Transcript FEDRA

Status and the
preliminary results of the
OPERA experiment
V.Tioukov (INFN, Napoli)
on behalf of the OPERA collaboration
V. Tioukov QFTHEP11, Sochi
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
V. Tioukov QFTHEP11, Sochi
OPERA
V. Tioukov QFTHEP11, Sochi
Detection principle
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t
t-
e-, -, h-
t
t-
3h-
t  e (17.8%)
t   (17.4%)
t  h (49.5%)
t  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)
V. Tioukov QFTHEP11, Sochi
V. Tioukov QFTHEP11, Sochi
CNGS t appearance potential
●
The beam is optimized for ντ appearance in the
atmospheric oscillation region. The present best
fit is now:
Δm232 = (2.43±0.13)×10-3 eV2
sin22θ23 = 1.0
●
Although the maximum of oscillation probability
at 730 km is at about 1.5 GeV, the ντ CC cross
section and the production threshold of 3.5 GeV
should be taken into account
<Eμ>
17 Gev
(e +e)/ μ
0.87%
 μ / μ
4%
t
prompt
negligible
Total p.o.t
22.5x 1019
μ CC + NC
~23600
e +e CC
~160
t
~115
V. Tioukov QFTHEP11, Sochi
Year
CNGS to OPERA
In 2008-2011
2008
Beam days Proton on
target(pot)
SPS eff
Events in
the bricks
123
1.78x1019
81%
1698
2009
155
3.52x1019
70%
3693
2010
187
4.04x1019
81%
4248
2011
Ongoing
4.11x1019
79%
4075
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
V. Tioukov QFTHEP11, Sochi
OPERA layout
Hybrid detector (electronic + emulsions) with a modular structure:
2 supermodules = 2*(31 walls + 1 spectrometer)
↳ 31 walls = 31*(56*64 bricks + 2 scintillator tracker planes)
The total target mass = 1.35 Kton
t
V. Tioukov QFTHEP11, Sochi
The OPERA electronic detectors
Target Tracker
• Made of plastic scintillation strips
with wavelength shifting fibers
• p.e/mip > 5
• Detection efficiency:
99 %
• Brick finding efficiency: ~80 %
Muon spectrometer
• RPC and drift tubes in 1.5T magnet
• charge miss id (<25 GeV/c): <1%
• ΔP/P (<50GeV/c)
~ 20%
• μ id (with TT)
~ 95%
V. Tioukov QFTHEP11, Sochi
t identification
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The target is divided in about 152000 ECC's
(Emulsion Cloud Chamber), so called “bricks”.
Each brick weights 8.3 kg

10.3 cm
One brick is made by a sandwich of:
56 (1mm) Pb sheets
57 (300m) FUJI emulsion layers
2 (300m) changeable sheets
7.5 cm = 10 X0
Long
decay
Short
decay
V. Tioukov QFTHEP11, Sochi
12.8 cm
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 X0
8.3kg
V. Tioukov QFTHEP11,
10.2 x Sochi
12.7
x 7.5 cm
Changeable sheet (interface films)
From meters to microns:
• OPERA: 10x10 m2
Hybrid target structure.
• TT – indicate brick ~ 1 cm accuracy
• CS – ~100 microns
• Inside brick near the vertex ~ 1 micron
Muon
• CS background requirements:
1 track/ 10x10 cm2
Doublet film for coincidence
Neutrino
No cosmic rays in CS!
Side view of a CS
doublet
160micron
muon track
Other products
600 microns
V. Tioukov QFTHEP11, Sochi
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 m
V. Tioukov QFTHEP11, Sochi
UTS, S-UTS automatic microscopes generation
(Japan)
S-UTS:
•75 cm2/hour
scanning
performance
•High speed CCD
Camera (3 KHz)
•Objective lens
moved by piezoelement
•Dedicated
hardware for the
reconstruction
algorithms
V. Tioukov QFTHEP11, Sochi
OPERA emulsion target
1 mm
t

Pb
• 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
Emulsion layers
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 t:
V. Tioukov
DONUT 2000
QFTHEP11, Sochi
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
V. Tioukov QFTHEP11, Sochi
Emulsion data reconstruction
1. Track following: TT->CS-Brick upstream till the vertex
2. Volume scan and reconstruction of all tracks around
the expected vertex position
All segments
Long tracks:
after alignment
and tracking
V. Tioukov QFTHEP11, Sochi
Vertex found
The first tau candidate
• In spring 2010 OPERA
present the first t 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)
V. Tioukov QFTHEP11, Sochi
The viewer of scintillation Target Tracker
 beam
Event ECC  pink color
V. Tioukov QFTHEP11, Sochi
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V. Tioukov QFTHEP11, Sochi
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.
V. Tioukov QFTHEP11, Sochi
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
-,e-
,e
D+
+
e+
h+
Hadrons re-interaction background



h
--, 
h
• Momentum range correlation: tested for the first t candidate event
• Misidentified muons from charm events: 3.28 % (was 5%)
• Factor 100 reduction of the BG for the τ -> µ channel: golden channel!
V. Tioukov QFTHEP11, Sochi
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 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)
V. Tioukov QFTHEP11, Sochi
Expected OPERA signal
Including all the improvements in the analysis
Decay channel
t→µ
t→ e
t→h
t → 3h
Total
Number of signal events expected for
Dm2 = 2.5×10-3 eV2
Analysed sample
22.5×1019 p.o.t.
1.79
0.39
2.89
0.63
2.25
0.49
0.71
0.15
7.63
1.65
In the analyzed sample (92% of ‘08+’09 data) one t
observed in the t  h channel compatible with the
expectation 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 angle
Decay
channel
Number of background events for:
22.5×1019 p.o.t.
Charm Hadron Muon
t→ µ
t→e
t→h
t → 3h
Total
Analysed sample
Total
Charm Hadron Muon
Total
0.025
0.00
0.07
0.09±0.04
0.00
0.00
0.02
0.02±0.01
0.22
0
0
0.22±0.05
0.05
0
0
0.05±0.01
0.14
0.11
0
0.24±0.06
0.03
0.02
0
0.05±0.01
0.18
0
0
0.18±0.04
0.04
0
0
0.04±0.01
0.55
0.11
0.07
0.73±0.15
0.12
0.02
0.02
0.16±0.03
V. Tioukov QFTHEP11, Sochi
OPERA events interaction, bricks extraction and processing rates
2011
2010
2009
2008
3765 interactions located,
3289 “decay
events
V. Tioukovsearched”
QFTHEP11, Sochi
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
V. Tioukov QFTHEP11, Sochi
Summary for the peculiar topologies found
Total
Events
Located
Decay
search
Charm
Candidates
e
t
candidates
3765
3289
52
20
1
V. Tioukov QFTHEP11, Sochi
Neutrino velocity measurement in OPERA
●
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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.
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 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
V. Tioukov QFTHEP11, Sochi
Summary of the principle for the TOF measurement
y
x
z
Measure dt =TOFc - TOF
V. Tioukov QFTHEP11, Sochi
31
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 V.LNGS
Tx CERN
Tioukov and
QFTHEP11,
Sochi updated every second
• 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 Earth’s 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:
δt = 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 = δt /(TOFc - δt) = (2.48 ± 0.28 (stat.) ± 0.30 (sys.)) ×10-5
with an overall significance of 6.0 σ.
• 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.
V. Tioukov QFTHEP11, Sochi
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 t 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 -t flavor transition, as well as of the study of the subleading -e oscillation
•In the coming months will be done the extensive campaign for
crosschecking and additional systematic errors study for the neutrino velocity
V. Tioukov QFTHEP11, Sochi
measurement