1. Preliminary results from the attenuation scans in BGO crystal. 1 F.Lacava CERN 17.12.2007

2. 2 Run #: 1554 – 1578 25 points HV: pm_Y: 1500 V (-10dB att), pm_UV: 1700 V Scope: ch # 1: 100 mV/div., ch # 2: 20 mV/div. Time: 2 ns/pt. x 36 cm60 cm Beam x 36 cm60 cm Beam Run #: 1787 – 1810 25 points HV: pm_Y: 1300 V, pm_UV: 1700 V Scope: ch # 1: 100 mV/div., ch # 2: 100 mV/div. Time: 0.8 ns/pt. Yellow filter UV filter Inverted filters 30 mm20 mm Two sets of run with the Yellow and UV filters exchanged.

3. Beam: 50 GeV electrons Events selection: 1 particle / event - x = x ± 1.7 cm ( 1 σ ) y= y ± 1.5 cm - Analysis of ADC for Yellow and UV filter pm’s. - Analysis of the signals at the oscilloscope 3

4. Typical signals for 50 GeV electrons Fit of the UV signal by Landau or other functions Difficult to perform an analysis fitting each event: ---> very large chisquare and with large fluctuations from run to run due to noise, pick up signals, etc. Yellow signal: a Fermi function * exponetial fit seems reasonable. UV Y Y 4

5. For the Yellow filter signal: same function used before for each event. To fit UV signal: a double Fermi funtion (black) overimposed to a Fermi function * exponential (green) : problems in the starting time of the scintillation component! Then move to study averaged signals UV YY 5

6. A Fermi function * exponetial function normalized on the tail to estimate the scintillation component in the UV filter signal. Cerenkov Signal = integral of 55-80 bins contents (50 ns) minus the scintillation contribution in the same interval from the previous fit. Yellow signal (Scint. Signal) : Fermi function * exponetial function fit. A more effective approach … 6

7. Events with filters in the initial configuration. - A small sinusoidal component is present in the ADC. - It was visible in the raw data plotted in the logbook at the test beam. - In the Cerenkov component from the UV signal it appears a sinusoidal component. 7 UV filter

8. Events with inverted filters. 8 UV filter - A very small sinusoidal component is present now in the scintillation component seen at the UV filter. - No or only a very small sinusoidal component in the Cerenkov signal.

9. 9 Attenuation ( λ ) and geometrical factor R(x) from Yellow filter ADC. x x S 1 (x) = R(x) e - λ x S 2 (x) = R(x) e - λ (L - x) S 1 (x) / S 2 (x) = e λ L e - 2 λ x S 1 (x) · S 2 (x) = e - λ L R 2 (x) Attenuation Geometrical factor (A.Cardini) Beam L attY ~ 45 cm (too small).

10. 10 Conclusion - A preliminary analysis of the attenuation scan has been presented. - A more extensive and detailed analysis has to be performed. - Cerenkov signals vs x has to be studied and understood : optical effects could be present in the observed signals. - It is possible to extract correction factors for other studies on the BGO crystal.