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Cascade Baryons: Spectrum and production in photon-nucleon reactions

Cascade Baryons: Spectrum and production in photon-nucleon reactions. Yongseok Oh ( Kyungpook National University, Korea). Workshop on “Extractions and interpretations of hadron resonances and multi-meson production  reactions with 12 GeV upgrade”, May 27-28, 2010. Overview. Introduction

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Cascade Baryons: Spectrum and production in photon-nucleon reactions

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  1. Cascade Baryons: Spectrum and production in photon-nucleon reactions Yongseok Oh (Kyungpook National University, Korea) Workshop on “Extractions and interpretations of hadron resonances and multi-meson production  reactions with 12 GeV upgrade”,May 27-28, 2010

  2. Overview • Introduction • Strangeness and baryons • In experiments • In theory • Photoproduction of X • Outlook

  3. 1. Introduction • What do we know about X baryons? • Strangeness baryons: (: light u/d quark) • Baryon number = 1, isospin = ½

  4. Baryons in SU(3) Baryons: made of three quarks Baryon octet Baryon decuplet

  5. 1. Introduction • What do we know about X baryons? • Strangeness baryons: (: light u/d quark) • Baryon number = 1, isospin = ½ • If flavor SU(3) symmetry is exact for the classification of all particles, then we have N(X*) = N(N*) + N(D*) • Currently, only a dozen of X baryons have been identified so far.(cf. more than 20 N*s & more than 20 D*s)

  6. X in PDG • What do we know about X baryons? Particle Data Group (2008): 11 X’s P is not directly measured Cf. Spin of ( was confirmed only recently by BaBar PRL 97 (2006) States whose is known

  7. 1. Introduction • What do we know about X baryons? • Strangeness baryons: (: light u/d quark) • Baryon number = 1, isospin = ½ • If flavor SU(3) symmetry is exact for the classification of all particles, then we have N(X*) = N(N*) + N(D*) • Currently, only a dozen of X baryons have been identified so far.(cf. more than 20 N*s & more than 20 D*s) • Only and are in the four star status • Only three states with known spin-parity  the quantum numbers of other states should be identified • Advantages & difficulties

  8. Advantages • Small decay widths • Identifiable in missing mass plots • Isospin is . (nonstrange sector: and ) • No flavor singlet state (unlike hyperons) Difficulties • In most cases, initial state has been used  no hadron beams for X physics • With initial state, • 3-body final states at least • cross section is very small ~ • other technical difficulties PDG 2008

  9. 1. Introduction • What do we know about X baryons? • Strangeness baryons: (: light u/d quark) • Baryon number = 1, isospin = ½ • If flavor SU(3) symmetry is exact for the classification of all particles, then we have N(X*) = N(N*) + N(D*) • Currently, only a dozen of X baryons have been identified so far.(cf. more than 20 N*s & more than 20 D*s) • Only and are in the four star status • Only three states with known spin-parity  the quantum numbers of other states should be identified • Advantages & difficulties • No meaningful information for the X resonances it can open a new window for studying hadron structure • Baryon structure from X spectroscopy • Properties of hyperons (in production mechanisms) • New particles

  10. 2.1 Strangeness and baryons (Expt.) Experiments WA89 (CERN-SPS) EPJC, 11 (1999), hep-ex/0406077 1690 -nucleus collisions

  11. CLAS@JLab PRC 71 (2005) PRC 76(2007)

  12. Questions PDG 2008 The 3rd lowest state Does really exist? or ?Most recent report on : NPB 189 (1981) What are their spin-parity quantum numbers?comparison with theoretical predictions CLAS: PRC 76(2007)

  13. 2.2 Strangeness and baryons (Theory) Direct extension of the classification in the quark model • Classify the states as members of octet or decuplet • Use spin-parity (if known) and Gell-Mann—Okubo mass relation • Works before 1975: reviewed by Samlos, Goldberg, Meadows RMP 46 (1974) • Recent work along this lineGuzey & Polyakov, hep-ph/0512355 (2005) • No dynamics Hadron models for X baryons • Most parameters of models are fixed by the and sector  in principle, no free parameter for the • Most models give (almost) correct masses for and • Requirement to survive • SU(3) group structure • But they give very different spectrum for the excited states!

  14. Nonrelativistic quark model Chao, Isgur, Karl PRD 23 (1981) • has ? • The first negative parity state appears at MeV. • Decay widths are not fully calculated by limiting the final state (but indicates narrow widths) The 3rd lowest state at 1695 MeV? from S. Capstick

  15. Relativistic quark model Capstick, Isgur PRD 34 (1986) • Negative states have lower mass • The third lowest has at MeV. • Where is ? The 3rd lowest state ? from S. Capstick

  16. One-boson exchange model Glozman, Riska Phys. Rep 268 (1996) • Negative states have lower mass • Degeneracy pattern appears • No clear separation between (+) and (–) parity states • Where is ? The 3rd lowest state ? from S. Capstick

  17. Large (constituent quark model) Large quark model • Based on quark model • Expand the mass operator by expansion • Mass formula (e.g. 70-plet) • Fit the coefficients to the known masses and predict.

  18. from J.L. Goity • Where is ? The 3rd lowest state ?

  19. Summary PRC 75 QM (Pervin, Roberts) 1325 1891 2014 1320 (expt.) 1520 1934 2020 1530 (expt.) 1725 1811 1820 (expt.) 1759 1826 : the 3rd lowest state Expt.: ,

  20. Summary Highly model-dependent ! • The predicted masses for the third lowest state are higher than 1690 MeV (except NRQM) • How to describe ? • The presence of is puzzling, if it exits. Cf. similar problem in QM:

  21. bound kaon Skyrme model Bound state approach(Callan, Klebanov) SU(3) is badly broken Anomaly terms • Push up the stateto the continuum}no bound state • Pull down the statebelow the threshold}bound state}give hyperons Treat light flavors and strangeness on the different footing L = LSU(2) + LK/K* Soliton provides background potential which traps K/K* (or heavy) meson

  22. Bound state model • Renders two bound states with negative strangeness • p-wave: lowest state • s-wave: excited state • After quantization • p-wave: positive parity hyperons • s-wave: negative parity hyperons 270 MeV energy difference Mass formula • Includes parameters • They should be computed with a given Lagrangian (dynamics). • Or fix them to known masses and then predict.

  23. Hyperon spectrum (expt.) parity undetermined negative parity 290 MeV positive parity 285 MeV 289 MeV

  24. Hyperon spectrum (Skyrme model) Recently confirmed by COSY PRL 96 (2006) BaBar : of is PRD 78 (2008) NRQM predicts High precision experiments are required! Unique prediction of this model. The should be there. still one-star resonance W’s would be discovered in future. spin-parity YO, PRD 75 (2007)

  25. More comments Two states • Kaons: one in p-wave and one in s-wave • () • : soliton spin (), : spin of the p(s)-wave kaon() • : both of them can lead to states • Therefore, two states and one state • In this model, it is natural to have two states and their masses are 1616 MeV & 1658 MeV! • Clearly, different from quark models Other approaches • Unitary extension of chiral perturbation theory • Ramos, Oset, BennholdPRL 89 (2002) • state at MeV • Garcia-Recio, Lutz, Nieves, PLB 582 (2004) • Claim that the and are states

  26. 3. Photoproduction of • Earlier work • A few experiments on inclusive photoproduction • Tagged Photon Spectrometer Collab. NPB 282 (1987) • photoproduction by CLAS@JLabPRC 76(2007) • The reaction of • Total cross sections • Differential cross sections for X andproduction angles • Invariant mass distributions in the KK and K X channels • Theoretical work Nakayama, YO, Haberzettl, PRC 74 (2006) • Strategy • Investigate the production mechanism using the currently available information only • Then consider other possible (and important) mechanisms

  27. Forbidden or suppressed mechanisms • In kaon—anti-kaon production, , meson production processes, especially meson production, are important. • In photoproduction, • such processes are suppressed since the produced meson should be exotic having strangeness in order to decay into two kaons. • by the same reason, -channel meson-exchange for is also suppressed as the exchange meson should have . E: exotic meson with

  28. Considered diagrams • Consider and exchange only. • Axial-vector mesons: lack of information & heavy mass • Scalar or mesons: not allowed since coupling is forbidden by angular momentum and parity conservation. • Consider • and • low-lying and hyperons • and + exchanged diagrams q1n q2

  29. Methods • Problems • There are many hyperon resonances of , which can contribute to the production process. • We start with a very simple model for the production mechanism by choosing only a few intermediate hyperon states. • Lots of unknown coupling constants and ambiguities. • We make use of the experimental (PDG) or empirical data (like Nijmegen potential) if available. • Or we use model predictions for the unknowns: SU(3) relations, quark model, ChPT, Skyrme model, chiral quark model etc. • Low mass hyperons: • Their couplings are rather well-known. • Higher mass hyperons: • Expect important role of higher mass hyperon resonances GeV • Photoproduction amplitude at the intermediate hyperon on-shell point)(), )(), • Consider and resonances only

  30. Intermediate hyperons Particle Data Group Decay widths (and couplings) are in a very wide range. No information for the other couplings.

  31. Total cross section CLAS: PRC 76(2007)

  32. Differential cross sections

  33. invariant mass distribution No structure Absence of exotic meson

  34. invariant mass distribution Needs higher-mass resonances More works are needed! hyperon resonancein the mass ~ 2 GeV ? NOT from a resonance

  35. 4. Outlook • Study on the spectrum of Xhyperons • Opens a new window for understanding baryon structure • Theoretical models for Xspectrum • Different and even contradictory predictions • What is the third lowest X resonance? And the quantum numbers? • Experimentally, more data are required! • Does exist? • Should confirm other poorly established Xresonances in PDG as well as their quantum numbers • Almost no information on the W baryon resonances • Role of L and S resonances in X photoproduction. • Offers a chance to study those hyperons. • Higher mass and high spin resonances

  36. Preliminary

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