Fix central 4t xsec

[bryates]

Our central tttt sample had the old, incorrect xsec.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 24.06%. Comparing base (bbb23ca) to head (8de7ff1).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #513   +/-   ##
=======================================
  Coverage   24.06%   24.06%           
=======================================
  Files          37       37           
  Lines        5664     5664           
=======================================
  Hits         1363     1363           
  Misses       4301     4301           

Flag	Coverage Δ
unittests	24.06% <ø> (ø)

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