Neutrino Oscillations: The Next Steps?

1. Neutrino Oscillations: The Next Steps? M. Shaevitz Columbia University WIN 05 Workshop Introduction MiniBooNE and LSND Determiningq13: Reactor Oscillation Experiments (Next talks: Feldman – Long baseline oscillation experiments – NovaMondal – Next generation atmospheric exp. – INO )

2. Possible New Surprises in the Next Step • 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 • 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 couldbe a key ingredient for explaining the matter-antimatter asymmetry in the universe • Then look at n versus n oscillations to measure d  New long baseline and reactor experiments are key

3. Possibility 1: The LSND Experiment  Sterile Neutrinos ? 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 s evidence for oscillation. Oscillations? LSND took data from 1993-98 - 49,000 Coulombs of protons - L = 30m and 20 < En< 53 MeV

4. (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 n osc. Additional “sterile” neutrinos involved in oscillations Why Sterile Neutrinos? Need better measurement in LSND region MiniBooNE

5. Booster MainInjector Use protons from the Fermilab 8 GeV booster Neutrino Beam <En>~ 1 GeV Booster Neutrino Experiment(MiniBooNE) MiniBooNE designed to check LSND signal by searching for ne appearance in a nm beam at Fermilab.

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

7. MiniBooNE Collaboration 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 consists of about 70 scientists from 13 institutions.

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 ne events in a pure nm beam (  e and  e )

9. Particle Identification • Separation of ne from nm events • Exiting nm events fire the veto • Stopping nm events have a Michel electron after a few msec • 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 Stopping muon event

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

11. MiniBooNE sees n events in the 8 ms NuMI beam window that agree with expectation. MiniBooNEDetector Elevation View Offaxis NuMI Beam q = 100 – 250 mr pand K decays NuMI Target NuMI Beam NuMI Dump NuMI NearDetector NuMI Beam Events in MiniBooNE(World’s 1st Offaxis Neutrino Measurement !!)  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. Dm2 = 1 eV2 Dm2 = 0.4 eV2 MiniBooNE Run Plan • At the current time have collected: • 5.6 × 1020 protons on target (original goal was 1 × 1021) • ~600k neutrino candidates (world’s largest sample in the 1 GeV region) • Blind analysis: Hide possible ne candidates; other ~90% events are openPlan is to “open the ne appearancebox” when the analysis has been substantiated and when sufficient data has been collected for a definitive result Current estimate is sometime in Late 2005 Next Step “Signal” No Signal“Limit”

13. If MiniBooNE sees no indications of oscillations with nm Need to run withnm since LSND signal wasnmne(Indications of CP violation) If MiniBooNE sees an oscillation signal Many m2 and mixing angles plus CP violation to determine  BooNE Experiment (with  and) Add another detector to MiniBooNE at 1-2 km distance(Also nt appearance searches.) The Next Step

14. Possibility 2: CP Violation in Neutrino Mixing

15. Unknown CP violation phase What do we know? Solar: 12 ~ 30° sin2 213 < 0.2 at 90% CL(or 13 < 13°) Atmospheric: 23 ~ 45° What is e component of 3 mass eigenstate? These two differentmass schemesare called:Mass HierarchyProblem

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

17. Methods to measuresin2213 Reactor experiments allow direct measurement of sin22: no matter effects, no CP violation, almost no correlation with other parameters. • Long-Baseline Accelerators: Appearance (nmne) at m22.510-3 eV2 NOA:<E> = 2.3 GeV, L = 810 km T2K: <E> = 0.7 GeV, L = 295 km Currently pursued Offaxis Exps. • Reactors: Disappearance (nene) at m22.510-3 eV2

18. 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 and Offaxis Exps. Are Complementary • Reactor experiment needed for determining q13  Is q13 large enough? • Then offaxis studies of n andn give sensitivity to CP violation Reactor Exp. Best for Determining q13 Reactor Can Lift q23 Degeneracy(Example: sin2223 = 0.95  0.01) 90% CL Δm2 = 2.5×10-3 eV2sin22q13 = 0.05 McConnel /Shaevitzhep-ex/0409028 90% CL Δm2 = 2.5×10-3 eV2sin22q13 = 0.05

19. Reactor and Offaxis Exps. (cont’d) Far future: Precision Osc.Parameter Measurements 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 • Require longer baseline experiments to measure CP and mass hierarchy • Measuring the full set of mixing parameters (q12,q13,q23, and d) is needed for addressing quark-lepton unification models. 90% CL (Add Reactor)

20. Consensus Recommendation 2 (of 3): An expeditiously deployed multi-detector reactor experiment with sensitivity … sin22q13=0.01 … A timely accelerator experiment with comparable … sensitivity … A proton driver … with an appropriate very large detector …

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

22. Nuclear reactors are a 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 From Bemporad, Gratta and Vogel Arbitrary Observable n Spectrum Cross Section Flux Reactor Measurements of 13 • Disappearance Measurement:Look for small rate deviation from 1/r2 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. e+ e = Photomultiplier Tube n Experimental Setup • 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)

24. Looking for a small change in the expected rate and/or shape of the observed event Past reactor measurements: Precision Reactor Disappearance Exp. Are Difficult • 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

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

26. Sin22θ13 Reactor Experiment Basics νe νe νe νe νe νe sin22θ13 Well understood, isotropic source of electron anti-neutrinos Oscillations observed as a deficit of νe E≤ 8 MeV 1.0 Unoscillated flux observed here Probability νe Survival Probability Distance 1200 to 1800 meters

27. How Do You Measure a Small Disappearance? • 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.

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

29. How Do You Measure a Small Disappearance? • 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. • Detector cross calibration may be used to further reduce the near/far normalization systematic error. • Use events and sources to cross calibrate • For example, n capture peaks •  Move far detectors to near site for cross calibration

30. How Do You Measure a Small Disappearance? • 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. • Detector cross calibration may be used to further reduce the near/far normalization systematic error. • Reduce background rate and uncertainty

31. 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 • 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

32. How Do You Measure a Small Disappearance? • 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. • Detector cross calibration may be used to further reduce the near/far normalization systematic error. • Reduce background rate and uncertainty • Go as deep as you can • Veto

33. Veto Detectors p n n m m Veto Background Events Fast neutrons Veto m’s and shield neutrons 9Li and 8He • Produced by a few cosmic ray muons through spallation • Large fraction decay giving a correlated β+n Shielding KamLAND Data 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. 6 meters

34. How Do You Measure a Small Disappearance? • 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. • Detector cross calibration may be used to further reduce the near/far normalization systematic error. • 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 • Multiple detectors at each site • See osc. signal in both rate and spectral distortion

35. 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 Types of Measurements Best to design for both “Rate” and “Shape”

36. Proposed Reactor Oscillation Experiments

37. small medium Comparisons of Proposed Reactor Oscillation Experiments small: sin22q13~0.02 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: sin22q13~ 0.005 to 0.01 • Make a discovery of q13 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: sin22q13~0.002-0.004?? • Measurement capability comparable to second generation offaxis experiments • Sensitivity mainly through energy shape distortions • MiniBooNE/Kamland sized detector (20,000 GW-ton-yrs)

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. Braidwood Experiment Design Design Goals: Flexibility, Redundancy, and Cross Checks • 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 Backgroundwith extensive, active veto system • 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. Braidwood90% 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

41. Braidwood Physics Reach • 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 Measurement Capability for sin22q13 = 0.02and Dm2 = 2.5 x 10-3 eV2

42. Other Physics: Neutrino Electroweak Couplings At Braidwood can isolate about 10,000ne – e (elastic scattering) events in the near detector allowing 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 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 rate.

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

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 mn 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. Maybe it was the ns !