Agenda

Minutes

Present: Igor, Hovanes, Beni, Moskov, Tim, Pavel, Edy, Sashi, Mikhail, Eugene, Marshall, Richard, Sean, Vitaly

Eugene said that the decision on JLAB capital funding is being delayed even more, probably until April. We cannot procure equipment, but Hall D was allowed to spend money on KLF design work.

Pavel used FLUKA to reproduce the SLAC data (Phys. Rev. D 7, 708 (1973)) where K_L were produced at 2° angle by 10 GeV electron beam. This was done to gauge FLUKA's ability to reproduce K_L production. Pavel's FLUKA points were in a good agreement with SLAC data points below 3 GeV, and FLUKA was overestimating kaon yields above 5 GeV. Pavel was surprised by such a good match since his expectation for K_L production rate uncertainty is about a factor of 2.

Eugene pointed out a discrepancy that 33cm and 1.75 radiation length are different amount of Beryllium. Pavel was sure he used 33cm, while it seems that the data points were from 1.75 X0 of beryllium. Pavel will redo his calculations with 1.75 X0 Be target (61.74cm) to benchmark FLUKA.

Hovanes pointed out that 33cm Beryllium for SLAC was assumed also by Moskov in his rate estimate presented during the last meeting, so that it also should be revised.

Pavel also produced a version 4 model of KPT beamline where instead of 5.5cm ID fat beam pipe after the PS magnet and before the shielding wall he uses 10cm ID thinner pipe to reduce the radiation in the hall.

The results for photon radiation doses confirm that this is a better configuration for the radiation. The impact of this shielding modification is less dramatic for neutron rates.

Pavel sees significant photon dose rates around the target area coming from beam photon interacting with the LH2 target. He verified it by running simulations without hydrogen in the target cell.

FLUKA simulations also predicts about 100 muons per second per cm² uniform flux on the GlueX detectors. He got a confirmation from Richard that these are taken into account in GEANT4 when estimating data rates. Igor' stated that effects of muons on this experiment were well understood a long time ago.

Pavel tried to estimate potential gains in K_L flux by increasing the diameter of the beryllium target at the expense of the copper block around it. He sees a total of ~30% increase of kaon rate at the LH2 target. The kaon momentum spectrum seems to be flatter with 7cm-wide Be target. Hovanes questioned if this increase is realistic since the permanent magnet would block kaons beyond R=3cm, but Pavel disagrees stating that the chamber in the magnet was too thin to have a strong effect on the kaon rate. Although it was not clear why there was such a gain in the rate, there were no disadvantages to 7cm diameter expressed by anyone at the meeting.

Richard studied detector rate dependencies on the size of the beamline aperture with a fixed tungsten plug of 14 cm. He had two ways of restricting the aperture: by restricting the whole beampipe (take 10) , and by restricting the radius of the baffle at the wall (take 11). Take 11 should allow for more kaon flux. The aperture in both cases was varied between D=4cm and D=6cm. The radiator thickness was 10% R.L. The variable that Richard was looking at were normalized to be interpreted as counts in 64ns bursts.

Start counter rates show that take 10 is better in terms of the detector rates. GlueX-II conditions are met at around 5.5 cm diameter beam pipe. The start counter used here was cylindrical one without the nose cone.

Similarly, CDC, FDC, and TOF rates are expected to be comparable to GlueX-II when using take 10 shielding model. Therefore, the general conclusion was that if 10% R.L. radiator was used with 14cm tungsten plug, a 5.5 ID beam pipe would allow us to run the detector. The ST most likely would have to be modified, there was not estimate for standard GlueX ST rates at these condition. GEANT4 model will be switched to 20% radiator once Pavel confirms it with his comparison with SLAC data. The rates will likely increase by about factor of 2 when the radiator thickness and beryllium target diameter are increased.

Pavel argued that there are significant hit rates from the target in the ST, so it may be useful to optimize the beamline with empty target. But then it was not clear what to do if the "optimized beamline" with empty target produced rates in the detector that were too high when target was filled. Also, Richard did not agree that the rates went quadratically versus beam aperture, he will check that.

Hovanes asked if the shielding wall in GEANT4 is at the location were PS detectors are now. Richard did not change that, and Mikhail confirmed that there is no way to keep that wall there since that space will be taken by KFM detectors. The wall should be moved to where the target cart starts. Richard liked the shielding wall style presented by Pavel, he will try that next. Tim thought that it should be possible to have a shielding wall like that, but extra support would need to be installed under the platform.

Tim asked if we already know the general layout of KPT and the downstream beamline. Hovanes thinks that the core of the KPT itself will be slightly modified to accommodate 20% radiation length radiator. The downstream beamline and the shielding is still being actively investigated. This was postponed until the next meeting.