Re: Interaction and Hadronic Energy.

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

Dear James,

Thank you for your note of a couple of weeks back.  Sorry I have been late
to reply, but our end-semester rush is over now.  I have put together a web
site to track our discussion on this topic (with figures).  Please look at
http://zeus.phys.uconn.edu/halld/trigstudies and see the latest entries quoted
below.

[from James Hubbard]

I've got a couple of questions. We've developed a couple of ideas about settings for a trigger. One cut involes the total energy in the barrel and forward cal as well as the whether the energy is greater in the barrel. The other cut involves the energy in the forward cal and whether or not there are any tracks in the time of flight.

1. Is there some way of changing the probability of a particles interacting without having to re-compile or do we need to modify geant? (If we need to modify geant can you point me to a place can make changes?)

The probability that a charged pion makes light in the LGD is 100%.  A 5GeV
pi+ leaves about the same amount of Cerenkov light in the lead glass as a
400MeV gamma even if it never has a hadronic interaction.  Since we want
to have photon acceptance much lower than this, it is safe to say that we
can expect to see signals from essentially all of the forward-going charged
pions.  What we want to know is the response function.  How precisely do
we need to know it?  I think that the simulation can give an initial estimate,
but I would not believe the shape to better than +/-10%.  Is that good enough
for your purposes?  If so then we should verify it against Scott's curve
to check out the fidelity, but I am skeptical that we will get ahead by going
in and starting to tweak the hadronic package.

2. It's basically the same, but I need to know if there is a way that I can modify the amount of hadronic energy being deposited? (Can you point me to a starting point where I can make changes?)
The whole reason for this is to see if a trigger based on the parameters can be tuned if the number of interactions and energy is off.

Before we start kludging the simulation, we need to see if there is a problem. When Scott says that the comparison looks good to him, he is not claiming that the plots are identical. As you have pointed out they are not. But they are not plots of exactly the same thing. His data were collected with a 18GeV pion beam, different cuts and some kind of clusterization in the LGD.

Some questions for you, Scott. Can you give more details about how your plot was produced? Your pions were tracked through a magnetic field and projected onto the LGD, right? Did you do a clusterization of the LGD hits and then take the closest cluster to the pion impact? What cuts did you make on that association? What were your clusterization parameters?

Richard Jones