Agenda

Minutes

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

Moskov announced that ODU group is interested in building a new start counter for KLF. It would be similar to GlueX start counter but it will a have wider opening (≥6cm) in the cone or will be cylindrical.
Eugene pointed out that making a cylindrical start counter will take shorter time.

Pavel continued simulations with his FLUKA model of the collimator cave and the main hall. He does two kind of simulations: full simulation with low energy thresholds for particles; and high energy simulations where the momentum threshold is 500 MeV for all particles, but is 20 MeV for neutrons.

Pavel tried both 10cm and 14cm tungsten plugs. Photon spectra for both thicknesses look similar, but the rate is reduces by about factor of 20 for 14 cm plug.

Kaon rate from FLUKA with a 14cm plug is 6.3 KHz, a ~25% reduction with respect to the original 10cm plug. Neutron rate is about 40KHz.

Pavel summarized his findings regarding the background in the hall: low energy photons hitting the target; high energy forward particles penetrating through the concrete around the beamline in the cave labyrinth walls; diverging beam cascading in the beamline. He thinks a combination of thicker (14cm according to Richard's optimization) plug, heavier core around the beam pipe in the walls of the cave, and shielded beam pipe may solve the high rates in the detector.

Having a shielded beam pipe with respect to unshielded pipe with 14cm tungsten plug reduces the dose rates in the location of CDC by about a factor of ~7.

Pavel stated that with 14cm plug the main background inside the beampipe is from neutrons while at 10cm the largest background source were the photons. The neutrons can be problem for FCAL considering the divergent nature of the beam.

Eugene suggested to have a beampipe with variable thickness, baffles, to reduce the background rate from cascading in the beampipe not only outside of the beampipe but also inside the beam pipe.

Hovanes asked what can be done about thicker beam pipe in the area of the flux monitor. Mikhail suggests that we have about two meter of the thin beam pipe there.

Hovanes reminded us that the beam pipe between the target refrigerator and the target cell is pretty wide, about the same size as the start counter. The upstream flange of the refrigerator could be a good place to place a collimator. The pipe may contain target plumbing inside it , though. Pavel would like to have drawings.

Moskov asked if Pavel can make any conclusions about the need for a new start counter, beam pipe, and tungsten plug thickness. Pavel thinks that his studies show the sources of the background and possible ways to shield them, but the optimization should be done using the actual detector rates which is what Richard is doing.

Richard implemented a mechanism in GlueX GEANT4 program that allows him to track the origin of the hits in any of the detectors all the way to the primary particle of the event. He already ran some simulations that completed earlier this morning. Richard did not have time yet to analyze the data he's got.

Richard only showed what he saw in the start counter looking at the origin of the particles that created the hit in the start counter. These parent particles are mostly electrons, and sometime photons. There are three regions in z where he sees the parents of the hit originate: the tungsten plug (parent particles are photons), beam pipe (electrons) and the start counter enclosure (electrons). Richard also looked at the x vs y distribution of the origin of the parent particles, and he sees an almost point-like narrow source at the plug, a ring consistent with the beam pipe radius, and a wider ring with a radius consistent with the size of the start counter.

Eugene suggested looking at only radial dependence of the origin of the parent particle. Mikhail also suggested looking at R vs Z plot.

Eugene asked if there is anything coming from the target based on these plots. Richard thinks that he sees some parent particles coming from the areas with the radii consistent with the area volume with LH2.

Pavel asked if the thick beam pipe just upstream of the target is in GEANT4. This could also be the source of the parent particles that come from the areas of radius of around 8cm. Richard and Sean were not sure if that pipe is in the model. Hovanes suggested that using z-cuts, one could separate the area of the start counter and the beam pipe just before it.

Moskov asked if Richard can already conclude that a start counter with a larger opening is necessary for KLF. Richard was not ready to answer this question at this time. More studies are needed.

Richard will study the origin of the rates in the other detectors. He can share his UCONN Jupyter Notebook with others so that more people can look at the results. But he was not sure if JLAB will give us access to UCONN Jupyter Notebook.