1. Active-Sterile Neutrino Oscillations in LENS
C. Grieb, J. Link and R. S. Raghavan
Virginia Tech
XII Neutrino Telescopes
Venice, March

2. LENS is a high-resolution, real time spectrometer for low energy solar neutrinos such as pp, Be etc
Why LENS for active-sterile oscillations?
Novel Technology brings unique tools in play for short baseline disappearance experiments using monoenergetic e-flavor neutrinos from a radioactive source
Parasitic measurement to solar neutrino program—sterile neutrinos are free!
Sensitivity highest, well beyond Miniboone projected - new physics and astrophysics irrespective of LSND and Miniboone result

3. Two part Talk
I LENS overview- Properties relevant to short baseline oscillations
II How to make a sensitive search for active-sterile oscillations in LENS ?

4. LENS-Sol / LENS-Cal Collaboration (Russia-US: 2004-)
INR (Moscow): I. Barabanov, L. Bezrukov, V. Gurentsov,
V. Kornoukhov, E. Yanovich
IPC (Moscow): N. Danilov, G. Kostikova, Y. Krylov
INR (Troitsk) I: J. Abdurashitov, V. Gavrin. et al.
II: V. Betukhov, A. Kopylov, I. Oriachov, E.Solomontin
U. S.:
BNL: R. L. Hahn, M. Yeh
UNC: A. Champagne
ORNL: J. Blackmon, C. Rasco, Qinlin Zeng, A. Galindo-
Uribarri
Princeton U. : J. Benziger
SCSU: Z. Chang
Virginia Tech: C. Grieb, J. Link, M. Pitt, R.S. Raghavan,
R. B. Vogelaar,
LENS-Sol / LENS-Cal Collaboration
(Russia-US: )

5. LENS is the only developed CC real time detector for solar neutrinos
Tagged ν –capture reaction in Indium
LENS is the only developed CC real time detector for solar neutrinos
Unique:
Specifies ν Energy
Eν = Ee + Q
Complete LE nu spectrum
Lowest Q known 114 keV
access to 95.5% pp nu’s
Target isotopic abundance ~96%
Powerful delayed coinc. Tag
Can suppress bgd =1011 x signal
Downside:
Bgd from 115In radioactivity to
( pp nu’s only) rate= 1011 x signal
Tools:
Time & Space coinc. Granularity (106suppression)
Energy Resolution
In betas <500 keV; ∑Tag = 613 keV
3. Other analysis cuts
signal
delay
Tag cascade

6. Expected Result from LENS
Background precisely and concurrently measured
Well resolved low energy solar nu spectrum –
 pp, 7Be, pep, CNO with 99+% of solar nu flux
Solar luminosity in nu’s
pp spectral shape accessible for first time

7. Light attenutation L(1/e)
Major Progress --LENS
< Towards Hi Precision pp >
Hi Quality InLS Developed
Background Analysis Insights
New Detector Design Invented
8.6 m after 8 months
Transparency of InLS
Status
Design of Detector
Cubic Lattice
Chamber
Composition
InLS
PC based: In content
Light attenutation L(1/e)
Signal Eff Pe/MeV
NEW : LAB based- Similar as in PC
>8%
>10m
900
Indium Mass(1900 pp/5y)
10 ton
Total Mass
125 ton
PMT’s
13,300
Neutrino detection eff.
64% (pp)
>85% all other
S/N (β+γ (All In decay modes)
~3 (pp)
>> 3 (ALL OTHER)

8. Indium --Background Structure – Space / Time coincidence
Signal
Signal Signature:
Prompt e- ( )followed by
low energy (e-/) ( )
and
Compton-scattered  ( )
->time/space coincidence
-> tag fixed energy 613keV
->compton scattered shower
E() -114 keV
116 keV
497 keV
115In
115Sn
e/ 
=4.76s
115In
β0 + n (BS)
(Emax = 499 keV)
498 keV
*Cattadori et al: 2003
β1 (Emax< 2 keV)
(b = 1.2x10-6)*
115Sn 
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).

9. Signal and Indium-Background Rates
pp Signal
/y /t In
Bgd tot
Bgd A1
Bgd A2
Bgd B
Bgd C
RAW
62.5
79 x 1011
Valid tag (Energy, Branching, Shower) in Space/Time delayed coinc. with prompt event in vertex 55
2.76 x 105
8.3 x 104
2.8 x 103
1.9 x 105
43.9
+ ≥3 Hits in tag shower
49.5
6.23 x 104
5.81 x 104
2.76 x 103
1.4 x 103
43.7
+Tag Energy = 613 keV
44.4
458
0.48
5.2
445
8.0
+Shower Radius
270
5.1
264
0.73
+Hit Separation
40.2
13.3 ±0.6
4.7
8.1
0.004
Signal / Background ~3 with pp- event detection efficiency 64%
Remember: only pp- events affected by Indium Background, 7Be, pep and CNO Background-free

10. Technology
Indium Liquid Scintillator Chemistry Robust
LENS-Grade Properties Demonstrated in Lab Scale
Large Scale Production Next
Detector Design
Novel Scintillation Lattice Invented
Optical properties simulated and analyzed for optimal Design
Prototypes in development

11. Indium Liquid Scintillator Status
1. Indium concentration ~8%wt
(higher may be viable)
2. Scintillation signal efficiency
(working value): 9000 h/MeV
3. Transparency at 430 nm:
L(1/e) (working value): 10m
4. Chemical and Optical
Stability: at least 1 year
5. InLS Chemistry - Robust
Basic Bell Labs Patent,
Chandross & RSR. 2004
8% InLS (PC:PBD/MSB)
hν / MeV
BC505 Std
12000 h/MeV
In 8%-photo
Light Yield from Compton edges
of 137Cs -ray Spectra
l (nm)
Norm. Absorbance in 10 cm
L(1/e)(InLS 8%) ~ L(PC Neat) !
ZVT39: Abs/10cm ~0.001;
 L(1/e)(nominally) >>20 m
InLS
PC Neat
Indium Liquid Scintillator Status
Milestones unprecedented
in metal LS technology
LS technique relevant to
many other applications

12. Long Term Stability of L1/e of InLS Abs@430nm at different time
Sample pH
In% S%
at different time
Begin
1 Mon
3 Mon
5 Mon
8 Mon
9 Mon
zVt39
7.24
8.7 64
0.001
0.002
0.003
0.009
0.012
0.013
zVt40
7.22
8.4 63
0.005
0.006
0.010 --
zVt41
7.09 59
 --
-- 
 0.008
zVt46
6.98
8.5 58
 0.007
0.008
zVt38
6.94
8.3 61
0.007
zVt47
6.92
8.0
0.0025
zVt45
6.88
8.2 56
0.004
zVt44
6.86
8.6
0.004 
 0.004
The S values of the samples were found not to change with time.
The L1/e of the samples synthesized at pH 6.88 were found to stabilize in 3 months, and their L1/e have stayed > 8 m for 8 months.
Optimum value for the extraction pH ~6.88

13. The Scintillation Lattice Chamber
New Detector Concept -
The Scintillation Lattice Chamber
Light propagation
in GEANT4
Concept
Test of transparent double foil
mirror in
3D Digital Localizability of Hit within one cube
 ~75mm precision vs. 600 mm (±2σ) by TOF in longitudinal modules
 x8 less vertex vol.  x8 less random coinc.  Big effect on Background
 Hit localizability independent of event energy

14. Light loss by Multiple Fresnel Reflection
A small part of light crossing
a gap is reflected back and undergoes multiple reflections,
thus, suffers extra bulk absorption in the liquid
Photoelectron yield versus number of cells:
Upper limit ~1700pe/MeV (L=10m) -
reach via antireflective coating on films?
Adopt
1020 pe/MeV
7.5 cm cells
4x4x4m Cube
Absorption length = 10m

16. Real life issue--Foil Surface Roughness and
Impact on the Hit Definition
100 keV event in 4x4x4m cube, 12.5cm cells
Perfect optical surfaces : 20 pe (per channel)
Rough optical surfaces : 20% chance of non- ideal optics at every reflection
12 pe in vertex + ~8 pe in “halo”
Conclusion - Effect of non-smooth segmentation foils:
No light loss - (All photons in hit and halo counted)
Hit localization accuracy virtually unaffected

17. Can we get away with a single foil optical structure-? “Hard Lattice”
No trapped air
Easier construction
More robust
Most photons still “channeled” crit~60
Still Good event localization
Less trapping
Greater light output
Solid Teflon Segmentation
Challenges:
How to deal with “spray”?
Background rate
Trigger logic

18. MINILENS InLS LS Envelope 500 mm Mirror Final Test detector for LENS 5”
PMT
Passive
Shield
Mirror
Opt segmentation cage
InLS
500 mm
LS Envelope
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

19. Table I: Characteristics of neutrino Sources for LENS-CAL
DecayMode /Produced by t
En (keV)
Ee=
En keV
Background
37Ar
Haxton
EC/ (n, a)
50.5 d
814(100%)
700
Int. Bremms ;
~S5x10-4 hn/decay
51Cr RSR
Kuzmin
EC/ (n,g)
40.1 d
751 (90%)
637
320g (10%)
Imp. g’s (MeV) %??
65Zn
Louis Alvarez
EC(b+)/ (n,g)
353 d
1350 (50%)
1236
1115 g (50%); 511 g (2%);
Imp. g’s.
Neutrino Energy typically 700 keV

20. Sterile neutrino tests in LENS
Unique advantages
Put strong articial Neutrino Source into LENS
Pure, e-flavor, monochromatic neutrino line
Measure Pee as function of Distance—Disappearance Measurement
3-D location allows measurement of RADIAL dependence of Pee
All systematic, normalization and spectral peeling errors endemic in broad beam reactor spectra drop out
Measure Pee (r) with100,000 detectors, not just 2 or 3

21. LENS OFFERS UNIQUE TEST For Sterile Neutrinos
Already planned: LENS Cal
MCi Cr Source in LENS
Calibrate In X-section
Parasitic measurement
For sterile neutrinos
Active Sterile Osc of mono-
Chromatic 753 keV
pure e-flavored neutrinos
Via
Spatial distribution of
Flavor Survival in ~5 m
Active-Sterile Oscillations

22. Sterile Neutrinos—( Neutrinos of the wrong helicity)
Physics well beyond the Standard Model
--Fourth (Fifh) mass state with high mass splitting triggered by LSND
Appearance of e flavor from μ beams at short base lines ~30m!
Implies Δm2 ~ 1 eV2

25. Pee = 1 − s2 (e4) s2 (41) – s2 (e5) s2( 51)
where cross terms such as s2 (e4)s2 (e5) are neglected. In (2) the mixing terms
s2( en) = sin2 2θen = [4U2 (en) (1-U2(en)]
and the frequencies s2 n1 =
sin2 [(1.27Δm(n1)2 eV2 ) x L(m)/Eν(MeV)) .
The values of s(en) and Δm2 are from
Ref 4 (Table 1). With Δm2 = 1 eV2 and
Eν ~0.753
MeV (from 51Cr), (2) full flavor recovery occurs in ~2m, directly observable in a lab-scale detector

27. Statistical precision of oscillation parameter measurement in LENS

30. Gail Maclaughlin (Private Comm.)

31. Conclusions
LENS offers a new and sensitive tool for searching for active-sterile nu oscillations
The advanced sensitivity allows the search in its own right towards new physics and astrophysics
Independent of LSND or Miniboone results
Parasitic measurement—No extra resources needed