Qweak scintillator prototype cosmic test (9)

Cosmic test results of the scintillator prototype using a finger lightguide.

A. Done the single photoelectron calibration to determine the location of the pedestal peak and single pe peak of L and R PMT, using the similar method applied to the triangular lightguide. Both the T and B trigger paddles were placed above the L (R) finger lightguide, with a V-shaped layout and 10 cm apart vertically. The HV of the L and R PMT was set to 2250 V, and the threshold of the paddles was 200mV. Had tried to use a lower HV for L and R PMT (HV=2040 V), but the obtained data could not separate the pedestal peak and the single pe peak. So, I used the same HV as the triangular lightguide.

1. Pedestal Peak and single pe peak with T and B paddles above the R finger lightguide. For the L PMT, the pedestal peak is at channel 53 and the single pe peak is at channel 93, which is the same as the triangular lightguide results.





2. Pedestal Peak and single PE peak with T and B paddles above the L finger lightguide. For the R PMT, the pedestal peak is at channel 75 and the single pe peak is at channel 95. As a comparison, for the triangular lightguide, the pedestal peak is at channel 74 and the single pe peak is at channel 93.





B. Studied the ADC and TDC response along the long axis of the scintillator bar. Changed the set-up by placing the T paddle above the SCIN bar and the B paddle below it with a V-shaped layout. Took cosmic data at Z=10, 110, 195 cm along the SCIN bar. 1. Photoelectron number of L and R PMT at different Z positions, and a comparison to the triangular lightguide results.





2. Time difference of the scintillation light traveling to the L and R PMT at different Z positions, and a comparison to the triangular lightguide results.





3. ADC histograms of one cosmic run taken at Z=110 cm. The L ADC signal was attenuated by 4/9 to keep the signal inside the measurable range of the V792 ADC (total 4096 adc channel).





4. TDC histograms of one cosmic run taken at Z=110 cm. According to the last histogram, the time resolution of L/R PMT is around 400 ps. For the triangular lightguide, the time resolution is around 600 ps.





C. Checked the TDC and ADC response along the short axis (y=4, 11.5, 19 cm) at Z=10, 195 cm respectively. Like the triangular lightguide set-up, found NO obvious blind spots along the short axis of the SCIN bar.

1. Photoelectron number at Y=4, 11.5, 19 cm for Z=10 cm (close to L PMT).





2. TDC response at Y=4, 11.5, 19 cm for Z=10 cm (close to L PMT).





In summary, according to our cosmic test, using a finger lightguide can gain more pe number (more than double in some location) and better time resolution than using a triangular lightguide, though both of them can meet the requirement of the Qweak experiment.