1 Luca Stanco, INFN-Padova (for the OPERA collaboration) Search for sterile neutrinos at Long-BL The present scenario and the “sterile” issue at 1 eV mass scale OPERA results for    and   e  searches Other results from MINOS and SuperK Perspectives and Conclusions

2 The “sterile” issue From masses to flavours: U is the 3 × 3 Neutrino Mixing Matrix mixing given by 3 angles,  23,  12,  13 transition amplitudes driven by ∆m 2 solar = ∆m 2 21 ∆m 2 atm = |∆m 2 31 | ≈ |∆m 2 32 | The wonderful frame pinpointed for the 3 standard neutrinos, beautifully adjusted by the  13 measurement, left out some relevant questions: -Leptonic CP violation -Mass values -Dark Matter -Anomalies and discrepancies in several results

3 The “sterile” issue (cnt.) The previous picture is working wonderfully. So it should stay whenever extensions are allowed ! Exploit 3+1 or even 3+2 oscillating models, by adding one or more “sterile” neutrinos sterile: not weakly interacting neutrinos ( B. Pontecorvo, JETP, 53, 1717, 1967) APPEARANCE DISAPPEARANCE with for APPEARANCE for DISAPPEARANCE when and

4 The “sterile” issue (cnt.)  Experimental hints for more than 3 standard neutrinos, at eV scale  Strong tension with any formal extension of 3x3 mixing matrix Reactor anomaly ~2.5σ Re-analisys of data on anti- neutrino flux from reactor short-baseline (L~ m) shows a small deficit of R=0.943 ±0.023 G.Mention et al, Phys.Rev.D83, (2011), A.Mueller et al. Phys.Rev.C 83, (2011). Gallex/SAGE anomaly ~3σ Deficit observed by Gallex in neutrinos coming from a 51 Cr and 37 Ar sources R = −0.08 C. Giunti and M. Laveder, Phys.Rev. C83, (2011), arXiv: Accelerator anomaly ~3.8σ Appearance of anti-ν e in a anti-ν μ beam (LSND). A.Aguilar et al. LSND Collaboration Phys.Rev.D (2001). Confirmed (?) by miniBooNE (which also sees appearance of ν e in a ν μ beam) A.Aguilar et al. (MiniBooNE Collaboration) Phys.Rev.Lett (2013) e disappearance e appearance No hint so far for   disappearance   appearance/disappearance

5 The oscillation scenario in terms of distance L from the source Atmospheric Neutrino Anomaly ( )  ν-oscillation no oscillation Solar Neutrino Anomaly ( )  ν-oscillation Reactor Antineutrino Anomaly (2011-)  ν-oscillation ? Long-Baseline exps with ν  -beams (OPERA, MINOS) mixing strength L Complicate picture at large L due to the contemporary presence of 3 or more neutrinos At first order phase given by  m 2 L/E  for L/E >>1 the disappearance averages to ½ of mixing strength: sin 2 (  m 2 L/4E)=0.5

6 Tau appearance in the presence of a sterile neutrino (3+1) neglect solar driven oscillation Δ 21 ~ 0 ~ standard oscillationpure exotic oscillation interference terms Mass Hierarchy dependence CP-violating (effective mixing)

7 At Long-Baselines and eV mass scale: Sensitive to mixing “sterile” angles, MH and phase CP-violation Separate analyses for NH and IH and maximize Likelihood as Use |  m 2 31 |= eV 2 for NH and eV 2 for IH effective mixing of standard  –  oscillation effective mixing of sterile with  and 

8 OPERA search for  sterile “anomalies” just published in JHEP, 6, 69 (2015) and arXiv: , based on 4 taus’ candidates Separate analyses for “high” and low |  m 2 41 | sin 2 2   < at 90% C.L. when integrating over  (quasi-equal results for NH and IH) Note: obtained if neglect interference terms For|  m 2 41 | > 1 eV 2 OPERA just observed a 5 th candidate ! (arXiv: , submitted to PRL)

9 Interplay of interference More events expected from 3+1 model Less events expected N.H. I.H. NEW: preliminary update of the analysis with 5  candidates

10 sin 2 2   < at 90% C.L. when integrating over  (quasi-equal results for NH and IH) For|  m 2 41 | > 1 eV 2 (Raster-scan à la Feldman&Cousins) PRELIMINARY

11 Complementary measurement wrt disappearance experiments OPERA PRELIMINARY (just sketched)

12 Full analysis with GLOBES (matter effects,  m 2 21 included, profiled out on  m 2 31 ) PRELIMINARY

13 OPERA can perform similar analysis based on e observation Old result from data sample (30% of total): JHEP 4, 1307 (2013) and arXiv: Compatible with expectation from intrinsic e component in the CNGS  beam: 0.9% We may put rough limits to exclude mixing on  14 with a 2 flavour model Approximate analysis, see our previous result and e.g. A.Palazzo, PRD 91, 91301(R) (2015) e candidates 194 background19.8± E<20 GeV

14 OPERA is extending the e analysis on the full data sample ! e candidates (30% data) 194 e candidates (all data) 529 E<20 GeV Good confirmation of e events from Electronic Detectors (via Boosted-Decision-Tree) e candidates selected by Emulsion Analysis PRELIMINARY

15 MINOS+ on  sterile “anomalies” CC and NC searches: -Excellent agreement with best-fit with 3 flavors -Extended range in  m 2 due to large energy span arXiv: arXiv:

16 increase tension with e sterile “anomalies” By combining MINOS 90% limit on  24 to Bugey reactor experiment limit on  14 Ongoing work on anti-  mode running

17 Ongoing Analysis on   e (Very recent blessed MINOS plots: public release at INFO2015 few days ago) SIGNAL Expected “sterile” effect Expected SENSITIVITY for 12x10 20 pot ICARUS/OPERA à la Palazzo |U e4 |=|U  4 | 4 2

18 SuperK on  sterile “anomalies” (Sterile neutrino oscillation in Atmospheric Neutrinos) SK excluded 90% C.L. PRD 91, (2015) even stronger tension with e anomalies 282 kton-year exposure ! CCFR MiniBooNE +SciBooNE 99% C.L.

19 Conclusions and perspectives -The sterile issue at eV mass scale can be studied also at Long-Baseline  beams -Many results from OPERA, MINOS, Super-K are already available -New preliminary result from OPERA on possible  sterile “anomalies” (presented at this conference) -Soon new results (without too restrictive assumptions) from OPERA on e  oscillation -Expected soon new results from MINOS+ on e  oscillation -Sterile mixing, if it exists, corresponds to low values (order of 1%) -New specific experiments should be settled and approved

20 BACKUP

21 90% C.L. JHEP, 6, 69 (2015) and arXiv: , based on 4 taus’ candidates OPERA search for  sterile “anomalies”

22 Number of expected  sterile events N.H. I.H.

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