Present: Chris Allgower, Andy Bacher, Chris Lavelle, Hermann Nann, John Olmsted, Tom Rinckel, and Ed Stephenson
SHIFT SCHEDULE
Ed presented the schedule from last time for discussion. There were no suggestions for a major rearrangement. Information on conflicts was collected from John Olmsted and Hermann Nann. A new schedule will be prepared and the draft circulated.
At the moment, we expect to have outside help from Paul Pancella (3/4 - 3/10) and Adam Smith (3/14 - 3/17). Mark Pickar will not be able to come. There is no word yet from Hal Spinka.
Jack Doskow leaves on spring break vacation and will not be in the lab on Friday, 3/8. Tom Rinckel leaves on 3/9.
SCALING FROM 3-He TO 4-He
We took data during the last test run at a cone angle of 0.95 deg. and 1.55 deg., corresponding to energies of 199.35 and 200.41 MeV. The Cooler circumference agrees within expected errors with the average circumference inferred from the data of May, 2001. Little variation was available in the Cooler combos, so we must assume that similar geometric restrictions apply to the d+d -> alpha+pi0. Thus it seems prudent to set up for a d+d cone angle of 1.2 deg., or an energy of 228.5 MeV (down from the proposed 231.4 MeV). Errors in the cross section from clipping the edge of the cone are large and hard to estimate.
The energy loss calculations now agree to within 0.1 ns with the time spread seen in the 3-He spectra. Other checks, such as total time of flight and scintillator pulse height span, also agree, but with cruder precision. So this is now the model for the switch from 3-He to 4-He.
Chris Allgower has asked for the time of flight from the target to the delta-E(1) and delta-E(2) scintillators so that changes in the delays can be made. These are:
| 3-He | 4-He | change | |
|---|---|---|---|
| to delta-E(1) | 37.66 ns | 33.28 ns | -4.38 ns |
| to delta-E(2) | 151.00 ns | 120.77 ns | -30.23 ns |
These values are averages over the recoil momentum span, assuming the cone angles quoted above.
Similarly, the average momentum of the recoil nuclei can be calculated for passage through the septum and the quadrupoles, taking into account energy loss. This leads to a B-rho scaling factor for the channel magnets:
| 3-He | 4-He | scaling | |
|---|---|---|---|
| septum | T = 59.90 MeV p = 538.12 MeV/c |
T = 106.37 MeV p = 896.82 MeV/c |
1.538 |
| quads | T = 41.75 MeV p = 486.05 MeV/c |
T = 93.12 MeV p = 486.05 MeV/c |
1.725 |
and to a new set of currents for the magnets:
| 3-He | 4-He | |
|---|---|---|
| Alpha-24 | 722.17 A | 1110.7 A |
| Trans-Rex | 721.38 A | 1109.5 A |
| Quad 1 | 250 A | 430 A |
| Quad 2 | 310 A | 535 A |
| Quad 3 | 210 A | 360 A |
A question was raised about whether there are saturation corrections to the septum current.
After the meeting Tom Rinckel checked on current values. The change at 14.2 kG is almost exactly 1%. So 1110 A becomes 1121 A. For the quadrupoles, we encounter a limitation on the full scale currents of these supplies. Quad 1 is limited at 400 A and Quad 2 at 500 A. The notion of reconfiguring the supplies does not match supplies to loads that can be driven with the voltage limitations of the supplies. Another solution is to reduce the scaling factor until all quads fit within the current limitations. This gives the values:
| Quad 1 | 400 A (at the limit) |
| Quad 2 | 497 A |
| Quad 3 | 335 A |
Projected scintillator pulse heights can be obtained from the energy loss calculations. The energy ranges are:
| 3-He | 4-He | |
|---|---|---|
| delta-E(1) | 9.2 - 10.7 MeV | 6.9 - 7.5 MeV |
| delta-E(2) | 23.6 - 37.3 MeV | 36.5 - 44.3 MeV |
| E | 29.3 - 51.0 MeV |
The location of the recoil group in the delta-E(1) by (2) scatter plot changes only a small distance. Further correction taking into account the conversion efficiency of energy loss into light were suggested.
LUMINOSITY ANALYSIS SCHEME
Ed presented a draft scheme for processing the information from the new luminosity scintillators.
A plot of the front against the read in each pair of detectors on a single side should show two bands (depending on the coincidence) for protons and deuterons. The bands will be spread from a pulse height ratio of 3.5 to 1/3.5 depending on the position of impact on the scintillator. This spread can be converted into a position using X = (F-R)/(F+R).
Particle that miss above or below will show up in only one of the two scintillators, which one tells whether high or low. The rate of these events compared to the double hit events (in coincidence with double hits on the opposite side) is a measure of the vertical displacement of the beam.
A scatter plot of left and right positions for the deuteron group can be resolved into two components along and perpendicular to a diagonal through the plot. When X(R) and X(L) rise or fall together, the beam z-position of the scattering is changing. A projection along this axis generates the target profile. Perpendicular to this is the scattering angle axis with theta(c.m.) = 90 deg. in the middle. A cut along this position defines the angle acceptance. If the events inside this box are projected along the z-axis, it becomes possible to select the central region of the target profile as a luminosity monitor.
Similar cuts are not possible for the p+d reference because the deuteron angle changes so slowly with changing center-of-mass angle. Some information on this can be recovered if a stopping detector is used at 25 deg. Then there should be a correlation between pulse height and position on the away-side 45-deg. detector.
The challenge of this system will be to obtain a known luminosity from the p+d scattering that can be used to calibrate the d+d scattering. It does not, however, need to use the same cuts or solid angle so long as the p+d solid angle is known and all other cuts are reproducible. A good comparison should be possible if the target is well localized so that weighting over the proton acceptance can be done.
Further thoughts on this scheme were encouraged.
ANALYSIS
John Olmsted presented some results from replay. The missing mass algorithm for 3-He is working, and now gives a resolution of 120 keV. Improvements to the resolution resulted from a better value for the distance from the target to MWPC-1 and a slewing correction for the time of delta-E(2), the PMT on the side opposite that used for start timing.
A check of adjustments to the 21.0 chan/ns calibration of the TDC system showed no improvement to resolution if other values were chosen.
Replay of the runs below threshold show that there are no double hits (on either side of the beam) in the Pb-glass array in coincidence with events inside the particle identification cuts on the scintillators. There are some in conjunction with events outside these cuts.
SMALL ITEMS:
Submitted by
Ed Stephenson