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Dong LiuState Key Laboratory of Particle Detection and Electronics
University of Science and Technology of China
ISSP, Erice, 2017
• Introduction of BESIII experiment• Motivation of the study• Data sample• Event selection• Efficiency and correction factor• Cross section and form factor• Uncertainty• Summary
Outline
ISSP, Erice, 2017 D. Liu USTC 2
BESI
II1 T Super conducting
Muon ID: RPCs
σp/p=0.5% @1 GeV, σ dE/dx=6%
σT=100 ps barrel, 65 ps endcaps
CsI crystal, ΔΕ/Ε = 2.5% @1 GeVBEPCII and BESIII
ISSP, Erice, 2017 D. Liu USTC 3
Motivation: Y(2175)
Y(2175)
in Flux Tube Model
9.8 23.1 0 0
167.21 211.9 148.7 378
PLB 657 (2007) 49
BESII PRL 100. 102003 (2008)in 𝐽/𝜓 → 𝜂𝜙𝑓((980)
BaBar PRD 74. 091103 (2006)in 𝑒/𝑒0 → 𝛾𝜙𝑓((980)
Motivation: precision
(GeV)s1 1.5 2 2.5 3 3.5 4 4.5 5
2 |K
|F
3−10
2−10
1−10
1
10
210
310
410
(GeV)s
2 2.2 2.4 2.6 2.8 3 3.2
2 |K
|F
0
0.05
0.1
0.15
BaBar PRD 88 (2013) 032013
ISSP, Erice, 2017 D. Liu USTC 5
(GeV)s1 1.5 2 2.5 3 3.5 4 4.5 5
2 |K
|F
3−10
2−10
1−10
1
10
210
310
410
(GeV)s
2 2.2 2.4 2.6 2.8 3 3.2
2 |K
|F
0
0.05
0.1
0.15
Motivation: FF
-e
+e
γ
s
s
u
u
FK = 16πα s s( ) f 2K / s
F q2( ) = d3rρ r( )eiq⋅r∫PRD 88 (2013) 032013
ISSP, Erice, 2017 D. Liu USTC 6Phys. Lett. 87B, 359 (1979)
Data samplesl Experimental data
l MC samples
ISSP, Erice, 2017 D. Liu USTC 7
• Good charged tracks: (MDC)– |Vr| < 1 cm, |Vz| < 10 cm, |cosθ| < 0.93, N+ = N- = 1– cosθ+<0.8, cosθ->-0.8
• E/p: (EMC+MDC)– E/p < (E/p)cut, cut optimized with signal to noise ratio
S/√(S+N), cut value ~0.6 – 0.8• Back to back: angle(1,2)>179°• TOF: |TOF1-TOF2| < 3 ns (TOF)
Event selection
Select 2-prong event
ISSP, Erice, 2017 D. Liu USTC 8
• K± separated from background with momentum
Event selection
(GeV)s2 2.2 2.4 2.6 2.8 3
p (G
eV/c
)
0.4
0.6
0.8
1
1.2
1.4
compare p of 2 tracks
epµpπpK
ppp
(GeV)s2 2.2 2.4 2.6 2.8 3
p (G
eV/c
)
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
p of 2 prong process
Kpµ
pσ1 σ3 σ5
Use momentum to select Kaon
pexp =E2
⎛⎝⎜
⎞⎠⎟2
−mK2
ISSP, Erice, 2017 D. Liu USTC 9
Signal extraction
(GeV/c)+Kp
0.6 0.7 0.8 0.9 1 1.1 1.2
(GeV
/c)
- Kp
0.6
0.7
0.8
0.9
1
1.1
1.2
1
10
210
310
signals
Signal: MC ⨂ GausBackground: MC ⨂ Gaus
p (GeV/c)0.85 0.9 0.95 1
Even
ts /
( 0.0
02 G
eV )
0
100
200
300 0.00016± = 0.87036 µ
0.00020± = 0.00470 σ
43.9±signal = 1824.0
/(100-10) = 0.6452χ
p in pexp± 3σ
σ = NL ⋅ε ⋅(1+δ )
Example at 2.0 GeV
ISSP, Erice, 2017 D. Liu USTC 10
Efficiency and 1+δ
(GeV)s1 2 3 4 5
(nb)
σ
3−10
2−10
1−10
1
10
210
310
410
σ = NL ⋅ε ⋅(1+δ )
BaBar PRD 88 (2013) 032013
ISSP, Erice, 2017 D. Liu USTC 11
Cross section
ISSP, Erice, 2017 D. Liu USTC 12
(GeV)s2 2.2 2.4 2.6 2.8 3 3.2
(nb)
σ
0.1
0.2
0.3
0.4
0.5BESIIIBABAR 2013BABAR 2015fit
0.0053 GeV±m = 2.2298
0.0120 GeV± = 0.1437 Γ
Cross section
ISSP, Erice, 2017 D. Liu USTC 13
Eur. Phys. J. C 39, 41–54 (2005)
ØForm factor extraction:
: dressed cross section; : bare cross section; : final-state correction
ØFitting function:
: strong couplingntheory = 2n = 1.94±0.09
(GeV)s2 2.2 2.4 2.6 2.8 3
2 | K|F
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
BESIII preliminaryBABAR resultfit only BESIII result
> 2.38 GeVswith
FK2 s '( ) = 3s '
πα 0( )2 βK2
σ KK s '( )CFS
σ KK s '( ) =σ KK0 s '( ) α s '( )
α 0( )⎛⎝⎜
⎞⎠⎟
2
σ KK σ KK0
βK = 1− 4mK2 / s CFS
FK2 = Aα s
2 s( ) / snα s
Form factor
ISSP, Erice, 2017 D. Liu USTC 14
Form factor
ISSP, Erice, 2017 D. Liu USTC 15
Uncertainty 7
TABLE IV: Systematic uncertainty (%) of the cross section of the e+e� ! K+K� process. The last line gives the totalsystematic uncertainty on the K+K� cross section.
Ecm
(GeV) 2.0000 2.0500 2.1000 2.1250 2.1500 2.1750 2.2000 2.2324 2.3094 2.3864 2.3960L 0.9 0.9 0.9 0.8 0.9 0.9 0.9 0.9 0.9 0.9 0.9✏ 0.2 0.2 0.2 0.2 0.3 0.2 0.2 0.2 0.2 0.3 0.31 + � 0.2 0.1 0.3 0.3 0.5 0.3 0.3 0.5 0.2 0.4 0.4p cut 0.7 < 0.1 0.2 < 0.1 < 0.1 0.3 0.4 0.1 < 0.1 0.2 0.3E/p 0.6 0.7 0.5 0.6 0.6 0.6 0.6 0.5 0.6 0.4 0.4open angle 0.8 0.7 0.8 0.7 0.7 0.7 0.8 0.8 0.7 0.9 1.0tracking e�ciency 0.9 0.2 0.1 0.5 0.5 0.6 0.6 0.5 0.1 0.7 0.8fitting range 0.0 0.7 0.1 0.3 0.1 0.1 0.5 0.2 0.6 0.5 0.4signal shape 0.2 0.2 0.2 0.2 0.3 0.4 0.4 0.5 0.7 1.0 1.0background shape 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.5 0.5 0.6sum 1.8 1.6 1.5 1.5 1.5 1.6 1.7 1.6 1.7 2.0 2.1
Ecm
(GeV) 2.5000 2.6444 2.6464 2.7000 2.8000 2.9000 2.9500 2.9810 3.0000 3.0200 3.0800L 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9✏ 0.3 0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.4 0.41 + � 0.2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3p cut 1.4 0.4 0.5 0.5 0.5 0.1 0.1 0.5 1.6 1.1 1.1E/p 0.6 0.6 0.6 0.4 0.7 0.4 0.4 0.5 0.4 0.5 0.4open angle 0.8 0.9 0.8 0.9 1.3 0.8 0.9 1.2 0.9 0.9 1.0tracking e�ciency 2.1 1.1 1.2 1.5 1.4 1.0 1.3 1.6 1.7 1.7 1.9fitting range 0.3 2.7 0.8 1.0 1.0 1.1 0.3 0.2 0.7 0.7 0.8signal shape 1.3 1.7 1.7 2.0 2.5 3.0 3.3 3.4 3.5 3.6 3.9background shape 0.6 0.7 0.8 1.2 2.1 3.0 3.5 3.8 3.9 4.1 4.6sum 3.2 3.8 2.8 3.3 4.1 4.7 5.2 5.6 6.0 6.1 8.8
[7] D. Bisello et al. (DM2 Collaboration), Z. Phys. C 39, 13305
(1988).306
[8] R.R. Akhmetshin et al. (CMD-2 Collaboration), Phys.307
Lett. B 669, 217 (2008).308
[9] J.P. Lees et al. (BaBar Collaboration), Phys. Rev. D 88,309
032013 (2013).310
[10] J.P. Lees et al. (BaBar Collaboration), Phys. Rev. D 92,311
072008 (2015).312
[11] M.R. Whalley, J. Phys. G: Nucl. Part. Phys. 29, A1313
(2003).314
[12] M. Bernardini et al., Phys. Lett. B 46, 261 (1973).315
[13] T.K. Pedlar et al. (CLEO Collaboration), Phys. Rev.316
Lett. 95 261803 (2005).317
[14] F.A. Harris et al., Int. J. Mod. Phys. A 24, 377 (2009).318
[15] BEPCII Group, BEPCII Design Report, IHEP- Proceed-319
ings, Aug. 2001.320
[16] M. Ablikim et al. (BESIII Collaboration), Nucl. Instrum.321
Meth. A 614, 345 (2010).322
[17] S. Agostinelli et al. (GEANT4 Collaboration), Nucl. In-323
strum. Meth. A 506, 250 (2003).324
[18] G. Balossini et al., Nucl. Phys. B 785, 227 (2006).325
[19] B. Andersson and H. Hu, hep-ph/9810285.326
[20] R.G. Ping, Chin. Phys. C, 38(8), 083001 (2014).327
[21] C. Bruch et al., Eur. Phys. J. C 39, 41(2005).328
[22] W.L. Yan et al., Chin Phys. C, 40(2), 026201(2016).329
Systematic uncertainty is only a few percent.
ISSP, Erice, 2017 D. Liu USTC 16
• With momentum and other requirement, the kaon is well separated from background.
• σ(e+ e- à K+ K-) measured with BESIII data are consistent with BaBar experiment.
• Precision of our result is much precise than previous experiments.
• From cross section, the form factors of charged kaon are extracted.
• Both cross section and form factor show clear structure near 2.2 GeV.
Summary
ISSP, Erice, 2017 D. Liu USTC 17
Disscussion
M (MeV)2000 2100 2200
(MeV
)Γ
0
100
200
300
400 (2170)φPDG: - K+BESIII preliminary: K
0 fφ η → ψBESII: J/ -π +π φ η → ψBESIII: J/
ISRγ η φBABAR:
ISRγ -π +π - K+BABAR: K
ISRγ -π +π - K+BELLE: K
ISRγ 0π 0π - K+BABAR: K
M (MeV)2050 2100 2150 2200 2250
(MeV
)Γ
0
200
400
600(2150)ρPDG: -K+BESIII preliminary: K
n0π ω → p -πGAMS: n0π ω → p -πGAMS:
γ -π +π(1285) 1BABAR: f γ -π +π' ηBABAR: - K+, K-π +πRVUE: )0π -π +π), 2(-π +πRVUE: 3(
ISSP, Erice, 2017 D. Liu USTC 18
backup
ISSP, Erice, 2017 D. Liu USTC 19
• (g-2)μ– hint of new physics– experiments: BaBar, Belle,
KLOE, BESIII, SND, CMD
Motivation
aµhad,LO =
αmµ2
3π⎛
⎝⎜⎞
⎠⎟ds R(s)K(s)
s2sth
∞
∫
ISSP, Erice, 2017 D. Liu USTC 20
Backup: Momentum spectra
p (GeV/c)0.85 0.9 0.95 1
Even
ts /
( 0.0
02 G
eV )
0
100
200
300 0.00016± = 0.87036 µ
0.00020± = 0.00470 σ
43.9±signal = 1824.0
/(100-10) = 0.6452χ
p (GeV/c)0.85 0.9 0.95 1
Even
ts /
( 0.0
02 G
eV/c
)
0
50
100 0.00028± = 0.89834 µ
0.00028± = 0.00451 σ
22.9±signal = 524.0
= 0.9082χ
p (GeV/c)0.9 0.95 1 1.05
Even
ts /
( 0.0
02 G
eV/c
)
0
50
100
150
200
0.00016± = 0.92661 µ
0.00028± = 0.00437 σ
38.2±signal = 1418.7
= 0.5962χ
p (GeV/c)0.9 0.95 1 1.05
Even
ts /
( 0.0
02 G
eV/c
)
0
0.5
1
1.5
310× 0.00006± = 0.94106 µ
0.00048± = 0.00999 σ
107.5±signal = 11088.7
= 1.1192χ
p (GeV/c)0.95 1 1.05 1.1
Even
ts /
( 0.0
02 G
eV/c
)
0
10
20
30
40
0.00044± = 0.95556 µ
0.00038± = 0.00486 σ
16.3±signal = 263.0
= 0.6422χ
p (GeV/c)0.95 1 1.05 1.1
Even
ts /
( 0.0
02 G
eV/c
)
0
50
100
150
0.00024± = 0.96887 µ
0.00024± = 0.00539 σ
33.9±signal = 1029.1
= 0.6472χ
p (GeV/c)0.95 1 1.05 1.1
Even
ts /
( 0.0
02 G
eV/c
)
0
100
200
0.00016± = 0.98307 µ
0.00027± = 0.00463 σ
41.4±signal = 1697.6
= 0.8322χ
p (GeV/c)1 1.05 1.1 1.15
Even
ts /
( 0.0
02 G
eV/c
)
0
50
100
150
200
0.00016± = 1.00055 µ
0.00055± = 0.01032 σ
40.4±signal = 1613.5
= 0.7162χ
p (GeV/c)1 1.05 1.1 1.15
Even
ts /
( 0.0
02 G
eV/c
)
0
100
200
0.00016± = 1.04343 µ
0.00120± = 0.01003 σ
47.2±signal = 2080.3
= 0.5682χ
ISSP, Erice, 2017 D. Liu USTC 21
Backup: Momentum spectra
p (GeV/c)1.05 1.1 1.15 1.2
Even
ts /
( 0.0
02 G
eV/c
)
0
50
100
150 0.00023± = 1.08614 µ
0.00050± = 0.01163 σ
36.1±signal = 1269.4
= 0.5172χ
p (GeV/c)1.05 1.1 1.15 1.2
Even
ts /
( 0.0
02 G
eV/c
)
0
200
400
0.00014± = 1.09155 µ
0.00153± = 0.01004 σ
70.6±signal = 3841.7
= 0.7532χ
p (GeV/c)1.1 1.15 1.2 1.25
Even
ts /
( 0.0
02 G
eV/c
)
0
5
10 0.00120± = 1.14783 µ
0.00757± = 0.01300 σ
7.5±signal = 53.4
= 0.7502χ
p (GeV/c)1.2 1.3 1.4
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100
150 0.00033± = 1.22664 µ
0.00086± = 0.00709 σ
40.2±signal = 1107.3
= 0.7642χ
p (GeV/c)1.2 1.3 1.4
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100
150 0.00030± = 1.22783 µ
0.00053± = 0.01300 σ
42.7±signal = 1145.1
= 0.5602χ
p (GeV/c)1.2 1.3 1.4
Even
ts /
( 0.0
03 G
eV/c
)
0
5
10
0.00183± = 1.25553 µ
0.00154± = 0.00844 σ
5.1±signal = 22.1
= 0.8022χ
p (GeV/c)1.3 1.4 1.5
Even
ts /
( 0.0
03 G
eV/c
)
0
5
10 0.00249± = 1.30994 µ
0.00672± = 0.00470 σ
6.5±signal = 28.0
= 0.6492χ
p (GeV/c)1.3 1.4 1.5
Even
ts /
( 0.0
03 G
eV/c
)
0
200
400
0.00029± = 1.36308 µ
0.00178± = 0.01300 σ
58.5±signal = 1997.5
= 1.1082χ
p (GeV/c)1.3 1.4 1.5
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100 0.00071± = 1.38987 µ
0.00084± = 0.00699 σ
21.5±signal = 265.1
= 0.7252χ
ISSP, Erice, 2017 D. Liu USTC 22
Backup: Momentum spectra
p (GeV/c)1.4 1.5 1.6
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100 0.00080± = 1.40591 µ
0.00079± = 0.00890 σ
21.0±signal = 287.0
= 0.6232χ
p (GeV/c)1.4 1.5 1.6
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100
0.00101± = 1.41595 µ
0.00746± = 0.01167 σ
18.8±signal = 223.7
= 0.6302χ
p (GeV/c)1.4 1.5 1.6
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100
0.00091± = 1.42528 µ
0.00162± = 0.01240 σ
23.3±signal = 264.6
= 0.6222χ
p (GeV/c)1.4 1.5 1.6
Even
ts /
( 0.0
03 G
eV/c
)
0
200
400
600
800 0.00047± = 1.45764 µ
0.00106± = 0.00915 σ
70.5±signal = 1417.1
= 1.3932χ
p (GeV/c)1.4 1.5 1.6
Even
ts /
( 0.0
03 G
eV/c
)
0
50
100
150
200 0.00103± = 1.45640 µ
0.00802± = 0.01300 σ
37.0±signal = 364.6
= 0.5882χ
ISSP, Erice, 2017 D. Liu USTC 23
Backup: open angle
angle
coun
t
0
50
100
150
dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
20
40
dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
50
100dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
angle
coun
t
0
10
20
dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
20
40
60
80dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
50
100
dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
angle
coun
t
0
50
100dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
50
100
150 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
50
100dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
ISSP, Erice, 2017 D. Liu USTC 24
Backup: open angle
angle
coun
t
0
100
200
300 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
2
4
6
8 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
50
100dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
angle
coun
t
0
50
100 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
2
4
6 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
2
4
6 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
angle
coun
t
0
100
200
300 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
20
40
60 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
20
40
60 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
ISSP, Erice, 2017 D. Liu USTC 25
Backup: open angle
angle
coun
t
0
20
40
60dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
20
40
60
80 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1angle
coun
t
0
100
200
300
400 dataMC KK
µµMC MC hadronMC sum
angle177 178 179 180
rela
tive
∆
1−
0
1
ISSP, Erice, 2017 D. Liu USTC 26
