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Recent Progress and Puzzles in Charmonium Physics

Recent Progress and Puzzles in Charmonium Physics. Bryan Fulsom University of British Columbia BaBar Collaboration ISMD 2007 Berkeley August 9, 2007. Outline. Introduction to quarkonium spectroscopy The experiments The X(3872) More new states (X, Y, Z, ...) Future outlook.

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Recent Progress and Puzzles in Charmonium Physics

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  1. Recent Progress and Puzzles in Charmonium Physics Bryan Fulsom University of British Columbia BaBar Collaboration ISMD 2007 Berkeley August 9, 2007 Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  2. Outline • Introduction to quarkonium spectroscopy • The experiments • The X(3872) • More new states (X, Y, Z, ...) • Future outlook Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  3. In the beginning... • November Revolution: simultaneous (SLAC/BNL) discovery of the J/y in 1974 • Bound state of c-cbar quarks: “charmonium” • First evidence of the charm quark • Strong confirmation of the quark model • Discovery of y(2S)J/y(e+e-) p+p- soon followed Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  4. Basic theoretical description • Analogous to known two-particle bound systems (ie: hydrogen, positronium) • Charmonium potential models (phenomenological): • non-relativistic (charm quarks are “heavy” compared to binding energy) • strong force potential via one gluon exchange (similar to Coulomb force) • quark confinement (increases linearly with separation) • Typical representation: plus extensions to include spin-dependent terms, relativistic corrections, etc. • NRQCD: Analytical calculations based on assumption of heavy quark mass • Lattice QCD: Discrete computation of quark interactions • NRQCD and Lattice are “real” QCD; now-mature methodologies • Theory produces many experimentally testable predictions (mass, width, BF): Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  5. Charmonium Spectrum Spectroscopic notation: N2S+1LJ where L=S,P,D,F,... Angular momentum: J = L+S S(qq) = 0 or 1 Parity: P = (-1)L+1 Charge conjugation C=(-1)L+S Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  6. Charmonium Production • Colour-suppressed bc decay • Predominantly from B-meson decays • e+e- annihilation/Initial State Radiation (ISR) • e+e- collision below nominal c.m. energy • JPC = 1-- • Double charmonium production • Typically one J/y or y, plus second ccbar state • Two-photon production • Access to C = +1 states • pp annihilation • All quantum numbers available Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  7. Charmonium Decays • Annihilation: • Generally suppressed for bound state • Decay to leptons is a clean experimental signal • Strong interaction: • Dominant above ~3.72 GeV (D mesons) • Suppressed below this mass threshold • Radiative: • EM radiative transition emitting photon • Emit gluons producing light quarks • Features: • Suppression of strong decays leads to (relatively) long lifetimes, narrow widths • Radiative decays are competitive; often most accessible transitions Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  8. The B Factories: BaBar and Belle Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  9. Other Experiments – CLEO, CDF/D0 Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  10. Observed Charmonium Decays Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  11. Discovery of the X(3872) • In 2003, Belle discovered a new signal in B+X K+, XJ/yp+p- • Narrow (G<2.3MeV) particle with mass m(X)=3871.2+/-0.6 MeV/c2 • Confirmed by CDF, D0 and BaBar X(3872) now well established Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  12. X(3872) Highlights • X(3872) has been extensively studied by BaBar and Belle • XJ/yg radiative decay confirmed by BaBar determines C = +1 • Belle/CDF dipion angular analysis in XJ/yp+p- favours JPC = 1++ • Decays via BD0D0(*)K • No B0/B+ mass difference • Mass 2.5s higher than W.A. • No charged partners found, doesn’t decay to cc1g or J/yh Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  13. X(3872) Interpretation • X(3872) is puzzling • Similar to charmonium, ie: narrow state decaying to J/yp+p- • However, above DD threshold expect to be wide and XDD dominant • Quantum numbers established: 1++ • It does not fit into the charmonium model • Note: • Leading contender is that this could be a bound state of two D mesons • i.e.: a D0D*0 molecule • Supported by predictions of mass, decay modes, JPC, branching fractions • Other exotic predictions: • “Tetraquark” 4-quark bound state • “Glueball” gluon bound state, charmonium-gluon hybrid Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  14. The alphabet grows: X(3940), Z(3930) • Belle discovered three new states in a similar mass range via distinct production methods and decay modes • X(3940) • Discovered by Belle in double-charmonium production e+e-J/y X(3940) • Decays to DD* but not DD • Likely a charmonium state (hc’’ or cc1’) • Z(3930) • Discovered by the two-photon process ggZ(3930)DDbar • Predicted mass and width match charmonium assignment of cc2’ Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  15. ...and grows...: the Y(3940) • Discovered by Belle the decay BKY(wJ/y) • Recently measured by BaBar (preliminary) • Reconstructed in same decay mode but parameter values differ • Possible cc1’ charmonium state • Requires further investigation Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  16. BaBar Discovery of Y(4260)J/yp+p- • BaBar discovers a new peak in ISR events • Found in the decay: Y(4260)J/y p+p- • Fitted shape is a broad structure with • e+e- requires quantum numbers JPC = 1-- • However, all of the 1-- charmonium states have already been discovered! • Very difficult to accommodate as ccbar, unless previous assignments are wrong Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  17. CLEO confirms the Y(4260) • After BaBar’s discovery of the Y(4260), CLEO performed an centre-of-mass energy scan and also collected data directly at the Y(4260) resonance • They reconstructed 16 decay modes, confirming BaBar’s discovery of Y(4260)J/y p+p- (11s) and adding Y(4260)J/y p0p0 (5.1s) Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  18. Recent Y(4260) results from Belle • Preliminary results presented at EPS in Manchester, mid-July 2007 • Confirm BaBar’s Y(4260) and finds an accompanying state • For Y(4260)J/y p+p-, they reproduce BaBar’s signal: but also claim a broad second shape: Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  19. BaBar’s search for Y(4260)y(2S)p+p- • Y(4260) decays to J/yp+p-, natural to search for the decay to y(2S)p+p- • Analysis in BaBar finds a new peak that does not match the Y(4260) mass/width! • Seems to be a different structure: • e+e- requires this state to be JPC = 1--, now overpopulated by two states • Impossible to assign this as charmonium Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  20. Belle’s latest results • Also presented at EPS in Manchester, mid-July 2007 • For Y(4320)y p+p-, BaBar result confirmed: and discovered a 5.8s new peak • (Note: a single bin in BaBar’s Y(4320) analysis showed a statistically insignificant excess in this region, but the dataset was ~2.5 times smaller) Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  21. Charmonium Spectrum Revisited Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

  22. Conclusions • The charmonium model has had great success below the DD threshold • Above DD threshold, several states remain undiscovered or need further study • A recent flood of experimental results from the B-factories is challenging our understanding of the strong force • Is the X(3872) a meson molecule? • If so, how well do we understand its mechanisms? If not, then what is it? • What is the nature of the new “Y” states? • Molecules? Tetraquarks? Hybrids? Glueballs? Something else? • Is this the beginning of a rich new spectroscopy? • Lattice and NRQCD theory takes the lead • Experimental status: • BaBar, Belle, and CLEO operational through 2008 • BES restarting, Super B factory potential for orders of magnitude more data • What other exciting new states await to be discovered? Recent Charmonium Results, ISMD 2007 Bryan Fulsom, Aug 9, 2007.

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