Opportunities in Meson Spectroscopy: 1) The big questions 2) Current topics quarkonia quarkonia hybrids hybrids glueballs glueballs multiquarks multiquarks Ted Barnes Physics Div. ORNL Dept. of Physics, U.Tenn. PD Workshop Fermilab, 6-9 Oct. 2004 1.) The Big Questions: We know L QCD but what does it predict? What types of hadrons exist (as resonances)? Isnt that just color singlets? What are their masses and quantum numbers? State composition? What are their social properties? GOALS: Establish and understand the spectrum. Observe and analyze decays (esp. strong; maybe radiative) Production Interactions The QCD flux tube (LGT, G.Bali et al; hep-ph/ ) LGT simulation showing the QCD flux tube Q Q R = 1.2 [fm] funnel-shaped V QQ (R) Coul. (OGE) linear conft. (str. tens. = 16 T) Confinement happens Nave physically allowed hadrons (color singlets) 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. qqg, q 3 g, hybrids maybe 1-3 e.g.s 100s of e.g.s exotica : _ qq mesons states The quark model treats conventional mesons as qq bound states. Since each quark has spin-1/2, the total spin is S qq tot = x = Combining this with orbital angular momentum L qq gives states of total J qq = L qq spin singlets J qq = L qq +1, L qq, L qq -1 spin triplets 2.a. Quarkonia 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 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 , Plausible J PC -exotic candidates = hybrids, glueballs (high mass), maybe multiquarks (fall-apart decays). The resulting qq NL states N 2S+1 L J have J PC = Approx. status, light (u,d,s) qq spectrum to ca. 2.1 GeV. Well known to ca. 1.5 GeV, poorly known above (except for larger-J). n.b. ss is poorly known generally... an argument for K p Strong decays give M, , J PC of qq candidates. Q Several recent candidates, e.g. a 1 (1700), a 2 (1750). I=1 shown, dashed = expected New band of meson excitations predicted, starting at ca. 1.9 GeV. Flavor nonets x 8 J PC = 72 states. Includes 0 , 1 and 2 J PC -exotics. Hybrids: Glueballs: New I=0 mesons starting with a scalar at ca. 1.6 GeV. Then no states until 2+ GeV. No J PC -exotics until 4 GeV. 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! Cant predict molecules w/o understanding soft 2 -> 2 hadron scattering. Add X(3872) to the list??? Extensive strong decay tables (ca present) 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, in prep. [cc mesons] 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: Example of the detailed theor. predictions for light qq meson strong decays: Some new results for strange meson decays (BBP paper): 3 F 2 ss -> K 1 (1273) K confirms Blundell and Godfrey. 3 F 3 ss -> K 2 * K dominant 3 F 4 ss (max J) typically ARE dominated by the lowest few allowed modes. (Cent. barrier.) The five narrowest unknown (?) ssbar states below 2.2 GeV: state tot Favored modes [expt?] D 2 (1850)129 MeV KK* [WA102 2 (1617)- 2 (1842): nn ss mixing?] 2) F f (2200) 156 MeV K*K*, KK, KK* [LASS 2209; Serp. E ] 3) 3 1 S 0 s (1950) 175 MeV K*K*, KK* 4) 2 1 P 1 h 1 (1850) 193 MeV KK*, K*K*, [ss filter] 5) 1 3 D 2 2 (1850) 214 MeV KK*, The strangest state In the strange spectrum. K*(1414). (< K(1460) ???) (Mass and decays.) Mass: recall nn 1 states (1465), (1419). Decays: Expt. K B.F. 6% (LASS) Mixing with K-hybrid state? 2.b. Hybrids Hybrid = qqg 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, 1 , is especially attractive. It is predicted in the f.t. model to be relatively narrow and to have unusual decay modes. Hybrid Meson Decays: flux-tube model 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 Expt Hybrid mesons? The current best signal for a J PC = 1 exotic. (Cant be qq.) ca p ( ) p a q (Current best of several reactions and claimed exotics.) Follow up expts planned at CEBAF; HallD or GlueX. (photoprod.) exotic 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). The glueball spectrum from an anisotropic lattice study Colin Morningstar, Mike Peardon Phys. Rev. D60 (1999) The spectrum of glueballs below 4 GeV in the SU(3) pure-gauge theory is investigated using Monte Carlo simulations of gluons on several anisotropic lattices with spatial grid separations ranging from 0.1 to 0.4 fm. Theor. masses (LGT) 2.c. 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 nave glueball flavor-symmetric way to KK. qq G mixing? Psi rad (2230) = G / ss brou ha ha Originally reported by Mark III at SLAC; R.M.Baltrusaitis et al., PRL56, 107 (1986). Not seen by DM2 with better statistics. Claimed by BES (?) but status unclear. Tensor glueball candidate? (1440) f 0 (1710) J/ KK ? CLEO-c will resolve this. WA102 Central meson production Quantum numbers of the pomeron? Acts like 1 - exchange rather than 0 + G and qq candidates strongly distinguished by cuts on exchanged |p1 p2|, dp T . ca. 10 papers by WA102 Collaboration and by F.E.Close and A.Kirk AK and FEC, hep-ph/ , PLB397, 333 (1997) (most cited). p p WA102 Central meson production glueballs and hybrids? f Scalar glueball candidate f f Tensor glueball candidate? 2 -+ overpopulation and a D.Barberis et al. hep-ex/ PLB474, 423 (2000). nonexotic hybrid? (S+P decay mode) 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. 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 cc from LGT exotic cc-H at 4.4 GeV oops cc has been withdrawn. Small L=2 hfs. A LGT e.g.: X.Liao and T.Manke, hep-lat/ (quenched no decay loops) Broadly consistent with the cc potential model spectrum. No radiative or strong decay predictions yet. X(3872 ) Belle Collab. K.Abe et al, hep-ex/ ; S.-K.Choi et al, hep-ex/ , PRL91 (2003) J MeV = 3 D 1 cc. If the X(3872) is 1D cc, an L-multiplet is split much more than expected assuming scalar conft. MeV X(3872) confirmation (from Fermilab) G.Bauer, QWG presentation, 20 Sept n.b. most recent CDF II: M = pm 0.7 pm 0.4 MeV CDF II Collab. D.Acosta et al, hep-ex/ , PRL to appear X(3872) also confirmed by D0 Collab. at Fermilab. Perhaps also seen by BaBar cc from the standard potential model S.Godfrey and N.Isgur, PRD32, 189 (1985). 2 3 ( 3 D 2 is a typo) 2 The obvious guess, if cc, is 2 or 2 . No open-flavor strong decays: narrow states. A conventional assignment? X(3872) = cc? Charmonium Options for the X(3872) T.Barnes and S.Godfrey, hep-ph/ , PRD69 (2004) (n.b. Eichten, Lane and Quigg have similar results.) Our approach: Assume all conceivable cc assignments for the X(3872) : all 8 states in the 1D and 2P cc multiplets. Nominal Godfrey-Isgur masses were 3 D 3 (3849) 2 3 P 2 (3979) 3 D 2 (3838) 2 3 P 1 (3953) 3 D 1 (3.82) [ (3770)] 2 3 P 0 (3916) 1 D 2 (3837) 2 1 P 1 (3956) We assigned a mass of 3872 MeV to each state and calculated the resulting strong and EM partial widths. Strong Widths: 3 P 0 Decay Model 1D 3 D [MeV] 3 D D 1 43 [MeV] 1 D 2 - DD 23.6(2.7) [MeV] Parameters are = 0.4 (from light meson decays), meson masses and wfns. X(3872) (New strong and EM decay results from Barnes, Godfrey and Swanson, in prep.) E1 Radiative Partial Widths 1D -> 1P 3 D 3 3 P [keV] 3 D 2 3 P 2 70 [keV] 3 P [keV] 3 D 1 3 P 2 5 [keV] 3 P [keV] 3 P [keV] 1 D 2 1 P [keV] 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??? n.b. molecule.ne. multiquark A DD* molecule??? 2.d. Molecules and Multiquarks 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 DD* molecule options This possibility is suggested by the similarity in mass, N.A.Tornqvist, PRL67, 556 (1991); hep-ph/ F.E.Close and P.R.Page, hep-ph/ , PLB578, 119 (2004). C.Y.Wong, hep-ph/ E.Braaten and M.Kusunoki, hep-ph/ , PRD69, (2004). E.S.Swanson, hep-ph/ n.b. The suggestion of charm meson molecules dates back to 1976: (4040) as a D*D* molecule; (Voloshin and Okun; deRujula, Georgi and Glashow). X MeV D D* MeV (I prefer this X assignment.) Interesting prediction of molecule decay modes: E.Swanson, hep-ph/ , PLB588, 189 (2004): 1 D o D* o + molecule (additional comps. due to off-diagonal FSI rescattering). J J Predicted total width ca. = expt limit (2 MeV). Very characteristic mix of isospins: comparable J and J decay modes expected. Nothing about the X(3872) is input: this all follows from O E and C.I. X(3872) update: BELLE hep-ex/ (1 Sep 2004): J observed, consistent withJ Ratio J J Theor. prediction (Swanson) for D 0 D * 0 molec. was ~ 2/3. D * sJ (2317) + : where it all started. BABAR 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 * sJ (2463) + 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 possibly 0 + D * sJ (2317) + cs ? Sector of the 1 st shocking new discovery: cscs SP PS LGT 0 + : GeV. S.Godfrey and R.Kokoski, PRD43, 1679 (1991). Decays of S- and P-wave D D s B and B s flavor mesons. 3 P 0 flux tube decay model. Mixing of 3 P P states Is cited as an interesting and open problem. (L*S mixing vs mixing through decay channels) Charm decays (God91) cs cs cn; cs (Godfrey and Isgur potential model.) Prev. (narrow) expt. states in gray. DK threshold Theorists responses to the new D sJ * states Approx. 80 theoretical papers have been published since the discovery. There are two general schools of thought: 1) They are cs mesons, at a lower mass than expected by qq potential models. [Fermilab] 2) Are they DK molecules ? [UT,Oxon,Weiz.] 3) They are somewhere between 1) and 2). [reality] M.A.Nowak, M.Rho and I.Zahed, PRD48, 4370 (1993). W.A.Bardeen and C.T.Hill, PRD49, 409 (1994) BEH, PRD68, (2003). 2. DK molecules [UT,Oxon,Weiz.] T.Barnes, F.E.Close and H.J.Lipkin, hep-ph/ , PRD68, (2003). 3. reality Reminiscent of Weinstein and Isgurs KK molecules. (loop effects now being evaluated) Future: Unquenching the quark model Virtual meson decay loop effects, qq M1 M2 mixing. D sJ * states (mixed cs DK , how large is the mixing?) Are the states close to |cs> or |DK>, or are both basis states important? A perennial question: accuracy of the valence approximation in QCD. Also LGT-relevant (they are usually quenched too). Loops Summary regarding meson spectroscopy for PD: 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 low masses hence tiny widths; also perhaps new molecular states. 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 QCD. Exciting discoveries in meson spectroscopy are often serendipitous: J/ D s0 *(2317) D s1 (2463) X(3872) Summary regarding meson spectroscopy for PD: Beams? p, p Traditional light meson spectroscopy, e.g. BNL AGS. (all types). Detect ALL strong modes, hermetic, PWA. K - p strange and ss mesons (LASS at SLAC). pp central - G/qq discriminator (WA102; HE useful). pp glueballs and hybrids (LEAR); cc and cc-H (GSI future). END