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

Hadrons 101

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

Physically allowed hadron states (color singlets) (naïve, valence) qq q3q3 Conventional quark model mesons and baryons. q 2 q 2, q 4 q,… multiquarks the “multiquark fiasco” -N.Isgur g 2, g 3,… glueballs maybe 1 e.g. f 0 (1500 or 1710) qqg, q 3 g,… hybrids maybe 1-3 e.g.s  1 (1600) best Incl. exotic J PC ! 100s of e.g.s “exotica” : ca e.g.s of (q 3 ) n, maybe 1-3 others X(3872) = DD*! (q 3 ) n, (qq)(qq), (qq)(q 3 ),… nuclei / molecules _ Basis state mixing may be very important in some sectors. (q 2 q 2 ),(q 4 q),… multiquark clusters dangerous: may not exist as resonances e.g. 

Parity P qq = (  ) (L+1) C-parity C qq = (  ) (L+S) 1S: 3 S 1 1   ; 1 S 0 0   2S: 2 3 S 1 1   ; 2 1 S 0 0   … 1P: 3 P 2 2  ; 3 P 1 1  ; 3 P 0 0  ; 1 P 1 1    2P … 1D: 3 D 3 3  ; 3 D 2 2  ; 3 D 1 1  ; 1 D 2 2    2D … J PC forbidden to qq are called “J PC -exotic quantum numbers” : 0   ; 0  ; 1  ; 2  ; 3  … x Plausible J PC -exotic candidates = hybrids (have all J PC ), glueballs (high mass), maybe multiquarks (fall-apart decays). The resulting qq N,L states N 2S+1 L J have J PC = qq mesons quantum numbers Quarkonia:q

 s = b = [GeV 2 ] m c = [GeV]  = [GeV] Fitted and predicted cc spectrum Coulomb (OGE) + linear scalar conft. potential model blue = expt, red = theory. S*S OGE L*S OGE – L*S conft, T OGE Quarkonia: cc e.g.

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, (2008) and PRD78, (2008) n.b. PRD79, (again) (2009) includes rad. transitions! Results for cc still rather difficult to distinguish from quark model. Final LQCD predictions fm JLAB: J PC exotics (non-qq) “cc” “cc hybrids (?)” Exotic cc-H 1  4300(50), Nonexotic cc-H 1  4400(60).

J.J.Dudek, R.G.Edwards and C.E.Thomas, Exotic and excited-state radiative transitions in charmonium from lattice QCD PRD79, (2009), arXiv: [hep-ph]. Paper quotes  c     exotic  J  keV. non-exotic   hybrid rad. trans. A typical “robust” cc radiative width. GlueX is justified. Radiative widths of exotics = ? (The BIG question for GlueX.)

Approx. status, light (u,d,s) qq spectrum to ca. 2.1 GeV. States are well known to ca. 1.5 GeV, poorly known above (except for larger-J). n.b. ss is poorly known generally. Strong decays give M, , J PC of qq candidates. Several recent candidates, e.g. a 1 (1700), a 2 (1750). I=1 shown, dashed boxes = expected Status of light meson spectroscopy (I=1 e.g.) Quarkonia: nn e.g.

Theor. guides for expt qq searches: Extensive strong decay tables 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, (2003). [strange mesons] [43 states, all 525 modes, all 891 amps.] T.Barnes, S.Godfrey and E.S.Swanson, PRD72, (2005). [charmonia: 1 st 40 cc mesons, all open-charm strong decay amps, all E1 and many M1 transitions] F.E.Close and E.S.Swanson, PRD72, (2005). [open-charm mesons: D and D s ] qq meson decays: 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] Mainly light (u,d,s) hadrons in f.-t. or 3 P 0 models. A few references:

Exotica: G/H/M

The glueball spectrum from an anisotropic lattice study Colin Morningstar, Mike Peardon Phys. Rev. D60 (1999) Theor. masses (LQCD) Glueballs No J PC -exotics until 4 GeV ! 1 GeV 2 GeV 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 J PC - exotic G until > 4 GeV. (= forget it)

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

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. e.g.s BNL  - p -> mesons + baryon LEAR (CERN) pp annih. All light-q and g mesons, incl. qq, glueballs, hybrids, multiquarks.

Glueball discovery? Crystal Barrel expt. ca. 1995) pp   0  0  0 Evidence for a scalar resonance, f    0  0 n.b. Some prefer a different scalar, f   PROBLEM: Neither f 0 decays in a naïve glueball flavor-symmetric way to . qq  G mixing?

“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  hadron scattering. Add X(3872) to the list? Molecules

X(3872 ) Belle Collab. K.Abe et al, hep-ex/ ; S.-K.Choi et al, hep-ex/ , PRL91 (2003)         J   D   D*   MeV  MeV n.b.  D   D*   MeV MeV Charm in nuclear physics??? A DD* molecule??? Molecules

The trouble with multiquarks: Multiquark models found that most channels showed short distance repulsion: E(cluster) > M 1 + M 2. Thus no bound states. (Remember θ(1540) ! ) Only 1+2 repulsive scattering (continuum) in this sector of Hilbert space. nuclei and hypernuclei weak int-R attraction allows “molecules” If E(cluster) < M 1 + M 2 … bag model: u 2 d 2 s 2 H-dibaryon, M H - M  =  80 MeV. n.b.   hypernuclei exist, so this H was wrong. Exceptions: V NN (R)  2m N RR “V  (R)”  2m  2) 1) Q 2 q 2 (Q = b; c?) 3) Heavy-light n.b. multiquark.ne. molecule “Fall-Apart Decay” (actually not a decay at all: no H I )

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

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

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: v1 Most recent LQCD results for light exotics, J PC = 1 , 2 , 0 . m q incr.  u,d 2.5 GeV 2.0 GeV 1.5 GeV    1.0 GeV n.b. All 3 of these exotic J PC s were degen. in the flux-tube model. In the bag model, 1  is lighter.

N.Isgur, R.Kokoski and J.Paton, PRL54, 869 (1985). Gluonic Excitations of Mesons: Why They Are Missing and Where to Find Them    b   f     S+P “S+P” modes (poorly studied exptally; multimeson final states) 1  exotic is observably narrow! some hybrids are predicted to be VERY broad Hybrid Meson Decays: flux-tube model Hybrids

 hybrid    hybrid; b   mode Close and Page: some notably narrow nonexotic hybrids in the f-t model F.E.Close and P.R.Page, NPB443, 233 (1995).

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

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

(Light) Hybrids: Experiment

   E.I.Ivanov et al. (BNL E852) PRL86, 3977 (2001). 1  exotic reported in   p  ‘ p ’ is a nice channel because nn couplings are weak for once (e.g. the a 2 (1320) noted here). The reported exotic P-wave is dominant! The (only) strong J PC -exotic H candidate signal.   p   ‘ p

A.Alekseev et al. (COMPASS Collab.) Observation of a J P C =1 - + exotic resonance in diffractive dissociation of 190 GeV pi- into pi- pi- pi+ ArXiv: v3 (Sept. 2009) M = MeV, Gamma = MeV.    J PC exotic (confirmed) n.b. resonant phase motion (confirmed but not shown here) is of course the crucial test

Summary regarding meson spectroscopy and exotics: Theorists expect new types of mesons (glueballs and hybrids) starting at ca GeV. A few candidates exist. Looking for J PC -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/ D s0 *(2317) D s1 (2460) X(3872) Y(4260)

Hybrids: JLAB and elsewhere (final comments)

Existing and planned facilities (the competition?): BES-III (Beijing) [now] e  e  to sqrt(s) ca. 4.2 GeV. Mainly very large J/  and  ’ 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   beam available, former E852 people (S.U.Chung) revisiting  p but at higher E (more diffractive). Have seen evidence for the  1 (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 f 0 (1500) glueball candidate, and has a large  1 (1400) signal. * * Not really. Discovery of unusual hadrons requires confirmation by other experiments.

GlueX at JLAB: Photoproduction (~new expt approach) accesses exotic-J PC easily (S=1 beam) “plucking the string” - Isgur. [or is it vec dom?] Several production mechanisms, 2 are: t-channel CEX, e.g.         diffr., e.g.  P   (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?).

Recent e.g. of 3pi CEX photoproduction (CLAS), showing a 2 (1320) and  2 (1670) qq states. a2a2 22

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!

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