Accelerator Neutrino Oscillation Physics Lecture I

1. Accelerator Neutrino Oscillation PhysicsLecture I Deborah Harris SUSSP St. Andrews, Scotland August 15, 2006

2. What have Accelerator-based Experiments told us so far? • No nm→nt mixing at high Dm2 • CHORUS • NOMAD • First Accelerator-based ne appearance: LSND • Still remains to be confirmed or completely refuted • Confirmation of “Atmospheric Neutrino Anomaly” and improved precision on Dmatm2 (or Dm132) • K2K: 1.4GeV, 250km • MINOS: 3.5GeV, 735km • Confirmation of limits on q13 from CHOOZ • K2K Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

3. What do we want Accelerator Oscillations Experiments to tell us? • Are there sterile Neutrinos? • What is the larger mass splitting (Dm232) • q13 and CP violation: are they non-zero? • Neutrino Mass Hierarchy: are n’s like charged fermions? Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

4. Goals of Long Baseline Oscillation Measurements • Measurements of “atmospheric neutrino oscillation parameters”, Dm23 and sin22q23: nm disappearance as a function of neutrino energyP(nm→nm) = 1-sin22q23sin2(Dm232L/4E) • Verify Oscillation Framework: nt appearanceP(nm→nt) ≈ sin22q23sin2(Dm232L/4E) • Search for Sterile Neutrinos: Neutral Current disappearance, looking for three distinct Dm2 • Searches for CP violation and understanding the neutrino mass hierarchy: P(nm→ne) andP(nm→ ne) L=Baseline, E=Neutrino Energy Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

5. P(nm→ne) on one slide (3 generations) P(nm→ne)=P1+P2+P3+P4 P(nm→ne)% Minakata & Nunokawa JHEP 2001 The ± is n or n Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

6. Could you simplify please? Note: this is for Dm122<<Dm232, and for L/E such that sin2 (Dm232L/4E)=1 Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

7. Outline for the rest of this talk • To reach all of the goals, we will need several accelerator-based experiments…. • At this point, you could hear a sequence of mini-talks about the following experiments: • K2K • MINOS • MiniBooNE • OPERA • T2K • NOvA And I would have earned my trip to Scotland…but that’s not the way I think about these experiments…so I’ll talk about them all at once, step by step Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

8. Measuring Oscillation Probabilities with Accelerator-Based n Beam • Fnm: Neutrino Flux (beamline design: lecture I) • snx: Neutrino Cross Section (McFarland) • exMfar: Signal efficiency  Detector Mass(detector design: lecture II) • How well have we done/can we do? (Lecture III) Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

9. Neutrino Beam Fundamentals Cosmic Ray • Atmospheric Neutrino Beam: • High energy protons strike atmosphere • Pions and kaons are produced • Pions decay before they interact • Muons also decay • Conventional Neutrino Beam: very similar! p, K μ e nm nm ne Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

10. But we do more than just make pions… • Major Components: • Proton Beam • Pion Production Target • Focusing System • Decay Region • Absorber • Shielding… Most nm’s from 2-body decays: p+→m+nm K+→m+nm Most ne’s from 3-body decays: m+→e+nenm K+→p0e+ne n energy is only function of np angle and p energy Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

11. Proton Beam • Rules of Thumb • number of pions produced is roughly a function of “proton power” (or total number of protons on target x proton energy) • The higher energy n beam you want, the higher energy protons you need… Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

12. Directing Protons is not trivial… • Example from NuMI: extract beam from between two other beamlines, then make it point down at 3.5o so it comes through the earth in Soudan Minnestota, 735km away: • Example from T2K: Proton source on prime real estate, direction to K2K determined, need to bend HE protons in small space: “combined function” magnets (D and Q) Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

13. Integrated proton power vs time… LSND Nomad/ Chorus CNGS goal MINOS goal First MINOS Restults (1020) K2K MiniBooNE 2 n flavors Discovery of NC’s Plot courtesy Sacha Kopp Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

14. Neutrino Production Targets • Have to balance many competing needs: • The longer the target, the higher the probability the protons will interact • The longer the target, the more the produced particles will scatter • The more the protons interact, the hotter the target will get—targeting above ~1MW not easy! • Rule of thumb: want target to be 3 times wider than +- 1 sigma of proton beam size Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

15. Target Photo Album MiniBooNE Image courtesy of Bartoszek Engineering. CNGS Shapes are similar, but cooling methods vary…some water cooled, some air cooled NuMI Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

16. Focusing Systems • Want to focus as many particles as possible for highest neutrino flux • Typical transverse momentum of secondaries: approximately LQCD, or about 200MeV • Minimize material in the way of the pions you’ve just produced • What kinds of magnets are there? • Dipoles—no, they won’t focus • Quadrupoles • done with High Energy neutrino beams • focus in vertical or horizontal, need pairs of them • they will focus negative and positive pions simultaneously Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

17. What focusing would work best? • Imagine particles flying out from a target: • When particle gets to front face of horn, it has transverse momentum proportional to radius at which it gets to horn B Field from line source of current is in the F direction but has a size proportional to 1/r How do you get around this? (hint: pt  B l ) Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

18. What should the B-Field be? FROM TO • Make the particles at high radius go through a field for longer than the particles at low radius. (B1/r, but make dl  r2) • Horn: a 2-layered sheet conductor • No current inside inner conductor, no current outside outer conductor • Between conductors, toroidal field proportional to 1/r • There are also conical horns—what effect would conical horns have? Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

19. Tuning the Neutrino Beam Energy • The farther upstream the target is, the higher momentum pions the horns can “perfectly focus”..see this by considering 2R z As z gets larger, then ptune gets higher for the same R Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

20. Horn Photo Album MiniBooNE K2K NUMI CNGS Horn World Record (so far): MiniBooNE horn pulsed for 100M pulses before failing T2K Horn 1 Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

21. Horn Question: • Given two horns that are each 3m long and 16cm diameter, what kind of current would you need to give a 200MeV kick to produced secondary particles? 1) 2000 Amps 2) 20,000 Amps 3) 200,000 Amps For pion going through “sweet spot”, assume r/rmax=1/2 For MINOS, for example: (2 horns) r=0.08m, l=3mx2: so for a 200MeV pt kick, I=180kAmps! Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

22. Designing what provides the 180kA is almost as important as designing the horn itself! Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

23. What happens if you have 2 Horns? Overfocused by Horn 1 Underfocused by Horn 1 Focused by Horn 1, through 2 Hits only Horn 2 Goes through Horns 1, 2 • Can predict components of spectra from apertures of horns. • p ~ pT/p = rneck / zhorn. p qp Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

24. How do these pions (and Kaons) decay? • In the center of mass of the pion: 2 body means isotropic decay, neutrino only has one energy • Now boost to the lab frame: you can show (easily) that • And furthermore, you can show (slightly less easily) that the flux of neutrinos at a given location is simply g =boost of pion in lab q =angle between pion andn Thought question: What about 3-body decays? n Energy n Flux versus Angle Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

25. p+(in peak) p p+(in tail) B  Besides target location, how else can you lower the neutrino energy? • Reduce Current in the horns • No, this just gives you fewer neutrinos in the peak Events (arb) MINOS Far Detector Spectra For 3 different Horn Currents nEnergy (GeV) Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

26. Thought Question • How much does peak n rate on axis change when you input half as much current? I=200kA, 100kA, 0kA At MINOS (735km) Events (arb) (Note: 2.53=16, 1.53=3.4) nEnergy (GeV) Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

27. Off Axis Strategy • Trick used by T2K, NOvA (first proposed by BNL) • Fewer total number of neutrino events • More at one narrow region of energy • For nm to ne oscillation searches, backgrounds spread over broad energies Only a consequence of 2-body decay! Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

28. Decay Regions • How long a decay region you need (and how wide) depends on what the energy of the pions you’re trying to focus. • The longer the decay region, the more muon decays you’ll get (per pion decay) and the larger ne contamination you’ll have • Again, tradeoffs between evacuating the decay volume and needing thicker vacuum windows to hold the vacuum versus filling the decay volume with Helium and thin windows, or with air and no windows… T2K Decay Region: Can accommodate off axis Angles from 2 to 3 degrees Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

29. Decay Pipe Photo Album T2K CNGS NUMI (downstream) NUMI NUMI (upstream) Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

30. Slide courtesy C.K.Jung Decay Pipe Cooling Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

31. Beamline Decay Pipe Comparison You can all show that neglecting things hitting the side of the decay pipe… yp=the number of pion lifetimes in one decay pipe… Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

32. Neutrino Beam Divergence • For a perfectly focused monochromatic pion beam, how wide is the neutrino beam? At what q is Φ(q)= Φ(0)/4? Where is Φ(q)= Φ(0)x0.99? Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

33. Follow Up Question: • How much additional divergence is added due to multiple scattering? • Filling the decay pipe with air? • a 1mm Aluminum window? x=gct=g(7.8m) X0=304m x=1mm X0=89mm Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

34. Additional Question • How does the loss of neutrinos from divergence compare to the loss of neutrinos due to pion interactions? • Filling the decay pipe with Air: • 1mm Aluminum Window x=gct=g(7.8m) lint=692m/0.66 Lose 0.007g x=1mm lint=390mm/0.66 Lose 0.002 Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

35. Decay Pipe Effect Summary Remember, for a Flux ratio of 0.99, Moral of this story: Different p energies imply very different decay pipe choices Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

36. Absorbing Hadrons • As proton power gets higher and higher, have to think more and more about what will collect all the un-interacted protons! • MINOS Absorber (1kton): • Water-cooled Al core • Surround with Steel • Surround with concrete • CNGS Absorber • Graphite core + Al cooling modules • Surround with cast iron • Surrounded by rock • Note: for 1020 protons on target per year, roughly 1019 per year hit the absorber… MINOS CNGS Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

37. How can you measure the beam performance? • Remnant Proton Measurements • Tales from the front line: NuMI and the target leak • Muon Measurements • 7o muon spectrometer (MiniBooNE) • “Range stack” Muon Monitor system (MINOS) Pions+… Neutrinos protons Muons+… Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

38. Neutrino Beamline Instrumentation • Proton Beam • Number of Protons on Target • Position and angle • Spot size of beam on target • Proton Losses before target • Target • Position and angle • Is it intact? • Temperature • Horns • Position and angle • Current • Is it intact? • Temperature • Absorber • Temperature Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

39. What about seeing the Protons at the end of the decay pipe? • Proton spot size at end of pipe is large: cannot just put in a new secondary position monitor • Proton rates are now very intense: can use ionization chambers, but they must be very resistant to radiation damage, and can be low gain • Question: what else makes it down to the end of the decay pipe? • Muons from pion decay • Undecayed pions • Secondary shower particles Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

40. Seeing protons at end of pipe No target in the way Target in the way For most beamlines, this “hadron monitor” is really a proton monitor: it tells you about the protons and the target, but not about how well you are making neutrinos Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

41. Lesson Learned: be prepared for disasters… Look at what is between targetand baffle by shooting protons there! • Leaky Target at NuMI • the target has pipes around it that carry water to cool it • March 2005, discovered a leak: speculate the target surrounded by water… • Use Hadron Monitor to verify that water was there, and to check that it hasn’t reappeared since we solved the problem… Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

42. Monitors to Study n Beam (MINOS) m+ m+ nm m+ m+ p p+ m+ m+ Hadron Monitor: sees uninteracted protons after decay pipe Muon Monitors: 3 different depths means three different muon momentum spectra Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

43. Getting to Neutrino Spectrum from Muon Spectrum (MINOS) • As you get to higher muon energies, you are looking at higher pion energies…which in turn mean higher neutrino energies… Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

44. Muon Monitors in Different Energy Neutrino Beams • By looking at the rates in the three different muon detectors, can see how the energy distributions of the muons changes • Can study neutrino fluxes by moving the target and seeing how you make more high energy neutrinos the farther back you move the target • Can study fluxes by changing the horn current and see how you make more low energy neutrinos as you increaste the horn current. Graphs courtesy S. Kopp Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

45. Oscillation Experiments: Beams past, present, and near future… MiniBooNE OPERA T2K MINOS NOvA K2K Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

46. Conventional Neutrino Beam Summary • Major Components: • Proton Beam • Production Target • Focusing System • Decay Region • Shielding • Monitoring Ways to Understand n Flux: Hadron Production Proton Beam measurements Pion Measurements Muon Measurements at angles vs momentum at 0o versus shielding Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

47. What else you can do with muons:Measure K/p ratio in Beam • ne’s from muon decay constrained by nm spectrum (since they are part of the same channel) • Kaons have no such constraint • Remember problem set: to get the ne /nm Ratio you would also need to know the K/p production ratio (and focusing differences) Any way this can be measured in the beam? Beam too hot to add Cerenkov counters to get track/track information Think 2-body decay kinematics: Center of Mass Lab Frame Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

48. Example from MiniBooNE Backgrounds from muons that scatter in the dirt/collimator • By adding collimator and spectrometer at 7o, they will measure • p/K ratio from difference in peaks • K/KL ratio from m+ versus m- Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

49. Measuring p angular distribution in real beamline • K2K Gas Cerenkov counter: measures angular distribution of Pions as function of momentum • Located right after horns • Works for pions above 2GeV Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I

50. Measuring p angular distribution in real beamline Deborah Harris, Accelerator Neutrino Oscillation Physics Lecture I