siPixelUtils Namespace Reference

Functions
float	generic_position_formula (int size, int q_f, int q_l, float upper_edge_first_pix, float lower_edge_last_pix, float lorentz_shift, float theThickness, float cot_angle, float pitch, float pitchfraction_first, float pitchfraction_last, float eff_charge_cut_low, float eff_charge_cut_high, float size_cut)

Function Documentation

generic_position_formula()

float siPixelUtils::generic_position_formula	(	int	size,
		int	q_f,
		int	q_l,
		float	upper_edge_first_pix,
		float	lower_edge_last_pix,
		float	lorentz_shift,
		float	theThickness,
		float	cot_angle,
		float	pitch,
		float	pitchfraction_first,
		float	pitchfraction_last,
		float	eff_charge_cut_low,
		float	eff_charge_cut_high,
		float	size_cut
	)

A generic version of the position formula. Since it works for both X and Y, in the interest of the simplicity of the code, all parameters are passed by the caller.

Parameters

size	Size of this projection.
q_f	Charge in the first pixel.
q_l	Charge in the last pixel.
upper_edge_first_pix	As the name says.
lower_edge_last_pix	As the name says.
lorentz_shift	L-shift at half thickness
cot_angle	cot of alpha_ or beta_
pitch	thePitchX or thePitchY
eff_charge_cut_low	Use edge if > w_eff &&&
eff_charge_cut_high	Use edge if < w_eff &&&
size_cut	Use edge when size == cuts

Definition at line 16 of file SiPixelUtils.cc.

References funct::abs().

Referenced by PixelCPEGeneric::localPosition().

    {
    float geom_center = 0.5f * (upper_edge_first_pix + lower_edge_last_pix);

    //--- The case of only one pixel in this projection is separate.  Note that
    //--- here first_pix == last_pix, so the average of the two is still the
    //--- center of the pixel.
    if (size == 1) {
      return geom_center;
    }

    //--- Width of the clusters minus the edge (first and last) pixels.
    //--- In the note, they are denoted x_F and x_L (and y_F and y_L)
    float w_inner = lower_edge_last_pix - upper_edge_first_pix;  // in cm

    //--- Predicted charge width from geometry
    float w_pred = theThickness * cot_angle  // geometric correction (in cm)
                   - lorentz_shift;          // (in cm) &&& check fpix!

    //--- Total length of the two edge pixels (first+last)
    float sum_of_edge = pitchfraction_first + pitchfraction_last;

    //--- The `effective' charge width -- particle's path in first and last pixels only
    float w_eff = std::abs(w_pred) - w_inner;

    //--- If the observed charge width is inconsistent with the expectations
    //--- based on the track, do *not* use w_pred-w_innner.  Instead, replace
    //--- it with an *average* effective charge width, which is the average
    //--- length of the edge pixels.
    //
    //  bool usedEdgeAlgo = false;
    if ((size >= size_cut) || ((w_eff / pitch < eff_charge_cut_low) | (w_eff / pitch > eff_charge_cut_high))) {
      w_eff = pitch * 0.5f * sum_of_edge;  // ave. length of edge pixels (first+last) (cm)
                                           //  usedEdgeAlgo = true;
    }

    //--- Finally, compute the position in this projection
    float q_diff = q_l - q_f;
    float q_sum = q_l + q_f;

    //--- Temporary fix for clusters with both first and last pixel with charge = 0
    if (q_sum == 0)
      q_sum = 1.0f;

    float hit_pos = geom_center + 0.5f * (q_diff / q_sum) * w_eff;

    return hit_pos;
  }