Observation of anticorrelation between scintillation and ionization for MeV gamma rays in liquid xenon

A strong anticorrelation between ionization and scintillation signals produced by MeV γ rays in liquid xenon has been measured and used to improve the energy resolution by combining the two signals. The improvement is explained by reduced electron-ion recombination fluctuations of the combined signal compared to fluctuations of the individual signals. Simultaneous measurements of ionization and scintillation signals were carried out with ¹³⁷Cs, ²²Na, and ⁶⁰Co γ rays, as a function of electric field in the liquid. A resolution of 1.7%(σ) at 6620.3em0exkeV was measured at 10.3em0exkV∕cm, significantly better than the resolution from either scintillation or ionization alone. A detailed analysis indicates that further improvement to less than 1%(σ) is possible with higher light collection efficiency and lower electronic noise.