test of qcd in 2-5 gev with besii

ICHEP2002, Amsterdam

Zhengguo Zhao, Weiguo Li 1

Test of QCD in 2-5 GeV with BESII

Weiguo Li, Zhengguo Zhao (Representing BES Collaboration)

IHEP of CAS, Beijing, ChinaUniversity of Michigan, Ann Arbor, MI, USA

I. Final Results of R-values in 2-5 GeV

II. distribution and 2nd binomial moment

III. Summary



Definition of RR: one of the most fundamental quantities

in particle physics, counts directly the number of

quarks, their flavor and colors

R -

e+

e-

+

h a d ro n s-e

e+

q-

q

f la v o rc o lo r

= Qf2

lowestorder

)1(

1

had

bghad

L

NNR

Experimentally

Nhad: observed hadronic events

Nbg: background events

L: integrated luminosityhad: detection efficiency for

hadronic events : radiative correction



Reducing the uncertainty of (MZ

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

242

22

)(

)(Re

3

)0()(

m Z

ZZhad iMss

sRds

MM

)()(

3 242

2

sRs

sKds

ma

m

had

• Relative contributions to the uncertainties of a and (MZ

2)



• 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 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)

BES’s R Scan



N0

e+e-e+e-

+

+-

e+

e-e- -

e+ + +

e- e-

e+ e+

e+

e-

Nhad

e- e-

e+ e+

+-

qq

N0

e+e-e+e-

+

+

-e

e +

q-

q

Events Recorded by BESII

Data

MC



Tune the parameters to reproduce

14 distributions of the observed kinematic variables and hadronic event shape.

Hatched region: MCHistogram: Data

Variation of Detection Efficiency and ISR in 2-5

GeV

Some Hadronic Event Shapes at Ecm=2.2 GeV

(LUARLW)



R Values in 2-5 GeV



R Below 10 GeV

Before BES R Scan After BES R Scan



The SM Fit to mH

GeVm

GeVm

H

H

170

62 5330

(95% C.L.) GeVm

GeVm

H

H

212

98 5838

(95% C.L.)

Without BES dataWith BES data



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(MZ).

Using R at 3.0 and 4.8 GeV, one has:

BES:

PDG2000:

Evaluation of s and s(MZ) from R(BES)

q n

n

sqQR

0

23

123.0047.0130.0046.0369.0)0.3(

GeVs053.0059.0057.0064.0183.0)8.4(

GeVs

011.0014.0

)5( 124.0)( Zs M

D. Michel

002.01181.0)()5( Zs M

J.H. Kuhn, M.Rreinhauser Nucl. Phys. B619(2001)588



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-/

),,(21

0 effLPHD

h

hQfK

)/5.0ln(0 effs

]}sinh)21([coshsinh

16{

sinh4

sinh)21(cosh)(

4

)/,(

2

2

2

b

NI

bN

edx

Bb

C

sf

cB

B

c

BF

effMLLA

*

MLLA/LPHD fitwith BES data

BES Preliminary



Multiplicity and Second Binomial Moment

Average multiplicity:

NLO:

0

)(n

chchch nPnn

3/211

96,

3/21127

10

4

1

])(1[)]([ )(/

ff

f

sscb

sch

nc

n

nb

sdesan s

61728/)404455(

))(1(8

11)1(22

f

s

ch

chch

nc

scn

nnR

BES Preliminary



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 and R2 are consistent with e+e-, ep and N data at high energy. - consistent with MLLA/LPHD predictions, R2 consistent with NLO – 0.07.

• CLEOC and BESIII can provide more accurate data at continuum to test QCD at a few percent level.



Error of R Measurement at BESIISource BESII (%) BESIII Goal(%)

Luminosity 2 – 3 1

Detection effi. 3 – 4 1 - 2

Trigger effi. 0.5 0.5

Radiation corr, 1 - 2 1

Hadron decay model

2 - 3 1 – 2

Statistical 2.5 --

Total 6 – 7 2 - 3



Thrust and Mean ThrustThrust:

Mean thrust: 1-T

i i

i Ti

p

npT

||

||max

;2/)(~

;~)2(~

;

2

s

ABA

ss

sspert

powerpert

A, B constant

)](1ln2

)()(~[24

2

0

0

0

sKs

ss

MC

sI

sIIFpower

I

sI

I

dp

00 )()(~Free para.

)2(~),( 0 GeVM Zs

BES Preliminary



[e+e-(K) + X] and Fragmentation Function, S/U Ratio

Fragmentation function Dq

h(x,s)

[e+e-(K) + X] are also needed to help determine polarized parton density

q z

qhq

tot

szxdx

dsxD

z

dz

dx

Xheed

1

),/(),(

)(1

S/U: input parameters in hadron production generatorneeded for determining h

0.15 0.20 0.25 0.30 0.35 0.40 0.45

K+p exp.

N exp.

eN exp.

20.9 K*/

20.9 K/BESII(3.0) preliminary

S/U

test of qcd in 2-5 gev with besii

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