(A Few) Recent Developments in Hadron Spectroscopy (setting the stage for subsequent spectroscopy talks) Topics: I. Basic hadronics II. Some exciting areas of current research: a. Charm hadrons b. Exotics III. Future Ted Barnes Physics Div. ORNL ICHEP2010 Paris, 23 July 2010

1. Basic hadronics

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 g 2, g 3,… glueballs maybe 1 e.g. : f   qqg, q 3 g,… hybrids maybe 1-3 e.g.s 1 is “solid” :    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 (q 2 q 2 ),(q 4 q),… multiquark clusters dangerous e.g.  _ Basis state mixing may be very important in some sectors.

Parity P qq = (-1) (L+1) C-parity C qq = (-1) (L+S) qq mesons: quantum numbers 1S: 3 S 1 1   ; 1 S 0 0   2S: 2 3 S 1 1   ; 2 1 S 0 0   3D … 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 … The resulting qq N,L states N 2S+1 L J have J PC = qq (allowed): N L

2.a. Charm hadrons

Charmonium (cc) A nice example of a QQ spectrum. Expt. states (blue) are shown with the usual L classification. Above 3.73 GeV: Open charm strong decays (DD, DD* …): broader states except 1D 2 2   2  3.73 GeV Below 3.73 GeV: Annihilation and EM decays. , KK*,  cc, , l  l ..): narrow states.

Minimal quark potential model physics: OGE + linear scalar confinement; Schrödinger eqn (often relativized) for wfns. Spin-dep. forces, O(v 2 /c 2 ), treated perturbatively. Here… Contact S*S from OGE; Implies S=0 and S=1 c.o.g. degenerate for L > 0. (Not true for vector confinement.)

 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

Fitted and predicted cc spectrum Coulomb (OGE) + linear scalar conft. potential model blue = expt, red = theory. Two narrow states are expected, with J PC = 2  and 2 . The 1D multiplet is theoretically close to degenerate, near the  D   (3770).

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: Exotic cc-H 1  4300(50), Nonexotic cc-H 1  4400(60). J PC exotics (non-qq)

The new “XYZ” states: 2P cc? 3S cc? Molecules? cc hybrids? Nonresonant enhancements? Experimental errors? How to test these possibilities? Recommended reading: “The New Heavy Mesons: A Status Report” E.S.Swanson, Phys. Reports 429, (2006). “What’s new with the XYZ mesons?” S.L.Olsen, arXiv: v3 [hep-ex]13 Feb “The Exotic XYZ Charmonium-like Mesons.” S.Godfrey and S.L.Olsen, arXiv: [hep-ph] Jan submitted to Ann. Rev. Nucl. Part. Phys.

“Selections from…” (Godfrey and Olsen review, list of new states):

cc spectrum, potential models (dashed: nonrel L, Godfrey-Isgur R) vs data Possible new cc states at these masses and elsewhere! “XYZ” states 2P or not 2P? Reminder: Three as yet unknown 1D states. Predicted to have  < 1 MeV! BGS, hep-ph/ , PRD72, (2005).

e  e  collisions: Initial state radiation (ISR) The traditional approach, s-channel annihilation, but can use higher energy beams. Still restricted to J PC = 1 . J/ 

Y(4260) a (nonexotic) charmonium hybrid?

Y(4260) e  e   Y(4260) ISR, Y     J /  log scale Not seen in R. Hmmm?! [ref] = BaBar, PRL95, (2005). closed-flavor decay mode !?

cc spectrum, potential models (dashed: nonrel L, Godfrey-Isgur R) vs data Possible 1  state Y(4260). Note no plausible cc assignment exists. A 1  charmonium hybrid??

QQ-hybrid closed-flavor decays predicted by LGT: We are hoping that closed-flavor decays are a signature for charmonium hybrids (and not charmonia). If so, nature has been kind. This is a nice experimental signature. Searches for other decay modes of the Y(4260) are in progress…

e  e  collisions: Double charmonium production. The traditional approach, s-channel annihilation, but can now make C=(+) charmonia! J PC = J P  J/  C=(+) cc

c’c’ 00 cc X(3943) An interesting new charmonium production mechanism! Allows access to C=(+) cc states in e  e  w/o using . No   or   !? X(3943) [ref] = Belle, hep-ex/ , 8 Jul n.b. Eichten: X(3943) may be the 3 1 S 0 cc  c ’’.

X(3872) a charmed meson molecule?

        J   D   D*   MeV Accidental agreement? X = cc (2  or 2  or …), or a DD* molecule?  MeV Alas the known  = 3 D 1 cc fixes the mass scale of 1D cc states. If the X(3872) is 1D cc, an L-excited multiplet is split much more than expected assuming scalar confinement. n.b.  D   D*   MeV MeV Belle Collab. K.Abe et al, hep-ex/ ; S.-K.Choi et al, hep-ex/ , PRL91 (2003) X(3872) from KEK Charm in nuclear physics???

The trouble with multiquarks: “Fall-Apart Decay” (actually not a decay at all: no H I ) Multiquark models found that most channels showed short distance repulsion: E(cluster) > M 1 + M 2. Thus no bound states. Only 1+2 repulsive scattering. nuclei and hypernuclei weak int-R attraction allows “molecules” 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  Q 2 q 2 (Q = b, c?) 2) 1) 3) Heavy-light

Interesting prediction of molecule decay modes: E.S.Swanson: 1  D o D* o molecule - maximally isospin violating! with additional comps. due to rescattering. J  “  ” J    Predicted total width ca. = expt limit (2 MeV). Very characteristic mix of isospins: comparable J     and  J  “  ”  decay modes expected. Appears to be confirmed experimentally! Nothing about the X(3872) is input: this all follows from O  E and C.I.

D * s0 (2317) and D s1 (2457) cs mesons or DK molecules? (or both) Not to forget the first of the new discoveries: The unexpected, very long-lived mesons in the cs sector!

Where the trouble all started: BABAR D * s0 (2317) + in D s +  0 D.Aubert et al. (BABAR Collab.), PRL90, (2003). M = 2317 MeV (2 D s channels),  < 9 MeV (expt. resolution) (Theorists expected L=1 cs states, e.g. J P =0 +, but with a LARGE width and at a much higher mass.) … “Who ordered that !?”  I.I.Rabi, about the  - Since confirmed by CLEO, Belle and FOCUS.

And another! CLEO: D s1 (2460) + in D s * +  0 Since confirmed by BABAR and Belle. M = 2457 MeV. D.Besson et al. (CLEO Collab.), PRD68, (2003). M = 2463 MeV,  < 7 MeV (expt. resolution) A J P =1 + partner of the 0 + D * s0 (2317) + cs ?

(Godfrey and Isgur potential model.) Prev. (narrow) expt. states in gray. DK threshold What caused large downwards mass shifts? Mixing with 2 meson continuum states? (Believed true.)

2.b. Exotics

qq mesons vs. exotics: quantum numbers 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 -exotic quantum numbers : Plausible J PC -exotic candidates = hybrids, glueballs (high mass), maybe multiquarks (fall-apart decays)   0 + - 1 - + 2 + - 3 - + … not qq: qq (allowed):

     p    ’  p E.I.Ivanov et al. (E852) PRL86, 3977 (2001).  1 (1600)   exotic reported in   ’ ’ 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.

A.Alekseev et al. (COMPASS Collab.) Observation of a JPC =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

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 n.b. All 3 of these exotic J PC s were degen. in the flux-tube model. In the bag model, 1  is lighter.    1.0 GeV

3. Future

Future… Spectroscopy involves an active interplay between theory and experiment. Consequently, future topics will depend on developments in both areas. Experiment: BES-III is currently gathering high statistics cc data (J/  and ‘ ) in e+e-. COMPASS has reported new results on light exotic spectroscopy in HE hadroproduction. GlueX will use protoproduction to search for light hybrids (incl. exotic JPC) at JLAB, start ca PANDA will search for cc-hybrids (incl. exotics) at GSI, start ca Theory: LQCD is being extended to light quarks; we should have accurate J PC -exotic mass estimates and predictions of EM couplings and (open flavor) strong decays in the next few years.

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