Comparisons among S1 S5 Runs LIGOG06000902Z

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LLO' 4km-S1 (2002 ÔSB7): LLO 4km-S2 (2003 0301) LHO 4km-S3 (2001 01 04)7T LHO 4km-S4 (2005 02 26) LLO 4km-S5 (2006 06 04) LIGO I SRD Goal, 4km —

LLO' 4km-S1 (2002 ÔSB7): LLO 4km-S2 (2003 0301) LHO 4km-S3 (2001 01 04)7T LHO 4km-S4 (2005 02 26) LLO 4km-S5 (2006 06 04) LIGO I SRD Goal, 4km —

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Seismic Noise

Shot Noise

Fig. 3. Interferometer noise in each of the five LIGO science runs. The solid thick black curve is design goal of LIGO. There are two changes of slope indicated by dashed thick black lines. These correspond to changes in the dominant noise source - the three noise regimes are marked. Over four years of commissioning, the noise floor was reduced by approximately three orders of magnitude.

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Seismic Noise

Shot Noise

Fig. 3. Interferometer noise in each of the five LIGO science runs. The solid thick black curve is design goal of LIGO. There are two changes of slope indicated by dashed thick black lines. These correspond to changes in the dominant noise source - the three noise regimes are marked. Over four years of commissioning, the noise floor was reduced by approximately three orders of magnitude.

Apparent in Fig. 3 is the remarkable progress that has been made in lowering the noise floor and the other noises superimposed upon it in going from S1 to S5. Indeed, at S5, LIGO matches or exceeds its design specification over most frequency bands, including the most sensitive region from approximately 100-300 Hz. When S5 is over and S5 data is analyzed, it will provide by far the best opportunity to date to detect gravitational waves.

The degree to which improvements in the noise floor such as those in Fig. 3 correspond to increase detection probabilities depend on the shape of the noise floor and the signal being sought. For neutron star binary inspiral signals, one can devise a figure of merit called the inspiral range. This is the distance, averaged over all sky positions and orientations, to which an instrument can expect to see a 1.4-1.4 Mq binary with signal-to-noise ratio (defined below) of 8. For S2, typical inspiral ranges for L1 were just below 1 Mpc. For the LIGO design curve, the inspiral range is approximately 14 Mpc [63].

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