MINILENS -A Scalable Prototype Detector for

LENS

LONU-LENS: Mini-Workshop on Low-Energy Solar Neutrinos and LENS

Blacksburg, VA, October 14-15

Mark PittVirginia Tech

5” PMTPassiveShield Mirror 5” PMTPassiveShield Mirror

Opt segmentation cage

InLS500 mm

InLS

LS Envelope

500 mm

• 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)

MINILENSFinal Test detectorfor LENS

5” PMTPassiveShield Mirror 5” PMTPassiveShield Mirror

Opt segmentation cage

InLS500 mm

InLS

LS Envelope

500 mm

MINILENSFinal Test detectorfor 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

MINILENS Mark Pitt, Virginia Tech, October 2006

Cosmic Proton SecondariesCC -capture in 115In to excited isomeric level in 115Sn

SneeIne115

s)4.76( tagdelayedsignalsolar

115 )/(

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 usedas a PROXY for the solar neutrino events.

MINILENS Mark Pitt, Virginia Tech, October 2006

Indium --Background Topology – Space / Time coincidence

Background

Signal

E() -114 keV

116 keV

497 keV

115In

115Sn

e/

=4.76s

Background:

Random time and space coincidencebetween 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).

Signal Signature:

Prompt e- ( )followed bylow energy (e-/) ( )and Compton-scattered ( )

115In

β0 + n (BS) (Emax = 499 keV)

498 keV

*Cattadori et al: 2003

β1 (Emax< 2 keV)(b = 1.2x10-6)*

115Sn

MINILENS Mark Pitt, Virginia Tech, October 2006

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

Proxy pp- events in MINILENS

MINILENS Mark Pitt, Virginia Tech, October 2006

• 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 spectracurrently 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)

Physics from MINILENS

MINILENS Mark Pitt, Virginia Tech, October 2006

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)

Summary

● 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

Current work on MINILENS:

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