Calibration of the NEXT-White detector using ^83mKr decays

The NEXT-White (NEW) detector is currently the largest radio-pure high-pressure xenon gas time projection chamber with electroluminescent readout in the world. NEXT-White has been operating at Laboratorio Subterráneo de Canfranc (LSC) since October 2016. This paper describes the calibrations performed with ^83mKr decays during a long run taken from March to November 2017 (Run II). Krypton calibrations are used to correct for the finite drift-electron lifetime as well as for the dependence of the measured energy on the event position which is mainly caused by variations in solid angle coverage. After producing calibration maps to correct for both effects we measure an excellent energy resolution for 41.5 keV point-like deposits of (4.553 ± 0.010 (stat.) ± 0.324 (sys.)) (3.804 ± 0.013 (stat.) ± 0.112 (sys.)) volume. Using naive 1/√(E) scaling, these values translate into resolutions of (0.516 ± 0.0014 (stat.) ± 0.0421 (sys.)) (0.4943 ± 0.0017 (stat.) ± 0.0146 (sys.)) Q_ββ energy of xenon double beta decay (2458 keV), well within range of our target value of 1