The Status of Exotics *

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The Status of Exotics *. Ted Barnes Physics Div. ORNL, Dept. of Physics, U.Tenn. Color singlets and QCD exotica Early history: states, spectrum and decays LGT predictions Current expt. candidates. * Specifically, hybrids (quark+gluon excitations). QCD Exotics Basics.
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The Status of Exotics*Ted BarnesPhysics Div. ORNL,Dept. of Physics, U.Tenn.
  • Color singlets and QCD exotica
  • Early history: states, spectrum and decays
  • LGT predictions
  • Current expt. candidates
  • *Specifically, hybrids (quark+gluon excitations).QCD Exotics BasicsLGT simulation showing the QCD flux tubeColor singlets and QCD exotica“confinement happens”.QQR = 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)(q2q2),(q4q),…(q3)n, (qq)(qq),(qq)(q3),…multiquark clustersnuclei / moleculescontroversiale.g. Q(1540)ca. 106 e.g.s of (q3)n, maybe 1-3 others X(3872) = DD*!g2, g3,…qqg, q3g,…q2q2, q4q,…glueballshybridsmultiquarksmaybe 1 e.g.maybe 1-3 e.g.sPhysically allowed hadron states (color singlets)_Conventional quark modelmesons and baryons. qqq3100s of e.g.sBasis state mixing may be very important in some sectors.“exotica” :qq mesons; states and spectrum.The nonrelativistic quark model treats conventional mesons as qq bound states.Since each quark has spin-1/2, the total spin is Sqq = ½ x ½ = 1 + 0Combining this with orbital angular momentum Lqq gives statesof total Jqq = Lqqspin singlets Jqq = Lqq+1, Lqq, Lqq-1spin tripletstot.Allowed qq quantum numbers: Spatial parity Pqq = (-1)(L+1) C-parity Cqq = (-1)(L+S)(both established by observed decay modes, X -> even pos -> PC=(++).)The complete list of allowed qq JPC quantum numbers has gaps!The JPC forbidden to qq are called “JPC-exotic quantum numbers”. If you find a resonance with exotic JPC, you are certainly beyond the naive qq quark model. Plausible JPC-exotic candidates = hybrids, glueballs (high mass), maybe multiquarks (fall-apart decays). Exotic JPC =0- -; 0+-, 1-+, 2+-, 3-+ …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 statesexcept 1D2 2- +, 2- -3.73 GeVBelow 3.73 GeV: Annihilation and EM decays.(rp, KK* , gcc, gg, l+l-..):narrow states.Fitted and predicted cc spectrumCoulomb (OGE) + linear scalar conft. potential modelblue = expt, red = theory.L*S OGE – L*S conft, T OGEas = 0.5538b = 0.1422 [GeV2]mc = 1.4834 [GeV]s = 1.0222 [GeV]S*S OGEHybrid Mesons SpectrumThe earliest hybrid spectrum calculations used the bag model and QCD sum rules.Among the 1st bag model refs: T.Barnes and F.E.Close, PLB123, 89 (1983), NPB224, 241 (1983); TB PhD (Caltech, 1977). M.Chanowitz and S.R.Sharpe, NPB222, 211 (1983).JPC exoticsThis multiplet was split by pQCD effects, e.g. :p1(1400) !(for amusement only)Refs. in hep-ph/9501405, PRD52, 5242 (1995). (JPC = 0-+, 0+-, 1-+, 1+-,2-+ , 2+-; 1++ , 1--) Ä flavor 9 = 72 states, 1st H multiplet! N.Isgur, R.Kokoski and J.Paton, PRL 54, 869 (1985).LGT spectrum calculationsApproach:1. Choose an operator OÖ that couples to the state of interest (correct quantum numbers) when operating on the vacuum state <state| OÖ |0> ¹ 02. Use Monte-Carlo techniques to evaluate the imaginary-time correlation function!d3x <0| O(x,t) OÖ(0,0) |0> At larget this decays exponentially as exp(- Mstatet), whereMstate is the mass of the lightest state with these quantumnumbers. Complication: usually quenched approx, neglects closed quark loops, assumes stable hadrons. (Decays make thelightest I=1, JPC = 1- - system created by OÖqq = pp, not r(770).) LGT spectrum calculationsJ.N. Hedditch et al,hep-lat/0402016Some examples of local operatorsOfor conventional and exotic mesons:JPC exoticNote that true exotic states (1- + channel) can only be made from qGq operators.States in the other (nonexotic) channels can be excited by qq or qGq operators(the latter couple to the hybrid components of conventional mesons).Many useful cross-checks: the same mass Mstate should follow from any operator pair in the same channel. A summary of LGT 1-+ exotic hybrid masses.X.Q.Luo and Z.H.Mei, hep-lat/0209049,Nucl. Phys. Proc. Suppl. 119 (2003) 263. nn - Hcc - HA LGT e.g.: X.Liao and T.Manke, hep-lat/0210030 (quenched – no decay loops)Broadly consistent with the cc potential model spectrum. No radiative or strong decay predictions yet. cc from LGT<-1- + exotic cc-H at 4.4 GeVSmall L=2 hfs.1+ - cc has returned. Recent LGT 1-+ exotic hybrid mass results, light quarks.C.Bernard et al., hep-lat/0301024, PRD68 (2003), 074505. (Actually finds Hss1- +ca. 2.07 pm 0.1 GeV.)n.b. nf = 0 is quenched.LGT spectrum calculations (recent devs.)J.N. Hedditch et al,hep-lat/0402016Confirmation of equal LGT “qq meson” masses using qqor qGq sources.0-+1--Hybrid Mesons DecaysHybrid Decays(light u,d,s quarks, f.-t. model)Gluonic Excitations Of Mesons: Why They Are Missing And Where To Find ThemN.Isgur, R.Kokoski and J.Paton, PRL 54, 869 (1985).Considers JPC-exotic hybrids (0+-, 1-+, 2+-) in the lightest f.-t. multiplet. S+P decay modes dominant in f.-t. decay model.p1 -> b1p a nice case for experiment. pr, ph, ph’ etc should be small. The Production and Decay of Hybrid Mesons by Flux-Tube BreakingF.E.Close and P.R.Page, NPB443, 233 (1995). “IKP-2”Confirms prev. results and also considers nonexotics (0-+, 1+-, 2-+ ,1++,1-- ) in the lightest f.-t. multiplet. Some special cases of nonexotics predicted to be rathernarrow if MH = 1.6 GeV; extra w and p2 notable. The f.-t. hybrid p2 decays strongly to b1p in the f.-t. decay model.Hybrid Meson Decays: flux-tube modelN.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+Pp1 -> b1p, f1pp2(2000) hybrid;b1p modeI =1narrow nonexotichybrids1 - + exoticsClose and Page: some notable nonexotic hybrids in the flux tube modelI =0h2(2000) hybridw(2000) hybrid… and much narrower if M ƒ1750 MeV !LGT studies of strong decays“The two ways to learn about hadrons are lattice gauge theory and experiment.” -Sanderling report (draft), 2000 LGT has been applied to strong decays of glueballs, conventional light mesons, and heavy-quark hybrids.The results are all “to be confirmed”, and some LGT practitioners are skeptical. Nonetheless here are some references and results: G decaysStrong MPs dependence of the G-PsPs coupling reported in an early LGT study. This complicates nn-ss-G mixing angle determinations from f0(1500) decays that assume flavor-blind G decay amplitudes. J.Sexton, A.Vaccarino and D.Weingarten, NPB (PS) 42, 279 (1995); PRL75, 4563 (1995).Q decaysExtracting r -> pp decay couplings on the latticer -> pp3-pt. functionC.McNeile and C.Michael (UKQCD), PLB556, 177 (2003).r -> pptransitionH decaysC.McNeile, C.Michael and P.Pennanen (UKQCD), PRD65, 094505 (2002).Very interesting prediction for experimenters: Heavy-quark hybrids have large closed-flavor decay modes!H ->c+S. (estm. 61(14) MeV for b)Suggests very nice experimental signatures, however it’s a surprise, recally’ -> J/Y pp is very small, ca. 100 keV. Needs confirmation. Hybrid/Exotic Mesons Experiment“Leading” expt. candidates for hybrid mesons (exotic and nonexotic)statereportedinp1(1400) h pp1(1600) rp, h’p, f1p , b1pp1(2000) f1p, b1pp2 and h2 overpopulation (nonexotic)others discussed include higher-mass r and p overpopulationin more detail…Hybrid mesons candidates (exotic)p1(1400)Theh pchannel has a long, messy history.It sounds like a good idea; I =1 hence no G, no final meson spins,all odd-L are exotic and even-L are nonexotic. “Just ” extract fhp(W), and PWA it.1stexpt,GAMS, was surprised to find a nonzero exotic hp 0P-wave near 1.4 GeV (weak and broad), and speculated that it was nonresonant.2ndexpt,KEK, concluded the P-wave was resonantbut had the a2(1320)mass and width. (Feedthrough now presumed.)3rdexpt,E852, found a weak, broad P-wave in hp -near 1.4 GeV.No consensus within the collaboration regarding it’s interpretation. 4th expt,CBarrel, found a signal similar to E852 in pp->hpp, and support a resonant interpretation.S.U.Chung et al. (E852)PRD60, 092001 (1999).p1(1400)a2(1320)p-p ->h p- pThe famous claimed and disputedE852 broad, weak P-wave p1 (1400)inhp-near 1.4 GeV.Crystal Barrel sees a similar effect in pp -> hppnear 1.4 GeV…It grows curiouser and curiouser.A.Abele et al. (CBar), PLB446, 349 (1999).Hybrid mesons candidates (exotic)p1(1600)Claimed inrp, h’p, f1p ,b1pE852r p once a fairly strong signal, now being “revisited”. h’p is the strongest evidence for an exotic hybrid at present. b1p (recent result, follows).VEShas reported mass enhancements near 1600 MeV inrp, h’p, f1pS.U.Chung et al. (E852)PRD65, 072001 (2002).p1(1600)Possible 1 -+ exotic in p-r0p-p -> p+p-p- pA.R.Dzierba et al. (E852 V IU)hep-ex/0502022 10 Feb 2005p1(1600) ?p-p -> p+p-p- p p-p0p0 pNo 1 -+ exotic in prE.I.Ivanov et al. (E852)PRL86, 3977 (2001).p1(1600)p-p ->p-h’pp1(1600)1-+ exotic reported in p-h’ph’is a nice channel because nn couplingsare weak for once (e.g. the a2(1320) noted here). The reported exotic wave is dominant!Hybrid mesons candidates (exotic)p1(2000)Claimed inf1p ,b1p.Not seen in wr.E852f1pb1p (recent result, follows).J.Kuhn et al. (E852)PLB595, 109 (2004).Hybrid mesons candidates (exotic)p1(2000)p-p ->hp+p-p- pf1p (E852): higher-mass p1 state needed to explain phase motionof the f1p 1-+ wave relative to 1++ and 2-+ waves.No clear evidence of a p1(2000) in the 1-+ wave intensity.Hybrid mesons candidates (nonexotic)J.Kuhn et al. (E852)PLB595, 109 (2004).…and while we are here…p-p ->hp+p-p- p[9] P.Page, E.S.Swanson and A.P.Szczepaniak, PRD59, 034016 (1999).M.Lu et al. (E852)PRL94, 032003 (2005).Hybrid mesons candidates (exotic)p1(2000)p-p ->p+p-p-p0p0 pb1p (E852): higher-mass p1 state needed to explain phase motionof the b1p 1-+ wave relative to 2++ and 4++rw waves.No clear evidence of a p1(2000) in the 1-+ wave intensity.Hybrid mesons candidates (exotic and nonexotic)M.Lu et al (E852), PRL94, 032003 (2005).E852: wr- and b1pp-p ->p+p-p-p0p0pHybrid mesons candidates (nonexotic):Extra p2(~1900)M.Lu et al (E852), PRL94, 032003 (2005).E852: wr- and b1pOverpopulation of higher-mass p2 states in wr- P-waves?p-p ->p+p-p-p0p0pp2(~1900) regionp2(1670)Hybrid mesons candidates (nonexotic):Extra h2(~1850)J.Adomeit et al. (CBar)ZPC71, 227 (1996).pp-> h p0p0a2 p0h2(1645) nn1D2p2(1670) partnerAlso evidence in gg-> h p0p0,central production (WA102) of 4p and hpp,and now in photoproduction…f2 hh2(~1850) ?Overpopulation of nn1D2 sector:2-+ hybrid?Hybrid mesons candidates (nonexotic):Extra h2(~1850)T.Handler et al. (FOCUS)prelim, unpub.g p ->6pXClear higher-mass h2 (?) peak in a2+p- photoproduction!…and from yesterday’s discussion,a2 p is suddenly the preferredI = 1, 2+- exotic-H diffractive photoproduction channel. Ï(a2+p-has I =1, 2+-as well as I = 0, 2-+ )Hybrid mesons candidates (nonexotic):Extra h2(~1850)Could this h2 instead be evidencefor Zweig mixing in the 2-+ sector? |h2> = s|nn> + c|ss> ?This can be tested: relative BFs anddecay amplitudes for flavor-mixed qqh2 states have been calculated.PRD68, 054014 (2003).n.b. Mixed qq doesn’t work, it predicts f2h << a2p.Pros Iqaki !Flavor-tagging J/y-> V f hadronic decays, an e.g.:J.J.Becker et al. (MarkIII)SLAC-PUB-4243 (Feb.1987)DEAR CLEO, PLEASE DON’T FORGET:Against w, you see the f0(1710).No f2’(1525) (ss).Against f, you see the f2’(1525) (ss).Weak f0(1710) shoulder claimed.Against g you see both.No nn/ss flavor discrimination.Hybrid Baryons Spectrum of light (n=u,d) |nnng> + … hybrid baryons.Several bag model calculations, early/mid 1980s. T.Barnes and F.E.Close, PLB123, 89 (1983) (shown), E.Golowich, E.Haqq and G.Karl. Phys.Rev.D28, 160 (1983), err.D33, 859 (1986).C.E.Carlson, T.H.Hansson and C.Peterson, PRD27, 1556 (1983).Spectrum of light (n=u,d) hybrid baryons.(flux tube model)S.Capstick and P.R.Page, nucl-th/0207027, Phys. Rev. C66 (2002) 065204.M (MeV)…waiting for the dawn.J/y -> g f, V fy’-> g f, V f g -> f
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