1. Atmospheric Neutrinos Barry Barish Bari, Bologna, Boston, Caltech, Drexel, Indiana, Frascati, Gran Sasso, L’Aquila, Lecce, Michigan, Napoli, Pisa, Roma I, Texas, Torino MACRO

3. Neutrino event topologies in MACRO Detector mass ~ 5.3 kton Event Rate: (1) up throughgoing  (ToF) ~160 /y (2) internal upgoing  (ToF) ~ 50/y (3) internal downgoing  (no ToF) ~ 35/y (4) upgoing stopping  (no ToF) ~ 35/y Absorber Streamer Scintillator (1)(2)(3) (4)

4. Energy spectra of events detected in MACRO  ~ 100 GeV for throughgoing   ~ 5 GeV for internal upgoing   ~ 4 GeV for internal downgoing  and for upgoing stopping   Low energy events allow us to investigate the oscillation parameter space independently of the throughgoing muon data

5. Neutrino induced upward-going muons identified by the time-of-flight method   scintillator streamer track   T 2 -T 1 ) * c / l

6. Upward throughgoing muons External -interactions768 events upward vs downward muons

7. Background source for  events: pion production by downward  ’s (MACRO Collab., Astroparticle Phys. 9(‘98)105) rate of downgoing  ’s ~10 5 x rate of upgoing  ’s background mainly pions produced at large angles by  interactions in the rock around the detector (  + N  +  ± + X) Estimated background in MACRO: ~ 5% for the stopping muon sample (MACRO Coll., PL B478 (‘00) 5) ~ 1% for the up-throughgoing m (>200 g/cm 2 cut) MACRO Coll., PL B434 (‘98) 451)  

8. Pion production at large angle upgoing charged  produced by  interactions in the rock under the detector a background source for upward stopping and throughgoing muons studied 243 events with downgoing  plus upgoing particles  Estimated background - upward throughgoing  ’s: ~1% - low energy events:~5%

9. Total observed flux and comparison with Monte Carlo Data number of events: 768 events background (wrong  )18 background (  ’s from muons)12.5 Internal neutrino interactions14.6 Total 723 events Prediction (Monte Carlo) 989 ± 17% Bartol neutrino Flux (±14%) GRV-LO-94 cross section (± 9%) Lohmann muon energy loss (± 5%) data/prediction R = 0.731 ± 0.028 stat ± 0.044 syst ± 0.124 theor

10. Effects of  oscillations on MACRO events Flux reduction depending on zenith angle for the upward throughgoing events Earth  underground detector L ~ 10 - 10 4 km distortion of the angular distribution

11. Zenith angle distribution E  > 1 GeV

12. Probabilities of    oscillations (for maximal mixing) Probability The peak probability from the angular distribution agrees with the peak probability from the total number of events Probability for no-oscillation: ~ 0.4 %

13. Probabilities for sterile neutrino oscillations with maximum mixing Peak probabilities lower than that for tau neutrinos: from the angular distribution: 4.1 % from combination: 14.5 % Probability

14. Probabilities for sterile neutrino oscillations

15. Test of oscillations with the ratio vertical / horizontal Ratio (Lipari- Lusignoli, Phys Rev D57 1998) can be statistically more powerful than a  2 test: 1) the ratio is sensitive to the sign of the deviation 2) there is gain in statistical significance Disadvantage: the structure in the angular distribution of data can be lost. Measured value ~ 2  (and one sided) from the expected value for sterile neutrino

16. Internal upward going  events From MC simulation: E ~ 5 GeV ~ 87% due to  -CC interactions Results: Phys. Lett. B478 (2000) 5 (141 events) Data - Background = 135 events  distribution after all analysis cuts: Upgoing internal muons

17. Internal Downgoing  ’s and Upward Going Stopping  ’s from MC simulation : E ~ 4 GeV mixture  upward going stopping  ~ 50%  internal downgoing  ~ 87% from  –charged current events DATA - Background = 229 events Upward going stopping Internal downgoing

18. Data vs Monte Carlo Predictions  : Bartol flux with geomagnetic cutoffs (error ~ 20%)  = Q.E. + 1  (Lipari et al., PRL74 (1995) 4384) + DIS (GRV-LO-94 PDF) (error ~ 15%)  (E ,  zenith ): detector response and acceptance (systematic error ~ 10 %) MC: 247  25 sys  62 theo DATA:135  12 stat MC:329  33 sys  82 theo DATA:229  15 stat Internal down + Upgoing stop Internal upward going  ’s Low Energy Neutrino Events

19. Internal upward events maximum mixing  m 2  = 2.5 x 10 -3 eV 2 expected 247 ± 62 thor real data 135 ± 12 stat - - - 146 events Data consistent with a constant deficit in all zenith angle bins (  2 /d.o.f. = 3.1/4 on shape) Probability for NO oscillations: ~ 4.3% (one side)

20. Internal downward + Upward stopping events expected 329 ± 82 th real data 229 ± 15 stat - - - 252 events maximum mixing  m 2  = 2.5 x 10 -3 eV 2 Data consistent with a constant deficit in all zenith angle bins Probability for NO oscillations: ~ 12% (one side)

21. (Internal upward) / (Internal downward + Upward stopping) Most of the theor. uncertainties canceled (<5%) Systematic errors reduced (~6%) Data: R = 0.59 ± 0.07 stat Expected (No oscillations): R = 0.75 ± 0.04 sys ± 0.04 th compatibility ~ 2.7% Expected    oscillations R = 0.58 ± 0.03 sys ± 0.03 th ( maximal mixing and  m 2 = 2.5 x 10 -3 eV 2 ) Ratio of event types at low energy

22. + upgoing internal upgoing stop internal downgoing Most of the theor. uncertainties canceled < 5% Systematic errors reduced ~ 6% Data: R = 0.59 ± 0.07 stat Expected (No oscillations): R = 0.75 ± 0.04 sys ± 0.04 th Expected    oscillations R = 0.58 ± 0.03 sys ± 0.03 th maximal mixing  m 2 = 2.5 x 10 -3 eV 2

23. MACRO  events: confidence level regions for    oscillation

24. Summary and Conclusions  High energy events:     oscillation favoured with large mixing angle and  m 2 ~ 2.5x10 -3 eV 2  sterile disfavoured at ~ 2  level  Low energy events:  event deficit with respect to expectation different for Internal upward, and internal downward + Uuward going stopping  no zenith angle distortion  compatibility between result and expectation (no oscillations) with a probability < 3 %  agreement with hypothesis of  oscillation with large mixing angle and 10 -3 <  m 2 < 2x10 -2 eV 2  A consistent scenario arises from both high and low energy MACRO events