introduction 2

http://dustbunny.physics.indiana.edu/HallD

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


References

The Hall D ProjectDesign ReportVer 3

November, 2000

Mapping quarkconfinement byexotic particles

The search forQCD exotics

Sept, 2000 Sept/Oct, 2000


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


QCD and confinement

Large DistanceLow Energy

Small DistanceHigh Energy

PerturbativeRegime

Non-PerturbativeRegime

High EnergyScattering

GluonJets

Observed

Spectroscopy

GluonicDegrees of Freedom

Missing


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


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


Lattice QCDFlux tubes realized

Flux

tube

forms

between

qq

π/rground statetransverse phonon modes

qq

Confinement arises from flux tubesand their excitation leads to a newspectrum of mesons


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


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


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


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-+


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


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 ?


Crystal barrel

0

1

2

3

0 1 2 3m2(π0π0)[GeV2]

500,000Events

p p → 3π0

Evidence for fo(1500)


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


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


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


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


cosθcosθ cosθ

Decay Angular Distributions

JPC=2++ JPC=3--

πb πe

π1

π2

θ

C.M.S.

dNd cosθ( )

∝ Y J0 2

JPC=1--


E852 Results

π+π+π−

π+π−

Decompose this

π−p → π +π−π −p @ 18 GeV


Results of PWA

And the exotic


An Exotic Signal in E852

1−+

ExoticSignalLeakage

FromNon-exotic Wave

Correlation ofPhase

&Intensity

Mass (GeV)Mass (GeV)


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( )


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.


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


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


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


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


Hall D at JLab


DetectorLead GlassDetector

Solenoid

Electron Beam from CEBAF

Coherent BremsstrahlungPhoton Beam

Tracking

Target

CerenkovCounter

Time ofFlight

BarrelCalorimeter


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


Solenoid

Superconducting SolenoidBuilt at SLAC for LASS

Now at LANL - used in MEGA

At SLAC

At LANL

Central field: 2.5 T


LGD

Built by the IndianaGroup for BNL

Exp 852

3000 PbO blocksPM’s/ADC’s

Transferred toJLab

July, 2000

σE GeV( )

= 2 +5E

⎡ ⎣ ⎢

⎤ ⎦ ⎥%


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


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


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


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


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]


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


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.


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

introduction 2

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