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## Significance OverviewThis page reviews some of the methods and tools we use to calculate the significance, as well as a brief overview of the cross-section calculation. This page is currently prepared for use with MC only (expected values) and will have to be modified to include information about how to find observed, data values. |

28 Sep 2009 - Main.JennyHolzbauer

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## Significance OverviewThis page reviews some of the methods and tools we use to calculate the significance, as well as a brief overview of the cross-section calculation. This page is currently prepared for use with MC only (expected values) and will have to be modified to include information about how to find observed, data values. | ||||||||

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This method is much more complicated than the previous one, and takes much longer to generate a significance (~hours, not seconds). The use of the tier three is highly recommended if you are going to use this method, especially for significances expected to be large (5, 6 sigma). This method generates many ensembles, each of which are varied by systematics, and a log-likelihood ratio (LLR) is calculated for each. Note that both background and signal systematics are included for this method. The ensembles are generated with and without signal included. The significance is based on the number of ensembles with only background that have an LLR value greater than the mean of the ensembles with signal and background both included. In other words, it finds the odds that background can fluctuate enough to look like signal. The trouble is that calculating 6 sigma, for instance, requires 1000 sets with 1 million ensembles in each set (at this number of ensembles, it is more productive to generate smaller sets of ensembles each with a different random number seed which can run separately on the tier 3 and add them together rather than one long run generating ensembles). For running on the tier three, at this time sets of 1 million ensembles (or less) are recommended at this time. These should take about half an hour to run each and not overload the memory of the computer you are using for that set. This method is less conservative than method 1, and also allows the user to find the significance for a combination of channels. However, again, it takes awhile to generate these numbers. This is the method used at the Tevatron for the single-top observation. | ||||||||

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24 Sep 2009 - Main.JennyHolzbauer

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## Significance OverviewThis page reviews some of the methods and tools we use to calculate the significance, as well as a brief overview of the cross-section calculation. This page is currently prepared for use with MC only (expected values) and will have to be modified to include information about how to find observed, data values. |

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