Transcript BES-CLEOc Workshop

R Scan and QCD Study at BESIII
Haiming Hu
R Group, IHEP
January 13-15, 2004, Beijing
Outline
Motivation
R scan
QCD related topics
Summary
Motivation (R value)
R value is an important parameter in the test
of the Standard Model .
In 1998 -1999, two R scans were done in
2-5GeV with about error 7% at BES2.
In order to decrease the uncertainty of the
calculations of the Standard Model
parameters, more precision R measurement
at BES3 are appealed.
Motivation (QCD topics)
QCD is the unique candidate theory of strong
interaction.
QCD can describe the evolutions of the quark and
gluon with large momentum transferring.
QCD can not give complete calculations from the
primary qurks and gluons to hadrons.
 The knowledge of hadronization at low energy are
rather poor or even blank.
The pQCD needs more experiments to test and to
develop.
The low energy accelerators in the world
Ecm
DANE
(Italy)
VEPP2000
(Russian)
BEPC3 CLEO-c
(China)
(US)
0.5 – 1.4
0.5 –2.0
2 –4
3.1 – 12
1000
500
(GeV)
Luminosity 50 (500)
(1030cm-2s-1)
100
@3.70GeV
R value measurement
R values between 2-5 GeV at BES2
(1998 and 1999)
Broad resonant structure
R value status at some energy points
Phys.Rev.Lett.88,(2002)101802-1
Nhad
N+N
L(nb-1)
had
1+obs
2.0
1155.4
19.5
47.3
49.50
1.024
2.18
3.0
2055.4
24.3
135.9
67.55
1.038
2.21
4.0
768.7
58.0
48.9
80.34
1.055
3.16
4.8
1215.3
93.6
84.4
86.79
1.113
3.66
Ecm
(GeV)
R
Ecm
Nhad
trig
L
had
1+obs
2.0
7.07
0.5
2.81
2.62
1.06
8.13
3.0
3.30
0.5
2.30
2.66
1.32
5.02
4.0
2.64
0.5
2.43
2.25
1.82
4.64
4.8
3.58
0.5
1.74
3.05
1.02
5.14
Total
(GeV) error (%) error (%) error (%) error (%) error (%)
%
QED running coupling constant
Before BES experiments, the ratio
of R error contribution to s) in 2-5
GeV account for about 53%.
After BES measurement of R,
the ratio of error contribution
reduce to about 30% in 2-5GeV.
Error estimation of the R measurement in 2004
(estimated according to R scan in 1999)
blue figures : R99
pink figures : R04
In 2004, R value at 2.2 Gev, 2.6GeV, 3.0 GeV will be measured
Ecm
Nhad
(GeV)
events
selct
(%)
Lum.
1+δ
εhad
(%)
(%)
(%)
error
stat
(%)
error
sys
(%)
error
total
(%)
2.2
1,444
2,000
5.54
4.0
2.48
2.2
1.29
1.0
3.49
2.5
2.88
2.2
7.04
5.0
7.61
5.5
2.6
1,734
20,000
4.43
2.0
2.77
1.5
1.26
1.0
3.83
2.0
2.71
0.8
6.50
3.3
7.04
3.5
3.0
2,055
20,000
3.30
2.0
1.70
1.5
1.32
1.0
2.66
2.0
2.49
0.8
5.02
3.3
5.61
3.5
 Hadronic efficiency εhad will be determined by using new developed
detector simulation Monte Carlo (BIMBES) based on GEANT3
The R errors of measured at BESII
and the estimated R error at BESIII
BESII (%) BESIII (%)
error sources
Luminosity
2-3
1
Hadronic model
2-3
1-2
Trigger efficiency
0.5
0.5
Radiative correction
1-2
1
Hadronic event selection
3
2
Total systematic error
7
2.5– 4
The change of the uncertainty of QED s
with the decrease of R error in 2-5 GeV
(If R error in other energy region fixed)
R error in 2-5 GeV
5.9 %
0.02761±0.00036
3.0 %
0.02761±0.00030
2.0 %
0.02761±0.00029
The aim of the precision of R measurement
at BES3 (2-4%) is reasonable and hopeful
Some methods used in R
measurement at BESII
(Some of them may be used at BES3)
Luminosity
 Two independent ways were used to select wideangle Bhabha events, one sample to calculate the
luminosity, another to estimate the efficiency.
 The main luminosity error was the statistical error
of the two samples. Large event sample will help
for reducing the luminosity error.
 Use Bhabha, two-photon and  events to analysis
luminosity and to find systematic errors.
Integrated luminosity cross check
Lee (nb-1)
Lμμ (nb-1)
2.6
292.9±6.5
268.2±18.9 266.7±12.0
3.2
109.3±3.4
108.9± 8.6 106.0± 5.9
3.4
135.3±4.0
125.1± 9.8 130.7± 7.1
3.55
200.2±5.2
192.1±14.5 191.1± 9.7
Ecm
Lγγ (nb-1)
(GeV)
Backgrounds
 Use M.C to estimate the residual QED backgrounds
Nll= ll ·L · ll , (l=e,,)
N= · L · 
 Use vertex-fitting to estimate
beam-associated backgrounds.
 The better track resolution of
BES3 is benefit for reducing
beam associated backgrounds
Gaussian+2 order
polynomial fitting
Initial state radiative corrections
Some schemes are studied
(1) G.Bonneau, F.Martin
Nucl.Phys.B27,(1971)381
(2) F.A.Berends, R.Kleiss
Nucl.Phys. B178, (1981)141
(3) E.A.Kureav, S.V.Fadin
Sov.J.Nucl.Phys.41,(1985)3
(4) A.Osterheld et.al.
Fenyman figures for ISR
(to α3 order)
No.SLAC-PUB-4160(1986) (used)
In BES3 experiments more precision schemes are needed
Formula used for ISR calculation
The radiative correction factor
The difference of (1+) between scheme (3)
calculated by scheme (4)
and (4), which is 1% in non-resonant region
Hadronization Picture
Lund area law
Lund area law
Lund area law
Phase space
Partition function
Define n-particle multiplicity distribution
N and p are two free parameters tuned by data
Pn is used for controlling fragmentation hadron number in MC
BES raw data spectrum compared with
LUARLW + detector simulation at 2.2 GeV
BES raw data spectrum compared with
LUARLW + detector simulation at 2.5 GeV
BES raw data spectrum compared with
LUARLW + detector simulation at 3.0 GeV
Check RQCD prediction
RQCD has 1σdeviation from both BES
and  measurements.
Central value of Rexp and
RQCD agree well.
Is this the experimental error or new physics?
Is it true or due to error?
Determination of the running s
R value is predicted by pQCD
Where,
Solving the equation
R
exp
R
One may obtain s
QCD
Determination of the running s
Charged particle differential cross section
q
: momentum
ηch : neutral particle correction
In QCD
Measure the differential cross section, one may get s
QCD Related topics
① Inclusive distribution
e+ e- → h + X
(h : π, K etc)
 The inclusive spectrums are governed by hadronization dynamics.
 In general, the single particle distributions are the function of (s, p// ,p ) .
 The two questions are needed to answer:
(i) how do the inclusive distributions change with (p// ,p) when s fixed?
 depends on the type of the initial state and the final state.
(ii) how do the distributions change with the center of mass energy s?
 Feynman scaling assume the distributions are the function of
the scaling variable x and p at large energies.
 Scaling assumption is a good approximate behave at high energy,
but it has not been tested precisely at low energy.
 The αs may be determined by the scaling deviation.
②  Spectrum (to be published in PRD)
Variable :
Parameters :
MLLA : Modified leading log approximation
LPHD : Local parton and hadronic duality
BES
2
BES2
Veriation of KLPHD as
the function of Ecm
eff from different
experiments
BES data are reasonably well
described by MLLA/LPHD.
③ Form Factors
 Exclusive cross section is expressed as the product
of the phase space factor and form factor.
 The measurement of the form factor may check
the phenomenological model, which is also the
effective method to find short life-time particle.
 The following channels may be measured with
large sample obtained at BES3
e+ e- π+π- π+π-, π+π- π+π- π0 ,
π+π- π0π0 , π+π-, π+π-K+K-,
π+π-, K+K-, ppbar
④
+
+
e e π
π
+
π
π
(BES2)
form factor
ND, DM2 data
BES data
Cross section (nb)
Phase-space factor
ND, DM2 data
BES data
Form factor
e+e- 2(π+ π- ) at BES3
BES3 has better
momentum resolution
and larger acceptance
than BES2, which will
be helpful to the events
selection and reduce the
backgrounds.
2.2GeV
2.2GeV
BES3
BES3
BES2
2.6GeV
2.6GeV
BES3
BES3
BES2
M4πdistribution
Ptotal distribution
⑤
+
e
e
→p pbar at BES2
Form factor
Form factor by BES2
Form factor combined
other experiments
⑤ e+ e- →p pbar
( momentum resolution of BES2 and BES3)
experiment
<===BES2===>
<=== BES3===>
Ecm
pexp
p
p
p
p
2.0
0.347
0.315
0.022
0.346
0.006
2.2
0.575
0.563
0.024
0.574
0.008
2.4
0.748
0.739
0.027
0.747
0.010
2.6
0.900
0.891
0.032
0.898
0.012
2.8
1.039
1.029
0.038
1.037
0.015
3.0
1.171
1.161
0.039
1.168
0.018
Momentum resolution at BES3 is much better than BES2
⑤ e+ e- →p pbar
(efficiencies of BES2 and BES3)
BES2
Ecm (GeV)
2.0
2.2
2.4
2.6
2.8
3.0
BES3
|cosθ|≤0.75
|cosθ|≤0.75
|cosθ|≤0.90
0.6328
0.6752
0.6217
0.6467
0.6248
0.6448
0.3567
0.5847
0.6067
0.6209
0.6077
0.6014
0.4288
0.7183
0.6764
0.6937
0.6823
0.6774
⑥ Multiplicity Distribution
 The multiplicity is the basic quantity in reactions:
multiplicity distribution: Pn(s)
average multiplicity: <nch(s)>=nPn(s)
 pQCD predicts the ratio of multiplicity of the
gluon fragmentation to qurk fragmentation
r=<nG>/<nF> → CA /CF =9/4.
This may be tested by analyzing :
J/ data (gluon-fragmentation events account for 95%)
3.07 GeV data (gluon events may be neglected).
Multiplicity Distribution of BES2
(To be published in PRD)
The results of BES2
⑦ Correlation function
 The measurement of the correlation effects is more
valid way to abstract the dynamical informations from
data than from the single particle spectrum.
 Correlation function C(x1,x2)=CL(x1,x2)+CS(x1,x2)
(x1,x2): kinematical observable for two particles,
CL/CS : long/short-range correlation functions.
Lund model prediction to
C(x1,x2)=C L(x1,x2)+CS(x1,x2)
⑧The Bose-Einstein correlation
 The identical bosons is symmetric for the communication of any
two bosons of same kind, which leads to the special statistic
correlation, i.e. Bose-Einstein correlation (BEC).
 BEC contains the space-time information of the hadronic sources.
 The space-time properties of hadronic source may be inferred by
measuring the BEC functions R(Q2 ) for same charged /K pairs,
where Q2 =(p1 –p2 )2 .
 It is expected that the following subjects may be measured :
(a) two-body correlation
(b) inflections of multi-body correlation
(c) inflections of the final state electromagnetic/strong interactions
(c) multiplicity dependence of BEC
(d) space-time form of hadronic source
(e) BEC in the resonance decay, e.g. in J/ decay.
⑨ Fractal properties at low energy
 One usually paid the attention to averaged distributions only.
 The fluctuations are thought as the statistical phenomena for the
finite particles number.
 The events with abnormal high particle density condensed in
small phase-space have been observed in several kinds of
reactions at high energy.
 The important questions to these discover are:
(a) do the anomalous fluctuations have their intrinsic dynamics origins?
(b) is the phase-space of the final state the isotropic or not?
(c) is the phase-space the continuous or fractal?
(d) do the intermittency observed at high energy exist at low energy?
(e) can the intermittency be explained by the known theories (cascade , BEC)?
⑨ Fractal properties at low energy
The study of this topic has two aspects:
(i) experiment aspect：
- measure the fractal moments
- measure the Hurst index
(ii) mechanism problem：
- whether the asymptotic fractal behavior in the
perturbative evolution of partons may be kept
after the hadronization processes?
- and so on…
Summary
 The high luminosity of BEPC2, the large geometry
acceptance, good space and momentum resolution, good
particle identification of BES3 will be beneficial to the
R measurement and QCD studies at low energy.
 The goal of the R measurement at BEPC2/BES3 is to
reach the precision about 2-4%.
 Some subjects which are interesting to low energy QCD
will be studied experimentally with high precision.