Measurement of Luminosityat energy 2.23 GeV, 2.4 GeV, 2.8 GeV and 3.4 GeV

Geng Cong

Center for Particle Physics and TechnologyUniversity of Science and Technology of China

September 3, 2012

Geng Cong (CPPT-USTC) Luminosity September 3, 2012 1 / 14

Outline

Introduction

Measurement with e+e− → e+e−

Measurement with e+e− → γγ

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Introduction

Luminosity (integrated Luminosity, denoted as L ) is a keyparameter of high energy physics and an important input value ofmany analyses. Precise measurement of Luminosity is desired inany experiments.

In e+e− collider, the precise measurement is always achieved dueto the well-understood QED processes e+e− → (γ)e+e−,e+e− → (γ)γ+γ− and e+e− → (γ)µ+µ−.

For a special physical process, the corresponding events rate isN = L · σ(·ε), where the σ is cross section of the physical processand ε denotes the efficiency. So, conversely, using thewell-understood processes, the Luminosity is determined as:

L =N

σ · ε

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Measurement with e+e− → e+e−: Event Selections

Tracks

Vr < 1.0cm, |Vz | < 10.0cm

N+ = N− = 1

180− arccos−→P+·−→P−

|P+||P−| < 50

Shower

| cos θ| < 0.8

Eshower > 1.3 GeV for 3.4 GeVEshower > 1.0 GeV for 2.8 GeVEshower > 0.8 GeV for 2.4 GeVEshower > 0.7 GeV for 2.23 GeV

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Generators and Results

Two generators, Babayaga and Bhwide, are used to generate MC events ofe+e− → e+e−. The check by Bhwide is in progress.

2.23 GeV 2.4 GeV 2.8 GeV 3.4 GeVnumber of events 706237 785791 629424 193949

cross section (nb) 818.3 708.1 521.1 353.9Babayga efficiency (%) 32.8 32.5 32.2 31.7

Luminosity (pb−1) 2.631 3.415 3.751 1.729

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Comparisons between data (Red) and MC (Black)

)­

(eθcos

­0.8 ­0.6 ­0.4 ­0.2 0 0.2 0.4 0.6 0.80

2000

4000

6000

8000

10000

12000

14000

16000

)+

(eθcos

­0.8 ­0.6 ­0.4 ­0.2 0 0.2 0.4 0.6 0.80

2000

4000

6000

8000

10000

12000

14000

16000

Acollinearity

0 1 2 3 4 5 60

5000

10000

15000

20000

25000

30000

180− arccos−−→Pe+ ·−−→Pe−

|Pe+ ||Pe− |

φ∆

­50 ­40 ­30 ­20 ­10 0 10 20 30 40 50

1

10

210

310

410

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Momentum and Energy: data (Red) and MC (Black)

) (GeV)­

momentum (e

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.80

5000

10000

15000

20000

25000

) (GeV)+

momentum (e

1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.80

5000

10000

15000

20000

25000

30000

E

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.90

2000

4000

6000

8000

10000

12000

14000

E

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.90

2000

4000

6000

8000

10000

12000

14000

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Check by Bhwide

)­

(eθcos

­0.8 ­0.6 ­0.4 ­0.2 0 0.2 0.4 0.6 0.80

2000

4000

6000

8000

10000

12000

14000

16000

)+

(eθcos

­0.8 ­0.6 ­0.4 ­0.2 0 0.2 0.4 0.6 0.80

2000

4000

6000

8000

10000

12000

14000

16000

Acollinearity

0 1 2 3 4 5 60

5000

10000

15000

20000

25000

30000

φ∆

­50 ­40 ­30 ­20 ­10 0 10 20 30 40 50

1

10

210

310

410

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Measurement with e+e− → γγ: Event Selections

Shower

| cos θ| < 0.8

Eshower > 1.3 GeV for 3.4 GeVEshower > 1.0 GeV for 2.8 GeVEshower > 0.8 GeV for 2.4 GeVEshower > 0.7 GeV for 2.23 GeV

Nshower = 2

180− arccos−→P1·−→P2

|P1||P2| < 50

−20 < 180− |φ1 − φ2| < 40

Tracks

Vr < 1.0cm, |Vz | < 10.0cm

Ntrack = 0

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e+e− → e+e− and e+e− → γγ

Without taking into account the number of tracks in MDC.

φ∆

­50 ­40 ­30 ­20 ­10 0 10 20 30 40 500

2000

4000

6000

8000

10000

12000

14000

16000

18000

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Results

Babayaga is used to generate MC events of e+e− → γγ.

2.23 GeV 2.4 GeV 2.8 GeV 3.4 GeVnumber of events 81222 91036 73041 22694

cross section (nb) 56.07 48.52 35.69 24.24Babayga efficiency (%) 55.0 54.9 54.5 53.8

Luminosity (pb−1) 2.634 3.418 3.755 1.740

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Comparisons between data (Red) and MC (Black)

θcos

­0.8 ­0.6 ­0.4 ­0.2 0 0.2 0.4 0.6 0.80

200

400

600

800

1000

Acollinearity

0 1 2 3 4 5 60

200

400

600

800

1000

1200

1400

1600

1800

φ∆

­10 ­8 ­6 ­4 ­2 0 2 4 6 8 10

10

210

310

E

1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.90

500

1000

1500

2000

2500

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Another generator: Radgg

Radgg generate MC events with full geometric coverage. Efficiency is 6.7% andcross section is 210 nb. The calculated luminosity is 1.613 pb−1.

φ∆

­10 ­8 ­6 ­4 ­2 0 2 4 6 8 10

10

210

310

Acollinearity

0 1 2 3 4 5 60

200

400

600

800

1000

1200

1400

1600

1800

θcos

­0.8 ­0.6 ­0.4 ­0.2 0 0.2 0.4 0.6 0.80

200

400

600

800

1000

1200

1400

1600

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Summary

2.23 GeV 2.4 GeV 2.8 GeV 3.4 GeVLuminosity(e+e− → e+e−) (pb−1) 2.631 3.415 3.751 1.729Luminosity(e+e− → γγ) (pb−1) 2.634 3.418 3.755 1.740difference 0.1% 0.1% 0.1% 0.6%Radgg (pb−1) 2.464 3.202 3.517 1.613online (pb−1) 1.466 2.341 3.099 1.658

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