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Luminosity Dependence
We observe that the ratio of neutrons to protons identified by the neutron detector changes with luminosity. This was tracked to a decrease in the normalized (after corrected for electronic and DAQ deadtime, and an estimate of the tracking efficiency) proton yield as the luminosity increased, while the neutron yield is largely insensitive.
A few definitions:
During kin4, we took runs on the Hydrogen- and Nitrogen-filled reference cell at a couple of different beam currents, and (accidentally) at two different pressures for the Nitrogen cell. The runs used for this study and their conditions are in the table below:
The atomic densities of the hydrogen and nitrogen targets are about 17.8amg, while the helium-3 target had an atomic density of 10.7amg. The effect on the 'dilution factor' for Helium-3 (the fraction of detected neutrons that left the target as neutrons) of using the ratio from the different luminosity conditions:
Presently we are using a dilution factor of Dn = 0.658 calculated from all the available data and assuming the ratios were independent of luminosity. To look into this, I have looked into a couple of items.
Also looked at the BB tracking yield per Coulomb for T2 triggers. The image below shows the number of tracks found in BB with B.tr.p0>0 for T2 triggers. The track yield is normalized by the density of protons in the target, the accumulated charge, and corrected for the T2 DAQ livetime. The red points are from the hydrogen runs at different currents, and green from the nitrogen runs at different pressure. Four of the points show a stable tracking efficiency as the luminosity changed. However the highest current Hydrogen run 4596 shows a ~15% drop compared to the other hydrogen runs, due to the MWDC's dropping out during the middle of the run. Correcting the accumulated charge, neglecting this period, leads to T2-tracks/Coloumb that is independent of luminosity. Created by: feuerbac last modification: Friday 08 of June, 2007 [17:27:16 UTC] by feuerbac |
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