Recent results on (3770) production & decays from BES/BEPC
description
Transcript of Recent results on (3770) production & decays from BES/BEPC
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.
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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+
+-
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
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Comparison of R measurements from different experiments
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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
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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
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)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
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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