Histogram Analyser
Recap: What is the major difference between a histogram and a bar graph?
The x variable of a histogram is continuous, grouped into ranges or ‘bins’.
Physicists use cuts to select events of interest. Cuts preferentially remove the unwanted processes (background) but leave as much as possible of the desired process (signal). It is useful to have a good understanding of the physics processes involved when applying cuts.
We have created two Histogram Analysers, to help visualise the data:
The first Histogram Analyser displays just simulated (MC) events.
The second Histogram Analyser displays both real data and simulated events.
Both histogram analysers display four physics processes. These are: , , and . Each process is represented by a different colour in Histogram Analyser. A more in depth discussion of them can be found in the next chapter.
Make cuts using your cursor.
Use the cursor to select a specific range in one of the histograms. These will be coloured, whilst non-selected ranges will be greyed out. When you make cuts on a variable, the relative contributions of each of the four processes will change.
To clear your selection on a specific histogram: click on the white background within the histogram area.
To clear all your selections: click on "Histogram Analyser" under Get Started in the main top menu.
The histograms explained
Higgs to WW - simulated data Histogram Analyser displays nine histograms. The description of each follows.
The histograms can take about 30 seconds to load. Whilst loading you'll only see the histogram titles. Once loaded you'll see the histograms appear under their titles.
We think it really helps to be able to see all nine histograms on your screen at the same time. So if this isn't the case to start with, we suggest decreasing the zoom in your web browser until you can see all nine (e.g 67%).
Would you like to make more detailed cuts, increase the number of bins, or include a larger set of data? Try coding your data analysis!
Expected Number of Events for 10/fb
This histogram shows the number of events expected to be detected, reconstructed and recorded by ATLAS for 10 inverse femtobarn (10/fb) of data.
Ten inverse femtobarns correspond to approximately 1000 trillion proton-proton collisions.
The expected number of events reconstructed and recorded by ATLAS is different to the number of events produced.
Some events will not be reconstructed due to the way the detector is constructed, the resolution of the sub-detectors, reconstruction efficiency and other inefficiencies.
With no cuts, we have 124 events, with a total background of 7342087 events. The majority of the background is boson production.
The significance of the