Minutes of the CALCOM Analysis Meeting, October 10, 1997
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 Agenda:
             L. Elouadrhiri -  A first look at particle id with
                               hit-matched tracks in the TOF counters

                     K. Joo -  Some event reconstruction issues

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 The next meeting will be held Friday October 31, 1:30pm in room A110.

  Tentative agenda: 
                 
              (1)   Status of drift chamber calibration   
               
              (2)   EC and LAEC calibration status 

              (3)   Status of projects to be studied for e1


 I ask the various working groups and individuals to come prepared to the
 meeting.
                  Volker Burkert
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Individual reports:
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L. Elouadrhiri: Particle Identification and TOF calibration
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In the first stage of this analysis, we looked at the identification of 
positive charged particles.
This involves matching the informations for each track between the drift
chamber and the TOF system, together with  good electron identification.

Using SEB (Simple Event Builder), we selected events for which an electron and
an other positive charged particle are present. The tracks reconstructed with
DC are required to match  a hit in the TOF system. 
The electron is identified with the calorimeter, knowing its path length 
we determined the flight time, by subtracting this time from the TOf TDC one can
determine the $t_o$ of the event. From this information and the TOF TDC 
for the other charged particle, present in the event, one can calculate the 
mass of the hadron.
The first result of the mass distribution from run 5991 (1.6 GeV) showed two 
peaks one at 2 GeV and one at 0.5 GeV. If everything were calibrated perfectly 
one should observe from this data one peak at the pion mass and an other peak 
at the proton mass.  

In the first step of this calibration procedure, we Selected elastic reaction 
by requiring that the electron is in sector 1 and the proton in the opposite 
sector 4 and with an additional cut on W distribution $0.8 GeV < W < 1.1$ GeV.
In this case the mass distribution is one single peak at 2 GeV.
The calibration of this mass distribution to be at the mass of the proton
leads to a 27 ns time difference between sector 1 and 4.
The same work has been done when the electron is detected in sector 2 and 3
and the hadron is detected respectively in sector 4 and 5. The result of this 
calibration leads also to a calibration constant of 27ns between sector 2 and 5,
sector 3 and 6. We expect few ns between sectors instead of 27ns. The 
discrepancy was explained during the meeting by an offset of 25ns between 
sector 1, 2, 3  and 4, 5, 6; falsely introduced in the TDC calibration.

Outlook: After making this correction in the TDC calibration, we will extend 
the  procedure described above for the other sectors and also from channel to 
channel, which will provide the first particle ID.
 



K. Joo:
------
I presented the primitive results from p(e,e'pi+)n and p(e,e'p)pi0 
channels using run 5991 with a beam energy of 1.645 GeV utilizing 
particle identification using TOF information. The electrons are 
identified with EC, SC and DC(-) and hadrons are identified with SC 
and DC(+). I selected only 2-track events. This analysis is based 
on hit base tracking. To identify pi+ and proton separately, I used 
the recent TOF analysis done by Latifa. 

For more details please look up the offline analysis web page under
K. Joo analysis: http://www.cebaf.gov/~manak/offline_analysis.html.
In figure(a), hadron mass squared calculated using TOF information,
is plotted. As you can see, there are 3 peaks. The second one 
corresponds to pi+ mass and the third corresponds to proton mass, but
the firt one is not identified. It turns out that if I take only the
events with electrons from sectors 1, 2 and 3, then the first peak
disappeared and there are two peaks, the first one for pi+ and
the second one for proton as shown in the figure(b). 
It was confirmed by Latifa that only sector 1, 2 and 3 for electrons 
were calibrated and the rest of them haven't been done yet.
In figure(c), the missing mass distribution for p(e,e'pi+)n channel
is plotted without any correction. In figure(d), the same thing is
plotted after the cut on pi+ mass from the hadron mass squared histogram
obtained using TOF information. It clearly shows that the background
is substantially reduced with a few loss of p(e,e'pi+)n events.

Similar figures were also presented for p(e,ep)pi0 channel at the
meeting.