1. May 31, 2006 CIPANP 2006 1 Glueballs, Hybrids & Exotics Curtis A. Meyer Carnegie Mellon University May 31, 2006 An Experimental & Phenomenological Overview

2. May 31, 2006 CIPANP 2006 2 Outline of Talk Introduction Meson Spectroscopy Glueballs Expectations Experimental Data Interpretation Hybrid Mesons Expectations Experimental Data Interpretation The Future

3. May 31, 2006 CIPANP 2006 3 Strong QCD See and systems. white Color singlet objects observed in nature: Allowed systems:,, Nominally, glue is not needed to describe hadrons. Focus on “light-quark mesons”

4. May 31, 2006 CIPANP 2006 4 quark-antiquark pairs u d s u d s J=L+S P=(-1) L+1 C=(-1) L+S G=C (-1) I (2S+1) L J 1 S 0 = 0 -+ 3 S 1 = 1 -- ,K*  ’,K L=0 1 -- 0 -+ a 2,f 2,f’ 2,K 2 a 1,f 1,f’ 1,K 1 a 0,f 0,f’ 0,K 0 b 1,h 1,h’ 1,K 1 L=1 2 ++ 1 ++ 0 ++ 1 +-  3,  3,  3,K 3  2,  2,  2,K 2  1,  1,  1,K 1  2,  2,  ’ 2,K 2 L=2 3 -- 2 -- 1 -- 2 -+ radial orbital Non-quark-antiquark 0 -- 0 +- 1 -+ 2 +- 3 -+ … Normal Mesons

5. May 31, 2006 CIPANP 2006 5 1.0 1.5 2.0 2.5 qq Mesons L = 01234 Each box corresponds to 4 nonets (2 for L=0) Radial excitations (L = qq angular momentum) exotic nonets 0 – + 0 + – 1 + + 1 + – 1 – + 1 – – 2 – + 2 + – 2 + + 0 – + 2 – + 0 + + Glueballs Hybrids Lattice 1 -+ 1.9 GeV Spectrum 0 ++ 1.6 GeV

6. May 31, 2006 CIPANP 2006 6 QCD is a theory of quarks and gluons What role do gluons play in the meson spectrum? Lattice calculations predict a spectrum of glueballs. The lightest 3 have J PC Quantum numbers of 0 ++, 2 ++ and 0 -+. The lightest is about 1.6 GeV/c 2 Morningstar et al. f 0 (980) f 0 (1500) f 0 (1370) f 0 (1710) a 0 (980) a 0 (1450) K* 0 (1430) Glueball Mass Spectrum

7. May 31, 2006 CIPANP 2006 7 Glue-rich channels G M M Radiative J/  Decays Proton-Antiproton Annihilation Central Production (double-pomeron exchange) Where should you look experimentally for Glueballs? 0 -+  (1440) 0 ++ f 0 (1710) Large signals

8. May 31, 2006 CIPANP 2006 8 Decays of Glueballs? Glueballs should decay in a flavor-blind fashion.  ’=0 is true for any SU(3) singlet and for any pseudoscalar mixing angle. Only an SU(3) “8” can couple to  ’. Flavor-blind decays have always been cited as glueball signals. Not necessarily true.

9. May 31, 2006 CIPANP 2006 9 f 0 (1500) f 2 (1270) f 0 (980) f 2 (1565)+  700,000  0  0  0 Events Crystal Barrel Results: antiproton-proton annihilation at rest f 0 (1500) 250,000  0 Events Discovery of the f 0 (1500) f 0 (1500)   ’, KK, 4  f 0 (1370)   Crystal Barrel Results Establishes the scalar nonet Solidified the f 0 (1370) Discovery of the a 0 (1450)

10. May 31, 2006 CIPANP 2006 10 The f 0 (1500) Is it possible to describe the f 0 (1500) as a member of a meson nonet? Use SU(3) and OZI suppression to compute relative decays to pairs of pseudoscalar mesons Get an angle of about 143 o 90% light-quark 10% strange-quark Both the f 0 (1370) and f 0 (1500) are

11. May 31, 2006 CIPANP 2006 11 WA102 Results Central Production Experiment Recent comprehensive data set and a coupled channel analysis. CERN experiment colliding p on a hydrogen target.

12. May 31, 2006 CIPANP 2006 12 BES Results 0.665 10 -4 0.34 10 -4 3.1 10 -4 2.64 10 -4 1.33 10 -4 9.62 10 -4 3.1 10 -4 Clear Production of f 0 (1500) and f 0 (1710), no report of the f 0 (1370). f 0 (1710) has strongest production.

13. May 31, 2006 CIPANP 2006 13 Model for Mixing meson Glueball meson Glueball meson 1 r2r2 r3r3 flavor blind? r Solve for mixing scheme F.Close: hep-ph/0103173

14. May 31, 2006 CIPANP 2006 14 Meson Glueball Mixing Physical Masses f 0 (1370),f 0 (1500),f 0 (1710) Bare Masses: m 1,m 2,m G (G) (S) (N) f 0 (1370) -0.69  0.07 0.15  0.01 0.70  0.07 f 0 (1500) -0.65  0.04 0.33  0.04 –0.70  0.07 f 0 (1710) 0.39  0.03 0.91  0.02 0.15  0.02 m 1 =1377  20 m 2 =1674  10 m G =1443  24 octet piece Lattice of about 1600

15. May 31, 2006 CIPANP 2006 15 Glueball Expectations Antiproton-proton: Couples to Observe: f 0 (1370),f 0 (1500) Central Production: Couples to G and in phase. Observe: f 0 (1370),f 0 (1500), weaker f 0 (1710). Radiative J/  : Couples to G, |1>, suppressed |8> Observe strong f 0 (1710) from constructive |1>+G Observe f 0 (1500) from G Observe weak f 0 (1370) from destructive |1>+G Two photon: Couples to the quark content of states, not to the glueball. Not clear to me that has been seen.

16. May 31, 2006 CIPANP 2006 16 Higher mass glueballs? Lattice predicts that the 2 ++ and the 0 -+ are the next two, with masses just above 2GeV/c 2. Radial Excitations of the 2 ++ ground state L=3 2 ++ States + Radial excitations f2(1950), f2(2010), f2(2300), f2(2340)… 2’nd Radial Excitations of the  and  ’, perhaps a bit cleaner environment! (I would Not count on it though….) I expect this to be very challenging.

17. May 31, 2006 CIPANP 2006 17 m=0 CP=(-1) S+1 m=1 CP=(-1) S Flux-tube Model ground-state flux-tube m=0 excited flux-tube m=1 built on quark-model mesons CP={(-1) L+S }{(-1) L+1 } ={(-1) S+1 } S=0,L=0,m=1 J=1 CP=+ J PC =1 ++,1 -- (not exotic) S=1,L=0,m=1 J=1 CP=- J PC =0 -+,0 +- 1 -+,1 +- 2 -+,2 +- exotic normal mesons Hybrid Mesons 1 -+ or 1 +-

18. May 31, 2006 CIPANP 2006 18 linear potential ground-state flux-tube m=0 excited flux-tube m=1 Gluonic Excitations provide an experimental measurement of the excited QCD potential. Observations of exotic quantum number nonets are the best experimental signal of gluonic excitations. QCD Potential

19. May 31, 2006 CIPANP 2006 19 Hybrid Predictions Flux-tube model: 8 degenerate nonets 1 ++,1 -- 0 -+,0 +-,1 -+,1 +-,2 -+,2 +- ~1.9 GeV/c 2 Lattice calculations --- 1 -+ nonet is the lightest UKQCD (97) 1.87  0.20 MILC (97) 1.97  0.30 MILC (99) 2.11  0.10 Lacock(99) 1.90  0.20 Mei(02) 2.01  0.10 ~2.0 GeV/c 2 In the charmonium sector: 1 -+ 4.39  0.08 0 +- 4.61  0.11 Splitting = 0.20 1 -+ 0 +- 2 +- Splitting  0.20 S=0 S=1

20. May 31, 2006 CIPANP 2006 20 Decays of Hybrids Decay calculations are model dependent, but the 3 P 0 model does a good job of describing normal meson decays. 0 ++ quantum numbers ( 3 P 0 ) The angular momentum in the flux tube stays in one of the daughter mesons (L=1) and (L=0) meson. L=0: , , , ,… L=1: a,b,h,f,… , , … not preferred.  1  b 1,  f 1, ,  a 1 87,21,11,9 MeV (partial widths)

21. May 31, 2006 CIPANP 2006 21   p    p (18 GeV) The a 2 (1320) is the dominant signal. There is a small (few %) exotic wave. Interference effects show a resonant structure in  . (Assumption of flat background phase as shown as 3.)    Mass = 1370 +-16 +50 -30 MeV/c 2 Width= 385 +- 40 +65 -105 MeV/c 2 a2a2  E852 Results

22. May 31, 2006 CIPANP 2006 22   (1400) Crystal Barrel Results: antiproton-neutron annihilation Mass = 1400 +- 20 +- 20 MeV/c 2 Width= 310+-50 +50 -30 MeV/c 2 Same strength as the a 2. Produced from states with one unit of angular momentum. Without  1  2 /ndf = 3, with = 1.29     CBAR Exotic

23. May 31, 2006 CIPANP 2006 23 Controversy In analysis of E852  ± data, so evidence of the  1 (1400) In CBAR data, the  ± channel is not conclusive. Analysis by Szczepaniak shows that the exotic wave is not resonant – a rescattering effect. The signal is far too light to be a hybrid by any model. This is not a hybrid and may well not be a state.

24. May 31, 2006 CIPANP 2006 24 At 18 GeV/c suggeststo partial wave analysis E852 Results

25. May 31, 2006 CIPANP 2006 25 An Exotic Signal Leakage From Non-exotic Wave due to imperfectly understood acceptance Exotic Signal Correlation of Phase & Intensity  1 (1600) 3  m=1593+-8 +28 -47  =168+-20 +150 -12  ’ m=1597+-10 +45 -10  =340+-40+-50

26. May 31, 2006 CIPANP 2006 26  - p   ’  - p at 18 GeV/c The  1 (1600) is the Dominant signal in  ’ . Mass = 1.597  0.010 GeV Width = 0.340  0.040 GeV  1 (1600)   ’  E852 Results In Other Channels 1-+ in  ’ 

27. May 31, 2006 CIPANP 2006 27  - p   +  -  - p  1 (1600)  f 1  E852 Results  - p   0  - p  1 (1600)  b 1  Mass = 1.687  0.011 GeV Width = 0.206  0.03 GeV Mass=1.709  0.024 GeV Width=0.403  0.08 GeV In both b 1  and f 1 , observe Excess intensity at about 2GeV/c 2. Mass ~ 2.00 GeV, Width ~ 0.2 to 0.3 GeV In Other Channels 1-+ in f 1  and b 1 

28. May 31, 2006 CIPANP 2006 28  1 (1600) Consistency 3  m=1593  =168  0  m=1597  =340 f 1  m=1709  =403 b 1  m=1687  =206 Not Outrageous, but not great agreement. Mass is slightly low, but not crazy. Szczepaniak: Explains much of the  0 signal as a background rescattering similar to the  Still room for a narrower exotic state.

29. May 31, 2006 CIPANP 2006 29 New Analysis Dzierba et. al. PRD 73 (2006) Add  2 (1670) !  (L=3) Add  2 (1670) !  3  Add  2 (1670) ! (  ) S  Add a 3 decays Add a 4 (2040) 4-5 times statistics in 2 each of two channels Get a better description of the data via moments comparison No Evidence for the  1 (1670)

30. May 31, 2006 CIPANP 2006 30 Exotic Signals  1 (1400) Width ~ 0.3 GeV, Decays: only  weak signal in  p production (scattering??) strong signal in antiproton-deuterium.  1 (1600) Width ~ 0.16 GeV, Decays ,  ’ ,(b 1  ) Only seen in  p production, (E852 + VES)  1 I G (J PC )=1 - (1 -+ )  ’ 1 I G (J PC )=0 + (1 -+ )  1 I G (J PC )=0 + (1 -+ ) K 1 I G (J PC )= ½ (1 - )  1 (2000) Weak evidence in preferred hybrid modes f 1  and b 1  NOT A HYBRID Does this exist? The right place. Needs confirmation.

31. May 31, 2006 CIPANP 2006 31 Photoproduction of Exotics A pion or kaon beam, when scattering occurs, can have its flux tube excited  or  beam Quark spins anti-aligned Much data in hand with some evidence for gluonic excitations (tiny part of cross section) q q before q q after q q q q before  beam Almost no data in hand in the mass region where we expect to find exotic hybrids when flux tube is excited Quark spins aligned _ _ _ _

32. May 31, 2006 CIPANP 2006 32 Exotics NN  e X  , ,   1 I G (J PC )=1 - (1 -+ )  ’ 1 I G (J PC )=0 + (1 -+ )  1 I G (J PC )=0 + (1 -+ ) K 1 I G (J PC )= ½ (1 - ) 1 -+ nonet in Photoproduction Need to establish nonet nature of exotics:    0 Need to establish more than one nonet: 0 +- 1 -+ 2 +-

33. May 31, 2006 CIPANP 2006 33 0 +- and 2 +- Exotics NN  e X b 0 I G (J PC )=1 + (0 +- ) h 0 I G (J PC )=0 - (0 +- ) h’ 0 I G (J PC )=0 - (0 +- ) K 0 I(J P )=½(0 + ) b 2 I G (J PC )=1 + (2 +- ) h 2 I G (J PC )=0 - (2 +- ) h’ 2 I G (J PC )=0 - (2 +- ) K 2 I(J P )= ½(2 + ) a1,f0,f1a1,f0,f1 f0,f1,a1f0,f1,a1 f0,f1,a1f0,f1,a1 ,  a 1,  f 0,  f 1  f 0,  f 1,  a 1  f 0,  f 1,  a 1 In photoproduction, couple to ,  or  ? “Similar to  1 ” Kaons do not have exotic QN’s

34. May 31, 2006 CIPANP 2006 34 Exotics and QCD In order to establish the existence of gluonic excitations, We need to establish the nonet nature of the 1 -+ state. We need to establish at other exotic QN nonets – the 0 +- and 2 +-. In the scalar glueball sector, the decay patterns have provided the most sensitive information. I expect the same will be true in the hybrid sector as well. DECAY PATTERS ARE CRUCIAL

35. May 31, 2006 CIPANP 2006 35 The Scalar Mesons 1.5 0 ++  2.5 1.5 0 ++  Central Production WA102 Three States f 0 (1370) f 0 (1500) f 0 (1710) Overpopulation Strange Decay Patterns Seen in glue-rich reactions Not in glue-poor Glueball and Mesons are mixed. Scheme is model dependent. J/  Decays? Awaiting CLEO-c What about 2 ++ and 0  ? The Scalar Mesons Crystal Barrel proton-antiproton annihilation

36. May 31, 2006 CIPANP 2006 36 What will we learn? There is a clear signal for hybrid mesons – Exotic quantum numbers – but confirmation requires the observation of a nonet, not just a single state. Mapping out more than one exotic nonet is necessary to establishing the hybrid nature of the states. Decay patterns will be useful for the exotic QN states, and necessary for the non-exotic QN states.

37. May 31, 2006 CIPANP 2006 37 Summary The first round of J/  experiments opened the door to exotic spectroscopy, but the results were confused. LEAR at CERN opened the door to precision, high-statistics spectroscopy experiments and significantly improved both our understanding of the scalar mesons and the scalar glueball. Pion production experiments at BNL (E852) and VES opened the door to states with non-quark-anti-quark quantum numbers. CERN central production (WA102) provided solid new data on the scalar sector, and a deeper insight into the scalar glueball. BES is collecting new J/  data. CLEO-c can hopefully add with the  0 program.

38. May 31, 2006 CIPANP 2006 38 The Future The GlueX experiment will be able to do for hybrids what Crystal Barrel and WA102 (together) did for glueballs. What are the properties of static glue in hadrons and how is this connected to confinement. The antiproton facility at GSI (HESR) will look for hybrids in the charmonium system – PANDA.

39. May 31, 2006 CIPANP 2006 39 Significance of signal.

40. May 31, 2006 CIPANP 2006 40 Exotic Hybrid Results 1 +-  1 (1400) 1 +-  1 (1600) 1 +-  1 (2000)