[Halld-offline] t0 for DMCThrown

[Richard Jones]

Paul,

The behavior you describe is correct, but it was my intention that the
physics simulation would not modify  the MC record written by the
generator. It was supposed to pass that unchanged, and any new information
it wanted to add was supposed to be found in subsequent tags. The physics
simulation would have its own clock synchronized to the accelerator, but
the generator could generate chains of delayed decays without worrying
about the beam structure. Since then, there has been a move away from that
towards using a hybridized MC record, with some of the information coming
from the generator and some being added or overwritten by the physics
simulation, maybe mcsmear, maybe others FAIK.

I agree with you that there should be a consistent clock for all times
within the MC record, and as of now that is not the case. I am checking in
a change right now that gives the behavior you would expect: the original
t=0 from the generator for the primary vertex is now being overwritten with
the value of the accelerator-synced clock in hdgeant at the instant that
the primary interaction occurs. This makes all of the t values in the MC
record use the same clock, which is t=0 for the primary vertex before
hdgeant, and t sync'ed to the beam structure after hdgeant.

-Richard Jones


On Thu, Jun 26, 2014 at 11:04 PM, Paul Mattione <pmatt at jlab.org> wrote:

> Hey Richard, my understanding is that when running an event through
> hdgeant (e.g. from bggen), the start time t = 0 for the event is defined to
> be when the photon crosses the target midplane:
>
>
> https://halldweb1.jlab.org/wiki/index.php/How_HDGeant_defines_time-zero_for_physics_events
>
> However, after running hdgeant, the time in the DMCThrown objects is still
> 0, even after the start vertex has been moved to a different position.
> Also, the t0 is 0 for secondary particles that are produced in the BCAL,
> etc.  This is low priority, but could you please fix this in hdgeant when
> you get the chance?  Thanks.
>
>  - Paul
>
>
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