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
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, CASInstitute of High Energy Physics, CAS
Outline
• Motivation initiated by Belle results
• Photoproduction of Z(4430)
• Summary
Belle results
b
s
u u
d
d
c
c W
B+ Z+(4430)
K0
u
d
c
c c
c
d u
Z+(4430)
Belle Collaboration, PRL(2008); arXiv:0708.1790[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 (qq) 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?
• … …
qq Hybrid Glueball Tetraquark
Molecule state
Low-lying scalar nonet
a2(1320) uu -ddf2(1270) uu +dd
K2(1430) sd
f’2(1525) ss
qq tensor nonet
puzzling scalar nonet
qq , q2q2 , meson molecule ?
f0(980) ss , [suus +sdds ]
(800) sd , [suud ]
f0(600) uu +dd , [uddu ]
a0(980) uu -dd , [ussu -dssd ]
Jaffe, PRD(1977); Slide from B.S. Zou
Difficult to distinguish a hidden ss from excited qq.
Photoproduction mechanism
u
d
c
c c
c
d u
Z+(4430)
*
Z+(4430) Z+
p n
Implication of the strong Z coupling
Quantum numbers
A vector (1) and pseudoscalar (0) can make a Z of JP= 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+
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
Z+
p n
Numerical results
a0
• 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] )
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:
With and
the cross sections are still sizeable.
Dalitz plot
Z(4430) bandTotal 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 ! Thanks !
