#############1
The StMuHelix in StRoot/StMuDSTMaker/COMMON will work, since it does derive from TObject, but

you'll have to rebuild it out of the StPhysicalHelix call.

That is to say, when you ask for the StMuTrack::helix it actually

rebuilds an StPhysicalHelix out of the StMuHelix, so you will

have to reverse this.  Take a look at the code in $STAR/StRoot/StMuDSTMaker/COMMON/StMuTrack.cxx



Alternatively, if you don't want to make the code dependent on StRoot/StMuDSTMaker/COMMON

just store all the info that is used to build the StPhysicalHelix, i.e. parse through the various

methods of the StPhysicalHelix to get the information so that you can redo this call in your code:

StPhysicalHelixD StMuTrack::helix() const{

return StPhysicalHelixD(mHelix.p(),mHelix.origin(), mHelix.b()*kilogauss, mHelix.q());}

where mHelix is an StMuHelix, not an StPhysicalHelixD.

--J
############2

To be clear, if you have an StMuTrack* track and an StMuDst* mu

you can make an

StMuHelix *helix = new StMuHelix(track->helix(),mu->event()->runInfo().magneticField());

and store that in your class.

Then in your later code you can convert it into an StPhysicalHelixD by doing

StPhysicalHelixD thelix = StPhysicalHelixD(mHelix.p(),mHelix.origin(), mHelix.b()*kilogauss, mHelix.q());

where mHelix is an StMuHelix.

and use all the methods of StPhysicalHelixD.

For example,
/// path length at given r (cylindrical r)

    pair<double, double> pathLength(double r)   const;

/// path length at given r (cylindrical r, cylinder axis at x,y)

    pair<double, double> pathLength(double r, double x, double y);

/// path length at distance of closest approach to a given point

    double  pathLength(const StThreeVector<double>& p, bool scanPeriods = true) const;

/// path length at intersection with plane

    double       pathLength(const StThreeVector<double>& r,const StThreeVector<double>& n) const;

/// path length at distance of closest approach in the xy-plane to a given point

    double       pathLength(double x, double y) const;

/// path lengths at dca between two helices

    pair<double, double> pathLengths(const StHelix&) const;

 /// minimal distance between point and helix

    double       distance(const StThreeVector<double>& p, bool scanPeriods = true) const;

as documented in the StarClassLibrary stuff available at

http://drupal.star.bnl.gov/STAR/comp/sofi/tutorials/specDocs

pp. 45-47.



--J

##############3

StPhysicalHelixD *h = new StPhysicalHelixD
TFile fout("test.root","RECREATE")
TTree *t = new TTree("test","Helix test")
t->Branch("helix","StPhysicalHelixD",&h)
t->Fill()
t->Show(0)
	

--M