1. 1 Prototyping Megaton-Scale  Detectors Jason Trevor DOE Review July 25, 2007 Developing a New Lower-Cost Scintillator Design

2. 2 The Problem  Neutrino and cosmic ray physics continue to require ever larger detectors for measurements of interest.  All existing technologies have limitations  Water Cerenkov – Cheap, but limited by low energy cut-off  Liquid Scintillator – High light yield, but difficult to work with and environmentally hazardous  Solid Scintillator – Many desirable characteristics, but too expensive for use in very large detectors  Water Soluble Scintillator – Highly desirable, but no practical scintillators of this type are currently known  Conclusion: Construction of future large-scale detectors will require the development of new technologies which will lower unit detector cost.

3. 3 An idea inspired by MACRO and MINOS Scintillator  In a MINOS scintillator strip, only 5-10% of the light produced actually makes it into the WLS fiber.  There are three main cause of light absorption before the WLS fiber:  Self absorption by the fluors and polystyrene in the scintillator.  Imperfect surface reflectivity.  Absorption through either of the preceding processes after the light has reflected off the fiber/glue/polystyrene interface. MINOS Scintillator Strip WLS Fiber TiO2 Cladding Polystyrene

4. 4 Plastic Scintillator Granules in Water?  What would happen if granules of plastic scintillator are mixed into water at a 5% concentration with a grid of WLS fibers?  The effective attenuation length of the bulk material is increased by about a factor of 20  Absorption in the reflector is reduced  A better optical coupling is achieved for light at the WLS fiber boundary  Water is free - Cost per unit mass is reduced by 80-90% (est.) PMT ~Water Scintillator Granules WLS Fibers

5. 5 Proof of Principle  19cm x 19cm x 13cm  Constructed using left-over MINOS scintillator and WLS Fiber  Water and scintillator granules were circulated by small pumps  Light output in this prototype was lower than the nominal goal for a practical large detector, but  The scintillator was of poor quality  The prototype was too small… losses were still dominated by absorption in the walls  Solution: Scale up volume by a factor of 200

6. 6 One Cubic Meter Tank Detector  Our ADR grant proposal was funded (1yr $48k)  Scintillator strands replaced granules  Easier to extrude high quality scintillator  No circulation system required  More realistic configuration for larger tank detectors  But, more difficult to construct  Construction is complete (with the help of Caltech Undergrads) WLS Fibers (A 1 m cube) Scintillator Strands PMT

7. 7 Detector Construction

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9. 9 Completed Detector

10. 10 Readout Topology  Tank is divided into eight regions  All WLS fibers from a given region are routed to one of eight phototube boxes  Muon triggers are centered over the inner four regions  Inner regions are 30cm x 30cm  Muon Triggers are 18cm x 18cm 6 5 2 07 4 3 1 Meter 1

11. 11 A Few Events  Two typical events  Event 897 – Single trigger event – These are mostly muon events  Event 4 – Multiple trigger event – Other stuff (Electrons, hadrons, etc)  Numbers shown are estimated light output in P.E.s – exact calibration still needs to be completed  Preliminary numbers suggest the light output is ~2 – 5 times that of MINOS – A more detailed analysis is necessary to confirm this

12. 12 Preliminary Analysis 01 234 5 67

13. 13 Summary  Construction of the one cubic meter prototype is complete – undergrad student labor was an essential part of the construction effort  Initial results suggest the light output is 2 – 5 times that of MINOS, but more detailed analysis is necessary  Recent addition of Leon Mualem and Alex Himmel has accelerated progress.  This is a promising new technology  More R&D is necessary – The design is far from optimal  We plan to apply for further ADR funding  A paper is in the works