Flux

tube

forms

between

qq

The Jefferson Lab Hall D Project

Curtis A. Meyer

Carnegie Mellon University

SLAC Seminar, 10 January, 2002

The Search for QCD Exotics and

q

qbe

fore

q

q

befo

re

q

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befo

re

q

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befo

reOutline

Meson spectroscopy and gluonic excitations

Experimental Evidence

The Hall D Project

History and Timelines

Summary

qq

Light Quark Meson Spectroscopy

q

q

J = L + S

P = (1)L

C = (1) (L+S)

Nonets

uds

Orb

ital

exc

itat

ion

s

Radial excitations

QCD is a theory of quarks and gluons

What role do gluons play in the mesonspectrum?

Lattice calculations predict a spectrumof glueballs. The lightest 3 have JPC

Quantum numbers of 0++ , 2++ and0-+.

The lightest is about 1.6 GeV/c2

Glueball Mass Spectrum

Morningstar et al.f0(980)

f0(1500)

f0(1370)

f0(1710)

a0(980)

a0(1450) K*0(1430)

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

š/r

ground state

transverse phonon modes

Lattice QCD Flux tubes realized Flux

tube

forms

between

qq

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

LS

S

1

2

S = S + S1 2

J = L + S

C = (-1)L + S

P = (-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

JPC = 1-- 1++

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

f0(1500)

f2(1270)

f0(980)

f2(1565)+700,000 000 Events

Crystal Barrel Results: antiproton-proton annihilation at rest

f0(1500)

250,000 0 Events

Discovery of the f0(1500) Discovery of the a0(1450)

f0(1500) ’, KK, 4

f0(1370)

The Scalar Mesons

1.5

0++

2.5 2.51.5

0++

Central Production WA102Observes f0(1370)f0(1500)f0(1710)

OverpopulationStrange Decay PatternsSeen in glue-rich reactionsNot in glue-poor

Glueball and Mesonsare mixed, but what isthe mixing scheme?

J/ Decays?

f0(1370) seenf0(1500) ????f0(1710) seen

Awaiting CLEO-c

What about 2++ and 0?

ppE852 Results (18 GeV)

The a2(1320) is the dominantsignal. There is a small (few %)exotic wave.

Interference effects showa resonant structure in .(Assumption of flat backgroundphase as shown as 3.)

Mass = 1370 +-16+50

-30 MeV/c2

Width= 385 +- 40+65-105 MeV/c2

a2

(1400)

Crystal Barrel Results: antiproton-neutron annihilation

Mass = 1400 +- 20 +- 20 MeV/c2

Width= 310+-50+50-30 MeV/c2

Same strength as the a2.

Produced from states with one unit

of angular momentum.Without 1 2/ndf = 3, with = 1.29

E852 Results p p

At 18 GeV/c

suggests p 0 p

p

to partial wave analysis

M( ) GeV / c2 M( ) GeV / c2

Results of Partial Wave Analysis

a1

a2

BenchmarkResonances

a1(1270)a2(1320)2(1670)

2

Benchmarksare needed toshow resonant behavior.

An Exotic Signal in E852

LeakageFrom

Non-exotic Wavedue to imperfectly

understood acceptance

ExoticSignal

1

Correlation ofPhase

&Intensity

M( ) GeV / c2

1(1600)

3 m=1593+-8+28-47 =168+-20+150

-12

’ m=1597+-10+45-10 =340+-40+-50

Current Evidence

Glueballs Hybrids

Overpopulation of thescalar nonet and LGT

predictions suggest thatthe glueball and the

scalar mesons are mixed

JPC = 1-+ states reported

1(1400)

1(1600) ’

by BNL E852, CBARand VES

Complication ismixing with conventional qq

States

Need to observe additionalglueball states

Not without controversy

Not in expected decay modes

Have gluonic excitations been observed ?

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

New Arc

5 NewCryomodules

5 New Cryomodules

Photon Tagger

Hall D

The Jlab 12 GeV UpgradeThe Jlab 12 GeV Upgrade

Up to 11 GeV electrons

12.2 GeVelectrons

Polarized

Photons

20 Cryomodules

20 Cryomodules

Intense tagged, linearly polarized photons

$70 Million Accelerator$35 Million for Hall D$45 Million for A,B and C

DetectorLead GlassDetector

Solenoid2.5Tesla

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

Now at JLab

Recycling of existing equipment

Being Moved to JLab

BNL E852 Pb-Glass ArrayLASS/MEGA Solenoid

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

Optimal Photon Energy

1.0

0.8

0.6

0.4

0.2

0.0

rela

tive

yie

ld

11109876

beam photon energy (GeV)

m[x] = 1.0 GeV = 1.5 GeV = 2.0 GeV = 2.5 GeV

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

Why Photoproduction ?

A pion or kaon beam, when scattering occurs,

can have its flux tube excitedor

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

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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

__

__

Very little photoproduction data exist.What little there is hint at a differentresonance structure than what is seenin pion production.

In one year of initialrunning, expect 100times pion statistics

In one year of initialrunning, expect 100times pion statistics

Detector designed to do Partial Wave Analysis

Double blind studies of 3 final states

p

n

X

Polarization

m [GeV/c2]

GJ

a2

Detection of Exotic Mesons

f1, b1high multiplicity)’aa

Hybrids predicted to decay to S+P mesons S= nonets P=bj,aj nonets

Predicted Observed?

p -> [, ,

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 0 3

0 2

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 b1For example, for hybrids: favored

not-favoredX Measure many decay modes!

-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(GJ)

5 GeV

Mass(X) = 1.4 GeV

Mass(X) = 1.7 GeV

Mass(X) = 2.0 GeV

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

GJ

-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(GJ)

8 GeV

Mass(X) = 1.4 GeV

Mass(X) = 1.7 GeV

Mass(X) = 2.0 GeV

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

GJ

-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(GJ)

12 GeV

Mass(X) = 1.4 GeV

Mass(X) = 1.7 GeV

Mass(X) = 2.0 GeV

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

GJ

p -> n

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(GJ)

5 GeV

Mass(X) = 1.4 GeV

Mass(X) = 1.7 GeV

Mass(X) = 2.0 GeV

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

GJ

-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(GJ)

8 GeV

Mass(X) = 1.4 GeV

Mass(X) = 1.7 GeV

Mass(X) = 2.0 GeV

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

GJ

-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(GJ)

12 GeV

Mass(X) = 1.4 GeV

Mass(X) = 1.7 GeV

Mass(X) = 2.0 GeV

-3 -2 -1 0 1 2 30

0.2

0.4

0.6

0.8

1

GJ

p -> p p Xn n

p Xn 00n

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

Complete Study of neutral and charged final states

Hybrids are expected to decay into complicated final states.Exotic QN’s are smoking guns, but there are non exotic QN’s as well. Need to know decay patterns to understand mixing.

Initial running will be at 5*107 /s, will eventually reach 108

One year of initial running will yield 100 times pion statistics in the channel. Many weaker channels will have sufficient statistics for full PWA. (Will probe fraction of nb cross sections)

PWA is sensitive to channels at about 0.5% of major component and to widths of several hundred MeV.

If Exotics are there, they will be seen. If they are not there, then we will need to reexamine our understanding of QCD.The first hints of exotic states already disagree with what we think we understand about them.

PROJECT STATUS

January 1999 Letter of Intent to Jlab PACDecember 1999 Cassell Committee Review of ProjectAugust 2000 Key Part of the JLAB 12 GeV UpgradeDecember 2000 Presentation at NSAC Town MeetingApril 2001 Reccomendation in NSAC LRPAugust 2001 DOE Review of JLAB, push for CD0January 2002 NSAC LRP ReleasedWinter 2002 CD0 Status at DOE .... 2007 Start Data Taking (hopefully).

SummaryQCD predicts a spectrum of states directly associated with the gluonic degree of freedom and confinement. Exotic Quntum numbers are a definitive signature

Experiments have started to observe states with exotic quantum numbers, but the observations are few, and not in agreement with theoretical expectations.

Photoproduction is expected (vector meson beams) are expected be a very good, yet unexplored way to produce these states.

Hall D will be able to map out a detailed picture of these states and their decays with statistics 100 times better than current pion experiements. Such information will yield important data on the dynamics of glue and its role in QCD.