Physics at BES Shan JIN (for the BESIII Collaboration) Institute of High Energy Physics (IHEP)...
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Transcript of Physics at BES Shan JIN (for the BESIII Collaboration) Institute of High Energy Physics (IHEP)...
Physics at BES
Shan JIN(for the BESIII Collaboration)
Institute of High Energy Physics (IHEP)
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
3
Linac Storage Ring
BES BSRF
Beijing Electron Positron Collider (BEPC) at IHEP
BESI: 1989-1998
BESII: 1999-2004
L ~ 51030 /cm2s at J/
Ebeam~ 1 – 2.5 GeV
BESIII: 2008- Physics run started in March, 2009. 100M (2S)
and 200M J/ events collected
BEPCII: L reached 31032/cm2s at (3770) designed L: 1033/cm2s
注入器长 202 米
储存环的周长为 240.4米
对撞能量 2-5GeV 物理目标
北京正负电子对撞机( BEPC )示意图
Why tau-charm physics is interesting
Abundant resonances(J/ family, huge Xsections) Tau-charm threshold production(in pairs tagging backg
round free, no fragmentation, kinematic constrains, quantum coherence,…)
Charm quark: A bridge between pQCD and non-pQCD A ruler for LQCD J/decayGluon rich environment Flavor physics Complementary to LHC: virtual vs real A broad spectrum & efficient machine:
in the past in the era of LHCin the future
bsd
tcu
e
e
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• mixing and CPV SM and beyond
Charmonium physics• Spectroscopy and transition pQCD & non-pQCD• New states above open charm thresholds exotic hadr
ons ?• pQCD: 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
DDhep-ex/0809.1869
Light hadron spectroscopy Motivation:
• Establish spectrum of light hadrons• Search for non-conventional hadron
s• Understand how hadrons are forme
d • Study chiral symmetry in QCD
Why at a tau-charm collider ?• Gluon rich• Larger phase space than at higher e
nergies • Clean environment, JPC filter
Glueball spectrum from LQCDGlueball spectrum from LQCD
Y. Chen et al., PRD 73 (2006) 014516
Many results in BESII: ~ 50 publicationsMuch more from BESIII:100 statistics, 10 resolution
Multi-quark State, Glueball and Hybrid
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 )
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 n
on-pQCD• Calibrate LQCD• How quarks form a ha
dron ?
Why at a tau-charm collider ?• A clean environment • Tagging possible • Abundantly produced
Examples of interesting/long standing issues: • puzzle• Missing states ?• Mixing states ?• New states above open charm thre.(X,Y,Z,…)
Highlights at BESII
BESII
VC: xy = 100 m TOF: T = 180 ps counter: r= 3 cm MDC: xy = 220 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.5 % = 7.9 mr B field: 0.4 T p/p=1.7%(1+p2) z = 2.3 cm
World J/ and (2S) Samples (106)
J/ (2S)
0
10
20
30
40
50
60
MarkI I I DM2 BES I BES I I
0
2
4
6
8
10
12
14
MKI MKII MKIII CBAL BESI BESII
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)
At BESII: Observation of X(1835) in
The +- mass spectrum for decaying into +- and
Statistical Significance 7.7
JBESII
J
MeVm 7.21.67.1833
MeV7.73.207.67
Phys. Rev. Lett. 95, 262001 (2005)
The same origin as ppbar mass threshold? a ppbar bound state?
BES II
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)
M2()
M2 (
) BackgroundX(1810)
Observation of mass threshold structure X(1810) in J/ at BESII
M()
Phys. Rev. Lett., 96 (2006) 162002
2
21926
MeV/c 2820105
MeV/c 181812
M
Jpc favors 0++
Possible theoretical interpretations: glueball, hybrid, multiquark?
BES II
)1580(X
Background
0)1580(X
Very broad 1- - resonance X(1580) observed in K+K- mass spectrum in J/ K+K-0 at BESII
1
MeV/c )818(2
)1576(2
264 22133 23
98 4991 55
PCJ
iiM
Phys. Rev. Lett. 97 (2006) 142002
So far the only reasonable interpretation is a multiquark statedue to its very broad width
BES II
σ at BES BES II observed σ in J/ +-.
Pole position from PWA:
BES II
M
MeVi )42252()39541(
κ at BESII
BESII firmly established neutral in J/ K*0K KK in 2006:
PWA result
Pole position:
BES II
24872
8173 MeV/c )45309()30841(
i
Observation of charged at BESII
New result: Charged observed at BESII in
Different parameterizations are tried in PWA.
The pole position:
0*/ KKKJ s
M(K0) GeV/c2
BESII Preliminary
K*(1410), K*(1430)26430
1428 MeV/c )101288()51841(
i
consistent with neutral
QCD studies at low energies Understand where exactly pQCD becomes invalid Precision measurement of s running
Precision measurement of R input to Related to QED (s), prediction of higgs mass and g-2
A new measurement at BESII on R• Precision at ~ 3.5%
• A new determination of s(s):
s(M2Z) = 0.1170.012
?
Phys.Lett.B677,(2009)239
Ecm(GeV)
L(pb-1) R s(S)
2.60 1.222 2.180.020.08
3.07 2.291 2.130.020.07
3.65 6.485 2.140.010.07
In good agreement with previous results
BESIII: < 2%
Resonance parameter fit Heavy charmonia parameters were fitted with the data betwee
n 3.7–5.0GeV, taking into accounts the phase angles, interference, energy-dependent width, etc.
Phys. Lett. B660, (2008)315
Probability =31.8%
PRL101 (2008) 102004
Black dots: dataRed dots: data subtracting J/and continuum contribution
Green line: fit with one (3770) hypothesis;Red line: fit with two cross sectionBlue line: fit with two amplitude
Anomalous (3770) lineshape
Check all lines !!!
quantity Two AM Two AM One AM Y(3770)+G(3900)
2 125/103 112/102 182/106 170/104
(3686) (MeV) 3685.50.00.5 3685.50.00.5 3685.50.00.5 3685.50.00.5
M1 (MeV) 3765.02.40.5 3762.611.80.5 3773.30.50.5 3774.40.50.5
M2 (MeV) 3770.50.60.5 3781.01.30.5 3943.0(Fixed)
Status of BESIII and preliminary results
BEPC II Storage ringBEPC II Storage ring:: Large angle, double-ring
RFRF SR
IP
Beam energy: 1.0-2 .3GeVLuminosity: 1×1033 cm-2s-1
Optimum energy: 1.89 GeVEnergy spread: 5.16 ×10-4
No. of bunches: 93Bunch length: 1.5 cmTotal current: 0.91 A
BESIII detector
BESIII Commissioning and data taking milestones Mar. 2008: first full cosmic-ray eventApril 30, 2008: Move the BESIII to IPJuly 18, 2008: First e+e- collision event in BESIIINov. 2008: ~ 14M (2S) events collectedApril 14, 2009 ~100M (2S) events collectedMay 30, 2009 42 pb-1 at continuum collectedJuly 28, 2009 ~200M J/ events collected
Peak Lumi. @ Nov. 2008: 1.2 1032cm-2s-1 Peak Lumi. @ May 2009: 3.21032cm-2s-1
Detector performance and calibration
● Layer 7● Layer 22
Wire reso. Design: 130 m
dE/dx reso.: 5.80%Design : 6-8%
CsI(Tl) energy reso. Design: 2.5%@ 1 GeV
Barrel TOF reso.: 78 psDesign : 80-90 ps
Bhabha
E1 transitions: inclusive photon spectrum
c2c1
co
c1,2 J/
c
BESIII preliminary
Observation of hc: E1-tagged (2S)0hc,hcc
Select E1-photon to tag hc
A fit of D-Gaussian signal+ sideband bkg. yield:
M(hc)Inc = 3525.16±0.16±0.10 MeV
(hc)Inc = 0.89±0.57±0.23 MeV (First measurement)
Br(’hc )×Br(hcc )Inc =(4.69±0.48(stat)) ×10-4 ((hc) floated) =(4.69±0.29(stat)) ×10-4 ((hc) fixed at (c1))
background subtracted
Systematic errors under study
CLEO’s results (arXiv 0805.4599v1) : M(hc)Inc= 3525.35±0.23±0.15 MeV Br(’hc )×Br(hchc )Inc =(4.22±0.44±0.52) ×10-4 ((hc) fixed at (c1) ~0.9MeVCLEOc: Combined E1-photon-tagged spectrum and exclusive analysis M(hc)avg= 3525.28±0.19±0.12 MeV Br(’hc )×Br(hchc )avg =(4.19±0.32±0.45) ×10-4
BESIII preliminary
BESIII preliminary
N(hc)= 2540±261 2/d.o.f = 39.5/41.0
(arXiv 0805.4599v1)
Observation of hc : Inclusive (2S)0hc
Select inclusive 0
A fit of D-Gaussian signal + 4th Poly. bkg yield
N(hc) = 9233±935, 2/d.o.f = 38.8/38.0
Combined inclusive and E1-photon-tagged spectrum
Br(’hc ) =(8.42±1.29(stat)) ×10-4 (First measurement)
Br(hcc) =(55.7±6.3(stat))% (First measurement)
31
background subtracted
Inclusive recoil mass spectrum
Systematic errors under study
BESIII preliminary
BESIII preliminary
BR (10-3) c0 c2
00 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
Study of (2S)→ 00 , → , 0 → 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.
2S)00
Nc0 16645±175 Nc2 4149±82
2S)
Nc0 1541±56 Nc2 291±23
Confirmation of the BESII observation: pp threshold enhancement in J/decays
PRL 91 (2003) 022001
/J pp
BES III preliminary
(2S)→ J/
M=1864.6 ± 5.3MeV/c2
< 33 MeV/c2 (90% CL)
M=1859 MeV/c2
< 30 MeV/c2 (90% CL)
+3 +510 25
0.3
/J pp BES II
M(pp)-2mp (GeV)
Confirmation of BESII observation: No pp threshold enhancement in ’ decays
No significant narrow enhancement near threshold(~2 if fitted with X(1860))
Mpp (GeV)
BES III preliminary
PRL 99 (2007) 011802
BES II
No enhancement in ’ decays
pp pp
In fact, no enhancement in ψ’ ,ϒ(1S) decays and in the process of J/ ppbar show that FSI unlikely .
0c1c
2c
Study of cJ VV, V= Test QCD-based theory at cJ decays
Puzzles for c0 VV: no helicity suppress
c1 highly suppressed owing to symmetry of identical particles
c1 OZI doubly suppressed
BESIII preliminary
0c 1c 2c
c0 f or KKm K K c1 f or KKm K K c2 f or KKm K K
BESII results:
BR(10-
3)c0 c2
0.930.20 1.50.3
2.30.7 2.00.7
• Backgrounds from sideband & 100M MC events
• Clear c1 signal
• to be understood
(GeV)K K
m
(GeV)m
0
First observation of c1
Background from sideband & 100M MC events Clear signal from c1 (K+K-)
0c
1c2c
BESIII preliminary
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: Leptonic and semi-leptonic decays
Vcb: Hadronic decays Vtd /Vts: fD and fDs from Leptonic decays Vub: 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 SMand 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 s at low energies Hadron production at J/’, and continium Multiplicity and other topology of hadron eve
nt BEC, correlations, form factors, resonance,
etc.
R-value measurement
Error on R (5)had (MZ
2)
5.9% 0.02761 ±0.00036
3% 0.02761 ±0.00030
2% 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:
• 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.
510~)()/( hhGBRGJBR
310 210
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 (J/ G).
• 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/KK• It was observed at BES I in J/KK, , ppbar• It was not observed at DM2.
BES-I (2230) Result
(2230)
The situation at BESII
The mass plots shows no evident (2230) peaks in J/KK, , ppbar, 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) .
00/ ss KKJ
KKJ /
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/ G)xBR(Ghh) 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
No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in
Again:• LQCD reliable?• Production rate could be v
ery low.• Glueball width could be ve
ry large.
...',
*,*,,/
KKKKJ
'M
)1835(X
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 shutdo
wn, ~5 months until next summer Possible plans:
• 500-1000 M J/events (2-4 months)• 500-1000 M (2s) (2-4 months)• 2fb-1 (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)• Novosibirsk(super tau-charm factory)• Fermilab
TeV fixed target exp. ? Ppbar exp. ?
To be decided in Nov.
L ~ 1035-36 cm-2s-1
Expand the life time of tau-charm colliders to > 50 years !