Determine the cause of patch-to-patch detection-significance variation

Determine the origin of the variation in connected 4PCF detection significances among the approximately equal-volume DESI Year 1 luminous-red-galaxy patches, including the lower significance obtained for South Galactic Cap Patch 1 when small tetrahedra are included.

Background

The authors expected patches with approximately similar volumes to yield more comparable detection significances. Instead, the measured values vary substantially from patch to patch, and South Galactic Cap Patch 1 shows a decrease in significance when small tetrahedra are included, contrary to the general trend.

Systematics tests did not identify the considered observational systematics as the cause, so the origins of both the patch-to-patch variation and the anomalous South Galactic Cap Patch 1 behavior remain unresolved.

References

We would have expected the four patches to yield more comparable detection significances, and the origin of these differences is not fully understood. Similarly, the decrease observed in SGC Patch~1 when going from no-ST'' toST'' does not follow the general trend seen in the other sectors, and its origin is also not fully understood.

— A Finely-Binned Measurement of the Connected Even-Parity Galaxy 4-Point Correlation Function of DESI Year 1 Luminous Red Galaxies  (2609.09340 - Leonard et al., 8 Sep 2026) in Appendix A, subsection “Detection Significances,” Table T2_det_table caption