Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

27
Experimental Approaches to Experimental Approaches to Sterile Neutrinos Using Sterile Neutrinos Using Low Energy Neutrinos Low Energy Neutrinos Jonathan Link Jonathan Link Center for Neutrino Physics Center for Neutrino Physics Virginia Tech Virginia Tech NOW 2012 NOW 2012 9/14/12 9/14/12

description

Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link Center for Neutrino Physics Virginia Tech NOW 2012 9/14/12. 115 In + ν e → 115 Sn * + e - → 115 Sn + 2 γ. The LENS-Sterile Proposal. Scintillation Lattice: - PowerPoint PPT Presentation

Transcript of Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Page 1: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Experimental Approaches to Sterile Experimental Approaches to Sterile Neutrinos Using Low Energy NeutrinosNeutrinos Using Low Energy Neutrinos

Jonathan LinkJonathan Link

Center for Neutrino PhysicsCenter for Neutrino PhysicsVirginia TechVirginia Tech

NOW 2012 NOW 2012

9/14/129/14/12

Page 2: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The LENS-Sterile ProposalThe LENS-Sterile Proposal

Proposal to insert a Mega-Curie 51Cr source in the center of the LENS detector to observe multiple wavelengths of large Δm2 oscillations in a few meters.

115In + νe → 115Sn* + e-

→ 115Sn + 2γ

LENS: R.S. Raghavan, Phys. Rev. Lett. 37, 259 (1976).

Scintillation Lattice:Voxels separated by clear films channel light down the coordinate axis by total internal reflection.

Spatial resolution of order of cell size over root 12.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 3: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The LENS-Sterile ProposalThe LENS-Sterile ProposalRaju Raghavan

1937-2011

115In + νe → 115Sn* + e-

→ 115Sn + 2γ

LENS: R.S. Raghavan, Phys. Rev. Lett. 37, 259 (1976).

Proposal to insert a Mega-Curie 51Cr source in the center of the LENS detector to observe multiple wavelengths of large Δm2 oscillations in a few meters.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 4: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Gallex, Sage, Gallex, Sage, 5151Cr and Sterile NeutrinosCr and Sterile Neutrinos

Giunti and Lavender (Mod. Phys. Lett. A22, 2499) noted that the low ratio of observed to expected ν +71Ge interactions in the Gallex and SAGE source experiments:

R = 0.88 ± 0.05

may be due to sterile neutrino oscillations.

Now commonly known as the “Gallium Anomaly”

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 5: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The Gallium AnomalyThe Gallium Anomalyνe disappearance in Gallex and SAGE from 51Cr and 37Ar source

9/14/20129/14/2012Jonathan LinkJonathan Link

C. Giunti and M. Laveder, Phys. Rev. C83, 065504 (2011).

Page 6: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Electron Capture Neutrino SourcesElectron Capture Neutrino SourcesElectron capture isotopes decay to two bodies and as such produce a mono-energetic beam of neutrinos at low energies.

51Cr + s-shell e- → 51V + νe (+ X-ray)

Sources such as this have played a critical role in the calibration of radiochemical experiments as a proxy source of solar neutrinos with a well known flux.

Advances in detector technology such as:

Borexino’s ability to do real time detection of 7Be neutrinos

have created new opportunities for groundbreaking neutrino physics using electron capture sources.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 7: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

90% of the time the capture goes directly to the ground state of 51V and you get a 750 keV neutrino.

10% of the time it goes to an excited state of 51V and you get a 320 keV photon plus a 430 keV neutrino.

K shell capture

L shell capture

5151Cr as a Mono-Energetic Neutrino SourceCr as a Mono-Energetic Neutrino Source

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 8: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Advantages of Advantages of 5151CrCr

1. Can be easily produced with thermal neutron capture (50Cr has a ~17 barn neutron capture cross section).

2. Has a long, but not too long, lifetime (39.9 days).Longer lifetimes require more neutrons to get high rates Shorter lifetimes lose too much rate in shipping and handling

3. Has one, relatively easy to shield, gamma that accompanies 10% of decays.5 cm of tungsten reduce 320 keV γ rate from 1 MCi to 1 Hz19 cm are needed to reduce 1 Ci of 1 MeV γ to 1 Hz

4. Mega-Curie scale sources have been produced by both Gallex and SAGE.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 9: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The High Flux Isotope Reactor (HFIR) at ORNLThe High Flux Isotope Reactor (HFIR) at ORNLHFIR operates at 85 MW with 23 operating days each fuel cycle.HFIR operates at 85 MW with 23 operating days each fuel cycle.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 10: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The High Flux Isotope Reactor (HFIR) at ORNLThe High Flux Isotope Reactor (HFIR) at ORNLThermal neutron flux of 2.5Thermal neutron flux of 2.5×10×101515 /cm /cm22/s in the target region./s in the target region.

40 times larger 40 times larger neutron flux than neutron flux than what was used by what was used by GallexGallex

4 times higher mean 4 times higher mean capture cross section capture cross section than what was used than what was used by SAGEby SAGE

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 11: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Solar Neutrino Detectors & Source Sterile Searches Solar Neutrino Detectors & Source Sterile Searches What works for LENS may work for other low energy solar neutrino detectors. (ES rate ~102× larger than 115In rate in LENS)

Mono-energetic neutrinos → known neutrino energy → You don’t need a charged current process

You still need good spatial resolution to fix L/E

Candidate detectors include:

Large liquid noble gas scintillating detectors: Clean, XMASS, Xenon100

Large LS detectors: Borexino, SNO+, Kamland

All these detectors would use electron elastic scattering

NC detection is another interesting idea (Formaggio et al, Phys. Rev. D 85, 013009)

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 12: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Large Detectors and Centrally Located SourcesLarge Detectors and Centrally Located Sources

(3+1)

(3+2)

A centrally located source maximizes the interaction rate per MCi.

With no oscillation the event rate is a flat function in radius.

A source inside the detector would need to be well shielded.

Models from the fit of Kopp, Maltoni & Schwetz arXiv:1103.4570 [hep-ph]

Initial 2 MCi Source for a 70 day Run

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 13: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Real Time Detectors Require Serious Real Time Detectors Require Serious γγ Shielding Shielding

energy (keV)

gam

mas

/sec

·10

keV

Possible source and W-alloy shielding configuration…

But what is the activity of W?

The 320 keV gamma (10% of decays) is a non-issue compared to the internal bremsstrahlung in ~0.05% of decays.

Spherical

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 14: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

9/14/20129/14/2012Jonathan LinkJonathan Link

Low-Background Counting of Tungsten AlloyLow-Background Counting of Tungsten Alloy

238U < 5mBq/kg (from 234Pa)232Th <40 mBq/kg (from 228Ac)40K < 220 mBq/kg214Bi = 150±50 mBq/kg

Signal Sample

Background

214Bi

214Bi 214Bi

214Pb

208Tl

40K

Measured at the Kimballton Underground Research Facility (KURF)

Background Subtracted

234Pa

228Ac

Page 15: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

SNO+ Source Deployment Case StudySNO+ Source Deployment Case Study

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 16: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Signal to Noise Ratio as a Function of RadiusSignal to Noise Ratio as a Function of Radius

Assuming a uniform detector BG out to the fiducial radius.

Detector BG grows as r2

Source BG falls as e−r/λ

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 17: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

3+1 contours from Kopp, Maltoni & Schwetz arXiv:1103.4570 [hep-ph]

Sensitivity based on a χ2 fit to signal and BG over the full energy range.

1.Not that sensitive to backgrounds

2.Source normalization and spatial resolution are critical to large Δm2 resolution.

3.Statistics limited measurement.

SNO+ SensitivitySNO+ Sensitivity

90% CL contours GLoBES

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 18: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

9/14/20129/14/2012Jonathan LinkJonathan Link

Borexino SensitivityBorexino Sensitivity

Source Under Detector

8.25 m

(See Aldo Ianni’s Talk)

10 MCi Source

Borexino is the only detector where we know this will work.

One can use the vast solar phase to subtract backgrounds.

Page 19: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

ConclusionsConclusions

1. Mega-Curie scale sources of electron capture isotopes are a excellent source of low energy, mono-energetic neutrinos.

2. 51Cr is likely the best source candidate for the future experimental program.

3. Sources as strong a 2 MCi could likely be produced at HFIR.

4. Such a source could be used for a sensitive search for eV sterile neutrinos with large, low-background scintillating detectors like Borexino and SNO+

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 20: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

9/14/20129/14/2012Jonathan LinkJonathan Link

Question Slides

Page 21: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Electron Capture Neutrino SourcesElectron Capture Neutrino SourcesIn 1973 Luis Alvarez proposed using a 65Zn source to calibrate Ray Davis’ chlorine detector.

Since then several such source have been proposed:

Isotope τ½ Eν Max Production Mechanism Gammas Notes65Zn 244 d 1.3 MeV Thermal neutron capture 770 & 345 keV (50%) Proposed by Alvarez51Cr 27.7 d 750 keV Thermal neutron capture 320 keV (10%) Proposed by Raghavan, used by Gallex and SAGE

152Eu 13 y 1.05 MeV Unknown 121 keV -1.7 MeV (100%) Proposed by Cribier and Spiro37Ar 34.9 d 812 keV Fast neutron 40Ca(n,α)37Ar Internal Brem. only Proposed by Haxton, used by SAGE

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 22: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The Gallex SourcesThe Gallex Sources• Made in the Siloé reactor in Gernoble, France (35 MW)

• Two sources produced from the same enriched Cr (38.6% 50Cr)

The average temperature across the Cr was ~525 K, which gives a flux averaged cross section of ~16 barns.

(My production estimates arescaled from these numbers assuming that their entire neutron flux is thermal.)

1.67 MCi1.67 MCi 1.89 MCi1.89 MCi

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 23: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

The Sage SourceThe Sage Source• Made in the BN-350 fast breeder reactor at Aktau, Kazakhstan.

• Irradiated 512.7 g of Cr (enriched to 92.4% 50Cr)

• Fast neutron flux of 5×1015/(cm2 s) was locally moderated near the Cr to give an average cross section of about 4 barns.

• Longer exposure: 90 days at 520 MW and 16 days at 620 MW.

Source strength of 516 kCi.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 24: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Source Production Scaling from SiloSource Production Scaling from Siloé to HFIRé to HFIRUsing

1. the initial amount of 50Cr, 2. the source strength after irradiation, and 3. the 51Cr decay rate,

The survival lifetime of 50Cr (τ50) in the Siloé Reactor is calculated to be about 13,500 days.

Similarly, τ50 for locations the HFIR core are calculated, accounting for the differences in core temperature and thermal neutron flux.

Location n Flux (cm−2s−1)

τ50

(days)Cr-50

(grams)Exposure

Time (days)Activity (MCi)

Siloé (GALLEX) 5.20E+13 13488 13715 23.83 1.721Small Vertical Experiment Facility 6.18E+14 984 908 23 1.504Large Removable Beryllium Facilitiy 1.40E+15 434 408 23 1.506Flux Trap Target 2.13E+15 286 272 23 1.502

This does not include 51Cr production from non-thermal neutrons.

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 25: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Check of the HIFR Production ModelCheck of the HIFR Production Model

In the 1980’s ORNL studied 51Cr production in HFIR using rods of natural chromium in the Small VXF and Large VXF locations.

With a 5.7 cm diameter rod in the Large VXF location they got 0.0673 MCi.

While the 3.1 cm rod in the Small VXF yielded 0.0707 MCi.

The thermal neutron attenuation length in natural chromium is 4.5 cm, so the difference from expectation at the large VXF may be due in part to self-shielding.

Fraction of n to Cr-51 Production 0.2806HFIR Location n Flux

(cm−2s−1)τ Prod. (days)

Grams Cr-50

Exposure Time (days)

Activity (MCi)

True Activiy

Large Vertical Experiment Facilities 4.24E+14 1435.43 392.2 41 0.1780 0.0673Small Vertical Experiment Facilities 6.18E+14 984.30 112.1 41 0.0737 0.0707

5353Cr (9.5%) has a larger n capture x-section than Cr (9.5%) has a larger n capture x-section than 5050Cr (4.4%)Cr (4.4%)

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 26: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Chromium Self-ShieldingChromium Self-Shielding

Self-shielding was also likely an effect at Siloé.

The neutron attenuation length in Siloé was about 4.1 cm.

The chromium was in two parallel boxes 50 cm high by 12.6 cm long by 1.4 cm wide.

Chromium scans from large VXF

9/14/20129/14/2012Jonathan LinkJonathan Link

Page 27: Experimental Approaches to Sterile Neutrinos Using Low Energy Neutrinos Jonathan Link

Sterile Neutrino White PaperSterile Neutrino White PaperFor more information see the Light Sterile Neutrinos: A White Paper (arXiv:1204.5379 [hep-ph])

Outline:1. Theory and Motivation (editors Barenboim & Rodejohann)2. Astrophysical Evidence (Abazajian & Wong)3. Evidence from Oscillation Experiments (Koop & Louis)4. Global Picture (Lasserre & Schwetz)5. Requirements for Future Experiments (Fleming & Formaggio)6. Appendix: Possible Future Experiments (Huber & Link)

Written from an international perspective for an audience including both the scientific community and funding agencies.

Visit http://cnp.phys.vt.edu/white_paper/

9/14/20129/14/2012Jonathan LinkJonathan Link