ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li1 Test of QCD in 2-5 GeV with BESII Weiguo Li, Zhengguo Zhao (Representing BES Collaboration) IHEP of CAS, Beijing, China University of Michigan, Ann Arbor, MI, USA I.Final Results of R-values in 2-5 GeV II.  distribution and 2 nd binomial moment III.Summary

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li2 Definition of R R: one of the most fundamental quantities in particle physics, counts directly the number of quarks, their flavor and colors Experimentally N had : observed hadronic events N bg : background events L: integrated luminosity  had : detection efficiency for hadronic events  : radiative correction

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li3  Reducing the uncertainty of  (M Z 2 )  essential for precision tests of the SM  Hunting for new physics from a   (g-2)/2  Interpretation of E821 at BNL Motivations of the R Scan Relative contributions to the uncertainties of a  and  (M Z 2 )

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li4 Total 91 energy points 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 E cm < 3 GeV D, D *, D s, D s * 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) BES’s R Scan

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li5 Events Recorded by BESII Data MC

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li6 Tune the parameters to reproduce 14 distributions of the observed kinematic variables and hadronic event shape. Hatched region: MC Histogram: Data Variation of Detection Efficiency and ISR in 2-5 GeV Some Hadronic Event Shapes at E cm =2.2 GeV (LUARLW)

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li7 R Values in 2-5 GeV

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li8 R Below 10 GeV Before BES R Scan After BES R Scan

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li9 The SM Fit to m H (95% C.L.) Without BES data With BES data

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li10 R(pQCD) and R(BES) pQCD calculation agree amazingly well with BES data Exhibits QCD correction known to O(  s 3 (s)) so far. Precision meas. of R can determine  s and thus evaluate  s (M Z ). Using R at 3.0 and 4.8 GeV, one has: BES: PDG2000: Evaluation of  s and  s (M Z ) from R(BES) D. Michel J.H. Kuhn, M.Rreinhauser Nucl. Phys. B619(2001)588

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li11  Distribution:  =-ln(2p/  s) MLLA/LPHD calculations Limiting spectrum when Q 0 =  eff B=a/b, a=11N c /3+2n f /3N c 2, b=(11N c -2n f )/3 C F =(N c 2 -1)/2N c =4/3, N c : quark flavor = 3 n f : # qark flavor produced I B : modified Bessel Function.  =  0 +ix, where tanh  0 =2  -1,  =1-  /  ** MLLA/LPHD fit with BES data BES Preliminary

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li12 Multiplicity and Second Binomial Moment Average multiplicity: NLO: BES Preliminary

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li13 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: m Higgs 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  and R 2 are consistent with e + e -, ep and N data at high energy. -  consistent with MLLA/LPHD predictions, R 2 consistent with NLO – CLEOC and BESIII can provide more accurate data at continuum to test QCD at a few percent level.

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li14 Error of R Measurement at BESII Source BESII (%) BESIII Goal(%) Luminosity 2 – 3 1 Detection effi. 3 – Trigger effi. 0.5 Radiation corr, Hadron decay model – 2 Statistical Total 6 –

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li15 Thrust and Mean Thrust Thrust: Mean thrust:  1-T A, B constant Free para. BES Preliminary

ICHEP2002, Amsterdam Zhengguo Zhao, Weiguo Li16  [e + e -   (K  ) + X] and Fragmentation Function, S/U Ratio Fragmentation function D q h (x,  s)  [e + e -   (K  ) + X] are also needed to help determine polarized parton density S/U: input parameters in hadron production generator  needed for determining  h K + p exp. N exp. eN exp K * /  20.9 K/  BESII(3.0) preliminary S/U