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GlueX + Exotic Hadron Spectroscopy

GlueX PAC @ JLAB 23 Aug 2010. Ted Barnes Physics Div. ORNL Dept. of Physics and Astronomy, U.Tenn. GlueX + Exotic Hadron Spectroscopy. 1. Hadrons 101 2. Exotica: glueballs, hybrids and multiquarks/molecules 3. Hybrids: theoretical expectations and

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GlueX + Exotic Hadron Spectroscopy

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  1. GlueX PAC @ JLAB 23 Aug 2010 Ted Barnes Physics Div. ORNL Dept. of Physics and Astronomy, U.Tenn. GlueX +Exotic Hadron Spectroscopy 1. Hadrons 101 2. Exotica: glueballs, hybrids and multiquarks/molecules 3. Hybrids: theoretical expectations and experimental status 4. GlueX@JLAB; g prod of (hybrid) exotics

  2. Hadrons 101

  3. LGT simulation showing the QCD flux tube Color singlets and QCD exotica “confinement happens”. Q Q R = 1.2 [fm] “funnel-shaped” VQQ(R) linear conft. (str. tens. = 16 T) Coul. (OGE) QCD flux tube (LGT, G.Bali et al.; hep-ph/010032)

  4. (q2q2),(q4q),… (q3)n, (qq)(qq),(qq)(q3),… nuclei / molecules multiquark clusters ca. 106 e.g.s of (q3)n, maybe 1-3 others X(3872) = DD*! dangerous: may not exist as resonances e.g. Q(1540) g2, g3,… qqg, q3g,… q2q2, q4q,… glueballs hybrids multiquarks the “multiquark fiasco” -N.Isgur maybe 1-3 e.g.s p1 (1600) best Incl. exotic J PC! maybe 1 e.g. f0(1500 or 1710) Physically allowed hadron states (color singlets) (naïve, valence) _ Conventional quark model mesons and baryons. qq q3 100s of e.g.s Basis state mixing may be very important in some sectors. “exotica” :

  5. Quarkonia: qq qq mesonsquantum numbers ParityPqq = (-)(L+1)C-parityCqq = (-)(L+S) The resulting qq N,L states N2S+1LJ have JPC= 1S: 3S11-- ; 1S00 -+ 2S: 23S11-- ; 21S00 -+ … 1P: 3P22+ + ; 3P11+ + ; 3P00+ + ; 1P11+-2P … 1D: 3D33- - ; 3D22- - ; 3D11- - ; 1D22-+2D … JPC forbidden to qq are called “JPC-exotic quantum numbers” : 0 - - ; 0 + - ; 1 - + ; 2 + - ; 3 - + … x Plausible JPC-exotic candidates = hybrids (have all JPC), glueballs (high mass), maybe multiquarks (fall-apart decays).

  6. Quarkonia: cce.g. Fitted and predicted cc spectrum Coulomb (OGE) + linear scalar conft. potential model blue = expt, red = theory. L*S OGE – L*S conft, T OGE as= 0.5538 b = 0.1422 [GeV2] mc = 1.4834 [GeV] s = 1.0222 [GeV] S*S OGE

  7. Best recent LQCD refs for cc and cc-hybrid (?) spectroscopy: (Summary of JLAB LQCD group results.) For references see: “Charmonium excited state spectrum in lattice QCD.” J.J.Dudek, R.G.Edwards, N.Mathur and D.G.Richards, Phys. Rev. D77, 034501 (2008) and PRD78, 094504 (2008) n.b. PRD79, 094504 (again) (2009) includes rad. transitions! Results for cc still rather difficult to distinguish from quark model. Final LQCD predictions fm JLAB: “cc” Exotic cc-H 1- + 4300(50), • Nonexotic cc-H 1- - 4400(60). J PC exotics (non-qq) “cc hybrids (?)”

  8. Radiative widths of exotics = ? (The BIG question for GlueX.) J.J.Dudek, R.G.Edwards and C.E.Thomas, Exotic and excited-state radiative transitions in charmonium from lattice QCD PRD79, 094504 (2009),arXiv:0902.2241 [hep-ph]. non-exotic 1-- hybrid rad. trans. Paper quotes G(hc1 (1-+exotic) -> J/y g ) ~ 100 keV. A typical “robust” cc radiative width. GlueX is justified. 

  9. Quarkonia: nn e.g. Status of light meson spectroscopy (I=1 e.g.) Approx. status, light (u,d,s) qq spectrum to ca. 2.1 GeV. I=1 shown, dashed boxes = expected States are well known to ca. 1.5 GeV, poorly known above (except for larger-J). n.b. ss is poorly known generally. Several recent candidates, e.g. a1(1700), a2(1750). Strong decays give M, G, JPCofqq candidates.

  10. Theor. guides for exptqq searches: Extensive strong decay tables Mainly light (u,d,s) hadrons in f.-t. or 3P0models. A few references: qq meson decays: S.Godfrey and N.Isgur, PRD32, 189 (1985). T.Barnes, F.E.Close, P.R.Page and E.S.Swanson, PRD55, 4157 (1997). [u,d mesons] T.Barnes, N.Black and P.R.Page, PRD68, 054014 (2003).[strange mesons][43 states, all 525 modes, all 891 amps.] T.Barnes, S.Godfrey and E.S.Swanson, PRD72, 054026 (2005). [charmonia: 1st 40 cc mesons, all open-charm strong decay amps, all E1 and many M1 transitions] F.E.Close and E.S.Swanson, PRD72, 094004 (2005). [open-charm mesons: D and Ds] qqq baryon decays: S.Capstick and N.Isgur, PRD34, 2809 (1986). S.Capstick and W.Roberts, PRD49, 4570 (1994); PPNP 45, S241-S331 (2000). [BPs, BV modes of u,d baryons]

  11. Exotica: G/H/M

  12. Glueballs Theor. masses (LQCD) The glueball spectrum from an anisotropic lattice study Colin Morningstar, Mike Peardon Phys. Rev. D60 (1999) 034509 3 GeV G = new I=0 mesons starting with an “extra” scalar at ca. 1.6 GeV. Then no new G states until > 2 GeV. No JPC- exotic G until > 4 GeV. (= forget it) 2 GeV 1 GeV No JPC-exotics until 4 GeV !

  13. Glueballs G = 1 “extra” I=0 scalar meson at ca. 1.6 GeV. “f0(~1600)” = The worst possible quantum numbers experimentally! Several broad overlapping states. Then no new G states until > 2 GeV. No JPC- exotic G until > 4 GeV. (= forget it)

  14. How to make new (u,d,s,g) hadrons: Hit things together. A + B -> final state You may see evidence for a new resonance in the decay products. Reactions between hadrons (traditional approach) are “rich” but usually poorly understood. All light-q and g mesons, incl. qq, glueballs, hybrids, multiquarks. e.g.s BNL p-p -> mesons + baryon LEAR (CERN) pp annih.

  15. Glueball discovery? Crystal Barrel expt. (LEAR@CERN, ca. 1995) pp->p0 p0 p0 Evidence for a scalar resonance, f0(1500) ->p0 p0 n.b. Some prefer a different scalar, f0(1710) -> hh, KK. PROBLEM: Neither f0 decays in a naïve glueball flavor-symmetric way to pp, KK, hh. qq<-> G mixing?

  16. Molecules “Extra” hadrons just below two-hadron thresholds. S-waves easiest – look for quantum numbers of an S-wave pair. Nuclei are examples… MANY molecules exist! Can’t predict molecules w/o understanding soft 2 -> 2 hadron scattering. Add X(3872) to the list?

  17. X(3872) Molecules BelleCollab. K.Abe et al, hep-ex/0308029; S.-K.Choi et al, hep-ex/0309032, PRL91 (2003) 262001. B+ / - -> K+ / -p+p-J /Y G < 2.3MeV M = 3872.0 +- 0.6 +- 0.5 MeV A DD* molecule??? M( Do + D*o) = 3871.5 +- 0.5 MeV Charm in nuclear physics??? n.b. M( D+ + D*-) = 3879.5 +- 0.7MeV

  18. The trouble with multiquarks: “Fall-Apart Decay” (actually not a decay at all: no HI) Multiquark models found that most channels showed short distance repulsion: E(cluster) > M1 + M2. Thus no bound states. (Remember θ(1540) ! ) Only 1+2 repulsive scattering (continuum) in this sector of Hilbert space. n.b. multiquark .ne. molecule Exceptions: 2) If E(cluster) < M1 + M2 … bag model: u2d2s2 H-dibaryon, MH - MLL = - 80 MeV. n.b. LLhypernuclei exist, so this H was wrong. 1) nuclei and hypernuclei weak int-R attraction allows “molecules” “VLL(R)” VNN(R) -2mN -2mL 3) Heavy-light R R Q2q2 (Q = b; c?)

  19. (Light; u,d,s) Hybrids:Theory and Experiment

  20. Hybrids [flux-tube model] New RICH band of meson excitations expected, starting at ca. 1.9 GeV. Flavor nonets x 8 JPC = 72 states. Includes 0+-, 1-+and 2+-JPC-exotics. [bag model] ca. 1.5 GeV. Lowest exotic is 1-+ (TE gluon) 0+-and 2+-are at higher mass (TM)

  21. Most recent LQCDresults for light exotics, JPC = 1- +, 2+ -, 0+ -. J.J.Dudek, R.G.Edwards, M.J.Peardon, D.G.Richards and C.E.Thomas, ([JLAB] Hadron Spectrum Collaboration) Toward the excited meson spectrum of dynamical QCD arXiv: 1004.4930v1 n.b. All 3 of these exotic J PCs were degen. in the flux-tube model. In the bag model, 1-+is lighter. 2.5 GeV 2.0 GeV p1(1600) 1.5 GeV 1.0 GeV u,d mqincr.->

  22. Hybrid Meson Decays: flux-tube model Hybrids N.Isgur, R.Kokoski and J.Paton, PRL54, 869 (1985). Gluonic Excitations of Mesons: Why They Are Missing and Where to Find Them HL=1 -> S+P “S+P” modes (poorly studied exptally; multimeson final states) p1 -> b1p, f1p 1- + exotic is observably narrow! some hybrids are predicted to be VERY broad

  23. p2(2000) hybrid; b1p mode F.E.Close and P.R.Page, NPB443, 233 (1995). Close and Page: some notably narrownonexotic hybrids in the f-t model w(2000) hybrid

  24. Hybrids (Theory Summary) Hybrid = qq“g” states (with q=u,d,s) span flavor nonets, hence there are many experimental possibilities. flux-tube model Models agree that the lightest hybrid multiplet contains JPC-exotics. f.t. model predicts 8 JPC x 9 flavors = 72 “extra” resonances at the hybrid threshold. 3/8 JPC are exotic, 0+-, 1-+, 2+-. The remainder, 0-+, 1+-, 2-+, 0+-, 1--, 1++ are “overpopulation” rel to the quark model. Mestm ca. 1.5 - 2.0 GeV. f.t. 1.9 GeV is famous. LGT mass similar to f.t. for 1-+ . JPC = 1-+ with I=1, “p1”, is especially attractive. It is predicted in the f.t. decay model to be relatively narrow and to have unusual decay modes.

  25. Hybrid baryons Non-exotics in a rich N* background spectrum Spectrum of light (n=u,d) hybrid baryons. S.Capstick and P.R.Page, nucl-th/0207027, Phys. Rev. C66 (2002) 065204. (flux tube model) M (MeV)

  26. (Light) Hybrids:Experiment

  27. E.I.Ivanov et al. (BNL E852) PRL86, 3977 (2001). 1(1600) The (only) strong JPC-exotic H candidate signal. p-p -> p-h ‘ p 1- + exotic reported in p-p -> p- h ‘ p ph’ is a nice channel because nn couplings are weak for once (e.g. the a2(1320) noted here). The reported exotic P-wave is dominant!

  28. A.Alekseevet al. (COMPASSCollab.) Observation of a J P C =1 - + exotic resonance in diffractive dissociation of 190 GeV pi- into pi- pi- pi+ ArXiv:0910.5842v3 (Sept. 2009) M = 1660 +-10 +0 -64 MeV , Gamma = 269 +-21+42 -64 MeV. n.b. resonant phase motion (confirmed but not shown here) is of course the crucial test p1(1600) JPC exotic (confirmed)

  29. Summary regarding meson spectroscopy and exotics: Theorists expect new types of mesons (glueballsand hybrids) starting at ca. 1.5 - 2 GeV. A few candidates exist. Looking for JPC-exotics is a good strategy. Also overpopulation - need to better establish the qq sector above 1.5 GeV and ss! Charm mesons (cs and cc sectors) have surprised people recently – cs low masses hence tiny widths; also perhaps new molecular states and hybrids. Data on the spectrum is needed to compare with models and LGT. Strong and EM widths are also useful information. Strong decays are poorly understood in terms of QCD. n.b. Exciting discoveries in meson spectroscopy are often serendipitous: J/Y Ds0*(2317) Ds1(2460) X(3872) Y(4260)

  30. Hybrids:JLAB and elsewhere(final comments)

  31. * Existing and planned facilities (the competition?): BES-III (Beijing) [now] e+e- to sqrt(s) ca. 4.2 GeV. Mainly very large J/y and y’ event samples. Charmonium decays, in future unusual cc sector states? Y(4260)? Application to light and exotic spectroscopy? Could do e.g. rad decays. COMPASS (CERN) [now] High energy p- beam available, former E852 people (S.U.Chung) revisiting p p but at higher E (more diffractive). Have seen evidence for the p1(1600), will proceed to other interesting final states. PANDA (GSI) [2017+] Dedicated spectroscopy experiment. Official goal is cc hybrids. pp annihilation to sqrt(s) ca. 5 GeV (higher energy LEAR). Light spectroscopy “for free”. n.b. Lower energy pp produced the f0(1500) glueball candidate, and has a large p1(1400) signal. * Not really. Discovery of unusual hadrons requires confirmation by other experiments.

  32. GlueX at JLAB: • Photoproduction (~new expt approach) accesses exotic-JPCeasily (S=1 beam) • “plucking the string” - Isgur. [or is it vecdom?] • Several production mechanisms, 2 are: • t-channel CEX, e.g. g (-> r0) + p+ - -> p1+ - • diffr., e.g. g + P -> 2 +- • (Also s- and u-channel baryon resonances.) • n.b. You get the poorly explored ss sector for free. • Theorists can contribute by • 1. LGT spectroscopy and decays, • 2. modeling photoproduction of both exotic and ordinary (qq) resonances • (CLAS data?).

  33. Recent e.g. of 3pi CEX photoproduction (CLAS), showing a2(1320) and 2(1670) qq states. a2 2

  34. The importance of GlueX at JLAB: (Summary. C.Meyer presentation follows) The light (u,d,s,g) meson spectrum is poorly known above ca. 1.5 GeV. Theorists expect a rich new spectroscopy of hybrids, including exotics, starting not far above this mass. Widths and decay mechanisms are obscure [models], will be explored by LQCD in the near future. GlueX’s goal is to establish the meson spectrum to ca. 2.5 GeV, and “see what’s out there”. [serendipity in spectroscopy] Past lessons (4pi detector, hermiticity, neutral and final modes, studies of all decay modes, robust PWA) have been learned (LEAR, E852) and are being implemented. It will be very exciting!

  35. END

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