Exotic Hybrid Mesons. J. D. Kellie Department of Physics and Astronomy Glasgow University.

1. 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 andtheir excitation leads to a new spectrum of mesons Lattice QCD → 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. JPC = 0– +0++1– – 1+ –2++ … Allowed combinations JPC = 0– –0+ –1– +2+ – … Not-allowed: exotic 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.

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

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

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

12. Meson Map – PANDA mass range.

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

14. Lead Glass Detector Barrel Calorimeter Solenoid Coherent Brem. Photon Beam Time of Flight Note that tagger is 80 m upstream of detector Tracking Cerenkov Counter Target GlueX / Hall D 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. 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. X g e N N g  ,, How Exotic Hybrid Mesons are produced at GLUEX Basic interaction. The incident photons – vector mesons –are excited into states Xwhich 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. Incoherent & coherent spectrum 40% polarization in peak collimated tagged with 0.1% resolution Coherent Bremsstrahlung 12 GeV electrons flux This technique provides requisite energy, flux and polarization photons out 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 (100 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. Use a large acceptance detector hermetic coverage for charged and neutral particles.typical hadronic final states:f1h KKph KKpppp b1p wpp ppppp rp ppphigh data acquisition rate. How exotic hybrid mesons can be identified and their properties measured. 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 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  ,K,g X n,p p t-channel meson photoproduction photons pions protons 10-60o ~1GeV/c

28. Background Topologies  ,K,g X  n,p  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. protons pions photons forward backwards slow pions

29. The GlueX Detector Particle ID Tracking Calorimetry Magnetic Field

30. Calorimetry Forward Calorimeter LGD Existing lead glass detector ~2500 blocks E/E · 0.036+0.073/E1/2 » 100 MeV · E· 8 GeV Barrel Calorimeter BCAL Lead-scifiber sandwich 4m long cylinder E/E · 0.020+0.05/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 Detectorfor 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 forglueballs, quark molecular states etc. • GlueX and PANDA arecomplementary experiments with common physics goals, but using entirely different types of facilities.