1. Luminosity Determination
03rd March Dieter Prasuhn

2. Outline Definition of Luminosity Determination of Luminosity Accuracy
Count rate of reaction products with known cross section
Beam lifetime measurement
Energy loss measurement
Accuracy
03 March 2009
Dieter Prasuhn

3. Definition of Luminosity
Count rate:
Luminosity:
Measurement of frevolution: Schottky spectrum
Number of circulating particles: Beam Current transformer, BPM, …
03 March 2009
Dieter Prasuhn

4. Measurement of target thickness
Comparison of beam life times without target (only residual gas) and with target
Measurement of the mean energy loss
03 March 2009
Dieter Prasuhn

5. Beam life time measurement
Average vacuum pressure over the ring: 5*10-9 mbar
(corresponding to 2.5*1012 cm-2)
beam life time without target:
twithout=859 minutes
beam life time with target:
twith=2.4 minutes
Target thickness = 352*2.5*1012
= 8.8*1014 cm-2
03 March 2009
Dieter Prasuhn

6. After target optimization
Average vacuum pressure over the ring: 5*10-9 mbar
(corresponding to 2.5*1012 cm-2)
beam life time without target:
twithout=859 minutes
beam life time with target:
twith=77.3 seconds (!!)
Target thickness = 667*2.5*1012
= 1.7*1015 cm-2
03 March 2009
Dieter Prasuhn

7. Estimate of target thickness by energy loss measurement
Measurement of h:
Measurement of frequency shift:
Dp/p (over 160 s)= 2.3*10-3
This corresponds to an effective target thickness of 2.5*1015 cm-2
03 March 2009
Dieter Prasuhn

8. Accuracy
At COSY-11 we found an agreement with experimental data on the level of 10%
The WASA data show an agreement within 30%.
With higher accuracy for all measurements a level of 10% accuracy is achievable.
03 March 2009
Dieter Prasuhn