Reactor Neutrinos Sterile Neutrino Searches with Precision - - PowerPoint PPT Presentation

Reactor Neutrinos

Sterile Neutrino Searches with Precision Measurements at Very Short Baselines

Jim Napolitano Temple University for the PROSPECT collaboration

Amherst Center for Fundamental Interactions 14-16 December 2015

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Distance (m) 10

2

10

3

10 Data / Prediction 0.6 0.8 1 1.2 Previous data Daya Bay Global average Experiments Unc. σ 1- Model Unc. σ 1-

Reminder: The Reactor Neutrino Anomaly

2

Deficit Is the deficit due to antineutrino disappearance?

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Distance (m) 10

2

10

3

10 Data / Prediction 0.6 0.8 1 1.2 Previous data Daya Bay Global average Experiments Unc. σ 1- Model Unc. σ 1-

Reminder: The Reactor Neutrino Anomaly

2

Deficit Is the deficit due to antineutrino disappearance? “Kopp Best Fit”: Point Source @4 MeV

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Reminder: The Status of Sterile Neutrinos

3

Δm2 ≈few ev2 and sin22θ “not so small”

14

θ 2

2

sin

2 −

10

1 −

10 1 ]

2

[eV

14 2

m ∆

2 −

10

1 −

10 1 10

Sensitivity: CL σ Disappearance (Giunti), 2

e

ν SBL Reactor + Gallium Anomaly (LSN), 95% CL SBL Reactor Anomaly (Kopp), 95% CL Disappearance Expts (Kopp), 95% CL

e

ν All Gallium Anomaly (Kopp), 95% CL

Gallium PRC 83(2011)065504 BOONE, MiniBOONE AnnRev 63(2013)45 Global fits JHEP 1305(2013)050 PRD 88(2013)073008 References

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Reactor Anomaly and Reactor Calculations

4

AD1 AD2 AD3 AD4 AD5 AD6 Model / GW / day

2

cm

• 18

10 × Y 1.5 1.6 1.7 / fission

2

cm

• 43

10 ×

f

σ 5.8 6.0 6.2 6.4 Daya Bay (stat.) Daya Bay w/ fission fraction corr. (stat.) Daya Bay near site combined (syst.) Huber + Mueller ILL + Vogel

Power Reactors: Mixture of 235U, 239Pu, 241Pu, 238U

Reference: arXiv 1508.04233

ILL+Vogel (1980’s): e− spectra, plus calculation for 238U Huber + Mueller (2011): Inversion with β-decay corrections

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

More Reactor Surprises: The “Bump”

5

Prompt Positron Energy (MeV) 2 4 6 8 Entries / 250 keV 5000 10000 15000 20000 Data Full uncertainty Reactor uncertainty ILL+Vogel Integrated Prompt Energy (MeV) 2 4 6 8 Ratio to Prediction 0.8 0.9 1 1.1 1.2

(Huber + Mueller) Prompt Energy (MeV) 2 4 6 8 contribution

2

χ 4 − 2 − 2 4 )

i

χ ∼ ( 10 10 10 10 10 10 1

arXiv 1508.04233

1 2 3 4 5 6 7 8

Events / 0.2 MeV

5000 10000 15000

Data MC

Near

(a)

Prompt Energy (MeV) 1 2 3 4 5 6 7 8

(Data - MC) / MC

0.1 − 0.1 0.2

Events / 0.2 MeV

(Data - MC) / MC

arXiv 1511.05849

Daya Bay RENO

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

➥ New “Direct” Reactor Calculations

6

PRL 114(2015)012502 PRD 92(2015)033015

]

• 1

fission

• 1

) [MeV

ν

S(E ×

ν

σ 0.1 0.2 Nuclear Calculation Conversion, Huber

• β

Conversion, Mueller

• β

Nuclear Calc., Fallot

(c)

Antineutrino Energy [MeV] 2 3 4 5 6 7 8 )

ν

(E

conv.

• β

) / S

ν

S(E 0.8 0.9 1 1.1

Daya Bay RENO Double CHOOZ

(d)

2 3 4 5 6 7 EPrompt (MeV) 0.9 0.95 1 1.05 1.1 1.15 Normalized Ratio to Huber-Mueller

Huber-Mueller uncert. JEFF-3.1.1 ENDF/B-VII.1 Daya Bay

1 2 3 4 5 6 7

EPrompt (MeV)

0.9 0.95 1 1.05 1.1 1.15

Normailzed ratio to Huber-Mueller

Huber-Mueller uncert. JEFF-3.1.1 ENDF/B-VII.1 RENO

Different approaches (and nuclear data bases) give different results, and may point to 238U as the source of “The Bump.”

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Nuclear Power Plant Reactors

7

Daya Bay, et.al., use “Near+Far” for oscillations, but…

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Nuclear Power Plant Reactors

7

Daya Bay, et.al., use “Near+Far” for oscillations, but…

• Nuclear fuel

evolution uncertainty

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Nuclear Power Plant Reactors

7

Daya Bay, et.al., use “Near+Far” for oscillations, but…

• Nuclear fuel

evolution uncertainty

• Relatively

large size of reactor core

(Research)

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Nuclear Power Plant Reactors

7

Daya Bay, et.al., use “Near+Far” for oscillations, but…

• Nuclear fuel

evolution uncertainty

• Relatively

large size of reactor core

(Research)

• Hard to get within meters of

the reactor core

• Restricted information and

no control over source

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Nuclear Power Plant Reactors

7

➥ Nuclear power plants are not ideal sources for Sterile Neutrino Searches Daya Bay, et.al., use “Near+Far” for oscillations, but…

• Nuclear fuel

evolution uncertainty

• Relatively

large size of reactor core

(Research)

• Hard to get within meters of

the reactor core

• Restricted information and

no control over source

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Precision Experiments at Research Reactors

8

See http://aap2015.phys.vt.edu

• STEREO @ ILL
• J. Phys. Conference Series 593(2015)012005
• SOLID @ BR2 MTR

https://www2.physics.ox.ac.uk/research/mars- project/solid

• NEOS @ HANBIT #5 (Power Reactor!)

(See AAP conference presentations)

★ PROSPECT @ HFIR

Recent full description at arXiv:1512.02202

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

SoLiD and STEREO

9

SoLi∂

reactor core SoLid detector modules BR2 ha 5.5 m

distance Energy

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

PROSPECT

10

A PRecision Oscillation and SPECTrum measurement using an array of functionally independent detectors

• Collaboration: BNL, Drexel, IIT, Le Moyne, LLNL,

NIST, ORNL, SYSU, Temple, Tennessee, Waterloo, William & Mary, Wisconsin, Yale

• High Flux Isotope Reactor (HFIR) at ORNL
• Phase I: Single movable detector ≈7m from core,

definitive exclusion of “Kopp Best Fit” region

• Phase II: Second detector at greater distance, for

complete exclusion of allowed region See arXiv:1512.02202

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Schematic of the Experiment

11

180 cm Phase I Detector HFIR Core 7 to 10 meters

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

ν̅e ν̅e

Liquid Scintillator p

e+ 15 cm

Schematic of the Experiment

11

180 cm Phase I Detector HFIR Core 7 to 10 meters

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

ν̅e ν̅e

Liquid Scintillator p

e+ 15 cm

Schematic of the Experiment

11

180 cm Phase I Detector HFIR Core 7 to 10 meters n

n+6Li→α+t

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

ν̅e ν̅e

Liquid Scintillator p

e+ 15 cm

Schematic of the Experiment

11

180 cm Phase I Detector HFIR Core 7 to 10 meters n

n+6Li→α+t

Detection is contained in single cell (or neighbors)

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Realization: Phase I

12

b#

• HFIR

Core Reactor Shielding

PROSPECT Phase I

AD-I LiLS Segments Passive Shielding

(a) (b) AD-I Active Volume (d) AD-I Segments and Containment

14.6 cm 14.6 cm Separator Corner Rod 170.0 cm Section A-A 146.5 cm 200.0 cm 120.0 cm 175.3 cm 230.0 cm 120 cm

(c) AD-I Unit Segment

• ptical fiber

fiber+sleeve+diffuser detector segments antineutrino detector with optical and source calibration source deployment system with string and guide tubes motor system source path detector segments

• ptical calibration system

with string and guide tubes routing between segments and PMT modules

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Extended Capability: Motion & Phase II

13

HFIR Core

Antineutrino Detector I Antineutrino Detector II

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Extended Capability: Motion & Phase II

13

HFIR Core

Antineutrino Detector I Antineutrino Detector II

In Phase I the detector can move ≈3m

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Extended Capability: Motion & Phase II

13

HFIR Core

Antineutrino Detector I Antineutrino Detector II

In Phase I the detector can move ≈3m Second detector for greater coverage in Phase II

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

High Flux Isotope Reactor (HFIR)

14

• 85 MW, highly enriched 235U, light water moderated
• Regular reactor-on periods lasting 25 days, with

roughly equal periods of down time in between

• Well understood reactor core, including simulation

https://neutrons.ornl.gov/hfir

37.5 cm 60 cm

Fuel

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Dealing with Backgrounds

15

Nucl.Instrum.Meth. A806 (2016) 401-419

!3 !2 !1 1 2 3 4 5 y (m) 1 2 3 4 x (m)

3000 2500 2000 1500 1000 500

3000 2000 1000

z = 0.1 m

(1)! (2)! (3)! (4)!

Energy (MeV) 1 2 3 4 5 6 7 8 Counts/MeV/s 1 10

2

10

3

10

• Config. (1)
• Config. (2)
• Config. (3)
• Config. (4)

Identifying neutron capture signals via Pulse Shape Discrim. Also helps identify proton recoil from neutron scattering.

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Implications from P20 Prototype

16

(b)

(c)

μ μ

Reactor Off

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Implications from P20 Prototype

16

(b)

(c)

μ μ

Reactor Off

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Implications from P20 Prototype

16

(b)

(c)

μ μ

Reactor Off Reactor background effectively eliminated

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Expected Signal from ν̅e Capture

17

prompt ionization [MeV] prompt ionization [MeV] 2 4 6 8 10 Event rate [mHz/MeV] 0.5 1.0 1.5 2.0 2.5 3.0

After all cuts (Simulation)

Cuts IBD signal Cosmic BG PSD 1630 2.1e6 Time (1, 2, 3) 1570 3.4e4 Spatial (4, 5) 1440 9900 Fiducial (6) 660 250

Events Per Day Significant Cosmic Ray Rate in this Configuration

ν̅e Signal Remaining background

Cosmic Ray and Reactor Backgrounds are a challenge, but we are confident that we can achieve S:N=1:1 or better

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Sensitivity: Sterile Neutrinos

18

14

θ 2

2

sin

2 −

10

1 −

10 1 ]

2

[eV

14 2

m ∆

1 −

10 1 10

Sensitivity: σ Phase I (1 yr) at 3 σ Phase I (3 yr) at 3 σ Phase I + II (3+3 yr) at 3 σ Phase I + II (3+3 yr) at 5 SBL Anomaly (Kopp), 95% CL Disappearance Experiments (Kopp), 95% CL

e

ν All SBL + Gallium Anomaly (LSN), 95% CL Daya Bay Exclusion, 95% CL

14

θ 2

2

sin

2 −

10

1 −

10 1 ]

2

[eV

14 2

m ∆

1 −

10 1 10

σ Phase I for 1 year at 3 Sensitivity: Front Position Movable Position Middle Position SBL Anomaly (Kopp), 95% CL Disappearance Experiments (Kopp), 95% CL

e

ν All SBL + Gallium Anomaly (LSN), 95% CL

Phase I and Phase II Phase I with Positioning

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Sensitivity: Sterile Neutrinos

18

14

θ 2

2

sin

2 −

10

1 −

10 1 ]

2

[eV

14 2

m ∆

1 −

10 1 10

Sensitivity: σ Phase I (1 yr) at 3 σ Phase I (3 yr) at 3 σ Phase I + II (3+3 yr) at 3 σ Phase I + II (3+3 yr) at 5 SBL Anomaly (Kopp), 95% CL Disappearance Experiments (Kopp), 95% CL

e

ν All SBL + Gallium Anomaly (LSN), 95% CL Daya Bay Exclusion, 95% CL

14

θ 2

2

sin

2 −

10

1 −

10 1 ]

2

[eV

14 2

m ∆

1 −

10 1 10

σ Phase I for 1 year at 3 Sensitivity: Front Position Movable Position Middle Position SBL Anomaly (Kopp), 95% CL Disappearance Experiments (Kopp), 95% CL

e

ν All SBL + Gallium Anomaly (LSN), 95% CL

Phase I and Phase II Phase I with Positioning

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Sensitivity: Reactor Spectrum

19

Phase I, Phase I,

Specific tests of models for 235U

Napolitano: Sterile Neutrinos at Reactors UMass AFCI 14-16 Dec 2015

Conclusions

20

• Nuclear reactors are copious sources of ν̅e, but it is

difficult to understand the details at the level of 1%

• The best, most recent calculations indicate the ν̅e

flux is “anomalously low” ⇒ Sterile neutrinos? Other experiments support this hypothesis

• Several new experiments are under construction at

research reactors to measure the spectrum shape

• PROSPECT @ HFIR will eliminate or verify the

“Kopp Best Fit” sterile neutrino solution by 2018

Thank You!