The Babar Cherenkov DetectorDetection of Internally Reflected

Cherenkov

Yuen-Jung Chang

Cherenkov radiation Charge particle passes through an insulator at a constant speed greater than the speed of light in that

medium. The charged particles polarize the molecules of that medium, which then turn back rapidly to their

ground state, emitting prompt radiation

cos θ = 1/βn

DIRC

DIRC

Quartz BarsMaterial is actually synthetic fused silica (n = 1.473 )Cross section 17.25 mm x 35.0 mm.Four 1.225 m long bars glued together make one 4.9 m long DIRC bar.DIRC uses as a radiator 144 quartz bars arranged in a 12-sided polygon around the beam line

Photomultipliers (PMT)