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Glueballs, Hybrids & Exotics

Glueballs, Hybrids & Exotics. An Experimental & Phenomenological Overview. Curtis A. Meyer Carnegie Mellon University May 31, 2006. Outline of Talk. Introduction Meson Spectroscopy Glueballs Expectations Experimental Data Interpretation Hybrid Mesons Expectations

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Glueballs, Hybrids & Exotics

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

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

  4. Normal Mesons orbital r3,w3,f3,K3 r2,w2,f2,K2 r1,w1,f1,K1 p2,h2,h’2,K2 3-- 2-- 1-- 2-+ L=2 radial s u d a2,f2,f’2,K2 a1,f1,f’1,K1 a0,f0,f’0,K0 b1,h1,h’1,K1 2++ 1++ 0++ 1+- J=L+S L=1 (2S+1) L J s P=(-1) L+1 u d 1S0 = 0 -+ C=(-1) L+S r,w,f,K* p,h,h’,K 1-- 0-+ 3S1 = 1-- L=0 G=C (-1) I Non-quark-antiquark 0-- 0+- 1-+ 2+- 3-+ … quark-antiquark pairs CIPANP 2006

  5. Spectrum qq Mesons 2 – + 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 Each box corresponds to 4 nonets (2 for L=0) Radial excitations Lattice 1-+ 1.9 GeV 0++ 1.6 GeV (L = qq angular momentum) CIPANP 2006

  6. Glueball Mass Spectrum 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 JPC Quantum numbers of 0++ , 2++ and 0-+. The lightest is about 1.6 GeV/c2 f0(1710) f0(1500) a0(1450) K*0(1430) f0(1370) Morningstar et al. a0(980) f0(980) CIPANP 2006

  7. G M M Glue-rich channels Where should you look experimentally for Glueballs? Radiative J/ Decays 0-+ (1440) 0++ f0(1710) Large signals Proton-Antiproton Annihilation Central Production (double-pomeron exchange) 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. CIPANP 2006

  9. Crystal Barrel Results Crystal Barrel Results: antiproton-proton annihilation at rest f0(1500) app, hh, hh’, KK, 4p Discovery of the f0(1500) f0(1370) a4p Solidified the f0(1370) Establishes the scalar nonet Discovery of the a0(1450) 250,000 hhp0 Events 700,000 p0p0p0 Events f2(1565)+s f0(1500) f2(1270) f0(980) f0(1500) CIPANP 2006

  10. The f0(1500) Is it possible to describe the f0(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 143o 90% light-quark 10% strange-quark Both the f0(1370) and f0(1500) are CIPANP 2006

  11. WA102 Results CERN experiment colliding p on a hydrogen target. Central Production Experiment Recent comprehensive data set and a coupled channel analysis. 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 f0(1500) and f0(1710), no report of the f0(1370). f0(1710) has strongest production. CIPANP 2006

  13. meson Glueball meson meson meson meson Glueball meson meson Model for Mixing 1 r2 r3 flavor blind? r Solve for mixing scheme F.Close: hep-ph/0103173 CIPANP 2006

  14. Meson Glueball Mixing Physical Masses f0(1370),f0(1500),f0(1710) Bare Masses: m1,m2,mG (G) (S) (N) f0(1370)-0.690.07 0.150.01 0.700.07 f0(1500)-0.650.04 0.330.04 –0.700.07 f0(1710)0.390.03 0.910.02 0.150.02 octet piece m1=137720 m2=167410 mG=144324 Lattice of about 1600 CIPANP 2006

  15. Glueball Expectations Antiproton-proton: Couples to Observe: f0(1370),f0(1500) Central Production: Couples to G and in phase. Observe: f0(1370),f0(1500), weaker f0(1710). Radiative J/: Couples to G, |1>, suppressed |8> Observe strong f0(1710) from constructive |1>+G Observe f0(1500) from G Observe weak f0(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. CIPANP 2006

  16. Higher mass glueballs? Lattice predicts that the 2++ and the 0-+ are the next two, with masses just above 2GeV/c2. 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. CIPANP 2006

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

  18. QCD Potential excited flux-tube m=1 ground-state flux-tube m=0 linear potential 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. CIPANP 2006

  19. Hybrid Predictions Flux-tube model: 8 degenerate nonets 1++,1-- 0-+,0+-,1-+,1+-,2-+,2+- ~1.9 GeV/c2 S=0 S=1 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/c2 1-+ 0+- 2+- Splitting  0.20 In the charmonium sector: 1-+ 4.39 0.08 0+- 4.61 0.11 Splitting = 0.20 CIPANP 2006

  20. Decays of Hybrids Decay calculations are model dependent, but the 3P0 model does a good job of describing normal meson decays. 0++ quantum numbers (3P0) 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b1,f1,,a1 87,21,11,9 MeV (partial widths) CIPANP 2006

  21. E852 Results p-p -> hp-p (18 GeV) Mass = 1370 +-16+50-30 MeV/c2 Width= 385 +- 40+65-105 MeV/c2 p1(1400) The a2(1320) is the dominant signal. There is a small (few %) exotic wave. p1 a2 Interference effects show a resonant structure in 1-+. (Assumption of flat background phase as shown as 3.) CIPANP 2006

  22. CBAR Exotic Crystal Barrel Results: antiproton-neutron annihilation Same strength as the a2. Mass = 1400 +- 20 +- 20 MeV/c2 Width= 310+-50+50-30 MeV/c2 p1(1400) Produced from states with one unit of angular momentum. Without p1c2/ndf = 3, with = 1.29 hp0p- 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. CIPANP 2006

  24. E852 Results to partial wave analysis suggests At 18 GeV/c CIPANP 2006

  25. Correlation of Phase & Intensity Leakage From Non-exotic Wave due to imperfectly understood acceptance An Exotic Signal Exotic Signal p1(1600) 3p m=1593+-8+28-47G=168+-20+150-12 ph’ m=1597+-10+45-10G=340+-40+-50 CIPANP 2006

  26. In Other Channels E852 Results 1-+ in ’ p-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)  ’ CIPANP 2006

  27. In Other Channels E852 Results 1-+ in f1 and b1 p-p  +--p p-p  w0-p 1(1600)  b1 1(1600)  f1 Mass=1.7090.024 GeV Width=0.4030.08 GeV In both b1 and f1, observe Excess intensity at about 2GeV/c2. Mass ~ 2.00 GeV, Width ~ 0.2 to 0.3 GeV Mass = 1.6870.011 GeV Width = 0.2060.03 GeV CIPANP 2006

  28. 1(1600) Consistency 3 m=1593 =168 0 m=1597 =340 f1 m=1709 =403 b1 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. CIPANP 2006

  29. New Analysis No Evidence for the 1(1670) Dzierba et. al. PRD 73 (2006) 4-5 times statistics in 2 each of two channels Get a better description of the data via moments comparison Add 2(1670)! (L=3) Add 2(1670)!3 Add 2(1670)! ()S Add a3 decays Add a4(2040) CIPANP 2006

  30. p1 IG(JPC)=1-(1-+) K1 IG(JPC)= ½ (1-) h’1 IG(JPC)=0+(1-+) h1 IG(JPC)=0+(1-+) Exotic Signals 1(1400)Width ~ 0.3 GeV, Decays: only  weak signal in p production (scattering??) strong signal in antiproton-deuterium. NOT A HYBRID Does this exist? 1(1600) Width ~ 0.16 GeV, Decays ,’,(b1) Only seen in p production, (E852 + VES) 1(2000) Weak evidence in preferred hybrid modes f1 and b1 The right place. Needs confirmation. CIPANP 2006

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

  32. X g e N N p1 IG(JPC)=1-(1-+) K1 IG(JPC)= ½ (1-) g  ,, h’1 IG(JPC)=0+(1-+) h1 IG(JPC)=0+(1-+) Exotics in Photoproduction 1-+ nonet Need to establish nonet nature of exotics: 0 Need to establish more than one nonet: 0+- 1-+ 2+- CIPANP 2006

  33. X b0 IG(JPC)=1+(0+-) g e h0 IG(JPC)=0-(0+-) N N h’0 IG(JPC)=0-(0+-) b2 IG(JPC)=1+(2+-) K0 I(JP)=½(0+) h2 IG(JPC)=0-(2+-) h’2 IG(JPC)=0-(2+-) K2 I(JP)= ½(2+) 0+- and 2+- Exotics In photoproduction, couple to r, w or f? a1,f0,f1 wf0,wf1,ra1 ff0,ff1,ra1 wp, a1,f0,f1 “Similar to p1 ” wh,rp,wf0,wf1,ra1 fh,rp,ff0,ff1,ra1 Kaons do not have exotic QN’s 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 CIPANP 2006

  35. The Scalar Mesons The Scalar Mesons Overpopulation Strange Decay Patterns Seen in glue-rich reactions Not in glue-poor What about 2++ and 0-+ ? J/Y Decays? Awaiting CLEO-c Glueball and Mesons are mixed. Scheme is model dependent. Crystal Barrel proton-antiproton annihilation Central Production WA102 Three States f0(1370) f0(1500) f0(1710) 0++rr 0++ ss 1.5 2.5 2.5 1.5 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. 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. 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. CIPANP 2006

  39. Significance of signal. CIPANP 2006

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

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