Characterizing Beam-correlated Neutron Backgrounds in the ANNIE - - PowerPoint PPT Presentation

Characterizing Beam-correlated Neutron Backgrounds in the ANNIE detector

Amanda Weinstein

• n behalf on the ANNIE collaboration

Iowa State University

TAUP 2019 9/9/2019 1

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ANNIE Collaboration meeting – Spring 2019 at Fermilab

ANNIE Collaboration

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tank

Accelerator Neutrino Neutron Interaction Experiment (ANNIE)

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• Booster Neutrino Beam (Fermilab)
• 700 MeV peak energy
• 93% νμ purity
• 3-5x1012 POT per spill at 5Hz
• ANNIE: One νμ charged-current

interaction in the water every 150 spills

Primary physics goal: Study abundance of final-state neutrons from and measure cross-section of neutrino-nucleus interactions (in water) as a function of muon kinematics

Physics Motivation

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ANNIE Concept

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Reconstruct muon interaction vertex and momentum Muon momentum information (legacy from SciBooNE) Consider CC νμ interactions in fiducial volume

ANNIE Concept

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PMTs detect neutron capture on Gd after thermalization

Neutron Capture Cross-Section

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ANNIE and New Technologies

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See talk in Weds. New Technology Session for further details

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• Large Area Picosecond

PhotoDetectors (LAPPDs):

• 20x20 cm micro-channel

plates with ∼60-ps time resolution and <1 cm spatial resolution

Muon Range Detector (MRD)

• Gd-loaded water
• Enhances neutron

capture x-section

• Shifts de-excitation

gammas to higher energy

• Shortens neutron

capture time

ANNIE Neutron Backgrounds

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Secondary neutrons from beam dump that leak into atmosphere From beam neutrinos interacting in dirt, rock

• Constant-in-time (CIT) backgrounds controlled for using data taken in the absence of beam.
• Beam-correlated backgrounds must be measured.

Beam-correlated Background Measurement

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Neutron Capture Volume

Calibration: Scintillation paddles kinematically select cosmic muons

Sealed, optically isolated acrylic vessel EJ-335 liquid scintillator (0.25% Gd w/w)

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The Neutron Capture Volume (NCV)

Data Acquisition

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Two modes of data acquisition

CIT background estimation

Custom VME ADCs (500 MS/s, ~80 µs buffer)

Data Samples I

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Also six calibration runs with 252Cf neutron source

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Neutron candidate selection

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• All pulses
• Both NCV PMTs fire

within 40 µs

• No prior candidate

within 10 µs (afterpulsing)

• Energy deposition <

34 MeV (true neutrons < 9 MeV)

• 8 or fewer water

PMTs fire (vetos energy dep. from muons)

• Pre-beam, late-time data used to

subtract CIT background

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• Method II: from simulations, derive

fraction of events above measured energy threshold (4.76 MeV) ln L = d j

j

∑

ln f j − f j f j ε NCVα n, j +δ j,γ flashP

γ + Δt jR

( )

⇒ ε NCV = 9.60 ± 0.57stat% ⇒ ε NCV = 12.8 ± 0.9stat%

• Method I: use 252Cf neutron

source calibration

NCV efficiency measurements

Neutron rates vs. shielding

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• Dominant sources
• f syst. uncertainty:
• NCV efficiency
• CIT Background
• Skyshine dominates
• ver dirt neutrons
• Qualitative

agreement with previous SciBooNE results

Active volume

Skyshine Dirt neutrons

Notes: Neutron Capture Cross-Section

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vs Phase II:

Rates in NCV slightly higher Shielding effects somewhat lower

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Integrated per-spill neutron rate

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• vs. 0.42 primary

neutrons per CC νμ interaction Conclusion: background in

• ptically isolated

active volume acceptably low.

Active volume

Rn

tank = 0.053−0.025stat+syst +0.053stat+syst

Measurements in active volume to right of blue line

BACK-UP

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