Mott scattering #66
Mott scattering #66
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| /* ROOT TF1 takes in analytical formulas as strings. This is the conversion into strings */ |
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Is there any reason why this is implemented via TF1 and not as C++ code directly? All the functions are available in C++ STL too, so I don't see why you'd need ROOT.
In my experience the formula parsing in ROOT adds considerable overhead and degrades performance. For code that is executed multiple times during simulation, I would not recommend this approach.
| double KSIntCalculatorMott::GetEnergyLoss(const double& anEnergy, const double& aTheta){ | ||
| double M, me, p, anELoss; | ||
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| M = 4.0026 * katrin::KConst::AtomicMassUnit_eV(); // eV/c^2 |
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I think it would be useful to make the target mass M a user parameter that can be changed in the XML file.
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This calculator only works for Helium, so I guess the name is a bit misleading. Maybe I can change the name to he_mott_calculator?
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That is a good point! Would you also rename the classes and filenames then?
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Yes, I will update class names and filenames all together after I make the appropriate changes into a sole c++ implementation. I have to use rejection sampling to sample from the cross section, but I have never done this before so it might take me quite a bit of time. I originally used the TF1 class to shortcut this step, but using c++ will improve the performance as the other comment says
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Is there any update on this PR @juniorpena ? |
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Hi,
No updates as of now. Other projects came to the forefront, and I still have not gone back to update this code. I will probably not get back to this until sometime closer to the summer.
Best,
Junior
From: J B ***@***.***>
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Date: Monday, January 9, 2023 at 3:29 AM
To: KATRIN-Experiment/Kassiopeia ***@***.***>
Cc: Junior Ivan Pena ***@***.***>, Mention ***@***.***>
Subject: Re: [KATRIN-Experiment/Kassiopeia] Mott scattering (PR #66)
Is there any update on this PR @juniorpena<https://github.com/juniorpena> ?
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Hello, I've eliminated the use of ROOT in this scattering calculator. Now the GetTheta function uses inverse transform sampling and rejection sampling. I've also updated it to allow for both He and Ne Mott Scattering |
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Hey, thank you very much! Could you add documentation of the added objects to https://github.com/KATRIN-Experiment/Kassiopeia/blob/main/Kassiopeia/XML/Complete/Interactions.xml ? That is helpful both for users and for the review. (Related, but independent issue: #106 ) |
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I've added the documentation |
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After looking through the code, I had three remaining comments after which this looks good to merge!
Btw. if there will be a thesis describing a use case of this, one can also advertise it in the top comment of KSIntCalculatorMott.h, since it is always useful to see what the original use case for components of Kassiopeia was.
| if (aContainer->GetName() == "theta_min") { | ||
| aContainer->CopyTo(fObject, &KSIntCalculatorMott::SetThetaMin); | ||
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| if ((fObject->GetThetaMin() == 0.0)) { |
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| if ((fObject->GetThetaMin() == 0.0)) { | |
| if ((fObject->GetThetaMin() <= 0.0)) { |
| std::vector<double> theta_arr; | ||
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| // Populate theta_arr | ||
| for (int i = 0; i <= 1000; ++i) { | ||
| theta_arr.push_back(fThetaMin + i * (fThetaMax - fThetaMin) / 1000.0); | ||
| } |
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For a fixed-size array, std::array is better than std::vector. However, in this case, I think the array is not needed, as you just build it and directly afterwards use it - one could just calculate theta on the fly in the second loop. Also, it makes sense to document in a comment where the 1000 comes from and when it is valid?
| amu = 4.0026; | ||
| } else if (fNucleus == "Ne") { | ||
| amu = 20.1797; |
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Please add a source for such numbers so one can more easily understand and update them (there are many hard-coded numbers besides these two further down as well).
This change is implementing Mott scattering of high energy electrons off of Helium nuclei. I uploaded the files from my Kassiopeia setup on my local machine into a repo I forked, and I made changes to the appropriate CMakeLists.txt files.