fix error propagation in helixToZ #353
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slava77
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Sep 7, 2021
| errorProp(n,1,5) = deltaZ*cosa*( cosP*cosP*sCosPsina + sinP )/(cosT*cosT); | ||
| const float pxcaMpysa = pxin*cosa - pyin*sina; | ||
| errorProp(n,0,2) = -tanT * ipt * pxcaMpysa;; | ||
| errorProp(n,0,3) = 2*k*pt*pt*sinah*(sinP*sinah - cosP*cosah) + deltaZ*tanT*pxcaMpysa; |
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based on our discussion on skype, this and (1,3) term may need to be refactored to group the large terms (using deltaZ*tanTheta = k*pt*alpha)
here - 2*k*pt*pt*sinah*cosP*cosah = - k*pt*pt*cosP*sina in the first large term is supposed to [almost] cancel out with the right hand side deltaZ*tanT*pxin*cosa = k*pt*pt*alpha*cosP*cosa because - sina + alpha*cosa goes to zero; so, it would be best to have this subtraction explicit instead of shuffled with other terms to avoid loss in numerical precision.
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... that's for the follow up PR
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This PR fixes an issue in error propagation in helixToZ.
The effect is to recover the number of strip layers in the high pT 10 mu sample:
http://uaf-10.t2.ucsd.edu/~cerati/plots_Sep05_10mu_testzfix_gcc/plots_building_initialStep/hitsLayers.pdf
This does not have much effect on ttbar.
More plots for both 10mu and ttbar at:
http://uaf-10.t2.ucsd.edu/~cerati/plots_Sep05_10mu_testzfix_gcc/
http://uaf-10.t2.ucsd.edu/~cerati/plots_Sep05_ttbar_testzfix_gcc/
A document with the math I used to derive the jacobian can be found at this link: https://www.overleaf.com/9112147731xmvddqxtwgxq