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Make track param estimation more accurate #684

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Merged
krasznaa merged 1 commit into from
Aug 16, 2024
Merged

Make track param estimation more accurate #684

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14 changes: 5 additions & 9 deletions core/include/traccc/seeding/track_params_estimation_helper.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -82,20 +82,16 @@ inline TRACCC_HOST_DEVICE bound_vector seed_to_bound_vector(
scalar A = (uv2[1] - uv1[1]) / (uv2[0] - uv1[0]);
scalar B = uv2[1] - A * uv2[0];

// Curvature (with a sign) estimate
scalar rho = -2.0f * B / getter::perp(vector2{1., A});
// The projection of the top space point on the transverse plane of
// the new frame
scalar rn = local2[0] * local2[0] + local2[1] * local2[1];
// Radius (with a sign)
scalar R = -getter::perp(vector2{1.f, A}) / (2.f * B);
// The (1/tanTheta) of momentum in the new frame
static constexpr scalar G = static_cast<scalar>(1.f / 24.f);
scalar invTanTheta =
local2[2] * std::sqrt(1.f / rn) / (1.f + G * rho * rho * rn);
local2[2] / (2.f * R * math::asin(getter::perp(local2) / (2.f * R)));

// The momentum direction in the new frame (the center of the circle
// has the coordinate (-1.*A/(2*B), 1./(2*B)))
vector3 transDirection =
vector3({1., A, scalar(getter::perp(vector2{1., A})) * invTanTheta});
vector3({1.f, A, scalar(getter::perp(vector2{1.f, A})) * invTanTheta});
// Transform it back to the original frame
vector3 direction =
transform3::rotate(trans._data, vector::normalize(transDirection));
Expand All @@ -111,7 +107,7 @@ inline TRACCC_HOST_DEVICE bound_vector seed_to_bound_vector(

// The estimated q/pt in [GeV/c]^-1 (note that the pt is the
// projection of momentum on the transverse plane of the new frame)
scalar qOverPt = rho / getter::norm(bfield);
scalar qOverPt = 1.f / (R * getter::norm(bfield));
// The estimated q/p in [GeV/c]^-1
getter::element(params, e_bound_qoverp, 0) =
qOverPt / getter::perp(vector2{1., invTanTheta});
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