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Recent BESII Results and Future Prospects
Zhipeng ZHENG
Representing BES Collaboration
Institute of High Energy Physics, CAS
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Outline
Introduction
New observations at BESII
Study of the scalars
BESIII/BEPCII project
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Beijing Electron Positron Collider (BEPC)
L ~ 51030 /cm2s at J/ Ebeam~ 1 – 2.5 GeV
BESI started running in 1989BESII started running in 1997BESIII will start running in 2008
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0
10
20
30
40
50
60
CBA L 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
0
5
10
15
20
25
30
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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BEPC / BESBEPC / BES
mass measurementR measurementNew states in J/→pp … Candidates for Glueball
J/, ’, D and Ds physics … ̄  ̄
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Tau mass measurement, ( 1991 - 1992 )
World average (1991) BES result:
MeVm 7.26.31.1784
MeVm 30.027.096.1776
025.0941.0
g
g 0069.00005.1
g
g
Universality for lepton is stand up
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tau mass fit
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- universality comparation from 1992 to 1996
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BEPC/BES R measurement
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New observations at BESII
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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 0.33-body phase space
acceptance
2/dof=56/56
acceptance weighted BW +3 +5
10 25
pp
BES II
Phys. Rev. Lett. 91, 022001 (2003)
X(1860)
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X(1860) has large BR to pp
BES measured:
From Crystal Ball result, we estimate:
So we would have:
5107~))1860(())1860(/( ppXBRXJBR
3102))1860(/( XJBR
%4))1860(( ppXBR
Considering that decaying into pp is only from
the tail of X(1860) and the phase space is very small,
such a BR indicates X(1860) has large coupling to pp !
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B+ pp K+ at BaBar and Belle
BaBar
210 fb-1
Belle
BES II
ppJ / The pp threshold enhancement observed in J/ decay is different from the enhancements observed by Belle and BaBar in B decay.
The one in B decay can be explained by fragmentation.
X(1860)
KppB
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This result cannot be explained by pure FSI effect, since FSI is a universal effect.
FSI interpretation of the narrow and strong pp threshold enhancement is disfavored.
This narrow threshold enhancement is NOT observed in (1S)pp at CLEO
No enhancement near threshold
CL
JBrSBr
%90@%7.0
)X /(/)X )1((
PRD73, 032001(2006)
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This again disfavors FSI’
This narrow threshold enhancement is NOT observed in at BESII
No narrow strong enhancement near threshold
CL
JBrJBr
)X /(/)X/(
BESII Preliminary
ppJ /
Observations of this structure in other decay modes are desirable.
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Search for the strong mass threshold enhancement X(1860) in
A strong mass threshold enhancement was observed in
• No obvious strong mass threshold enhancement was observed in
acceptance
X(1860)
Fit
CL
ppXSB
))1860()2((6
pp
pp pp
ppS )2(
ppS )2(ppJ /
M(pp)-2mp (GeV)
0 0.1 0.2 0.3
M=1859 MeV/c2
< 30 MeV/c2 (90% CL)
+3 +510 25
5107~
))1860(/(
ppXJB
acceptance
BESII preliminary
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Statistical Significance 7.7
X(1835)7.7
2
2
MeV/c 7.73.207.67
MeV/c 7.21.67.1833
54264
M
Nobs
410)4.04.02.2()()( XBXJB
PRL 95 (2005) 262001
BES: X(1835) in '/J
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M = 1830.6 6.7 MeV
= 0 93 MeV
In good agreement with X(1835)
Include FSI curve from A.Sirbirtsev et al.(hep-ph/ 0411386) in the fit (I=0)
Fit to J/ pp including FSI
BES II Preliminary
I=0
I=1
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X(1835) could be the same structure as pp mass threshold enhancement.
It is likely to be a pp bound state since it dominantly decays to pp when its mass is above pp mass threshold.
’ mode is expected to be the favorable decay mode for a pp bound state below pp mass threshold
G.J. Ding and M.L. Yan, hep-ph/0502127
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Observation of p mass threshold enhancement in
J/pK-
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Observation of an anomalous enhancement near the threshold of mass spectrum at BES IIp
BES II pKJ /
3-body phase space
For a S-wave BW fit: M = 2075 12 5 MeV Γ = 90 35 9 MeV
Phys. Rev. Lett. 93, 112002 (2004)
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K- mass threshold enhancement
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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*
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A strong enhancement is observed near the mass threshold of MK at BES II.
Preliminary PWA with various combinations of possible N* 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.
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Observation of thresholdenhancement in J/
) ,( 0 KK
OZI DOZI KKJ ,/ /J
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M(+-0)
M(K
+K-
)
M(K+K-)
MeVMMKK
15||
MeVMMMeVKK
35||20
M(+-0)
Dalitz plot
Clear and signals
M2()
M2 (
)
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A clear threshold enhancement is
observed
Eff. curve
Phase Space
Side-bands
Side-bands do not have mass threshold enhancement!
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PWA shows: the enhancement favors 0++ over 0-+ and 2++
.
Is it the same 0++ observed in KK or (f0(1710), or f0
(1790)), or is it a glueball, or a hybrid …..?
2
21926
MeV/c 2820105
MeV/c 181812
M
Further look in , K*K*, …. is desirable !
410)65.027.061.2()()/( XBrXJBr
Phys. Rev. Lett., 96 (2006) 162002
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New observation of a broad 1-- resonance in J/ K+K- 0
Phys. Rev. Lett. 97 (2006) 142002
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J/ K+K-0
0
background 0 sideband
?
K*(892)
K*(1410)
X(1580)
PID and kinematic fit can significantly reducethe dominant background from J/ + - 0.
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What is the broad resonance? 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
Br
Big destructive interference among X, (1700) and PS 47.2
6.3-0 10)6.05.8( )KKX ,Xπ(J/ψ
232 1167 12
98 4991 55 MeV/c )409()1576(
i
1-- component
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Study of the scalars
There have been hot debates on the existence of and .
Lattice QCD predicts the 0++ scalar glueball mass in the range 1.5 - 1.7 GeV.
f0(1500) and f0(1710) are good candidates.
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study in
study in
study f0(980), f0(1370), f0(1500), f0(1710) and f0(1790) in
/' ,/ JJ
KKKKJ and / *
, / KKJ ,,
0++
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The study of evidence for a low mass pole in the early D
M2 and BESI data on J/ .
huge event concentration in the I=0 S-wave channel seen in M ~ 500 – 600 MeV in the pp central production exp.
to explain scattering phase shift data , should be introduced in chiral perturbative theory.
FNAL E761 exp. D+ +-+ dataMeV 21324 MeV, 17478 42
402423
M
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The pole in at BESII /J
M(+-)
BES, PLB 598 (2004) 149
MeV )42252()39541( i
Different parameterizations of BW are used in PWA.
Averaged pole:
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observation of in ’+-J/ Measure the universal pole position (552 - i232 MeV) World largest signal (with ~ 40,000 tagged events)
Phys. Lett. B 645 (2007) 19
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The study of A possible pole is controversial. Some analyses of LASS K scattering data need (800), some don’t.
Scadron et al. favors a nonet made up of , (800), f0(980) and a0(980).
Julich group used t-channel exchanges to explain K scattering data.
evidence of in FNAL E791 data on D+ K-++
slightly lower statistics of CLEO D0 K-+0 data find no evidence of
FOCUS data on K+K-++ require K*0 interfere with either a constant amplitude or a broad 0+ resonance in K
MeV 8743410 MeV, 4319797 M
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PWA result:
is needed in the fit.
Pole position of :
BES observed in J/K*KKK
BES II58 M J/
24872
8173 MeV/c )45309()30841(
i
Phys. Lett. B 633 (2006) 681
A possible pole is controversial.
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Lattice QCD:
the lightest scalar glueball in the region of 1.5- 1.7 GeV
Glueball searches should be performed in simultaneously.XXXJ ,,/
Study of other scalars
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0++ states: f0(980), f0(1370), f0(1500), f0(1710), f0(1790)
PDG 2006 values:
f0(980): M = 980 10 MeV, = 40 – 100 MeV
, KK
f0(1370): M = 1200 – 1500 MeV, = 200 – 500 MeV
2, 4, KK …
f0(1500): M = 1507 5 MeV, = 109 7 MeV
2, 4, , ’, KK …
f0(1710): M = 1714 5 MeV, = 140 10 MeV
2, 2K, 4, , ’ …
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Important parameters from PWA fit:
Large coupling with KK indicates big component in f0(980)
/J
KKJ /
f0(980)
21.025.021.4
1510165
68965
g
g
MeVg
MeVM
KK
ss
f0(980)
f0(980)
Phys. Lett. B 607 (2005) 243
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There has been 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)
MeV
MeVM
40265
501350
Phys. Lett. B 607 (2005) 243
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Clear f0(1710) peak in J/ KK.
No f0(1710) observed in J/ !
f0(1710)
KKJ /
/J
f0(1710)
NO f0(1710)
MeV
MeVM
20125
301740
CLKKfBR
))1710((
))1710((
0
0
Phys. Lett. B 603 (2004) 138
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KKJ /
00/ ss KKJ
)1710(0f
)1710(0f
MeV 166
MeV 41740155108
1025
M
PWA analysis shows one scalar in 1.7 GeV region
Phys. Rev. D 68 (2003) 052003
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A clear peak around 1790 MeV is observed in J/ .
No evident peak in J/ KK. If f0(1790) were the same as f0(1710), we would have:
Inconsistent with what we observed in J/ , KK
New f0(1790)??
/Jf0(1790)
KKJ /
?
MeV
MeVM6030
4030
270
1790
5.1~))1710((
))1790((
0
0
KKfBR
fBR
CLKKfBR
))1710((
))1710((
0
0
f0(1790) is a new scalar ??
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Scalars 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
Phys. Lett. B 642 (2006) 441
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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), f0(1710) and f0(1790)
f0(1710): It dominantly decays to KK (not to ) It is mainly produced together with (not ) What is it ?
f0(1370) and f0(1790) They dominantly decays to (not to KK) It is mainly produced together with (not ) What are they ?
Scalar Puzzle
dduu
dduu
ss
ss
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Future Prospects
BESIII/BEPCII project.
Government approved. Started construction from the end of 2003.
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BEPCII: a high luminosity double–ring collider
SC RF
Two rings tunnel
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BEPCII Design goal
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
Dual purpose machine
May achieve to Ebeam = 2.3 GeV
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BESIII Detector
Be beam pipe
SC magnet Muon Counter
Drift Chamber
CsI(Tl) calorimeter
TOF
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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 Two rings, 93 bunches:
• Luminosity
1033 cm s @1.89GeV
6 1032 cm s @1.55GeV
6 1032 cm s @ 2.1GeV
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MDCParametersR inner: 63mm ; R outer: 810mm Length (out.): 2582 mm Inner cylinder: 1.2 mm Carbon fiberOuter cylinder: 11.5 mm CF with 8 windowsSense wire : 25 micron gold-plated tungsten (plus 3%Rhenium ) ---
6796 Layers (Sense wire ): 43
Expected performance
Field wire: 110 micron gold-plated Aluminum --- 21884Gas: He + C3H8 (60/40)Cell: inner chamber --- 6 mm
outer chamber --- 8.1 mm
%6~
@1GeV/C%5.0~
130~
dxdE
P
m
dx
dE
P
x
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Wire Stringing Completed, bad wires are replaced, glue used to make gas tight
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CsI(Tl) crystal calorimeter Design goals:
Energy: 2.5% @ 1GeV Spatial: 0.6cm @ 1GeV
Crystals: Barrel: 5280 w: 21564 kg Endcaps: 960 w: 4051 kg Total: 6240 w: 25.6 T
France
Sanit -Gobain
Shanghai Institute of Ceramics
Beijing
Hamamatsu
Total
Ordered 2040(960) 1920 1320 5280(960)
Arrived 2023(824) 1920 1320 5263(824)
Rejected
87 322 79 488
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Mechanical structure
A 1/60 prototype
Status: Assembly will start soon.
Should be completed early next year.
By the end of the year, all FED boards should be tested and installed.
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晶体支撑架和工装架
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All RPC production, assembly, testing, and installation completed.
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BEPCII Status and Plan
Dec. 2006, ring commissioning, beam accumulation, Synchrotron run.
Dec. 07, BESIII moved to the beam line. 2008, Commissioning ring and detector together, test ru
n. Dec. 08, to achieve a lum. of 31032cm-2s-1.
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BESIII Collaboration
Institute of High Energy PhysicsUniversity of Science and Technol
ogy Peking University Tsinghua University Shangdong University Nankai University Central China Normal University University of Anhui University of Zhejiang University of Zhengzhou Nanjing Normal University Nanjing University Shanxi University Sichuan University Henan Normal University
University of Hawaii University of Washington University of Tokyo Joint Institute of Nuclear R
esearch, Dubna GSI University of Bochum University of Giessen
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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
Nevent/year = exp L T
Yearly Event Production
Huge J/ and (2S) samples at BESIII
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J/ Physics at BESIII/BEPCII
Search for glueballs, hybrids and multi-quark states
Systematic study of light hadron spectroscopy
Study of the excited baryon states Search for more J/ decay channels Probing for new physics in J/ decays c physics
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New states : X(1860), X(1835), X(2075), X(1812), X(1580) were observed
and studies
Other scalars
BESIII/BEPCII will start taking data in 2008.
Summary Summary
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