## Bug #1430

### PE smearing in Tracker MC

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**Description**

I am getting a non-sense value for the Tracker digit NPE. Following this back it looks like it is coming from the ADC smearing routine we decided to include after the code review last month.

`The heart of the ADC smearing is a Gaussian centered around the energy deposited in the fiber with standard deviation defined by the SciFi VLPC Energy Resolution which has a value of 4.0 MeV. Seeing as the average energy deposited per hit is something along the order of 0.06 MeV or so, this seems wildly inaccurate.`

`Further once we have this number, the whole thing is multiplied by 6, which is labeled as SciFi adc Factor. I can only assume that this number gives us the number adc counts per MeV (per keV?). This is finally checked to make sure it doesn't overload a 16bit number.`

`So I like how the function is looking in form, but all the numbers are screwy. Can someone please help me get this straight? Frankly I'm not even sure energy is what we should be smearing anyways.`

#### Updated by Heidt, Christopher about 10 years ago

That didn't really print out nice, here is a better looking version of what I wrote above:

I was working on getting my VLPC noise function pushed today when I noticed that I was getting a non-sense value for the digit NPE. Following this back it looks like it is coming from the ADC smearing routine we decided to include after the code review last month.

The heart of the ADC smearing is a Gaussian centered around the energy deposited in the fiber with standard deviation defined by the SciFi VLPC Energy Resolution which has a value of 4.0 MeV. Seeing as the average energy deposited per hit is something along the order of 0.06 MeV or so, this is wildly inaccurate.

Further once we have this number, the whole thing is multiplied by 6, which is labeled as SciFi adc Factor. I can only assume that this number gives us the number adc counts per MeV (keV?). This is finally checked to make sure it doesn't overload a 16bit number.

So I like how the function is looking in form, but all the numbers are screwy. Can someone please help me get this straight?