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Cascade Physics and Meson Decays in GlueX

Cascade Physics and Meson Decays in GlueX. Aleksandr Starostin Bernard Nefkens UCLA. Outline. Cascades in GlueX Motivation Cascade Photoproduction Detector Requirements Physics of Meson Decays Summary. Cascades: Physics Motivation. Review of Cascade physics:

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Cascade Physics and Meson Decays in GlueX

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  1. Cascade Physics and Meson Decaysin GlueX Aleksandr Starostin Bernard Nefkens UCLA

  2. Outline • Cascades in GlueX • Motivation • Cascade Photoproduction • Detector Requirements • Physics of Meson Decays • Summary A.Starostin, New GlueX Proposals

  3. Cascades: Physics Motivation Review of Cascade physics: Workshop “Cascade Physics: A New Window on Baryon Spectroscopy”, December 1-3, 2005, JLab Presentations available at http://conferences.jlab.org/cascade/ A.Starostin, New GlueX Proposals

  4. Summary of Physics with Cascades • Spectroscopy of cascade exited states including search for parity doubles (requires JP) • d-u quark mass difference (m(Ξ-)-m(Ξ0) ~ 6.5 MeV, requires good energy resolution) • Search for exotic states: Ξ+ and Ξ-- A.Starostin, New GlueX Proposals

  5. What is known about cascades? • Only 11 Ξ*; 6 “well-established” • Those we know aren't known well: only have JP for three states and a guess of a fourth • SU(3) symmetry requires one Ξ I=1/2 per octet and per decuplet: n(Ξ*)=n(N*) +n(Δ*) Ξ0 = uss, Ξ-= dss Adamovich et al., EPJ C5, 621 Hemingway et al., PLB 68, 197 A.Starostin, New GlueX Proposals

  6. Cascades in the Constituent Quark Model S.Capstick and N.Isgur • Most of the exited Ξ* states are narrow (10-100 MeV): the decay mode Ξ*->Ξπ is suppressed (relative to N*->Nπ and Δ*->Δπ) • Phase-space factor • Flavor overlap factor A.Starostin, New GlueX Proposals

  7. Width of the Cascades N* and Δ* resonances overlap, because of that spectroscopy N* and Δ* requires complicated and ambiguous phase-sift analysis Cascades are expected to be narrow, parameters of the cascades can be extracted directly from the mass spectra A.Starostin, New GlueX Proposals

  8. Search for parity doublets A.Starostin, New GlueX Proposals

  9. Search for parity doublets The high-mass light baryon spectrum exhibits occurrence of parity doublets. Glozman suggested to explain the mass degeneracy by assuming that chiral symmetry is restored in highly excited hadronic states. L.Y. Glozman, PL B 475, 329 (2000) T.D. Cohen and L.Y. Glozman PR D 65, 016006 (2001) R.L. Jaffe et al. Phys. Rep. 435, 157 (2006) M. Shifman and A. Vainshtein PR D 77, 034002 (2008) “Evidence for a Parity Doublet Δ(1920)P33 and Δ(1940)D33 from γp->pπ0η” I.Horn et al., PRL 101, 202002 (2008) A.Starostin, New GlueX Proposals

  10. Quark mass difference • Quark masses are parameters of the Standard Model • Cascades may provide d-u mass difference • The difference can be determined for all for exited of Ξ- and Ξ0 states A.Starostin, New GlueX Proposals

  11. Search for exotic Ξ+ and Ξ-- • Finding Ξ+ and/or Ξ-- would be a unique signature for a five-quark state, member of the antidecupled • Evidences for existance of Ξ–- were found by CERN NA49 (PRL, 92, 042003 (2004)) • Search was also conducted by CLAS A.Starostin, New GlueX Proposals

  12. Photoproduction of cascades • Cascades in CLAS g11 run • Number of events for the ground state – 7678, for the first exited state – 658 • for most of the run the maximum energy of tagged photons 3.8 GeV, some data with 4.8 GeV (the threshold is about 2.85 GeV) • Estimates for the γp -> 2K+Ξ- total cross section by Denis Weygand – between 3.5 GeV and 4.8 GeV cross section is flat, order of 10 nb. L. Guo et al. PRC 76, 025208 (2008) A.Starostin, New GlueX Proposals

  13. Detector requirements • Very good K/π separation • There are two detached vertices – high resolution tracking device is essential • For neutral cascades – high acceptance EM calorimeter • Hall-D: tagged photons with energies close to 12 GeV • GlueX: coverage close to 4π in particular for EM A.Starostin, New GlueX Proposals

  14. Decays of Light Mesons

  15. Physics of Meson Decays • Tests of Chiral perturbation theory and other theories of strong interactions • Measurements of electromagnetic form factors • Search for violation of discrete symmetries: C, P, CP, and T • Search for leptoquark and violation of lepton family number, • Most of the decays do not require a dedicated experiment JP = 0- : π0, η, η’(958) Jp = 1- : ρ(770), ω(782), ψ(1020) A.Starostin, New GlueX Proposals

  16. Tests of ChPT η->π0π0π0 η->π+π-π0 η’->ηπ0π0 η’->ηπ+π- Dalitz plot allows to study ππ andηπ interactions, slop parameters of the Dalitz plot, “cusp” at the opening of π0π0->π+π- (carries information on the a0-a2ππ scattering length) A.Starostin, New GlueX Proposals

  17. Dalitz and double Dalitz decays η->l+l-γ η->l+l-l+l- ω->l+l-π0 η’->l+l-γ η’->l+l-l+l- Spectrum of the l+l- mass in the Dalitz carries information on the EM form-factor of the decay vertex A.Starostin, New GlueX Proposals

  18. Tests of C A.Starostin, New GlueX Proposals

  19. More decays • Tests of P invariance: η->2π, η’->2π, η->4π, η’->4π • Search for leptoquaks: η->μ+μ-, η->e+e- • Search for violation of Lepton Family number: η->μe, η’->μe, etc • Tests of T invariance: absence of the transverse polarization of μ in η->γμ+μ- A.Starostin, New GlueX Proposals

  20. Branching Ratio of η->e+e- and existence of the leptoquark Leptoquark – a hypothetical particle suggested by A. Salam, carries interaction between quarks and leptons, encountered in various extensions of the Standard Model, such as technicolor theories or GUTs η->e+e- • The single-photon exchange mechanism is forbidden because of conservation of angular momentum • The decay is dominated by a two-photon intermediate state which is suppressed • Provides lower limits of the masses of leptoquarks and axions. D.Wyler, in proc. inter. workshop. “Rare decays of light mesons”, Gif-sur-Yvatte, France March 29-30, 1990. A.Starostin, New GlueX Proposals

  21. Summary • Universality and resolution of the GlueX detector combined with 12GeV tagged photon beam makes cascade program in Hall-D feasible. Both, charged and neutral cascades will be detected using missing mass and invariant mass • The objectives of the cascade program will be to establish spectrum of the exited states and their spin-parity. These data can be used to establish the existence of the cascade parity doublets, calculate d-u quark mass difference and search for the exotic cascade states • Both neutral and charged decays of light mesons can be detected in GlueX. This data sample will be used to test Chiral Perturbation Theory and other theories of strong interactions, search for violation discrete symmetries, and more. A.Starostin, New GlueX Proposals

  22. A.Starostin, New GlueX Proposals

  23. Predictions of the Cascade spectrum • Many quark models, 1/Nc expansions of QCD, etc. predict spectrum of exited baryon states • Predicted is a rich spectrum of exited states (the constituent quark model by S.Capstick and N.Isgur predicts 45 states below 2.3 GeV, the algebraic model by F.Iachello predicts 32 states) • The constituent quark model and the algebraic model predict the most of the cascade states to be narrow • Lattice QCD calculations? A.Starostin, New GlueX Proposals

  24. Tests P A.Starostin, New GlueX Proposals

  25. What is known about cascades? SU(3) symmetry requires one Ξ I=1/2 per octet and per decuplet Ξ0 = uss, Ξ+= dss Gell-Mann-Okubo mass relation in octet: Equal spacing mass relation in decuplet: A.Starostin, New GlueX Proposals

  26. Dalitz and double Dalitz decays Invariant mass of l+l- in the Dalitz and double Dalitz decays: η->l+l-γ, η->l+l-l+l-, ω->l+l-π0, η’->l+l-γ, η’->l+l-l+l- carries information on the EM form-factor of the decay vertex A.Starostin, New GlueX Proposals

  27. Cascades in 1/Nc expansion • 70-plet: • 7 masses in range 1750-2000 MeV • Two pairs of same J states nearly degenerate • L=2 56-plet: • 6 masses in range 2000-2250 MeV • Same J states separated by >140 MeV • Larger errors in predictions than in 70-plet • Parameter free mass relations rather well tested. Presented by J L Goity A.Starostin, New GlueX Proposals

  28. Search for “Cascaderium” NN scattering length a =-17.3 fm. If ΞΞ 1S0 potential is same as for NN: predicted a BOUND STATE: dibaryon S=-4 decays weakly to ΞΛπ->NN4π ΞΞ binding predicted by many potential models γd -> 2K+ 2K0 [Ξ0 Ξ-] γα -> 2K+ 2K0 [Ξ0 Ξ-] n p Neutral cascades are preferred to avoid repulsion (J.Miller, Cascade workshop) Figure by R.Jones A.Starostin, New GlueX Proposals

  29. Test of Time reversal invariance A.Starostin, New GlueX Proposals

  30. Search for exotic Ξ+ and Ξ-- • Ξ+ and Ξ–- are unique signatures for a five-quark state, member of the antidecupled • Evidences for existance of Ξ–- were found by CERN NA49 (PRL, 92, 042003 (2004)) • Search was also conducted by CLAS (run g12?) A.Starostin, New GlueX Proposals

  31. Cascades in quark models 45 cascades states with masses below 2.3 GeV S.Capstick and N. Isgur PRD 34 2809 (1986) A.Starostin, New GlueX Proposals

  32. Cascades in agebraic model A.R. Bijker, F.Iachello, and A. Leviatan Ann. Phys. 284 89 (2000) A.Starostin, New GlueX Proposals

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