Questions and Quandaries? The Neutrino Program at Fermilab

1. Questions and Quandaries?The Neutrino Program at Fermilab Michael Shaevitz Columbia University / Fermilab • Neutrinos and the Standard Model • Do neutrinos fit in like the other particles? • NuTeV High-Energy Neutrino Experiment • Neutrino Masses and Mixing • What is the mass spectrum and mixing of the different neutrinos? • Are there more than three types of neutrinos? • MiniBooNE and NuMI/Minos Neutrino Oscillation Experiments

2. Introduction to Neutrino Interactions

3. Neutrinos in the Standard Model • Neutrinos only interact through the “weak force” • Neutrino interaction with W and Z bosons is (V-A) • Neutrinos are left-handed(Antineutrinos are right-handed) • Neutrinos are massless (But we measure small masses) • Three types of neutrinos • Electron ne e • Muon nm m • Tau nt t

4. Highlights of Neutrino History Reines & Cowann Detector 1st Observedpmn decay

5. Neutrino Interactions • W exchange gives Charged-Current (CC) events and Z exchange gives Neutral-Current (NC) events In CC events the outgoing lepton determines if neutrino or antineutrino

6. Neutrino Cross Section is Very Small • Weak interactions are weak because of the massive W and Z boson exchange (Higgs gives this mass) sweak (1/MW)4 • For 100 GeV Neutrinos: • s(ne) ~ 10-40and s(nN) ~ 10-36cm2vs. s(pp) ~ 10-26cm2 • Mean free path length in Steel ~ 3109 meters! (Need big detectors) MW ~ 80 GeVMZ ~ 91 GeV sEM 1/Q4 At Hera see W and Z propagator effects - Also as EM strength falls off  CC  NC > EM

7. Linear rise with energy Resonance Production Neutrino-Nucleon Processes (Deep Inelastic Quark Scattering)

8. Helicity is projection of spin along the particles direction Frame dependent (if massive) Neutrinos only interact weakly with a (V-A) interaction All neutrinos are left-handed All antineutrinos are right-handed left-helicity right-helicity Neutrinos Are Left-Handed(Helicity and Handedness) • If neutrinos have mass then left-handed neutrino is: • Mainly left-helicity • But also small right-helicity component  m/E • Handedness (or chirality) is Lorentz-invariant • Only same as helicity for massless particles. • Only left-handed charged-leptons (e-,m-,t-) interact weakly but mass brings in right-helicity:

9. NuTeV Electroweak Measurements

10. Electroweak Theory • Standard Model • SU(2)  U(1) gauge theory unifying weak/EM interaction  weak Neutral Current interaction  Higgs particle gives massive W and Z • One parameter to measure! • Weak / electromagnetic mixing parameter sin2qW(Related to weak/EM coupling ratio g’=g tanW) • Neutrinos are special in SM • Only have left-handed weak interactions  W and Z boson exchange

11. History of EW Measurements Gargamelle CCFR, CDHS, CHARM, CHARM IIUA1 , UA2 , Petra , Tristan , APV, SLAC eD • Discovery of the Weak Neutral Current • Summer 1973 (CERN) • SM predicted: nmN  nmX • First Generation EW Experiments • Experiments in the late 1970’s • Precision at the 10% level • Tested basic structure of SM  MW,MZ • Second Generation EW Experiments • Experiments in the late 1980’s • Discovery of W,Z boson in 1982-83 • Precision at the 1-5% level • Radiative corrections become important • First limits on the Mtop • Current Generation Experiments • Precision below 1% level • Discovery of the top quark • Use consistency to search for new physics • Constrain MHiggs  Predict light Higgs boson (and possibly SUSY) GargamelleHPWF CIT-F NuTeV D0 CDF, LEP1 SLDLEPII APV , SLAC-E158

12. Current Era of Precision EW Measurements • Precision parameters define the SM: • aEM-1 = 137.03599959(40) 45ppb (200ppm@MZ) • Gm = 1.16637(1)10-5GeV-2 10ppm • MZ= 91.1871(21) 23ppm • Comparisons test the SM and probe for new physics • LEP/SLD (e+e-), CDF/D0 (p-pbar), nN , HERA (ep) , APV • Radiative corrections are large and sensitive to mtop and mHiggs • mHiggs constrained in SM to be less than196 GeV at 95%CL

13. Summary of Electroweak Measurements(Before NuTeV) • Most data suggest a light Higgs except AFBb • Global fit has c2=23/15 (9%) • AFBb is off about 3s

14. NuTeV Experiment at Fermilab High Energy (En~100 GeV) High Statistics (several million events)Neutrino Experiment (1996-97) using the Fermilab 800 GeV Proton Beam Charged-Current(CC) Neutral-Current(NC) For an isoscalar target composed of u,d quarks:

15. Before and After NuTEV • nN experiments before NuTeV had hit a brick wall in precision Due to systematic uncertainties (i.e. mc ....) NuTeV Technique Cross section differences remove these systematic uncertainties (from mainly sea quark contributions) But need to makemeasurement for bothneutrinos and antineutrinos

16. Use magnets after target to pick:p+ for neutrino modep- for antineutrino mode NuTeV Detector (690 tons of steel) Make ’s and K’s Make ’s fromp,K m n decays Slow down and stopall m’s in shielding Only n’s left !

17. 690 ton n-target Toroid Spectrometer Target / Calorimeter NuTeV Detector

18. NuTeV Collaboration Cincinnati1, Columbia2, Fermilab3, Kansas State4, Northwestern5, Oregon6, Pittsburgh7, Rochester8(Co-spokepersons: B.Bernstein, M.Shaevitz)

19. Neutral Current / Charged CurrentEvent Separation Separate NC and CC events statistically based on the “event length”defined in terms of # counters traversed

20. Events LcutRegion Events LcutRegion Determine Rexp: The Short to Long Ratio: Event Length DistributionNeutrinos NC CC Event Length DistributionAntineutrinos Cuts:- Ehad > 20 GeV- Fiducial Vol.

21. From Rexp to Rn Need detailed Monte Carlo to relate Rexp to Rn and sin2qW • Short nm CC’s(20% n , 10% n) • muon exits, range outat high y • Short ne CC’s (5%) • ne N  e X • Cosmic Rays (0.9%/4.7%) • Long nm NC’s (0.7%) • punch-through effects

22. Result from Fit to Rn and Rn • NuTeV result: (Previous neutrino measurements gave 0.2277  0.0036) Standard model fit (LEPEWWG): sin2qW = 0.2227  0.00037A 3s discrepancy ........... Discrepancy is n’s Discrepancy is left-handedcoupling to u and d quarks NC coupling is too small

23. Using sin2qW = 1-mW2/mZ2 relation with know mZ Compare to other mWmeasurements Comparison to Other EW Measurements Each electroweak measurement also indicates a range of Higgs masses

24. Possible Interpretations • Changes in Standard Model Fits • Change assumed quark distributions • Change Mhiggs  Need > 1000 TeV ! • “Old Physics” Interpretations: QCD • Violations of “isospin” symmetry • Strange vs anti-strange quark asymmetry • Are n’s Different? • Special couplings to new particles • Majorana neutrino effects • Neutrino oscillations – ne disappearance • “New Physics” Interpretations • New Z’ or lepto-quark exchanges • New particle loop corrections

25. Future Possibilities • Unfortunately, the high-energy neutrino beam at Fermilab has been terminated Need to rely on other experiments for progress • Upcoming new measurements: • SLAC E-158 Polarized electron-electron scattering (Low Q2) • NuMI/Minos near detector nmN NC/CC scattering at En~3 GeV • Fermilab Tevatron CDF/D0 Run 2 searches for Z’ and leptoquarks • Neutrino oscillation measurements ne disappearance

26. Neutrino Mass and Oscillation Phenomenology

27. Making Neutrinos Matter • Standard Model assumes that neutrinos are massless • No symmetry property or theoretical reason for mn = 0 • Neutrinos are partners of the massive charged leptons • Could imply right-handed n ’s, Majorana n =nor sterile n’s • Neutrino mass hierarchy ? t m entnm ne • Cosmological Consequences • Neutrinos fill the universe from the Big Bang (109n / m3) Even a small mass (~1 eV) will have effects • Models have hot (n) and coldDark Matter • Massive neutrino affect structure formation such as galaxies and clusters

28. Neutrino Mass: Theoretical Ideas • No fundamental reason why neutrinos must be massless • But why are they much lighter than other particles? • Grand Unified Theories • Dirac and Majorana Mass  See-saw Mechanism • Modified Higgs sector to accommodate neutrino mass • Extra Dimensions • Neutrinos live outside of 3 + 1 space Many of these models have at least one Electroweak isosinglet n • Right-handed partner of the left-handed n • Mass uncertain from light (< 1 eV) to heavy (>1016 eV) • Would be “sterile” – Doesn’t couple to standard W and Z bosons

29. Direct Neutrino Mass Experiments Direct decay studies have limited sensitivity at small n mass • Techniques • Electron neutrino: • Study Ee end point for 3H3He + ne + e- • Muon neutrino: • Measure Pm in pmnm decays • Tau neutrino: • Study np mass in t (np) nt decays < 2 eV m (keV) < 170 keV e(eV) t (MeV) < 18 MeV

30. Neutrino Oscillations • Direct measurements have difficulty probing small neutrino masses  Use neutrino oscillations • If we postulate: • Neutrinos have (different) mass  Dm2 = m12 – m22 • The Weak Eigenstates are a mixture of Mass Eigenstates Then a pure nm beam at L=0, will develop a ne component as it travels a distance L.

31. Oscillation Formula Parameters nmDisappearance neAppearance

32. 3-Generation Oscillation Formalism • But we have 3-generations: ne , nm, and nt (and maybe even more ….. the sterile neutrino ns’s ) where sij=sinqij and cij=cosqijThere are three angles q12 (solar) q23 (atmospheric) q13 (????) along with d = phase that could lead to CP violation

33. Oscillation Plots • If you see an oscillation signal with Posc = P  dP then carve out an allowed region in (Dm2,sin22q) plane. • If you see no signal and limit oscillation with Posc < P @ 90% CLthen carve out an excluded region in the (Dm2,sin22q) plane.

34. Neutrino Sources for Experimentation • Also: • Supernova Neutrinos( ~10 MeV) • Relic “Big-Bang” Neutrinos(250 meV)

35. Three Positive Signals Solar Neutrinos Atmospheric Neutrinos Low-E Accelerator Neutrinos Many negative searches Current Neutrino Oscillation Signals ???? Hard to check with charged leptonnumber violation:With n-osc with Dm2=310-3 eV2  B(tmg)~10-41

36. Booster MainInjector Upcoming Experiments SNO(Canada): Solar n’s 1000 tons D2O K2K(Japan): 1.4 GeV Acc. n’s 250 km to SuperK Det. MiniBooNE: 1 GeV Acc. n’s 500 m to Detector Also Borexino(Italy) NuMI: 3 GeV Acc. n’s 750 km to MINOS Det. Kamland (Japan): Reactor n’s 1000 m3 Liquid Scint. Also CNGS (CERN to Italy)

37. Questions to Answer Over the Next ~5 years • LSND Dm2 • Definitive determination if osc. • Measure Dm2/sin22q to 5-10% • If positive  New round of experiments: nm and e nt • Atmospheric Dm2 • Know if nm ntorns • Measure Dm2/sin22q to 10% if Dm2> 210-3eV2 • Maybe see nmne • Solar Dm2 • Restrictions to one solar solution • Know if ne nm,torns  Results from MiniBooNE Fermilab  Results from K2K, MINOS , CNGS Fermilab  Results from Kamland, Borexino, SNO

38. Recent Sudbury Neutrino Observatory (SNO) in CanadaResults for Solar Neutrinos • SNO has measured the total active neutrino flux coming from the sun using D2O SNO Measurements: Total flux = 5.09  0.64  106 cm-2s-1ne flux = 1.76  0.10  106 cm-2s-1 Solar Model Prediction: Total flux = 5.05  1.00  106 cm-2s-1 • Conclusive indication of oscillations to active (nm or nt) neutrinos • Constrains amount of oscillations to sterile neutrinos Also, CC day/night flux difference - Constrains possible solar oscillation solutions from matter effects in the earth.

39. NuMI / MINOS Oscillation Exp

40. NuMI / Minos Experiment at Fermilab • Recreate the atmospheric neutrino experiment using accelerator neutrinos – Only way to conclusively show that n-oscillations occur 15 km Super-K nmdeficit with azimuthBest fit: Dm2=2.410-3eV2 sin22q=1.0 Super-K AtmosphericOsc. Signal No Osc With Osc 13,000 km • NuMI Beam at Fermilab <En> ~ 3 GeV • For Dm2=210-3eV2, need L ~ 1000 km

41. Det. 2 Det. 1 The NuMI/MINOS Experiment Two Detector Neutrino Oscillation Experiment Far Detector: 5400 tons Near Detector: 980 tons

42. MINOS Collaboration

43. MINOS Oscillation Sensitivity Minos will see oscillatory behavior Minos can measure Dm2 and sin22qover the complete Super-K region 90% CLSensitivities 10 kt-yr Exposure(~1400 CC events/yr)

44. 4s Separation Region MINOS Oscillation Mode Sensitivity( Discriminate nm vs. nmsterile ) • Use CC/NC Ratio to distinguish between oscillations to ntor nsterile • Fornm , CC production of t’s will look like NC ~80% of the time CC/NC  down • Fornmsterile , both CC and NC will be suppressed. CC/NC stays ~ constant

45. (Calendar year) In an old iron mine (State Park)Soudan, Minnesota NuMI/Minos Project At Fermilabin Illinois Very Large Project: $170M Start early 2005

46. Tunnel BoringMachine NuMI Decay Tunnel - July 2001

47. MINOS Far Detector Double Cosmic- Ray Muon in MINOS Far Detector Far Detector InstallationPlane #100 on Jan. 17, 2002!

48. NuMI/Minos Physics Potential • Show that nm oscillate into other flavors with Dm2 ~ 210-3eV2 • See oscillatory behavior • Measure Dm2/sin22q to 10% • Determine if oscillation is nm ntornm ns • Search for nmneoscillations at Dm2 ~ 210-3eV2

49. MiniBooNE Oscillation Exp

50. The LSND Signal An accelerator based experiment that sees oscillations in the high Dm2 region