Physics reach of the Global Neutrinoless Double-Beta Decay Program and systematic uncertainties of the MAJORANA Project

We present a global analysis technique for extracting information about the mechanism underlying neutrinoless double-beta decay (0nubetabeta) by continuing the decay rate to the ground state across a number of isotopes. To this end, we also present work in support of the MAJORANA experiment, which will look for 0nubetabeta in 76Ge, aimed at pushing down systematic uncertainties to the level where the inclusion of 76Ge from MAJORANA in this analysis is possible (statistical uncertainty in any 0nubetabeta experiment will of course be set by the exposure and half-life, T0n1/2 for the isotope of interest). We proceed to enumerate likely sources of systematic uncertainty, paying particular attention to the efficacy and uncertainties for background and signal tagging via pulse shape and segmentation analysis, and background fluctuations in the MAJORANA experiment. We will also detail a proposed MAJORANA calibration program designed to reduce these systematic uncertainties.; We find that this global analysis for five different 0nubetabeta models is possible if the total uncertainty budget is less than 30% for four isotopes. If these four experiments were to reach an uncertainty budget (statistical plus systematic) of ≈ 20%, then this analysis would require matrix element uncertainties of only ≈ 12%. If we restrict this analysis to only light Majorana nu exchange (thus testing the different matrix element calculation methods), the total uncertainty budget increases to ≈ 64%. This leaves ≈ 31% for the matrix element uncertainty, assuming 20% from the experimental measurement. This global analysis technique is interesting because it is independent of the absolute scale of T0n1/2 for different isotopes. This means that whatever the actual level of lepton number violation in nature, we can extract information about the exchange mechanism underlying 0nubetabeta from the pattern of the decay rates for a variety of isotopes. It is very important to note that this analysis is based on a set of initial assumptions. Principally, we assume that future changes in the values of 0nubetabeta nuclear matrix elements will shift values uniformly across all isotopes, and that one mechanism for 0nubetabeta will be found to dominate over the others. These assumptions are stated more completely in the text.; We move from the total uncertainty budget goals from the global analysis to examine several of the more important systematic uncertainties in the M AJORANA experiment. We demonstrate fractional uncertainties in the survival probability for our pulse shape analysis cuts of 6.6% for single-site events and 3.8% for multi-site events. We also suggest some ways that this could be lowered somewhat in MAJORANA data. We also show that for smaller 76Ge exposures, fluctuations in the background and signal levels can lead to systematic shifts in the reconstructed 0nubetabeta rate of as much as 5%. These and the other systematic uncertainties expected in MAJORANA give a total systematic uncertainty budget of ≈ 11%.