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New results from the CHORUS Neutrino Oscillation Experiment

XXIX International Conference on High Energy Physics UBC, Vancouver, B. C., Canada July 23-29 1998. New results from the CHORUS Neutrino Oscillation Experiment. Pasquale Migliozzi CERN. Belgium CERN Germany Korea Japan Israel Italy Turkey The Netherlands Russia. Outline.

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New results from the CHORUS Neutrino Oscillation Experiment

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  1. XXIX International Conference on High Energy Physics UBC, Vancouver, B. C., Canada July 23-29 1998 New results from the CHORUS Neutrino Oscillation Experiment Pasquale Migliozzi CERN Belgium CERN Germany Korea Japan Israel Italy Turkey The Netherlands Russia

  2. Outline • The CHORUS experiment • Data • Present results • Outlook • Conclusions

  3. The CHORUS experiment • Search for using the WBB at CERN at the Dark Matter scale (Dm2~1 eV2) • Philosophy: • direct detection of t decay (kink) EMULSION AS “ACTIVE” TARGET

  4. The neutrino beam The mean energy of the nm beam at the CHORUS emulsion surface is The anti-neutrino contamination of the beam is The prompt ntcontamination

  5. n target and target tracker • Target: • ~800 kg nuclear emulsion (<1mm space resolution) • Observe the t decay topology (kink) in emulsion • Purpose of electronic detector • predict tracks back into emulsion • kinematical cuts • suppress background, e.g. D decays (particle id, kinematics)

  6. Data (data taking finished in 1997)

  7. Microscope event view 150 mm Emulsion to the beam Good tracks appear as dots (grains) 120 mm Tracking implies connection of dots in different layers

  8. Automatic scanning: Track Selector(developed in Nagoya)

  9. Identify the muon track and require 0>Pm>-30 GeV/c no other leptons at the primary vertex require a kink along the muon track with PT>250 MeV Flight length cut (l<5plates) Antineutrino charm production (D-) with the primary lepton not identified 1.6x10-6xNCC 1m channel Signal definition (BR=~18%) Background

  10. Identify a non-muon track and require -1>Ph>-20 GeV/c no other leptons at the primary vertex require a kink along the hadron track with PT>250 MeV Flight length cut (l<3plates) Antineutrino charm production (D-) with the primary lepton not identified 2.3x10-6xNCC Neutral current events with a p- kink-like interaction (white kink) 2x10-5xNCC 0m channel Signal definition (BR=~68%) Background

  11. Analysis steps • Event reconstruction by electronic detectors • track predictions in emulsion • Automatic scanning in interface emulsion sheets • Automatic scanning in bulk emulsion: vertex location and rejection of not-t candidates by • search for short decays (decay inside the vertex plate) • search for long decays (decay outside the vertex plate) • Semi-automatic eye scan and remeasuring of retained events • Event topology and kinematics (emulsion+electronic detector) • t- candidate or identified background

  12. Vertex location scan-back track Location efficiency Vertex location procedure

  13. Vertex validation Impact parameter measurement scan-back track Small IP = normal nm event Big IP = interesting event (nt?) Semi-automatic eye check

  14. t- kink detection (parent search) Principle: Parent track (t) can be detected by wider view and general angle scanning at the vertex plate • Offline selection • small impact parameter between • parent and daughter • kink point is in the vertex plate • Semi-automatic eye check • the events selected automatically are checked by eye for the final judgement scan-back track Impact parameter m or h t general scanning area

  15. Experimental check of the t detection efficiency • Computed using Montecarlo simulation • Checked using events with 2 muons in the final state (~2% of the total) • locate the muon tracks in the emulsion • scan the emulsion searching for a kink charm dimuon candidates (muonic D+ decays) • Yield in agreement with Montecarlo assuming scharm/sCC = 5% (measured)

  16. A special event CERN-EP/98-87 Parallel session 5 July 25th talk given by O. Melzer

  17. Results New data: 31974N1m+362N0m events have been analysed No ntcandidate has been found! @ 90% C.L. where if i=4 the m is not identified

  18. CHORUS efficiencies

  19. The exclusion plot (@ 90% C.L.)

  20. Outlook • Phase I (the present till the end of the year) • we will just complete the scanning of the whole statistics • we gain a factor 3 in the 1m sample • we gain a factor 6.7 in the 0m sample • Pmt~2x10-4 • Phase II (towards the final result) • improvements on the reconstruction algorithms are going on • because of the increasing scanning power the kink finding efficiency will improve by about a factor 2 • if no t candidate will be found, the proposal sensitivity will be reached Pmt~1x10-4

  21. Conclusions • Neutrino data taking finished in 1997 • Emulsion data taking in progress • CHORUS has shown that automatic scanning procedures are reliable and fast • No t candidate has been found so far • The proposal sensitivity can be reached

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