1 / 24

Vertex Location, Reconstruction and Analysis in OPERA

Vertex Location, Reconstruction and Analysis in OPERA. Regina Rescigno Salerno Emulsion Group - IPNL Lyon Erice, 48th Course of the International School of Subnuclear Physics 29 Aug 2010 – 07 Sept 010. The OPERA experiment.

carnig
Download Presentation

Vertex Location, Reconstruction and Analysis in OPERA

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Vertex Location, Reconstruction and Analysis in OPERA Regina Rescigno Salerno Emulsion Group - IPNL Lyon Erice, 48th Course of the International School of Subnuclear Physics 29 Aug 2010 – 07 Sept 010

  2. The OPERA experiment • The OPERA (Oscillation Project with Emulsion-tRacking Apparatus )experimentis designed to study the nm→nt oscillation observing the nt appearance in a pure nm beam. • The OPERA detector is installed underground in the Gran Sasso Laboratory, 730 km away from CERN, where the CNGS (CERN neutrino beam to Gran Sasso) nm beam is produced.

  3. m NO OSCILLATION nm nm t m (BR. 17.8 %) t e (BR. 17.3 %) h t (BR. 50.1 %) h (BR. 65.3 %) t Decay “kink” t 3h (BR. 15.2 %) OSCILLATION t m-, e-, h- nt nm  1 mm (...plus 3-prong decay modes) The Signal • The signal of the occurrence of nm→ntoscillation is the CC interaction nN→X. The tau lepton in the final state is detected through the decay topology (electron, muon and hadron channels available):

  4. 1 mm t n Pb 300mm Emulsion Film Hybrid target structure The heart of the experiment: THE ECC TARGET BRICKS The acquisition of emulsion images is performed by computer-controlled microscopes able to reconstruct particle tracks with sub-micron precision at high speed Stack of 57 OPERA films, 56 lead plates (10 X0 )

  5. Scan-Back Track Stop Vertex location and confirmation • Procedure steps: • CS scanning to confirm the brick suggested by electronic detectors • CS-Brick connection to locate CS tracks in ECC • Scan-back in the ECC until track disappearance (hint for primary vertex point) CS PB Beam 4) Volume scan in 1 cm × 1 cm (16 plates) around the track disappearance point 5) Reconstruction of scanning data and topological analysis 6) Visual inspection by operator to confirm/refine the output of the automatic reconstruction

  6. An interesting event Muonless event 9234119599, taken on 22 August 2009, 19:27 (as seen by the electronic detectors)

  7. Topological features of the event Large area scanning – full reconstruction of vertices and gammas g2 g1

  8. Analysis

  9. Decay Kinematics Kink angle OPERA nominal analysis flow applied to the hadronic kink candidates Used exp. Proposal selection criteria Pt at decay vertex cut 9 rad GeV/c 9

  10. Global Kinematics

  11. Background Sources • Prompt nt ~ 10-7/CC • Decay of charmed particles produced in ne interactions ~ 10-6/CC • Double charm production ~ 10-6/CC • Decay of charmed particles produced in nm interactions ~ 10-5/CC • Hadronic reinteractions (UPDATE wrt OPERA Proposal) ~ 10-5/CC

  12. m m  h  - h Signal and background Signal  CC interaction Backgrund from hadron interaction in mNC interaction To discriminate signal from background → variables in OPERA Proposal: • Missing Transverse Momentum (Missing Pt) • F Angle • Daughter Transverse Momentum • Daughter Momentum, • Kink angle Primary Vertex Decay Vertex

  13. Missing Pt • WHAT is Missing Pt ? Missing Pt is the unbalance in the total momentum in the neutrino transverse plane • WHICH are missing Pt sources? • Neutrinos Even for events without neutrinos in the final state there are other possible sources: • Nuclear re-interaction and Fermi motion • Measurement Errors • Undetected particles: • Neutral particles • Particles with large angles (stopping in lead, or appearing very far from vertex point) or protons with low energies

  14. Daughter momentum used Missing Pt due to undetected neutrino of decay vertex Tau Tau daughter Neutrino Visible particle Not visible particle Missing Pt – nmNC and ntCC events For nmNC and ntCC events: the initial Missing Pt is determined by the presence of neutrinos in the direction opposite the hadronic system Tau momentum not measurable X Neutrino not detected nmNC X ntCC

  15. Missing Pt Missing Pt at primary vertex Blue: MC NC Black: MC - t Missing Pt at primary vertex cut cut GeV/c

  16. nmNC F F ntCC j Angle j angle: the angle in neutrino transverse plane between parent track and total momentum of hadron t h Hadron Momentum in transverse plane

  17. j Angle j Angle Blue: MC - NC Black: MC - t cut 17 rad

  18. Reinteraction background Search for “kinks” and interactions along a total of 9 m of hadron track measured for scanned events. About 100 m are needed to fully validate the MC information Signal region • no events in the signal region • 90% CL upper limit of 1.54 x 10-3 kinks/NC event • the number of events outside the signal region is confirmed by MC (within the ~30% statistical accuracy of the measurement)

  19. Conclusion and outlook • The OPERA experiment at LNGS is aimed at the first detection of neutrino oscillations in appearance mode through the study of the nm- nt channel • The technique of vertex location, reconstruction and analysis in OPERA has been shown to work • The Collaboration has conducted the analysis of a sub-sample of the neutrino data taken in the CERN CNGS beam in the 2008-2009 runs. • One muonless event showing a t →1-prong hadron decay topology has been detected and studied in detail. It passes all kinematical cuts required to reduce the physics background. It is the first nt candidate event in OPERA.

  20. Thank you for your attention

  21. Backup Slides

  22. Statistical considerations We observe 1 event in the 1-prong hadron t decay channel, with a background expectation (estimating a 50% error for each component) of: 0.011 events (reinteraction) 0.007 events (charm) 0.018 ± 0.007 (syst) events 1-prong hadron all decay modes: 1-prong hadron, 3-prongs + 1-prong μ + 1-prong e 0.045 ± 0.020 (syst) events total BG (here we add up the errors linearly) By considering the 1-prong hadron channel only, the probability to observe 1 event due to a background fluctuation is 1.8%, for a statistical significance of 2.36 s on the measurement of a first nt candidate event in OPERA. If one considers all t decay modes that were included in the search, the probability to observe 1 event for a background fluctuation is 4.5%. This corresponds to a significance of 2.01 s.

  23. Event statistics Event statistics • Events collected by 2008-2009 run 5391 • Brick tagging efficiency times vertex location efficiency: ~ 60% • Total neutrino vertices found: 1921 (This is ~60% of the total 2008-2009 run statistics ) • Events for which “decay search” was completed: 1088 (187 NC) (This is ~35% of the total 2008-2009 run statistics, corresponding to 1.85 x 1019 pot) • With the above statistics, and for Dm223 = 2.5 x10-3 eV2 and full mixing, OPERA expects: ~ 0.5 ntevents 23

More Related