sPHENIX HCal discussion

[Edouard Kistenev <kistenev AT bnl.gov>]

With help of Rob Pisani we found this week that white tedlar used in demonstration wrap of HInner tiles is very leaky thing - lets a lot of light to get through. I got a bit anxious if black TEDLAR is that much better to protect our tiles from ambient light with one layer only 30mkm thick.

So we did a not so simple a test (took a bit of creativity from tester). Unwrapped tile was placed on a sheet of TYVEK and covered with another sheet of TYVEK and single sheet of black TEDLAR (see attached pictures). A thick (black on inside) box with a hole one one side and a source of blue light inside the box was pressed against the tedlar spread over top of the tile. Fiber exits were viewed by digital camera. Visually no difference in the amount of light exiting fibers when light source on and off was observed. Digital camera is not a great single photon registrar so the signal from fibers, using image processor from camera - no signal was firmly established for the 4s exposure. But 8s exposure processed through software does show clear presence of aa accumulated single photon hits opposite the fiber exits. 

Estimated background -s <1hit in the signal aperture. Integral is unknown but I asked the kid who did this test ti dig on internet for means to estimate its value - then we will have a way to measure tile luminosity in 10 s .

Edward

Picture 1 - Illustration to the setup

Picture 2 - Processed image with 4s exposure

Picture 3 - Processed image with 8s exposure