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Updated results of the OPERA long baseline neutrino experiment

Updated results of the OPERA long baseline neutrino experiment . On behalf of the OPERA Collaboration S.Dusini – INFN Padova. OPERA experiment.

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Updated results of the OPERA long baseline neutrino experiment

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  1. Updated results of the OPERA long baseline neutrino experiment On behalf of the OPERA Collaboration S.Dusini – INFN Padova S.Dusini - INFN Padova

  2. OPERA experiment The aim of OPERA experiment is the direct detection of neutrino oscillation in appearance mode in the νμ®ντ channel, an important missing tile in the neutrino oscillation physics. Requirment: 1) long baseline, 2) high neutrino energy, 3) high beam intensity, 4) large mass, 5) detect short lived ’s Requirements L = 730 km LNGS CERN Tflight = 2.44 ms Expected neutrino interactions for 22.5x1019 pot: ~ 23600  CC + NC ~ 520 anti- CC + NC ~ 160 e +anti-e CC ~ 115  CC (m2 = 2.5 x 10-3 eV2) S.Dusini - INFN Padova

  3. nm - n no-oscillation -  How to detect a tau The separation of the ntCCfrom the dominant nminteractions is based on the identification, event-by-event, of the peculiar decay topology of the t. oscillation nm nt + N  t-+ X (11% of Non-Scaling QE and 89% DIS) --,   h (ct~ 87 μm ≈ 600 μm of path) (35% of Non-Scaling QE and 65% DIS) nm Decay “kink” Emulsion Cloud Chamber = sandwich of lead plate and emulsion films t- - Background components: nt Hadronic interactions in lead: Bck. to t  h or tot  m (if hadron misid or mismatched with muon) Production of charmed particles in CC interactions (all decay channels)   -,e- ,e h + e+ h+ Coulomblarge angle scattering of muons in lead Bck. tot  m D+ S.Dusini - INFN Padova

  4. CNGS beam performance As 4/07/2011 In 2011 in dedicated mode (no other fixed target exp.) from March 18th to June 7th Expected to run for 223 days  ≈5x1019 pot pot S.Dusini - INFN Padova

  5. Observation of first ntcandidate • In spring 2010 OPERA present the first ntcandidate base on the analysis of 35% of ‘08/’09 statistics. • Data selection was done using the cuts defined at the time experimental proposal (2001) Phys. Lett. B 691 (2010) 138-145 S.Dusini - INFN Padova

  6. Update and improvements of the analysis • Completed (92%) the 2008-2009 data analysis = 4.8 1019 pot • Statistic2.6 larger then previous publication • Improvements in signal and background based on: • Search of highly ionizing tracks in hadronic interactions • Follow down of the tracks in the emulsion to reduce • charm background searching for muons not observed by the Electronic Detector • Hadronic background due to muonmis-matched to hadrons • Full simulation chain with emulsion off-line reconstruction. • Better knowledge of Charm production cross section from CHORUS. No new nt found Paper submitted to Physics Letter B, (arXiv:1107.2594 [hep-ex]). S.Dusini - INFN Padova

  7. 85% are events induced by neutrino interaction outside OPERA target 2008-2009 sample NC events This corresponds to the 92% of the expected sample that could be decay searched: 2978±75 n Location efficiency: 74% for CC 48% for NC OPERA data Reconstructed MC Full simulation chain including newly developed off-line emulsion reconstruction software S.Dusini - INFN Padova

  8. Track follow down For the first nt candidate we followed down all the tracks to search for possible muon not identified by the Electronic Detector --,   h • We can suppress backgrounds due to • Charm • Hadron interactions in nmCC with misidentified m(t ® hchannel) • Hadron interactions in µ CC and NC (→µchannel)   -,e- ,e h Hadron interactions background Charm background + e+ h+ D+ S.Dusini - INFN Padova

  9. Track Follow Down • Classification of the tracks: • Interaction visible in the brick • dE/dx at end point of the track for p/m separation • Momentum/Range correlation L = track lengthRlead = moun range in leadρaverage = average density along the pathρlead= lead density p = momentum measured in the emulsion Discriminating variable • Results: • Mis-ID muons in Charm events:3.28% ( 34% reduc.) • 2 orders of magnitude reduction of hadronic background to →mdue to µ mismatch in CC and NC events Hadrons and muon stopping in the brick S.Dusini - INFN Padova

  10. Search for highly ionizing particles in hadron interactions Hadron interactions background can be reduced by increasing the detection efficiency of protons and nuclear fragments emitted in the cascade of intra-nuclear interactions and in nuclear evaporation process Found fragment 1 Found fragment 2 • Specific tool for scanning • Validation on the test-beam sample of hadronic interactions • No highly ionizing particle found in OPERA ntcandidate S.Dusini - INFN Padova

  11. Test beam for highly ionizing particles search • Study of 64 interactions of 8 GeV p- beam • Search of “black” tracks ( γβ < 0.5 ) in a large field of view 2.5x2.1 mm2 • Highly ionizing tracks detection in 57±7% of casesExpected from Fluka : 53% Backward Forward Test beam dataMC Fluka S.Dusini - INFN Padova

  12. Kink probability Fluka simulation • Taking into account the larger acceptance of the new scanning tool and the lower momentum threshold for additional protons and fragments the probability for a hadron to produce a single prong “kink” with • P > 2 GeV • ( Pt > 0.6 GeV ) or ( Pt > 0.25 GeV+gamma ) • over 2 mm of lead Pi+ Pi- Momentum GeV/c Momentum GeV/c K+ K- Momentum GeV/c Momentum GeV/c Probability in 10-4 units 1.53 x 10-4 / NC -20% previous estimation p • Old selection • New selection Momentum GeV/c S.Dusini - INFN Padova

  13. Pion interaction studies Hadron tracks in OPERA neutrino interactions with kink topology far from primary vertex Hadron interactions search in 4 GeV π test beam Signal region Signal region 14 m, equivalent to 2300 NC events No events found in signal region,signal boundary region (Pt>200 MeV/c):  10 events observed (10.8 events expected by updated simulation including black tracks search) S.Dusini - INFN Padova

  14. Charm cross section and fragmentation Results recently published by CHORUS - arXiv:1107.0613 [hep-ex] scaled at OPERA energies Fragmentation OLD NEW Muonic BR OLD(1998) NEW(2010) The D+has the main background contribution to all channels due to the higher efficiency for the kinematical cuts. The charm background increase goes from x1.57 to x2.43 depending on channel (h-mu) S.Dusini - INFN Padova

  15. 2008-2009 charm sample Angle between the charmed particle and the primary µ in the transverse plane Decay length of charmed particles OPERA ’08+’09MC OPERA ‘08+’09MC S.Dusini - INFN Padova

  16. Updated OPERA sensitivity Including all the improvements in the analysis In the analyzed sample (92% of ‘08+’09 data) one nt observed in the t ® hchannel compatible with the expectation of 1.65 signal events. S.Dusini - INFN Padova

  17. Summary of background Very clean channel The expected background in the t ® hchannel is 0.05 ± 0.01 The probability of a background fluctuation up to at least one event is 5%. The total expected background is 0.16 ± 0.03 and the probability a background fluctuation is 15%. S.Dusini - INFN Padova

  18. Outlook 2011 2010 2009 2008 3513 interactions located in the bricks, 3232 “decay searched” events S.Dusini - INFN Padova

  19. Summary • The analysis ’08-’09 data sample has been completed (92%) and submitted to PLB, (arXiv:1107.2594 [hep-ex]). • Analysed statistic 2.6 larger then previous publication. • The signal and background expectations have been updated • Full simulation chain with emulsion off-line reconstruction • Track Follow Down technique – hadronic background to t ® m killed • Search for protons/fragments in hadronic interactions • New charm cross section (CHORUS paper) • One nt observedin the t ® h channel compatible with the expectation of 1.65 signal events and a background of 0.05±0.01. • Probability of a background fluctuation is 5% S.Dusini - INFN Padova

  20. Thank you S.Dusini - INFN Padova

  21. Muon reconstruction with ED ντsignal in arbitrary units • OPERA (‘08-’09) • MC S.Dusini - INFN Padova

  22. OPERA electronic detector performance • OPERA (‘08-’09) • MC • OPERA (‘08-’09) • MC S.Dusini - INFN Padova

  23. Side view Event topological features 7 1 5 3 g2 g1 4 4 8 daughter 2 6 S.Dusini - INFN Padova

  24. Event tracks’ features muonless event (favored hypothesis) S.Dusini - INFN Padova

  25. Features of the decay topology Decay length red bands: values for the “interesting” event with uncertainties Kink angle Daughter momentum reject < 20 mrad cut Stefano Dusini - ISTITUTO NAZIONALE di FISICA NUCLEARE - Padova rad GeV/c mm A. Ereditato - LNGS - 31 May 2010

  26. Kinematical cuts to be passed Blue: MC NC Black: MC - t Missing Pt at primary vertex Missing Pt at primary vertex Reject NC events with larger missing Pt (neutrino) cut cut GeV/c Pt at decay vertex Reject hadron interactions cut Stefano Dusini - ISTITUTO NAZIONALE di FISICA NUCLEARE - Padova GeV/c 26

  27. f X(hadron shower) Signal : f =180o Azimuthal angle between the resulting hadron momentum direction and the parent track direction t-decay t- p- nt ntN t-X BG: small f Blue: MC - NC Black: MC - t kink x f p- p- cut nm Stefano Dusini - ISTITUTO NAZIONALE di FISICA NUCLEARE - Padova nmN nmp-X 27 rad

  28. Detection of short lived particle with Emulsion Cloud Chamber (ECC) To accommodate Large Mass – High Tracking Resolution we use thin metal plates (neutrino target) interleaved with nuclear photographic emulsion on films. ECC technique successful applied in DONUT experiment for the discovery of nt(2000) Iron 3D tracking: 32 grains/100mm 0.3 mm accuracy DONUT event Changeable Sheet (CS)removable emulsion sheets to interface electronic detector O(mm) with emulsion O(mm) resolution. Use electronic detectors to provide “time resolution” to the emulsions and preselect the interaction region S.Dusini - INFN Padova

  29. Brick: 57 nuclear emulsion films interleaved with 56 lead plates (1mm thick) ~150,000 bricks (total target mass ~ 1.25 kt) arranged in 54 walls 10.2cm 12.5cm OPERA detector Changeable Sheet Doublet(CS) in separate envelope SM1 SM1 SM2 SM2 Mechanical structure 20 m 6m ECC Brick Target: Walls of ECC brick interleaved plastic scintillator tracker walls Instrumented dipolar magnet for muon spectrometry S.Dusini - INFN Padova

  30. LNGS of INFN CERN • Largest underground laboratory for astro-particle physics. • underground area: 18 000 m2 • 1400 m rock coverage • cosmic µ reduction= 10–6 (1/m2h) 730Km LNGS CNGS OPERA S.Dusini - INFN Padova

  31. RPC + drift tubes in spectrometers: • muon ID, • momentum, • charge • Target Trackers • neutrino trigger • brick localization Oscillation Project with Emulsion tRacking Apparatus Super Module 2 Super Module 1 Detector supermodules construction: Sept. 2003 - spring 2007 RPC Target ECCs scint. strips Veto Drift tubes Muon Spectrometer 10 m 10 m 20 m • BRICK WALLS • 2850 bricks/wall • 53 walls BMS Brick Manipulator system HIGH PRECISION TRACKERS 6 drift-tube layers/spectrometer spatial resolution < 0.5 mm • TARGET TRACKERS • 2x31 scintill. strips walls • 256+256 X-Y strips/wall • WLS fiber readout • 64-channel PMTs • 63488 channels • 0.8 cm resol., e 99% • rate 20 Hz/pixel @1 p.e. • INNER TRACKERS • 990-ton dipole magnets • (B= 1.55 T) instrumented with 22 RPC planes • 3050 m2, ~1.3 cm res. S.Dusini - INFN Padova

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