John Learned, University of Hawaii at Manoa (& other colleagues at UH and elsewhere)

1. One GeV Neutrino Physics in Liquid Scintillator Detectors John Learned, University of Hawaii at Manoa (& other colleagues at UH and elsewhere)

2. Outline • NEW GeV Neutrinos: Fermat Surface • new recognition, ’09 • competitor for long baseline expts • Challenges • better light detectors • giant cost-effective instruments John Learned at ANT09

3. New Idea (1/09) • Using Liquid Scintillation detectors for ~1 GeV studies .... accelerator beams and nucleon decay! • Formerly assumed that events in this range would be purely isotropic... a big calorimeter only. • Use first light to PMTs to reconstruct tracks. • arXiv:0902.4009 jgl “High Energy Neutrino Physics with Liquid Scintillation Detectors”, 2/09 John Learned at ANT09

4. The “Fermat Surface” • Central idea: • Scintillation radiation is isotropic at each point along track (think of Huygens wavelets). • Large (many kiloton) scintillation detector PMTs would have > 100 PE/PMT @ 1 GeV • First hit is very close to Fermat Surface (Cherenkov cone & spherical caps) • Huge statistics determining surface… each tube has good data. • Large difference between equi-charge and equi-time surfaces reflect topology of interaction (i.e. muon or electron). • There is much more information… how complex a topology can we extract? • High Energy ~1 GeV neutrino interactions may thus be studied (& Nucleon Decay) • Potential for long baseline experiments, and many others • Does not interfere with lower energy (MeV) physics (e.g. reactors, geonus, supernovae, etc.) Much useful work done by muon fitting using Fermat Principle by KL folks: Mitsui, Tajima, Enomoto and others. Thanks to UH colleagues (Jason, Misha, Shige, Steve, Stephanie, Sandip) for discussions that launched this investigation. John Learned at ANT09

5. Fermat and Equi-Charge Surfaces center of time First hit times Strong separation between mu’s and e’s just on point fits to centers of time and charge Angles to <1 degree center of charge Charge Contours John Learned at ANT09

6. Simple Point Fits (Q and T) Give Center of Track and point Near Origin results of line fit for muon Chisquare/DOF Equivalent e Muon angular resolution to <1 Degree  10 sigma better fit to line than shower profiles Vertex location to few cm with first point fit. John Learned at ANT09

7. There is much more information in the Fermat Surface: Multiple particles resolvable? • Huge statistics on shape of surface. • Local vectors determine shape (Q and T) • Surface in some regions has texture. • Key question for LB experiments: How well at resolving asymmetric pi-zeroes relative to Water Cherenkov. Needs detailed Monte Carlo study. (e.g. can see gap in pi0 production?) • Need good model of light propagation in LS, including Cherenkov. John Learned at ANT09

8. Can Do Tomography to Reconstruct Event Topology But wait, more…. • very early and encouraging results follow John Learned at ANT09

9. Fermat Surface Crossection for Two Tracks • Equi-time contours. • How well can we resolve multi-track events via Fermat Surface fitting? John Learned at ANT09

10. Pictorial Fermat Surface Crossection for Two Tracks • Project back from PMT clusters by first-PE-time gradient (Plane wave fit) • Do it in 3D, and include time (back projections crossing at same time). • A form of tomography • Demands high time resolution and dealing with prepulses. John Learned at ANT09

11. First Results on Tomographic Reconstruction from Fermat Surface Example: Single 1 GeV Muon track before cuts after contrast cuts We should be able to reconstruct bubble chamber like images from multiple tracks jgl 10 July ‘09

12. Back Propogation • There may be better ways to do this with techniques developed for medical imaging. • For example, back propagate a spherical surface in time from each PMT, add up coinciding signals, make contrast cuts. • Put the load on computing! • Can do hierarchical reconstruction. John Learned at ANT09

13. Further: Much Information in Time Distribution of Hits (PMT Waveform) Sample PMT hit time distributions from top of detector 1 GeV Muon 1 GeV e Shower Given real world problems (PMTs, scint lifetime, scattering….), how much of this can we utilize? Needs detailed modeling. Juha Peltoniemi (Finland/Munich) has started doing just this. John Learned at ANT09

14. Measuring high-energy neutrinos with LENA(from Juha Peltoniemi) • Studying the capacity to measure 1-5 GeV neutrinos with a large volume liquid scintillator. • Simple home-made simulation code (”scinderella”). • Most but not yet all physics included. • Better framework under development (Wurm et al)‏ • Use time profile information of all PMT's for track reconstruction. • Include muon decay and neutron absorption signatures. • All QES and most SPP events can be satisfactorily reconstructed. Energetic DIS events still a challenge. • Good flavor identification, fair charge identification • Excellent energy resolution

15. Juha’s Monte Carlo Simulation(he gives usual cautions about being preliminary… to me very encouraging). He is already fitting rather complex events by using full PMT waveform! John Learned at ANT09

16. Prospects • Long Baseline with accelerators ~ 1 GeV now seen to be attractive • LENA with CERN beam? • Hanohano with Tokai Beam? (Demonstration) • DUSEL Experiment with Fermilab Beam? • Nucleon Decay (high free proton content) • & see details of decays such as Kaon modes • Particle Astrophysics (low mass WIMPS,…) • All the Low Energy Physics (geonus, reactor studies, monitoring, solar neutrinos….. As with KL, SNO+, Hanohano, LENA) unimpeded! • Idea only really works for >10kT size detectors (due to need for containment of muons, and to a lessor extent electron events). • For this meeting, note that this viewpoint puts technical emphasis on fast PMTs and waveform recording for large LS detectors. • Much work to be done, fancier calculations in progress. Help needed. • A bright future!?! John Learned at ANT09

17. Further Idea: Make Small ~1Ton Detector for Reactors, Using Fast PMTs and Back Propagation We propose to build prototype model Parameters: 1 m3 with fast liquid scintillator fill 2mm x 2mm pixels => 1.5 x 106 chnls Time resolution 20-60 ps Spatial Resolution ~ 1 cm 4 MeV event ~ 40 k hits Occupancy < 1% => single PEs Back propagation challenge Consequences: Excellent neutrino direction resolution. Very high background rejection. Can handle high rates. Excellent new candidate for surface deployed reactor monitor Easily fits into cargo container -> With LAPD will be inexpensive! John Learned at ANT09