Download - Test of QCD in 2-5 GeV with BESII
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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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 2
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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 3
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)
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 4
• 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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 5
N0
e+e-e+e-
+
+-
e+
e-e- -
e+ + +
e- e-
e+ e+
e+
e-
Nhad
e- e-
e+ e+
+-
N0
e+e-e+e-
+
+
-e
e +
q-
q
Events Recorded by BESII
Data
MC
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 6
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)
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 7
R Values in 2-5 GeV
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 8
R Below 10 GeV
Before BES R Scan After BES R Scan
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 9
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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 10
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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 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-/
),,(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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 12
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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 13
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.
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 14
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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 15
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
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ICHEP2002, Amsterdam
Zhengguo Zhao, Weiguo Li 16
[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