Emulsion analysis in the OPERA experiment Taup 2009 1 N. Naganawa (Nagoya University) On behalf of OPERA collaboration
The OPERA Collaboration 150 physicists, 34 institutions in 12 countries Belgium Israel Korea Technion Haifa Jinju ULB Brussels Russia Italy Bulgaria INR RAS Moscow Bari Sofia NPI RAS Moscow Bologna ITEP Moscow LNF Frascati SINP MSU Moscow L’Aquila, Croatia JINR Dubna LNGS IRB Zagreb Obninsk Naples Padova Switzerland France Rome Bern LAPP Annecy Salerno ETH Zurich IPNL Lyon IPHC Strasbourg Japan Aichi Turkey Toho Germany METU Ankara Kobe Hamburg Nagoya Münster Rostock Utsunomiya (http://operaweb.web.cern.ch/operaweb/index.shtml 2
Motivation and Conceptual Design OPERA (Oscillation Project with Emulsion tRacking Apparatus) is a long baseline neutrino oscillation experiment The goal of the experiment is to detect neutrino oscillation for the first time in an appearance mode. Using an almost pure ν μ beam, the ν μ � ν τ oscillation is detected by observing the τ lepton decay, induced after a neutrino-lead CC interaction ● τ lepton decay is observed by the method of Emulsion Cloud Chamber. ● The detector is located on the CNGS (CERN Neutrinos to Gran Sasso) beam line at a distance from the neutrino source of 730 3 km
The CNGS beam The beam is optimized for ν t appearance in the atmospheric oscillation region ν μ Δ m 23 2 = (2.43 ± 0.13) × 10 -3 eV 2 CERN SPS sin 2 2 θ 23 = 1.0 730km conventional ν beam ν ν μ ( m -2 / pot) 7.45x10 -9 τ Appearance ? ν μ CC / pot / kton 5.44x10 -17 10 in 5 years? < E > ν ( GeV ) 17 ( ν e + ν e ) / ν μ 0.85 % INFN Gran Sasso ν μ / ν μ 4.0 % Underground Laboratory ν t prompt negligible 4
Principle of detecting tau neutrino ν τ ν μ c τ = 87 micron τ - ν τ μ , e, h, 3h Topology Selection τ → 17.8 ％ h Kink e τ → μ 17.4 ％ h τ → 49.5 ％ h τ → 15.2 ％ Trident 3h (h h h) 5
OPERA Detector @ Gran sasso 1400m underground 6 ν
OPERA Detector Emulsion Detector (ECC brick) ν 7 1.25 kton = 150,000 ECC bricks
An ECC brick, Emulsion Cloud Chamber 125mm 75.4mm Changeable Sheet (CS) Two films 8.3kg Easily detached 10X 0 Neutrino Beam OPERA emulsion film 100mm : 300micron 57 emulsion films and 8 56 Pb plates piled up. Pb plate : 1mm
The OPERA Film The OPERA emulsion film Sub micron crystal 3D tracking device Recorded as silver grain emulsion along the line particle passed through plastic base 50 micron emulsion Resolution of 0.3 micron Microscopic Image 9
OPERA Detector ν How to reach 100-micron-scaled 10 event in this huge detector…
OPERA Detector Em ulsion + Muon Target Tracker ν spectrom eter 11 Emulsion - Electronic Detectors Hybrid Detector
Flow of analysis 12
13 Flow of analysis ECC ν
Flow of analysis extraction The most probable ECC brick is tagged by TT with brick finding algorithm ν ECC CS Only CS Developed → Scanning Check tracks from interaction really exist 14 or not. half @ Gran sasso, half @ Japan
Changeable Sheet (CS) Roles of CS • Pick up tracks from neutrino interaction • Helps tagging ECC � Saving Scanning load and Target Mass O P E R A f i l m x 2 O P E R A f i l m O P E R A f i l m 160micron 10cm Neutrino beam Base 205micron Base 205micron 12.5cm 600micron 15 X E m u l s i o n l a y e r s 4 4 m i c r o n Z
Flow of analysis extraction ? If no track from the event is found in CS attached to the most probable ECC brick, ν The second probable one will be extracted and its CS will be analyzed. ECC 16
CS scanning Japanese Scanning System European Scanning System Scanning speed: 75cm2/h Scanning speed: 20cm2/h High speed CCD camera (3 kHz) Customized commercial optics and mechanics Piezo-controlled objective lens asynchronous DAQ software 17 FPGA Hard-coded algorithms
(European) Principle of scanning emulsion 16 Tomographic Images taken through 44-micron Emulsion Layer Movable stage 18
Principle of scanning emulsion (Japanese) High speed CCD L ~60 m µ Move objective lens along inclined axis D ~50 m Objective lense µ 16 layers Emulsion 44 micron Driving in constant velocity 19
Scanback location Method CS Doublet 5 mm ν ECC Brick (57 emulsions + 56 Pb) 20
21 [micron] [rad] CS-ECC connections [micron] [rad]
Scanback location Method CS Doublet Stopping Plate 5 mm ν ECC Brick (57 emulsions + 56 Pb) 22
Scanback location Method CS Doublet Stopping Plate NetScan Fiducial Volume 5 mm 1cm 2 x10 plates ν ECC Brick (57 emulsions + 56 Pb) The vertex is confirmed by scanning a volume around the stopping position; recording all the track segments within a given angular acceptance: NetScan data taking. The fiducial volume is 1cm2x10 films in total. 23
How to analyze ECC data Offline tracking and vertex reconstruction Reconstruct full At least 2-segment vertex topology connected tracks Eliminate passing Track segments through tracks overlapped 24
beam x z Event: 228913162 y Brick: 29373 Type: CC 25 Neutrino beam
Number of events identified (located) in ECC bricks under microscope NC CC Total Bricks received in the labs 208 904 1112 Scanning started 183 836 1019 CS to brick connected 171 789 960 Vertices located in the brick 106 640 746 Passing through 11 39 50 Vertices in the dead material 4 15 19 (In 1690 events triggered by Target Tracker) 26 Now going on
Lead plates; not only for mass 1.Momentum measurement by multiple coulomb scattering 13.6 （ MeV/c ） x P β ＝ δθ X ０ 27
Test exp. @ CERN (May2001) Lead plates; not only for mass 2. Electromagnetic shower MC Data ΔΕ Energy determination 0 . 4 ~ @ a few GeV Ε by calorimetric method E ( GeV ) 28
Material thickness of ECC bricks (10 X 0 ) and vertex finding μ In the case of CC-like events, it is simple to reach vertices of μ neutrino interaction by tracing back muon tracks. ν In the case of NC-like events, If the vertices are placed upper stream in the bricks, it will get more difficult to reach vertices of neutrino interactions because of electromagnetic shower and 29 Interactions or decays of hadrons.
Vertex depth and the comparison of numbers of NC-like and CC-like events Ratio NC/CC But from the data, NC-like events has no reduction of their finding efficiency is seen comparing to CC-like ones. neutrino beam 19films 19films 19films from upstream in the middle from downstream 57 films in one ECC 30 Thickness of 10X 0 is no problem.
τ detection category c τ = 87 micron Short flight decay ： 70% IP > 5um Min_pt > 250Mev 70% of τ leptons decay in the same IP lead plate with vertex. Long flight decay ： 30% θ θ kink > 20mrad pt > 250Mev 31
High resolution to identify the topology of τ decay Minimum distance between pairs of tracks from neutrino interaction (data, P>1GeV/c) IP of a decay daughter of τ (Monte Carlo) Minimum distance[micron] 32 1mm Lead plate is OK.
A charm candidate Event# 234539244, Brick# 51248 • 1ry VTX is PL33. (100960, 52357) • mu + Decay P t ~ 460MeV/c depth=380micron up of film. • 5 tracks found @ PL33. Kink angle Charm = 209mrad ax ay IP 1. 0.1325 0.0624 (PL33) 6.6 � proton? Flight Length 2. 0.0097 -0.0663 (PL33) 4.5 = 1330micron 3. 0.0876 0.6656 (PL33) 2.3 � 1ry mu 4. -0.0390 -0.1354 (PL33) 1.4 � charm 5. 0.2215 0.4319 (PL33) 10.3 6. -0.0876 0.0418 (PL31) 18.9 � e-pair 7. 0.0893 -0.0638 (PL33) 4.3 • Charm Flight length : 1330micron. 1ry muon Decay: in Lead (PL33-PL32 ) 340micron up of PL32. Kink angle : 209mrad. • Daughter Particle : muon (~2.2GeV) 33 IP : 262micron. Decay Pt : ~ 460MeV/c
Run status May 2006: completion of electronic detectors commissioning. Aug 2006: technical run, 0.076 19 pot collected E 19 pot 0.076 E 319 muons from interactions in detector front rock 319 Target Tracker and CS worked well . Oct 2007: short physics run (~40% target) 0.082 19 pot collected E 19 pot 0.082 E 38 neutrino events collected in ECC targets 38 Full chain analysis was done. E 19 pot Jun- Nov 2008: run with full target 1.782 1.782 E 19 pot collected 1690 neutrino events collected in ECC targets 1690 0.7 tau tau candidates expected and none observed so far candidates expected and none observed so far. . 0.7 @ Δ m 2 = 2.43 * 10 -3 eV 2 @ E 19 pot 27, May 2009-: We require 4.5 4.5 E 19 pot. . 4300 neutrino events should be collected in ECC targets, 4300 2.5 tau tau candidates expected in the data collected in 2008 and 2009. candidates expected in the data collected in 2008 and 2009. 2.5 34
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