Active-Sterile Neutrino Oscillations in LENS

C. Grieb, J. Link and R. S. RaghavanVirginia Tech

XII Neutrino TelescopesVenice, March 8 2007

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

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 ?

Russia INR (Moscow): I. Barabanov, L. Bezrukov, V. Gurentsov,

V. Kornoukhov, E. YanovichIPC (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. YehUNC: A. ChampagneORNL: J. Blackmon, C. Rasco, Qinlin Zeng, A. Galindo- UribarriPrinceton U. : J. BenzigerSCSU: Z. ChangVirginia Tech: C. Grieb, J. Link, M. Pitt, R.S. Raghavan, R. B. Vogelaar,

LENS-Sol / LENS-Cal Collaboration(Russia-US: 2004-)

115In ( 95.7%) = 6.4x1014 y

115Sn

B(GT) = 0.17; Q=114

e1

(e/)2 115.6 (e/ = 0.96)

3 497.3

115 In(p,n)100.8 (e/ =5.7)

= 4.76 s

max = 498.8

= 16 ps

= 231s

9/2+

1/2+

3/2+

7/2+

11/2-

0

497.3

612.8

713.6

7/2+ 1857

B(GT) ~0.01; Q =1362

e

115In ( 95.7%) = 6.4x1014 y

115Sn

B(GT) = 0.17; Q=114

e1

(e/)2 115.6 (e/ = 0.96)

3 497.3

115 In(p,n)100.8 (e/ =5.7)

= 4.76 s

max = 498.8

= 16 ps

= 231s

9/2+

1/2+

3/2+

7/2+

11/2-

0

497.3

612.8

713.6

7/2+ 1857

B(GT) ~0.01; Q =1362

e

The Indium Low Energy Neutrino Tag

115In ( 95.7%) = 6.4x1014 y

115Sn

B(GT) = 0.17; Q=114

e1

(e/)2 115.6 (e/ = 0.96)

3 497.3

115 In(p,n)100.8 (e/ =5.7)

= 4.76 s

max = 498.8

= 16 ps

= 231s

9/2+

1/2+

3/2+

7/2+

11/2-

0

497.3

612.8

713.6

7/2+ 1857

B(GT) ~0.01; Q =1362

e

115In ( 95.7%) = 6.4x1014 y

115Sn

B(GT) = 0.17; Q=114

e1

(e/)2 115.6 (e/ = 0.96)

3 497.3

115 In(p,n)100.8 (e/ =5.7)

= 4.76 s

max = 498.8

= 16 ps

= 231s

9/2+

1/2+

3/2+

7/2+

11/2-

0

497.3

612.8

713.6

7/2+ 1857

B(GT) ~0.01; Q =1362

e

The Indium Low Energy Neutrino Tag

SnSneIne115*115115 2

Tagged ν –capture reaction in IndiumLENS 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

signalDownside:• Bgd from 115In radioactivity to ( pp nu’s only) rate= 1011 x

signalTools:1. Time & Space coinc.

Granularity (106suppression)2. Energy Resolution In betas <500 keV; ∑Tag =

613 keV3. Other analysis cuts

signal delay Tag cascade

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

  Status

Design of Detector Cubic Lattice Chamber

Composition InLS

PC based: In contentLight attenutation L(1/e)

Signal Eff Pe/MeV NEW : LAB based- Similar as in PC

>8% >10m900

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)

Major Progress --LENS < Towards Hi Precision pp >• Hi Quality InLS Developed• Background Analysis Insights• New Detector Design Invented

UV/Vis absorbance of zVt45 (pH 6.88) with time

-0.01

0

0.01

0.02

0.03

0.04

0.05

350 390 430 470 510 550 590 630 670l (nm)

Nor

mal

ized

Abs

orb

ance

10/06/05

01/23/06

03/22/06

05/31/06

8.6 m after 8 months

Transparency of InLS

Indium --Background Structure – Space / Time coincidence

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 ( )->time/space coincidence-> tag fixed energy 613keV->compton scattered shower

115In

β0 + n (BS) (Emax = 499 keV)

498 keV

*Cattadori et al: 2003

β1 (Emax< 2 keV)(b = 1.2x10-6)*

115Sn

Signal and Indium-Background Ratespp Signal

/y /t In

Bgd tot

/y /t In

Bgd A1

/y /t In

Bgd A2

/y /t In

Bgd B

/y /t In

Bgd C

/y /t In

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 43.9 270 0.48 5.1 264 0.73

+Hit Separation 40.2 13.3 ±0.6 0.48 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

Technology

Indium Liquid Scintillator Chemistry RobustLENS-Grade Properties Demonstrated in Lab ScaleLarge Scale Production Next

Detector DesignNovel Scintillation Lattice InventedOptical properties simulated and analyzed for optimal DesignPrototypes in development

1. Indium concentration ~8%wt (higher may be viable)2. Scintillation signal efficiency (working value): 9000 h/MeV3. Transparency at 430 nm: L(1/e) (working value): 10m4. Chemical and Optical Stability: at least 1 year5. InLS Chemistry - Robust

Basic Bell Labs Patent,Chandross & RSR. 2004

1

10

100

1000

10000

0 50 100 150 200 250

8% InLS (PC:PBD/MSB) 10800 hν / MeV

BC505 Std12000 h/MeV

In 8%-photo

Light Yield from Compton edgesof 137Cs -ray Spectra

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

350 390 430 470 510 550 590 630 670l (nm)

Nor

m.

Abs

orba

nce

in 1

0 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

Sample pH In% S%Abs@430nm 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 0.001 0.003 0.005 0.006 0.010 --

zVt41 7.09 8.4 59 0.003  -- --   0.008 0.009 --

zVt46 6.98 8.5 58 0.002  --  --  0.007 0.008 --

zVt38 6.94 8.3 61 0.002 0.003 0.005 0.005 0.006 0.007

zVt47 6.92 8.0 59 0.0025  -- 0.005 --  0.006 --

zVt45 6.88 8.2 56 0.003 0.004 0.005 0.005 0.005 --

zVt44 6.86 8.6 56 0.003 0.004  0.004   0.004 0.005 --

Long Term Stability of L1/e of InLS

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

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

Test of transparent double foilmirror in liq. @~2bar

New Detector Concept -The Scintillation Lattice Chamber

Light propagationin GEANT4

Concept

Light loss by Multiple Fresnel ReflectionA small part of light crossing

a gap is reflected back and undergoes multiple reflections, thus, suffers extra bulk absorption in the liquid

Upper limit ~1700pe/MeV (L=10m) - reach via antireflective coating on films?

Adopt1020 pe/MeV7.5 cm cells

Photoelectron yield versus number of cells:

4x4x4m CubeAbsorption length = 10m

100 keV event in 4x4x4m cube, 12.5cm cellsPerfect 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

Real life issue--Foil Surface Roughness andImpact on the Hit Definition

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

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

Source DecayMode /Produced by

EkeV) Ee=

E0.114 keV

Background

37Ar Haxton

EC/ (n, 50.5 d 814(100%) 700 Int. Bremms. 0-814;~5x10-4 h/decay

51Cr RSRKuzmin

EC/ (n,) 40.1 d 751 (90%) 637 320 (10%) Imp. ’s (MeV) %??

65Zn Louis Alvarez

EC(+)/ (n,) 353 d 1350 (50%) 1236 1115 511 (2%); Imp. ’s.

Table I: Characteristics of neutrino Sources for LENS-CAL

Neutrino Energy typically 700 keV

•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

Already planned: LENS CalMCi Cr Source in LENSCalibrate In X-section

Parasitic measurementFor sterile neutrinos

Active Sterile Osc of mono-Chromatic 753 keVpure e-flavored neutrinos

ViaSpatial distribution ofFlavor Survival in ~5 m

Active-Sterile Oscillations

LENS OFFERSUNIQUE TESTFor Sterile Neutrinos

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

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

Statistical precision of oscillation parameter measurement in LENS

Gail Maclaughlin (Private Comm.)

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