qiang zhao theory division institute of high energy physics chinese academy of sciences

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 !