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Re: Thoughts on motivating tof for Review



Hi Elke

I wanted to add to your comments....

With regard to BCAL and timing w.r.t to PID, as you once pointed
BCAL might be used for pi/proton separation but not for pi/K.
In my kinematics note (GlueX-doc-838) I showed the momentum
spectrum for charged particles hitting BCAL from the K*K*p
reaction (K-pi-K-pi p).  There are no particles with momentum
less than 1 GeV and the pion spectrum peaks at 2 GeV and the
K spectrum at about 3 GeV.  (Fig 25c).   The charged particles
have to have pt > 0.435 GeV to hit BCAL.  Even with the pessimistic
timing for MIP, the BCAL timing resolution of about 420 ps for
MIPS is sufficient to separate any proton reaching BCAL from
a pion.  Recall that Stefano felt that our  current estimate of
BCAL timing for MIPS (based on cosmic rays) was probably too
pessimistic - I think he said KLOE achieved 300 ps.  But even this
would not suffice for pi/K separation.   It is true that we are
working on overall timing for BCAL -- especially for photons
(time difference and mean time) -- and I think we'll have solid
results soon but they will not change the overall conclusions
above re PID.  And one last comment here:  Stefano also said
that the KLOE calorimeter could also be used to identify
protons via their characteristic energy deposition.  I think
Zisis is studying this for BCAL>

One more comment - I agree that Pythia is great for understanding
the backgrounds.  I also found that the K*K*p reaction, leading to
two K's and two pi's, kinematically describes most of the interesting
signal reactions that will lead to this final state (e.g. K_1-K where
K_1 ->K* pi, etc....).  The conclusion is that we need a well-performing
forward TOF  AND a RICH.

For those doing the PID and tracking studies, GlueX-doc-838  has
more information about relevant kinematics - including the challenge
of measuring rho decays - in particular with respect to helicity angles.

Cheers
Alex


At 5:52 AM -0500 2/25/08, Elke-Caroline Aschenauer wrote:
>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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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Alex R. Dzierba
Chancellor's Professor of Physics (Emeritus)
Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
JLab Visiting Fellow
Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 / 757-269-7577
Home Phone: 812-825-4063  Cell:  812-327-1881  Fax: 866-541-1263
http://www.dzre.com/alex
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~