| E08-010 Run Plan |
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The table above lists the different kinematic configurations used in the N-Delta experiment. In the upper right-hand corner is
a drop-down bar that can be used to view the different forms of the run plan over the course of the experiment. The first table, "Original Proposal Kinematics", contains data from the initial experiment proposal. In that proposal, 14 kinematic configurations were suggested, based on an inital beam energy of 1115 MeV and a set of Q2, W, and θpq* values. From those values, angles and momenta for the two spectrometers were calculated. Additionally, beamtime amounts were suggested, based on an assumed current of 75 µA and a target size of 6 cm. As the experimental run period approached, it was learned that the beam energy would actually be 1160 MeV, so corrections to the angles and momenta were needed to maintain the same Q2, W, and θpq*, as seen in the second table, "Original Kinematics with Beam Energy Correction". In order to obtain the same total charge, a new current was used, resulting in new proposed beamtime values. One important change was that a Q2 value of 0.041 (GeV/c)2 was no longer possible, so that value was increased to 0.045 (GeV/c)2. Just prior to the experiment, it was learned that a 6 cm target was unavailable, so new kinematics needed to be calculated, as seen in "New Kinematics". It was decided that a 4 cm target would be used for the first four kinematics, while a 15 cm target would be used for the rest. Additionally, the θpq* angles for several of the kinematics would be changed to increase any effects due to that angle. The thinking behind the different target sizes is this: a 15 cm target has physically more material for the beam to interact with, which increases the rate and decreases the amount of beamtime necessary. But the 15 cm target also increases the amount of background events which could obscure the real data. At the same time, the kinematics with smaller angles will tend to have more background noise as well. In an effort, then, to keep the background as low as possible, the smaller target was used with the more forward angles, while the 15 cm target could be used with the larger angles. Additionally, the 15 cm target increases the risk of boiling, so currents must be kept lower than with the 4 cm target. Real particles traveling through the spectrometer would lose energy as they pass through physical barriers, and that energy loss must be taken into account when adjusting the momentum setting for the spectrometer magnets. With this in mind, another table, "New Kinematics with Energy Loss Correction", was created with the momenta adjusted. As with any experiment, reality did not quite match up with expectations, and the actual kinematics are not quite the same as predicted, as seen in the last table, "Actual Kinematics". Specifically, the angles were rounded to half-degrees and the momenta were rounded to the nearest MeV/c. Additionally, the θpq* for Kinematics 11 and 12 was changed as well. The experiment began with Kinematic 1, but it was quickly discovered that there was a rather serious problem with the deadtime, and any attempt to collect data with a current higher than 15 µA resulted in a deadtime of more than 20%, which greatly increased the amount of beamtime necessary to collect data for the first three kinematics and necessitated the elimination of Kinematic 4. The deadtime problem was ultimately found to be due to a problem with ROC 10, which was corrected prior to taking production data for Kinematic 6. Data for the first three kinematics were collected in order, but it was decided to collect additional data for Kinematic 1 after Kinematic 3. After this second round of data collection for Kinematic 1, it was decided to jump to Kinematic 6 instead of Kinematic 5, due to the small angle associated with Kinematic 6 and regulations concerning angles less than 14°. Following Kinematic 6, the spectrometers were moved to Kinematic 7, and then back to Kinematic 5. Runs in these last three kinematics were all taken with the 4 cm target rather than the earlier proposed 15 cm, but because the deadtime issue had been resolved, the current could be increased to offset the smaller target and keep the rates high. Following Kinematic 5, the experiment jumped to Kinematics 11 and 12, also using the 4 cm target. After Kinematic 12, the experiment went back to Kinematic 8, where data was taken with both the 4 cm and 15 cm targets, to allow a comparison between the two targets, as the rest of the kinematics would be taken using the 15 cm target. After that, the remaining kinematics were taken in order. |