PndCircleTools.h

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//****************************************************************************
//*                   This file is part of PandaRoot.                        *
//*                                                                          *
//*            PandaRoot is distributed under the terms of the               *
//*              GNU General Public License (GPL) version 3,                 *
//*                 copied verbatim in the file "LICENSE".                   *
//*                                                                          *
//*  Copyright (C) 2006 - 2024 FAIR GmbH and copyright holders of PandaRoot  *
//*     The copyright holders are listed in the file "COPYRIGHTHOLDERS".     *
//*               The authors are listed in the file "AUTHORS".              *
//****************************************************************************

#pragma once

#include "FairHit.h"
#include "TVector2.h"

namespace PANDA {
namespace CircleTools {

double PtFromCircle(double B, double r)
{
  // 0.01 to recalculate [cm] in [m]
  // 0.3 from constants when setting Lorentz force equal to centrifugal force
  // pT [GeV/c] = 0.3 * B [T] * abs(r [cm]) * 0.01;
  return 0.003 * B * abs(r);
}

double PhiForHit(FairHit *hit, TVector3 &circle)
{
  TVector2 hitV(hit->GetX(), hit->GetY());
  TVector2 circleCenter(circle.X(), circle.Y());
  return (hitV - circleCenter).Phi();
}

int RotationDirection(FairHit *firstHit, FairHit *nextHit, TVector3 &circle)
{
  double phiFirst = PhiForHit(firstHit, circle);
  double phiNext = PhiForHit(nextHit, circle);

  if (phiNext - phiFirst > 0)
    return -1;
  else
    return 1;
}

TVector2 PositionOnCircle(FairHit *hit, TVector3 &circle)
{

  double phiHit = PhiForHit(hit, circle);

  TVector2 circleCenter(circle.X(), circle.Y());
  TVector2 result(circle.Z(), 0);
  result = result.Rotate(phiHit);
  result += circleCenter;
  return result;
}

TVector2 PtOnCircle(FairHit *hit, TVector3 &circle, int direction, double B)
{
  TVector2 result(0, PtFromCircle(B, circle.Z()));
  double phiOnCircle = PhiForHit(hit, circle);
  if (direction > 0) {
    phiOnCircle += TMath::Pi();
  }
  return result.Rotate(phiOnCircle);
}

} // namespace CircleTools
} // namespace PANDA