HARPO Analysis

New reconstruction algorithm: no tracking Simulation Quick reminder: HARPO data “Old” reconstruction Preliminary results New reconstruction algorithm: no tracking Simulation Resolution and polarimetry 2018-09-11

HARPO reminders 2018-09-11

NewSUBARU Beam 2018-09-11

HARPO events 2018-09-11

Main issue: Electronics saturation Understood phenomenon saturation on cumulated charge on single channel response function not calibrated yet Additional crosstalk poorly understood Affects a very large fraction of the events energy dependent flagging and removing is not an option Important due to beam geometry should not affect (much) cosmic photons 2018-09-11

Example of saturation 74 2018-09-11

Reconstruction v2.0 Clustering “classic” T and C clusters (Shaobo) Tracking “Hough” good for straight separated tracks (cosmics) problems with shared vertex and scattering Tracking “Kalman” closest neighbour search in T and C direction straight line fit Track matching XZ ↔ YZ independent of tracking method problem with electronics saturation 2018-09-11

Polarisation Pairs of matched tracks get POCA & DOCA cut on distance between POCA and first signal in TPC Combine data from runs with different TPC orientation Ratio (P=100%)/(P=0) 2018-09-11

Polarisation 2018-09-11

Polarisation 2018-09-11

Polarisation 2018-09-11

Limitations Low efficiency ~10%=Nreconstructed/Non beam Low angular resolution straight line fit with large multiple scattering benefit of Kalman lost around vertex Difficult to improve complex algorithm very sensitive to parameter changes 2018-09-11

Reconstruction v3.0 2018-09-11

Reconstruction v3.0 Focus on finding vertexes No tracking Simple bloc clustering Find ROI (vertex candidates): “corner shape” Refine vertex position Find peaks in polar distribution around vertex Vertex matching (same or switch) 2018-09-11

Vertex Finding Reduce data: simple clustering Find “corner” shape Draw circle Find longest arc with no data Select arcs longer than π Refine position CoG of RoI (circle) 2018-09-11

Vertex Finder φ>π φ<π 2018-09-11

Vertex Finding Simple Robust local characteristics: works on complex events Weaknesses many fake vertexes (e.g. track ends) needs continuous signal, low noise Potential for improvement better position 2018-09-11

Vertex Fitting Polar charge distribution around vertex delta electron 2018-09-11

Vertex Fitting Clean up: keep only straight lines 2018-09-11

Vertex Fitting Peak finding: track directions 2018-09-11

Vertex Fitting Simple Robust: ignores obvious scattering and background potential for small opening angle Potential for improvement better peak finding use of distance info (focus on short distance for large opening angle, long distance for small) 2018-09-11

Vertex Matching As before: compare charge profile 1: match vertexes if there are several with same Z position 2: match the tracks in the vertex (simple: only 2 possibilities) 2018-09-11

Vertex Matching Assign signal to tracks 2018-09-11

Vertex Matching Compare profiles: X(1,2) ↔ Y(1,2) “same” 2018-09-11

Vertex Matching Compare profiles: X(1,2) ↔ Y(2,1) “switch” 2018-09-11

Vertex Matching Same Switch 2018-09-11

Vertex Matching Simple (again) Robust (again) small number of combinations works if 1 of the 2 tracks has a problem (e.g. electronics saturation) Potential for improvement ? 2018-09-11

Example with saturation 2018-09-11

Simulation 2018-09-11

Simulation very basic Geant4 cube of gas, list of charged particles complete TPC simulation drift, electron capture, diffusion, gain fluctuations HARPO geometry pad/strips geometry, shaping, noise, saturation Good description of the data still needs to be properly calibrated 2018-09-11

Results 2018-09-11

Polarisation: v2.0 2018-09-11

Polarisation: v3.0 2018-09-11

Polarisation: Simulation 2018-09-11

Polarisation: summary Greatly improved efficiency → Higher statistics Good agreement with simulation Asymmetry smaller than expected resolution? matching? 2018-09-11

Angular resolution 2018-09-11

Angular resolution Agreement with theoretical prediction relatively small contribution of tracking Excellent agreement with simulation effect of saturation dominates at high energy Potential for improvement estimation of track momentum event 100% resolution should significantly improve 2018-09-11

Conclusions An new, simpler, reconstruction has boosted the performance of HARPO + more robust, higher efficiency – relies on low noise, many fakes The data is well described by simulation better calibration needed for more direct comparisons Performance is good without optimisation It can probably still be improved 2018-09-11

Future... 2018-09-11

Future... ST3G 2018-09-11

Future... 2018-09-11

Backup 2018-09-11

Efficiency 2018-09-11

Polarisation asymmetry 2018-09-11