Conventional Neutrino Beams

1. Conventional Neutrino Beams Deborah Harris NuFact05 Summer Institute Anacapri, Italy June 12-13, 2005

2. Fundamentals • Conventional Neutrino Beam • Neutrino Factory Deborah Harris, Conventional Neutrino Beamlines

3. Using Pions to make Neutrinos • 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, Conventional Neutrino Beamlines

4. 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 neutrino beam you want, the higher energy protons you have to start with… • Proton Sources around the world… Deborah Harris, Conventional Neutrino Beamlines

5. 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 MN: • 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, Conventional Neutrino Beamlines

6. 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, Conventional Neutrino Beamlines

7. Target Photo Album CNGS MiniBooNE Image courtesy of Bartoszek Engineering. Shapes are similar, but cooling methods vary…some water cooled, some air cooled NuMI Deborah Harris, Conventional Neutrino Beamlines

8. 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—has been done with High Energy neutrino beams, but focus in vert. or horiz. Deborah Harris, Conventional Neutrino Beamlines

9. 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, Conventional Neutrino Beamlines

10. 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 • For the record, there are also conical horns—what effect would conical horns have? Deborah Harris, Conventional Neutrino Beamlines

11. ( /kt/4e20 p) nm CC evts / kt / 4e20 p / GeV Tuning the Neutrino Beam Energy • The farther upstream the target is, the higher momentum the horns can “perfectly focus”..see this by considering As l gets longer, then ptune gets higher for the same R Deborah Harris, Conventional Neutrino Beamlines

12. Horn Photo Album MiniBooNE CNGS K2K NUMI Horn World Record (so far): MiniBooNE horn pulsed for 100M pulses before failing T2K Horn 1 Deborah Harris, Conventional Neutrino Beamlines

13. Designing what provides the 180kA is as important as designing the horn itself! Deborah Harris, Conventional Neutrino Beamlines

14. 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 pretty much predict components of spectra just from apertures of horns. • p ~ pT/p = rneck / zhorn. p qp Deborah Harris, Conventional Neutrino Beamlines

15. Are there ways to change (lower) the neutrino energy? • Reduce Current in the horns • Yes, but this mostly just gives you fewer neutrinos in the peak but the same number in the tail • Move target closer to the horn • Yes, but eventually you hit the inner conductor • What happens if you move the detector off the main axis of the beamline? p+(in peak) p p+(in tail) B  Deborah Harris, Conventional Neutrino Beamlines

16. 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 Deborah Harris, Conventional Neutrino Beamlines

17. 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, Conventional Neutrino Beamlines

18. Decay Pipe Photo Album T2K CNGS NUMI NUMI NUMI Deborah Harris, Conventional Neutrino Beamlines

19. Slide courtesy C.K.Jung Decay Pipe Cooling Deborah Harris, Conventional Neutrino Beamlines

20. Beamline Decay Pipe Comparison Let yp (ym) be the number of pion (muon) lifetimes in one decay pipe… Deborah Harris, Conventional Neutrino Beamlines

21. Decay Pipe Effect Summary Remember, for a Flux ratio of 0.9, Deborah Harris, Conventional Neutrino Beamlines

22. 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 • Note: for 1020 protons on target per year, roughly 1019 per year hit the absorber… • For scale: NuTeV experiment “pre-oscillation era neutrino experiments” took about 3x1018 protons over entire run Deborah Harris, Conventional Neutrino Beamlines

23. Review of what was covered today • Targets • Horns • Decay Volumes • Hadron Absorber 207m Questions to answer tomorrow: How can you look at what’s happening each time you send protons to the target? How can you predict precisely how many neutrinos you are making? Deborah Harris, Conventional Neutrino Beamlines