1

Recent results on (3770) production & decays from BES/BEPC

Gang RONG(for BES Collaboration)

Institute of High Energy Physics, Beijing 100049, P.R. China

CNHEP’06

27 -- 31 October, 2006, Guilin

2

Introduction

Outline

Summary

])3770([ DDBF R

Resonance parameters of (3770) and (3686) &

values and

Search for decays of (3770) DDnon

Measurement of R values

]non)3770([ DDBF

3

IntroductionWhy are we interested in R(s) ?

Vacuum polarization correction (in the photon propagator ) needs the R(s) values, which plays an important role in the precision test of the Standard Model.

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

4

Precision measurements of R values in open charm region are also important in understanding 1-- resonance production, for searching for new states, study of dynamics …

Introduction

(3770) production & decaysIt is believed to be a mixture of and states of system. It is thought to decay almost entirely to pure DD-bar.

131 D 1

32 S cc

Long-standing puzzle of (3770) production and decays:

Previously published data indicate that more than about 35% of (3770) does not decay to DD-bar ? This conflicts with theoretical prediction.

nb 8.16.11))3770((12

2)3770(

)3770( eeBFM

prd

Cross section at peak (PDG04 parameters)

nb 0.50.5)( DDeeobs (Mark-III)

nb 7.01.7)( DDeeprdbefore BES-II & CLEO-c

However

previous measurements

5

New MeasurementsRecently BES and CLEO-c measured the DD and (3770) production at 3.773 GeV based on the data taken below DD threshold and at 3.773 GeV.

A better way to measure the cross sections, the widths of the resonance and the DD branching fractions of (3770) is to analyze the line-shapes of (3770), (3686) and DD production simultaneously.

BES made a fine cross section scan covering both the (3686) and (3770) to measure the resonance parameters, branching fractions and search for non-DD decays …

A better way: cross section scanTo uncover the

puzzle

6

(3770) data~17.3 pb-1 of data taken at 3.773 GeV.

~15 pb-1 of (cross section scan ) data taken in between 3.665 GeV and 3.878 GeV (Mar. 2003 data set & Dec. 2003 data set) .

6.5 pb-1 of data collected at 3.650 GeV.

BES-II data samples

Equivalent to ~27 pb-1 at (3770) peak

Ecm= 3.650, 3.665 GeV

~1 pb-1 of data collected at 3.665 GeV.

Data taken over hundred energy points.

7

Measurements of R values

BornhadR

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 !

8

MC generator & simulation

Full energy range ISR Generator

GeV 783.s )3770(

)3686(/J

)1700(

[GeV] energy Effective

Nch KNOφ

Thrust Oblatenesscosθ

Sphericity

Aplanarity

Jet axis cosθ

x η Y

Pt <PTin2>

<PTout2>

Den

sity

[n

b/G

eV]

BES-II (3770) and (3686) scan

MARK-I, MARK-II, DELCO, … smooth eff. curve

hadronsISR ee

had

9When scan over 3.770 GeV

Just before the scan experiment

Mass [MeV]

PDG04

BEPC

BEPC

BEPC

011.0916.3096

05.030.3095

034.0093.3686

01.090.3684

02.050.3684

BEPC energy calibration

'

'

'J/

J/

3095.33684.8

MM3095.3)(EME

PDGJ/ψ

PDG

ψBEPCPDG02J/ψ

true'

EBEPC is the energy of BEPC set in the experiment,

Etrue is the true energy

01.070.3684

8.36842

9.36847.3684

During the cross section experiment, we performed 4 fast cross section scans over J/ and ’ resonances to calibrate the BEPC energy.

10

Events Recorded by BESII

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

Cosmic-ray and beam associated background

The distributions of the averaged Z of events

could be estimated based on cross sections, luminosity and acceptancebN

bN

bN

hadn

)1( hadNhad

n

Radiative correction could remove the effects of high order processes from the observed cross section, and gives

The

eve

nts

obse

rved

in th

e ex

peri

men

t

)hadrons( eeB

11

2

0

expecthad |))1((1|))1(( ),( )(

max xsxssxFdxsx B

ISR corrections

functionsampling issxF ),(

sections crossorder Born is )(sB

Kuraev & Fadin

HSVxsxF 1),(

the electron equivalent radiator thickness

1ln

22em

s

4

372ln

3

1

242

1

34

31 2

2

22

e

SV

m

s

HHH21

211

xH

xx

x

x

xxH 6)1ln(

)1(311ln)2(4

8

1 22

2

s

sx

'

1

Effective c.m. energy

Moninal c.m. energy

12

...)()(1)(1

1 2

sss

Vacuum polarization change the photon propagator

results in

2|)(1| s

BB

Vacuum polarization correction

lh )](

)([

4

''

'

2sids

ss

sPV

s BB

h

llvacl

2

11

)4

()(2

)(2

vac s

mx, xfs lll

)1( ,11

11log

6

)2(1

39

5)(

xx

xxxxxf

)1( ,1

1tan

3

)2(1

39

5)( 1

xx

xxxxf

)(1 222 qq

ig

q

ig

B

expecthad)1( Radiative correction factor

13

ECM [GeV] σobshad R

3.650

3.665

3.773

udstot R and R

22.098.18

27.030.18

27.068.27

16.058.14

21.013.14

22.086.22

02.024.2

03.019.2

04.075.3

)hadrons(0 ee

GeV 3.773 @ 20.004.075.3 R

(pre

limin

ary

!)

09.002.022.2 udsR

11.005.026.2 udsR

Obtained by fitting the (3770) and (3686) cross sections

see before

Obtaining by fitting to the R values measured by BES in the range from 2.0 to 3.0 GeV

14.026.2| GeV 3.0 to 2.0 udsR

stat. & p-to-p systematic error

R values measured at three energy points

14

Comparison of R measurements from different experiments

15

Born)3770((3770) & R σ

udsEcm RERRcm

GeV 3.773)3770( |)(

Taking the R for light hadron production to be a constant, then

13.004.053.1)3770( RWe obtain

nb 80025.032.9Born)3770( .

nb 74.108.11))3770(()1(

122

)3770(VP

Born)3770(

eeBF

M

)024.0047.1()1( VP obtained based on PDG04 (3770) resonance parametersPLB 603(2004)130

My

calc

ula

tio

n It is consistent with

)non)3770(( DDBF determined with DDσR &

Preliminary

Including (3770)

16

)()(

)(12)( 2222 sMMs

ss

tot

feeB

2/41

0|))1((1|))1(( ),( )(

2

xsxssxfdxssM Bobs

DD

D

Assuming that decay exclusively into (3770) DD

Radiative correction

PR D62 (2000)012002-1024.0047.1)1(|))1((1| 2

vpxs

Radiative correction factor B

obs

g

Born

obsDD

Born

BornDDDD

σgN

NDDBF

)3770(IIBES)3770(prd

(3770)

prd

))3770((

Obtained from analysis of R

Determination of branching fractions withobs

DD Born

)3770(and

014.0770.0IIBES g

Some systematic uncertainties can be canceled out

Radiative correction factor obtained based on new (3770) resonance parameters measured by BES-II.

Assuming that there are no other new structures and effects except (3770) and continuum hadron production in the energy region from 3.70 to 3.87 GeV, we have

17

preliminary

)%4.31.17.35())3770(( DDBF )%8.33.19.49())3770(( 00 DDBF

)%8.57.15.85())3770(( DDBF

)%8.57.15.14())3770(( DDnonBF

Results of branching fractions

With BES previously measured cross sections for DD production.

PLB603(2004) 130

These result in the non-DD branching fraction

nb 0.63)0.19(7.09obs)3770(

nb 0.80)0.25(9.22Born)3770(

)1( Is calculated with the (2S) resonance parameters measured by scanning the (2S) peak. PLB 641 (2006) 145

18

)%6.32.14.37())3770(( DDBF )%1.43.14.52())3770(( 00 DDBF

)%1.68.18.89())3770(( DDBF )%1.68.12.10())3770(( DDnonBF

Results of branching fractions

09.002.026.2 udsR nb 0.79)0.25(8.88Born)3770(

Considering the possible interference between the two amplitudes …

If we consider the possible interference …

nb 0.62)0.19(6.84obs)3770(

PLB 641 (2006) 145

)1( Is calculated with the (2S) resonance parameters measured by scanning the (2S) peak.

19

trgcmhadcm

hadcm

obshad EEL

nE

)( )()(

1

0

exp ))1(( ),( )( xssxFdxs Becthad

)()(

)(12)( 2222 sMMs

ss

tot

feeB

(Kuraev and Fadin)

functionsampling issxF ),(

Observed cross section

For (3770), we use energy-

dependent total width )(tot s

)hadrons( ee

The distribution of event vertex in Z

Fitting the distribution of the event vertex gives the number of hadronic events nhad.

Resonance parameters of (3770) , (3686) and branching fractions

20

)mode(2

)()(

tag single

tag single

D

D

DBL

ENE

cm

cmobs

DD

KD0

KD

Distributions of invariant masses of

mKn

Energy dependent cross sections

KD0

DD-bar production

combinations at different c.m. energies

Mar. 2003 data set

21

00DD

DD

DD

Inclusive hadrons

Inclusive hadrons

Ob

serv

ed c

ross

sec

tio

n f

or

had

ron

pro

du

ctio

n [

nb

]

Observed cross sections

(3686) resonance region

(3770) resonance region

Mar. 2003 data set

22

)()(

)(12222

0

sMMs

s

tot

DDeeBDD

2expobs2expobs2expobs

2

)(

)()(

)(

)()(

)(

)()(

00

0000

j

jj

j

jj

i

ii

DD

DDDD

DD

DDDD

had

hadhad

Fitting the observed inclusive hadron and DD-bar cross sections to the theoretical cross sections, we obtain the branching fractions

)()(

)(12222

0

)3770( sMMs

s

tot

toteeB

)()()()( 00ssss

DDnonDDDDtot

))3770(()(

)(

)(1

)(1)2()(

0030

3

2

20

00

0

0

0

000DDB

p

p

rp

rpMEs

D

D

D

DDcmDD

))3770(()(

)(

)(1

)(1)2()( 30

3

2

20

0

DDBp

p

rp

rpMEs

D

D

D

DDcmDD

))3770(()3770((1()(00

0

DDBDDBsDDnon

Fit to the observed cross sections

momentum of D at peak

momentum of Dthreshold function(3770) total width

Blatt-Weisskopf penetration factor

The total energy dependent width has three components:

23

had

nethad

had L

Ni

)(obs

had

nethad

had L

ni

)(exp

obsDD

obshad

nethad NNN expexp

DDhadnethad nnn

3322110)3770(exp )()1( BBBBBLn ISR

prdDD

))3770((00

0 DDBB

))3770(( DDBB

Independent hadron and DD-bar data sample

Branching fraction for the singly tagged D channel

These relations remove those hadronic events which also appear in the DD-bar samples, so that the inclusive hadronic and DD-bar samples are independent.

hadhadhad Ln expexp

24

Mainly due to vacuum polarization corrections

(3770)

(3686)

(3686)

To measure the resonance parameters of (3770) or (3686), one had better to simultaneously fit (3686) and (3770) resonances, since there are strong correlations between the fitted parameters of the two resonances.

If one do not consider the effects of vacuum polarization corrections on the observed cross sections in the data reduction, the total width of (3686) would decrease by about 40 keV!

PRL 97 (2006) 121801

After subtraction of (3686) , (3770) and J/ from the observed cross sections, one obtains the expected cross sections of the continuum hadron production.

Mar. 2003 data set

25

Comparison of (3770) Resonance Parameters

nb 0.3566.063.9|MeV 3.3772)3770(

s

prd

109.0054.0262.2uds R

nb 0.2848.094.6|MeV 3.3772

obs)3770(

s

nb 56.112.8|MeV 3.3772

obs)3770(

swhich is consistent within error with

obtained based on PDG04 parametersMar. 2003 data set

)3770(M)2()3770( SMMM

tot)3770(

ee)3770(

PRL 97 (2006) 121801

26

experiment

E760

BES-II

PDG04

This work

(MeV) M ' (keV) tot' (keV) '

ee

AN / 27264 21.044.2

03.009.3686 17281 12.012.2

3.00.05.3685 258331 11.004.033.2

1636306 3.01.00.3686

Comparison of (3686) Resonance Parameters

)%033.0122.0704.0(])3686([ eeB

510)03.006.093.0()])3770([( eeB 510)17.012.1()])3770([( eeB

)%031.0755.0(])3686([ eeB

PDG04

Obtained based on cross section scan

Mar. 2003 data setPRL 97 (2006) 121801

27

00DD

DD

Inclusive hadrons

Branching fractions

)%8.27.39.36())3770(( DDBF

)%3.27.47.46())3770(( 00 DDBF

)%2.43.76.83())3770(( DDBF

)%2.43.74.16())3770(( DDnonBF

Obtained from fitting to the inclusive hadron and the DD-bar production cross sections simultaneously.

where the first error is statistical and second systematic, which arises from the un-canceled systematic uncertainties in hadron cross sections (~4.4 %), neutral DD-bar cross sections (~4.5 %) and charged DD-bar cross sections (~7.4 %).

Mar. 2003 data set

PRL 97 (2006) 121801

28

Φ

π0 η

Φ signal

Φ sideband

Ecm [GeV] Φ π0 Φη

around 3.773

0 5.2±2.5

3.65 0 0

Search For (3770) decay to Φπ0 and Φη

Φ

π0 η

Ecm around 3.773 GeV (L=33 pb-1) Ecm=3.65GeV (L=6.5 pb-1)

29

Ecm Φ π+ π- ΦK+K- Φpp

Around 3.773 GeV (L=33 pb-1)

6.0 ±3.5 27.3 ±5.8 2

3.65 GeV (L=6.5 pb-1) 2 4.9 ±2.6 0

K+K- π+ π-

K+K- pp

Search For (3770) decay to Φπ+π-, ΦK+K- and

ΦppEcm around 3.773 GeV (L=33 pb-1) Ecm=3.65GeV (L=6.5 pb-1)

K+K- π+ π-

K+ K- K+K-K+K- K+ K-

K+K- pp -

30

2(π+ π-)η

2(π+ π-) π0

KKπ+ π-π0

ppπ+ π-π0

ppπ0

2(K+K-)π0

3(π+ π-) π0

DD-bar events have been removed.

Search for (3770) decay to multi-

body final states containing π0 or ηAround 3.773GeV

Ecm=3.65GeVAround 3.773GeV (L=33 pb-1)

Ecm=3.65GeV (L=6.5 pb-1)

31

Observed Cross Sections Preliminary !

No obvious cross section discrepancy at the two energy points is observed. However, to extract the non-DD-bar branching fractions of (3770) decays, one needs to consider the interference between the two amplitudes of the continuum and the resonances, and to consider the difference of ISR & vacuum polarization corrections at two energy points.

Search for charmless decays of (3770)

32

BES-II observed the first non-DD events of (3770) decays. CLEO-c conformed the BES observation of the non-DD decay.

)%09.014.034.0()/)3770(( JBF

)%022.0189.0()/)3770(( 007.0004.0

JBF

/)3770( J

CLEO-c

BES-II

CLEO-c PRL96,082004(2006)

PLB 605 (2005)63

The two measurements are consistent within the errors.

J/

J/mainly

8.48.17 /J BES-II

33

SUMMARY

BES measured the R values at 3.773 GeV and around 3.666 GeV with average uncertainties of

BES measured the resonance parameters of (3770) and (3686) with the improved precision on (3770) resonance parameters and with precision in measuring leptonic width of (3686) comparable to the current PDG04.

.

.

(preliminary !)

GeV 3.773s @ 0.190.043.75 R

GeV 66.3s @ 0.090.022.22 udsRGeV 3.89 to 3.67 from range the in @ 0.122.26udsR

%5~

Obtained from fitting to (3686) and (3770)

nb 80025.032.9Born)3770( . nb 63020.018.7obs

)3770( .

34

BES measured the branching fractions for inclusive non-DD-bar decays of (3770) using two different data samples and two different methods

.(preliminary !)

SUMMARY

)%4.31.17.35())3770(( DDBF )%9.33.19.49())3770(( 00 DDBF

)%8.57.15.85())3770(( DDBF )%8.57.15.14())3770(( DDnonBF

Determined from analysis of R values and DD-bar cross sections

)%8.27.39.36())3770(( DDBF )%3.27.47.46())3770(( 00 DDBF

)%2.43.76.83())3770(( DDBF )%2.43.74.16())3770(( DDnonBF

Obtained from fitting to the inclusive hadron and the DD-bar production cross sections simultaneously.

.BES observed the first non-DD events of J/ , and established this hadronic transition process. BES searched for some charmless final states around 3.773 GeV and at 3.65 GeV, but did not observe obvious cross section discrepancy at the two energy points for most decay modes.

35

Gang RONG

(for BES Collaboration)

Institute of High Energy Physics, Beijing 100049, P.R. China

Backup slides

36

Comparison with those measured by CLEO-c

BES-II CLEO-c)%2.42.74.16())3770(( DDnonBF

nb 0.080.01 0.410.30-)3770(

DDnon

nb 0.086.38 0.410.30-)3770(

obs

hadrons

Based on analysis of inclusive hadron and DD-bar cross section scan data.

(hep-ex/0512038); PRL 96 (2006) 092002

nb 0.106.39 0.170.08-

obsDD

Actually, considering the errors, the two results are not in contradiction.

nb 0.280.486.94obs)3770(

nb 0.61.1 )3770(

DDnon

PLB 141 (2006) 145

37

BES-II CLEO-cnb 0.500.126.14 obs

DD nb 0.106.39 0.17

0.08-obs

DD

nb 0.4212.00.95 )3770(

DDnon

nb 0.080.01 0.410.30-)3770(

DDnonnb 0.086.38 0.41

0.30-)3770(

obshadrons

Based on measured R values.

Comparison with those measured by CLEO-c

Method:BES measured near DD-bar threshold and R at 3.773 GeV with traditional method, then calculate the Born order cross section for (3770) production. By comparing the cross sections for DD-bar and (3770) production, BES obtained the branching fraction. BES used an ISR generator to simulate the decay e+e- hadrons and obtain the efficiency for e+e- hadrons.

udsRMethod:CLEO-c directly count the number of hadronic events observed at 3.773 GeV, and subtract the backgrounds from J/, (2S) radiative tails and continuum QED background. CLEO-c used the efficiency for the decay (3770) J/ π+ π- to estimate the efficiency for e+e- hadrons.

nb 0.630.197.09obs)3770(

Use parameter keV 33.2)2( eeS Use parameter keV 54.2)2( ee

S

Assuming that there are interference between the two amplitudes of continuum and resonance

nb 0.4212.00.62 )3770(

DDnonnb 0.620.196.76obs

)3770(

38

BES-II CLEO-c

Comparison with those measured by CLEO-c

Method: Method:

nb 0.080.01 0.410.30-)3770(

DDnon

Discussion

if we use to calculate the ISR & vacuum polarization correction factor, and assuming that there are interference between the two amplitudes of the continuum and the resonance, we would obtain

CLEO-c did not consider the difference of ISR & vacuum polarization corrections for continuum hadron production at two energy points (3.671 GeV and 3.773 GeV) when subtracting background at 3.773 GeV.)2( S

keV 54.2)2( eeS

nb 42.00.110.48 )3770(

DDnon

)% 4.68.17.3())3770(( DDnonB

PRL 97 (2006) 121801

39

obsDD

[nb]

Comparison of measurements of the cross sections for DD-bar production

GeV) 7713( .s

GeV) 7683( .s

GeV) 7743( .s

GeV) 7733( .s

GeV) 7733( .s

GeV) 7733( .s

My estimation, Input with PDG04 Br

40

Comparison of measurements of the cross sections for DD-bar production

nb 28049.5obs

.DD

nb 15025.6obs

.DD

weighted average

nb 14008.6obs

.DD

07.007079.2 .

BrD D

obs)or (

obs

DD

obsDD

My estimation

My estimation

41

Branching fraction of (3770) to non-DD-bar

MeV 4213771)3770( ..M

nb 5.15.11produced)3770(

nb 14008.6| tagdoubleandsingle

obs.DD

72.0|)1( GeV7703ISR .Ecm

produced)3770(ISR

obs

)1())3770((

σ

DDBF DD

Which is obtained based on the data from MARK-I, MARK-II, MARK-III, BES-II and CLEO-c.

PDG065100.14)(1.05)ee(3770)( BF

)%2.114.73())3770(( DDBF

)%2.116.26())3770(( DDnonBF My estimation

42

Branching fraction of (3770) to non-DD-bar

MeV 4213771)3770( ..M

nb 5.15.11produced)3770(

nb 10039.6| 17.008.0tagdouble CLEO

obs .

DD 72.0|)1( GeV7703ISR .Ecm

produced)3770(ISR

obs

)1())3770((

σ

DDBF DD

Which is obtained based on the DD-bar cross section measured by CLEO and PDG06 psi(3770) resonance parameters.

PDG065100.14)(1.05)ee(3770)( BF

)%3.102.77())3770(( DDBF

)%3.108.22())3770(( DDnonBF My estimation

nb 16039.6| tagdouble CLEOobs .

DD

43

obshad

cmE ]GeV[

MARK-I

MARK-II

DELCO

BES-II

PRL39 (1977) 526

PRL40 (1978) 671

hep-ex/0605107

44

Branching fraction of (3770) to non-DD-bar

MeV 4203770)3770( ..M

nb 8.16.11produced)3770(

nb 14008.6| tagdoubleandsingle

obs.DD

72.0|)1( GeV7703ISR .Ecm

produced)3770(ISR

obs

)1())3770((

σ

DDBF DD

Which is obtained based on the data from MARK-I, MARK-II, MARK-III, BES-II and CLEO-c.

PDG045100.17)(1.12)ee(3770)( BF

)%4.118.72())3770(( DDBF

)%4.112.27())3770(( DDnonBF My estimation