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Current Knowledge of Neutrino Cross-Sections and Future Prospects

Current Knowledge of Neutrino Cross-Sections and Future Prospects. D. Casper University of California, Irvine. Outline. Why do we care? What do we know from past experiments? What are current experiments telling us? Outlook for future experiments. “Normal”. “Inverted”. 3. 2. 1. 2. 3.

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Current Knowledge of Neutrino Cross-Sections and Future Prospects

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  1. Current Knowledge ofNeutrino Cross-Sectionsand Future Prospects D. Casper University of California, Irvine

  2. Outline • Why do we care? • What do we know from past experiments? • What are current experiments telling us? • Outlook for future experiments

  3. “Normal” “Inverted” 3 2 1 2 3 1 Neutrino Oscillation: Goals • Probe fundamental parameters of Standard Model: • Precision measurement of |m223| • Precision measurement of 23 • Measurement of unknown angle 13 • Determination of mass hierarchy sgn(m223) • Search for leptonic CP violating phase  • Measurements involve probabilities • Need number of oscillated neutrinos and number of starting neutrinos • Next generation experiments, starting with MINOS, will have impressive statistical power from high luminosity beams and massive detectors • Systematic uncertainties must be controlled at a level comparable to the statistical errors to take full advantage

  4. K2K C. Walter, NUINT02 NOA(13 nearCHOOZ bound) Normal Hierarchy Inverted Hierarchy Neutrino Oscillation: Requirements • Neutrino energy resolution for CC interactions • K2K/T2K: Quasi-elastic channel • MINOS/NOA: Calorimetry (Evis  E) • Control energy-scale systematics for high E-resolution sample at few percent level • Efficiency • Contamination • Control near/far beam flux and energy spectrum differences at few percent level • Control background for e appearance signature at few per-mille level • Beam e, CC, NC contributions • Control neutrino/anti-neutrino systematics at percent level for mass hierarchy and CP studies

  5. Neutrino Oscillation: Realities • Only well-known neutrino interaction cross-section is for electron scattering • Unfortunately useless for oscillation experiments with accelerators • Available data for few-GeV reactions: • Old (Early ’70s to mid 80’s) • Normalized to quasi-elastic measurements, using obsolete form factor parameters, and introducing complicated correlated errors • Beam spectrum and flux based on dubious hadron production models • Undocumented and inconsistent corrections for nuclear targets • Sparse • Energy, hadronic mass reach limited • Nuclear targets not applicable to common detector materials • Almost no data on > 1 exclusive channels • Anti-neutrino data even worse • Low-statistics • Neutral current 1 data based on a few dozens of events • Mutually inconsistent

  6. What About a Near Detector? • Near detectors are important, but not a panacea •  flux and spectrum differs far vs. near • Not identical even without oscillation, due to extended source • CC backgrounds and contamination extrapolate differently than NC+beam, due to oscillation • Optimal sensitivity dictates that far detector is at oscillation maximum, making the difference as large as it can be • Near/Far detectors usually not identical • Far detector must be large, coarse-grained • If identical, near detector has similar resolution and not suited to measure cross-sections • K2K/T2K solution: two near detectors… • Maximum physics reach requires: • Near detector similar in composition, performance and resolution to far detector • Good model/measurements of parent hadron beam • Good understanding of exclusive neutrino cross-sections NOAP() Nuance

  7. Extruded scintillator (15t) EM calorimeter 3m n Multi-anode PMT (64ch) 3m 1.7m Wave-length shifting fiber K2K Near Detectors En (GeV) SciBar SciFi

  8. MiniBooNE (H. Tanaka, WG2)

  9. CC Quasi-Elastic Scattering • Dominant reaction up to ~1 GeV energy • Essential for E measurement in K2K/T2K • The “well-measured” reaction • Uncertain to “only” 20% or so for neutrinos • Worse in important threshold region and for anti-neutrinos • Axial form-factor not accessible to electron scattering • Essential to modeling q2 distribution • Recoil proton reconstruction requires fine-grained design - impractical for oscillation detectors • Recent work focuses on non-dipole form-factors, non-zero GnE measurements

  10. (88% purity) K2K SciBar2-ring QE (70% purity) MiniBooNE K2K and MiniBooNE CCQE Rates • K2K and MiniBooNE rates agree with MC for CCQE • Only shape is measured, not absolute cross-sections • Same data is used to measure the neutrino flux!

  11. CC Resonant Single-Pion Production • Existing data inconsistent (factor 2 variations) • Treatment of nuclear effects unclear • Renewed theoretical interest with JLAB data Sato et al. Dynamical Model

  12. K2K/MiniBooNE CC Pion Production 1-kton 0 candidates • 1-kton: Study of 0proton decay background • MiniBooNE: 85% purity for CC ± sample(no results, in progress) Normalized to total events

  13. NC Single-Pion Production • Historical samples of NC single pion production: • ANL •  p n + (7 events) •  n n 0 (7 events) • Gargamelle •  p p 0 (240 evts) •  n n 0 (31 evts) • Crucial background for e appearance searches!

  14. K2K/MiniBooNE NC 0 Production K2K (Preliminary) MiniBooNE: Shape comparison only

  15. Deep-Inelastic Scattering • One area with lots of data and a clear theoretical framework, but uncertainties remain: • Nuclear effects? • Low-q2 regime • Connection/overlap with resonant production

  16. Quark/Hadron Duality • Recent JLAB data have revived interest in quark/hadron duality • Bodek and Yang have shown that DIS cross-sections can be extended into the resonance regime, and match the “average” of the resonant cross-section Bodek and Yang

  17. Nuclear Effects (QE/Resonant) All currently running detectors see anomalous suppression at low-Q2 1kton SciBar MiniBooNE SciFi One anomaly or two?

  18. 1.2 EMC NMC 1.1 E139 E665 1 0.9 0.8 0.7 0.001 0.01 0.1 1 Nuclear Effects (DIS) Fermi motion E = 5 GeV(NEUGEN) p+ LH on p- LH off original EMC finding shadowing x sea quark valence quark Hadron formation length effects Bound nucleon structure functions

  19. Final-State Interactions • Renewed theoretical interest, plus new data from JLAB NEUT MC

  20. “Hope is on the way…” • HARP data (next talk) • Hadron production measured with K2K, MiniBooNE targets at CERN • Will provide essential data for neutrino fluxes, aid absolute cross-section measurements • MINERA at NuMI (2006?) • T2K Near Detectors (2009?) • 280m: Fine-grained (design not finalized) • 2km: Water Cherenkov + fine-grained (not yet approved) • Potential to measure cross-sections around few GeV, if independent flux prediction available

  21. MINERA at a Glance • Scintillating strip design leverages DZERO, K2K, MINOS experience • Modular construction, good spatial resolution, 3d-tracking, fast timing and dE/dx measurement at attractive cost • Fully-active central volume surrounded by magnetized “calorimeters” • Inner fiducial mass > 3 tons • Iron + Lead planes upstream to vary nuclear target • Parasitic operation within current NuMI/MINOS run-plan yields 1.25M neutrino events/ton • Broad neutrino energy reach • MINOS near detector can substitute for downstream muon ranger • MIPP will measure NuMI hadron production within ~few percent, allowing precision absolute cross-section measurements

  22. MINERA CCQE Measurements Full simulated analysis, including realistic detector simulation and reconstruction

  23. MINERA Resonant Pion Production • Errors statistical only, assuming 50% efficiency

  24. MINERASimulated Measurements Coherent Pion Production • Neutral-current reaction important background for e appearance search • Realistically, 100% uncertainties in rate for oscillation experiments • Theoretical models vary significantly • CC reaction (easier to measure) closely related to NC • No data on light nuclei in energy region of relevance • K2K and MiniBooNE may help at low energies, but NC background to e appearance feeds down from high energies • Easier to distinguish with proton reconstruction and (for CC reaction) dE/dx

  25. Conclusions • Few-GeV neutrino interaction physics is (finally) leaving the “Dark Ages” • Multiple, synergistic lines of attack are beginning to peel back our ignorance: • Data from K2K and MiniBooNE • Electron scattering data • HEP/Nuclear collaboration (NUINT workshops) • Revived theoretical attention to different questions • MINERA and T2K can provide another quantum leap • Independent knowledge of fluxes are vital for absolute measurements • Continued progress on cross-sections will be invaluable for future oscillation experiments

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