1. 1 Neutrino Oscillations: The Next Steps? M. Shaevitz Columbia University WIN 05 Workshop Introduction MiniBooNE and LSND Determining   : Reactor Oscillation Experiments (Next talks: Feldman – Long baseline oscillation experiments – Nova Mondal – Next generation atmospheric exp. – INO )

2. 2 Possible New Surprises in the Next Step 1.Sterile Neutrinos: –New type of neutrino No weak interactions (effectively no interactions) Produced by mixing with normal neutrinos –Expected in many extensions to the standard model –They would give a whole new spectrum of mass states and mixings  MiniBooNE and follow-ups are key 2.Probing for CP violation (and the mass hierarchy) –CP violation comes about when a process has a different rate for particles and anti-particles –CP violation in the neutrino mixing could be a key ingredient for explaining the matter-antimatter asymmetry in the universe –Then look at  versus oscillations to measure   New long baseline and reactor experiments are key

3. 3 LSND took data from 1993-98 - 49,000 Coulombs of protons - L = 30m and 20 < E < 53 MeV Saw an excess of  e : 87.9 ± 22.4 ± 6.0 events. With an oscillation probability of (0.264 ± 0.067 ± 0.045)%. 3.8  evidence for oscillation. Oscillations? Possibility 1: The LSND Experiment  Sterile Neutrinos ?

4. 4 Why Sterile Neutrinos? (M.Sorel, J.Conrad, M.Shaevitz, PRD 70(2004)073004 (hep-ph/0305255) ) Possible explanations: One of the experimental measurements is wrong Explanations other that osc. Additional “sterile” neutrinos involved in oscillations Need better measurement in LSND region  MiniBooNE

5. 5 Booster Neutrino Experiment (MiniBooNE) Main Injector Booster Use protons from the Fermilab 8 GeV booster  Neutrino Beam   GeV MiniBooNE designed to check LSND signal by searching for e appearance in a  beam at Fermilab.

6. 6 MiniBooNE Neutrino Exp. At Fermilab 50m Decay Pipe 8 GeV Proton Beam Transport One magnetic Horn, with Be target  Detector 50 m

7. 7 MiniBooNE consists of about 70 scientists from 13 institutions. Y. Liu, I. Stancu Alabama S. Koutsoliotas Bucknell E. Hawker, R.A. Johnson, J.L. Raaf Cincinnati T. Hart, R.H. Nelson, E.D. Zimmerman Colorado A. Aguilar-Arevalo, L.Bugel, L. Coney, J.M. Conrad, Z. Djurcic, J. Link, J. Monroe, K. McConnel, D. Schmitz, M.H. Shaevitz, M. Sorel, G.P. Zeller Columbia D. Smith Embry Riddle L.Bartoszek, C. Bhat, S J. Brice, B.C. Brown, D.A. Finley, R. Ford, F.G.Garcia, P. Kasper, T. Kobilarcik, I. Kourbanis, A. Malensek, W. Marsh, P. Martin, F. Mills, C. Moore, P. Nienaber, E. Prebys, A.D. Russell, P. Spentzouris, R. Stefanski, T. Williams Fermilab D. C. Cox, A. Green, H.-O. Meyer, R. Tayloe Indiana G.T. Garvey, C. Green, W.C. Louis, G.McGregor, S.McKenney, G.B. Mills, H. Ray, V. Sandberg, B. Sapp, R. Schirato, R. Van de Water, D.H. White Los Alamos R. Imlay, W. Metcalf, M. Sung, M.O. Wascko Louisiana State J. Cao, Y. Liu, B.P. Roe, H. Yang Michigan A.O. Bazarko, P.D. Meyers, R.B. Patterson, F.C. Shoemaker, H.A.Tanaka Princeton B.T. Fleming Yale MiniBooNE Collaboration

8. 8 The MiniBooNE Detector 12 meter diameter sphere Filled with 950,000 liters (900 tons) of very pure mineral oil Light tight inner region with 1280 photomultiplier tubes Outer veto region with 241 PMTs. Oscillation Search Method: Look for e events in a pure  beam (   e and    e )

9. 9 Particle Identification Stopping muon event Separation of e from  events –Exiting  events fire the veto –Stopping  events have a Michel electron after a few  sec –Čerenkov rings from outgoing particles Shows up as a ring of hits in the phototubes mounted inside the MiniBooNE sphere Pattern of phototube hits tells the particle type

10. 10 Animation Each frame is 25 ns with 10 ns steps. Early Late Low High Time (Color) Charge (Size) Muon Identification Signature:  e    e after ~2  sec

11. 11 NuMI Beam Events in MiniBooNE (World’s 1 st Offaxis Neutrino Measurement !!) NuMI Target MiniBooNE Detector NuMI Dump NuMI Near Detector  = 100 – 250 mr NuMI Beam Offaxis NuMI Beam  and K decays Elevation View MiniBooNE sees  events in the 8  s NuMI beam window that agree with expectation.  NuMI Offaxis beam will be a calibration beam for MiniBooNE ( and we can look at electron neutrino interactions) (NuMI offaxis beam analysis done by Alexis Aguilar-Arevalo)

12. 12 MiniBooNE Run Plan At the current time have collected: – 5.6 × 10 20 protons on target (original goal was 1 × 10 21 ) –~600k neutrino candidates (world’s largest sample in the 1 GeV region) Blind analysis: Hide possible e candidates; other ~90% events are open Plan is to “open the e appearance  box” when the analysis has been substantiated and when sufficient data has been collected for a definitive result  Current estimate is sometime in Late 2005  m 2 = 0.4 eV 2  m 2 = 1 eV 2 No Signal “Limit” “Signal” Next Step

13. 13 The Next Step If MiniBooNE sees no indications of oscillations with    Need to run with   since LSND signal was    e (Indications of CP violation) If MiniBooNE sees an oscillation signal  Many  m 2 and mixing angles plus CP violation to determine  BooNE Experiment (with and  ) Add another detector to MiniBooNE at 1-2 km distance (Also  appearance searches.)

14. 14 Possibility 2: CP Violation in Neutrino Mixing

15. Solar:  12 ~ 30° Atmospheric:  23 ~ 45° What is e component of 3 mass eigenstate? What do we know? These two different mass schemes are called: Mass Hierarchy Problem Unknown CP violation phase sin 2 2  13 < 0.2 at 90% CL (or  13 < 13°)

16. What is value of  13 ? What is mass hierarchy? Do neutrino oscillations violate CP symmetry? –May give hints about possible “Leptogenesis” Value of   3 central to these questions; it sets the scale for experiments needed to resolve mass hierarchy and search for CP violation. Key questions Why are quark and neutrino mixing matrices so different? CP violating phase  sin   0  CP Violation sin  13

17. Methods to measure sin 2 2  13 Long-Baseline Accelerators: Appearance (   e ) at  m 2  2.5  10 -3 eV 2 T2K: = 0.7 GeV, L = 295 km Reactors: Disappearance (  e  e ) at  m 2  2.5  10 -3 eV 2 Reactor experiments allow direct measurement of sin 2 2   : no matter effects, no CP violation, almost no correlation with other parameters. NO A: = 2.3 GeV, L = 810 km Currently pursued Offaxis Exps.

18. 18 Reactor Exp. Best for Determining  13 Reactor and Offaxis Exps. Are Complementary Δm 2 = 2.5×10 -3 eV 2 sin 2 2  13 = 0.05 Reactor Can Lift  23 Degeneracy (Example: sin 2 2  23 = 0.95  0.01) 90% CL Braidwood (3 yrs) + Nova Nova only (3yr + 3yr) Double Chooz (3yrs) + Nova 90% CL McConnel / Shaevitz hep-ex/0409028 Braidwood (3 yrs) +T2K T2K only (5yr, -only) Double Chooz(3yr) +T2K Δm 2 = 2.5×10 -3 eV 2 sin 2 2  13 = 0.05 90% CL Reactor experiment needed for determining  13  Is  13 large enough? Then offaxis studies of and  give sensitivity to CP violation

19. 19 (Add Reactor) Far future: Precision Osc. Parameter Measurements 90% CL Other Guidance In many models,   could be very small  sin 2 2  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 –Require longer baseline experiments to measure CP and mass hierarchy Measuring the full set of mixing parameters (  12,  13,   3, and  is needed for addressing quark-lepton unification models. Reactor and Offaxis Exps. (cont’d)

20. 20 Consensus Recommendation 2 (of 3): –An expeditiously deployed multi- detector reactor experiment with sensitivity … sin 2 2  13 =0.01 … –A timely accelerator experiment with comparable … sensitivity … –A proton driver … with an appropriate very large detector …

21. Long History of Reactor Neutrino Measurements The original neutrino discovery experiment, by Reines and Cowan, used reactor anti-neutrinos… Reines and Cowan at the Savannah River Reactor The  ν e interacts with a free proton via inverse β-decay: νeνe e+e+ p n W Later the neutron captures giving a coincidence signal. Reines and Cowan used cadmium to capture the neutrons (modern exp. use Gadolinium) The first successful neutrino detector

22. 22 Reactor Measurements of  13 Nuclear reactors are a very intense sources of  ν e with a well understood spectrum –3 GW → 6×10 20  e /s 700 events / yr / ton at 1500 m away –Reactor spectrum peaks at ~3.7 MeV –Oscillation Max. for  m 2 =2.5  10 -3 eV 2 at L near 1500 m Arbitrary Flux Cross Section Observable Spectrum From Bemporad, Gratta and Vogel Disappearance Measurement: Look for small rate deviation from 1/r 2 measured at a near and far baselines –Counting Experiment Compare events in near and far detector –Energy Shape Experiment Compare energy spectrum in near and far detector

23. 23 6 meters Shielding n e+e+ ee 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 E ν = E vis + 1.8 MeV – 2m e n m Gd → m+1 Gd  ’s (8 MeV) Liquid Scintillator with Gadolinium = Photomultiplier Tube Experimental Setup Signal = Positron signal + Neutron signal within 100  sec (5 capture times)

24. 24 Past reactor measurements: How to do better than previous reactor experiments?  Reduce systematic uncertainties due to reactor flux and detector  Optimize baseline  Larger detectors  Reduce and control backgrounds Precision Reactor Disappearance Exp. Are Difficult Looking for a small change in the expected rate and/or shape of the observed event

25. 25 Use identical near and far detectors to cancel many sources of systematics. Use identical near and far detectors to cancel many sources of systematics. How Do You Measure a Small Disappearance?

26. 26 νeνe νeνe νeνe νeνe νeνe νeνe Distance Probability ν e 1.0 E  ≤ 8 MeV 1200 to 1800 meters Sin 2 2θ 13 Reactor Experiment Basics Unoscillated flux observed here Well understood, isotropic source of electron anti-neutrinos Oscillations observed as a deficit of ν e sin 2 2θ 13 Survival Probability

27. 27 How Do You Measure a Small Disappearance? Use identical near and far detectors to cancel many sources of systematics. Use identical near and far detectors to cancel many sources of systematics. Design detectors to allow simple analysis cuts that will have reduced systematic uncertainty. Design detectors to allow simple analysis cuts that will have reduced systematic uncertainty.

28. 28 Homogenous Volume Homogenous Volume Viewed by PMT’s Viewed by PMT’s Coverage of 20% or better Gadolinium Loaded, Liquid Scintillator Target Gadolinium Loaded, Liquid Scintillator Target Enhances neutron capture Pure Mineral Oil Buffer Pure Mineral Oil Buffer To shield the scintillator from radioactivity in the PMT glass. Detector Design Basics

29. 29 Use identical near and far detectors to cancel many sources of systematics. Use identical near and far detectors to cancel many sources of systematics. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. 1.Use events and sources to cross calibrate For example, n capture peaks For example, n capture peaks 2.  Move far detectors to near site for cross calibration How Do You Measure a Small Disappearance?

30. 30 Use identical near and far detectors to cancel many sources of systematics. Use identical near and far detectors to cancel many sources of systematics. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Reduce background rate and uncertainty Reduce background rate and uncertainty How Do You Measure a Small Disappearance?

31. 31Backgrounds 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 materialsReduced by limiting radioactive materials Directly measured from rates and random trigger setupsDirectly measured from rates and random trigger setups –Correlated backgrounds from: Neutrons that mimic the coincidence signalNeutrons that mimic the coincidence signal Cosmogenically produced isotopes that decay to a beta and neutron ( 9 Li and 8 He)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 Veto system is the prime tool for tagging/eliminating and measuring the rate of these coincidence backgrounds

32. 32 Use identical near and far detectors to cancel many sources of systematics. Use identical near and far detectors to cancel many sources of systematics. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Reduce background rate and uncertainty Reduce background rate and uncertainty ─ Go as deep as you can ─ Veto How Do You Measure a Small Disappearance?

33. 33 Veto Detectors p n   n Veto Background Events Fast neutrons Veto  ’s and shield neutrons 6 meters Shielding A few second veto after every muon that deposits more than 2 GeV in the detector or veto will reduce this rate to an acceptable level. 9 Li and 8 He Produced by a few cosmic ray muons through spallation Produced by a few cosmic ray muons through spallation Large fraction decay giving a correlated β+n Large fraction decay giving a correlated β+n KamLAND Data

34. 34 Use identical near and far detectors to cancel many sources of systematics. Use identical near and far detectors to cancel many sources of systematics. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Design detectors to eliminate the need for analysis cuts that may introduce systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Detector cross calibration may be used to further reduce the near/far normalization systematic error. Reduce background rate and uncertainty Reduce background rate and uncertainty ─ Go as deep as you can ─ Veto ─ Use vetoed events to measure the background Redundant measurements to give convincing signal Redundant measurements to give convincing signal ─ Multiple detectors at each site ─ See osc. signal in both rate and spectral distortion How Do You Measure a Small Disappearance?

35. 35 Types of Measurements Counting (Rate) Measurement –Compare total number of observed events in near and far detector –Systematic uncertainty Relative near/far efficiency and normalization Fairly insensitive to relative energy calibrations –Only method available for small detector exp’s (> 300 ton-GW-yrs) Energy (Spectral) Shape Analysis –Compare the energy distribution in the near and far detectors –Systematic uncertainty Largest due to the energy calibration, offsets and scale Insensitive to relative normalization and efficiency –Need large detectors in order to obtain required statistics (> 2000 ton-GW-yrs) –Need single baseline Multiple baselines may wash out energy variation Best to design for both “Rate” and “Shape”

36. 36 Proposed Reactor Oscillation Experiments

37. 37 Comparisons of Proposed Reactor Oscillation Experiments small: sin 2 2  13 ~0.02 to 0.03 –Goal: fast experiment to explore region x3-4 below the Chooz limit. –Sensitivity through rate mainly –Example: Double-Chooz, Kashiwazaki experiments (300 GW-ton-yrs) medium: sin 2 2  13 ~ 0.005 to 0.01 –Make a discovery of  13 in region of interest for the next 10-20 year program –Sensitivity enough to be complementary to offaxis measurements –Sensitivity both to rate and energy shape –Example: Braidwood, Daya Bay (3000 GW-ton-yrs) large: sin 2 2  13 ~0.002-0.004?? –Measurement capability comparable to second generation offaxis experiments –Sensitivity mainly through energy shape distortions –MiniBooNE/Kamland sized detector (20,000 GW-ton-yrs) small medium

38. 38 Braidwood Braidwood Reactor Experiment Exelon Corporation: - Enthusiastic and very supportive of the project - VP has sent letter of support to funding agencies - Security and site access issues not a problem - Have helped with bore holes at near/far locations

39. 39 Braidwood Experiment Design –Four identical 65 ton detectors Outside Radius = 3.5 m Fid. Radius = 2.6 m –Two zones (Inner: Gd Scint, Outer: Pure oil) –Redundant detectors at each site Cross checks and flexibility –Moveable detectors Allows direct cross calibration at near site –Flat overburden at 450 mwe depth –Optimized to use both rate and shape analysis –Mitigate Correlated Background with extensive, active veto system Design Goals: Flexibility, Redundancy, and Cross Checks Baseline Cost Estimate: –Civil Costs: $34M + $8.5M (Cont.) –Detector and Veto System: $18M + $5M (Cont.) Schedule: –2004: R&D proposal submission. –2005: Full proposal submission –2007: Project approval; start const. –2010: Start data collection

40. 40 Braidwood 90% CL Sensitivity vs Years of Data Information from both counting and shape fits Combined sensitivity for sin 2 2  13 reaches the 0.005 level after three years

41. 41 Braidwood Physics Reach For three years of Braidwood data and  m 2 > 2.5 x 10 -3 eV 2 –90% CL limit at sin 2 2  13 < 0.005 –3  discovery for sin 2 2  13 > 0.013 Measurement Capability for sin 2 2  13 = 0.02 and  m 2 = 2.5 x 10 -3 eV 2

42. 42 Other Physics: Neutrino Electroweak Couplings At Braidwood can isolate about 10,000  e – e (elastic scattering) events in the near detector allowing 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 (NuTeV) = 0.3001  0.0014 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 g L 2 - g L 2 (SM) 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 rate.

43. 43 Reactor Experiments Will Join a Strong Program of Worldwide Neutrino Physics

44. 44 Summary Neutrinos have mass and flavor mixing –Observed masses and differences are much smaller than charged lepton partners ?? –Mixings are very large  near 100% ?? But expect small mixings if m is from the “See-Saw” –If all indications true, need to add more neutrinos (“sterile”, heavy?) Neutrinos may have an important role in producing the baryon-antibaryon asymmetry in the universe –Need CP violation in the neutrino mixing –Need sterile neutrinos (also needed for “See-Saw”) Are we on the verge of a next neutrino revolution? Many ideas and projects being proposed …… great time for young theorists and experimentalists to take the lead.

45. 45 Maybe it was the s !