LSC Detector Characterization Working Group

Goals

In order to detect and investigate sources of gravitational radiation, one must understand in detail the nature of the instrument. This working group's ultimate goal is to characterize the LIGO interferometers (2 at Hanford, 1 at Livingston) so that astrophysical searches can be carried out with confidence.

There are many aspects to characterizing the detector and a number of tasks that must be carried out as part of that effort, including routine diagnostics. Members of the LIGO Global Diagnostics System (GDS) group are therefore automatically members of this working group and naturally form its core. Ideally, in fact, all of the algorithms developed by this working group to characterize the detector will eventually become routine online or offline diagnostics.

At least for the present, it is expected that non-GDS members of the working group will contribute mainly to offline, passive monitoring software.  Consequently, the organization of group efforts will initially focus on this area. It should be kept in mind, though, that many of the most useful techniques for characterizing the detectors are quite invasive; these include measurement of transfer functions via swept sines; measurement of individual arm cavity optical parameters via single-arm locks with or without additional, parasitic rf sidebands; variation of servo electronic gains, deliberate (dc and ac) misalignment of mirrors; and many others. LSC members who will reside for long periods at one of the sites are strongly encouraged to participate in these studies and to assist the GDS group.

The most important goal of offline detector characterization is understanding instrumental noise. That noise falls naturally into two broad categories: steady-state (or slowly varying) and transient noise, where the boundary between the two may be fuzzy in some cases, depending on the astrophysical source one seeks (10 seconds? 1 minute? 1 hour?). In searching for coalescing compact binaries, the transients are the greater concern, and a subgroup devoted to Transient Analysis has been formed. In searching for periodic and quasi-periodic sources of gravitational radiation, the steady-state Performance Characterization is equally important. The Detector Characterization working group's main charge is to develop algorithms for understanding these two types of noise.

Two additional subgroups have been formed to develop essential tools in this effort. One is devoted to providing convenient and rapid customizable offline Data Reduction. The other is devoted to Data Set Simulation which is to include (eventually) detailed modelling of the interferometers as provided by the End-to-End model.


 
 

Special Task:   LIGO Mock Data Challenge

As part of preparing for LIGO data analysis, the Detector Characterization working group, together with the LSC Astrophysical Source Indentification and Signatures  and Detection Confidence and Statistical Analysis  working groups, will participate in the LIGO-initiated Mock Data Challenge.  This is an exercise meant to stimulate analysis work in the groups and to serve as a diagnostic on that work. Although this challenge will eventually entail comprehensive and realistic LIGO detector simulation, initial efforts will focus on analyzing data taken with the 40-Meter prototype instrument at Caltech.