’ properties of wavelength shifting films for the CBM - RICH detector - thickness dependence and efficiency ∗

P-terphenyl (PT) and tetraphenyl-butadiene (TPB) have been investigated as possible wavelength shifting materials for use in Ring Imaging Cherenkov (RICH) detectors. Wavelength shifting films made out of these organic molecules absorb light in the UV region and re-emit fluorescence photons at larger wavelength. Used on top of photomultiplier tubes (PMT), they therefore can enhance the quantum efficiency of the PMTs in the UV region. For an application in Cherenkov counters, gain factors for the number of measured photoelectrons for a cutoff wavelength of 200 nm (Emax = 6.2 eV) are 1.71 ± 0.17 for PT and 1.27 ± 0.13 for TPB compared to a PMT with borosilicate windows. See [1] for a summary of these results.