Recent results on the observation of n m -> n t oscillation in the OPERA experiment

1. Korea Jinju Belgium ULB Brussels Italy Bari Bologna LNF Frascati L’Aquila LNGS Naples Padova Rome Salerno Russia INR RAS Moscow LPI RAS Moscow ITEP Moscow SINP MSU Moscow JINR Dubna Croatia IRB Zagreb France LAPP Annecy IPHC Strasbourg Switzerland Bern ETH Zurich Japan Aichi edu. Kobe Nagoya Toho Utsunomiya Germany Hamburg Turkey METU Ankara Israel Technion Haifa Recent results on the observation of nm -> nt oscillation in the OPERA experiment NakatsukaYuji Nagoya University On behalf of OPERA collaboration ICISE Qui Nhon 2013 Aug 14 Rencontres du Vietnam Windows on the Universe

2. ~1 mm Aim and Principle Aim : Observation of neutrino oscillations in appearance mode through the  channel. Principle of OPERA Experiment :  decay “kink” -   oscillation  -  , h- , e-  plus 3-prong decay modes Direct detection of nm -> nt oscillation

3. sin22θ23 = 1.0，　 Δm232 = (2.43±0.13)×10-3 eV2 [ Phys.Rev.Lett.101:131802,2008.] < E > ( GeV ) 17 (e + e) /  0.89, 0.06 %  /  2.1 %  prompt Negligible Covers the region indicated by Super-K, K2K & MINOS CNGS Beam 732km LNGS

4. The OPERA detector Underground@GranSasso, ~1400m  Target Super-Module Muon Spectrometer Target Mass ~1.2kton

5. ECC selection Typical  NC-like event 20 m 7.5cm 12.5cm Changeable Sheet (CS) Interface emulsion films for ECC selection and track connection. 8.3kg Emulsion Cloud Chamber (ECC) Stack of 57 emulsion films, 56 lead plates (10X0). ~150,000 ECC installed in the OPERA detector 10cm Pb 1mm Neutrino Beam (vertical to films)

6. Vertex plate Event location in ECC Follow back in the ECC tracks found in CS until they disappear: vertex plate TT hit ECC CS Large area ~100 cm2 Point scan ~100x100 mm2 neutrino emulsion emulsion TT hit Lead emulsion Lead emulsion Lead emulsion Lead emulsion Lead emulsion Lead emulsion Lead emulsion 6 14

7. 200nm AgBr Crystal OPERA Film 210um plastic base 44um emulsion ~30 developed silver grains / 100 mm M.I.P. track M.I.P. 10GeV π- Fog 100mm 20μm 125mm A compton track

8. Event reconstruction European Scanning System (ESS) Japanese Scanning System (S-UTS) All track data ~ 1cm x 1cm Scanning speed/system: 20cm2/h *Customized commercial Optics and mechanics *Asynchronous DAQ software Scanning speed/system: 75cm2/h *High speed CCD camera (3 kHz) *Piezo-controlled objective lens *FPGA Hard-coded algorithms Required plate-plate connection Tracks converge to vertex point

9. nt CC detection Short flight decay Impact Parameter distribution Decay point n IP  ntevents (MC) NC+CC nm events (MC) NC+CC nm events (Data) Primary vertex (Mean 104.3 m) 1mm Pb Short : Long ~ 2:8 Without muon Long flight decay Decay point 10 m ↔(c = 87m) IP n   decay mode Primary vertex 1mm Pb

10. nt candidate events 1stnt candidate t -> 1h, May 2010 (t->rnt, r->p0p, p0->2g) 2nd nt candidate t -> 3h, June 2012

11. The 3rdnt candidate event : t -> m decay mode μm 11

12. Event Display 2.8 GeV muon

13. pt pri. h ph total f=154.5° e-pair Event analysis n beam transverse plane

14. τ→μ MC τ→μ candidate excluded region Passed all cuts of t -> m decay criteria

15. Muon sign 1.55T Target tracker hits Spectrometer 4hits curvature radius ~ 85cm muon charge is negative 5.6 s nt -> t- : identification of oscillated nt interaction (≠ nt )

16. BG1 : Charm Decay • Charm BG The same topology - e h charm m+ t- m- miss id charm decay tdecay the decay muon charge is plus.

17. BG2 : Muon Large Angle Scattering Prob quark muon kink point PbFilm Tranverse momentum PDF Scattering probability is proportional to the amount of material. Pb : 10-6 film (emulsion + plastic base) : 10-8 - 10-7 107 104 690MeV/c at base Upper limit : Proposal Value 10-5 (S.A. Akimenko et at al, NIM A423 1986 518) 0 500 1000 PT (MeV/c)

18. Summary of nm -> nt search status • Three nt candidates have been found, 1st : t - > h, 2nd : t -> 3h, 3rd : t ->m. • The 3rd nt event is pure t -> m channel with low background and tagged as nt by its muon sign. • Probability explained by only background ~ 7.29 x 10-4 • The singnificance value : counting method : 3.2 s of non-null observation, likelihood approach : 3.5 s

19. Conclusions and Prospects • OPERA ran on the CNGS beam successfully 2008-2012, 17.97x1019 POT, ~80 % of proposal value of CNGS beam • Analysis stasus : completed 2008, 2009 events. 2010 - 2012 events are on going, main part (1st ECC) will finish in 2013. • Three nt candidates have been found, counting method 3.2 s of non-null observation, likelihood approach : 3.5 s • Searches are on going for more interesting events, within reach 4s observation.

20. backup

21. Charm Decay Event Candidates

23. Beam exposure and analysis status CS scanned 14802 CS found 10776 ECC scanned 9981 Located 6211 DS 5036 (13 Jul 28) Run 2008 → 2012 p.o.t. event ‘08 ‘09 ‘10 ‘11 ‘12 date date Completed: 2008, 2009 2010-12 on going with optimised strategy (ALL NC-like events and CC-like events with m momentum < 15GeV/c) Beam: 5 years (965days) 17.97×1019 p.o.t. Overall 80% of the proposal value (22.5×1019 p.o.t.)

24. The first nt“appearance” candidate (2010) Candidate nt interaction and t decay from nm nt oscillation

25. First tau neutrino candidate event Muonless event 9234119599, taken on 22nd August 2009 (as seen by the electronic detectors) G. De Lellis - Fermilab - 4 June 2010

26. Event reconstruction in the brick τ−→ρ− ντ ρ−→π0 π- π0 → γ γ

27. PL17 PL18 PL19 PL20 PL21 5 7 1 3 1 Primary vertex kink point 4 8 careful visual inspection of the films behind/in front of the secondary vertex: no “black” or “evaporation” tracks. Support topological hypothesis of a particle decay 2 6 1mm lead

28. Kinematical variables • Kinematical variables are computed by averaging the two independent sets of measurements • g1 and g2 both attached to 2ry vertex

29. Second neutrino tau candidate event taken on 23rd April 2011 as seen by the electronic detector event display

30. SecondntCandidate Event animation 2000 mm

31. Schematics of the event Φ Beam View Φ=167o Secondary Interaction In Emulsion With four Nuclear fragments

32. Zoom of the primary interaction and decay region Decay point In Plastic Base No Nuclear fragment Flight length 1.54mm

33. Momentum measurement and particle identification of event tracks Independent momentum measurements carried out in two labs

34. Kinematics of the second Candidate Event

35. Kinematics of the second candidate event candidate cut Satisfying the criteria for ντ  3hadron decay

36. Analysis of the interface films μ track Sign of electromagnetic shower

37. Third tau neutrino eventτ μ μm

38. Event tracks’ features γ attachment

39. Muon charge and momentum reconstruction Bending by the magnetic field Muon momentum by range in the electronic detector: 2.8±0.2 GeV/c MCS in the brick consistent 3.1 [2.6,4.0] GeV/c ϑ (mrad) Cells

40. Track follow down to assess the nature of track 2 Track 2 interacting in the downstream brick without visible charged particles track value Hadrons and muon stopping in the brick Momentum/range inconsistent with μ hypothesis 0.9 GeV/4 cm Lead cut value L = track lengthRlead = µ rangeρaverage = average density ρlead= lead density p = momentum in emulsion D variable

41. THE MAGNETIC SPECTROMETERS • 1.55 T magnetic field bending particles in the horizontal plane • 24 slabs of magnetized iron interleaved with 24 RPC planes • 6 drift tube stations for precision measurement of the angular deflection • momentum resolution: • 20% below 30 GeV

42. µ→e analysis 4.1 GeV electron ≈ 30 events found in the analyzed sample

43. Electron neutrino search in 2008 and 2009 runs: one of the νe events with a π0 as seen in the brick Interface films 19 candidates found in a sample of 505 neutrino interactions without muon

44. Background from µNC (0→) Gamma-ray 1micron BG: 0.17 events (less than 1%) A close-up of an electron pair

45. Energy distribution of the 19 νe candidates Observation compatible with background-only hypothesis: 19.8±2.8 (syst) events 3 flavour analysis Energy cut to increase the S/N 4 observed events 4.6 expected ⇒ sin2(2θ13)<0.44 at 90% C.L.

46. Search for non-standard oscillations at large Δm2 values: exclusion plot in the sin2(2θnew) - Δm2new plane arXiv:1303.3953 Submitted to JHEP Caveat: experiments with different L/E values

47. Background estimation (hadron) Error bars : Experimental data Histogram : Simulated data 2GeV/c 4GeV/c 10GeV/c We confirmed MC simulation estimation of hadron backgrounds by using the data analysis of ECC bricks exposed to 2GeV/c , 4 GeV/c and 10GeV/c pion beams and reduced systematic uncertainty. 2GeV/c 4GeV/c 10GeV/c Multiplicity Multiplicity Secondary track emission: 30% nuclear fragments:10% MC: b < 0.7 0 5 0 5 0 8 0 15 0 15 0 15 Well reproduced by MC They argee well Kink angle (1-prong) Emission angle(cos q) 0 0.6 0 0.6 0 0.6 0° 0° 0° 180° 180° 180° Backward Forward Backward Forward Backward Forward New technique for background reduction Nuclear fragment associated probability 100% ・ data - MC nuclear fragments in emulsion 10GeV/c 2 4 8 0% 47 Hadronic background was reduced by “40%”by requiring no association of large angle nuclear fragments.

48. Track recognition method • Take 16 tomographic images by microscope optics. • Shift images to aim at specific angle tracks. • Sum up 16 images to examine coincidence. • Find signal of tracks. • Repeat for all angles in space, >2000 times Invented by K.Niwa in 1974