1. Recent BESII Hot Topics
Kanglin He
(for BES Collaboration)
IHEP, Beijing
FPCP08, Taipei, 5—9 May, 2008

2. BESII@BEPC VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm
MDC: xy = m BSC: E/E= 22 % z = 5.5 cm
dE/dx= 8.5 %  = 7.9 mr B field: T
p/p =1.7%(1+p2) z = 3.1 cm

3. BESII Data Samples √s
J/y y´
y´´
data
~58M
~14M
~30pb-1
The construction of new machine/detector, BEPCII/BESIII
are almost ready, we’re expected to get beam in the
beginning of this June
(see Dr. Yangheng Zheng’s talk for detail)

4. I will talk about Y(2175) in J/yhff0(980) h(2225) in J/ygff
Board 1– resonance in J/yK+K-p0
KL mass threshold enhancement in J/ypKL , nKsL
y´radiative decays

5. The Y(2175) Y(2175) f0(980) Babar measured e+e-→ +- and f0(980)
observed the Y(2175) f0(980).
L=232 fb-1
Y(2175) f0(980)
J/
M = 2175 ± 10 MeV
 = 58 ± 16 MeV
Phys. Rev. D 76, (2007)

6. Y(2175) in J/ f0(980) Final states: , K+K-, f0(980)+-
58 M J/ decays
Define , , f0(980) signal regions and sideband regions.

7. Y(2175) in J/ f0(980)
Clear enhancement at around 2.2 GeV in f0(980) invariant mass, band shows in Dalitz plot.
About 50% background!

8. Y(2175) in J/ f0(980)
Simultaneous fit to signal and sideband events with BW+p3
~5
M = 2186 ± 10 ± 6 MeV
= 65 ± 23 ± 17 MeV
B(J/Yf0(980) )
=(3.23 ± 0.75 ± 0.73)x10-4
Nature of the Y?
Very likely it is an excited  state,
Yf0(980) is an OZI allowed decay.
arXiv: ; PRL100, (2008)

9. (2225) in J/  
MarkIII, PRL65 (1990)

10. (2225) in J/   Final states:
1K+K-, 2KSKL
Signal and background in data sample.

11. (2225) in J/  
Signal is very different from phase space distribution, enhancement close to threshold.
Fit with a pseudoscalar state is better than scalar or tensor.
Phase space MC

12. (2225) in J/   In good agreement with Mark-III measurement.
Resonance parameters of a pseudoscalar:
In good agreement with Mark-III measurement.
arXiv: ; PLB (in press)

13. J/ K+K-0 0 background ? 0 sideband
X(1580)
PID and kinematic fit can significantly reduce
the dominant background from J/  + - 0.

14. What is this broad structure?
JPC should be 1--, 3--, …(Parity conservation)
PWA results
Following components are needed K*(892), K*(1410), (1700), X
1– is much better than 3—
Pole position of X is
Big destructive interference among X, (1700) and PS
1-- component

15. Observation of a strong enhancement near the threshold of mass spectrum at BES II
NX*
BES II
PS, eff. corrected
(Arbitrary normalization)

16. BESII preliminary Best PWA fit: (JP=½- is favored)
Fitted as N(1535) (becomes worse by about
5  (2=28 with d.o.f.=2)).
Big Br.
BESII preliminary

17. Nx* is N(1535)? From BESII measurements:
If Nx* is N(1535), its coupling to K is much stronger than that to p.
Then N(1535) would have very large ssbar component
(a 5-quark system).

18. Observation of 
BES II Preliminary KS

19. More statistics and PWA are needed for the detail information
BES II Preliminary N* *
An enhancement near S threshold is evident
N* and * found in the S and nS spectrum
More statistics and PWA are needed
for the detail information

20. ’ radiative decays Only limited modes measured by BESI
, ’ [PRD58, (1998)]
KK,  [PRD67, (2003)]
Try to measure more modes
B(’+X)
2-prong: +-, K+K-, ppbar, +-
4-prong:2(+-), +-K+K-, +-ppbar, 2(K+K-), KSK+-+c.c.
6-prong: 3(+-), 2(+-)K+K-
Published in
PRL99, (2007)
PRD74, (2006)

21. Observation of ’ radiative decays
Expected 1% BR, but only 0.05% observed.
Potential channels for hadron spectroscopy study, including search for non-qqbar states, provided statistics is enough (BESIII?).
~ 0.1% more observed in this analysis.
Mode
BR (10-5)
[m<2.9 GeV/c2]
 pp-bar
2.9 ± 0.4 ± 0.4
 ’
12.6 ± 2.9 ± 1.5
 2(+-)
39.6 ± 2.8 ± 5.0
 KSK+-+c.c.
25.6 ± 3.6 ± 3.6
 +-K+K-
19.1 ± 2.7 ± 4.3
 +-ppbar
2.8 ± 1.2 ± 0.7
 2(K+K-)
< 4.0
 3(+-)
< 17
 2(+-)K+K-
< 22
PRL99, (2007)

22. ’ +- and K+K- arXiv: 0710.2324 M(+-) Fit with incoherent BWs
Mode
BR (10-5)
f2(1270) +-
22 ± 1 ± 2
f0(1500) +-
1.5 ±
f0(1710) +-
2.4 ±
f4(2050) +-
2.8 ±
f0(2200) +-
4.6 ±
f2(1270) K+K-
1.9 ±
f’2(1525) K+K-
0.69 ±
f0(1710) K+K-
3.1 ±
M(+-)
Fit with incoherent BWs
ISR produced  and  consistent with prediction
f2(1270) +- helicity amplitudes
J/: x=0.89
y=0.46
M(K+K-)

23. Summary Thanks a lot ! Observation of Y(2175) in J/ decays.
Measurement of (2225) resonance parameters.
Observation of a board 1– resonance state X(1580)
Observation of KL mass threshold enhancement
Observation of new ’ radiative decay modes.
Thanks a lot !