Report on the 3D-projection Scintillator Tracker (3DST) as part of - PDF document

Report on the 3D-projection Scintillator Tracker (3DST) as part of the DUNE Near Detector Concept Study S. Kettell and E. Worcester Brookhaven National Laboratory K. Siyeon and C.H. Jang Chung Ang University S. Bordoni, A. De Roeck, F. Pietropaolo, M. Nessi, and D. Sgalaberna CERN, European Organization for Nuclear Research Y. Kudenko INR, Institute for Nuclear Research J. Maneira University of Lisbon T. Kutter Lousiana State University R. Gran University of Minnesota, Duluth C. Mauger University Pennsylvania H. Su, D. Naples, and V. Paolone University of Pittsburgh T. Cai, R. Flight, S. Manly, K. McFarland, and A. Olivier University of Rochester C.K. Jung, C. McGrew, J. Palomino, K. Wood, and G. Yang Stony Brook University 1

M. Kordosky and E. Valencia College of William and Mary (Dated: March 14, 2018) Abstract This note summarizes ongoing efforts to explore the case for including a 3D-projection scintillator tracker (3DST) as part of the DUNE near detector. The 3DST is a fully active detector with 3 dimensional, fast readout. It is dense enough to provide a large statistics sample with reasonable containment of hadrons and photons from neutrino interactions, and sensitivity to neutrons. The high statistics and granularity of the 3DST will allow the study/use of many different interaction morphologies and differential studies. The physics mission of the 3DST depends to some extent on the other components of the near detector and how they are configured, as well as whether or not elements of the detector are moved off-axis during running. In the DUNE era, data from the 3DST will be easily comparable to the large catalog of past neutrino results taken on plastic scintillator, and (potentially) with data recorded by the functionally identical SuperFGD in the lower energy, narrow band T2K beam, which is peaked at ( ∼ 0.6 GeV) near the DUNE 2nd oscillation maximum. The comparisons will allow us to fine-tune the neutrino interaction models which will be critical in reducing systematic uncertainties. These characteristics combine to form an addition to a DUNE near detector complex that is relatively insensitive to backgrounds and capable of providing useful handles for understanding the beam, near detector environment, and constraints for the analysis in the DUNE far detector. 2

CONTENTS I. Introduction 4 II. Statistics 7 III. Detector simulation 7 IV. Tracking efficiency 9 V. Answers to questions posed by concept study group 14 A. What is the angular and energy resolution of the 3DST 14 1. Angular resolution 14 2. muon energy resolution 17 3. electron energy resolution 18 B. How well can the 3DST do neutrino-electron scattering? 18 C. How large does the 3DST need to be to do reasonably well on pizero and neutron topologies? 21 1. pizero photon containment 21 2. neutron containment 22 D. Can the 3DST do something with neutron counting/angles? 25 1. Neutrons in scintillator and the 3DST 28 E. Does the 3DST need to be in a magnetic field? 31 1. Charge separation efficiency 32 2. wrong-sign backgrounds 32 3. electron neutrino constraints on hadroproduction 33 F. What is the complementary physics for the 3DST relative to the other trackers? How would it improve CP sensitivity? 33 1. Synergy with the Liquid argon TPC 36 2. Synergy with the straw tube tracker 38 3. Synergy with the high pressure gaseous argon TPC 38 G. Selected physics processes 39 1. neutrino-electron scattering 39 2. coherent charged and neutral pion production 39 3

3. low- ν 40 4. inclusive CC 42 5. NC/CC neutral pion production 42 VI. Potential U.S.-Japan Cooperation funding 43 VII. Other geometries 43 A. 3DST inside HPGArTPC 43 VIII. R&D 45 IX. References 50 Acknowledgments 50 References 50 I. INTRODUCTION The 3DST detector will be made of many optically independent cubes of extruded scin- tillator. The design is very similar to that being proposed by the T2K collaboration as part of the T2K ND280 detector upgrade [12, 14]. The cubes in this detector are read out along three orthogonal directions by wavelength shifting (WLS) fibers. A schematic of the detector is shown in Fig. 1. Scintillator cube WLS fibers FIG. 1: Schematic of the 3DST/Super-FGD structure. This figure is from reference [14]. 4

The 3DST is proposed as a component of the DUNE near detector for a number of reasons. The complementarity of the 3DST to the rest of the detector is contingent to some extent on the other components of the near detector and the location and size of the 3DST. In general, the 3DST provides: • a large statistics sample of neutrino interactions with true 4 π coverage in a magnetic field; • a fine-grained spatial resolution sufficient to identify and measure most neutrino in- teraction morphologies; • a transparent connection to the vast catalog of cross section results coming out of plastic scintillator experiments, i.e., MINERvA and T2K; • a detector that is functionally identical to the T2K Super-FGD which, by the time DUNE sees a neutrino beam, will have taken much data in a narrow-band, lower energy beam that happens to peak in the energy region of the DUNE second oscillation maximum; • a fast detector, with the insensitivity to backgrounds that implies; • a detector with substantial sensitivity to neutrons in the final state of neutrino inter- actions; • a relatively high density detector that will convert a substantial fraction of photons from π 0 decays. Achieving a full 4 π acceptance at the near detector is fundamental to avoid any bias in the extrapolation of the cross-section model to the far detector. We know the neutrino cross section is poorly understood and it is not totally clear this issue will be solved by when the DUNE experiment will start collecting data. There are many reasons why we should be careful about a detector without a full solid angle acceptance, in particular considering the fact that the LAr near detector would not be magnetized. The wrong-sign background may largely affect the precision on δ CP and we know that the difference between neutrino and antineutrino cross sections is poorly modeled, resulting in large systematic uncertainties. 5

A clear example is given by the so-called “2p2h” process, where the (anti)neutrino inter- acts with a neutron (proton) but, because of short range correlations, two nucleons (e.g. a proton and a neutron) or more can be ejected instead of one, providing a bias in the neutrino energy reconstruction. This process occurs for neutrino energies of about 1 GeV/c and has a strong effect on the neutrino energy reconstruction, in particular for the DUNE neutrino flux. We do not expect this process to be the same for neutrinos and antineutrinos and this difference is correlated with the direction of the outgoing lepton angle and the neutrino energy. Another issue is given by the fact that the theoretical models (for example the so-called “Martini” and “Valencia” models) show larger discrepancies for muons produced at high angles than along the neutrino direction [2]. The constraint on the cross-section model systematic uncertainties would certainly profit by the detection of all the pions, protons and, possibly, neutrons produced at any angle, also to provide a precise measurement of the transverse missing momentum. Recently the GiBUU theoretical group presented an updated model that expects the 2p2h processes to mainly populate that part of the phase space where a muon ejected with angle large with respect to the neutrino direction. Consequently a large effect in the forward region would be due to final state interactions (FSI) [4]. This is in contrast with other models (e.g. “Martini” and “Valencia”) that expect to find 2p2h neutrino events mainly in the forward region. The neutrino physics community is aiming to a unified neutrino-interaction model that could describe all the data from all the experiments at different energies and nuclei. This implies that the model must suit well the neutrino-carbon (oxygen), neutrino-argon and neutrino-hydrogen interaction data. However, these nuclei are very different (C 12 , Ar 40 ) and the solution may not be trivial. For example the FSI and secondary interactions (SI) are expected to rapidly change with the size of the nucleus and, consequently, to be larger in argon than carbon. The possibility to measure neutrino interactions not only in argon but also in plastic, would allow us to cross check our data with many other experiments both in the energy range of the first (Minerva) and second (T2K) oscillation probability maximum. Furthermore it would help to solve the degeneracy between the effects due to the neutrino- nucleus interaction and FSI and SI. The situation is still quite unclear and we may find issues in the extrapolation from carbon- to argon- based models. A high-precision 4 π plastic 6