Minutes of the January 16 Liquid Argon Simulations meeting I didn't take full attendance of the phone attendees, and so am missing names. Apologies to those not listed. Present: Herb Greenlee, Jim Stewart, Stan Seibert, Eric Church, Tom Junk, Brian Rebel, Ben Jones, Tyler Alion, Matt Szydagis, Jonathan Insler, Denver Whittington, Zepeng Li Tyler gave an update on the LBNE geometry. The photon detector paddles are already in the geometry, after discussions with Stuart Mufson and David Warner, the baseline geometry is settled. The hillside and service building work Mike Kirby has put in needs some debugging work to mesh with the rest of the geometry -- the rotations used are incompatible. Tyler is working on the detector geometry for now with the hillside and the service building disabled, as a step to get going; the inactive material will be restored after the higher priority items are put in. Tyler has been debugging the wire wrapping functions in concert with Brian, Mike, Jae, and Xinchun. At issue is that wires wrap around to more than one TPC -- discussions are ongoing to include the functionality in a way that keeps the code clean and general. Jonathan Insler has been making progress with the digitization, adding in customizable waveforms and zero-suppression, starting with the Argoneut digitization utilities. The waveforms are read in from an external file, and Brian mentioned that Jonathan should get in touch with Herb Greenlee, and that the MicroBooNE setup is a better starting point, as the waveforms are provided in a service. The zero-suppression can be applied in addition to the Huffman coding that exists for MicroBooNE. There are several options for storing data -- read-all, zero-suppressed, Huffman coded, and zero-suppressed and then Huffman coded. Tom worries about the 2 Gbyte size of storing uncompressed raw data in memory after unpacking, and wonders if hit-finding algorithms can be applied one wire at a time and the unpacked data deleted before unpacking the next wire. For LBNE we may have to adopt strategies to subdivide the simulation and reconstruction tasks within the program to save memory. Zepeng has worked on photon detector simulation along the lines that Ben has developed for MicroBooNE https://cdcvs.fnal.gov/redmine/documents/578 Some work will have to be done in order to make the photon simulation LBNE-specific -- putting in sensitive bars instead of PMT's (Tyler has the geometry built, see above), and the choice of voxelization. The symmetry of the LBNE far detector can be exploited to make the photon library more compact. Existing data structures for the raw data can be repurposed for LBNE use -- no need to redefine the output format, but the output will mean the digits from SiPM's instead of PMT's for example. They are generically named Photon Detectors instead of PMT's in the code. We need to figure out where in the simulation routines the Y location of the photon striking the paddle is (in LArSoft coordinates, along the paddle, or along gravity). We had discussed last time splitting this into 10 bins, though if we carry this through the library parameterization, it will multiply the library size by 10. But even if we do not include this as one of the library's parameters, we would still have to integrate over Y and put in the appropriate response function as a function of Y. Matt Szydagis reported on electron and photon production, comparing NEST, Icarus's Geant model, and available data. Icarus adds in a normalization factor on top of Birks' Law, which breaks the anticorrelation between light and charge yield. An alternative to fix that is to change the exponent on the Birks' constant as a function of the applied electric field. A second refinement is to apply the Thomas-Imel "box model" of recombination. In Xenon data, Birks' law reproduces the photon yield as a function of the energy of incident gamma rays above about 20 keV, but departs sharply from it below. The Thomas-Imel model works much better for incident photons below that energy. See M. Szydagis et al., arxiv:1106.1613 for details. Even though the energies are very low, they are applicable to us, as the particles in the last splittings and scatterings of EM showers have very low energies. Using the Thomas-Imel law at low energies can eliminate the need for scale factors (though you need Geant4 to have a very short track-length cutoff for fully simulating this). NEST can simultaneously match low and high LET data well. We should think about how to use LBNE prototypes -- LAPD, LArIAT, existing ArgoNeut data, the Los Alamos argon detector prototype, and possibly the 35T detector to construct tests that help distinguish which model is the best to use. Small detectors may be the most flexible for changing operating conditions and making measurements that are relevant to the charge and light yield models. Large detectors are more sensitive to other variables that scale with the drift distance, such as electron lifetime, argon purity, light absorption and scattering, and space charge. Next meeting: Wednesday, January 30, 1:00 PM CST Jim Stewart is asking for an extra day at the beginning of the March Collaboration meeting dedicated to simulations. We should start planning for work to be done and presentations to make targeting that date.