MINILENS - A Scalable Prototype Detector for LENS

1. MINILENS - A Scalable Prototype Detector for LENS LONU-LENS: Mini-Workshop on Low-Energy Solar Neutrinos and LENS Blacksburg, VA,October 14-15 Mark Pitt Virginia Tech

2. MINILENS LS Envelope InLS InLS 500 mm 500 mm Opt segmentation cage Passive Passive Mirror Mirror 5 5 ” ” PMT PMT Shield Shield Final Test detector for LENS • 6 x 6 x 6 array of cubic • cells, 12.5 cm on a side • Optical foil segmentation cage • InLS : 128 L • PC Envelope (active shield) : 200 L • Indium mass ~ 20 – 40 kg • (8 – 16 % by weight) • Read out with 108 5 inch PMT’s • (on three perpendicular faces; • mirrors on other sides)

3. MINILENS LS Envelope InLS InLS 500 mm 500 mm Opt segmentation cage Passive Passive Mirror Mirror 5 5 ” ” PMT PMT Shield Shield Final Test detector for LENS • Goals for MINILENS • Test detector technology •  Medium Scale InLS production •  Design and construction • Test background suppression of In • radiations by 10-11 •  Expect ~ 5 kHz In -decay singles • rate; adequate to test trigger • design, DAQ, and background • suppression schemes • Demonstrate In solar signal detection in the presence of high background (via “proxy”) • Direct blue print for full scale LENS

4. Cosmic Proton Secondaries CC -capture in 115In to excited isomeric level in 115Sn Excitation of the 713.6 keV isomeric state via 115In (p,n) from cosmic proton secondaries  can produce the same tag that mimics neutrino capture At 2000 mwe, this will be suppressed: BUT at surface this mechanism can be used as a PROXY for the solar neutrino events.

5. Indium --Background Topology – Space / Time coincidence β1 (Emax< 2 keV) (b = 1.2x10-6)* E() -114 keV 115In =4.76s 115In e/ 116 keV β0 + n (BS) (Emax = 499 keV)  498 keV  497 keV 115Sn 115Sn *Cattadori et al: 2003 Signal Signal Signature: Prompt e- ( ) followed by low energy (e-/) ( ) and Compton-scattered  ( ) Background: Random time and space coincidence between two -decays ( ); Extended shower ( ) can be created by: a) 498 keV  from decay to excited state; b) Bremsstrahlungs -rays created by ; c) Random coincidence (~10 ns) of more -decays; Or any combination of a), b) and c). Background

6. Proxy pp- events in MINILENS • Proxy pp  events in MINILENS from cosmogenic 115In(p,n)115Sn isomers • Pretagged via , p tracks • Post tagged via 115In(n,) and • 230  s delay •  Gold plated 100 keV • events (proxy pp), • Tagged by same cascade • as In- events • Can measure detection efficiency of  tag for our analysis cut scheme • Expect ~ 40 events of this type per year at the surface

7. Physics from MINILENS • 115In -decay is a rare fourth forbidden unique type; current best measurements of it are from 1979 Bell Labs In-spectra with only ~ 100 g of In • MINILENS will provide high statistics measurements of both the beta and bremsstrahlung spectra from 115In -decay  needed to validate the input spectra • currently being used in the Monte Carlo • Recently there has been a claim of a rare < 2 keV endpoint energy beta branch in 115In decay; these high statistics measurements could confirm its existence and measure its properties if it does exist (such a low endpoint energy case could be of interest to direct neutrino mass measurements)

8. Summary Current work on MINILENS: • ●Ongoing work on the optical foils • Teflon identified as best material (nylon breaks down in the acidic PC) • both single and double foil schemes being investigated • Anti-reflection coating with SiO2 nano-particles being investigated to • minimize Fresnel losses Plan for MINILENS: First phase: Run at surface where we expect ~ 40 “proxy” events per year Second phase: Run at ~ 2000 mwe depth at the VT-NRL low background facility at the Kimballton mine MINILENS: Scalable prototype LENS detector to test all the concepts and the technology developed so far & demonstrate Indium solar signal detection (via cosmic proton proxy)