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Re: Thoughts on motivating tof for Review
On Fri, 22 Feb 2008, Elton Smith wrote:
Elton,
did you discuss this on Friday?
Okay, I think before we can talk about PID we need to know the performance
of the detectors. So I would think we need to make sure we know the timing
performance of the BCal and the latest mails on this indicate we need a
bit of work on this, but are already very close.
For the forward tof we need the hardware performance, the uncertainty on
the momentum and path length. If we have this we can look into the
performance.
I don't need a MC to know we basically have in the full momentum angle
range a factor 1 to 10 for kaons to pions, so we will have a hard time to
get kaon id. so all comes to pion to proton separation. Actually there
will be also protons in the forward direction.
If you talk about pid, than we might also consider some wider physics
program, like we want to discuss in a week and than we need also electron
id, which of course is not to difficult to get with our em-calorimeters,
e/p gives normally a factor 100 suppression of hadrons in the lepton
sample. Which might be okay, not great but ...
As I was saying I asked Eugene to repeat his studies he did some time ago
for the Cerenkov more focusing on the tof in the BCal and the forward.
I think pythia gives a very nice possibility to do this, we could for
example look to sigmas or lambda(1520) reconstruction if we want to make
statements on kaons.
For getting a good particle id you actually best measure parent
distributions of your final detector with beam and than use the Bayes
theorem to get probabilities. I showed this in my talk on the Hermes pid
in the collab meeting last October.
for the trigger and your timing questions. we should not to much focus on
10^7, because as I said in my other email the start counter will have a
rough time at 10^8 and so will the tagger, so we should from the beginning
have a start time which will work for all rates 10^7 and 10^8. So again
what is wrong with the machine clock.
For the trigger, I'm not sure how much we have to discuss in detail the
trigger, because there we look for hits. I think the new material budget
in the beam brings the rates down by a factor of 5 ( I have not all
numbers here) so this will give us a certain hit rate in 100ns per paddle.
We could make the inner paddles a factor of 2 smaller in width, this is
not at all a cost problem. Actually one test would be to make the air in
the beam pipe He and see what that helps in addition.
I think in the barrel dE/dx has to be included in the picture, of course
the threshold for protons coming out of the target is an issue, because it
is close to what the range of protons is which can be detected by the CDC.
This is something we have to look into very carefully, because the start
counter contributes to this threshold for sure quite a bit.
If the final pid includes a aerogel rich, which with the improvements in
aerogel lello presented is the best thing to do, we will have actually
pion id from 0.5 geV on, which is very nice, because having 2 pid
detectors overlapping will increase your purity a lot. that is also true
combining the rich and the em-calos for leptons.
One other thing we have to make sure that the beam hole in the tof is
matched to the one of the FDC.
so this has become a long email, but as I was not present at the
discussion, I thought I type some of my ideas into an email.
I guess we will have a detailed discussion on Friday. I can be available
for a phone meeting earlier if needed.
cheers elke
> Friends,
>
> I spent some time with Matt and Beni to go over the motivation/arguments
> for tof in the detector, given that kaon id is very limited. I put these
> out for comments/discussion especially in order to define what
> calculations/work might need to be done in preparation for the review. We
> came up with the following points
>
> - pion purity (how often are we fooled by other topologies?)
> - positive proton id (mostly in the barrel)
> - forward tof input to trigger
> - timing information for analysis (start time for drift times, rejection
> of accidentals coincidences with the tagger)
> - part of future comprehensive pid detector package for detector (covering
> pi/K id below 2 GeV).
>
> I would appreciate comments suggestions on what to emphasize and priority
> for any studies that are required.
>
>
> Questions:
> - What is the granularity (segmetation) required due to rate
> considerations?
> - What is the spectra of all particle species (pi,K,p) over the detector
> (e.g. what is the ratio of particle types in the Bcal and the TOF?)
> - Study acceptance of charge particles (actual trajectories in B field)
> for the 1deg beam hole and at the largest angles?
>
>
>
>
>
>
> Elton Smith
> Jefferson Lab MS 12H5
> 12000 Jefferson Ave
> Suite # 16
> Newport News, VA 23606
> elton@jlab.org
> (757) 269-7625
> (757) 269-6331 fax
>
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