Observation of the relativistic rise in bubble density in a neon-hydrogen bubble chamber

In a bubble chamber containing a neon-hydrogen mixture surrounding a hydrogen-filled track sensitive target, electrons with momenta above 100 MeV/ c are observed to have (1.25 ± 0.02) times more bubbles per unit length in neon-hydrogen than pions with momenta between 400 and 1500 MeV/ c . We interpret this difference as due to a relativistic rise in bubble density, such as has been observed previously in a freon bubble chamber. The total magnitude of the rise from minimum to plateau is estimated to be (28 ± 2)%. This should provide a method for distinguishing between relativistic pions, kaons and protons of the same momentum. It could in particular be exploited in high energy experiments using the track sensitive target technique in large bubble chambers such as BEBC.