Braidwood Neutrino Experiment Introduction and Motivation

Braidwood Neutrino Experiment • Introduction and Motivation • Collaboration • Project Description • Physics Capabilities • Status, Schedule, and Summary M. Shaevitz Columbia University Presentation at the Nu. SAG Meeting June 1, 2005 1

Braidwood Introduction (Motivated By Theoretical and Experimental Requirements) • Sensitivity (90% CL) down to sin 22 13 = 0. 005 • Discovery potential (3 s) for sin 22 13 > 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 2

3 Motivation Reactor Exp. Best for Determining 13 Reactor Can Lift 23 Degeneracy (Example: sin 22 23 = 0. 95 0. 01) Braidwood (3 yrs) +T 2 K only (5 yr, n-only) Double Chooz(3 yr)+T 2 K 90% CL Δm 2 = 2. 5× 10 -3 e. V 2 sin 22 13 = 0. 05 Far future: Precision Osc. Parameter Measurements 90% CL (Add Braidwood) 90% CL Δm 2 = 2. 5× 10 -3 e. V 2 sin 22 13 = 0. 05 Mc. Connel / Shaevitz hep-ex/0409028 Braidwood (3 yrs) + Nova only (3 yr + 3 yr) Double Chooz (3 yrs) + Nova Other Guidance • In many models, 13 could be very small sin 22 13 < 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 ( 12, 13, 23, and d) is needed for addressing quark-lepton unification models.

Braidwood Neutrino Collaboration 4 14 Institutions 70 Collaborators

5 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- 13 physics (Group leaders: Janet Conrad, Joe Formaggio) • Management and Oversight (Group Leader: Ray Stefanski) • Education & Outreach (Group Leader: Paul Nienaber) 6

7 • Nuclear reactors are very intense sources of νe with a well understood spectrum From Bemporad, Gratta and Vogel Observable Spectrum n Flu – 3 GW → 6× 1020 e/s 700 events / yr / ton at 1500 m away – Reactor spectrum peaks at ~3. 7 Me. V – Oscillation Max. for Dm 2=2. 5 10 -3 e. V 2 at L near 1500 m Arbitrary Reactor Measurements of 13 ss x o Cr o cti Se • Disappearance Measurement: Look for small rate deviation from 1/r 2 measured at near and far baselines – Counting Experiment • Compare events in near and far detector – Energy Shape Experiment • Compare energy spectrum in near and far detector

8 Experimental Setup • The reaction process is inverse βdecay (IBD) followed by neutron capture – Two part coincidence signal is crucial for background reduction. • Positron energy spectrum implies the neutrino spectrum Eν = Evis + 1. 8 Me. V – 2 me • The scintillator will be doped with gadolinium to enhance capture n m. Gd → m+1 Gd ’s (8 Me. V) = Photomultiplier Tube Liquid Scintillator with Gadolinium Shielding e+ e n 6 meters Signal = Positron signal + Neutron signal within 100 msec (5 capture times)

9 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 Uncorrelated Backgrounds – ambient radioactivity – accidentals – cosmogenic neutrons Braidwood Singles Rate at 450 mwe 12 B mainly 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 8 He (T 1/2=119 ms) eg. 9 Li (T 1/2=178 ms)

10 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 • 180 m 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 11

Braidwood Design Sensitivity Experiment designed to have: 1. Discovery potential (at 3 s) for sin 22 13 > 0. 01 and 2. Sensitivity (90% CL) down to the sin 22 13 = 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 12 B (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. 12

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% 13

14 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 12 m x 14 m x 32 m and house two detectors with their veto systems • Detailed cost estimates were done by the Hilton and Associates engineering firm. – Total cost = $29 M + $5 M (EDIA) + $8. 5 M (Contingency) (Shafts: 2@$9. 8 M, Caverns: 2@$2. 4 M, Tunnels: $1. 7 M, and $3. 2 M mobilization)

15 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 (200 m) 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 460 mwe. – Reduces contingency required for underground construction – Demonstrated willingness of Exelon to allow construction on their site. 16

Movable Detectors 17 • Transport is necessary to move detectors from construction/filling area to below ground halls • Cost estimate is $250 K for one movement campaign (2 to 3 campaigns envisaged) Period • Only minimal moving required for cross checks Near Far A B 3 year data run A C B D Final check – Example scenario: Initial 3 months 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 (7 m diameter) • 1000 low activity glass 8” PMTs evenly distributed on inside surface (25% coverage) – Inner acrylic Gd-Scint containment vessel (5. 2 m diameter) – Top access port can be used to insert calibration sources 18

Detector Design and Optimization • Detectors and analysis strategy designed to minimize relative acceptance differences • 2 zone detector design: Central zone (r=2. 6 m) with Gd-loaded scintillator (0. 2% by weight) surrounded by mineral oil buffer region (r=3. 5 m). • Neutrino detection by Fiducial mass determined by volume of Gd-loaded scintillator. • Event selection based on coincidence of e+ signal (Evis>0. 5 Me. V) and s released from n+Gd capture (Evis>6 Me. V). No explicit requirement on reconstructed event position; little sensitivity to E requirements. Reconstructed Positron Energy Reconstructed Neutron Capture Energy 19

2 Zone Detector Design Calibration from neutron capture peaks 20 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%.

21 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). Chooz degradation was 0. 4%/day ~6 months BNL Measurements

22 Detector Cost Estimate – $4. 2 M /detector with veto system + $1. 3 M (Cont. ) – Other detector related items $1 M with cont. Total for 4 detectors: $23 M with cont.

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 (9 Li and 8 He) Veto system is the prime tool for tagging/eliminating and measuring the rate of these coincidence backgrounds 23

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 /m 2/sec – Average muon energy = 110. 1 Ge. V Material Chemical composition Density (g/cm 3) Depth of top of layer (m) Soil Si. O 2 1. 60 0. 0 Mudstone Si. O 2 2. 46 11. 3 Mudstone Si. O 2 2. 52 27. 1 Limestone Ca. CO 3 2. 61 42. 7 Limestone Ca. CO 3 2. 63 61. 0 Mudstone Si. O 2 2. 60 63. 1 Dolomitic Limestone 0. 63* Ca. CO 3 + 0. 37*Mg. CO 3 2. 58 82. 6 Dolomitic Limestone 0. 63* Ca. CO 3 + 0. 37*Mg. CO 3 2. 62 98. 8 Dolomitic Limestone 0. 63* Ca. CO 3 + 0. 37*Mg. CO 3 2. 71 116. 4 Dolomitic Limestone 0. 63* Ca. CO 3 + 0. 37*Mg. CO 3 2. 62 135. 0 Limestone Ca. CO 3 2. 63 142. 3 Limestone Ca. CO 3 2. 71 157. 6 Dolomitic Limestone 0. 63* Ca. CO 3 + 0. 37*Mg. CO 3 2. 66 168. 9 24

Veto (Tagging) System 25 • Veto system being designed using GEANT 4 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 – Absorb neutrons produced by muons that miss the veto p 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 26

27 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 GEANT 4 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 12 B events to measure: • Near/far relative target mass from the total rate • Near/far energy calibrations from the relative energy distribution 12 B Beta decays t 1/2 = 20 ms (can tag to muon) 13. 4 Me. V endpoint • ~50, 000 12 B 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 28

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 GEANT 4 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 Me. V • n-Gd capture: Evis > 6 Me. V Signal Region 29

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: 30

90% CL Sensitivity vs Years of Data • Information from both counting and shape fits • Combined sensitivity for sin 22 13 reaches the 0. 005 level after three years 31

Sensitivity and Discovery Potential • For three years of Braidwood data and Dm 2 > 2. 5 x 10 -3 e. V 2 – 90% CL limit at sin 22 13 < 0. 005 – 3 s discovery for sin 22 13 > 0. 013 Summary of Uncertainties for 3 yr Data 32

Braidwood Measurement Capability For 3 years of data and a combined counting plus shape analysis – Dm 2 = 2. 5 x 10 -3 e. V 2 and sin 22 13 = 0. 02 33

Other Physics: Neutrino Electroweak Couplings At Braidwood can isolate about 10, 000 e – e events that will allow the measurement of the neutrino g. L 2 coupling to ~1% – This is 4 better than past -e experiments and would give an error comparable to g. L 2(Nu. Te. V) = 0. 3001 0. 0014 g. L 2 - g. L 2(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 Me. V) away from background 34

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 q 13 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. 35

Braidwood Status and Schedule • Engineering / R&D Proposal ($1 M) 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: $34 M + $8. 5 M (Cont. ) – 4 Detectors and Veto Systems: $18 M + $5 M (Cont. ) • Schedule: – – – 2004: R&D proposal submission. 2004: Bore hole project completed on Braidwood site. 2005: First Nu. SAG review 2006: Full proposal submission 2007: Project approval; start construction 2010: Start data collection 36

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. 37

Summary • Braidwood is an ideal location for an experiment in the US to measure 13 – 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 sin 22 13 = 0. 005 – Discovery potential (3 s) for sin 22 13 > 0. 01 • Engineering/R&D support and funding at this point is crucial – Need ~$100 K soon to prepare an improved design/cost estimate in anticipation of P 5 etc. and to continue the scintillator development – Need the full funding in timely fashion as outlined in our Engineering/R&D proposal ($1 M) to prepare the final proposal and engineering packages. 38

39 Backups and Other Slides

Experiment Setup and Rates 40