Log entry time 03:33:10 on October 15, 2005

Entry number 156901

Followups:

• 156902 10/15/05 04:04 R. Michaels Dipole change (but R-arm refuses)

Figs 1 and 2 show what we did on Wed night. First I aligned the R-arm
by moving the elastic peak 53 MeV. The logic is that you want to move
the right edge of the peak to a place which is comfortably inside the
detector. The width of the detector is shown as a blue line which is
also placed on the elastic peak to show where it chops. This analysis
is done all with one run at dP = -2%. The detector outline is selected
with HAPPEX triggers while the elastic peak is visible with S0 triggers.

So, this movement (fig 1) was reasonable and very conservative.

Then Rob F. aligned the L-arm, moving 55 MeV, see fig 2. I would have
moved it 5 MeV further, but then maybe that's just me.

A more clear view of the quality of the alignment is the X-Y distribution
of tracks, fig 3. Again, the HAPPEX detector with dP = -2% shows the
borders of the detector (plots on left). The "final" alignment runs
show the location of the elastic peak (plots on right). The L-arm
is packed very tightly towards the edge of the detector. I would
suggest moving it 2 cm left in X, which is an increase of 5 MeV,
consistent with the momentum plot. The R-arm is, if anything, a bit
too far from the edge (but not bad). We could bump it over ~1 cm to
the right in X, which is lowering the momentum 2.5 MeV (I'll do 2 MeV)

Therefore I recommend
P0L = 3125.4 MeV
P0R = 3115.6 MeV

I will go ahead and make this change now. If someone objects to
this, we can discuss it.

A copy of this log entry has been emailed to: moffit@jlab.org,feuerbac@jlab.org,david@jlab.org

Figure 1

Figure 2

Figure 3