TPeak

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TPeaks are used to fit photopeaks to a Gaussian + skewed gaussian. The background includes a step function. TPeaks inherit from TF1, which means the can be named, and can be written to TTrees and TFiles.

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How To Use

TPeaks can be created as follows:

TPeak *peak = new TPeak(centroid, low_range, high_range);

To fit the TPeak, call:

peak->Fit(histogram);

where histogram is the TH1 attempting to be fit. You can also use the same options as when fitting a TF1. For example,

peak->Fit(histogram,"+");

To add the TPeak to the histogram. Once the TPeak is fitted, you can call

peak->Print();

To see the basic properties of the TPeak

   Name:        Chan1173_1160_to_1190
   Centroid:    1173.172270 +/- 0.005742
   Area:          1885626.302501 +/- 1409.848616

Or, to see more properties, such as the value and uncertainty in each parameter, use the option Print("+").

##Parameters The first time a TPeak is fit, the parameters are initialized based on the histogram passed to the TPeak::Fit function. When a TPeak is created, the parameters are uninitialized. The names of the paramters are as follows:

• "Height": The height of the unskewed gaussian
• "centroid": The centroid of the unskewed gaussian
• "sigma": The width of the unskewed gaussian
• "beta": The "skewedness" of the skewed gaussian
• "R": The relative height of the skewed gaussian
• "step": The size of the step function in the baskground
• "A": The constant part of the background
• "B": The linear part of the background
• "C": The quadratic part of the background
• "bg_offset": The offset in the background in the x direction

To fix a particular component of the TPeak, for example, the width to 1.0, use:

peak->FixParameter(GetParNumber("sigma"),1.00);

To Release the paramater use:

peak->ReleaseParameter(GetParNumber("sigma"));

and to set the paramater to an initial value use:

peak->SetParameter("sigma",1.00);

which maintains its fixed/freeness.