1. Test of QCD in 2-5 GeV with BESII
Z.G. Zhao
6/27/2002, PSI
Test of QCD in 2-5 GeV with BESII
W.B. Yan, Z.G. Zhao
(Representing BES Collaboration)
University of Michigan, Ann Arbor, MI, USA
IHEP of CAS, Beijing, China
Final Results of R-values in 2-5 GeV
 distribution, thrust and 2nd binomial moment
e+e-(K)+X
Summary
ICHEP2002, Amsterdam
Z.G. Zhao
Z.G. Zhao

2. Definition of R Experimentally R: one of the most
Z.G. Zhao
6/27/2002, PSI
Definition of R
R: one of the most
fundamental quantities in
particle physics, counts
directly the number of quarks,
their flavor and colors
Experimentally
Nhad: observed hadronic events
Nbg: background events
L: integrated luminosity
had: detection efficiency for Nhad
: radiative correction
ICHEP2002, Amsterdam
Z.G. Zhao
Z.G. Zhao

3. Motivations of the R Scan
Hunting for new physics from a(g-2)/2  Interpretation of E821 at BNL
Reducing the uncertainty of (MZ2)  essential for precision tests of the SM
Relative contributions to the
uncertainties of a and (MZ2)
ICHEP2002, Amsterdam
Z.G. Zhao

4. BES’s R Scan Total 91 energy pts in 2-5 GeV Single and separated beam
collision to study beam associated background
Special runs taken at J/, 2.6, 3.0, 3.5 GeV with larger data sample to determine trg
L measured by large angle Bhabha
LUARLW is developed to improve JETSET for had low energy region, particularly for Ecm< 3 GeV
D, D*, Ds, Ds* productions are simulated according to Eichiten Model
A generator is built into LUARLW to handle decays of resonances in the radiative return processes e+e- J/ or (2S)
ICHEP2002, Amsterdam
Z.G. Zhao

5. Events Recorded by BESII
Events collected at BESII
Data MC
ICHEP2002, Amsterdam
Z.G. Zhao

6. Some Hadronic Event Shapes at Ecm=2.2 GeV (LUARLW)
Variation of Detection Efficiency and ISR in 2-5 GeV
Tune the parameters to reproduce 14
distributions of the observed
kinematic variables and hadronic
event shape.
Hatched region: MC
Histogram: Data
ICHEP2002, Amsterdam
Z.G. Zhao

7. R Values in 2-5 GeV
ICHEP2002, Amsterdam
Z.G. Zhao

8. R Below 10 GeV Before BES R Scan After BES R Scan ICHEP2002, Amsterdam
Z.G. Zhao

9. The SM Fit to mH (95% C.L.) (95% C.L.) With BES data Without BES data
ICHEP2002, Amsterdam
Z.G. Zhao

10. Evaluation of s and s(MZ) from R(BES)
R(pQCD) and R(BES)
Exhibits QCD correction known to
O(s3(s)) so far. Precision meas. of R
can determine s and thus evaluate
s(MZ).
Using R at 3.0 and 4.8 GeV, one has:
BES:
PDG2000:
D. Michel
pQCD calculation agree amazingly well with BES data
J.H. Kuhn, M.Rreinhauser Nucl. Phys. B619(2001)588
ICHEP2002, Amsterdam
Z.G. Zhao

11.  Distribution: =-ln(2p/s)
MLLA/LPHD calculations
Limiting spectrum when Q0=eff
B=a/b, a=11Nc/3+2nf/3Nc2, b=(11Nc-2nf)/3
CF=(Nc2-1)/2Nc=4/3, Nc: quark flavor = 3
nf: # qark flavor produced
IB: modified Bessel Function.
= 0+ix, where tanh 0 =2 -1, =1-/ *
MLLA/LPHD fit
with BES data
BES Preliminary
ICHEP2002, Amsterdam
Z.G. Zhao

12. Multiplicity and Second Binomial Moment
Average multiplicity:
NLO:
BES Preliminary
ICHEP2002, Amsterdam
Z.G. Zhao

13. Thrust and Mean Thrust Thrust: Mean thrust: 1-T Free para.
BES Preliminary
A, B constant
Free para.
ICHEP2002, Amsterdam
Z.G. Zhao

14. Summary
BES measured R in 2-5 GeV with average uncertainties of 6.6% (a factor of 2-3 improvement)
significant impact on the SM fit: mHiggs moves up from 61 GeV to 90 GeV, up limit from 170 GeV to 210 GeV
R scan data at continuum can be used to test QCD
- Preliminary results of , T, and R2 are consistent
with e+e-, ep and N data at high energy.
- , T consistent with MLLA/LPHD predictions, but
R2 differs to NLO calculation
CLEOC and BESIII can provide more accurate data at continuum to test QCD at a few percent level.
ICHEP2002, Amsterdam
Z.G. Zhao

15. [e+e-(K) + X] and Fragmentation Function, S/U Ratio
Dqh(x,s)
[e+e-(K) + X] are also
needed to help determine
polarized parton density
0.15
0.20
0.25
0.30
0.35
0.40
0.45 K +
p exp. n
N exp.
eN exp.
20.9 K * / r
20.9 K/ p
BESII(3.0) preliminary
S/U
S/U: input parameters in hadron
production generatorneeded for
determining h
ICHEP2002, Amsterdam
Z.G. Zhao