sign in sign up
<<
Home , Kaon

A new way to probe the sterile Kaon decay-at-rest

Joshua Spitz, MIT 2/5/2013 New Directions in Neutrino Physics, Aspen The Liquid Scintillator Neutrino Detector Antineutrinos from an accelerator seem to appear

LSND observed ⌫ ⌫ at 3.8σ • µ ! e significance with Δm2~1 eV2. • That’s odd. There are two independent mass splittings in the three neutrino picture and they are precisely measured.

Joshua Spitz MIT The Liquid Scintillator Neutrino Detector Antineutrinos from an accelerator seem to appear! ) 4 /c 2 | (eV 2 m

Δ LSND observed ⌫ ⌫ at 3.8σ | µ e 10 • ! significance with Δm2~1 eV2. • That’s odd. There are two 1 independent mass splittings in the three neutrino picture and they

LSND best fit are precisely measured. 10-1 LSND 90% CL

10-4 10-3 10-2 10-1 2 sin (2θµe)

Joshua Spitz MIT The MiniBooNE anomalies

⌫ ⌫ µ ! e

Neutrinos and antineutrinos from an accelerator seem to appear!

⌫ ⌫ µ ! e

Joshua Spitz MIT The reactor anomaly

Reactor antineutrinos seem to disappear! ⌫ ⌫ e ! x

0.927 0.023 ± observed/expected antineutrino rate

Joshua Spitz MIT Limits (let’s not forget)

• There do exist a number of strict limits on νμ/νe disappearance and νe appearance. • In particular, the lack of observed neutrino/antineutrino disappearance causes issues when trying to form a coherent picture of the .

0.01-0.10? <0.1 0.001?

Joshua Spitz MIT Global fit • A global, all experiment analysis certainly leaves room for the possibility of at least one sterile neutrino. Global neutrino Global antineutrino

Ignarra, et al. arXiv:1207.4765

Joshua Spitz MIT Present status • A number of experiments hint at a new neutrino mass eigenstate around 1 eV. • A definitive probe of the sterile neutrino is necessary.

Joshua Spitz MIT If (neutrino) history has taught us anything it is this:

Pursue experimental anomalies

Joshua Spitz MIT How to probe the sterile neutrino?

1. Make a lot of *. 2. Count them. 3. Compare to how many you expected.

Joshua Spitz MIT How to probe the sterile neutrino?

1. Make a lot of neutrinos*. 2. Count them. 3. Compare to how many you expected.

*Choose a smart baseline (L) and energy (E) so that you are probing the relevant oscillation parameter space (Δm2, θ).

2 2 2 m L GeV P ⇥,=⇥ = sin (2)sin 1.267 E eV2 km e.g. (L, E)=(240 m, 235 MeV) probes Δm2 ~1.2 eV2

Joshua Spitz MIT A sterile neutrino search w/ kaon decay at rest

J. Spitz, PRD 85 093020 (2012)

Detector

Monoenergetic (235 MeV) neutrino! Backgrounds {

Joshua Spitz MIT A sterile neutrino search w/ kaon decay at rest

J. Spitz, PRD 85 093020 (2012)

Detector

Monoenergetic (235 MeV) neutrino! Backgrounds {

Joshua Spitz MIT A sterile neutrino search w/ kaon decay at rest

⌫ ⌫ ? µ ! e

9 Neutrino flux ×10

/MeV] 25 2

+ + νµ from K → µ νµ 20

15

/(3E20 POT)/m Signal ν [ 10 (νe) Φ

5

0 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 Eν (GeV) Joshua Spitz MIT A sterile neutrino search w/ kaon decay at rest

⌫ ⌫ ? µ ! e

9 SignalNeutrino flux ×10 ν from K+→ π0e+ν , K0→ π-e+ν e e L e

/MeV] 25 2

+ + νµ from K → µ νµ 20

15

/(3E20 POT)/m Signal ν [ 10 (νe) Φ Background

5

0 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 Eν (GeV) Joshua Spitz MIT A sterile neutrino search w/ kaon decay at rest

Detector ⌫ ⌫ ? µ ! e Neutrino rate 8 + + νe from K → µ νµ, P[νµ → νe]=0.001 ⌫ n ep + 0 e 7 ν from K → π0e+ν , K → π-e+ν ! e e L e • The concept is analogous to a 6 Signal region neutrinoless double beta decay 5 search. 4 3 You look for an excess near the Background • 2 Signal (νe) endpoint of a well understood and events/MeV/(2 kton)/(2E21 POT) 1 measured background distribution. 0 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 Erec (GeV) Joshua Spitz MIT Background prediction is in-situ

8 + + νe from K → µ νµ, P[νµ → νe]=0.001 7 ν from K+→ π0e+ν , K0→ π-e+ν e e L e 6 Signal region

5

4 Background 3

2 Signal (νe)

events/MeV/(2 kton)/(2E21 POT) 1

0 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 Erec (GeV) Identify a signal region and measure background in sidebands Joshua Spitz MIT KDAR misID?

• Is ID (muon vs. ) a problem? The 235.5 MeV νμ to νe ratio at Posc=0.001 is 700:1. • Detector discrimination power. • The KDAR appearance signal is expected in a very tight energy window. • All fast muon interactions leading to an electron/gamma (decay, radiative capture, etc.) result in a significant amount of missing energy.

Muon Electron ∑ ∑ protons Arbitrary units Arbitrary units

0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.05 0.1 0.15 0.2 0.25 0.3 Kinetic energy (GeV) Kinetic energy (GeV) A sterile neutrino search w/ kaon decay at rest ) 4 /c • This experiment can be 2

accomplished at a number of | (eV 2

intense >3 GeV facilities m Δ around the world. | • Gives >5σ sensitivity to most of the LSND allowed region with a simple counting measurement.

Proton target (Tp) Copper (8 GeV) Exposure 2 1021 protons on target ⇥ Baseline 160 m Neutrino target 40Ar (22 ) Neutrino target mass 2 kton 2 sin (2θμe)

J. Spitz, PRD 85 093020 (2012)

Joshua Spitz MIT KDAR requirements

• A lot of protons

• A big detector

• Energy resolution

Joshua Spitz MIT So, that’s the original “KDAR” idea.

But, wouldn’t it be even better to study neutrinos from kaon and /muon decay-at-rest with the same experiment?!

Yes.

Joshua Spitz MIT “piDAR” (LSND-like)

Target GeV-scale protons Kaons

Neutrino flux from pion and muon decay-at-rest ⌫ ⌫ ? µ ! e

Joshua Spitz MIT Sterile neutrino experiment at J-PARC’s MLF (working group)

Joshua Spitz MIT inos Neutrons @ JPARC

Joshua Spitz MIT piDAR + KDAR Neutrino source Liquid scintillator detector (piDAR requires free protons for ⌫ p e + n ) e !

protons

Hg target

Veto barrier Geant4 simulation Detector parameters are under consideration (baseline, active volume, etc.)

Joshua Spitz MIT T=3 GeV protons on 'semi-realistic'piDAR Hg target (Geant4) ⌫ p e+n e ! 10-1 ⌫µ ⌫e ? ! νµ

/MeV/POT -2

10ν νµ ν 10-3 e Background νe 10-4

10-5

10-6

10-7

10-8 0 0.05 0.1 0.15 0.2 0.25 0.3 Eν (GeV)

Joshua Spitz MIT T=3 GeV protons on 'semi-realistic'KDAR Hg target (Geant4) ⌫ n ep e ! 10-1

νµ ⌫µ ⌫e ?

/MeV/POT -2

10ν ! νµ ν 10-3 e

νe 10-4

-5 Background 10

10-6

10-7

10-8 0 0.05 0.1 0.15 0.2 0.25 0.3 Eν (GeV)

Joshua Spitz MIT T=3 GeV protons on 'semi-realistic' Hg target (Geant4) 12 12 ⌫ C e N e ! gs

-1 10 ⌫e ⌫e ? ! νµ

/MeV/POT -2

10ν νµ ν 10-3 e

νe 10-4

10-5

10-6

10-7

10-8 0 0.05 0.1 0.15 0.2 0.25 0.3 Eν (GeV)

Joshua Spitz MIT T=3 GeV protons on 'semi-realistic' Hg target (Geant4) 12 12 ⌫ C ⌫ C⇤ µ ! µ 10-1 ⌫ ⌫ ? µ ! µ νµ

/MeV/POT -2

10ν νµ ν 10-3 e

νe 10-4

10-5

10-6

10-7

10-8 0 0.05 0.1 0.15 0.2 0.25 0.3 Eν (GeV)

Joshua Spitz MIT Beam timing

106

105 piDAR steady state background is reduced

arbitrary units by ~10,000 compared to LSND. 104 Allows separation of neutrinos from pion 3 10 and muon. total from 102 from µ KDAR steady state background is negligible. from K 10

1 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Global time (ns)

540 ns Beam structure 80 ns 80 ns Joshua Spitz MIT Advantages over LSND (in terms of piDAR only)

LSND MLF experiment Notes

Baseline 30 m Under consideration

Detector in front Detector behind Reduced decay-in-flight Orientation of beam beam background

Beam power 0.8 MW 1 MW (eventually)

600 μs, Beam pulse width 80 ns (x2), 25 Hz Reduced steady-state background 120Hz More statistics (but higher Beam kinetic energy 798 MeV 3000 MeV background)

Detector mass 167 ton Under consideration

Liq. scint. w/ higher QE, Detector technology Liq. scint. photocoverage

Joshua Spitz MIT Experimental parameters are still under consideration Example 1: 5 year, 500 ton, 40 m length, 40 m mid-baseline 2

) 10 4 /c 2

π DAR 5σ sensitivity | (eV 2

m 10 KDAR 5σ sensitivity Δ |

1

-1 10 LSND 90% CL

10-4 10-3 10-2 10-1 2 sin (2θµe)

Joshua Spitz MIT Experimental parameters are still under consideration Example 2: 5 year, 500 ton, 20 m length, 60 m mid-baseline 2

) 10 4 /c 2

π DAR 5σ sensitivity | (eV 2

m 10 KDAR 5σ sensitivity Δ |

1

-1 10 LSND 90% CL

10-4 10-3 10-2 10-1 2 sin (2θµe)

Joshua Spitz MIT Experimental parameters are still under consideration Example 3: 5 year, 500 ton, 20 m length, 120 m mid-baseline 2

) 10 4 /c 2

π DAR 5σ sensitivity | (eV 2

m 10 KDAR 5σ sensitivity Δ |

1

-1 10 LSND 90% CL

10-4 10-3 10-2 10-1 2 sin (2θµe)

Joshua Spitz MIT A definitive probe • Sensitivity to oscillations in multiple channels and with neutrino and antineutrino! • Provides discovery confidence. • If it exists, precision measurements of sterile properties.

Joshua Spitz MIT Current status

• 1 ton of scintillator has recently been brought from KEK to the MLF. • The scintillator will be used to measure the fast and neutron capture rates for determining background rate and measurement feasibility at a near location.

On-going efforts for background studies by KEK and JAEA

Joshua Spitz MIT Conclusions • Kaon decay-at-rest is a new idea to search for the sterile neutrino. A >3 GeV proton source is required along with a lot of protons, a big detector, and strong energy resolution.

• KDAR can be combined with LSND-like pion/muon decay- at-rest in a single-detector-experiment for a sensitive sterile search with both neutrinos and antineutrinos and with both appearance and disappearance.

• This idea is currently being pursued for possible deployment at the 3 GeV, 1 MW Material and Life Science Facility at JPARC.

Joshua Spitz MIT Backup Assumptions PID and energy resolution

Separating and protons (LSND) 25% photocoverage, high QE

piDAR assumption: 5% neutrino energy resolution

KDAR assumptions: 5% electron energy resolution, 20% proton energy resolution

Depends on Cerenkov cone, angle, and time. What do we know about the light sterile neutrino? • Sterile equals no interactions.

We know the Z decays into three neutrinos.

Z-boson width

• Can participate in oscillations with active flavors. ⌫ ⌫ ,⌫ ⌫ ,⌫ ⌫ e ! s µ ! s ⌧ ! s Joshua Spitz MIT Where does it fit?

New neutrino mass state • The observation of neutrino mass implies that there can be sterile, right-handed neutrinos. So, this is not unexpected. • A light sterile neutrino would have profound effects on: • Radiation density in the early universe. • Supernova evolution. • Possible warm dark candidate? • Active neutrino oscillations and in general.

Joshua Spitz MIT Current status

• We are considering deploying the KEK 250 L LArTPC at the MLF. • Can measure kaon/proton yield with 235.5 MeV νμ events. • ~250 fully-contained kaon-induced νμ events/year (500 kW)! • There is a lot of available as well. • Ongoing effort is focussed on a charged particle beam test by J-PARC Test Experiment T49 (KEK, Iwate U., ). T32 (KEK, Waseda U, Iwate U., ETH-Zurich)

(From test run, Fall 2010)

Joshua Spitz MIT