Re: CDC hits in MC data

[Richard Jones <richard.t.jones@uconn.edu>]

Dave and all,

Regarding your explanation below,
> The "tdrift" member of the DCDCTrackHit class gives the drift time 
> plus time of flight from the vertex (at t=0 by definition) in ns. 
please remember that the times generated by the Monte Carlo are not 
referenced to the vertex time.  I don't know what you are doing in the 
DCDCTrackHit class, but if you are just taking the time values out of 
the Monte Carlo output record and assuming that they are referenced to 
the vertex time, this is not correct.  They are timed against the 
machine bucket clock, not the vertex time.  This includes physics events 
from an external MC generator.  The difference is just the z vertex 
position relative to the center of the target in ns, so for tracking you 
can ignore this nuance.  For pid with ToF, the difference is important.  
You probably know all this, but I was not sure just now reading your 
exchange with Mark.

Richard J.

David Lawrence wrote:
>
> Hi Mark,
>
>    Want you want is to get the DCDCTrackHit objects rather than the 
> DCDCHit objects. These two have a 1:1 correlation, but the 
> DCDCTrackHit has a pointer to a DCDCWire object which has the info you 
> want. Note that DCDCWire inherits from DCoordinate system which has an 
> "origin" member that points to the center of the wire in the standard 
> lab coordinate system in cm. The "udir" member points in the direction 
> along the wire (including any stereo tilt). The "L" member gives the 
> total length of the wire.
>
>    The "tdrift" member of the DCDCTrackHit class gives the drift time 
> plus time of flight from the vertex (at t=0 by definition) in ns.
>
>    I don't know that any formal documentation currently exists of this 
> information so feel free to ask if you have additional questions.
>
> Regards,
> -David