Shadowing Update 24 June 2019 Kevin Ewart and Thomas Rainbolt - PowerPoint PPT Presentation

Shadowing Update 24 June 2019 Kevin Ewart and Thomas Rainbolt Indiana University

Background  The photodetecting bars are located φ behind the three TPC wire planes, as well as a conducting mesh  Currently, the shadowing effects are implemented as a position-independent 70% transmission  This is an approximation that is known to be inaccurate, especially near the APA plane Bruce Howard (wire spacing exaggerated 10x)

Background  Two basic approaches to improve on the current method, both using geometric optics: − Approximation-heavy method using a modified version of the simple shadowing formula (“approximate method”)  Advantages: fast, easy to understand  Disadvantages: inaccurate in certain regimes − Nearly exact (in the limit of geometric optics) method (“robust method”)  Advantages: detailed geometric optics effects, high accuracy in most regimes  Disadvantages: slow

Approximate method- diagram and methodology Light source ● Based loosely on Bruce Baller's method − lbne docdb-4134 θ gauge pitch  For each wire that goes over the detector, use the simple shadowing pitch * cos(θ) formula: θ Wires  Return the average of all the resulting transmission coefficients Photodetector

Robust method- diagram and methodology Light source ● For each wire that goes over the detector, project its shadow onto the photodetector ● Then, calculate the solid angle subtended by that shadow – This is the same as the solid angle subtended by the wire that intersects the projection of the Wires photodetector ● Then return Photodetector T = 1 – (sum of wire solid angles ) / (solid angle subtended by the photodetector)

Robust method- overlapping shadows ● In extreme cases, wire shadows may Block start to overlap shadow ● If this happens, the rest of the photodetector in that direction will be totally shadowed ● Instead of calculating per-wire Light source shadowing, this entire block of shadow is lumped together Wires Photodetector Overlapping shadows

Both methods- getting the final transmission ● First, the APA frame's shadow is projected onto the photodetector. Due to the central support bar, this means there are two sub-bars. It is also possible in extreme cases that one or both sub-bars is entirely shadowed by the frame. ● For each sub-bar that is not totally shadowed: – Perform the chosen method for all three wire planes, as well as the horizontal and vertical wires of the mesh (total of five planes) – Multiply the resulting transmission coefficients to get the transmission for that sub- bar – Convert this final coefficient into an effective shadowed solid angle ● Then add all effective shadowed solid angles (including the shadows from the APA frame), and divide by the total solid angle of the full photodetector.

Approximations ● We assume an infinite wire plane – This is almost entirely accurate in the full code, due to APA frame shadowing ● We assume the change in shadowing due to the exact positions of the wires is a negligible effect ● If the one-plane wire shadows do not overlap, two plane shadowing is EXACT ● We neglect all reflections ● We assume geometric optics is an adequate description of shadowing ● NOT currently accounting overlapping wire shadows giving non-exact two-plane shadowing (known to be non-negligible) ● We assume triple shadowing effects are negligible – Effect is less than 1.4%

Results ● For the following plots, we will be using the “local” coordinates of the photodetector. The local origin is positioned on the surface of the bar, at the lower left-hand corner of the bar as defined by the figure below y z Origin Wires MUST be sloped in this direction, z-axis is mirrored if necessary to make this true. x-axis potentially mirrored so that the light source is out of the page with positive x This results in a left-handed local coordinate system (oops), which should not matter.

Results ● Light source positioned at x=10cm, y=variable , z=110cm (center of bar) ● φ=90° from the vertical, i.e. wires parallel to the photodetector ● y-coordinate on the horizontal axis, transmission coefficient for a single wire plane on the vertical axis ● Photodetector extends from y=0 to y=8.6cm

Results ● Light source positioned at x=50cm, y=4.3cm (center of photodetector), z=variable ● φ=0° from the vertical, i.e. wires perpendicular to the photodetector ● z-coordinate on the horizontal axis, transmission coefficient for a single wire plane on the vertical axis ● Photodetector extends from z=0 to z=220cm

Results ● Light source positioned at x=10cm, y=4.3cm (center of photodetector), z=variable ● φ=0° from the vertical, i.e. wires parallel to the photodetector ● z-coordinate on the horizontal axis, transmission coefficient for a single wire plane on the vertical axis ● Photodetector extends from z=0 to z=220cm

Results ● Light source positioned at x=variable , y=4.3cm, z=110cm (center of photodetector) ● φ=0° from the vertical, i.e. wires parallel to the photodetector ● x-coordinate on the horizontal axis, transmission coefficient for a single wire plane on the vertical axis

Results ● Light source positioned at x=50cm ● z-coordinate on the horizontal axis, y- coordinate on the vertical axis, contoured by transmission coefficient ● Full simulation of 3 wire planes + mesh + APA frame

Results ● Light source positioned at x=10cm ● z-coordinate on the horizontal axis, y- coordinate on the vertical axis, contoured by transmission coefficient ● Full simulation of 3 wire planes + mesh + APA frame

Results ● Deviates from currently implemented T=0.7 by 10% – Approximate method: for x < 220cm – Robust method: for x < 210cm ● For one wire plane the two methods deviate by – 10% from each other for x < 40cm – 1% for x < 100cm ● For 3+mesh+APA the two methods deviate by – 10% for x < 25cm – 1% for x < 30cm

Conclusions ● A position-dependent shadowing method has been implemented ● There are significant deviations from the current implementation of position- independent T=0.7 for most of the detector ● This is especially important for understanding Argon 39 backgrounds ● Robust method more sensitive to the shape of the photodetector

Moving forward- implementation ● Several possible methods: – Build shadowing into the photon library ● If we are moving away from the library, not this one – Add shadowing methods to PhotonVisibilityServiceS2 – Add shadowing as its own service, edit the relevant photon visibility services to call it ● Unless there are other opinions, I will implement both the approximate and robust method, and add a fcl parameter as to which, if either, to use ● Adding support for the ARAPUCAs is easy, I just have not done it yet.

Questions?