Abstract
Detailed MC simulation studies of muoninduced neutrons [1] revealed our initial overestimation of the (Formula presented.) Xe activation by neutron capture on (Formula presented.) Xe in the DARWIN TPC located at LNGS. The insitu (Formula presented.) Xe production rate must be corrected to (0.82 ± 0.10) atoms/(t (Formula presented.) yr), a factor of 8.4 lower than the initially estimated value. This reduces the previouslydominant intrinsic background contribution from (Formula presented.) Xe to a level similar to the (Formula presented.) B neutrino background via (Formula presented.)  (Formula presented.) scattering. This increased importance of the formerly subdominant (Formula presented.) B background calls for a revision of its initially simplified calculation. The neutrino flux spectrum is now convolved with the energydependent electron neutrino survival probability (Formula presented.) , according to the MSWLMA solution [2]. Accordingly, Table 3 and Figures 6, 7 and 8 of the initial manuscript are corrected. The DARWIN sensitivity to the (Formula presented.) decay of (Formula presented.) Xe is recalculated with the updated background rates. The figureofmerit estimator (section 6.1 of the original manuscript) projects a halflife sensitivity at 90% confidence level (C.L.) of (Formula presented.) ((Formula presented.)) after 10 (4) years of exposure. The frequentist profilelikelihood analysis (section 6.2) yields a (Formula presented.) sensitivity limit of (Formula presented.) for a 10 year exposure with (Formula presented.) fiducial mass. The corresponding (Formula presented.) discovery potential after 10 years is (Formula presented.). (Table presented.) Expected background index averaged in the (Formula presented.) ROI of [2435–2481] keV, the corresponding event rate in the (Formula presented.) FV and the relative uncertainty by origin Background source Background index Rate Rel. uncertainty [events/ (t (Formula presented.) yr (Formula presented.) keV)] [events/yr] External sources ((Formula presented.) FV): (Formula presented.) Bi peaks + continuum 0.313 (Formula presented.) Tl continuum 0.143 (Formula presented.) Sc continuum 0.001 (Formula presented.) B ((Formula presented.) scattering) 0.035 (Formula presented.) Xe ((Formula presented.) induced ncapture) 0.039 (Formula presented.) Xe (Formula presented.) 0.001 (Formula presented.) Rn in LXe (0.1 (Formula presented.) Bq/kg) 0.071 Background rate in the ROI versus fiducial mass. External contributions are combined. Fiducial volume independent intrinsic sources are shown per contribution. Bands indicate (Formula presented.) uncertainties Predicted background spectrum around the (Formula presented.) ROI for the (Formula presented.) fiducial volume. A hypothetical signal of 0.5 counts per year corresponding to (Formula presented.) is shown for comparison. Bands indicate (Formula presented.) uncertainties DARWIN median (Formula presented.) sensitivity at 90% C.L. as a function of fiducial volume mass for 10 years of operation (left) as well as of the time for the optimized fiducial volume (right). The baseline design is compared to different optimistic scenarios. The latter assume a reduction of the external (ext.) and the intrinsic ((Formula presented.) Rn and (Formula presented.) Xe) backgrounds and improved spatial separation threshold of (Formula presented.) (red) or (Formula presented.) (blue, green). The green line assumes only irreducible intrinsic backgrounds, dominated by (Formula presented.) B neutrinos. Sensitivity projections for future (Formula presented.) Xe (Formula presented.) experiments are shown for comparison The now corrected intrinsic background is dominated by the (Formula presented.) decay of (Formula presented.) Bi in the baseline scenario (black in Figure 8). Reducing the BiPo tagging inefficiency to 0.1 (Formula presented.) leads to a similar background contribution from (Formula presented.) B, (Formula presented.) Xe, and (Formula presented.) Rn for DARWIN at LNGS (red). Combining a 0.01 (Formula presented.) inefficiency with a (Formula presented.) efficient timed veto on (Formula presented.) Xe activation (discussed in section 7) suppresses the nonneutrino intrinsic backgrounds to approximately half of the (Formula presented.) B contribution (blue). As in the initial manuscript, the optimistic scenarios assume a reduction of the external background and improved topological discrimination.
Original language  English 

Article number  996 
Journal  European Physical Journal C 
Volume  83 
Issue number  11 
DOIs 

State  Published  Nov 2023 
All Science Journal Classification (ASJC) codes
 Engineering (miscellaneous)
 Physics and Astronomy (miscellaneous)