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

Electron Sign Determination in GENIE ve Events in Magnetized GAr

Tom Junk DUNE GARTPC ND Meeting January 5, 2018

The question: What fraction of electrons in veCC 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 ve and ve events (CC and NC). NC will be not representative because the

ve spectrum is harder than v𝜈 . 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.

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 2

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 dcut 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 rcut in 3D from any trajectory point on any other charged particle, including delta rays.

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 3

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 scut 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 dcut, rcut, and scut depend on detector parameters and hide a lot
• f ignorance in the procedure.

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 4

• Initial guess: dcut = rcut = scut = 0.5 cm. Maybe a little small, due

to the 7mm pixel dimension along one axis.

• Needed a log scale to show small contributions

Results Example

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 5

Ncorrect = 1456 Nmissing = 27 (no charge sign assigned or no electron) Nincorrect = 5 NNC,background = 10 NNC,rejected = 502

An example Correct-Sign Event

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 6

Magenta: Electrons Blue: Protons Red: Pions Black: Muons Event display centered on primary vertex Material interactions not classified (APA's cryostat) ROOT/X drawing bug puts magenta pixels on protons. Electron goes backwards a bit but still is measured properly.

An example Incorrect-Sign Event

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 7

Magenta: Electrons Blue: Protons Red: Pions Black: Muons Event display centered on primary vertex Material interactions not classified (APA's cryostat)

An example "missing" Event (no sign assignment)

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 8

Magenta: Electrons Blue: Protons Red: Pions Black: Muons Event display centered on primary vertex Material interactions not classified (APA's cryostat)

An example "missing" Event (no sign assignment)

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 9

Magenta: Electrons Blue: Protons Red: Pions Black: Muons Event display centered on primary vertex Material interactions not classified (APA's cryostat) Electron track possibly too straight for isolated points

• Initial guess: dcut = rcut = scut = 0.7 cm
• Needed a log scale to show small contributions

Results Example 2

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 10

Ncorrect = 1454 Nmissing = 28 (no charge sign assigned or no electron) Nincorrect = 6 NNC,background = 7 NNC,rejected = 505

Results Summary: big detector

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 11

Set 1 Set 2 Set 3 Set 4 dcut (cm) 0.5 0.7 0.5 2 rcut (cm) 0.5 0.7 1.5 2 scut (cm) 0.5 0.7 0.7 2 Ncorrect 1456 1454 1442 1423 Nmissing 27 28 37 55 Nincorrect 5 6 9 10 NNC,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.

electron from primary vertex

hit isolation

sagitta cut

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

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 12

• C. Lippmann, Physics Procedia 37 (2012) 434-441

A more realistic detector size

• Tried putting a cut on the YZ track length of 1m and the X distance of

2m

• Keep dcut = rcut = scut = 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

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 13

A more realistic detector size

• YZ length < 1m and X length < 2m
• dcut = rcut = 0.5 cm, scut = 0.05 cm
• Getting Better!

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 14

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)

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 15

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.

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 16

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

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 17

numubar CC Argon Hadr E Frac

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 18

numu CC carbon Hadr Efrac

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 19

numubar CC carbon Hadr Efrac

Jan 5, 2018 Tom Junk | GArTPC Electron Sign ID 20