J. Kissel, J. Rollins

We're putting the final touches on the estimate of the uncertainty on the calibrated data stream, and have found that my factors of 3x and 4x reduction of the low frequency calibration line heights on 2023-03-30 (LHO:68289) were a little but too much of a reduction given the current status of ER15 noise, which we assume will be representative of early O4 noise. We intend for the uncertainty in the transfer function for each of the calibration lines to be less than 0.5%*** (as computed by sqrt( (1 - C) / (2 N C) ) -- where N = 13 averages using an "FFT Length," i.e. a DEMOD low pass filter with time constant of 10 sec). We've found that the uncertainty is regularly 0.8 to 1.0%, and not because of glitches in the detector noise.

As such, I've increased the amplitude of the H1 SUS ETMX UIM (L1) and PUM (L2) 15.6 and 16.4 Hz Calibration Lines,
                                         O3-era      Mar 30      May 12       May/Mar ratio       May / O3 ratio
    H1:SUS-ETMX_L1_CAL_LINE_CLKGAIN       75.0        20.0        35.0          1.75x                0.46x
    H1:SUS-ETMX_L2_CAL_LINE_CLKGAIN      120.0        35.0        50.0          1.43x                0.41x

Attachment 3 shows how the uncertainty has improved over time with this increase in amplitude compared against 0.005, or 0.5%.

The first two attachments show what needs changing, and their acceptance in the SDF system.

*** 0.5% is, as with a lot of how the uncertainty on the time-dependent correction factors, an arbitrary threshold. The threshold was set in O3 as "when the uncertainty in the TDCFs is larger that 0.5%, then it's starting to 'substantially' impact / dominate the overall response function uncertianty, i.e. the overall uncertainty in the calibrated data stream." Where 'substantially' is defined by thinking about what the uncertainty in the calibration is at ~20 Hz == in O3 this was around 5% == so a factor of ten less than that is 0.5%. Also, since no one likes a "measurement" or "statistical" uncertainty to "dominate" an uncertainty budget (can you hear folks asking "wait, why don't you just integrate for longer?"), we increase the amplitude of these lines.

Here's the latest list of calibration lines:
Freq (Hz)   Actuator               Purpose                      Channel that defines Freq             Since O3
15.6        ETMX UIM (L1) SUS      \kappa_UIM excitation        H1:SUS-ETMY_L1_CAL_LINE_FREQ          Amplitude Change; THIS ALOG previously changed Apr 2023 (LHO:68289)
16.4        ETMX PUM (L2) SUS      \kappa_PUM excitation        H1:SUS-ETMY_L2_CAL_LINE_FREQ          Amplitude Change; THIS ALOG previously changed Apr 2023 (LHO:68289)
17.1        PCALY                  actuator kappa reference     H1:CAL-PCALY_PCALOSC1_OSC_FREQ        Amplitude Change on Apr 2023 (LHO:68289)
17.6        ETMX TST (L3) SUS      \kappa_TST excitation        H1:SUS-ETMY_L3_CAL_LINE_FREQ          Amplitude Change on Apr 2023 (LHO:68289)
33.43       PCALX                  Systematic error lines       H1:CAL-PCALX_PCALOSC4_OSC_FREQ        New since Jul 2022 (LHO:64214, LHO:66268)
53.67         |                        |                        H1:CAL-PCALX_PCALOSC5_OSC_FREQ        Frequency Change on Apr 2023 (LHO:68289)
77.73         |                        |                        H1:CAL-PCALX_PCALOSC6_OSC_FREQ        New since Jul 2022 (LHO:64214, LHO:66268)
102.13        |                        |                        H1:CAL-PCALX_PCALOSC7_OSC_FREQ           |
283.91        V                        V                        H1:CAL-PCALX_PCALOSC8_OSC_FREQ           V
284.01      PCALY                  PCALXY comparison            H1:CAL-PCALY_PCALOSC4_OSC_FREQ        Moved from PCALX 410.2 to PCALY 284.01 LHO:69354
410.3       PCALY                  f_cc and kappa_C             H1:CAL-PCALY_PCALOSC2_OSC_FREQ        No Change
1083.7      PCALY                  f_cc and kappa_C monitor     H1:CAL-PCALY_PCALOSC3_OSC_FREQ        No Change
n*500+1.3   PCALX                  Systematic error lines       H1:CAL-PCALX_PCALOSC1_OSC_FREQ        No Change (n=[2,3,4,5,6,7,8])