MiniBooNE and the Hunt for Low Mass Sterile Neutrinos 1H. Ray, University of Florida.

H. Ray, University of Florida 1

MiniBooNE and the Hunt for Low Mass Sterile Neutrinos


Intriguing Mysteries• Need a dark matter candidate

• What about dark radiation? (2σ)– Excess relativistic energy density at decoupling

• SM has no way for νs to acquire mass

• Anomalous results from neutrino sector– Short baseline (SBL) oscillation appearance expt. excesses (2.8 –

3.8σ)– Reactor neutrino flux deficit (3σ)– Radioactive source (Ga) deficit (2.7 – 3.1σ)– IceCube flux deficit due to observed GRBs (3.7x lower)


Not One-Stop Shopping!

Sterile mass Allow ν to acquire mass

Dark Rad, SBL,

Reactor, Ga

Dark matter candidate

Find via a direct search

100 – 160 GeV YES NO NO NO

20 – 30 GeV YES NO NO YES

keV - GeV YES NO YES YES

eV YES YES NO YES

Gnineko, Gorbunov, Shaposhnikov, arXiv:1301.5516


Not All Compatible!

• Short baseline oscillation expt. excesses: ~1 eV• Reactor + Ga deficits: ~1 eV• Cosmology dark radiation candidate: ~1eV

• ex:– SBL compatible with CMB in 3+1, 3+2

– Incompatible with cosmological mass constraints from CMB, Large Scale Structure (sum of all ν masses < 0.3 – 0.6 eV)

– Can be compatible with LSS if include initial lepton asymmetry

Riemer-Sørensen, Parkinson, Davis, arXiv:1301.7102


What to Do?

• Propose experiments to further explore each anomaly

• Expts. to perform more precise measurements and searches for eV scale sterile neutrinos in reactors, radioactive decay, and SBL experiments

• My focus: SBL appearance results and prospects for the future

H. Ray 6

SBL Anomalies: LSND• 800 MeV proton beam + H20

target, copper beam stop

• 167 ton tank, liquid scintillator, 25% PMT coverage

• E ~20-50 MeV• L ~25-35 meters

• anti-e + p e+ + n – n + p d + (2.2 MeV)


SBL Anomalies: LSND

• LSND observed excess of anti-νe in an anti-νμ beam

• Excess: 87.9 ± 22.4 ± 6.0 (3.8σ)Phys. Rev. Lett. 77:3082-3085 (1996)Phys. Rev. C 58:2489-2511 (1998)Phys. Rev. D 64, 112007 (2001)

Fit to oscillation hypothesis

Backgrounds Posc = sin22θ sin2 1.27 Δm2 L

E

Δm2 = 1.2 eV2

sin22θ = 0.003


MiniBooNE vs LSNDLSND• (anti) Neutrino beam from

accelerator (DAR, average Eν 35 MeV)

• νμ too low E to make μ or π

• Proton beam too low E to make K

MiniBooNE• Neutrino beam from accelerator

(DIF, average Eν 800 MeV)

• Detector placed at 500 m from neutrino beam creation point, preserve LSND L/E

• New backgrounds: νμ CCQE and NC π0 mis-id for oscillation search

• New backgrounds: intrinsic νe from K decay (0.5% of p make K)


SBL Anomalies: MiniBooNE• 2.8σ antineutrino mode• 3.4σ neutrino mode• 3.8σ combined excess

– All in 200 – 1250 MeV range• 7σ stat – so not a statistical

fluctuation!

• Antineutrino excess consistent with LSND

• Neutrino excess not so much

• All backgrounds fully constrained • Need some new anomalous

background process to explain low energy excess, if not invoking a sterile neutrino explanation

Phys.Rev. Lett. 110, (2013) 16801

11.27 x 1020 POT

6.5 x 1020 POT


SBL Anomalies: Summary

Antonello, et al. arXiv:1307.4699

Δm2 = 3.14 eV2

sin22θ = 0.002Δm2 = 0.043 eV2

sin22θ = 0.88


Resolving the SBL Mystery

• Need definitive experiments – no more carving out small portions of the allowed sterile neutrino phase space– No longer good enough to see an excess or deficit – need to see

those wiggles!– Need to see wiggles as a function of energy!

• Need them to be cost-effective• Preferably short-term, to use as input to longer-term

projects

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Proposed Experiments

H. Ray, University of Florida

de Gouvea et al, arXiv:1310.4340

RUNNING• MicroBooNE

• MINOS+

PROPOSED• ICARUS /

NESSIE

• J-PARC

• LAr1-ND / LAr1

• MiniBooNE+

• nuSTORM

• OscSNS


MiniBooNE Low-E Excess

• Largest backgrounds in region of excess are muon neutrino Neutral Current – mis-ID neutral pions and gammas that look identical to e+/e- in our detector


MiniBooNE Low-E Backgrounds

• Both NC backgrounds are constrained by in-situ measurements

• NC π0 directly measured• NC γ (radiative Δ decay) constrained to NC π0

• Also, recent theoretical calculations agree with MBPhys. Rev. D 81 (2010) 013005


MiniBooNE Low-E Excess• Photons or electrons?

MicroBooNE MiniBooNE+


Booster Neutrino Beam at FNAL

dirt

target and horn(174 kA)

π+

π-

K+

K0

✶

✶

μ+

✶

decay region(50 m)

oscillations?

FNAL booster(8 GeV protons)

Neutrinos from pions decaying in flightMean neutrino E ~500 MeV


MicroBooNE

• 170 ton LAr TPC, ~450 m from neutrino creation point• Beautiful separation between electrons and photons

• Different target nucleus from MiniBooNE• Lower event rates – same POT exposure as MB ν dataset means only a few

10s of events• Has less self-shielding b/c smaller, may be more prone to dirt backgrounds

• Will begin collecting data ~this summer• Run for 3 years, 2.2e20 POT / year, neutrinos only

1 GeV electron shower 1 GeV π0 decay


MiniBooNE+• Add scintillator to MiniBooNE to enable

reconstruction of 2.2 MeV neutron-capture photons

• Re-run neutrino mode oscillation search

• Neutron-capture enables separation of CC oscillation events from NC backgrounds– CC: e + n e- + p

• 1-10% of all interactions will produce a neutron

– NC: μ + 12C Δ or π0 + p or n • equal chances of getting n or p• n + p d + 2.2 MeV

Reconstructed vs True Eν, Signal

Reconstructed vs True Eν, Backgrounds

arXiv 1310.0076


MiniBooNE+• Need to know the (1-10%) vs 50% very well for this

analysis!

• These numbers come from previous data/models

• Will measure in MB+

• Can measure n fraction in νμ CC events (not the oscillation channel)

• Can measure n fraction in pristine NC π0 events


MiniBooNE+• Same as previous analysis, same

excess

• Require n-capture events– Red: if excess is truly due to CC νe

events, excess disappears– Blue: if excess is truly due to a NC

process (ie not oscillations), excess remains

• Yields 3.5σ NC/CC separation for this test, for combined 5σ MB excess


MiniBooNE+ and MicroBooNE• Complementary Effort• MicroBooNE: use photon/electron separation • MB+: use nucleons (neutrons), no energy threshold

• MicroBooNE: precision tracking, low event rates• MB+: Cerenkov/calormetric reconstruction, higher event rates

• MB+: larger fiducial volume, concurrent running may help with dirt backgrounds

• Important to keep 800 ton MB (CH2) running in the BNB as the event rates will be higher than any of the new or proposed LAr devices. Very important to understand any changes in beam.


SBL Anomalies

MINOS+ LAr1ICARUS

OscSNS

nuSTORM

J-PARC

LSND, MB ((anti)νμ (anti)νe, (anti)νe app)sensitive to combo of θ14 and θ24

Reactors (νe disappearance)sensitive to θ14

MINOS+ (νμ or anti-νμ CC disappearance) sensitive to θ24, little sensitivity to

θ14


Liquid Argon At Fermilab• Uses MiniBooNE’s beamline

• microBooNE can distinguish electrons from photons

• need 2nd detector to tell if the excess occurs at a distance or is intrinsic to the beam

• microBooNE won’t collect anti-ν data because of their smaller size– lower xsec means almost no events or too long to run


LAr1-ND

C. Adams, et al., arXiv:1309.7987

• 100 m = in existing SciBooNE enclosure

• 40 ton fiducial volume LArTPC

• 4.9 m length, along the beam direction (7 m wide, ~11.5 m high)

• muon detector downstream

• Use as prototype development for LBNE technology

• 1 kton LArTPC at 700 m

• Run for last year of microBooNE’s run, collect 2.2e20 POT

• Total run time will have 48 events in microB, 310 in LAr1-ND, assuming MB ν mode excess, and that the excess is not L dependent (vs MB’s 129)


LAr1-ND

4σ coverage of best fit point around 1 eV2, with full microBooNE data set and 1 year of LAr1-ND running

C. Adams, et al., arXiv:1309.7987


ICARUS at FNAL

• 2 detectors, one at ~150 m and one at 700 m– T150 = 200 tons of Ar (100 ton fiducial)– T600 = 760 tons of Ar (430 ton fiducial)– Can’t use SciBooNE Hall – need a new hole in ground

• Near = larger mass than LAr1-ND• Far = less mass than LAr1, plus B field (1T)

• Need 2 years from funding agency green-light to upgrade, then move to FNAL– Thermal shields, external insulation, pmts photo-detectors, B

fieldarXiv:1312.7252


ICARUS at FNAL

Neutrino Run6.6e20 POT

Anti-Neutrino Run +B

field11e20

POT


NuMI Neutrino Beam at FNAL

• Movable target and magnetic focusing horn– Tunable neutrino beam energy– Run in neutrino, anti-neutrino mode

Graphite target


MINOS+

• Long baseline experiment• L/E ~500 km/GeV (atm. Δm2)

• 2 detectors: near & far• Magnetized, tracking sampling calorimeters

• Measure Δm223, sin2(2θ23) for ν, anti-ν

Graphite target


MINOS+• Runs MINOS near and far detectors in the

NuMI medium energy configuration– 3 yrs, starting 2013

• CC disappearance between both detectors• Exploring odd dip for MINOS• NC events for sterile search (θ34)

Green: excluded by νμ disappearanceBlue: excluded by NC disappearance

MINOS+ Fermilab Proposal 1016


OscSNS

32

- absorbed by target

+ DARMono-Energetic!= 29.8 MeV

E range up to 52.8 MeV

• Spallation Neutron Source at Oak Ridge

• ~1 GeV protons+Hg target (1.4 MW)

• Free source of neutrinos


OscSNS Detector• Homogeneous liquid scintillator detector

– Mineral oil + b-PBD– 8 m diameter x 20.5 m length– ~800 tons, 25% PMT coverage

– Flexible arm deployment system for 1 – 50 MeV

calibration sources – 16N, 8Li, 252Cf

• 60 m in the backward direction, ~150 degrees from incident proton beam

Proton beam

OscSNS Detector HallarXiv:1307.7097


OscSNS nm -> ne Experiment vs LSND

• More Detector Mass (x5)

• Higher Intensity Neutrino Source (x2)

• Lower Duty Factor (x1000) (less cosmic background)

• Separation of nm & ne / anti-nm fluxes with timing

• Negligible DIF Background (backward direction)

• Lower Neutrino Background (~x2) (60m vs 30m)

• For LSND parameters, expect ~100-200 ne oscillation events & ~50 background events per year!

(Assuming Dm2 < 1 eV2)


Oscillation Goals

• anti-nm -> anti-ne appearance

• ne -> ns disappearance

• nm -> ns disappearance

• nall -> ns disappearance


Appearance Sensitivity

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anti-nm anti-ne appearance sensitivity for 1 & 3 years of running:

anti-ne p e+ n; n p d g (2.2 MeV)

LSND & KARMENAllowed

LSND & KARMENAllowed

CONTINUOUS!

Already at 5σ!

50% detector efficiency, ~85% Ee cut efficiency, oscillation probability of 0.26%


Appearance Sensitivity

Assuming 5y of data & sin22q = 0.005, Dm2=1 eV2Assuming 5y of data & sin22q = 0.005, Dm2=4 eV2

L/E (m/MeV) L/E (m/MeV)

Statistical errors, 20% bgd

P(

n m ->

n e )

CONTINUOUS!50% detector efficiency, ~85% Ee cut efficiency, oscillation probability of 0.26%


Disappearance Sensitivity

ne C e- Ngs , Ngs Cgs e+ ne

Assuming 5y of data & sin22q = 0.15, Dm2 = 1 eV2 Assuming 5y of data & sin22q = 0.15, Dm2 = 4 eV2

L/E (m/MeV) L/E (m/MeV)

P(

n e ->

n s )

50% detector efficiency

Statistical errors, 1% bgdCONTINUOUS!


J-PARC Neutrino Beamline• Spallation Neutron Source at J-PARC

• Muons DAR to produce neutrinos

• Primarily μ+ e+ anti-νμ νe

• 50 ton fiducial mass liquid scintillator detector at 17 m

• Use CCQE appearance analysis (anti-νμ anti-νe)

• Use νe CC disappearance

• Above ground, may have issues with neutron backgrounds

4 years operation

Blue = 5σ CLGreen = 3σ CL

T. Maruyama et al., arXiv:1310.1437


Sensitivitiesνμ νe, νe νμ appearance searches

neutrino and anti-neutrino modes

App only fit + LBL reactors, Kopp, Machado, Maltoni, Schwetz, arXiv:1303.3011

Global fit, Giunti, Laveder, Li, Long, arXiv:1308.5288

• ICARUS curve is for CERN, not FNAL

• Difference in opinion of how to do fits


Abazajiana, et al. arXiv:1204.4219


Event Rates

LAr1-ND100 m

ICARUS150 m, E < 5 GeV

ICARUS700 m, E < 5

GeV

MiniBooNE200 to 1250 MeV

OscSNS J-PARC

νμ CC Inclusive(anti-νμ)

2,500,000(291,000)

387,000(56,900)

νe CC Inclusive(anti-νe)

26,200(1,780)

4,460(312)

νμ νe

app (1.15 eV2, 1.5e-3)

310 signal322 bgd

400, 380 signal 2,520, 1860 bgd(E < 5 GeV, 2 GeV)

233 sig (expect)162 sig (obs)

790 bgd

anti-νe p e+ n app (1.2 eV2, 3e-3)

100 sig (expect) 78 sig (obs)

400 bgd

480 signal168 bgd

337 signal494 bgd

νe + 12C e- 12Ngs

dis9412 signal

96 bgd22,934

2.2e20 POT (1 yr, full run)

200 – 475 MeV

Neutrino: 6.6e20 POT (3 yr full run)Anti-neutrino: 11e20 POT (5 yr full run)

12e22 POT(4 yrs, full run)

10.96e23 POT(4 yrs)same as ICARUS


Cost Estimates


J-PARC μ-DAR anti-νμ anti-νe app. J-PARC small (~<5 M) Same target nucleon

as LSND, MB

Shorter-term


Summary and Conclusions• Many outstanding mysteries in the neutrino sector

• Even mysteries that indicate a similar solution aren’t compatible

• Need new era of 5σ, definitive, and cost-effective experiments to explore & resolve

• Many experiments on the horizon, need to decide as a community what to push, to get full funding

MiniBooNE and the Hunt for Low Mass Sterile Neutrinos 1H. Ray, University of Florida.

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Transcript of MiniBooNE and the Hunt for Low Mass Sterile Neutrinos 1H. Ray, University of Florida.