1. Department of Physics and Astronomy
Exotic Hybrid Mesons.
J. D. Kellie
Department of Physics and Astronomy
Glasgow University.
Presentation to IoP Manchester 2005.

2. Summary of talk. Introduction. Exotic Hybrid Mesons
a) Why they are of interest.
b) How they can be produced.
How they can be identified and their properties measured.
Current experimental evidence.
3. Conclusions.

3. Introduction.
This talk presents two experiments designed to investigate QUARK CONFINEMENT by attempting to find evidence of gluonic excitations within mesons in both the light (u, d, s) and charmed (c) quark sectors.
The experiments are GLUEX which forms part of the Jefferson Laboratory upgrade which will increase the electron beam energy from 6 to 12 GeV, and PANDA which is part of the GSI upgrade.
GLUEX will use tagged linearly polarised photons – a source of vector mesons – incident on a hydrogen target. A hermetic spectrometer, based on a superconducting solenoid, will measure the reaction products. Photons of around 9 GeV are required.
The upgrade has obtained U.S. Department of Energy support.

4. PANDA will be located in the high-energy storage ring HESR at the international FAIR facility at GSI, and will use anti-proton proton annihilation to study gluonic excitations, glueballs and hybrids in the charmonium mass range.
The antiproton beam – momentum extending to 15 GeV/c – is incident on a fixed hydrogen target inside a superconducting solenoid, which, together with a forward large acceptance dipole magnet, will form the basis of the PANDA spectrometer.

5. Why Exotic Hybrid Mesons are of interest.
Quark confinement can be explained in terms of the interaction which arises from gluonic exchange between the quarks.
Mesons, with their structure, are ideal for studying the interaction.
states have well defined quantum numbers. If gluonic degrees of freedom are added, the resulting states are hybrid mesons. When hybrid meson states have quantum numbers that do not belong to the basic set of states they are called exotic hybrid mesons.
If states with exotic quantum numbers are discovered, this will clarify the role played by gluons in the confinement of quarks.
GLUEX and PANDA are specifically designed to measure the quantum numbers of excited mesons.

6. Confinement arises from flux tubes and their excitation leads to a new
Lattice QCD
Confinement arises from flux tubes and their excitation leads to a new
spectrum of mesons
→ Flux Tube Model
Quark Confinement.
neutron (d,u,d)
(d, u ) proton (u,u,d)
From G. Bali

7. Understanding Confinement
The Ideal Experiment
The Real Experiment

8. Normal Mesons – qq color singlet bound states
Spin/angular momentum configurations & radial excitations generate our known spectrum of light quark mesons.
Starting with u - d - s we expect to find mesons grouped in nonets - each
characterized by a given J, P and C.
JPC = 0– – – 1+ – 2++ …
Allowed combinations
JPC = 0– – 0+ – 1– – …
Not-allowed: exotic

9. Hybrid Mesons
Hybrid mesons
1 GeV mass difference (p/r)
Normal mesons

10. Quantum Numbers of Hybrid Mesons
Excited Flux Tube
Quarks
Hybrid Meson
like
Exotic
Flux tube excitation (and parallel quark spins) lead to exotic JPC
like

11. Meson Map – GLUEX mass range
Radial
excitations
1.0
1.5
2.0
2.5
qq Mesons
L = 0 1 2 3 4
Meson Map – GLUEX mass range
Each box corresponds
to 4 nonets (2 for L=0)
Mass (GeV)
exotic
nonets
0 – +
0 + –
1 + +
1 + –
1– +
1 – –
2 – +
2 + –
2 + +
0 + +
Glueballs
Hybrids
(L = qq angular momentum)

12. Meson Map – PANDA mass range.

13. Upgrade magnets and power supplies
CHL-2
Upgrade magnets and power supplies
12 GeV CEBAF
add Hall D
(and beam line)
Enhance equipment in existing halls

14. GlueX / Hall D Detector Detector Review Oct 20-22, 2004 Lead Glass
Solenoid
Coherent Brem.
Photon Beam
Tracking
Target
Cerenkov
Counter
Time of
Flight
Barrel
Calorimeter
Note that tagger is
80 m upstream of
detector
Detector Review
Oct 20-22, 2004
Electron Beam from CEBAF

15. HESR storage ring at FAIR.
PANDA facility.

16. PANDA spectrometer.

17. Participation of the GLASGOW group at
GLUEX and PANDA.
GLUEX.
Design of the GLUEX tagging spectrometer.
Assessment of suitable diamond radiators.
PANDA.
Solenoid and Forward Spectrometer magnetic field design studies.
Development of Grid Computing.
Design of Cerenkov detectors – with Edinburgh.

18. Field component along the axis.
PANDA magnetic field calculations – showing the effects of field clamps.
Vertical section:
Field component along the axis.
Vertical section:
Field component transverse to the axis.

19. How Exotic Hybrid Mesons are produced at GLUEX
Basic interaction. N g e X
g  ,,
The incident photons – vector mesons –are excited into states X which decay into many different channels. A hermetic spectrometer detects the reaction products.
Requirements.
JLab energy upgraded from 6 to 12 GeV.
Source of linearly polarised photons, (determine parity).
New detector to measure reaction products.

20. Production of Linearly Polarised Photons.
When the electron beam of energy interacts with a carefully aligned thin diamond wafer, linearly polarised coherent bremsstrahlung, as well as incoherent bremsstrahlung, is produced.
If the energies E of the residual electrons are measured in a tagging spectrometer, the energy of the bremsstrahlung photon is
The ratio of coherent to incoherent bremsstrahlung is enhanced if the photons pass through a narrow collimator.

21. Coherent Bremsstrahlung
12 GeV electrons
Incoherent &
coherent spectrum
flux
This technique provides requisite energy, flux and polarization
tagged
with 0.1% resolution
40%
polarization
in peak
photons out
collimated
electrons in
spectrometer
diamond
crystal
Eg (GeV)

22. The GLUEX tagger.
Two identical magnets, each ~50 tonnes.
Vacuum chamber, designed to withstand vacuum force of ~ 70 tonnes.
Focal Plane
The focal plane consists of a broad-band low resolution hodoscope covering used for diamond alignment and monitoring, and a high resolution microscope positioned for
and operating at per channel.

23. Diamond Assessment using X-rays.
X-ray topography
Rocking curve measurements.

24. Diamond X-ray Analysis - very good diamond.
Topographs.
Topographs of 3 slices ( in thickness) cut from a single synthetic diamond with the top slice nearest the seed. Each shows the same pattern, but the relative area of the central region increases with distance from the seed.
dbg
dbr
Rocking Curves for bottom slice.
dbb
FWHM~10 microradians

25. How exotic hybrid mesons can be identified and their properties measured.
Use a large acceptance detector hermetic coverage for charged and neutral particles. typical hadronic final states: f1h KKph KKpppp b1p wpp ppppp rp ppp high data acquisition rate.
Perform partial-wave analysis
identify quantum numbers as a function of mass.
check consistency of results in different decay modes.

26. Rates High statistics means high rates Initially 107 tagged /s
At 107, the total hadronic rate is » 37kHz
the tagged hadronic rate is » 1.4kHz
At 108, the total hadronic rate is » 370kHz
the tagged hadronic rate is » 14kHz
Initially 107 tagged /s
Design detector for 108
JLab CLAS runs at 107 already.
Running at 107 for 1 year will exceed current photoproduction
data by several orders of magnitude and will exceed current
 data.

27. Topologies photons pions protons  t-channel meson photoproductionX
,K,g
n,p
t-channel meson photoproduction
photons
pions
protons
10-60o
~1GeV/c

28. Background Topologies p X
,K,g
n,p  
/N* production is a significant background
to the simple t-channel production.
There is interesting physics in this channel,
it is just more complicated to analyze.
photons
pions
protons
forward
backwards
slow pions

29. The GlueX Detector
Tracking
Calorimetry
Particle ID
Magnetic Field

30. Calorimetry Forward Calorimeter LGD Existing lead glass detector
~2500 blocks
E/E · /E1/2
» 100 MeV · E · 8 GeV
Barrel Calorimeter BCAL
Lead-scifiber sandwich
4m long cylinder
E/E · /E1/2
~20MeV · E · » 3 GeV
200ps timing resolution
z-position of shower
time-of-flight
Expected o and  resolutions
Upstream Photon Veto UPV
Veto photons
~20MeV · E · 300 MeV

31. Tracking Forward Region FDC 4 packages of planar drift chambers
anode + cathode readout
six planes per package
xy=150m
active close to the beam line.
Central Region CDC
cylindrical straw-tube chamber
23 layers from 14cm to 58cm
6o stereo layers
r=150m z» 2mm
minimize downstream endplate
dE/dx for p<450 MeV/c
Necessary for protons

32. Particle Identification
Time-of-flight Systems
Forward tof ~80ps
BCAL ~200ps
Start counter
Cherenkov Detector
DIRC  K p separation
dE/dx Information
The CDC will do dE/dx
p<450 MeV/c

33. Requirements for a good partial wave analysis.
Hermetic Detector for charged particles
and photons.
Uniform, understood acceptance.
Excellent resolution to reduce backgrounds.
Linear polarized photons.
High statistics data sets.
Sensitive to many final states.

34. Current Experimental Evidence for Exotic Hybrid Mesons.
BNL E852 Experiment with on a hydrogen target. a)
- PWA mass peak unstable.
Statistics for b) are low, but more in line with LQCD in terms of mass and decay modes. GlueX will have much higher statistics and be able to find nonets of states.

35. CONCLUSIONS.
The discovery of exotic hybrid mesons will provide strong evidence that quarks interact by the exchange of gluons, and hence greatly increase our understanding of quark confinement.
The GlueX and PANDA experiments have the required versatility, acceptance, resolution and particle ID to determine the quantum numbers of mesonic states.
In addition to being able to identify exotic hybrid mesons, GlueX and PANDA will measure the spectroscopy of meson states in both the light and charmed quark sectors.
GlueX and PANDA have the potential to search for glueballs, quark molecular states etc.
GlueX and PANDA are complementary experiments with common physics goals, but using entirely different types of facilities.