Material Interaction #282
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Material Interaction #282
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beomki-yeo
commented
Jul 24, 2022
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| struct pointwise_material_interactor : actor { | ||
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| struct state {}; |
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@niermann999
I am writing a material interactor inherited from actor
I need to access the tracking geometry information (material_store) in actor chain but propagation state doesn't have the tracking geometry information. What would be the ideal way to retrieve the geometry info?
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I think, it might be a good idea to move the detector pointer from the navigator into the navigator state and give it an access call. Then you could do smth like this: propagation._navigation.tracking_geometry(). Would that work for you?
…at-material-interaction
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This PR is rewritten in #301, so let me it... |
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Apr 12, 2023
This PR fixes the Bethe energy loss function in `Interactions.cpp` `Acts::computeEnergyLossBethe` and `Acts::computeEnergyLossLandau` is implemented from equation 33.5 and 33.11 of [Review in Particle Physics](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.030001) And their first term is computed with `computeEpsilon` function, following the notation of equation 33.11: ```c++ /// Compute epsilon energy pre-factor for RPP2018 eq. 33.11. /// /// Defined as /// /// (K/2) * (Z/A)*rho * x * (q²/beta²) /// /// where (Z/A)*rho is the electron density in the material and x is the /// traversed length (thickness) of the material. inline float computeEpsilon(float molarElectronDensity, float thickness, const RelativisticQuantities& rq) { return 0.5f * K * molarElectronDensity * thickness * rq.q2OverBeta2; } ``` Problem is that the epsilon term of equation 33.5 for Bethe function doesnt have the `0.5f` term Eq. 33.5  Eq. 33.11  If we are going to use the same epsilon term, we need to multiply 2 in the next term of Bethe energy loss function After the change, the output of `Acts::computeEnergyLossBethe` gets consistent with Figure 33.2 of the reference. ### Update July 18th Looks like there is a _literature_ error in Landau energy loss function (eq. 33.11). It used the mass term of the incident particle (`m`), but I guess it should be the mass of electron (`m_e`) as equation 33.5. **I need a cross-check from someone who can access [Straggling in thin silicon detectors](https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.60.663), which I cannot** (Update: It is confirmed that it should be the rest mass of electron) Finally, to get a consistent result of energy loss function, we need to fix the `computeDeltaHalf` term as well. But this is already mentioned in the comment which says: "Should we use RPP2018 eq. 33.7 instead w/ tabulated constants?" ```c++ /// Compute the density correction factor delta/2. /// /// Uses RPP2018 eq. 33.6 which is only valid for high energies. /// /// @todo Should we use RPP2018 eq. 33.7 instead w/ tabulated constants? inline float computeDeltaHalf(float meanExitationPotential, float molarElectronDensity, const RelativisticQuantities& rq) { ``` Yeah it does make big difference between 33.6 (valid for very high energy particles) and 33.7. **I am not going to include delatHalf term correction in this PR**, but it is included in acts-project/detray#282 After fixing codes (including the deltaHalf term), the Bethe energy loss function matches to the value in ([PDG](https://pdg.lbl.gov/2022/AtomicNuclearProperties/index.html)) In the following figure, Bethe energy loss (dE/dx) in Silicon is compared for Acts main, this PR, acts-project/detray#282, and PDG value. The value from this PR is not accurate yet due to the incorrect deltaHalf term <img src="https://user-images.githubusercontent.com/63090140/179622322-6c7170c9-7773-4eb4-a621-63e7429e3425.png" width="700"> For the most probable energy loss from Landau equation under the same condition of Figure 33.7 of [Review in Particle Physics](https://journals.aps.org/prd/abstract/10.1103/PhysRevD.98.030001) , detray#282 got 0.526 MeV, which is very close to the value in the figure. This PR got 0.739 MeV due to the incorrect delatHalf term
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