Photon yield maps

Comparison of photon yield for BABAR DIRC, PANDA Barrel DIRC, and GlueX DIRC, sim/measured

 

 

 

 

 

 

 

Photon yield is shown for two upper bar boxes. Relativistic 4 GeV/c muons were used. Optical properties of the materials used in the simulation can be found here.

The difference in refractive index between quartz and optical coupling (cookies, grease) is modest, therefore, photon loss is caused mainly by the attenuation length of the optical joint. The photon loss in this case is uniform over the DIRC wall.

In case of air gap the main reason for photon loss is refraction on the quartz-air interface. The average photon incidence depends on the position, where the charged particle hit the DIRC wall, therefore, photon loss for the geometry with an air gap is not uniform over the bar box.

The use of Belle II cookie lead to the photon loss at the order of 1-4% (keep in mind that the implementation of the Belle II cookie material has no realistic attenuation length) compared to the ideal case, when photons go directly from the quatrz window to the photosensor window.

The EJ560 silicon rubber (pre-made cookies) cause photon loss of about 21-25% in case of 2 mm thick layer and 13-17% in case of 1 mm thick layer.

Optical grease layer with thickness of 0.1 mm lead to photon loss of about 5%, whereas 1 mm thick layer cause about 13% photon loss (compare to PANDA results).

The air gap with thickness of 0.1 mm cause 15-37% photon loss, in case of 2.5 mm thick gap the photon loss goes up to 20-50%.

 

1. No gap, distance between the IP and DIRC is 4000mm 

2. Silicon cookie (const n = 1.402), distance between the IP and DIRC is 4000mm

3. Grease layer of 0.1 mm   

 

4. Grease layer of 1 mm 
5. Air gap 2.5 mm 
6. Air gap 0.1 mm

7. Cookie made of EJ560 silicon rubber (2 mm thick)

8. Cookie made of EJ560 silicon rubber (1 mm thick)

Relative photon yield

Photon yield relatively to the case without gap, where the barbox window is directly coupled to the EV. Same cases as before. 

The plots show the difference between the photon yield in case of gap i and the photon yield with no gap, divided by the photon yield with no gap:

1. Belle II cookie (2.5 mm thick, n = 1.406)

2. Grease layer of 0.1 mm

 
3. Grease layer of 1 mm 

 

4. Air gap 2.5 mm

5. Air gap 0.1 mm 

6. Cookie made of EJ560 silicon rubber (2 mm thick)

7. Cookie made of EJ560 silicon rubber (1 mm thick)