Measurement of the scintillation resolution in liquid xenon and its impact for future segmented calorimeters

We report on a new measurement of the energy resolution that can be attained in liquid xenon when recording only the scintillation light. Our setup is optimised to maximise light collection, and uses state-of-the-art, high-PDE, VUV-sensitive silicon photomultipliers. We find a value of 4.2% +- 0.2% FWHM at 511 keV, a result much better than previous measurements and close to the Poissonian resolution that we expect in our setup (5.4% +- 0.8% FWHM at 511 keV). Our results are compatible with a null value of the intrinsic energy resolution in liquid xenon, with an upper bound of 0.4% FWHM at 95% CL at 511 keV, to be compared with 3--4% FWHM in the same region found by theoretical estimations which have been standing for the last twenty years. Our work opens new possibilities for apparatus based on liquid xenon and using scintillation only. In particular it suggests that modular scintillation detectors using liquid xenon can be very competitive as building blocks in segmented calorimeters, with applications to nuclear and particle physics as well as Positron Emission Tomography technology.