Present: L. Weinstein, R. Niyazov, S. Stepanyan, D. Branford,
D. Rowntree, J.Zhao, A. Skabelin
Items discussed:
1) target
2) trigger
3) data analysis
4) simulation
5) schedule (with additional information from B. Mecking)
6) Next meeting: Wednesday April 29 at 3:00 pm.
Wednesday June 3 at 3:00 pm.
Sincerely,
Larry Weinstein
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1) We are planning to use the Saclay cryotarget for 3He and 4He. (The
French are planning to test it this summer with 3He.)
For solid targets, we will build a solid target mover that will
position very small solid targets 2-3 cm downstream of the
cryotarget. The targets will be mounted on an approximately 8mm wide
thin film (with holes punched out for the targets). The targets will
be positioned by moving the film. We discussed aspects of the
mechanism involved. We will need either an in-vacuum encoded motor or
a rotary feedthrough (linear feedthroughs leak too much). We will
also need some form of motor-independent position readout (in case the
film jams or falls off sprockets).
The target must be installed in CLAS by February 1999.
L. Weinstein and an ODU tech will work with Yuri Sharabian on this.
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2) Trigger: We need a level 2 trigger. Only 15-30% of events from the
level 1 trigger have good electrons. If we have 1500 events/sec
with very high efficiency we might not need to prescale.
J. Zhao calculated the CLAS geometrical acceptance as a function of
angle.
J. Zhao and A. Skabelin will look at the Aluminum data to see if the
data rate matches our calculations.
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3) Data analysis: A. Skabelin has been analyzing 2.4 GeV Aluminum
(target empty) data taken by e1. The timing is now good enough to
identify protons up to almost 2 GeV/c.
For all events with protons, the missing mass squared distribution
[(m_p+omega)^2 - q^2] is flat with a large peak at (m_p)^2 [about 1.5
times flat level] and a much smaller peak at the Delta.
3-vector q is flat from 0.8 to 2.2 GeV/c. 4-vector Q^2 peaks at 0.5
GeV^2 and tails off to 2 GeV^2.
He looked at (e,e'pp) events:
* the 2p invariant mass peaks at 0.1 GeV/c (+2m_p).
* the missing energy (omega-Tp1-Tp2) is flat from 0 to
0.5 GeV and then decreases to 2.0 GeV.
* he plotted the q-projections of the outgoing proton
momenta (p1.q/|q| vs p2.q/|q|) against each other. There is no
obvious signature for one of the protons having absorbed the virtual
photon.
* the difference of the q-projections of the outgoing protons is peaked
at zero and extends out to about +/-1.5 GeV/c. If one of the protons
had absorbed the virtual photon, then there would be a hole in this
difference spectrum at 0.
* the relative angle of the two outgoing protons has a slight peak at 90
degrees, even after being corrected for phasespace by 1/sin alpha.
D. Branford suggested looking at low emiss events
S. Stepanyan suggested looking for high momentum backward going
protons. (There are some, not a lot.)
For details, talk to Alex.
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4) Simulation.
Work is proceeding on making GSIM run faster (Rowntree and Zhao).
L. Weinstein will write some 2N knockout event generators so can
compare them to data. This will be a long iterative process.
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5) Schedule (aka bitching and moaning)
e2 was originally tentatively scheduled to run first in 1999. Hall A
has now requested high polarization (80%) beam for Gmn (H. Gao) in
February. Since e1 is approved for polarized beam (and we are not),
e1 will run at the same time as Hall A Gmn. Thus, they will run in
February and March and we will run in April and May.
The current schedule (now being made up by B. Mecking) has e2 running
from 4/12 to 5/24. This is 33 days of beam (more than the 30 approved
for the first phase by the collaboration and less than the 34 we have
always asked for). The beam energies will be 2.2 GeV and 4.4 GeV
(since Hall A parity will be running at 3.3 GeV). We will get
maximally polarized beam (approx 40%) at 2.2 GeV and 80% of maximum at
4.4 GeV.
I have expressed to Bernhard my strong disappointment at this latest
delay. This is the second time we have been delayed. I told him that
it will be completely unacceptable if this happens again. Please
contact him yourselves and add your voices to this chorus.
If the high polarization source cannot deliver high current, then it
will not be used in February (since Hall C will need 20-30 uA). If
that is the case, then we will run before e1.
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6) next meetings
Wednesday April 29 at 3:00 pm.
Wednesday June 3 at 3:00 pm.
The date of the second meeting has been delayed by one week so as to
coincide with the Hall B meeting which starts on June 4.