1. Surdo • INFN - Lecce Oscillations in Atmospheric Neutrinos with Bari, Bologna, Boston, Caltech, Drexel, Indiana, Frascati, Gran Sasso, L’Aquila, Lecce, Michigan, Napoli, Pisa, Roma I, Texas, Torino • Summary • Analysis of High and Low energy neutrino events • Sterile vs Tau neutrino oscillations (matter effects)

2. MACRO @ Gran Sasso • GUT Monopole and rare particle search • Cosmic ray physics • Neutrino bursts from stellar collapses • Study of atmospheric neutrinos • Neutrino astronomy • Indirect search for WIMPs Data taking: Mar 1989 – Dec 2000 (complete detector since Apr ’94)

4. Neutrino event topologies in MACRO In up Up through Absorber Streamer Scintillator In down (2) (1) Up stop (4) (3) • Detector mass ~ 5.3 kton • (1) Up throughgoing m(ToF) • (2) Internal Upgoing m (ToF) • (3) Internal Downgoing m(no ToF) • (4) UpGoing Stopping m (no ToF)

5. Energy spectra of n events detected in MACRO • Emedian ~ 50 GeV for Throughgoing muons; • Emedian~ 4.5 GeV for Internal Upgoing (IU) m; • Emedian~ 3.5 GeV for Internal Downgoing (ID) m and for UpGoing Stopping (UGS) m; Low energy events (IU, ID+UGS) allow to investigate the n oscillation parameter space independently from throughgoing muons

6. Upward Throughgoing muons Analysis and Data Set Event selection based on time-of-flight method *b evaluation: T3 T4 +1 m L>2.5m Streamer tube track -1 m T1 T2 * Background rejection cuts: • 1) agreement between streamer track and scintillator • counter hits (position from times at the ends) • 2) -1.25 < 1/b < -0.75 • 3) 2m (~200 g/cm2) of absorber crossed to reduce at 1% level the • bck due to p’s produced by muons (Astrop. Phys. 9 (1998) 105) • Automated data selection procedure (no visual scan) • 863 n induced upward through-going muons during: Mar 89-Nov 91 (1.4y)Dec 92-Jun 93 (0.4y)Apr 94-Dec 2000 (5.5y) 1/6 lower detector Lower detectorComplete detector Phys. Lett. B357 (1995) 481Phys. Lett. B434 (1998) 451 (until Nov ‘98)

8. Measured flux and comparison with Monte Carlo • Data • number of events: 863 • background (wrong b) 22.5 • background (p’s from muons) 14.2 • Internal neutrino interactions 17 • Total 809 events • Monte Carlo prediction1122 ± 17% • - Bartol atmospheric neutrino Flux(±14%) • - GRV-LO-94 PDF for  DIS cross section(± 9%) • - Lohmann et al. muon energy loss (± 5%) • * Detector response simulation using GEANT • * Same analysis chain as the data R = data/prediction = 0.721 ± 0.026stat ± 0.043syst ± 0.122theor

9. Upward Through-Going Muons Angular Distribution 2 test on the angular distribution (10 bins) with prediction normalized to data : • 2 = 9.6/9 d.o.f for  with maximum mixing and m2 ~ 0.0025 eV2P = 37 % • 2 = 25.9/9 d.o.f. for no - oscillations P = 0.2 %

11. MACRO UPMU Probabilities for sterile neutrino oscillations • Sterile neutrino matter effects • reduction of angular distortion (max mixing) P.Lipari and M.Lusignoli, hep-ph/ 9803440 Q.Y.Liu et al, PLB440 (1998) 319, Peak probability for the shape = 1.8% Peak probability for the combination = 8% Max mixing Probabilities lower than that for t neutrinos

12. Ratio vertical / horizontal Lipari -Lusignoli, Ph Rev D57 (1998) Monte Carlo optimized: • The plot is for maximum mixing • P(sterile) = 0.033% • P(t) = 8.4% • Sterile neutrino disfavored with respect to t at • >99% C.L. for any mixing(7% systematic on the ratio) (Results in hep-ex/0106049, to be published on Phys. Lett.,)

13. Partially contained events Phys. Lett. B478 (2000) 5 Selection criteria: Internal Upgoingm’s(IU) (a)time-of-fligthbetween central / top SC layers (b)topological criteria forvertex containment inside lower detector(~1 % bck after this cut) Internal Downgoing m’s(ID) + Upgoing Stopping m’s(UGS) ID UGS (a) No T.o.F. measurement (b) topological constraints on track (bottom SC layer + track inside fiducial volume) (c) visual scan procedure for final selection (d) >100 g cm-2 of material crossed in the detector

14. IU events From MC simulation: • En ~ 5 GeV • ~ 87% due to m -CC interactions DATA: 5.5 live-y • From Apr. 1994 up to Dec. 2000 • 1/b distribution after all analysis cuts: DATA - Bck(1/b) = 154 events

15. Data vs Monte Carlo Predictions • GEANT based program for the simulation • of detector response • Simulated events processed through • the same analysis chain as the data • Fn: Bartol n flux with geomagnetic cutoffs • (error ~ 13%) • sn = Q.E. + 1p(Lipari et al., PRL74 (1995) 4384) • + DIS (GRV-LO-94 PDF) (error ~ 15%) • e(Em,qzenith):detector response and acceptance • (systematic error ~ 10 %) Internal Upward going m’s DATA: 154 ± 12stat MC: 285 ± 28sys± 57theo MC-oscill: 168 ± 17sys± 34theo Internal down + Upgoing stopping m’s DATA: 262 ± 16stat MC: 376 ± 38sys± 76theo MC-oscill: 284 ± 28sys± 57theo

16. Angular Distributions MC expectation (no oscillations) maximal mixing ,m2 = 2.5 x 10-3 eV 2 • Data consistent with a constant deficit in all • zenith angle bins (IU: 2 /d.o.f. = 3.1/4 on shape) • Probability for NO oscillations (one side): • RIU: ~ 2.3%R(ID+UGS) ~ 9.3%

17. Ratio of event types at low energy Internal Upgoing R = Internal Downgoing Upgoing Stop + • Most of the theor. uncertainties canceled (<5%) • Systematic errors reduced (~6%) • Data: R = 0.59 ± 0.06stat • Expected (No oscillations): R = 0.76 ± 0.04sys ± 0.04th • >>> compatibility ~ 1.9% • Expected  oscillations: R = 0.59 ± 0.04sys ± 0.03th • (maximal mixing andm2 = 2.5 x 10-3 eV2 )