Transcript New Results from BES

Physics at BES
Shan JIN
(for the BESIII Collaboration)
Institute of High Energy Physics (IHEP)
[email protected]
USTRON09, Poland
September 12-16, 2009
Outline
 Introduction of BES experiments and
Physics at BES
 Highlights at BESII
 Status of BESIII and preliminary results
 Future prospects at BESIII
 Conclusion
Beijing Electron Positron Collider (BEPC) at IHEP
Linac
Storage Ring
BESI: 1989-1998
BESII: 1999-2004
L ~ 51030 /cm2s at J/
Ebeam~ 1 – 2.5 GeV
BSRF
BES
BESIII: 2008Physics run started in March, 2009. 100M (2S) and
200M J/ events collected
31032/cm2s
3
BEPCII: L reached
at (3770)
designed L: 1033/cm2s
北京正负电子对撞机（BEPC）示意图
储存环的周长为240.4米
注入器长202米
对撞能量2-5GeV
物理目标
Why tau-charm physics in the past
in the era of LHC
is interesting
in the future
 Abundant resonances(J/ family, huge Xsections)
 Tau-charm threshold production(in pairs tagging 
background free, no fragmentation, kinematic constrains,
quantum coherence,…)
 Charm quark: A bridge between pQCD and non-pQCD
 A ruler for LQCD
 J/decay  Gluon rich environment
 Flavor physics Complementary to LHC: virtual vs real
 A broad spectrum & efficient machine:
e


 e




  
u

d
c
s
t

b
What (highlight) physics interested us
 Light hadron spectroscopy
• Full spectra: normal & exotic hadrons QCD
• How quarks form a hadron ? non-pQCD
 Charm physics
• CKM matrix elements  SM and beyond
• D D mixing and CPV  SM and beyond
 Charmonium physics
hep-ex/0809.1869
• Spectroscopy and transition  pQCD & non-pQCD
• New states above open charm thresholds  exotic
hadrons ?
• pQCD: rp puzzle  a probe to non-pQCD or ?
 Tau physics and QCD
• Precision measurement of the tau mass and R value
 Search for rare and forbidden decays
Precision test of SM and search for new physics
Light hadron spectroscopy
 Motivation:
• Establish spectrum of light hadrons
• Search for non-conventional
hadrons
• Understand how hadrons are formed
• Study chiral symmetry in QCD
 Why at a tau-charm collider ?
• Gluon rich
• Larger phase space than at higher
energies
• Clean environment, JPC filter
Many results in BESII:
~ 50 publications
Much more from BESIII:
100 statistics,
10 g resolution
Glueball spectrum from LQCD
Y. Chen et al., PRD 73 (2006) 014516
Multi-quark State, Glueball and Hybrid

Hadrons consist of 2 or 3 quarks：
Naive Quark Model：
Meson（ q q ）
Baryon（q q q）

New forms of hadrons:
•
Multi-quark states ：Number of quarks >＝ 4
•
Hybrids ： qqg，qqqg …
•
Glueballs ： gg， ggg …
How quarks/gluons form a hadron is far from being well understood.
Multi-quark states, glueballs and hybrids have
been searched for experimentally for a very long
time, but none is established.
However, the effort has never been stopped,
especially, during the past three years, a lot of
surprising experimental evidences showed the
existence of hadrons that cannot (easily) be
explained in the conventional quark model.
Searches for new forms of hadrons are of
special importance at BES since J/psi decays are
believed as an ideal factory to search and to
study exotic hadrons.
Charmonium physics
 What to study ?
• Production, decays,
transition, spectrum
 For what ?
• A lab for pQCD and
non-pQCD
• Calibrate LQCD
• How quarks form a
hadron ?
 Why at a tau-charm
collider ?
• A clean environment
• Tagging possible
• Abundantly produced
Examples of interesting/long standing issues:
• rp puzzle
• Missing states ?
• Mixing states ?
• New states above open charm thre.(X,Y,Z,…)
Highlights at BESII
BESII
VC: xy = 100 m
TOF:
MDC: xy = 220 m
BSC:
dE/dx= 8.5 %
p/p=1.7%(1+p2)
T = 180 ps
E/E= 22 %
 = 7.9 mr
z = 2.3 cm
 counter: r= 3 cm
z = 5.5 cm
B field: 0.4 T
World J/ and (2S) Samples (106)
(2S)
J/
60
14
50
12
10
40
8
30
6
20
4
10
2
0
0
MarkIII
DM2
BESI
BESII
MKI
MKII
MKIII
CBAL
BESI
BESII
Observation of an anomalous enhancement near
the threshold of pp mass spectrum at BES II
BES II J/gpp
acceptance
weighted BW
M=1859 +3 +5 MeV/c2
-10 -25
G < 30 MeV/c2 (90% CL)
c2/dof=56/56
0
Phys. Rev. Lett. 91, 022001 (2003)
3-body phase space
0.1
0.2
M(pp)-2mp (GeV)
acceptance
0.3
At BESII: Observation of X(1835) in
 J   g p p 
Statistical Significance 7.7 
BES II
BESII J   g p p - 
m  1833.7  6.1  2.7MeV
G  67.7  20.3  7.7MeV
The same origin as ppbar
mass threshold?
 a ppbar bound state?
Phys. Rev. Lett. 95, 262001 (2005)
The p+p- mass spectrum for  decaying into
p+p- and  gr
Observation of an anomalous enhancement near
the threshold of p mass spectrum at BES II
BES II
J /  pK
3-body phase space
Phys. Rev. Lett. 93, 112002 (2004)
For a S-wave BW fit: M = 2075 12  5 MeV
Γ = 90  35  9 MeV
Observation of w mass threshold structure
X(1810) in J/  gw at BESII
BES II
M2(g)
X(1810)
Background
M2(gw)
2
M  1812 -19

18
MeV/c
26
G  105  20  28 MeV/c
2
M(w)
Jpc favors 0++
Phys. Rev. Lett., 96 (2006) 162002
Possible theoretical interpretations:
glueball, hybrid, multiquark?
Very broad 1- - resonance X(1580) observed in
K+K- mass spectrum in J/ K+K-p0 at BESII
BES II
X (1580
)
0
p
X (1580)
Background
M-
i
i
49  98
 22  64
2
G  (1576 -55
)
(
818
)
MeV/c
-91
- 23 -133
2
2
J PC  1- Phys. Rev. Lett. 97 (2006) 142002
So far the only reasonable interpretation is a multiquark state
due to its very broad width
σ at BES
 BES II observed σ in J/  wp+p-.
BES II
M p p  Pole position from PWA:
(541  39) - i (252  42) MeV
κ at BESII
BES II
 BESII firmly established
neutral  in J/  K*0Kp
 KpKp in 2006:
 PWA result
Pole position:
48
2
(841  30 -81
73 ) - i (309  45 - 72 ) MeV/c
Observation of charged  at BESII
New result: Charged  observed at BESII in
J /  K *   K sp  K p 0
 Different
parameterizations are tried in PWA.
BESII Preliminary
The pole position:
64
2
(841  51-14
28 ) - i ( 288  101-30 ) MeV/c
K*(1410), K*(1430)
consistent with neutral 

M(Kp0) GeV/c2
QCD studies at low energies
 Understand where exactly pQCD becomes invalid
 Precision measurement of as running
 Precision measurement of R
 input to
?
 Related to aQED (s), prediction of higgs mass and g-2
 A new measurement at BESII on R
• Precision at ~ 3.5% BESIII: < 2%
• A new determination of as(s):
as(M2Z) = 0.1170.012
Ecm(Ge
V)
L(pb-1)
R
2.60
1.222
2.180.020.08
3.07
2.291
2.130.020.07
3.65
6.485
2.140.010.07
as(S)
In good agreement with previous results
Phys.Lett.B677,(2009)239
Resonance parameter fit
 Heavy charmonia parameters were fitted with the data between
3.7–5.0GeV, taking into accounts the phase angles,
interference, energy-dependent width, etc.
Probability =31.8%
Phys. Lett. B660, (2008)315
Anomalous (3770) lineshape
Black dots: data
Red dots: data
subtracting J/,(3686)
and continuum
contribution
Green line: fit with one
(3770) hypothesis;
Red line: fit with two
cross section
Blue line: fit with two
amplitude
Check all lines !!!
PRL101 (2008) 102004
quantity
Two AM
Two AM
One AM
Y(3770)+G(3900)
c2
125/103
112/102
182/106
170/104
3685.50.00.5
3685.50.00.5
3685.50.00.5
3773.30.50.5
3774.40.50.5
M(3686) (MeV) 3685.50.00.5
M1 (MeV)
3765.02.40.5
3762.611.80.5
M2 (MeV)
3770.50.60.5
3781.01.30.5
3943.0(Fixed)
Status of BESIII
and preliminary results
BEPC II Storage ring: Large angle,
double-ring
RF
SR
RF
Beam energy:
1.0-2 .3GeV
Luminosity:
1×1033 cm-2s-1
Optimum energy:
1.89 GeV
Energy spread:
5.16 ×10-4
No. of bunches:
93
Bunch length:
1.5 cm
Total current:
0.91 A
BESIII detector
IP
BESIII Commissioning and data taking milestones
Mar. 2008: first full cosmic-ray event
April 30, 2008: Move the BESIII to IP
July 18, 2008: First e+e- collision event in BESIII
Nov. 2008: ~ 14M (2S) events collected
April 14, 2009 ~100M (2S) events collected
May 30, 2009 42 pb-1 at continuum collected
July 28, 2009 ~200M J/ events collected
Peak Lumi. @ Nov. 2008:
1.2 1032cm-2s-1
Peak Lumi. @ May 2009:
3.21032cm-2s-1
Detector performance and calibration
Wire reso.
● Layer
Design: 130 m
●
dE/dx reso.: 5.80%
Design：6-8%
7
Layer 22
Barrel TOF reso.: 78 ps
Design：80-90 ps
CsI(Tl) energy reso.
Design: 2.5%@ 1 GeV
Bhabha
E1 transitions: inclusive photon spectrum
cc2
cc1
cco
cc1,2g J/
c
BESIII preliminary
Observation of hc: E1-tagged (2S)p0hc,hcgc
background subtracted
BESIII preliminary
N(hc)= 2540±261
c2/d.o.f = 39.5/41.0


BESIII
preliminary
Select E1-photon to tag hc
Systematic errors
A fit of D-Gaussian signal+ sideband bkg. yield:
under study
M(hc)Inc = 3525.16±0.16±0.10 MeV
G(hc)Inc = 0.89±0.57±0.23 MeV (First measurement)
Br(’p0hc )×Br(hcgc )Inc =(4.69±0.48(stat)) ×10-4 (G(hc) floated)
=(4.69±0.29(stat)) ×10-4 (G(hc) fixed at G(cc1))
CLEO’s results (arXiv 0805.4599v1) :
M(hc)Inc= 3525.35±0.23±0.15 MeV
Br(’p0hc )×Br(hcghc )Inc =(4.22±0.44±0.52) ×10-4 (G(hc) fixed at G(cc1) ~0.9MeV
CLEOc: Combined E1-photon-tagged spectrum and exclusive analysis
M(hc)avg= 3525.28±0.19±0.12 MeV
(arXiv 0805.4599v1)
Br(’p0hc )×Br(hcghc )avg =(4.19±0.32±0.45) ×10-4
Observation of hc : Inclusive (2S)p0hc
background subtracted
BESIII
preliminary
Inclusive p0 recoil
mass spectrum
BESIII
preliminary
 Select inclusive p0
Systematic errors
under study
 A fit of D-Gaussian signal + 4th Poly. bkg yield
N(hc) = 9233±935,
c2/d.o.f = 38.8/38.0
 Combined inclusive and E1-photon-tagged spectrum
Br(’p0hc ) =(8.42±1.29(stat)) ×10-4 (First measurement)
Br(hcgc) =(55.7±6.3(stat))% (First measurement)
31
Study of (2S)→ gp0p0 , g ( → gg , p0 → gg )
 Interesting channels for glueball
searches
 Based on 110M (2S)
 BK study from 100M inclusive MC
sample and 42pb-1 continuum sample
 Unbinned Maximum Likelihood fit:
• Signal: PDF from MC signal
• Background: 2nd order Poly.
BR (10-3)
cc0
cc2
p0p0
BESIII
3.25±0.03(stat)
0.86±0.02(stat)
PDG
2. 43±0.20
0.71±0.08
CLEO-c
2.94±0.07±0.35
0.68±0.03±0.08
BESIII
3.1±0.1(stat)
0.59±0.05(stat)
PDG
2.4±0.4
<0.5
CLEO-c
3.18±0.13±0.35
0.51±0.05±0.06

CLEO-c arxiv:0811.0586
(2S)gp0p0
Ncc0 16645±175
Ncc2 4149±82
(2S)g
Ncc0 1541±56
Ncc2 291±23
Confirmation of the BESII observation:
pp- threshold enhancement in J/decays
BES II
J /  g pp
BES III preliminary
(2S)→ ppJ/
J /  g pp
0.3
M(pp)-2mp (GeV)
M=1859 +3 +5 MeV/c2
-10 -25
G < 30 MeV/c2 (90% CL)
PRL 91 (2003) 022001
M=1864.6 ± 5.3MeV/c2
G < 33 MeV/c2 (90% CL)
Confirmation of BESII observation:
- threshold enhancement in ’ decays
No pp
BES II
   g pp
BES III preliminary
   g pp
Mpp (GeV)
No significant narrow enhancement
near threshold
(~2 if fitted with X(1860))
PRL 99 (2007) 011802
No enhancement in ’ decays
In fact, no enhancement in ψ’ ,ϒ(1S) decays and
in the process of J/  wppbar show that FSI
unlikely .
Study of ccJ  VV, V=w,
 Test QCD-based theory at ccJ decays
 Puzzles for cc0  VV: no helicity suppress
 cc1  ,wwhighly suppressed owing to
symmetry of identical particles
 cc1  wOZI doubly suppressed
cc0
c c1
cc 2
BESII results:
BR(10-3) cc0
cc2

0.930.20
1.50.3
ww
2.30.7
2.00.7
• Backgrounds from sideband
& 100M MC events
• Clear cc1  signal
• to be understood
cc 2
BESIII preliminary
cc0
m KK for c c0   K  K -
m KK for c c1   K  K -
m KK for c c2   K  K -
c c1
First observation of cc1  w
m K  K - (GeV)
cc0
BESIII preliminary
c c1
  p p -p 0
cc 2
mp p -p 0 (GeV)
 Background from sideband & 100M MC events
 Clear signal from cc1  w(pp-p0/rp0)(K+K-)
Future prospects at BESIII
Event statistics at BESIII
Physics
Channel
Energy
(GeV)
Luminosity
(1033 cm–2s –1)
Events/year
J/
3.097
0.6
1.0×1010

3.67
1.0
1.2×107
’
3.686
1.0
3.0 ×109
D
3.77
1.0
2.5×107
Ds
4.03
0.6
1.0×106
Ds
4.14
0.6
2.0×106
*CLEO took 10 nb D production cross section while we took 5 nb
Precision measurement of CKM:
Branching rations of charm mesons




Vcd /Vcs:
Vcb:
Vtd /Vts:
Vub:
Leptonic and semi-leptonic decays
Hadronic decays
fD and fDs from Leptonic decays
Form factors of semi-leptonic
decays
 Unitarity Test of CKM matrix
CKM matrix elements measurement
Current
BESIII
Vub
25%
5%
Vcd
7%
1%
Vcs
16%
1%
Vcb
5%
3%
Vtd
36%
5%
Vts
39%
5%
Precision test of SM
and Search for new Physics
 DDbar mixing
DDbar mixing in SM ~ 10 –3 - 10 –10
DDbar mixing sensitive to “new physics”
Our sensitivity : ~ 10-4
 Lepton universality
 CP violation
 Rare decays
FCNC, Lepton no. violation,...
QCD and hadron production





R-value measurement
pQCD and non-pQCD boundary
Measurement of as at low energies
Hadron production at J/,’, and continium
Multiplicity and other topology of hadron
event
 BEC, correlations, form factors, resonance,
etc.
R-value measurement
Error on R
5.9%
3%
2%
a(5)had (MZ2)
0.02761 ±0.00036
0.02761 ±0.00030
0.02761 ±0.00029
Errors on R will be
reduced to 2% from
current 6%
Prospects of glueball searches
at BESIII
J/ decays are an ideal factory to search for
and study light exotic hadrons:
 The production cross section of J/ is high.
 The production BR of hadrons in J/ decays are
one order higher than ’ decays (“12% rule”).
 The phase space to 1-3 GeV hadrons in J/
decays are larger than  decays.
 Exotic hadrons are naively expected to have
larger or similar production BR to conventional
hadrons in J/ decays.
 Clean background environment compared with
hadron collision experiments, e.g., “JP, I” filter.
One Important Physics Goal of BESIII
With 1010 J/psi events, we hope to answer:
 Whether glueballs exist or not?
• Naively, we estimate in each exclusive decay mode:
BR ( J /  gG)  BR (G  hh) ~ 10-5
10 -3
10 -2
• If the eff. is about 20%, we would have 20000 events
for each decay mode
 we should observe a relative narrow (width:
50~200MeV) glueball if it exists.
Difficulties (I)
 Theoretically:
• Predictions on glueball masses from LQCD may be
unreliable due to quench approximation.
• No predictions on the widths so far (even the order).
• No prediction on the production rate G(J/  gG).
• Mix with qqbar mesons or even with 4q, qqg
mesons? (dirty?) What is the mixing mechanism
from the first principle?
Difficulties (II)
 Experimentally:
• Data sample is not big enough (it is not a problem
for BESIII)
• No good way modeling background at low energy, in
many cases we have to study bck via data.
• Interferences among mesons make the mass/Dalitz
plots very complicated 
 PWA is crucial for hadron spectroscopy at BESIII
 But PWA may face many uncertainties.
About scalar glueball
 Many scalar mesons in the mass range 1.4~1.8
GeV, where a scalar glueball is predicted to be.
More studies will be performed at BESIII.
 More theoretical studies are also needed:
•
•
•
•
Not only glueball mass, but also width
Decay patterns
Production rate in J/psi radiative decays
Mixing mechanism
2++ glueball candidates
 Lattice QCD predicts the 2++ glueball mass in
the range of 2.2~2.4 GeV
 (2230) was a candidate of 2++ glueball:
• It was first observed at MARKIII in J/gKK
• It was observed at BES I in J/gKK, gpp, gppbar
• It was not observed at DM2.
BES-I (2230) Result
(2230)
The situation at BESII
J /  gK  K -
J /  gK s0 K s0
 The mass plots shows no
evident (2230) peaks in
J/gKK, gpp, gppbar, which
is clearly different from BESI.
 Careful PWA is needed to
draw firm conclusion on its
existence since it may be still
needed in the PWA although
no clear mass peak observed.
 Difficult to draw firm
conclusion at present. We
hope to give a final answer at
BESIII on (2230) .
Other 2++ glueball candidates
 No other obvious good candidates have been
observed in J/psi radiative decays in the mass
range predicted by LQCD.
 What does it mean:
• LQCD prediction might not be very reliable, or
• BR(J/  gG)xBR(Ghh) is small ( <10-4 ) so that
we don’t have the sensitivity to observe it ( quite
possible ), or,
• The width of a glueball is very large ( ~1GeV,
E.Klepmt ).
Where to search for the 0-+ glueball?
 Lattice QCD predicts the 0-+ glueball mass in
the range of 2.3~2.6 GeV.
 (1440) and X(1835) were suggested being
possible candidates, but their masses are
much lower than LQCD predictions.
No 0-+ glueball candidate observed in the
mass range 2.3~2.6 GeV
X (1835)
 No evidence for a
relatively narrow state
( 100 ~ 200 MeV width )
above 2GeV in
J /   gKKp , gww , gK * K *,
gpp, g 'pp ...
 Again:
M  'pp
• LQCD reliable?
• Production rate could be
very low.
• Glueball width could be
very large.
Summary
 Physics at BES (tau-charm threshold) are very rich.
 There are many exciting discoveries at BESII.
 BESIII is operational since 2008:
• Detector performance excellent, ready for physics
• High quality data samples in hand
• Analysis in progress, papers in a few months
 With much more statistics of data sample and much
improved detectors at BESIII, more exciting discoveries
can be expected.
 Some fundamental questions, such as the existence of
glueballs, might be answered at BESIII with close
collaboration with theorists.
Thanks! 谢谢！
Prospects: a bright future
 BESIII will resume data taking after summer
shutdown, ~5 months until next summer
 Possible plans:
•
•
•
•
500-1000 M J/events (2-4 months)
500-1000 M (2s) (2-4 months)
To be decided in Nov.
-1
2fb (3770) (4 months)
Lineshape scan of (3770) (2 weeks)
 Future charm programs
• LHCb at CERN（soon）
• BELLE II at SuperB factory（~ 2014 ）
• PANDA at GSI（~ 2015）
 New programs under discussion:
• Frascati(super flavor factory)
L ~ 1035-36 cm-2s-1
• Novosibirsk(super tau-charm factory) Expand the life time of
• Fermilab
tau-charm colliders to
 TeV fixed target exp. ?
 Ppbar exp. ?
> 50 years !