+
ω
φ
Vector
JPC = 1--
JPC = 0-+
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Meson Map-2
exotics
0 – +
0 + –
1 + +
1 + –
1– +
1 – –
2 – +
2 + –2 + +
0 – +
2 – +
0 + +G
lueballs
Hybrids
Mas
s (G
eV)
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
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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
π1(1400) ηπ
π1(1600) ρπ
See results fromBNL E852
Complication ismixing with conventional qq
states
Not withoutcontroversy
Have gluonic excitations been observed ?
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Crystal barrel
0
1
2
3
0 1 2 3m2(π0π0)[GeV2]
500,000Events
p p → 3π0
Evidence for fo(1500)
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Crystal Barrel - II
0
1
2
3
0 1 2 3m2(π0π0)[GeV2]
10,000Events
0
1
2
3
0 1 2 3m2(π0π0)[GeV2]
1,000Events
Low Statistics
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Why photoproduction ?
A meson beam when scattering occurs
can have its flux tube excited
π
beam
S = 0
Much data in hand but not overwhelmingevidence for gluonic excitations
q
q
q
q
befo
re
after
π and γ really are different probes
γ
beam
S = 1
Almost no data on in the mass regionwhere we expect to find exotic hybrids
when flux tube is excited
q
q
q
q
befo
re
after
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Compare pion and Photoproduction Data
π+π−π− Mass GeV( )
π−p → π +π−π −p
BNL
@ 18 GeV
Compare statistics and shapes
28
4
Eve
nts
/50
MeV
SLAC
π+π+π− Mass GeV( )
γp → π +π +π −n @ 19 GeV
SLAC
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Partial Wave Analysis (PWA)A simple example - identifying states which decay into ππ
Decay into ππ implies J=L, P=(-1)L and C=(-1)L
Production and decay
point the way
N N
π1
π 2
πe
πb
π−p→ π+π−n mππ = p1+p2( )2
t = pb −p1 −p2( )2
πb πe
π1
π2
θ
C.M.S.
dNd cosθ( )
∝ Y J0 2
Line shape and phase consistent with Breit-Wigner line shape
Low t
production
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cosθcosθ cosθ
Decay Angular Distributions
JPC=2++ JPC=3--
πb πe
π1
π2
θ
C.M.S.
dNd cosθ( )
∝ Y J0 2
JPC=1--
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E852 Results
π+π+π−
π+π−
Decompose this
π−p → π +π−π −p @ 18 GeV
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An Exotic Signal in E852
1−+
ExoticSignalLeakage
FromNon-exotic Wave
Correlation ofPhase
&Intensity
Mass (GeV)Mass (GeV)
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Hybrid Decays
Gluonic excitations transfer angular momentum in their decays not tothe relative angular momentum of meson pairs but to the internal orbitalangular momentum of the qq pairs.
Favored: X[1-+] Sqq + Pqq
NotFavored: X[1-+] Sqq + SqqX → π+η X → π+ρ
We want to determine this and be sensitive to a wide variety of decaymodes to test models and to certify the PWA.
X → π+b1
b1 → ωπω→ π0γ → 3γ
ω→ π0π+π−→ 2γπ+π−
⎧ ⎨ ⎪
⎩ ⎪
X → π+ηη → 2 γ
η → π0π+π−→ 2γπ+π−
⎧ ⎨ ⎩
X → π+b1 1235( )
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What is Needed?
PWA requires that the entire event be identified - all particlesdetected, measured and identified.
The detector should be hermetic with excellent resolution and capabilityof identifying photons and π from K from protons.
The beam energy should be sufficiently high to produce mesons in thedesired mass range with sufficient acceptance.
Too high an energy will introduce backgrounds, reduce many cross-sectionsof 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 107 photons/sec and a 30-cm LH2 target a 1 µb cross-section will yield 60M events/yr.This would about 1M exotics in a given channel.
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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
M[x] is producedmeson mass
rela
tive y
ield
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Electron Beam Energy
12
10
8
6
4
2
0121110987
photon beam momentum (GeV)
endpoint energy = 12 GeV = 11 GeV = 10 GeV
Photon Flux inCoherent Peak
Total Hadronic RateConstant at
approx 20 KHz
0.6
0.5
0.4
0.3
0.2
0.1
0.0121110987
photon beam momentum (GeV)
endpoint energy = 12 GeV = 11 GeV = 10 GeV
LinearPolarization
electron energy
photon energy
Electron energy
Photon energy
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Linear Polarization - I
p p
Mγ
Y11 θ,φ( )∝ sinθ⋅eiφ
Y1−1 θ,φ( ) ∝sinθ⋅e−iφ
R
L
V
J=0Suppose we produce a vector via exchange
of spin 0 particle and then V SS
For circular polarization
W θ,φ( )∝ sin2 θ
x =R + L
2∝ sinθ⋅cosφ
y =−iR −L
2∝sinθ⋅sinφ
For linear polarization
Px: W θ,φ( )∝ sin2 θ⋅cos2 φ
Py:W θ,φ( )∝ sin2 θ⋅sin2φ
Loss in degreeof polarization
requires correspondingincrease in stats
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Linear Polarization - II
p p
Mγ
J=0– or 0+
V
Xphotonfor X, J = 0Center of Mass of VX = exchange particle
L =0,1,or2
PV =Pγ ⋅PX ⋅−1( )L
Suppose we want to determineexchange: O+ from 0- or AN from AU
V = vectorphoton
m = 1
m = -1
R
L
AN +AU
AN −AU
Parity conservation implies:
With linear polarizationwhich is sum or diff ofR and L we can separateLinear Polarization Essential
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DetectorLead GlassDetector
Solenoid
Electron Beam from CEBAF
Coherent BremsstrahlungPhoton Beam
Tracking
Target
CerenkovCounter
Time ofFlight
BarrelCalorimeter
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Photon Beam
Photon beam energy (GeV)
Flu
x
Coherent bremsstrahlung will deliver the necessaryPolarization, energy and flux concentrated in the region of interest
Coherent and incoherent spectrumFor 15 micron diamond radiator
Collimation enhancescoherent over incoherent
component
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Solenoid
Superconducting SolenoidBuilt at SLAC for LASS
Now at LANL - used in MEGA
At SLAC
At LANL
Central field: 2.5 T
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LGD
Built by the IndianaGroup for BNL
Exp 852
3000 PbO blocksPM’s/ADC’s
Transferred toJLab
July, 2000
σE GeV( )
= 2 +5E
⎡ ⎣ ⎢
⎤ ⎦ ⎥%
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200
150
100
50
0
2.01.81.61.41.21.00.80.6
M(ηγ)GeV
Cut-away of Radphi Detectorlocated in Hall B
γp→ Vp
ρ→ ηγ + ω→ ηγ
φ→ ηγ
Rare Radiative Decaysof the meson
Events
/10
MeV
Phi decaysPhi experiment
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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
γ -> p nπ+π+π−
-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
γ -> p pηπ0π0γp → Xn → π +π +π −n
γp → Xn → ηπ 0π 0n
Acceptance in
Decay Angles
Gottfried-Jackson frame:
In the rest frame of Xthe decay angles aretheta, phi
assuming 8 GeVphoton beam
Mass [X] = 1.4 GeV
Mass [X] = 1.7 GeV
Mass [X] = 2.0 GeV
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Monte Carlo PWA
The Mix:
Events were generated,smeared and passed to
PWA fitter.
The % refer to thefraction of the wave inthe original data set.
Errors correspond toabout 1 day’s running
7.5% 0.8%
88% 1.5%
γp→ Xn→ ρπn
a1 1260( ) S,D[ ]
a2 1320( ) D[ ]
π2 1670( ) P,F[ ]
π1 1600( ) P[ ]
a1 1260( ) S[ ]
a1 1260( ) D[ ]
a2 1320( ) D[ ]
π2 1670( ) P[ ]
reson
an
ce
L b
etw
een
ρ an
d π
Exotic wave
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Finding the Exotic Wave
The JPC exotic was in themix with other wavesat the level of 2.5%
The generated mass andwidth are compared withthose from PWA fits:
Mass
Input: 1600 MeV
Width
Input: 170 MeV
Output: 1598 +/- 3 MeV
Output: 173 +/- 11 MeV 1.2 1.4 1.6 1.8 2.0M3π [GeV]
0
100
200
300
400
500
Generated vs PWA JPC
=1-+ exotic (π1)
• generated input
• r esults of PW A fits
Mass (GeV)
Even
ts/2
0 M
eV
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Collaboration - I
US Experimental Groups
Alex Dzierba (Spokesperson) - IUCurtis Meyer (Deputy Co-Spokesperson) - CMUElton 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
R. Clark, P. Eugenio, G. Franklin, C. A. Meyer, B. Quinn, R. Schumacher [Carnegie Mellon University]
H. Crannel, D. Sober [Catholic University of America]
D. Doughty, D. Heddle [Christopher Newport University]
R. Jones [University of Connecticut]
W. Boeglin, L. Kramer, P. Markowitz, B. Raue, J. Reinhold [Florida International University]
L. Dennis, R. Dragovitsch, G. Riccardi [Florida State University]
A, Dzierba, R. Heinz, E. Scott, P. Smith, C. Steffen, T. Sulanke, S. Teige [Indiana University]
D. Abbott, I. Bird, R. Carlini, H. Fenker, G. Heyes, C. Sinclair, E. Smith, D. Weygand, E. Wolin [JLab]
R. Mischke, A. Palounek, J-C Peng [Los Alamos National Lab]
M. Khandaker, V. Punjabi, C. Salgado [Norfolk State University]
G. Dodge, A. Klein, S. Kuhn, P. Ulmer, L. Weinstein [Old Dominion University]
D. Carman, K. Hicks [Ohio University]
S. Dytman, J. Mueller [University of Pittsburgh]
G. Adams, J. Cummings, A. Empl, J. Napolitano, P. Stoler [Renssalaer Polytechnic Institute]
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Collaboration - II
o D. Leinweber, W. Melnitchouk, A. Thomas, A. Wiliams [CSSM & University of Adelaide]o S. Gofrey [Carleton University]o R. Kaminski, L. Lesniak [Henryk Niewodniczanski Institute of Nuclear Physics- Cracow]o J. Goity [Hampton University]o C. Horowitz, T. Londergan, M. Pichowski, A. Szczepaniak, C. Wolfe [Indiana University]o P. Page [Los Alamos]o A. Afanasev [North Carolina Central University]o E. Swanson [University of Pittsburgh]o T. Barnes [University of Tennessee/Oak Ridge]o R. Davidson [Rensselaer Polytechnic Institute ]
J. Annand, I. Anthony, D. Ireland, J. Kellie, K. Livingston, D. MacGregor, C. McGeorge, B. Owens, G. Rosner, D. Watts [U. of Glasgow - Scotland]
S. Denisov, N.Fedyakin, A. Gorokhov, V. Samoilenko, A. Schukin [Institute for HEP - Protvino]
V. A. Bodyagin, A. M. Gribushin, N. A. Kruglov, V. L. Korotkikh, M. A. Kostin, A. I. Demianov, O. L. Kodolova, L. I. Sarycheva, A. A. Yershov [Moscow State University]
V. Druginin, V. Ivanchenko, E. Solodov [Budker Institute - Novosibirsk]
E. J. Brash, G. M. Huber, G. J. Lolos, Z. Papandreou [University of Regina]
Experimental Groups outside the US
Theory Group
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Review
David Cassel Cornell (chair)Frank Close RutherfordJohn Domingo JLabBill Dunwoodie SLACDon Geesaman ArgonneDavid Hitlin CaltechMartin Olsson WisconsinGlenn Young ORNL
The Committee
Project Reviewed Dec, 1999
Executive Summary Highlights:
The experimental program proposed in the Hall D Project is well-suited for definitive searches ofexotic 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
The collaboration will be ready to begin work on a Conceptual Design Report once a Project Office with Project Director is in place
An R&D program is required to ensure that the magnet is usable, to optimize many of the detector choices, to ensure that novel designs are feasible and to validate cost estimates.
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ConclusionsRole of glue in strong QCD is needed for an understanding of confinement
Physics
Unambiguous identification of gluonic excitations will start with exotic hybrids Goal
Flux, duty factor, energy & polarization available at an energyupgraded CEBAF & and JLab is unique Beams
Detector is state of the art & based on several existing subsystems and will yield excellent coverage, resolution & unprecedented statistics
Detector
Exotic hybrids are expected precisely where there is little experimental information
Photoproduction