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Qiang Zhao Theory Division Institute of High Energy Physics Chinese Academy of Sciences 第十届全国粒子物理学术会议,南京, 2008 年 4 月 26-29 日 Search for Z(4430) in meson photoproduction X.-H. Liu, Q.Z. and F.E. Close, PRD in press; arXiv:0802.2648[hep-ph] Institute of High Energy Physics, CAS
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Outline Motivation initiated by Belle results Photoproduction of Z(4430) Summary
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Belle results bb ss u u dd d cc c WW B+B+ Z + (4430) K0K0 u dd cc c cc c dd u Belle Collaboration, PRL(2008); arXiv:0708.1790[hep-ex]
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First charmonium with isospin I=1 ! Tetraquark state? ( Ebert etal; Rosner; Maiani et al; Lee ) Molecular state of D* D1? ( Bugg; Liu et al ) Subthreshold effects due to D* D1? ( Bugg; Chao et al ) Baryonium? ( Qiao ) …… Why not seen in J/ ? Can it couple to c ? Where are its flavor partners? …… Strong coupling for Z(4430)
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Why care exotics? QCD does not eliminate the existence of hadrons beyond simple (q q) or (qqq) as a color-singlet system. How confinement manifests itself at large distances? What leads to the chiral symmetry spontaneous breaking? What are the proper effective degrees of freedom for a hadron? … … qqqq Hybrid Glueball Tetraquark Molecule state
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Low-lying scalar nonet a 2 (1320) uu - dd f 2 (1270) uu + dd K 2 (1430) sd f ’ 2 (1525) ss qq tensor nonet puzzling scalar nonet qq, q 2 q 2, meson molecule ? f 0 (980) ss, [ su us + sd ds ] (800) sd, [ su ud ] f 0 (600) uu + dd, [ ud du ] a 0 (980) uu - dd, [ us su - ds sd ] Jaffe, PRD(1977); Slide from B.S. Zou Difficult to distinguish a hidden s s from excited q q.
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Photoproduction mechanism u dd cc c cc c dd u Z + (4430) ** Z + (4430) Z+Z+ p n Implication of the strong Z coupling
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Quantum numbers A vector (1 ) and pseudoscalar (0 ) can make a Z of J P = 1 , 0 , 1 , 2 in a relative S or P wave. , 1 Z + (4430) , 0 L = 0, 1
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with Form factor for pion exchange: Z+Z+ p n Approach with effective Lagrangians
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V ( , , , J/ , …) Vector meson dominance model V * effective coupling: EM field in terms of vector meson fields: ** e+ e- ** e+ e- = ** e+ e-
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pion-nucleon coupling Form factor for pion-nucleon coupling: p n Transition amplitude:
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Other mechanism a0a0 Z+Z+ p n
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Numerical results a0a0 Forward peaking due to pion exchange Threshold enhancement similar to charged production Negligibly small a0 exchange Other quantum numbers 1 and 0 are also investigated (X.-H. Liu, Q.Z. and F.E. Close, PRD in press; arXiv:0802.2648[hep-ph] ) 11 11
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H1 at DESY Peak area for Z(4430)
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Background contributions Experimentally, one looks at n as final particles in the detector. (I) Signal transitions are as below: (II) Background contributions due to diffractive production: Vacuum Pomeron exchange
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Contributions from J/ Define: Withand the cross sections are still sizeable.
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Dalitz plot Z(4430) band Total xsection for p + n Z(4430), if exists, will stand out of the background in photoproduction.
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Perspective Z(4430) could be the first indisputable exotic meson, a hidden charm system with isospin I=1. If it is a genuine resonance, its photoproduction will be favored in n channel. A search for it at H1 and ZEUS might help clarifying this issue. A search for Z(4430) and its partners is necessary.
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Thanks !
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