Status and results from OPERA Tomoko Ariga LHEP, University of Bern on behalf of OPERA Swiss groups of Bern and ETHZ

OPERA Aiming to prove the flavor-mixing neutrino oscillation hypothesis by appearance method. – Appearance of new flavor: nu-mu  nu-tau – Search in the region predicted by other disappearance experiments. Direct observation of nu-tau events in nuclear emulsion detectors. – Sub-micron resolution – 1.25 kt of target mass  (F.L. ~500  m) 1ry vertex non-mu  CC interaction

CNGS beam 17 GeV L730 km ( e + e ) /  0.87%  /  4%  prompt negligible  Expected interactions in 5 years: ~25400  CC + NC ~170 e + e CC ~125  CC (  m 2 = 2.5 x eV 2 ) L = 732 km CERN LNGS T flight = 2.44 ms CERN LNGS 730 km ~10 tau decays are expected to be observed after 5 years running

10.2 cm 12.5 cm 7.5 cm neutrino OPERA target ECC brick OPERA Brick = 57 nuclear emulsion films interleaved by 1 mm thick lead plates OPERA Film = 2 emulsion layers (44  m thick) poured on a 205  m plastic base OPERA Film × 57 plates Lead x 56 plates OPERA Film Lead plate 1mm 0.3mm The OPERA target consists of about 150,000 bricks. Total target mass: 1.25 kton

OPERA detector SM1SM2 VETO Target areaMagnet and RPCs PT Brick Manipulator System Extract and validate the ECC brick. Develop and send to scanning labs.

Parallel analysis of ECC bricks Validated bricks are sent to the scanning labs. – 10 scanning labs share the scanning. Swiss scanning station scanned the highest number of bricks in Europe for 2008 run. To Japan Padova To Mosccow LHEP GS Scanning labs: Nagoya (JP) LHEP Bern (CH) Napoli, Bari, Salerno, Bologna, Padova, Roma, Frascati (IT) Dubna (Ru)

Swiss scanning station in LHEP Bern Largest scanning group in Europe – 10 physicists (Bern + ETHZ) – 5 microscopes with full-automatic plate changer. – Capability to scan more than 15 bricks/week.

Total: 1.78·10 19 pot 18kV cable repair MD PS magnet exchange, septum bakeout MD SPS timing fault: vacuum leak & magnet exchange CNGS maintenance SPS extraction line: Magnet ground fault MD CNGS maintenance Nominal: 4.5 · pot/yr for 5 years Beam to CNGS, LHC, FT, MD Beam to CNGS, LHC, FT Beam to CNGS, MD 2008 CNGS run (18 June - 03 Nov 2008): first physics run

Located neutrino interactions Brick Brick Emulsion gives 3D vector data. In ECC brick, we can reconstruct vertices with an accuracy of a few micron. (The frames correspond to emulsion films. The other colored line shows the extrapolation of measured tracks. The color indicates the Z-depth in the module.) 1 cm Brick (animation)

Status of event location in ECC for 2008 run Scanning for 2008 run will be completed by September with muonwithout muonTotal Events in target1663 Bricks developped Vertices located in ECC Vertices in the dead material17421 Impact parameter distribution mm

Analysis for located events Goal of 2008 run – Check nu-tau detection efficiency by detecting charmed particles (similar life time and mass with tau) Charm particles are produced in nu-mu CC interactions ~23 events are expected for ~1200 nu-mu CC events – Nu-tau detection 0.7 event is expected No clear candidate up to now ParticleMass (MeV/c 2 )Life time ( s)cτ (micron) τ D+D Ds+Ds Λc+Λc

Charm candidate: (di-muon event) kink x-view 1ry vertex 4 mm 1.3 mm flight length: 1330 micron kink angle: 209 mrad IP of daughter: 262 micron daughter muon: 2.2 GeV/c decay Pt: 0.46 GeV/c 1ry muon daughter muon (animation)

Charm candidate: Both 1ry vertex and decay point are in lead plate. muon Lead plate 1ry vertex IP w.r.t. muon (micron) IP w.r.t. decay point (micron) Momentum (GeV/c) Daughter Daughter micron muon (animation)

muon Lead plate (1 mm) Hypothesis (1) D 0 candidate Hypothesis (2)  candidate? minimum kink angle: 312 mrad muon momentum: 17 GeV/c Pt > 5.3 GeV/c Excluded by Pt: Pt > maximum decay Pt of  (0.9 GeV/c) 1ry vertex 1ry vertex D0D0 

Charm candidates Expected ratioNumber of candidates 1-prong37 %5 2-prong30 %4 3-prong19 %1 4-prong7 %1 Analysis ongoing for located ~700 nu-mu CC events. Up to now, we have collected 11 candidates. 13 events are expected for 700 nu-mu CC events. (23 events are expected for 1200 nu-mu CC events.)

Activities of Swiss group in OPERA analysis Common for all labs – Decay search – Kinematical analysis Unique to Swiss group – Study of hadronic background for tau – Gamma detection, energy estimation, π 0 reconstruction – MC studies on tau and charm – Electron ID, energy estimation – Low momentum muon ID – Development of 3D display for event analysis

Study of hadronic background for tau Motivation – Hadronic re-interaction is a major source of background for hadronic decay channel of tau. Monte Carlo has large uncertainties (MC says a hadron track of 1mm length creates a decay-like topology with a probability of ). Method – Analyze the particles from neutrino interaction vertices. Measure the number of decay-like interactions and study Pt distribution etc. tau hadron 1ry vertex non-mu Hadronic re-interaction background from  NC interaction  CC interaction

Study of hadronic background for tau Status: 4.8 m was scanned and studied by Swiss group. 2ry vertices were found for 12 events. Analysis is in progress. Goal: ~30 m track length to measure background for the total decay search length for NC events collected in 5 years. 1ry2ry 1ry 2ry

Gamma detection and π 0 reconstruction E ~0.5 GeV E ~8.1 GeV 2 e-showers give a reconstructed mass ~ 160 MeV/c 2 70% of 1-prong tau hadronic decays include  0. Important to detect gamma from tau decay to improve S/N. We are working on gamma detection from nu-mu interactions to prove the method. π 0 reconstruction is in progress.   e-pair

Status and prospect for the on-going 2009 run 1.54x10 19 pot have been already collected up to Aug 17 th. 4.5x10 19 pot are requested. ~2 tau events are expected to be detected x10 19 pot0 int.Commissioning x10 19 pot38 int.Commissioning x10 19 pot1663 int.First physics run x10 19 pot up to now (Aug 17 th ) 1629 int.3.2x10 19 pot are expected at end of the run

Summary The OPERA experiment is taking data in the CNGS beam. 1.78x10 19 pot were collected during the first physics run in The analysis of 2008 data is in progress. The evaluation of total efficiencies is ongoing. In 2009 run, 1.54x10 19 pot were already collected. – 4.5x10 19 pot are requested. – 3.2x10 19 pot are expected at the end of the run. – Detection of ~2 nu-tau events is expected…SOON.

BACKUP

OPERA signal and background  decay channel B.R. (%) Signal  m 2 = 2.5 x 10-3 eV 2 Background        e   h   3h Total Full mixing, 5 years run, 4.5x10 19 pot /year Main background sources: Production and decay of charmed particles Hadron re-interactions Large angle muon scattering

Pt estimation for charm candidate 72853

Tau background by D 0  Neutral charmed particle decay vertex mistaken as primary vertex in events where only a muon and D 0 are produced at primary vertex    channel Cut on the invariant mass to be used to reduce this background source

Pt cut Daughter particle of τ Daughter particle of hadronic re-interactions Pt(GeV/c) MC