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leonarski_fandClaude Fable 5.1 38bb511d23 Make a first-pass detector tilt no mounting can have prove itself on the spots

The first-pass rotation fit refines the spindle-perpendicular detector tilt
freely, and on a sweep whose seed spots reach only a few degrees of 2theta the
keystone that would determine it is a pixel or two. The fit then commits
whatever the centroids' own systematics prefer - measured 2.5 deg on one sweep
seeded to 11.7 A - and that tilt mispredicts the detector corners by 20-60 px
against a 6 px integration disc, collapsing the run from 2.8 A to 6.35 A and
biasing the metric-symmetry arbiter to a = b on the way. On synthetic data the
same runaway is reproducible: a 1.5 deg detector error on 6 A reflections walks
the free fit to 3.9 deg, on 8 A reflections to 37.

Three data-driven discriminators were tried first and refuted on the corpus:
a blanket restraint (0.13-0.16 A and up to 28% of ISa lost on the crystals
whose tilt is largest and real, and in-house runs pinned at a header tilt known
to be wrong), the distance's held-out excitation criterion (the rocking angles
move by a tenth of their noise whether the tilt is real or not), and a keystone
comparison of the fitted and header tilts with the beam free in both arms
(236-set battery: ~30 sets moved, one collapsed from P1 to C2, one lost a
screw axis; differences of 0.007-0.6 sigma held the header on right and wrong
cases alike). For a tilt of a few tenths of a degree the keystone is a fraction
of a pixel and nothing in the spots says whether it is real. What separated the
cases was the tilt's size: every set the keystone arm moved carries 0.08-0.46
deg, and a survey of 211 corpus sets leaves the file's tilt by more than 0.56
deg on exactly one - a 2theta arm swung out 12.8 deg that its file records as
square, which the free fit recovers and the held arm refuses by 90 sigma.

So the hardware prior decides whether to ask, and the spots decide. Below
1 deg of walk from the tilt the pass started at the fit is trusted as before,
by construction. Beyond it the winning candidate is refined again from its
start with the tilt held there - the beam centre taking the shift the tilt is
equivalent to, so the header tilt is never paired with a beam fitted beside a
refused tilt - and the two are judged as the rounds of one chain already are,
on the spots each indexes inside the wide gate: the walked tilt stands only
when it leads by more than the count's own noise. A real tilt of degrees has a
keystone of tens of pixels over the seed spots and wins outright; an artefact
has none and loses on a tie. Held rather than bounded, because a box the fit
lands on is the same wrong answer at a smaller size. Decided at the fit, so
every pass and arm of a run handles itself and nothing is carried between
passes; the unconstrained alternative is re-solved beside a refused tilt too.
The chain that drives a candidate to its fixed point becomes a lambda so it
can be run on the held candidate.

The run logs the walk, what it would have moved the far corner by, the shift
the beam took instead and both spot counts; where it was refused the report's
REFINED_DETECTOR_TILT is the starting tilt and REFUSED_DETECTOR_TILT what the
fit had walked to. Tests: a half-degree tilt is found, kept and not reported as
a walk; a walk past the prior is made on synthetic data, and the result's
verdict, counts and geometry agree with each other.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nW6FNRP1bBJJ8pfHiByAT

2026-09-23 19:01:08 +02:00