1. 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

2. 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?

3. 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/ v4
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?

4. 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?

5. 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/ v1)
MiniBoone Collab, PRL (2010)
Also A.Friedland, C.Lunardini and C.Pena-Garay,
Phys. Lett. B (2004)
Why?

6. 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

7. 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

8. 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

9. 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

10. 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
~ inch PMT’s
Active Veto & Passive Shielding
400 npp events/yr
Concept

11. 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

12. 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

13. 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

14. 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

15. 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

16. Liquid Handling System
KURF
Dark Containment
Electronics Tent
Liquid Handling System
mLENS
Prototyping

17. 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

18. 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

19. 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