User name J. Volmer
Log entry time 11:37:01 on November 11,1999
Entry number 342
keyword=Missing Mass MysteryFig 1 shows a survey I did on the missing mass peaks for 1H(e,e'pi+).
From top left to bottom right I plotted them against HMS theta, HMS P0, SOS theta and SOS P0.
The colour code is: Q2=0.6 red, 0.75 blue, 1.0 green, 1.6 black.
The bullets are high epsilon, open circles are low epsilon.
Notice that the outliers are the high epsilon runs of Q2=1.0 (low) and Q2=1.6 (high). The two cases require different explanations.
Q2=1.0: this kinematic setting was done directly after Q2=0.75, which looks fine. It can't be the beam energy, though we don't have a Heep run for this setting. The most plausible explanation is to be found in a missetting of the SOS central momentum. With P0=1.48 GeV/c, there are no data to back up our parameterization of the SOS P0 correction curve. A 0.1% error is not out of the question, which is the amount seen here.
Q2=1.6: At SOS P0 of 1.63 GeV/c, we are sitting on a very steep flank in the P0 correction. The smaller correcion here would be a 0.025% reduction of the beam energy, or 1 MeV. This is below the sensitivity of Heepcheck.
In both cases there are no strong data to contradict the findings. For the sake of doing a consistent L/T separation,
it is a small price to pay to rerun the Q2=1.0 and 1.6 high epsilon data with above adjustments.
FIGURE 1
