# Presentation: 802788

## Using Reactor Anti-Neutrinos to Measure sin22θ13

- Using Reactor Anti-Neutrinos to Measure sin22θ13

- Jonathan Link
- Columbia University
- Fermilab Long Range Planning Committee, Neutrino Session
- November 7, 2003

- Byron, Illinois

## Sin22θ13 Reactor Experiment Basics

- Distance

- Probability νe

- 1.0

- Eν ≤ 8 MeV

- 1200 to
- 1800 meters

- Sin22θ13 Reactor Experiment Basics

- Unoscillated flux observed here.

- Well understood, isotropic source of electron anti-neutrinos.

- Oscillations observed as a deficit of νe.

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Nuclear Reactors as a Neutrino Source

- Arbitrary

- Flux

- Cross Section

- Observable   Spectrum

- From Bemporad, Gratta and Vogel

-  Nuclear reactors are a very intense sources of  νe deriving from the -decay of the neutron-rich fission fragments.
-  Each fission liberates about 200 MeV of energy and generates about 6 electron anti-neutrinos.  So for a typical commercial  reactor (3 GW thermal energy)
- 3 GW ≈ 2×1021 MeV/s → 6×1020 e/s

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Reactor Neutrino Event Signature

- Two part coincidence signal is crucial for background reduction.
- Minimum energy for the primary signal of 1.022 MeV from *e***+***e***−*** *annihilation at process threshold.
- Positron energy spectrum implies the anti-neutrino spectrum
- In pure scintillator the neutron would capture on hydrogen
- Scintillator will be doped with gadolinium which enhances capture

- e* *p*→ e****+***n
-                     n* *capture

- n* *H *→ *D* *  (2.2 MeV)

- n* **m*Gd *→ **m+1*Gd* *’s (8 MeV)

- Eν = E*e *+ 0.8 MeV ( **=***m*n*m*p+*m*e1.022)

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Detector Design Basics

- Detector

- Larger version of CHOOZ (or smaller KamLAND)
-  Homogenous Volume
-  Viewed by PMT’s (coverage of 20% or better)
-  Gadolinium Loaded, Liquid Scintillator Target (**~**50 tons)
-  Pure Mineral Oil Buffer  (To shield the scintillator from radioactive isotopes in the PMT glass)

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## What is the Right Way to Design the Experiment?

- Start with the dominate systematic errors from previous experiments and work backwards...

- CHOOZ Systematic Errors, Normalization

- Near Detector

- CHOOZ Background Error
- BG rate                                        0.9%

- Statistics may also be a limiting factor in the sensitivity, but we should design the experiment to avoid this.

- Identical Near and Far Detectors

- Movable Detectors

- Muon Veto and Neutron Shield (MVNS)

- (All normalization errors reduce to one measurable, relative efficiency error)

- Vogel and Beacom have reduced this theoretical error since CHOOZ

- The combination of these two plus a complex analysis gives you the anti-neutrino flux

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Movable Detectors to Control Systematics

- The far detector spends about 10% of the run at the near site where the relative efficiency of the two detectors is measured head-to-head.
- Build in all the calibration tools needed for a fixed detector system and verify them against the head-to-head calibration.

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Reducing Background

- Go as deep at you can  (300 mwe → 0.2 BG/ton/day at CHOOZ)

- Veto ’s and shield neutrons  (*Big effective depth*)
- Measure the recoil proton energy and extrapolate into the signal region.  (Understand the BG that gets through and subtract it)

- 6 meters

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Characterizing BG with Vetoed Events

- From CHOOZ

- interactions

- ?

- Matching distributions from vetoed events outside the signal region to the non-veto events will provide an estimate of correlated backgrounds that evade the veto.

- Proton recoils

- Other Useful Distributions:
-  Spatial separation prompt and delayed events
- Faster neutrons go farther
-  Radial distribution of events
- BGs accumulate on the outside of the detector.

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Sensitivity vs. Δm2

- Sensitivity vs. Δ*m*2

- This is a full shape plus rate analysis, and includes all sources of systematic error.
- At the Super-K preferred  Δ*m*2 of 210-3, the sensitivity to sin22θ13 is 0.01 at 90% CL.

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Discovery Potential vs. Time

- After one year, the discovery potential is below the 90% CL limit from Minos (sin22θ13< 0.06).

**3****σ**** Discovery Potential**

- Rate only analysis

- Preferred Δ*m*2 from Super-K

- After three years the discovery potential is down to 0.02 to 0.03.

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Is this program a good match for Fermilab?

-  Detector Experience:
- The detectors will be similar to the MiniBooNE detector.
-  Tunneling Experience:
- The size of the tunnel and the geology are similar to the NuMI beam line tunnel.
- Future machines at the lab will require deep tunnels and this project will help to maintain that expertise.
-  Physics Parameters:
- The value of sin22θ13 is an important input for designing the future neutrino oscillation experimental program (*e.g.* NuMI Off-axis).

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Is this program a good match for Fermilab?

- Top 30 U.S. Sites by Power Performance

-  Overlap with Lab Theorists:
- Stephen Parke, Boris Kayser, John Beacom, etc. have done a lot of work in this area.
-  Administrative Structure:
- Project management, safety training, etc. would have to be replicated for this project.
-  Proximity to Reactor Sites:
- Many of the best reactor sites in the U.S. are located in Illinios.

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Location of Reactors Near Fermilab

- Braidwood

- La Salle

- Byron

- 80 km

- 60 km

- 50 km

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Experiment Timeline

- 2003

- 2004

- 2005

- 2006

- 2007

- 2008

- 2009

**Site Selection**

- 2010

**Run**

- 2011

**Construction**

- Years

- 1 year	        2 years                2 years                  3 years (initially)

-  JHF-SK and NuMI Off-axis are both slated to start in 2009.
-  This timeline could slip by 6 months and a well executed reactor experiment would still make the first observation of non-zero θ13.
-  Even if it’s not first, a precise reactor measurement helps to resolve the degeneracies inherent in the off-axis experiments.

**Proposal**

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003

## Conclusions and Recommendation

-  Nuclear reactors are an excellent source of anti-neutrinos to use for a νe disappearance search related to sin22θ13.
-  Sensitivity to sin22θ13 at the 0.01 level is possible if steps are taken to control systematic errors.
-   Many of the best reactor sites in the U.S. are located in Illinois (and we have the support of Exelon to study the feasibility of an experiment at these reactors!)
-  The reactor experiment is a good match to the physics and capabilities of the lab.

***Recommendation:***
*Fermilab should participate in a reactor based sin**2**2**θ**13** experiment, and should pursue locating the experiment at an Illinois reactor. *

- Jonathan Link, Columbia University                                 FLRPC Neutrino Public Meeting

- 11/7/2003