1. Understanding Neutrino Events at Liquid Argon Detectors
Shirley Li
Collaborator: A. Friedland
Precision Investigations of the Neutrino Sector, July 2019

2. Measuring 𝛿 CP and MH ~1000 km 0.5—5 GeV 𝜈 𝜇 𝜈 𝑒
DUNE CDR
Need to measure 𝑁( 𝐸 𝜈 𝑒 )
Shirley Li (SLAC)
2/31

3. Detects charged particles above thresholds
DUNE detector
40 kton liquid argon TPC
DUNE and NOvA
Detects charged particles above thresholds
Shirley Li (SLAC)
3/31

4. The overarching question
How well can we measure neutrino energy?
Simulated with GENIE+FLUKA
Friedland & Li, 2018
Shirley Li (SLAC)
4/31

6. No consensus in the field
Energy resolution from prior work
Romeri, Fernandez-Martinez & Sorel, 2016
Shirley Li (SLAC)
5/31

7. Two types of performance studies
Fast Monte Carlo type
DUNE CDR
See physical connection; not quantitative
Shirley Li (SLAC)
6/31

8. Two types of performance studies
Full propagation type
Romeri, Fernandez-Martinez & Sorel, 2016
Complete; hide physical connection
Shirley Li (SLAC)
7/31

9. No consensus in the field
Energy resolution from prior work
Romeri, Fernandez-Martinez & Sorel, 2016
Shirley Li (SLAC)
8/31

10. Our goal: Understanding the physics of energy reconstruction
Shirley Li (SLAC)

11. Calorimetric energy reconstruction
Signal: 𝜈 𝑙 +𝐴→𝑙+𝑋
Simulated with GENIE+FLUKA
Friedland & Li, 2018
Separate 𝑙 and hadronic system
𝐸 𝑙 : total collected charge -> energy
𝐸 ℎ : total collected charge -> energy
𝐸 𝜈 = 𝐸 𝑙 + 𝐸 ℎ or 𝐸 𝜈 =𝑓( 𝐸 𝑙 , 𝐸 ℎ )
How to characterize its performance?
Shirley Li (SLAC)
10/31

12. Calorimetric energy reconstruction
Signal: 𝜈 𝑙 +𝐴→𝑙+𝑋
Should work perfectly if 𝐸 𝑙 →ionization dE dx → charge
Problem arises if 𝐸 ℎ → ionization missing energy
Understanding missing energy is the key
Shirley Li (SLAC)
11/31

13. Hadronic system Prompt 𝜈 vertex: 𝜈 𝑙 +𝐴→𝑙+𝑋
Friedland & Li, 2018
GENIE default model
30 – 40% of neutrino energy, large fluctuations
Shirley Li (SLAC)
12/31

14. Multiple species contribute, large fluctuations
Hadronic system
GENIE simulation
Friedland & Li, 2018
Varied composition
Multiple species contribute, large fluctuations
Shirley Li (SLAC)
13/31

15. Prompt neutrons are the biggest issue
Missing energy in 𝐸 ℎ
After primary vertex
Friedland & Li, 2018
Prompt neutrons are the biggest issue
Shirley Li (SLAC)
14/31

16. Secondary particle propagation
Charged particles
Friedland & Li, 2018
Many re-interactions
Shirley Li (SLAC)
15/31

17. Secondary particle propagation
Friedland & Li, 2018
Neutrons
Simulated with FLUKA
Neutron deposit ~ 50% of its energy in ionization
Shirley Li (SLAC)
16/31

18. Secondary particle propagation
Friedland & Li, 2018
Neutrons
Simulated with GENIE+FLUKA
Extremely challenging to reconstruct neutrons
Shirley Li (SLAC)
17/31

19. Secondary particle propagation
Friedland & Li, 2018
Neutrons
Simulated with GENIE+FLUKA
Extremely challenging to reconstruct neutrons
Shirley Li (SLAC)
17/31

20. Secondary particle propagation
Friedland & Li, 2018
Neutrons
Simulated with GENIE+FLUKA
Extremely challenging to reconstruct neutrons
Shirley Li (SLAC)
17/31

21. After full propagation
Missing energy in 𝐸 ℎ
Recombination:
Nuclear breakup: 𝑝+40Ar→3𝑝+𝑋
Energy -> nuclear binding energy
Thresholds
Neutrons
After full propagation
charge ∝ 𝑑𝐸 𝑑𝑥
Friedland & Li, 2018
Shirley Li (SLAC)
18/31

22. Missing energy in 𝐸 ℎ Reducible vs. irreducible
Friedland & Li, 2018
Reducible vs. irreducible
Reducible: threshold, rec
Irreducible: nucl, 𝜈, neutron
Irreducible missing energy has to be simulated correctly
Shirley Li (SLAC)
19/31

23. Energy reconstruction results
Friedland & Li, 2018
CDR th: method as it is
Charge: collect all charges with no thresh.
Best rec: no thresh., correct for recombination
Shirley Li (SLAC)
20/31

24. Two types of performance studies
Shirley Li (SLAC)

25. Two types of performance studies
Full propagation
Fast Monte Carlo
DUNE CDR
Romeri, Fernandez-Martinez & Sorel, 2016
Shirley Li (SLAC)
22/31

26. Protons Energy distribution 23/31 Friedland & Li, in prep
Shirley Li (SLAC)
23/31

27. Protons Energy distribution 24/31 Friedland & Li, in prep
Shirley Li (SLAC)
24/31

28. Large missing energy fraction
Protons
Friedland & Li, in prep
Visible energy
Large missing energy fraction
Shirley Li (SLAC)
25/31

29. Neutron-created charges are important
Protons
Friedland & Li, in prep
Energy resolution
Neutron-created charges are important
Shirley Li (SLAC)
26/31

30. Charged pions
Friedland & Li, in prep
Shirley Li (SLAC)
27/31

31. Neutrons
Friedland & Li, in prep
Shirley Li (SLAC)
28/31

32. Friedland & Li, 2018
Shirley Li (SLAC)
29/31

33. Conclusions Basic performance of liquid argon were not understood
We understand missing energy of neutrino events: neutrons, nuclear breakup, recombination
Improve reconstruction strategy
Details in arXiv: , PRD 2019
Test beam data will be crucial for simulation validation
Shirley Li (SLAC)
30/31

34. Outlook
A framework to evaluate neutrino-nucleus cross section uncertainty impact on oscillations
Full propagation studies guarantee no missing physics
fastMC type studies need full, correct inputs
Easy to see physics connections
Shirley Li (SLAC)
31/31

35. Backup

36. Bi-probability plot

37. Comparisons to other work
Friedland & Li, 2018
Romeri, Fernandez-Martinez & Sorel, 2016
Further studies warranted
Shirley Li (SLAC)