Progress Towards Low Energy Neutrino Spectroscopy (LENS) Jeff Blackmon (Louisiana State University) on behalf of the LENS Collaboration The Low-Energy Neutrino Spectroscopy (LENS) collaboration aims to measure the full spectrum of neutrinos emitted from the sun via real-time, charged-current interactions Outline Why another solar neutrino experiment? The LENS detector concept Simulations & expected performance Prototyping at KURF MicroLENS MiniLENS Conclusion Outline

Solar neutrino lessons so far 8B flux ~4% precision Super-K, SNO, Borexino, . . . 7Be flux ~5% precision Borexino (see Raghavan next!) Others Radiochemical (integral) Borexino Collab, PRL 107 (2011) Neutrino flavor oscillation ® New Physics Neutrinos have mass Mass eigenstates ≠ Flavor eigenstates Measure of q12 But weak constraints on photospheric luminosity (pp fusion) The current measured solar neutrino spectrum is limited to the 8B neutrino with energy above 2.8MeV and 7Be neutrinos. The next step is a precise spectroscopic measurement of the pp, pep, and CNO neutrinos from the sun. The measurements will address important questions in solar physics and neutrino physics Why?

Gonzalez-Garcia, Maltoni & Salvado, arXiv:hep-ph/0910.4584v4 Neutrino Luminosity LENS aims for a precise measurement of the full spectrum of neutrinos (~95% of the neutrino spectrum), allowing <3% measurement of neutrino flux from pp fusion Comparing the current rate of energy production from fusion in the sun’s core to the photospheric luminosity Is the rate of energy production in the sun constant? Variability of the radiative zone? Is energy lost to magnetic fields? Is there another source of energy in the sun? Grieb & Raghavan, PRL 98 (2007) Ln = (1.00 ± 0.14) Lhf Gonzalez-Garcia, Maltoni & Salvado, arXiv:hep-ph/0910.4584v4 Direct test of solar models from pp spectrum The shape of the pp neutrino spectrum  temp and location of hydrogen fusion in the core Why?

CNO in Sun LENS will also measure flux of neutrinos from reactions originating on CNO nuclei Photospheric solar abundance analyses show 30-50% lower metalicities than previous Problem with helioseismology Reduces predicted CNO neutrino fluxes Measurements of CNO flux can shed light on this problem Cross-check of surface and core abundances would test homogeneous zero-age assumption of SSM [W. Haxton, A. Serenelli, ApJ 687 (2008)] Why?

Neutrino physics Precision test of  oscillations Pee(pp)=0.6 (vac. osc.) & Pee(8B)=0.35 (matter osc.) Do new physical phenomena show up only at the lowest energies, longest baselines, and high matter densities? Place stringent constraints on extensions to the Standard Model of particle physics Non-standard interactions Mass varying 's Magnetic moments Light Sterile 's Borexino Collab (arXiv:hep-ph/1110.3230v1) MiniBoone Collab, PRL (2010) Also A.Friedland, C.Lunardini and C.Pena-Garay, Phys. Lett. B (2004) Why?

LENS: CC Reactions on 115In ne + 115In ® 115Sn + b- In-loaded (~8%) liquid scintillator (PC or LAB) Good news: Low threshold Bad news: 115In is radioactive (t1/2 = 6x1014 yr) BUT 10 tons In  8x1013 decays/year = ~2 MHz How can we suppress this huge background? Measure isomeric transition & tag on delayed cascade signal #1 Time & space correlation can distinguish the signal But resolution is crucial signal #2 614 keV 115 keV threshold Phys. Rev. Lett. 37, 259 (1976). Concept

Technological Advances Breakthroughs in 2 areas now make indium a promising n target 1. Metal-loaded liquid scintillator technology  Based upon approaches developed at Bell Labs (Raghavan)  Improved techniques allow higher indium concentration with good light output and long attenuation length 2. Three dimensional scintillation lattice structure  Segmentation provides high “digital” spatial resolution  Also good time resolution from high light output and “direct” light Concept

Metal-loaded Scintillator Development previously focused primarily on pseudocumene (PC). Now developing Linear Alkyl Benzene (LAB) Metal loaded LS status InPC InLAB Indium concentration 8% Light yield (h/MeV) 7000 4700 Transparency L(1/e) at 430 nm 10 m 8 m Chemical Stability Stable >1.5 yr (aging tests in progress) L(1/e) down to ~2-4m at 30d. Oxidation of free HMVA? Why InLAB? Lower cost Lower toxicity Higher flash point (140°C vs 25°C) – better for underground Better compatibility with plastics Concept

Scintillation Lattice Architecture Optically segmented lattice using fluoropolymer film (n=1.34) Surrounded by PMT’s on the exterior matched to segmentation ~50% of light channeled by total-internal reflection at scintillator-film boundary “Digital” location of point of interaction by relative light in PMT’s Need ~ 3” Segmentation Photon path length Issue: Light losses in film Concept

Vision for Full Scale LENS 133 tons of In-loaded liquid scintillator (10 tons of In) Fiducial volume (64 x 7.8 cm)3 cells = (5 m)3 ~ 24576 3-inch PMT’s Active Veto & Passive Shielding 400 npp events/yr Concept

Apply cuts to event topology and time/energy resolution Signal vs. Background Random coincidence within shower radius required to mimic cascade  >107 background reduction Apply cuts to event topology and time/energy resolution Sims

Simulated Performance Cuts to distinguish signal: Time/space coincidence in the same cell required for trigger; B. Tag requires at least three ‘hits’; C. Narrow energy cut; D. A tag topology: multi- vs. Compton shower; Signal (pp) y-1 t In)-1 Bgd (In) y-1 (t In)-1 RAW rate 62.5 79 x 1011 A. Tag in Space/Time delayed coincidencewith prompt event in vertex 50 2.76 x 105 B. + ≥3 Hits in tag shower 46 2.96 x 104 C. +Tag Energy = 614 keV 44 306 D. +Tag topology 40 13 ± 0.6 Sims

Prototyping at KURF Kimballton Underground Research Facility See Vogelaar - Session NA Saturday Kimballton Underground Research Facility 6 experiments 3500 sq. ft. lab Near Blacksburg Limestone Mine 1400 mwe depth Drive-in access LENS Prototyping

Prototyping at KURF Phase I – MicroLENS (NOW): 100 liter prototype instrument Pure LAB (no Indium) Debug processes: Construction Fluid handling DAQ Studying light transport properties of the scintillation lattice Phase II – MiniLENS (2012): 410+ liter prototype In-loaded LAB Same topology as LENS Demonstrate full sensitivity of the combined technologies & benchmark Monte Carlo Prototyping

MicroLENS Construction Lattice supported by 1mm vertical quartz rods Fluoropolymer film weaved between rods Pre-creased with tool ® nice corners Completed lattice sealed in acrylic enclosure Exterior structure supports acrylic and PMT’s (see T. Wright – Session JA 1:30 Friday) Prototyping

Liquid Handling System MicroLENS @ KURF Dark Containment Electronics Tent Liquid Handling System mLENS Prototyping

Status Phase I Phase II Beyond Dark containment complete Tested with bare PMT’s Fluid handling system complete Tested with test chamber MicroLENS (100 liter prototype) Construction complete Ready to begin filling (by end of October) DAQ “Conventional” VME system now operating 32 channels of TDC’s and QDC’s Analog multiplexing scheme fully developed Flash digitizer implementation now in process MiniLENS (410 liter prototype) Design now being refined Incorporating lessons from microLENS Phase II Scaling to LENS – Now exploring: Engineering: buffer and shielding design Thin film development (transparency) Site: KURF, Homestake, Outside US? Beyond Prototyping

Data Acquisition for miniLENS Caen1721 MiniLENS will use Caen 1721 (VME) 500 MHz flash digitizers Oak Ridge National Lab ORPHAS acquisition system Using analog multiplexing with cable delay to achieve greater PMT coverage with fewer electronics channels ($) Waveform analysis determines relative contributions from 3 signals Up to 168 PMT’s possible with 7 (8 channel) digitizers 200 ns Linear Fan-In 100 ns PMT Testing setup Scintillator 100 ns Prototyping

Conclusion And especially to the students & postdocs LENS (In-loaded scintillator) is very promising approach for achieving sensitivity to the lowest energy solar neutrinos Breakthroughs in scintillator performance New detector designs with high segmentation Prototyping now aims to establish the performance – miniLENS in 2012 Special thanks to: National Science Foundation The LENS Collaboration Lead institutions: Virginia Tech (R. Raghavan – PI, D. Rountree - PM), Brookhaven National Lab & Louisiana State University And especially to the students & postdocs L. Afanasieva, M. Amrit, P. Jaffke, L. Hu, N. Passa, B. C. Rasco, M. J. Wolf, T. Wright, Z. W. Yokley Fin