Recent J/? Results from BESII

1
Recent J/? Results from BESII

• Nengfeng ZHOU
• Representing BES Collaboration
• Institute of High Energy Physics, CAS
• Rencontres de Moriond 2005
• QCD AND HIGH ENERGY HADRONIC INTERACTIONS

2
Outline

• Introduction
• Multiquark candidates at BES
• pp threshold enhancement in
• p? threshold enhancement in
• K? threshold enhancement in
• Study of the light scalar mesons
• Study of the excited baryon states
• Measurements of some J/? decays
• Summary

3
Introduction
World J/? and ?(2S) Samples (106)
BESII Detector
BESII 58M J/?
J/?
BESII 14M ?(2S)

• VC ?xy 100 ?m TOF ?T 180 ps
• MDC ?xy 220 ?m BSC ?E/?E 21
• ?dE/dx 8.5 ??
  7.9 mr
• ?p/p1.78?(1p2) ?z 2.3
  cm
• counter ?r? 3 cm B field 0.4 T
• ?z 5.5 cm

?(2S)
4
Multi-quark candidates

• Hadrons consist of 2 or 3 quarks
• Naive Quark Model
• New forms of hadrons
• Multi-quark states Number of quarks gt 4
• Hybrids qqg,qqqg
• Glueballs gg, ggg

Meson( q q ) Baryon(q q q)
5
Observation of an anomalous enhancement near the
threshold of mass spectrum at BES II
J/y?gpp
BES II
acceptance weighted BW
3 5 -10 -25
M1859 MeV/c2 G lt 30 MeV/c2 (90 CL)
c2/dof56/56
0
0.1
0.2
0.3
M(pp)-2mp (GeV)
3-body phase space
acceptance
Phys. Rev. Lett., 91 (2003) 022001
6
Observation of an anomalous enhancement near the
threshold of mass spectrum at BES II
?
Data/MC
The clear ? signal in data shows high purity of
signal.
7
Phase Space
PRL 93 (2004) 112002
Data
Data
8
Near threshold enhancement is also
observed in
Fix the parameters, 4? away from phase space.
9
Observation of a strong enhancement near the
threshold of mass spectrum at BES II
NX
BES II
PS, eff. corrected
(Arbitrary normalization)
10
PWA is performed for enhancement

• possible N and ?states listed in PDG are
  fitted
• N(1720), N(1900), ?(1520), ?(1690),
• many different combinations are tried
• different form factors are used
• different JP of Nx is tried

11

• An abnormal enhancement is observed in the mass
  threshold of MK?
• Its mass and width
• (large uncertainty near threshold, high
  statistics is crucial!)
• Mass 15001650MeV
• Width 70110MeV
• JP favors 1/2-
• large BR(J/??pNx)Br(Nx?K?) (?210-4).

What is it?? Possibly N(1535)
with large coupling to K? K? molecular state ??
12
Light Scalar Mesons s, ?, f0(980), f0(1370),
f0(1500), f0(1710), f0(1790)
13
Why are light scalar mesons interesting?

• There have been hot debates on the existence of
  ? and ? .
• Lattice QCD predicts the 0 scalar glueball mass
  from 1.5 - 1.7 GeV. f0(1500) and f0(1710) are
  good candidates.

14
The ? pole in
?
?
M(??-)
Pole position
MeV
PLB598, 149 (2004)
15
? at BES
BES II Preliminary

• BES II observed ? in J/??K ? ?K?K?.
• Preliminary PWA results
• Pole position

16
Study of f0(980), f0(1370), f0(1500), f0(1710)
from
17
f0(980) at BES

• Important parameters from PWA fit
• Large coupling with KK indicates big
  component in f0(980)

f0(980)
f0(980)
18
f0(1370) at BES

• There has been some debate whether f0(1370)
  exists or not.
• f0(1370) clearly seen in
• J/? ? ???, but not seen in J/? ? ???.

f0(1370)
NO f0(1370)
PWA 0 components
19
f0(1710) at BES

• Clear f0(1710) peak in J/? ? ?KK.
• No f0(1710) observed in J/? ? ??? !

f0(1710)
NO f0(1710)
20
f0(1710) in J/? ? ?KK
PWA analysis shows one scalar.
Phys. Rev. D 68 (2003) 052003
21
f0(1710) in J/? ? ???

• Two scalars in J/? ? ???
• One is around 1470 MeV, may be f0(1500)?
• The other is around 1765 MeV, is it f0(1790) or
  f0(1710) or a mixture of f0(1710) and f0(1790)?

BES II Preliminary
22
f0(1500) at BES

• One scalar with a mass 1466 ? 6 ? 16 MeV
  is needed in J/?? ???, is it f0(1500)? Why
  the mass is different from PDG?
• No peak directly seen in ???, ?KK, ???, ?KK.

23
OZI rule and flavor tagging in J/? hadronic
decays

• In J/? hadronic decays, an ? or ? signal
  determines the or
  component, respectively. ? OZI rule

24
Unusual properties of f0(1370) and f0(1710)

• f0(1710)
• It dominantly decays to KK (not to ??) ?
• It is mainly produced together with ? (not ?) ?
• What is it ?
• f0(1370)
• It dominantly decays to ?? (not to KK) ?
• It is mainly produced together with ? (not ?) ?
• What is it ?
• ? Scalar Puzzle

25
Excited baryon states
The evidence of 2 new N peaks
N(1520) N(1535)
N(1650) N(1675) N(1680)
N(1440)?
?
Missing mass spectrum (GeV/c2)
26

• Fitting formula momentum of proton
  momentum in
• Mx frame

? Possible new N resonance ? Detailed
information needs PWA
Submitted to P. R. L., hep-ex/0405030
27
Measurements of J/? decays
28
Measurement of J/? ? ??-?0
from direct J/? decay from ?(2S) decay

Br(J/ ????-?0) (21.35?0.04?1.85)?10-3
Br(J/ ????-?0) (20.9?0.2?1.1)?10-3
Combined BES value (21.0?1.1)?10-3
PDG (15.0 ? 2.0) ? 10-3
inconsistent !
Phys. Rev. D 70, 012005 (2004)
29
First measurement of J/? ?? f2(1270)f2(1270)??4?
2nd polynomial backgrounds
J/???f2 f2
?
f2?? background
The invariant mass spectrum of ? ?- with mass
cut M? ?- - 1.27lt0.185GeV for another ? ?-
pair is used to fit the signal. Four components
are used in the fit. The branching ratio is
measured for the first time to be
PRD70, 112008 (2004).
30
First measurement of J/??2(? ?- )?, 3(? ?- )?
?
?

Clear ? signal can be seen in the distribution of
M?? from J/?? ?? 2(? ?- ).
Clear ? signal can be seen in the distribution of
M?? from J/?? ?? 3(? ?- ).
The branching ratios of J/??2(? ?- )?, 3(? ?-
)? are measured for the first time Br (J/?? 2(?
?- )?) (2.260.080.27)10-3 Br (J/?? 3(?
?- )?) (7.240.961.11)10-4
31
Summary

• An threshold enhancement is observed in
• decay.
• The p? and K? threshold enhancements are observed
• in decay.
• Study of the scalars ?, ?, f0(980) ,f0(1370),
  f0(1500), f0(1710)
• New N peaks in
• Measurements of J/? decays are performed, some of
  the channels are first observation.

32
Thank you!