Transcript NOW2004 - University of Chicago

Braidwood Neutrino Experiment
• Introduction and Motivation
• Collaboration
• Project Description
• Physics Capabilities
• Status, Schedule, and Summary
M. Shaevitz
Columbia University
Presentation at the NuSAG Meeting
June 1, 2005
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Braidwood Introduction
(Motivated By Theoretical and Experimental Requirements)
• Sensitivity (90% CL) down to sin22q13 = 0.005
• Discovery potential (3s) for sin22q13 > 0.01
• Convincing results
– Observation of an oscillation signal in both counting and
energy shape measurement
– Cross checks on systematic uncertainties
– In situ measurements of backgrounds and efficiencies
To meet these goals requires a near/far experimental
setup with the same overburden shielding along with
multiple large detectors at each site
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Motivation
Reactor Exp. Best for Determining q13
Reactor Can Lift q23 Degeneracy
(Example: sin22 q23 = 0.95  0.01)
Braidwood (3 yrs) +T2K
T2K only (5yr,n-only)
Double Chooz(3yr)+T2K
90%
90%CL
CL
Δm2 = 2.5×10-3 eV2
sin22q13 = 0.05
Far future: Precision Osc. Parameter
Measurements
90% CL
(Add Braidwood)
90% CL
Δm2 = 2.5×10-3 eV2
sin22q13 = 0.05
McConnel /
Shaevitz
hep-ex/0409028
Braidwood (3 yrs) + Nova
Nova only (3yr + 3yr)
Double Chooz (3yrs) + Nova
Other Guidance
• In many models, q13 could be very small
 sin22q13 < 0.01 seems to be a dividing
level for both theory and exp.
– Such a low level might imply a new
underlying symmetry or change in
theory paradigm
– Longer baseline experiments needed
• Measuring the full set of mixing parameters
(q12, q13, q23, and d) is needed for addressing
quark-lepton unification models.
Braidwood Neutrino Collaboration
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14 Institutions
70 Collaborators
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Exelon Corporation also a “Collaborator”
• Enthusiastic and very
supportive of the project
• Exelon Vice President has
sent letter of support to
funding agencies
• Security and site access
issues not a problem
• Have helped us with bore
holes at near/far locations
– Example and proof of
principle for us doing civil
construction on site
Collaboration Organization
• Co-Spokepersons
(Ed Blucher and Mike Shaevitz)
• Background and Simulation
(Group leaders: Tim Bolton and Matt Worcester)
• Calibration
(Group leader: Josh Klein)
• Veto System
(Group leader: Peter Fisher)
• Electronics
(Group leader: Jim Pilcher)
• Detector mechanical engineering
(Group leader: Maury Goodman)
• Site and civil construction
(Group leader: Jon Link)
• Liquid Scintillator
(Group leader: Dick Hahn)
• Non-q13 physics
(Group leaders: Janet Conrad, Joe Formaggio)
• Management and Oversight
(Group Leader: Ray Stefanski)
• Education & Outreach
(Group Leader: Paul Nienaber)
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• Nuclear reactors are very intense sources
ofνe with a well understood spectrum
– 3 GW → 6×1020ne/s
700 events / yr / ton at 1500 m away
– Reactor spectrum peaks at ~3.7 MeV
– Oscillation Max. for Dm2=2.510-3 eV2
at L near 1500 m
Arbitrary
Reactor Measurements of q13
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From Bemporad, Gratta and Vogel
Observable n Spectrum
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Dm = 2.5 10 eV
Full Mixing
2
Observed Events
30
-3
2
25
• Disappearance Measurement:
Look for small rate deviation from 1/r2
measured at near and far baselines
No Osc.
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15
– Counting Experiment
10
1500 m
• Compare events in near and far detector
5
0
1.50
– Energy Shape Experiment
2.50
3.50
4.50
5.50
En (MeV)
6.50
7.50
8.50
• Compare energy spectrum in near and far
detector
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Experimental Setup
• The reaction process is inverse βdecay (IBD) followed by neutron
capture
– Two part coincidence signal is
crucial for background
reduction.
= Photomultiplier Tube
Liquid Scintillator
with Gadolinium
Shielding
n e p  e n
n capture
• Positron energy spectrum implies
the neutrino spectrum
Eν = Evis + 1.8 MeV – 2me
e+
ne
n
• The scintillator will be doped with
gadolinium to enhance capture
n mGd → m+1Gd g’s (8 MeV)
6 meters
Signal = Positron signal + Neutron signal within 100 msec (5 capture times)
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Experimental Challenges for Multi-Detector Disappearance Exp’s
• Relative Detector Uncertainties
Fiducial Volume
Acceptance
Energy scale and linearity
Deadtime
• Backgrounds to the
e+ - n coincidence signal
Braidwood Singles Rate at 450mwe
12B
mainly
Uncorrelated Backgrounds
– ambient radioactivity
– accidentals
– cosmogenic neutrons
Assume Kamland
radio-isotope
concentration
Correlated Backgrounds
– cosmic rays induce neutrons in the surrounding rock and buffer region of
the detector
– cosmogenic radioactive nuclei that emit delayed neutrons in the detector
8He (T1/2=119ms)
eg.
9Li (T1/2=178ms)
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Braidwood
Neutrino
Experiment
Braidwood Setup:
• Two 3.6 GW reactors
• Two 65 ton (fid vol) near
detectors at 270 m
Braidwood
• Two 65 ton (fid vol) far
detectors at 1510 m
• 180m shafts and
Project Summary:
detector halls at
- Overview
450 mwe depth
- Civil Construction
- Detector Design
- Backgrounds and Veto System
- Physics Capability
Braidwood Design Principles
Compare rate/shape in identical, large, spherical, on-axis detectors at
two distances that have equal overburden shielding
(Multiple detectors at each site: two near and two far)
 Systematic uncertainties cancel to first order and only have
uncertainties for second order effects
• Detectors filled simultaneously with common scintillator on surface
• Large (65 ton fiducial) detectors give large data samples
• Spherical detectors reduce any geometrical effects from neutrino
direction and reconstruction
• On-axis detectors eliminate any dependence on reactor power
variations in a multi-reactor setup.
• Equal overburden shielding gives equal spallation rates in near and
far that can be exploited for detector and background checks
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Braidwood Design Sensitivity
Experiment designed to have:
1. Discovery potential (at 3s) for sin22q13 > 0.01 and
2. Sensitivity (90% CL) down to the sin22q13 = 0.005 level
 With cross checks and redundancy to substantiate results
•
See signal in both total rate and energy shape measurements
•
Cross calibrate detector pairs at high-rate near site
•
Cross calibrate near/far detectors using spallation isotopes
like 12B (since detectors at same deep depth)
•
Multiple near and far detectors give direct cross checks on
detector systematics at 0.05% for the near set and 0.3% for far
•
Large detectors allow studies of the radial dependence of the
IBD signal and backgrounds.
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Overview of Braidwood Uncertainties
• Primary uncertainties associated with predicting the
relative near-to-far event ratio
• This combined with the statistical and background uncertainties
leads to the final sensitivity
With two near and two far detectors,
this leads to a total uncertainty in the
Near/far ratio of 0.33%
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Civil Construction
• Two detector locations at 200 m and 1500 m from the reactors
– A 10 m diameter shaft allows access to the detector caverns at 183
m below the surface
– Caverns are 12m x 14m x 32m and house two detectors with their
veto systems
• Detailed cost estimates were done by the Hilton and Associates
engineering firm.
– Total cost = $29M + $5M (EDIA) + $8.5M (Contingency)
(Shafts: 2@$9.8M, Caverns: 2@$2.4M, Tunnels: $1.7M, and $3.2M mobilization)
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Staging & Assembly Area
Braidwood
Connecting road
Reactors
Far Site
Near Site
PMT staging
Outer
Shell
Assembly
Area
& test
PMT
Installation
Acrylic Tank
Assembly
Final
Assembly
Area
Staging & Assembly Area
Oil Storage
Area
 Off to shaft
Bore Hole Project at the Exelon Site
Bore hole project completed in January 2005
– Bore holes drilled to full depth (200m)
at near and far shaft positions on
Braidwood site.
– Provided detailed information on
geology, ground water, radioactivity,
etc.
– Confirmed feasibility of detectors
down to depths of 460mwe.
– Reduces contingency required for
underground construction
– Demonstrated willingness of
Exelon to allow construction
on their site.
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Movable Detectors
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• Transport is necessary to move detectors from construction/filling area to
below ground halls
• Cost estimate is $250K for one movement campaign (2 to 3 campaigns
envisaged)
Period
• Only minimal moving required
for cross checks
– Example scenario:
Near
Far
Initial 3 months
A
B
3 year data run
A
C
B
D
Final check
A
D
B
C
• Possible method: Use climbing jack system with cable to lift and put units
on multi-wheeled trailer (standard method used in industry for such
projects.)
Goldhofer Trailer
Moving 400 tons
Detector Design and Engineering
• Engineering by: Argonne, Fermilab and Bartoszek & Associates
• Baseline design has:
– Outer steel buffer oil containment
vessel (7m diameter)
• 1000 low activity glass 8” PMTs
evenly distributed on inside
surface (25% coverage)
– Inner acrylic Gd-Scint containment
vessel (5.2m diameter)
– Top access port can be used to insert
calibration sources
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Detector Design and Optimization
• Detectors and analysis strategy designed to minimize relative acceptance
differences
• 2 zone detector design: Central zone (r=2.6m) with Gd-loaded scintillator
(0.2% by weight) surrounded by mineral oil buffer region (r=3.5m).
• Neutrino detection by n e  p  e  n; n  Gd  8MeV of g s ( ~ 20m sec)
Fiducial mass determined by volume of Gd-loaded scintillator.
• Event selection based on coincidence of e+ signal (Evis>0.5 MeV) and gs released
from n+Gd capture (Evis>6 MeV). No explicit requirement on reconstructed event
position; little sensitivity to E requirements.
Reconstructed
Positron Energy
Reconstructed Neutron
Capture Energy
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2 Zone Detector Design
Calibration from
neutron capture peaks
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2 zone design offers simpler construction,
optics, and source calibration, as well as
larger fiducial mass for a given detector
volume.
Large (r = 3.5 m) detector reduces surface
area to volume ratio, significantly reducing
sensitivity to energy scale.
 0.1%
uncertainty
Use neutron capture peaks from IBD events
to measure energy scale.
• In each far detector, E scale can be
measured to 0.3% every 5 days.
(This calibration averages over
detector in exactly the same way as
signal events.)
Acceptance uncertainty from energy scale
in 2-zone design should be ~0.1%.
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Gd - Liquid Scintillator (Gd-LS)
• BNL Nuclear Chemistry group is developing Gd-loaded liquid
scintillator for Braidwood experiment.
• We plan to use 0.2% Gd + PC + dodecane mixture.
– Long-term stability tests in progress
– So far, stable with attenuation length > 18 m.
Stability of Gd-LS
(Absorbance of 0.002 corresponds to
attenuation Length of ~20 m).
0.008
0.14% Gd in PC
0.007
0.2% Gd diluted in 20%PC 80% Dodecane
Chooz degradation was 0.4%/day
0.2% Gd in 20%PC 80% Dodecane
0.006
0.005
0.005
0.004
0.004
Abs at 430 nm
Abs at 430 nm by 10-cm Cell
0.2% Gd in PC
0.003
0.002
~6 months
0.001
12/9/04
12/29/04
1/18/05
2/7/05
2/27/05
Calendar Date
3/19/05
0.002
0.001
0
11/19/04
0.003
4/8/05
4/28/05
5/18/05
0.000
2/17/05
BNL Measurements
3/14/05
4/8/05
Calendar Date
5/3/05
5/28/05
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Detector Cost Estimate
– $4.2 M /detector
with veto system
+ $1.3M (Cont.)
– Other detector
related items
$1M with cont.
Total for 4 detectors:
$23M with cont.
Backgrounds
Backgrounds are important since the signal/background ratios in
the near and far detectors are different.
– Uncorrelated backgrounds from random coincidences are not a
problem
• Reduced by limiting radioactive materials
• Limestone rock at Braidwood site has low radioactivity wrt granite
• Directly measured from rates and random trigger setups
– Correlated backgrounds from:
• Neutrons that mimic the coincidence signal
• Cosmogenically produced isotopes that decay to a beta and
neutron (9Li and 8He)
Veto system is the prime tool for tagging/eliminating and
measuring the rate of these coincidence backgrounds
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Cosmic Muon Rates at Braidwood Depths
• Calculation of muon rate at 464 mwe (600 ft)
– Incorporate data from boreholes for density
and material
– Average muon flux = 0.213 /m2/sec
– Average muon energy = 110.1 GeV
Material
Chemical composition
Density
(g/cm3)
Depth of top
of layer (m)
Soil
SiO2
1.60
0.0
Mudstone
SiO2
2.46
11.3
Mudstone
SiO2
2.52
27.1
Limestone
CaCO3
2.61
42.7
Limestone
CaCO3
2.63
61.0
Mudstone
SiO2
2.60
63.1
Dolomitic Limestone
0.63* CaCO3 +
0.37*MgCO3
2.58
82.6
Dolomitic Limestone
0.63* CaCO3 +
0.37*MgCO3
2.62
98.8
Dolomitic Limestone
0.63* CaCO3 +
0.37*MgCO3
2.71
116.4
Dolomitic Limestone
0.63* CaCO3 +
0.37*MgCO3
2.62
135.0
Limestone
CaCO3
2.63
142.3
Limestone
CaCO3
2.71
157.6
Dolomitic Limestone
0.63* CaCO3 +
0.37*MgCO3
2.66
168.9
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Veto (Tagging) System
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• Veto system being designed using GEANT4 hit level simulation tools
–
–
–
–
Goal: < 1 neutron background event/day/detector
Measure muon trajectory and/or energy deposition in surrounding material
Composed of active detectors and shielding
Mechanical construction needs to:
1. Be modular for assembly
2. Have access to top port
3. Allow detector to be installed
and moved
• Requirements of veto system
– Identify muons which could
give neutron/isotope
background in the fiducial
region
Shielding
Veto
Detectors
p
– Absorb neutrons produced by
muons that miss the veto
n
n
– Muon identification must allow
in situ determination of the
residual background rate.
m
6 meters
m
Detector With Moveable Veto System and Shielding
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Background Calculations
Neutrons that reach the vessel wall
• Costs for system consistent with
initial estimates
Detector
– 170 n/ton/day produced in the
surrounding rock
– 4500 n/day emerging from the
rock
– A background rate of
0.2 to 0.7 events/ day
after the veto requirements.
Fraction of Neutrons
• For a veto system with 2 mwe of
shielding, both a GEANT4 and a
MARS calculation give:
Untagged
neutrons
Using Isotope Production to Measure Fiducial Mass
• Unique feature of the Braidwood set up:
– Near and Far detectors at equal well-understood
overburden
– Near and Far detectors have substantial shielding
 Can use produced 12B events to measure:
• Near/far relative target mass from the total rate
• Near/far energy calibrations from the relative energy
distribution
12B
Beta decays
t1/2 = 20ms (can tag to muon)
13.4 MeV endpoint
• ~50,000 12B beta-decay events per year per detector can be tagged and
isolated for a statistical uncertainty of 0.45%
• Systematic uncertainties related to the relative near/far overburden that
needs to be known to few percent from:
– Geological survey information (Bore hole data: near/far agreement at <1%)
– Cosmic muon rates in the near and far locations
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Simulations and Sensitivity Estimates
• Studies using hit level Monte Carlos to determine signal efficiencies,
resolutions, and background rates
– Uses a combination of parameterized and full GEANT4 detector
simulation tools
• Estimates of calibration and construction procedures used to set the
scale of uncertainties in relative energy scale/offset as well as relative
fiducial mass
Reconstructed Neutron vs Positron Energy
Reconstructed Energy Cuts:
• positron: Evis > 0.5 MeV
• n-Gd capture: Evis > 6 MeV
Signal Region
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Sensitivity Estimates
• The oscillation search is made by comparing the events in the near and
far detectors using:
– Total number of events integrated over energy (Counting Meas.)
– The distribution of events binned in energy (Shape Meas.)
– Both counting plus shape ( Combined Meas.)
• Systematic uncertainties associated with the near to far event or energy
spectrum are included as outlined in the table below:
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90% CL Sensitivity vs Years of Data
• Information from both counting and shape fits
• Combined sensitivity for sin22q13 reaches the 0.005 level after three years
1.000
3 years
sin22q 13 90% CL limit (1.28 s )
Dm2 = 2.5e-3 eV 2
count
shape
0.100
combine
0.010
0.001
0.1
1
10
Running Time (yrs)
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Sensitivity and Discovery Potential
• For three years of Braidwood data
and Dm2 > 2.5 x 10-3 eV2
– 90% CL limit at sin22q13 < 0.005
– 3 s discovery for sin22q13 > 0.013
Summary of Uncertainties for 3 yr Data
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Braidwood Measurement Capability
For 3 years of data and a combined counting plus shape analysis
– Dm2 = 2.5 x 10-3 eV2 and sin22q13 = 0.02
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Other Physics: Neutrino Electroweak Couplings
At Braidwood can isolate about 10,000ne – e events that will allow
the measurement of the neutrino gL2 coupling to ~1%
– This is 4 better than past n-e experiments and would
give an error comparable to gL2(NuTeV) = 0.3001  0.0014
gL2 - gL2(SM)
Precision measurement possible since:
– Measure elastic scattering relative to inverse beta decay
(making this a ratio, not an absolute, measurement)
– Can pick a smart visible energy window (3-5 MeV) away from
background
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Braidwood Elastic Scattering Measurement
• Aims to be the most precise measurement of neutrino-electron
scattering
• Preliminary investigations indicate systematics can be controlled
at the 1% level
• Continuing study to ameliorate systematic errors and identify any
gaps in our understanding of the measurement.
Braidwood is unique among q13 experiments
in having the potential to address this physics
because of having a near detector with high shielding
and high rates due to proximity to the reactor.
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Braidwood Status and Schedule
• Engineering / R&D Proposal ($1M) submitted in Nov. 2004
– Need this funding to complete the engineering for a proposal
•
•
•
•
Develop a “Design and Build” package for civil construction
Complete detector design at the bid package level
Complete and set up management plan and project oversight
Complete the development of the Gd-Scint and provide test batches for
prototypes
• Baseline Cost Estimate:
– Civil Costs: $34M + $8.5M (Cont.)
– 4 Detectors and Veto Systems:
$18M + $5M (Cont.)
• Schedule:
–
–
–
–
–
–
2004: R&D proposal submission.
2004: Bore hole project completed on Braidwood site.
2005: First NuSAG review
2006: Full proposal submission
2007: Project approval; start construction
2010: Start data collection
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The Value of Building a Reactor Experiment in the US
1) Local Investment both within and outside of physics.
2) High US Participation in the operations
since the travel costs are low.
3) More US undergrad and grad student participation possible
4) Support of near-by, well-established laboratories.
5) More direct and local control of management
6) Opportunities for education and outreach for the general
public, schools, and universities.
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Summary
• Braidwood is an ideal location for an experiment in the US
to measure q13
–
–
–
–
–
Flat overburden with deep, on-site locations for near and far detectors
Equal overburden for near/far stations allows cross checks
Close proximity to the “neutrino corridor” of Fermilab and Argonne
Cooperative reactor company with a high power facility
Capability to do additional physics with the near detector
• Strong collaboration which is making rapid progress in developing a
robust experiment with excellent sensitivity
– Sensitivity (90% CL) down to sin22q13 = 0.005
– Discovery potential (3s) for sin22q13 > 0.01
• Engineering/R&D support and funding at this point is crucial
– Need ~$100K soon to prepare an improved design/cost estimate in
anticipation of P5 etc. and to continue the scintillator development
– Need the full funding in timely fashion as outlined in our
Engineering/R&D proposal ($1M) to prepare the final proposal and
engineering packages.
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Backups and Other Slides
Experiment Setup and Rates
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