Recent J/ Results from BESII
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Recent J/ Results from BESII
Nengfeng ZHOU
Representing BES Collaboration
Institute of High Energy Physics, CAS
Rencontres de Moriond 2005QCD AND HIGH ENERGY HADRONIC INTERACTIONS
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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
Outline
pγpJ/ψ
ΛpKJ/ψ
ΛpKJ/ψ
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CBAL MK II MK III DM2 BES I BES II
BESII Detector
VC: xy = 100 m TOF: T = 180 psMDC: xy = 220 m BSC: E/E= 21 % dE/dx= 8.5 % = 7.9 mr p/p=1.78(1+p2) z = 2.3 cm counter: r= 3 cm B field: 0.4 T z = 5.5 cm
Introduction
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MKI MKII MKIII CBAL BESI BESII CLEOc
J/
(2S)
World J/ and (2S) Samples (×106) BESII
58M J/
BESII 14M (2S)
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Multi-quark candidates
Hadrons consist of 2 or 3 quarks :
Naive Quark Model :
New forms of hadrons:• Multi-quark states : Number of quarks > = 4 • Hybrids : qqg , qqqg …
• Glueballs : gg , ggg …
Meson ( q q )
Baryon ( q q q )
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Observation of an anomalous enhancement near the threshold of mass spectrum at BES II
M=1859 MeV/c2
< 30 MeV/c2 (90% CL)
J/pp
M(pp)-2mp (GeV)0 0.1 0.2 0.3
3-body phase space acceptance
2/dof=56/56
acceptance weighted BW +3 +5
10 25
pp
BES II
Phys. Rev. Lett., 91 (2003) 022001
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Observation of an anomalous enhancement near the threshold of mass spectrum at BES IIp
pKJ /
The clear Λ signal in data shows high purity of signal.
Data/MC
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Phase Space
Data Data
pM pM
pK Kp
PRL 93 (2004) 112002
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Near threshold enhancement is also observed inp pKS)2(
Fix the parameters, 4 away from phase space.
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)(GeV/c2
ΛKM
PS, eff. corrected
MMM KΛK
Observation of a strong enhancement near the threshold of mass spectrum at BES IIK
(Arbitrary normalization)
BES II pKJ /
NX pKJ /
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PWA is performed for enhancement K
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
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An abnormal enhancement is observed in the mass threshold of MK
Its mass and width:
(large uncertainty near threshold, high statistics is crucial!)Mass 1500~1650MeV
Width 70~110MeV
JP favors 1/2-
large BR(J/pNx)Br(NxK) (2*10-4). What is it??
Possibly N*(1535) with large coupling to K K molecular state ??
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Light Scalar Mesons:
σ, κ, f0(980), f0(1370),
f0(1500), f0(1710), f0(1790)
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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.
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The pole in /J
M(+-)
Pole position:
(541 39) (252 42)i MeV
PLB598, 149 (2004)
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BES II observed in
J/K* KK.
Preliminary PWA results
Pole position:
at BES
BES II Preliminary
MeVi )420~310()840~760(
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Study of f0(980), f0(1370), f0(1500), f0(1710) from:
KK
KK
KKJ
,
,
,/
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Important parameters from PWA fit:
Large coupling with KK indicates big component in f0(980)
/J
KKJ /
f0(980) at BES
21.025.021.4
1510165
68965
g
g
MeVg
MeVM
KK
ss
f0(980)
f0(980)
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There has been some debate whether f0(1370) exists or not.
f0(1370) clearly seen in
J/ , but not seen in J/ .
/J
/J
PWA 0++ components
f0(1370)
NO f0(1370)
f0(1370) at BES
MeV
MeVM
40265
501350
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Clear f0(1710) peak in J/ KK.
No f0(1710) observed in J/ !
f0(1710) at BES
KKJ /
/J
f0(1710)
NO f0(1710)
MeV
MeVM
20125
301740
CLKKfBR
))1710((
))1710((
0
0
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KKJ /
00/ ss KKJ
)1710(0f
)1710(0f
PWA analysis showsone scalar.
MeV 166
MeV 41740155108
1025
M
Phys. Rev. D 68 (2003) 052003
f0(1710) in J/ KK
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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)?
/J?)1500(0f ?)1710(0f
00/ J
BES II Prelim
inary
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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.
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OZI rule and flavor tagging in J/ hadronic decays
In J/ hadronic decays, an or signal deter
mines the or component, respe
ctively. OZI rule
dduu ss
/J /J
dduu
ss
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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
dduu
dduu
ss
ss
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The evidence of 2 new N* peaks
../ ccnpJ
Missing mass spectrum (GeV/c2)
N*(1440)?
N*(1520)
N*(1535)N*(1650)
N*(1675)
N*(1680)
?
Excited baryon states
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Fitting formula
: momentum of : proton momentum in
Mx frame
2 1
2 2 2 20 0 0( )
lq k
M M M
n
► Possible new N* resonance
► Detailed information needs PWA
+15 2 2-30M = 2065 3 MeV/c =175 12 40MeV/c
kq
Submitted to P. R. L., hep-ex/0405030
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Measurements of J/ decays
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Measurement of J/ → +-0
Br(J/ →+-0) = (21.350.041.85)10-3
from direct J/ decay: from (2S) decay:
Br(J/ →+-0) = (20.90.21.1)10-3
*******************
Combined BES value: (21.021.01.1)1.1)1010-3-3
PDG: (15.0 2.0) 10-3 inconsistent !Phys. Rev. D 70, 012005 (2004)
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PRD70, 112008 (2004).
42 2( / (1270) (1270) 4 ) (9.5 0.7 1.6) 10Br J f f
2nd polynomial backgrounds
J/f2 f2
f2 background
The invariant mass spectrum of + - with mass cut |M + - - 1.27|<0.185GeV 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:
First measurement of J/ f2(1270)f2(1270)4
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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( + - )) = (2.26±0.08±0.27)×10-3
Br (J/ 3( + - )) = (7.24±0.96±1.11)×10-4
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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.
ppppJ /
../ ccnpJ
pKJ /
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