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Braidwood Neutrino Experiment

Presentation on the Braidwood Neutrino Experiment discussing its motivation, project details, physics capabilities, and collaboration efforts to detect neutrinos from nuclear reactors.

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Braidwood Neutrino Experiment

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  1. Braidwood Neutrino Experiment • Introduction and Motivation • Collaboration • Project Description • Physics Capabilities • Status, Schedule, and Summary M. Shaevitz Columbia UniversityPresentation at the NuSAG MeetingJune 1, 2005

  2. 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

  3. 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. Motivation Braidwood (3 yrs) +T2K T2K only (5yr,n-only) Double Chooz(3yr)+T2K 90% CL Braidwood (3 yrs) + Nova Nova only (3yr + 3yr) Double Chooz (3yrs) + Nova Reactor Exp. Best for Determining q13 Reactor Can Lift q23 Degeneracy(Example: sin2223 = 0.95  0.01) Δm2 = 2.5×10-3 eV2sin22q13 = 0.05 McConnel /Shaevitzhep-ex/0409028 90% CL 90% CL Δm2 = 2.5×10-3 eV2sin22q13 = 0.05 Far future: Precision Osc.Parameter Measurements 90% CL (Add Braidwood)

  4. Braidwood Neutrino Collaboration 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

  6. 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)

  7. Nuclear reactors are very intense sources ofνe with a well understood spectrum 3 GW → 6×1020ne/s700 events / yr / ton at 1500 m away Reactor spectrum peaks at ~3.7 MeV Oscillation Max. for Dm2=2.510-3 eV2at L near 1500 m Reactor Measurements of 13 From Bemporad, Gratta and Vogel Arbitrary Observable n Spectrum Cross Section Flux • Disappearance Measurement:Look for small rate deviation from 1/r2 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 e+ e = Photomultiplier Tube n • The reaction process is inverse β-decay (IBD) followed by neutron capture • Two part coincidence signal is crucial for background reduction. • Positron energy spectrum implies the neutrino spectrum • The scintillator will be doped with gadolinium to enhance capture Liquid Scintillatorwith Gadolinium Shielding Eν = Evis + 1.8 MeV – 2me nmGd → m+1Gdg’s (8 MeV) 6 meters Signal = Positron signal + Neutron signal within 100 msec (5 capture times)

  9. Experimental Challenges for Multi-Detector Disappearance Exp’s Braidwood Singles Rate at 450mwe • Relative Detector Uncertainties Fiducial VolumeAcceptance Energy scale and linearity Deadtime • Backgrounds to the e+ - n coincidence signal Uncorrelated Backgrounds • ambient radioactivity • accidentals • cosmogenic neutrons 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 eg. 8He (T1/2=119ms) 9Li (T1/2=178ms) 12B mainly Assume Kamlandradio-isotopeconcentration

  10. Braidwood BraidwoodNeutrino Experiment • Braidwood Setup: • Two 3.6 GW reactors • Two 65 ton (fid vol) near detectors at 270 m • Two 65 ton (fid vol) far detectors at 1510 m • 180m shafts and detector halls at 450 mwe depth Project Summary: - Overview - Civil Construction - Detector Design - Backgrounds and Veto System - Physics Capability

  11. 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

  12. Braidwood Design Sensitivity Experiment designed to have: • Discovery potential (at 3s) for sin22q13 > 0.01 and • 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 crosschecks 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.

  13. 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%

  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 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)

  15. Staging & Assembly Area Braidwood Reactors Connecting road Far Site Near Site PMT staging & test Acrylic Tank Assembly Outer ShellAssembly Area  Off to shaft Final Assembly Area PMT Installation Oil Storage Area Staging & Assembly Area

  16. 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.

  17. 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) Only minimal moving required for cross checks Example scenario: 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.) Movable Detectors A B B C D A D A B C Goldhofer Trailer Moving 400 tons

  18. 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

  19. Detector Design and Optimization Reconstructed Positron Energy Reconstructed NeutronCapture Energy • 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 Fiducial mass determined by volume of Gd-loaded scintillator. • Event selection based on coincidence of e+ signal (Evis>0.5 MeV) and s released from n+Gd capture (Evis>6 MeV).No explicit requirement on reconstructed event position; little sensitivity to E requirements.

  20. 2 Zone Detector Design Calibration fromneutron capture peaks  0.1%uncertainty • 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. • 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) Chooz degradation was 0.4%/day • 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). BNL Measurements ~6 months

  22. Detector Cost Estimate $4.2 M /detectorwith veto system+ $1.3M (Cont.) Other detector related items$1M with cont. Total for 4 detectors: $23M with cont.

  23. 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

  24. 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

  25. Requirements of veto system Identify muons which could give neutron/isotope background in the fiducial region Absorb neutrons produced by muons that miss the veto Muon identification must allow in situ determination of the residual background rate. 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: Be modular for assembly Have access to top port Allow detector to be installed and moved Veto (Tagging) System Shielding Veto Detectors p n n 6 meters m m

  26. Detector With Moveable Veto System and Shielding

  27. For a veto system with 2 mwe of shielding, both a GEANT4 and a MARS calculation give: 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/ dayafter the veto requirements. Costs for system consistent with initial estimates Background Calculations Neutrons that reach the vessel wall Fraction of Neutrons Detector Untaggedneutrons

  28. Using Isotope Production to Measure Fiducial Mass Beta decays t1/2 = 20ms (can tag to muon) 13.4 MeV endpoint 12B • 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 • ~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

  29. Simulations and Sensitivity Estimates Reconstructed Neutron vs Positron Energy Signal Region • 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 Energy Cuts: • positron: Evis > 0.5 MeV • n-Gd capture: Evis > 6 MeV

  30. 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:

  31. 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

  32. Sensitivity and Discovery Potential Summary of Uncertainties for 3 yr Data • For three years of Braidwood dataand Dm2 > 2.5 x 10-3 eV2 • 90% CL limit at sin22q13 < 0.005 • 3 s discovery for sin22q13 > 0.013

  33. 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

  34. 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

  35. Braidwood Elastic Scattering 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. • 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.

  36. 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

  37. The Value of Building a Reactor Experiment in the US • Local Investment both within and outside of physics. • High US Participation in the operations since the travel costs are low. • More US undergrad and gradstudent participation possible 4) Support of near-by, well-established laboratories. • More direct and local control ofmanagement • Opportunities for education and outreach for the general public, schools, and universities.

  38. 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.

  39. Backups and Other Slides

  40. Experiment Setup and Rates

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