1. Accelerator searches for    oscillations Ioannina, 20-23 April 2000 Roumen Tzenov CERN and University of Sofia

2. Legend Introduction to neutrino oscillations   Short baseline accelerator searches for    –CHORUS –NOMAD Future long baseline accelerator searches

3. Associate neutrino flavour with the charged lepton flavour as seen in charged-current interactions : For massive neutrinos: flavour eigenstate need not be a mass eigenstate but can be a coherent superposition: Mixing matrix U is unitary The propagation of different mass eigenstates leads to flavour oscillation in vacuum: Simplification for 2 mixing flavours with mixing angle  (phase  ): Interactions are now nondiagonal with the mass eigenstates! Neutrino mixing

4. The probability that a neutrino oscillates (changes flavour): With definition: To have a large effect: Maximum at 1/4 oscillation length Neutrino oscillations

5. Two parametric oscillation plot 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 1 10 100  m 2 (eV 2 ) LSND Cosmologically relevant Solar + seesaw + DM ? Atmospheric Solar (MSW) Solar (vacuum oscillation) Kamiokande SuperKamiokande 10 -5 10 -4 10 -3 10 -2 10 -1 1. sin 2 2   e e e  CHOR US and NOMA D

6. TheCollaboration Belgium (Brussels, Louvain-la-Neuve), CERN, Germany (Berlin, Münster), Israel (Haifa), Italy (Bari, Cagliari, Ferrara, Naples, Rome, Salerno), Japan (Toho, Kinki, Aichi, Kobe, Nagoya, Osaka, Utsunomiya),Korea (Gyeongsang), The Netherlands (Amsterdam), Russia (Moscow), Turkey (Adana, Ankara, Istanbul)

7.  appearance in the SPS WBB  beam via oscillation P(    ) down to 110 -4 for  m 2 ~10 eV 2  direct detection in 770 kg nuclear emulsion target Tag: visible 1- and 3- prongs decay of primary  -lepton (decay path ~1.5 mm) CHORUS Main objective     2 2 -4  -    h -    n   e -   e  +  -  -   n    R     “Kink”

8. CHORUSNOMAD 124 m290 m408 m 450 GeV SPS protons Beryllium target hornreflector vacuum tunnel earth/iron shielding CERN West Area Neutrino Facility ~0.6 km;  L(rms)/L~0.2 WBB, = 26.6 GeV ~510 protons on target ~840K CC in CHORUS CC / CC ~ 3. 10  19 -6 (~0.1 background event)     

9. WANF West Area Neutrino Facility   -4      e  e  -4 The “horn”

10. SPS and WANF () neutrino beam SPS and WANF (  ) neutrino beam   -4      e  e  -4

11. CHORUS detector detectorCHORUS 770 kg emulsion target and scintillating fibre tracker Calorimeter Air core spectrometer and emulsion tracker Air core spectrometer and emulsion tracker Veto plane Muon spectrometer Muon spectrometer  - -  - - h-h- h-h- T=5° Nucl. Instr. Meth A 401 (1997) 7

12. Scintillating fibre trackers trackers Nucl. Instr. Meth A 412 (1998) 19   ~ 2 mrad,  xy ~150  m

13. External electronic detectors: detectors: P(h ± )<20 GeV/c  p/p ~25% P(h ± )<20 GeV/c  p/p ~25%  E/E ~35%/E(GeV) sign and momentum of pions Hadronic and e-m shower energy and direction Muon momentum and id Event pre-selection and post-scanning analysis 3<P(  ± ),GeV/c<100  p/p = 11-20% 3<P(  ± ),GeV/c<100  p/p = 11-20%

14. Neutrino data-taking collection efficiency 1994-1997 N.B. Longest/Largest emulsion exposure ever done

16. Predictions and Scanback tan  

17.   1947, first nuclear emulsions. Lattes et al., Brown et al.: Discovery of     e Nuclear emulsion yesterday

18. Target = 4 stacks (1.4  1.4 m 2 ) 1 stack = 36 plates MIP : 30  40 grains / 100  m –Grain size ~ 0.3 mm –Angular resolution  1.5 mrad 80  m 100  m emulsion 350 mkm base 90 mkm 1/4 plate CHORUS emulsion plate

19. CCD and XYZ stage New Track Selector Host CPU Network data storage CHORUS automatic microscopes

20. Megapixel CCD and XYZ stage High Performance optics DSPs Processing Cluster CHORUS automatic microscopes 1 m

21. Inside a “vertex plate” -54  m -36  m -21  m 0  m View size: 120x150  m 2 Focal depth : ~3  m Red frame: ~30x40  m 2 beam

22. Decay search

23. Offline selection small impact parameter between parent and daughter kink point is in the vertex plate  - kink detection ( parent search )   or h Principle Principle: Parent track (  ) can be detected by wider view and general angle scanning at the vertex plate Impact parameter scan-back track general scanning area

24. Off-line video-image analysis CHORUS Emulsion Display

25. Phys. Lett. B 435(1998) 458-464. Manual scanning on special events: Diffractive D* s production, double leptonic decay

26. * 0  decay search not finished yet (1996-1997), not included in current results Status of Phase I scanning

27.  Det efficiency : Ratio of Acceptances Located Vertexes S=N  if P  =1 A=detector acceptance N  =normalization  =Kink finding efficiency In the same way, it is applied to the 0  sample

28. 1  sample (  -   - ) –charm production from antineutrino CC (with primary lepton (e + or  + ) unidentified   contamination of the beam 0  sample (  -  h - ) –charm production from antineutrino CC –1-prong nuclear interaction without visible recoil or nuclear break-up (White kinks) BackgroundBackground     2 -4 T  ~10 - 6 / N  ~10 - 7 / N  ~210 -6 / N  ~2 10 -5 / N 

29. Includes also 17% systematic error (NIM A320 (1993) 331)     2 -4 CHORUS current limit sin 2 2   < 8 10 - 4 No  candidates found n  CC (expected) = P  S, S = 6003 ± 17% (syst) P  < 2.38 / 6003 = 410 -4 (@ 90% C.L.) No  candidates found n  CC (expected) = P  S, S = 6003 ± 17% (syst) P  < 2.38 / 6003 = 410 -4 (@ 90% C.L.) sin 2 2    m 2 /eV 2 Current Result

30. Outlook:Outlook: Phase I scanning: Going to finish this year Expected gain in sensitivity: ~1.2 from 1  (short decays, statistics) ~1.2 from 0  (3prongs, 0  96+97) Phase II scanning and analysis: years 2000-2001 New generation of automatic systems Upgraded predictions 3prongs dedicated search    e ? (electron id by MS in emulsion) Full vertex analysis (NETSCAN, General tracking)  charm physics:|V cd | 2,cc,D+/D0 P< 1.010 -4 (in absence of  -candidates) P  < 1.010 -4 (in absence of  -candidates)

38. What to dofurther with accelerator beams?

39. Long baseline experiments

40. Long base line beams compared to WANF

41. MINOS detector

42. ICANOE detector

43. OPERA detector 200 ton iron/emulsion sandwiches + muon identificator

44. OPERA module

45. Long baseline experiments’ claims...

46. Conclusion  Current short baseline accelerator searches for    oscillations have almost done their job; u No oscillations seen (so far) for large  m 2 and small mixing angles; u Atmospheric neutrino data suggest, on the opposite, small mass difference and large mixing angle; u Several long baseline accelerator experiments are on the start scratch to clarify the issue...