Events in Magnetized GAr Tom Junk DUNE GARTPC ND Meeting January - PowerPoint PPT Presentation

Electron Sign Determination in GENIE v e Events in Magnetized GAr Tom Junk DUNE GARTPC ND Meeting January 5, 2018 The question: What fraction of electrons in v e CC events have their signs correctly identified? Approximate answer: We expect this to be very good for a GArTPC in a magnetic field

Setup: Simulation • I'm using LArSoft with the 1x2x6 meter geometry • Set the density of LAr to that of GAr. • Set the magnetic field to 0.4 T • Run GENIE with nominal task force flux file: gsimple_dune10kt_v1_1x2x6_g4lbne_v3r4p2_QGSP_BERT_run15_12388_80GeV_neu trino_*.root • Flux is not oscillated, so flavor and energy composition is close (modulo geometric acceptance effects) • Generate only v e and v e events (CC and NC). NC will be not representative because the v e spectrum is harder than v 𝜈 . Sample size = 2000 events. • NC background is small in this study (we'll see...) • GEANT4 simulation of GENIE particles • No detector response simulation – looking at MCParticle trajectory steps. Bounded by voxel size of 0.3 mm. Also containment isn't right as the 1x2x6 APA detector is too big by far. Can always apply fiducial cuts in the ND. 2 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Setup: "Reconstruction" and Analysis • Cheat the primary vertex using the MCTruth Neutrino position (it's the end of the neutrino's trajectory). • Cheat electron identification by looking at PDG codes • Pick the highest-energy electron or positron which starts within d cut of the primary vertex (whether or not it is the electron from a charged- current interaction or something else) • Make plots as function of the true electron energy • Select trajectory points that are isolated from other particles' trajectory points. To be considered for selection, a trajectory point must be at least r cut in 3D from any trajectory point on any other charged particle, including delta rays. 3 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Setup: Analysis cont'd • From the list of isolated trajectory points, compute the sagitta incrementally: - Start from the beginning of the track and for each point i, calculate the maximum perpendicular distance of a track point from the line between the beginning to point i • Calculate sagitta in the ( y,z ) plane. B is along x . • If any sagitta calculated exceeds s cut in absolute value, use the signed sagitta (computed with a cross product) to determine the sign of the track. Keep stepping through points i until we run out. Provides protection against looping tracks. • The values of d cut , r cut , and s cut depend on detector parameters and hide a lot of ignorance in the procedure. 4 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Results Example • Initial guess: d cut = r cut = s cut = 0.5 cm. Maybe a little small, due to the 7mm pixel dimension along one axis. • Needed a log scale to show small contributions N correct = 1456 N missing = 27 (no charge sign assigned or no electron) N incorrect = 5 N NC,background = 10 N NC,rejected = 502 5 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

An example Correct-Sign Event Event display centered on primary vertex Magenta: Electrons Blue: Protons Red: Pions Material interactions Black: Muons not classified (APA's cryostat) Electron goes ROOT/X drawing backwards a bit bug puts magenta but still is measured pixels on protons. properly. 6 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

An example Incorrect-Sign Event Event display centered on primary vertex Magenta: Electrons Blue: Protons Red: Pions Material interactions Black: Muons not classified (APA's cryostat) 7 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

An example "missing" Event (no sign assignment) Event display centered on primary vertex Magenta: Electrons Blue: Protons Red: Pions Material interactions Black: Muons not classified (APA's cryostat) 8 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

An example "missing" Event (no sign assignment) Event display centered on primary vertex Magenta: Electrons Blue: Protons Red: Pions Material interactions Black: Muons not classified (APA's cryostat) Electron track possibly too straight for isolated points 9 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Results Example 2 • Initial guess: d cut = r cut = s cut = 0.7 cm • Needed a log scale to show small contributions N correct = 1454 N missing = 28 (no charge sign assigned or no electron) N incorrect = 6 N NC,background = 7 N NC,rejected = 505 10 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Results Summary: big detector Set 1 Set 2 Set 3 Set 4 electron from d cut (cm) 0.5 0.7 0.5 2 primary vertex r cut (cm) 0.5 0.7 1.5 2 hit isolation s cut (cm) 0.5 0.7 0.7 2 sagitta cut N correct 1456 1454 1442 1423 N missing 27 28 37 55 N incorrect 5 6 9 10 N NC,background 10 7 7 7 Incorrect events due to showering may be misestimated due to stray material in the FD geometry. Since we're cheating the electron track points, a track that goes through a dense region but comes out the other side is still useful with no hit misassociation. Hit isolation cut helps cover this kind of thing. 11 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

ALICE • ALICE has 5m diameter, and a space point resolution perpendicular to the B and E fields and the beam of about 1 mm (between 0.4 and 2mm). B=0.5T in ALICE. Up to 159 space points per track C. Lippmann, Physics Procedia 37 (2012) 434-441 12 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

A more realistic detector size • Tried putting a cut on the YZ track length of 1m and the X distance of 2m • Keep d cut = r cut = s cut = 0.5 cm • Makes a Big difference! • Expected (but did not see) the loss of sign ability at high momentum for the big detector. • A small detector with poor sagitta resolution struggles with the electron sign • Kind of a test to make sure the program isn't crazy 13 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

A more realistic detector size • YZ length < 1m and X length < 2m • d cut = r cut = 0.5 cm, s cut = 0.05 cm • Getting Better! 14 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Sagitta cut down to 100 microns • Still with a YZ track length cut of 1m and X track length of 2m • ALICE gets up to 159 points to fit. Averaging is strong • Not getting any incorrect ones yet (scattering) 15 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

Not done yet, but summary of conclusions • Biggest effect is from making sure that an electron has a measurable bend in the detector volume - Strong enough field – what is the minimum requirement? - Long enough track - Space-point resolution • Multiple scattering seems not to be a problem - otherwise we'd have more incorrect-sign assignments at low sagittas • Neutral Current BG seems not to troublesome - but I cheated the primary vertex location - no pileup. - would need to topologically identify conversions which are displaced from NC events but which might look like their own events or pileup. Two electrons, plus pointing to a hadronic recoil. 16 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

A Question from Asher in Dec. • What is the fraction of hadronic energy carried by protons and neutrons on an event-by-event basis? • Some plots follow, with KE thresholds of 20 MeV • First set at right: numuCC on Argon 17 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

numubar CC Argon Hadr E Frac 18 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

numu CC carbon Hadr Efrac 19 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID

numubar CC carbon Hadr Efrac 20 Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID