Status and the preliminary results of the OPERA experiment

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Status and the preliminary results of the OPERA
experiment
V.Tioukov (INFN, Napoli) on behalf of the OPERA
collaboration
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OPERA main goal detection of neutrino
oscillations in appearance mode After the
Super- Kamiokande discovery of oscillations with
atmospheric neutrinos and the confirmation
obtained with solar neutrinos and accelerator
beams the direct observation of the oscillation
appearance is still missing tile Requirements to
the beam 1) long baseline, 2) high neutrino
energy, 3) high beam intensity
LNGS largest underground laboratory (18000
m2) 1400 m rock shielding, Cosmic µ reduction
10-6 wrt surface
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CNGS neutrino beam
OPERA
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Detection principle
e-, ?-, h-
?-
? ? e (17.8) ? ? ? (17.4) ? ? h (49.5)
??
3h-
?-
??
? ? 3h (15.2)

• The detection of the t lepton requires an
  identification of a kink or trident topology
• The 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 (photographic emulsions)
• 3. Select neutrino interactions (electronic
  detectors)
• 4. Identify muons and their charge to reduce
  charm background (precision tracker and
  spectrometer)

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CNGS nt appearance potential

• The beam is optimized for ?t appearance in the
  atmospheric oscillation region. The present best
  fit is now
• ?m232 (2.430.13)10-3 eV2
• sin22?23 1.0
• Although the maximum of oscillation probability
  at 730 km is at about 1.5 GeV, the ?t CC cross
  section and the production threshold of 3.5 GeV
  should be taken into account

ltEnµgt 17 Gev
(ne ?ne)/ nµ 0.87
?n µ / nµ 4
nt prompt negligible
Total p.o.t 22.5x 1019
nµ CC NC 23600
ne ?ne CC 160
nt 115
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Year Beam days Proton on target(pot) SPS eff Events in the bricks
2008 123 1.78x1019 81 1698
2009 155 3.52x1019 70 3693
2010 187 4.04x1019 81 4248
2011 Ongoing 4.11x1019 79 4075
CNGS to OPERA In 2008-2011
Goal of the experiment 22.5x1019 pot 2010
close to nominal year (4.5x1019 pot) 2011 hit
record performance ? (expect 5x1019 pot for
223 days) Dedicated mode (no other fixed target)
from 18 March to 7 June. Until now
(2008-2011) 13.4x1019 pot Aim at
high-intensity runs in 2012 as well, with a
dedicated running period
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OPERA layout
Hybrid detector (electronic emulsions) with a
modular structure 2 supermodules 2(31 walls
1 spectrometer) ? 31 walls 31(5664 bricks
2 scintillator tracker planes) The total target
mass 1.35 Kton
nt
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The OPERA electronic detectors

• Muon spectrometer
• RPC and drift tubes in 1.5T magnet
• charge miss id (lt25 GeV/c) lt1
• ?P/P (lt50GeV/c) 20
• µ id (with TT) 95

• Target Tracker
• Made of plastic scintillation strips
• with wavelength shifting fibers
• p.e/mip gt 5
• Detection efficiency 99
• Brick finding efficiency 80

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t identification

• The target is divided in about 152000 ECC's
  (Emulsion Cloud Chamber), so called bricks.
  Each brick weights 8.3 kg
• One brick is made by a sandwich of
• 56 (1mm) Pb sheets
• 57 (300?m) FUJI emulsion layers
• 2 (300?m) changeable sheets

n
10.3 cm
12.8 cm
7.5 cm 10 X0
Long decay
Short decay
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Emulsion/lead target

• Brick filling is finished in July 2008
• 146621 bricks with 8 millions of nuclear
  emulsions plates

Bricks assembling was technologically
challenging The small mechanical industry
installed underground and worked in the red-light
dark room
10.2 x 12.7 x 7.5 cm
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Changeable sheet (interface films)

• From meters to microns
• OPERA 10x10 m2
• TT indicate brick 1 cm accuracy
• CS 100 microns
• Inside brick near the vertex 1 micron
• CS background requirements
• 1 track/ 10x10 cm2
• Doublet film for coincidence

Hybrid target structure.
Muon
Neutrino
No cosmic rays in CS!
Other products
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The automatic emulsion scanning
The European Scanning System. About 30 of them
installed in the European labs
15-16 frames/45 microns
Developed grains
frame
2-3 mm
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UTS, S-UTS automatic microscopes generation
(Japan)
S-UTS

• 75 cm2/hour scanning performance
• High speed CCD Camera (3 KHz)
• Objective lens moved by piezo-element
• Dedicated hardware for the reconstruction
  algorithms

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OPERA emulsion target

• Based on the concept of the Emulsion Cloud
  Chamber (ECC)
• 56 Pb sheets 1mm 57 emulsion plates
• Solves the problem of compatibility of large
  mass for neutrino interactions high space
  resolution in a completely modular scheme

• ECC are almost stand-alone detectors
• Neutrino interaction vertex and kink topology
  reconstruction
• Measurement of the momenta of hadrons by
  multiple scattering
• dE/dx pion/muon separation at low energy
• Electron identification and measurement of the
  energy of the electrons and photons

ECC Technique validated by the direct observation
of nt DONUT 2000
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Some numbers concerning the OPERA scanning

• Emulsion can be considered as a multi-layer
  optical storage media (like a DVD disk) with the
  storage capacity of about 1 Tb/100 cm2 (images
  level without data reduction)
• The mean area to be scanned is 200 cm2 per each
  OPERA event
• Considering 20000 events to process the full area
  to be scanned is 400 m2 of the emulsion surface
• With the old manual scanning the total tracks
  search in a wide angular range was difficult. The
  human scanning performance for this kind of data
  is less then 1 mm2/hour
• So if an experienced operator decides to analyze
  manually the full OPERA data it would takes him
  about 40000 years

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Emulsion data reconstruction

1. Track following TT-gtCS-Brick upstream till the
   vertex
2. Volume scan and reconstruction of all tracks
   around the expected vertex position

Long tracks after alignment and tracking
All segments
Vertex found
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The first tau candidate

• In spring 2010 OPERA present the first nt
  candidate base on the analysis of 35 of 08/09
  statistics.
• Data selection was done using the cuts defined at
  the time experimental proposal (2001)

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The viewer of scintillation Target Tracker
? beam
Event ECC ? pink color
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Work of the last year (after the candidate
detection)

• Completed (92) the 2008-2009 data analysis 4.8
  1019 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 the Electronic 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.

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BG reduction by the systematical tracks follow
down for the candidate events to improve the
muons id
In 95 of cases the muon should be identified by
the electronic detector But when it missed or
misidentified with hadron the following
topologies becomes the background
Charm background
Hadrons re-interaction background

• Momentum range correlation tested for the
  first nt candidate event
• ? Misidentified muons from charm events 3.28
  (was 5)
• ? Factor 100 reduction of the BG for the t -gt µ
  channel golden channel!

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Hadron re-interaction studies using the Pions
test-beam data and real OPERA data
Hadron tracks in OPERA neutrino interactions with
kink topology far from primary vertex
Hadron interactions search in 4 GeV p test beam
14 m, equivalent to 2300 NC events No events
found in signal region,signal boundary region
(Ptgt200 MeV/c) ? 10 events observed (10.8 events
expected by updated simulation including black
tracks search)
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Expected OPERA signal
Including all the improvements in the analysis
Decay channel Number of signal events expected for Dm2 2.510-3 eV2 Number of signal events expected for Dm2 2.510-3 eV2
Decay channel 22.51019 p.o.t. Analysed sample
? ? µ 1.79 0.39
?? e 2.89 0.63
? ? h 2.25 0.49
? ? 3h 0.71 0.15
Total 7.63 1.65
In the analyzed sample (92 of 0809 data) one
nt observed in the t h channel compatible with
the expectation of 1.65 signal events.
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Background summary

• Production and decay of charmed particles
• Hadrons re-interactions
• Muons scattering on the big angle

Decay channel Number of background events for Number of background events for Number of background events for Number of background events for Number of background events for Number of background events for Number of background events for Number of background events for
Decay channel 22.51019 p.o.t. 22.51019 p.o.t. 22.51019 p.o.t. 22.51019 p.o.t. Analysed sample Analysed sample Analysed sample Analysed sample
Decay channel Charm Hadron Muon Total Charm Hadron Muon Total
?? µ 0.025 0.00 0.07 0.090.04 0.00 0.00 0.02 0.020.01
? ? e 0.22 0 0 0.220.05 0.05 0 0 0.050.01
? ? h 0.14 0.11 0 0.240.06 0.03 0.02 0 0.050.01
? ? 3h 0.18 0 0 0.180.04 0.04 0 0 0.040.01
Total 0.55 0.11 0.07 0.730.15 0.12 0.02 0.02 0.160.03
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OPERA events interaction, bricks extraction and
processing rates
2011
2010
2009
2008
3765 interactions located, 3289 decay searched
events
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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 the detection efficiency
• Estimation of the background in progress prompt
  nu-e and gamma conversion contamination

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Summary for the peculiar topologies found
Events Located Decay search Charm Candidates ?e ?? candidates
Total 3765 3289 52 20 1
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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 point and end point with
  the 10 cm accuracy and the start time and finish
  time with 5 ns accuracy for this measurement in
  the global Reference System
• Using the GPS technique it is possible to know
  the global coordinate of the reference point with
  the accuracy of 1 cm
• Using the GPS in a special way and the atomic
  clocks it is possible to synchronize CERN and GS
  DAQ with 1 ns
• It is not possible to know the exact position of
  the neutrino decay point inside the decay tunnel
  but this do not change significantly the total
  travel time
• It is not possible to know the exact position
  inside the spill of the particular OPERA event
  but it is possible to make the statistical
  analysis if we know the exact shape of each spill.

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• 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 through proton waveforms
• Measurement of baseline by global geodesy 20 cm
  accuracy over 730 km
• Result 10 ns overall accuracy on TOF with
  similar stat. and sys. errors

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Summary of the principle for the TOF measurement
Measure dt TOFc - TOFn
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GPS and common view mode

• Data of the satellites seen simultaneously
  selected offline, ionospheric free P3 code used
• Delay of the Cs clock with respect to the GPS
  observation computed internally by the GPS
  receiver (RefC, RefG)

Time-link created between Tx LNGS and Tx CERN
updated every second
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• The analysis of data from the 2009, 2010 and
  2011 CNGS runs was carried out to measure the
  neutrino time of flight. For CNGS muon neutrinos
  travelling through the Earths crust with an
  average energy of 17 GeV the results of the
  analysis indicate an early neutrino arrival time
  with respect to the one computed by assuming the
  speed of light
• dt TOFc-TOFn (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
• (v-c)/c dt /(TOFc - dt) (2.48 0.28
  (stat.) 0.30 (sys.)) 10-5
• with an overall significance of 6.0 s.
• Despite the large significance of the
  measurement reported here and the stability of
  the analysis, the potentially great impact of the
  result motivates the continuation of our studies
  in order to identify any still unknown systematic
  effect.
• We do not attempt any theoretical or
  phenomenological interpretation of the results.

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Summary and outlook

• The Collaboration has completed the study of the
  neutrino data taken in the CNGS beam in the
  2008-2009 runs
• One muonless event showing a t ? 1-prong hadron
  decay topology has been detected and studied in
  details. It passes all kinematical cuts required
  to reduce the physics background
• The observation so far of a single nt candidate
  event is compatible with the expectation of 1.65
  signal events. The significance of the
  observation of one decay in the t?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 of direct appearance
  ??-nt flavor transition, as well as of the
  study of the sub-leading ??-ne oscillation
• In the coming months will be done the extensive
  campaign for crosschecking and additional
  systematic errors study for the neutrino velocity
  measurement