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 日 Search for Z(4430) in meson photoproduction X.-H. Liu, Q.Z. and F.E. Close, PRD in press; arXiv: [hep-ph] Institute of High Energy Physics, CAS

Outline Motivation initiated by Belle results Photoproduction of Z(4430) Summary

 Belle results bb ss u u dd d cc c WW B+B+ Z + (4430) K0K0 u dd cc c cc c dd u   Belle Collaboration, PRL(2008); arXiv: [hep-ex]

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) 

 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? … … qqqq Hybrid Glueball Tetraquark Molecule state

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.

 Photoproduction mechanism u dd cc c cc c dd u Z + (4430)   **    Z + (4430) Z+Z+ p n   Implication of the strong Z  coupling

 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

with Form factor for pion exchange:    Z+Z+ p n  Approach with effective Lagrangians

V ( , , , J/ ,  …)  Vector meson dominance model V  * effective coupling: EM field in terms of vector meson fields:  ** e+ e- ** e+ e-  =    ** e+ e-

 pion-nucleon coupling Form factor for pion-nucleon coupling:  p n Transition amplitude:

 Other mechanism   a0a0 Z+Z+ p n

 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: [hep-ph] ) 11 11

H1 at DESY Peak area for Z(4430)

 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

 Contributions from J/  Define: Withand the cross sections are still sizeable.

 Dalitz plot Z(4430) band Total xsection for  p   + n Z(4430), if exists, will stand out of the background in photoproduction.

 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.

Thanks !