The Accelerator Neutrino Neutron Interaction Experiment

ANNIE: The Accelerator Neutrino Neutron Interaction Experiment

Jonathan Eisch Iowa State University

DPF 2019 July 29, 2019 The ANNIE Collaboration annie

• Brookhaven National Laboratory • University of California, Davis • Fermi National Accelerator Laboratory • University of California, Irvine • 13 Institutions • Iowa State University • University of Chicago • Johannes Gutenberg University Mainz • University of Edinburgh • 3 Countries • Lawrence Livermore National Laboratory • University of Hamburg ! USA • The Ohio State University • University of Shefﬁeld • Queen Mary University " Germany # UK • 30+ Collaborators

First LAPPD Delivery, January 2017

Jonathan Eisch (Iowa State University) 2 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment What is ANNIE? annie • ANNIE is a water-Cherenkov neutrino experiment on the Booster Neutrino Beam at Fermilab. • ANNIE has two main goals: • Measure the abundance of ﬁnal state neutrons from neutrino interactions in water as a function of lepton kinematics. • Demonstrate new detection technologies such as: • LAPPDs with 10GHz digitization. • Neutron tagging in Gadolinium-loaded water. • ANNIE will run in two phases: • Phase I (Complete): Partial detector engineering demonstration and background measurement. Detector schematic • Phase II (Fall 2019): Physics measurement with advanced detection technologies.

Jonathan Eisch (Iowa State University) 3 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment ANNIE Neutrino-Nucleus Interactions annie • ANNIE will collect a high-statistics sample of GeV- scale charged-current neutrino interactions on water from the well-studied Booster Neutrino Beam (BNB). • High-efﬁciency neutron detection will provide a new handle for more detailed separation of ﬁnal-states. • This is an interesting energy range for neutrino- nucleus interactions.

CCQE 2p2h ANNIE Simulation Preliminary νμ ANNIE Simulation- Preliminary 0.15 μ νμ μ- 0.12

All Events All Events W W 0.1 Fiducial Events with Muon Stopping in MRD Fiducial Events with Muon Stopping in MRD 0.1 π p n p n 0.08 n n 0.06 BNB (ANNIE) Stuck pion Resonance NOvA 0.05νμ - 0.04 μ νμ μ- Fraction of Events Fraction of Events DUNE W 0.02 (DUNE 2nd oscillation maximum) + W + 0 Δ + π 0 n0 0.5 π n 1 1.5 2 0 1 2 3 4 5 2 2 Δ+ Hyper-K N EventN Q [GeV/cn ] n Neutrino Energy [GeV]

Figure 11: LEFT: The normalized Q2 distribution for all events (red line) and for 2.5-ton ﬁducial events with muonsJonathan ranging out Eisch in the MRD (Iowa (blue State line). RIGHT: University) The normalized E⌫ distribution4 for all eventsANNIE: (red The Accelerator Neutrino Neutron Interaction Experiment line) and for 2.5-ton ﬁducial events with muons ranging out in the MRD (blue line).

Table 2: Fiducial Event Counts for 1 Year of Running

NC CC CCQE CC-Other All 11323 26239 13674 12565 Entering MRD 2 7466 4279 3187 Stopping in MRD 2 4830 2792 2038 Fully Penetrating MRD 0 1454 761 693 Exiting Side of MRD 0 1181 726 455

rates measured in Phase I are discussed in Sec 6.3. Finally, the analysis will require precision reconstruction of the interaction point by the LAPPD system in order to select a sample of ﬁducial events far enough from the edges of the detector to fully contain any neutrons produced (Sections 6.4 and 6.5). Sucient LAPPD coverage may eventually permit the reconstruction NC events, resonant pion ﬁnal states, and interactions where the muon stops in the water volume without entering the MRD. Future studies will be needed to demonstrate these capabilities.

6.1 Event Rates and Geometric Acceptance The MRD is used to measure the final state muon and is central to determining the kinematics of the neutrino event. The kinematic distributions of incident neutrinos from the Booster Neutrino Beam, using simulations of the Phase II detector, are shown in Fig. 11 alongside the distribution of neutrino interactions with a muon stopping within the MRD. The distributions for the incident beam and the MRD acceptance neutrino events present only a small, expected skew toward higher neutrino energies and lower Q2 on the latter. Table 2 shows the number of expected fiducial NC, CC, CCQE and CC-Other interactions that enter, stop within, fully penetrate, or exit through the sides of the MRD. These numbers represent neutrino interactions within a 2.5-ton central fiducial volume, integrated over 1 year of running (2 1020 POT). For 64% of events with a muon entering the MRD (18% of all fiducial CC events), the muon is fully⇥ stopped, allowing complete track reconstruction and accurate energy estimation. These studies show that a significant number of neutrino interactions will have complete track reconstruction and accurate energy estimation. Furthermore, the kinematics of these interactions are reasonably representative of all incident beam neutrinos. Preliminary results of reconstructed Q2 distributions and reconstruction resolution are shown in Sec 6.6.

20 The ANNIE Detector annie • 26 ton water-Cherenkov detector. • 3 m diameter, 4 m tall steel tank with a plastic liner. • Filled with ultra-pure water loaded with Gadolinium sulfate. • Detection volume instrumented with conventional PMTs with 500 MHz full waveform digitization and newly developed high-speed photo-detectors. • Also includes an upstream muon veto Beam detector and the SciBooNE Muon Range Detector (muon tracker) installed downstream.

Jonathan Eisch (Iowa State University) 5 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment The ANNIE Water Volume annie

• 3 m diameter, 4 m tall steel tank with a plastic liner. • 26 tons of ultra-puriﬁed water loaded with gadolinium sulfate. • The water moderates and captures external neutrons. • PMTs and LAPPDs attached to a stainless steel inner structure. • Full-waveform digitization with custom 500 MHz ADCs.

Jonathan Eisch (Iowa State University) 6 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment Muon Range Detector annie

• Built by by the SciBooNE Collaboration. • Segmented tracker with 11 layers of scintillator read out by 310 PMTs (6 horizontal and 5 vertical planes). • Eleven 2” thick 9’x10’ sheets of steel. • Will range out muons up to 0.9 GeV. • PMT signals are discriminated and recorded by a TDC system.

Jonathan Eisch (Iowa State University) 7 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment ANNIE Detection Principle annie

3. 1. 2.

1. Charged current muon-neutrino interaction within the ﬁducial volume. 2. Cherenkov light from the muon is detected by photodetectors on the walls of the water volume. 3. Muon is tracked and ranges out in the Muon Range Detector (MRD).

Jonathan Eisch (Iowa State University) 8 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment ANNIE Detection Principle annie

4. Final-state neutrons scatter and thermalize within the water volume (~3 us).

Jonathan Eisch (Iowa State University) 9 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment ANNIE Detection Principle annie

5. Tens of microseconds later neutrons capture on the dissolved Gadolinium in the water, producing 8 MeV gamma cascades. 6. Photons from the gamma cascade are detected by the water- volume photodetectors.

Jonathan Eisch (Iowa State University) 10 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment ANNIE Operation Timeline annie

• Phase II - Physics Run: • Phase I - Engineering run and (Currently commissioning) Background Measurement: (Complete) (Spring ’16-Summer ’17) • Physics data will start with the return of Beam operations in the fall. • Operated with conventional PMTs and pure water with a small movable • Measure neutron multiplicity as a vessel ﬁlled with function of lepton kinematics. Gd-loaded liquid scintillator. • Gd-loaded water. • Measured neutron backgrounds as • Addition of LAPPDs and additional a function of position inside the tank. conventional PMTs. • LAPPD Testing, characterization and • Possible Phase III: integration R&D. • Operate with water-based liquid scintillator sub-volume.

Jonathan Eisch (Iowa State University) 11 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment annie

Phase I Measuring the neutron background

Jonathan Eisch (Iowa State University) 12 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment Phase I detector conﬁguration annie

• 60 PMTs installed on the bottom layer, reflective white tank liner installed. • PMTs used to detect cosmic-ray and beam- induced muons. • Neutron Capture Volume (NCV) • A movable acrylic vessel filled with gadolinium- loaded liquid scintillator used to measure neutron flux at different positions within the tank. 1.Neutrons capture on gadolinium and produce 8 MeV in gamma rays. 2.The gamma rays scatter electrons in the liquid scintillator producing light. 3.PMTs on the NCV detect this light. Phase I configuration

Jonathan Eisch (Iowa State University) 13 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment The NCV annie

• Acrylic vessel ﬁlled with gadolinium loaded liquid scintillator. • Two PMTs installed at the top of the vessel. • Optically isolated from the water volume.

After wrapping unwrapped design

Jonathan Eisch (Iowa State University) 14 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment NCV Position Scan annie • The NCV was moved vertically and horizontally to several different positions to measure the neutron ﬂux at each location. • The measured ﬂux is a combination of beam- induced neutrons from above and from neutrino interactions in and around the detector.

Jonathan Eisch (Iowa State University) 15 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment NCV Position Scan annie

• The NCV was moved vertically and horizontally to several different Elastically positions to measure the neutron ﬂux at each location. scatter off air above • N The measured ﬂux is a N the hall.

combination of beam- O induced neutrons from O N N n n above and from neutrino n n Sky shine neutronsn n n interactions in and around n n the detector. n n

Neutrino interactions produce neutrons in the dirt. n ν ν ν ν Booster Neutrino Beam ν ν ν ν n Jonathan Eisch (Iowa State University) 16 ANNIE: The Accelerator Neutrino Neutron Interaction Experiment NCV Position Scan annie Beam NCV Event Times 2.5

) ν-beam arrival s

µ position V4 / 2 3 position O m / V4 1.5 POT 12

10 1 Integrate region of interest ⇥ 5 O / 2 neutron candidates

0.5 10 (

0 0 10 20 30 40 50 60 70 80 time (µs)

Figure 9. Time distributions of the neutron event rates measured at NCV position V4 (top of the tank, black)• and0-10 at position us: 0 (center Pre-beam of the tank, purple). Inbackground the DAQ Mode A data shown here, the neutrino• beam10-15 arrives at 10us:µs. Proton recoils •15 us+: Neutron captures 506 9.4 Final Uncertainty Estimates

Jonathan Eisch (Iowa State University) 17 507 ANNIE:The combined The statistical Accelerator and systematic Neutrino uncertainty Neutron on the Interaction beam-induced Experiment neutron event NCV 508 rate, is estimated using the same Monte Carlo method described in section 8.1.1 R 509 while taking into account the additional statistical and systematic uncertainties on the tROI 510 scaling factors ✏NCV, , and VNCV. The uncertainties on the factors tpre and T (used P T0 511 to estimate the constant-in-time background at some NCV positions) were negligible and

512 therefore omitted. Except for the systematic uncertainty on Nn introduced by our treatment

513 of the after-pulsing cut (see section 9.2), all of these uncertainties are treated in each Monte

514 Carlo trial by adding a random correction to the relevante parameter. This correction is

515 sampled from a normal distribution with mean zero and standard deviation equal to the

516 quoted uncertainty of interest. The resulting uncertainties are given in the fourth column

517 of table 4.

518 10 Implications for the ANNIE Neutron Multiplicity Measurement

519 From this measurement, we can project both the dominant source and expected rate of

520 beam-correlated backgrounds for the main ANNIE physics measurement (Phase-II). Table 4

521 shows that the background event rate observed at the top center of the tank (i.e. position

– 22 – NCV Position Scan annie

0.20 0.18 vertical scan horizontal scan 0.16 POT 0.14 12

10 0.12

⇥ Average 0.02 neutrons/

5 0.10 3 / beam-spill/m in the 3 0.08 m Phase-II ﬁducial volume. 0.06 0.04 events / 0.02 0.00 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 water thickness (cm)

Figure 10. Beam-correlated neutron candidate event rates measured during ANNIE Phase-I. The insetJonathan diagram shows Eisch the NCV(Iowa positions State University) included in the red and blue18 datasets. TheANNIE: dashed The line Accelerator Neutrino Neutron Interaction Experiment indicates which NCV positions are contained within the active region of ANNIE Phase-II. Position 0 (the center of the tank) is shown in purple to indicate that it is included in both the red and blue data. For the blue dataset, the “water thickness” is the depth of the water above the top of the NCV. For the red dataset, it is the smallest distance between the side of the tube forming the NCV vessel and the beam side of the tank. Error bars shown in the plot include both statistical and systematic contributions.

522 V4) is signiﬁcantly larger than at all other positions, including the most upstream location,

523 H2. This result is consistent with the beam-induced neutron background being dominated

524 by sky-shine rather than dirt neutrons, and it qualitatively agrees with previous SciBooNE

525 results that showed a large excess of events near the top of the detector brieﬂy after the

526 beam crossing [5]. The rapid drop-o of these backgrounds by more than a factor of three

527 over just 15 cm of depth, indicates a soft energy spectrum for these background neutrons.

528 To make a more quantitative projection of expected rates, we need to take into account

529 the planned design of ANNIE Phase-II. As described in section 1, the main ANNIE Phase-

530 II analysis seeks to measure the multiplicity of ﬁnal-state neutrons following a prompt,

531 charged current neutrino interaction in coincidence with the beam spill. In order to ensure

– 23 – NCV Position Scan annie

0.20 0.18 vertical scan horizontal scan 0.16 POT 0.14 12

10 0.12

⇥ Average 0.02 neutrons/

5 0.10 3 / beam-spill/m in the 3 0.08 m Beam-induced neutron Phase-II ﬁducial volume. 0.06 0.04 background will not impact our events / 0.02 Phase II science goals! 0.00 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 water thickness (cm)

Figure 10. Beam-correlated neutron candidate event rates measured during ANNIE Phase-I. The insetJonathan diagram shows Eisch the NCV(Iowa positions State University) included in the red and blue19 datasets. TheANNIE: dashed The line Accelerator Neutrino Neutron Interaction Experiment indicates which NCV positions are contained within the active region of ANNIE Phase-II. Position 0 (the center of the tank) is shown in purple to indicate that it is included in both the red and blue data. For the blue dataset, the “water thickness” is the depth of the water above the top of the NCV. For the red dataset, it is the smallest distance between the side of the tube forming the NCV vessel and the beam side of the tank. Error bars shown in the plot include both statistical and systematic contributions.