Characterizing Beam-correlated Neutron Backgrounds in the ANNIE detector Amanda Weinstein on behalf on the ANNIE collaboration Iowa State University 9/9/2019 TAUP 2019 1
ANNIE Collaboration ANNIE Collaboration meeting – Spring 2019 at Fermilab tank 9/9/2019 TAUP 2019 2 1
Accelerator Neutrino Neutron Interaction Experiment (ANNIE) Booster Neutrino Beam (Fermilab) • 700 MeV peak energy • 93% ν μ purity • 3-5x10 12 POT per spill at 5Hz • ANNIE: One ν μ charged-current • interaction in the water every 150 spills 9/9/2019 TAUP 2019 3
Physics Motivation 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 9/9/2019 TAUP 2019 4
ANNIE Concept Reconstruct muon interaction vertex and momentum Muon momentum information (legacy from SciBooNE) Consider CC ν μ interactions in fiducial volume 9/9/2019 5
ANNIE Concept PMTs detect neutron capture on Gd after thermalization 9/9/2019 TAUP 2019 6
Neutron Capture Cross-Section 9/9/2019 TAUP 2019 7
ANNIE and New Technologies • Large Area Picosecond PhotoDetectors (LAPPDs) : 20x20 cm micro-channel • plates with ∼ 60-ps time Muon Range resolution and <1 cm Detector (MRD) spatial resolution • Gd-loaded water • Enhances neutron capture x-section • Shifts de-excitation See talk in Weds. New gammas to higher energy Technology Session for further • Shortens neutron details capture time 9/9/2019 TAUP 2019 8
ANNIE Neutron Backgrounds 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. 9/9/2019 TAUP 2019 9
Beam-correlated Background Measurement Calibration: Scintillation paddles kinematically select cosmic muons Neutron Capture Volume 9/9/2019 TAUP 2019 10
The Neutron Capture Volume (NCV) Sealed, optically isolated acrylic vessel EJ-335 liquid scintillator (0.25% Gd w/w) 9/9/2019 TAUP 2019 11
Data Acquisition Two modes of data acquisition Custom VME ADCs (500 MS/s, ~80 µs buffer) CIT background estimation 9/9/2019 TAUP 2019 12
Data Samples I Also six calibration runs with 252 Cf neutron source 9/9/2019 TAUP 2019 13
Neutron candidate selection 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 Pre-beam, late-time data used to • muons) subtract CIT background 9/9/2019 TAUP 2019 14
NCV efficiency measurements • Method I: use 252 Cf neutron source calibration ∑ ln L = ln f j − f j d j j ( ) f j ε NCV α n , j + δ j , γ flash P γ + Δ t j R ⇒ ε NCV = 9.60 ± 0.57 stat % • Method II: from simulations, derive ⇒ ε NCV = 12.8 ± 0.9 stat % fraction of events above measured energy threshold (4.76 MeV) 9/9/2019 TAUP 2019 15
Neutron rates vs. shielding • Dominant sources of syst. uncertainty : NCV efficiency • CIT Background • Active volume • Skyshine dominates Skyshine over dirt neutrons • Qualitative agreement with Dirt neutrons previous SciBooNE results 9/9/2019 TAUP 2019 16
Notes: Neutron Capture Cross-Section vs Phase II: Rates in NCV slightly higher Shielding effects somewhat lower 9/9/2019 TAUP 2019 17
Integrated per-spill neutron rate tank = 0.053 − 0.025 stat+syst + 0.053 stat+syst R n vs. 0.42 primary Active volume neutrons per CC ν μ interaction Conclusion: background in optically isolated active volume acceptably low. TAUP 2019 Measurements in active volume to right of blue line 9/9/2019 18
BACK-UP 9/9/2019 TAUP 2019 19
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