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Recent BESII ResultsRepresenting BESII Collaboration
Weiguo Li
Institute of High Energy Physics,
Beijing 100049, P.R. China
NSTAR Workshop
Bonn, Sep. 6, 2006
Outline
Introduction
Light Hadron Spectroscopy from J/ Decays
Study of Excited Baryon States
Selected BF Measurements
Summary
BESII DetectorBESII Detector
VC: xy = 100 m TOF: T = 180 ps counter: r= 3 cm MDC: xy = 250 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.4 % = 7.9 mr B field: 0.4 T p/p=1.8(1+p2) z = 2.3 cm Dead time/event: 〈 10 ms
Data from BESII
Ecm (GeV)
Physics BESII Data
2-5 R scan
2. 2. 2.2,2.6,3.0
R value,
QED, (g-2)
QCD
6+85 points
3.1 3.69 3.78
J/ (2S) (3770)
5.8107
1.46107
~27 pb-1
BESII finished data taking April 2004
Scalars: , clearly observed
X(1835) in J/ ’
The threshold enhancement in J/
New observation of a broad 1- - resonance in J/
K+K- 0
(1760) in J/
Light Hadron Spectroscopy from J/ Decays
The pole in at BESII
/J
M()
M(+-0)
M(+-
)
0
Averaged pole position: (541 39) (252 42)i MeV
Phys. Lett. B 598 (2004) 149
κ
24877
8173 MeV/c )45309()30841(
i
Phys. Lett. B 633 (2006) 681
Observation of X(1835) in at BESII
The +- mass spectrum for decaying into +- and
Statistical Significance 7.7
J
J
54264obsN
MeVm 7.21.67.1833
MeV7.73.207.67
PRL 95, 262001 (2005)
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, 022001 (2003)
Re-fit to J/pp including FSI
Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0)
M = 1830.6 6.7 MeV
< 153 MeV @90%C.L.
ppp mM 2
In good agreement with X(1835)
Candidate of 0-+ pp Bound State
X(1835) could be the same structure as pp mass threshold enhancement X(1860)/X(1830).
It could be a pp bound state since it dominantly decays to pp when its mass is above pp mass threshold.
Its spin-parity should be 0-+: this would be an important test.
There is already an (1760) nearby , so that X(1835) is very likely to be an unconventional 0-+ meson.
This result cannot be explained by pure FSI effect, since FSI is a universal effect.
This indicates that X(1860) has a production property similar to ’ meson.
This strong threshold enhancement is NOT observed in at CLEOpp )1( S
No enhancement near threshold
CL
JBrSBr
%90@%7.0
)X /(/)X )1((
)(%90@%4.0
)' /(/)' )1((
PDGCL
JBrSBr
Phys.Rev.D73, 032001(2006)
FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored.
This again indicates that X(1860) has a production property similar to ’ meson.
No strong threshold enhancement is observed in at BESIIpp '
No significant narrow strong enhancement near threshold(2.0 if fitted with X(1860))
..%90@%8
)X /(/)X '(
LC
JBrBr
%4~3
)' /(/)' '(
JBrBr
Phys.Rev.Lett.99, 011802 (2007)
J/ pp
Clear signal is seen,
B(J/ pp) =( 9.8 0.3 1.4 ) 10–4
B(J/ X(1860))B(X(1860) pp) < 1.5 10–5 @ 95% C.L.
This again disfavors FSI and indicates that X(1860) has a production property similar to ’ meson.
This also indicates X(1860) may have strong coupling to gluons as ’ meson.
This strong threshold enhancement is NOT observed in at BESIIpp / J
04.0
)' /(/)' /(
JBrJBr
Summary of new studies on pp mass threshold structure X(1860)
Pure FSI effect cannot explain X(1860) structure.
X(1860) has production properties similar to ’ meson • Why a baryonium (candidate) has a production prop
erties similar to ’ meson? ’ excitation? Why an ’ excitation dominantly deca
ys into ppbar above ppbar mass threshold?
We studied DOZI process:J/ + + +-0 K+ K-
recoiling against
mass threshold enhancement
Phys. Rev. Lett. 96,162002 (2006)
A clear mass threshold enhancement is
observed
Acceptance
Side-bands
The radiative decay of J/ has been observed in the 58M J/ data.
A significant structure of has been found near the mass threshold.
PWA shows the structure favors 0++, M = ,
=1052028 MeV, and the corresponding branch
fraction = (2.610.270.65)x10-4.
It could be a multiquark/hybrid/glueball state.
Its relation with f0(1710), f0(1790)?
MeV181812 1926
New observation of a broad 1– resonance
in J/ K+K- 0
0
background 0 sideband
?
K*(892)
K*(1410)
X(1580)
PID and kinematical fit can significantly reducethe dominant background from J/ + - 0.
Phys. Rev. Lett. 97 (2006) 142002
Four decay modes are included :
Amplitudes are defined by Covariant tensor formalism B.S. Zhou and D.V. Bugg, Eur. Phys. J. A16, 537(2003)
BW with energy-dependent width
J.H. Kuhn, A. Satamaria, Z. Phys. C48, 445 (1990).
fitPWA :hist
data : points
0*
0*
)1410(
)890(
: 1
KK
KK
component
)1410( ),890(
)(,)(/
),( ,))1700(,(/
***
0**
0
KKKwhere
KKKKJ
KKXXJ
122
22
2
))(
)(()()(
;)(
1)(
l
R
RRRR
RR
Mp
sp
s
MMs
ssiMssBW
PS
KK
KKX
component
)1700(
: 1
Partial Wave Analysis of J/ K+K- 0 events
Phys. Rev. Lett. 97 (2006) 142002
Parity conservations in J/ K+K- 0 requires that
spin-parity of K+K- should be 1--,3--,…
PWA fit with and
phase space (PS) gives:
( can be ruled out by much worse likelihood )
X pole position
big destructive interference among and PS
1PCJ
)1410( ),890( (1700), , ** KKX
232116712
98499155 / )(409 )1576( cMeVi
47.26.3
0 10)6.05.8()()/(
KKXBrXJBr
(1700) , X
3
Partial Wave Analysis of J/ K+K- 0 events
Broad X cannot be fit with known mesons or their interference
It is unlikely to be (1450), because:
• The parameters of the X is incompatible with (1450).
(1450) has very small fraction to KK. From PDG:
It cannot be fit with the interference of (770) , (1900) and (2150):
• The log-likelihood value worsens by 85 (2=170).
.).%95( 106.1))1450(( 3 LCKKBr
How to understand broad X(1580)?
Search of a similar structure in J/ KSK will help to determine its isospin.
X(1580) could have different nature from conventional mesons:
• There are already many 1- - mesons nearby.
• Width is much broader than other mesons.
• Broad width is expected for a multi-quark state.
M(+-0)(GeV/c2) M(+-0)(GeV/c2) M(+-0)(GeV/c2)
M(
+-0
)(G
eV/c
2 )
sideband
signal after best candidate selection (best masses)
signal with multiple entries
0 ,/ J
Phys. Rev. D 73 (2006) 112007
0-+ Meson
Eff. curve
Phase Space Side-bandM() M()
(1760) f0(1710)f0(1790)f0(1810)
PWA analysis
M()
Total
f2(1910) f2(160) BGUsing observed mass and width for f0(1810)in J/
f0(1710)
f2(1910)
f2(1640)
BG
(1760) > 10
f0
M() (GeV/c2)
The existence of (1760) is confirmed Its mass and width were first correctly measured with PWA.
3-
22421
2
100.32)0.08(1.98
))1760(())1760(/(
MeV/c 25244
MeV/c 15101744
BrJBr
M
Phys. Rev. D 73 (2006) 112007
Study of Excited Baryon States
Motivation
Probe the internal structure of light quark baryons
Search for missing baryons predicted by quark mod
el
Obtain a better understanding of the strong interacti
on force in the non-perturbative regime
Experimental Advantages
processes branching ratios(10-
3)N* decays
2.00.1
6.00.5
2.00.1
2.10.2
0.90.4
1.30.3
0/ ppJ ppJ /
relatively large branching ratios
npJ / ppJ /
'/ ppJ ppJ /
NN *
NN *NN *
NN *NN '* NN *
58 M J/ and 14 M (2S) at BES II
Pure isospin 1/2
Feynman diagram of the production
of
For and ,
and systems are limited to be pure isospin 1/2.
**,*,*, Np
NNJ / NNJ / N
N
N* in .
Phys. Rev. Lett. 97, 062001 (2006)
npπJ/ψ
N* in +c.c.
L=0 limits it to be
3/2+ or 1/2+
npπJ/ψ
N*(1440)
N*(1520)
N*(1535)
N*(1650)
N*(1675)
N*(1680)
?
npπJ/ψ nπpJ/ψ
About 10 K events are selected N*(1440) is observed directly in the mass spec
trum Possible new N* resonance
L=0 limits it to be 3/2+ or 1/2+ Detailed information need PWA
N* in +c.c.
221540- MeV/c 4014165 ,MeV/c 3 2068 M
npπJ/ψ
(2S) p . .n c c
Phys. Rev. D74, 012004 (2006)
Large accumulation below 1.5 GeV/c2 ，
which may be due to N(1440), N(1520),N(1535) etc.The cluster above 2 GeV/c2 is partlydue to the reflection of N(1440) etc.,and partly may due to high mass N*.No clear N(2065) peak, but we can notrule out its existence.
N* in . 0ppJ/
M
0
)p(M 02
M2(p0
)
N* in . 0ppJ/
0pM
0p
M
N* in . 0ppJ/ Resonances used in the PWA
N* in . 0ppJ/
data
Fit results
Fit results agree with data reasonably, especially in the low mass region.
N* in . 0ppJ/
Optimized masses and widths,
other resonances are fixed.
N* in . 0ppJ/
More than 10 K events were selected, and detailed PWA was performedN(2065) is needed in the fit, and JPC favor 3/2+
Only N(1710) is needed in the M = 1.7 GeV regionThe masses and widths of some other N* have also been given
3 2 2-4M 2040 25 MeV/c , 230 8 56 MeV/c
0(2S) pp ( )
A faint accumulation of events around 2065 MeV/c2
The enhancement between 1.4 and 1.7 GeV/c2
Possible N*(1535) in the p invariant mass
Phys. Rev. D71, 072006 (2005)
0
-J/ψ pK Λ+c.c.
-J/ψ pK Λ+c.c.
Phys. Rev. Lett. 93, 112002 (2004)
For a S-wave BW fit: M = 2075 12 5 MeV Γ = 90 35 9 MeV
-J/ψ pK Λ+c.c.
Two clear peaks at 1520, 1690 MeV/c2 in pK mass N* in K mass PWA is being performed
N*(1535)?
N*(1650)?*(1520) *(1690)
pKM KM
PS, eff. corrected(Arbitrary normalization)
MMM KΛK
A strong enhancement is observed near the mass threshold of MK at BES II.
Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure Nx*has:
Mass 1500~1650MeV
Width 70~110MeV
JP favors 1/2-
The most important is:
It has large BR(J/ψ pNX*) BR(NX* KΛ) 2 X 10-4 ,
suggesting NX* has strong coupling to KΛ.
A ΛK resonance predicted by chiral SU(3) quark model
Based on a coupled-channel study of ΛK and ΣK states in the chiral SU(3) quark model, the phase shift shows the existence of a ΛK resonance between ΛK and ΣK mass threshold.
( F. Huang, Z.Y. Zhang et al. Phys. Rev. C71: 064001, 2005 )
Ecm – ( MΛ+MK ) (MeV)
The KΛ mass threshold enhancement NX(1610) could be a KΛ bound/resonant state.
Whether NX(1610) is N(1535) needs further study.
0SnKJ/
KS
A enhancement near S threshold is evident
N* and * found in the S and nS spectrum
0SnKJ/
N* *
tested.rule" "12%
observed.symmetry SU(3) sample. data 2larger
a with BR remeasure BESI,by t measuremenFirst
S
)c/GeV(m 2
p
00
)c/GeV(m 2
p
)c/GeV(m 2
p
x 10-4 x 10-4
Angular distribution:2
Baryonic decays
Rich structure (N*s), statistics (~850 evts in each mode). Still low for a partial wave analysis.
PRD74, 012004 (2006)
2006 062001, PRL97,
obtained events 000,100
../ ccnpJ
27.091.1:27.086.1:1)'(:)'(:)'( 0 npBnpBppB
Test I-spin symmetry(prediction: 1:2:2)
’(J/) +0/ Is it really B(0)>B()?
arXiv: 0707.1127 [hep-ex]Submitted to PRD
First measurement!
background fromJ/ ΣΛπ
signal
J/ with 0p, p +
Clear is seen,
B(J / + c.c. ) = 1.52±0.08±0.16)10-3
BEPC II
Energy range 1 – 2.1 GeV
Optimum energy 1.89 GeV
Luminosity 1 x 10 33 cm-2s-1 @ 1.89 GeV
Injection Full energy injection: 1.55 1.89 GeV Positron injection speed > 50 mA/min
Synchrotron mode 250 mA @ 2.5 GeV
Upgrade of BEPCDouble-ring collider, 93 bunchesHigh luminosity
Design Goal
Magnet: 1 T Super conducting
MDC: small cell & He gas xy=130 m p/p = 0.5% @1GeV dE/dx=6%
TOF: T = 100 ps Barrel 110 ps Endcap
Muon ID: 9 layer RPC
EMCAL: CsI crystal E/E = 2.5% @1 GeV z = 0.6 cm/E
Trigger: Tracks & ShowersPipelined; Latency = 6.4 s
Data Acquisition: Event rate = 3 kHz Thruput ~ 50 MB/s
BESIII Detector
The detector is hermetic for neutral and charged particle with excellent resolution , PID adequate, and large coverage.
Resonance Energy(GeV)
Peak Lum.(1033cm-2s-1)
Physics Cross Section (nb)
Nevents/yr
J/ 3.097 0.6 3400 10 109
3.670 1.0 2.4 12 106
(2S) 3.686 1.0 640 3.2 109
D0D0bar 3.770 1.0 3.6 18 106
D+D- 3.770 1.0 2.8 14 106
DsDs 4.030 0.6 0.32 1.0 106
DsDs 4.140 0.6 0.67 2.0 106
Average Lum: L = 0.5×Peak Lum.; data taking time: T = 107s/year
Yearly Event Production
Huge J/ and (2S) samples at BESIII
Two rings are commissioned with normal quadrupole magnets,
with 100 mA in each beam of 20 bunches, with a luminosity clos
e to 1031 .
Two periods providing synchrotron Radiation users with a m
ax. current of 180 mA at 2.5 GeV.
SCQ and Detector SC magnet have been tested and fields wer
e measured.
Most detectors are assembled, will be fully assembled end of 2
007, and cosmic ray for 2 months, to the beam line end of March
2008.
Commissioning machine/detector together next summer.
Some test runs, luminosity to reach 31032 end of 2008 .
Summary
New states are observed in the hadron spectroscopy:
, , X(1835) in J/ ’, X(1580) in J/ KK, enhancement in J/ , (1760) in J/ ;
Excited baryons, N* observed in J/ pn ; J/ pp0 ; J/ nKS; Compared with (2S) decay;
Some N*, as N*(1535), N*(2065) better measured.
Some BF involving baryons are measured;
BEPCII/BESIII should collect data in 2008.
Thanks
0
5
10
15
20
25
30
MKI MKII MKIII CBAL BESI BESII CLEO CLEOc
(2s) data samples’ decays
Leptonic decays
Radiative decays
Hadronic decays
cJ decays
VV
PPP
3M
14M
4M
outline
26M
Also 6.42 pb-1 of data at Ecm=3.65 GeV for background study.
Discussion on KΛ mass threshold enhancement NX(1610)
NX(1610) has strong coupling to KΛ:• From (S&D-wave d
ecay) and is a P-wave decay, we can estimate
• From BESII,
• The phase space of NX to KΛ is very small, so such a big BR shows NX has very strong coupling to KΛ, indicating it has a big hidden ssbar component. (5-quark system)
3102)/( ppJBR )1600(/ XpNJ
3100.1)/( XpNJBR
4102~)()/( KNBRpNJBR XX
%20)( KNBR X
Non-observation of NX in suggests an evidence of new baryon :
It is unlikely to be N*(1535). If NX were N*(1535), it should be observed
in process, since:
•
• From PDG, for the N* in the mass range 1535~1750 MeV, N*(1535) has the largest , and from previous estimation, NX would also have almost the largest BR to KΛ.
Also, the EM transition rate of NXto proton is very low.
Kp
Kp)*()*()*( KNBRpNBRKNp
)*( pNBR
