张达华(for BES Collaboration)

Institute of High Energy Physics, Beijing 100049

第 7 届全国高能物理会议，桂林October 27--31 ， 2006

Measurement of the continuum Ruds, Ruds(c) ＋ Ψ(3770) and Rhad values in the range

from 3.660 to 3.872 GeV

Outline

Introduction

Cross section scan experiment

Data analysis

Radiative corrections

Results -- – R values

Introduction

R definition & measurements

0

0hadR

trighad

hadobshad L

N

)1(

obshadBorn

hadR -

e+

e-

+

h a d ro n s-e

e+

q-

q

f la v o rc o lo r

= Qf2

lowestorder

pQCD calculates the R ratio in continuum region

Experimentally, one measures

: # of hadronic hadN

: Luminosity L: Effs.hadhad ,

events

: radiative correction factor

)1(

22 (GeV)

nb 8544.86

cmee E

had)1( Have to be determined precisely !

Why are we interested in R(s) ?

The R values at all energies is needed to calculate the effects of vacuum polarization on the parameters of Standard Model. [ for example, and ]. A large uncertainty in this calculation arises from the uncertainties in the measured R values in the open charm threshold region (3.7 GeV to 5.0 GeV).

For the evaluation of the electromagnetic coupling at the Z mass scale, .

)( ZQED M

For determination of of the muon. 2/)2( ga

)()(

3

)0(

24

2

2LOhad, sR

s

sKdsa

m

)( ZQED M a

affects the determination of the mass of Higgs boson from the measurement of indirectly.

)( ZQED M

W2sin

Evaluate )(sSNon-DD decays of psi(3770)

Introduction

Introduction

R measured by BES and other experiments

Introduction

Introduction

Precision measurement of the cross sections in this region

Cross section experiment

• Cross section scan experiment

The data were collected at 67 energy points from 3.660 to 3.872 GeV, which begin from off-resonance, mainly cover (3770) and stop at DD* production threshold .

Separated beam collision data at 3 energy points were collected to study beam associated background.

Cross section experiment

快速数据重建，快速物理分析，快速信息反馈

“ 快速”重建数据信息质量的监测结果

动量 p GeV/c能量 E GeV

监测探测器状况

监测物理信号

Data analysis

hadtrg

bghadobshad εεL

NN

events hadronic observed the:obshadN

pairs(lepton background the:bgN

)eventsprocessphoton- twoand

luminosityintegrated: L

efficiency trigger :trg

)1(0

obshad

had

－eefor

section cross level tree: 0

correction radiative :)1(

0

0

hadR

Cosmic-ray and beam associated background

could be estimated based on cross sections, luminosity and acceptancebN

初态辐射修正可以删除高阶过程的影响

Data analysis

实验观测的强子事例 N

0

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

Distributions of the averaged Z of events

bN

hadn

)1( hadNhad

n

bN

径迹筛选

事例级筛选

好的螺旋度拟合径迹来源于原初顶点

TOFprotonTOF 6T2 t

2beam p1E1.0pp

0.84|cos| 立体角范围

GeV 1.0EBSCtrack

beamBSCtrack E 0.28E

3N trackgood

Beam gas associate background, cosmic-ray

Data analysis

强子事例筛选

Data analysis

数据和 Monte Carlo 事例的对比

Data analysis

强子事例选择条件的系统误差 Phys. Lett. B641 (2006)145

径迹筛选好的螺旋度拟合径迹来源于原初顶点

beamtracktrack E9.0)por (p

0.7|cos| 立体角范围

GeV 1.1EBSCtrack

去除加强筋区域m 0.77|Z| m 0.10 BSC

m 1.04|Z| BSC

Z向灵敏区

Data analysis

亮度测量

trig

eeicmeeicmee

icmbicmeeicm EE

EnENEL

)()(

)()()(

,,

,,,

• Luminosity of the precision scan data sets determined by

Δφ=|φ1-φ2|-1800

Number of events

Data analysis

数据和 Monte Carlo 事例的对比

DATA

M.C.

P1(GeV)

P2(GeV)

EBSC1(GeV)

EBSC2(GeV)

ZBSC

Number of events

DATA

M.C.

Accepted e+e- events are then examined for background contaminations by man visual scan.

污染率 : ~0.35%

Data analysis

数据和 Monte Carlo 事例的对比

Track 1 Track 1

Track 2 Track 2

Track 1 Track 1

Track 2 Track 2

EBSC [GeV]

P [GeV]

Number of events

Number of events

Sources ΔSYS (%)

VXY <= 0.015 m 0.18

|VXY| <= 0.15 m 0.48

|cos(θ)| <= 0.70 0.65

EBSC >= 1.1 GeV 0.27

P ＋ (or P － ) >= 0.9·Eb

1.33

0.10 m <= |ZBSC| <= 0.77 m

or |ZBSC| >= 1.04 m0.89

Total 1.83

Table. Systematic uncertainties due to Bhabha event selection

)(Nhadronshadronsbg

eeeeeeeeL

Data analysis

背景减除

The background from two-photon-exchange processes are also subtracted (<0.3%) in this analysis.

Data analysis

触发效率

Data analysis

强子效率• Full simulation Monte Carlo generator

High order ISR inclusive hadronic generator was developed to determine had in the all energy region

A wide region ISR return generator ISRAD drives a set of sub-generators to generate the physics processes in the energy region from 0.28 GeV to 4.0 GeV with Lorentz boost due to initial state photon emission.

DD-bar and D*D-bar productions are simulated by DDGEN and DsDGEN.

In the radiative return region, the decays of (2S) and J/ resonances are simulated byLUND_CRM (see PRD V62, 034003). One photon inclusive hadron prodution is simulated by LUND modified for BES energy region.

Data analysis强子效率

)()(

)(12)(

2222 sMMs

ss

tot

feeB

2

0

ISRhad |))1((1|))1(( ),( )(

max xsxssxFdxsx B

(Kuraev and Fadin)

function sampling is ),( sxF

Radiative corrections

初态辐射修正))(1(

)()(0

s

ss

obshad

had

...)(Re21|)(1|

12

ss

蔡永士（ SLAC ）公式

Berands, et al. have another approach to deal with the vacuum polarization.

从而导致

2|)(1|

s

BB

Radiative corrections

真空极化改变光子传播子Vacuum polarization correction

Results － R values

Sources ΔSYS (%)

Luminosity 1.8

Hadron selection 2.5

M.C. modeling 2.0

ISR 1.5

Ψ(3770) resonance parameters 2.7

Total (off Ψ(3770) region)

3.9

Total(within Ψ(3770) region)

4.9

)(

)()(

0

0

s

ssR had

R values

Table. Systematic uncertainties in the determination of R values

• Rtot(s)=Rhad(s)+ΣRres,i(s), Rres,i(s) is R values due to all 1 －－ resonances decay to hadrons except Ψ(3770).

Ruds = 2.134±0.025±0.085

RpQCDuds = 2.15±0.03

calculatea(M2

Z)

aμ=(g-2)/2

Results － R values

Rtot

Ruds

hadrons

hadrons

)()3770()( sR cuds )()( )3770()( sRsR cuds

udsR

above cc-bar threshold

below cc-bar threshold

BES-II Preliminary !Dec. 2003 data set

continuum Rudsc + RΨ(3770)hadrons

R values (This work)

Thank You

Introduction

Introduction