Status and the preliminary results of the OPERA experiment - Infn

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Status and the preliminary results of the OPERA experiment - Infn

Status and thepreliminary results of theOPERA experimentV.Tioukov (INFN, Napoli)on behalf of the OPERA collaborationV. Tioukov QFTHEP11, Sochi


OPERA main goal: detection of neutrino oscillations inappearance modeAfter the Super- Kamiokande discovery of oscillations with atmosphericneutrinos and the confirmation obtained with solar neutrinos and acceleratorbeams the direct observation of the oscillation appearance is still missing tileRequirements to the beam:1) long baseline, 2) high neutrino energy, 3) high beam intensityLNGS – largest undergroundlaboratory (18000 m 2 )1400 m rock shielding,Cosmic μ reduction 10 -6 wrtsurfaceV. Tioukov QFTHEP11, Sochi


CNGS neutrino beamOPERAV. Tioukov QFTHEP11, Sochi


Detection principleντ − e- , μ − , h −τ→e (17.8%)ττ→μ (17.4%)τ→h (49.5%)ντ − 3h−ττ→3h (15.2%)●●The detection of the τ lepton requires an identification of a “kink” or “trident”topologyThe detector must fulfil the following requests:1. Large mass due to small CC cross section (lead target)2. Micrometric and milliradian resolution to observe the kink (photographicemulsions)3. Select neutrino interactions (electronic detectors)4. Identify muons and their charge to reduce charm background (precision trackerand spectrometer)V. Tioukov QFTHEP11, Sochi


V. Tioukov QFTHEP11, Sochi


CNGS ντ appearance potential●The beam is optimized for ν τappearance in theatmospheric oscillation region. The present bestfit is now:Δm 232= (2.43±0.13)×10 -3 eV 2sin 2 2θ 23= 1.0●Although the maximum of oscillation probabilityat 730 km is at about 1.5 GeV, the ν τCC crosssection and the production threshold of 3.5 GeVshould be taken into account17 Gev(ν e+⎯ν e)/ ν μ0.87%⎯ν μ/ ν μ4 %ντ prompt negligibleTotal p.o.t 22.5x 10 19ν μCC + NC ~23600ν e +⎯ν e CC ~160ντV.~115 Tioukov QFTHEP11, Sochi


CNGS to OPERAIn 2008-2011Year Beam days Proton ontarget(pot)SPS eff2008 123 1.78x10 19 81% 16982009 155 3.52x10 19 70% 36932010 187 4.04x10 19 81% 42482011 Ongoing 4.11x10 19 79% 4075Events inthe bricksGoal of the experiment: 22.5x10 19 pot2010: close to nominal year (4.5x10 19pot)2011: hit record performance ?(expect ~5x10 19 pot for 223 days)Dedicated mode (no other fixed target)from 18 March to 7 June.Until now (2008-2011): 13.4x10 19 potAim at high-intensity runs in 2012 as wellwith a dedicated running periodV. Tioukov QFTHEP11, Sochi


τ identification●●The target is divided in about 152000 ECC's(Emulsion Cloud Chamber), so called “bricks”.Each brick weights 8.3 kgOne brick is made by a sandwich of:56 (1mm) Pb sheets57 (300μm) FUJI emulsion layers2 (300μm) changeable sheetsν7.5 cm = 10 X 012.8 cm10.3 cmLongdecayShortdecayV. Tioukov QFTHEP11, Sochi


Emulsion/lead target• Brick filling is finished in July 2008• 146621 bricks with ~ 8 millions ofnuclear emulsions plates10 X0Bricks assembling was technologically challengingThe small mechanical industry installedunderground and worked in the red-lightdark room8.3kg10.2 x 12.7 x 7.5 cmV. Tioukov QFTHEP11, Sochi


Changeable sheet (interface films)From meters to microns:• OPERA: 10x10 m 2• TT – indicate brick ~ 1 cm accuracy• CS – ~100 microns• Inside brick near the vertex ~ 1 micron• CS background requirements:1 track/ 10x10 cm 2Doublet film for coincidenceNo cosmic rays in CS!NeutrinoHybrid target structure.MuonSide view of a CSdoubletOther productsmuon track160micron600 micronsV. Tioukov QFTHEP11, Sochi


The automatic emulsion scanningThe European Scanning System. About 30 of them installed in the European labs15-16 frames/45 micronsDevelopedgrainsframe2-3 μmV. Tioukov QFTHEP11, Sochi


UTS, S-UTS automatic microscopes generation(Japan)S-UTS:•75 cm 2 /hourscanningperformance•High speed CCDCamera (3 KHz)•Objective lensmoved by piezoelement•Dedicatedhardware for thereconstructionalgorithmsV. Tioukov QFTHEP11, Sochi


OPERA emulsion targetν1 mm • Based on the concept of the Emulsion CloudChamber (ECC)τ• 56 Pb sheets 1mm + 57 emulsion plates• Solves the problem of compatibility of largemass for neutrino interactions + high spaceresolution in a completely modular schemePbEmulsion layersECC are almost stand-alone detectors:‣ Neutrino interaction vertex and kink topologyreconstruction‣ Measurement of the momenta of hadrons bymultiple scattering‣ dE/dx pion/muon separation at low energy‣ Electron identification and measurement of theenergy of the electrons and photonsECC Technique validated bythe direct observation of ν τ :V.DONUT 2000Tioukov QFTHEP11, Sochi


Some numbers concerning the OPERAscanning• Emulsion can be considered as a multi-layer optical storagemedia (like a DVD disk) with the storage capacity of about 1Tb/100 cm 2 (images level without data reduction)• The mean area to be scanned is ~200 cm 2 per each OPERAevent• Considering 20000 events to process the full area to bescanned is 400 m 2 of the emulsion surface• With the old manual scanning the total tracks search in a wideangular range was difficult. The human scanning performancefor this kind of data is less then 1 mm 2 /hour• So if an experienced operator decides to analyze manuallythe full OPERA data it would takes him about 40000 yearsV. Tioukov QFTHEP11, Sochi


Emulsion data reconstruction1. Track following: TT->CS-Brick upstream till the vertex2. Volume scan and reconstruction of all tracks aroundthe expected vertex positionAll segmentsLong tracks:after alignmentand trackingVertex foundV. Tioukov QFTHEP11, Sochi


The first tau candidate• In spring 2010 OPERApresent the first ν τcandidatebase on the analysis of 35%of ‘08/’09 statistics.• Data selection was doneusing the cuts defined at thetime experimental proposal(2001)V. Tioukov QFTHEP11, Sochi


The viewer of scintillation Target Trackerν beamEvent ECC pink colorV. Tioukov QFTHEP11, Sochi19


V. Tioukov QFTHEP11, Sochi


Work of the last year (after the candidate detection)• Completed (92%) the 2008-2009 data analysis = 4.8 10 19 pot• Statistic 2.6 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 theElectronic Detector• Hadronic background due to muon mismatched to hadrons– Full simulation chain with emulsion off-line reconstruction.– Better knowledge of Charm production cross section from CHORUS.V. Tioukov QFTHEP11, Sochi


BG reduction by the systematical tracks follow down for thecandidate events to improve the muons idIn 95 % of cases the muon should be identified by the electronic detectorBut when it missed or misidentified with hadron the following topologiesbecomes the background:Charm backgroundμ - ,e -ν μ,eD + μ +Hadrons re-interaction backgroundν μμ -- , ν μe +h + ν μν μhh• Momentum range correlation: tested for the first ν τ candidate event• Misidentified muons from charm events: 3.28 % (was 5%)• Factor 100 reduction of the BG for the τ -> µ channel: goldenchannel!V. Tioukov QFTHEP11, Sochi


Hadron re-interaction studies using the Pions test-beam dataand real OPERA dataHadron tracks in OPERA neutrinointeractions with kink topology farfrom primary vertexHadron interactions search in4 GeV π test beamSignal regionSignal region14 m, equivalent to 2300 NC eventsNo events found in signal region,signal boundary region (Pt>200 MeV/c): 10 events observed (10.8 eventsexpected by updated simulation includingblack tracks search)V. Tioukov QFTHEP11, Sochi


Expected OPERA signalIncluding all the improvements in the analysisDecay channel Number of signal events expected forΔm 2 = 2.5×10 ‐3 eV 222.5×10 19 p.o.t. Analysed sampleτ → µ 1.79 0.39τ→ e 2.89 0.63τ → h 2.25 0.49τ → 3h 0.71 0.15Total 7.63 1.65In the analyzed sample (92% of ‘08+’09 data) one ν τobserved in the τ → h channel compatible with theexpectation of 1.65 signal events.V. Tioukov QFTHEP11, Sochi


Background summary•Production and decay of charmed particles•Hadrons re-interactions•Muons scattering on the big angleDecaychannelNumber of background events for:22.5×10 19 p.o.t. Analysed sampleCharm Hadron Muon Total Charm Hadron Muon Totalτ→ µ 0.025 0.00 0.07 0.09±0.04 0.00 0.00 0.02 0.02±0.01τ → e0.22 0 0 0.22±0.05 0.05 0 0 0.05±0.01τ → h 0.14 0.11 0 0.24±0.06 0.03 0.02 0 0.05±0.01τ → 3h0.18 0 0 0.18±0.04 0.04 0 0 0.04±0.01Total 0.55 0.11 0.07 0.73±0.15 0.12 0.02 0.02 0.16±0.03V. Tioukov QFTHEP11, Sochi


OPERA events interaction, bricks extraction and processing rates20112010200920083765 interactions located,3289 “decay V. Tioukov searched” QFTHEP11, Sochievents


Other interesting events: nue• so far detected 20 nu-e events as the byproduct of nu-tau search• Developed the dedicated strategy for nu-e search to increase thedetection efficiency• Estimation of the background in progress: prompt nu-e and gammaconversion contaminationV. Tioukov QFTHEP11, Sochi


Summary for the peculiar topologies foundEventsLocatedDecaysearchCharmCandidatesν eν τcandidatesTotal 3765 3289 52 20 1V. Tioukov QFTHEP11, Sochi


Neutrino velocity measurement in OPERA●LBL (730 km) neutrino experiment with is well suited for this kind of test●Velocity = distance/time = (x2 - x1) / (t2 - t1) we need to know start pointand end point with the 10 cm accuracy and the start time and finish timewith 5 ns accuracy for this measurement in the global Reference System●Using the GPS technique it is possible to know the global coordinate ofthe reference point with the accuracy of 1 cm●Using the GPS in a special way and the atomic clocks it is possible tosynchronize CERN and GS DAQ with 1 ns●It is not possible to know the exact position of the neutrino decay pointinside the decay tunnel but this do not change significantly the totaltravel time●It is not possible to know the exact position inside the spill of theparticular OPERA event but it is possible to make the statistical analysisif we know the exact shape of each spill.V. Tioukov QFTHEP11, Sochi


OPERA sensitivity• High neutrino energy - high statistics ~16000 events• Sophisticated timing system: ~1 ns CNGS-OPERA synchronisation• Accurate calibrations of CNGS and OPERA timing chains: ~ 1 ns level• Precise measurement of neutrino time distribution at CERN throughproton waveforms• Measurement of baseline by global geodesy: 20 cm accuracy over 730km Result: ~10 ns overall accuracy on TOF with similar stat.and sys. errorsV. Tioukov QFTHEP11, Sochi


Summary of the principle for the TOF measurementyxzMeasure δt =TOF c-TOF νV. Tioukov QFTHEP11, Sochi31


GPS and commonview mode‣Data of the satellites seensimultaneously selected offline,ionospheric free P3 code used‣Delay of the Cs clock withrespect to the GPS observationcomputed internally by the GPSreceiver (RefC, RefG)Time-link created between Tx LNGS and Tx CERN updated every secondV. Tioukov QFTHEP11, Sochi


• The analysis of data from the 2009, 2010 and 2011 CNGS runs was carried out to measurethe neutrino time of flight. For CNGS muon neutrinos travelling through the Earth’s crust withan average energy of 17 GeV the results of the analysis indicate an early neutrino arrival timewith respect to the one computed by assuming the speed of light:δt = TOF c -TOF n = (60.7 ± 6.9 (stat.) ± 7.4 (sys.)) ns• We cannot explain the observed effect in terms of known systematic uncertainties. Therefore,the measurement indicates a neutrino velocity higher than the speed of light:with an overall significance of 6.0 σ.(v-c)/c = δt /(TOF c - δt) = (2.48 ± 0.28 (stat.) ± 0.30 (sys.)) ×10 -5• Despite the large significance of the measurement reported here and the stability of theanalysis, the potentially great impact of the result motivates the continuation of our studies inorder to identify any still unknown systematic effect.• We do not attempt any theoretical or phenomenological interpretation of the results.V. Tioukov QFTHEP11, Sochi


Summary and outlook•The Collaboration has completed the study of the neutrino data taken in theCNGS beam in the 2008-2009 runs• One muonless event showing a τ → 1-prong hadron decay topology hasbeen detected and studied in details. It passes all kinematical cuts required toreduce the physics background• The observation so far of a single ν τ candidate event is compatible with theexpectation of 1.65 signal events. The significance of the observation of onedecay in the τ→h channel is 95%•Our expectation is to collect by the end of 2012 a total statistics (2008-2012)as close as possible to the goal of the experiment: of 22.5x1019 p.o.t.•The main physics goal remains the statistically significant observation ofdirect appearance ν μ -ν flavor τ transition, as well as of the study of the subleadingν μ-ν oscillatione•In the coming months will be done the extensive campaign forcrosschecking and additional systematic errors study for the neutrino velocitymeasurementV. Tioukov QFTHEP11, Sochi

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