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The OPERA neutrino oscillation experiment
Paolo StrolinUniversity and INFN, Napoli
What is “Neutrino oscillation”Pontecorvo, 1957
Maki, Nakagawa and Sakata, 1962Pontecorvo and Gribov, 1969
• A phenomenon induced by m > 0 m = 0 in “Standard Model” of elementary particles
• The observed eand are “flavour eigenstates”, related by a mixing matrix to the invisible “mass eigenstates” 1 2 and 3
• At a large distance from the source, it implies an apparent “metamorphosis” of a flavour into a different one (e.g. )
• A very sensitive method to measure mi2
disappearance
(interpreted as → ) observed by
Super-Kamiokande
best fit: m2 = 2.4 10-3 eV2,
sin2 2 = 1
Independently observed by MACRO
Confirmed by K2K and
MINOS
still missing:direct observation (“appearance”) of
oscillated
Atmospheric neutrino oscillations
● Main aim: unambiguous evidence for oscillation in the parameter region indicated by the atmospheric neutrino disappearance
● Search for appearance in a pure beam at a long baseline (CNGS beam, <E> = 17 GeV, L = 732 km)
● Detection of CC interactions with the unstable lepton identified by the direct observation of its decay
● Hybrid set-up (nuclear emulsions + electronic detectors) needed to observe decays
OPERA
The CNGS beam
N NAMD (E)P
(E)CC (E)(E)dE
Beam main features
L 730 km
<E> 17 GeV
L/ <E> 43 km/GeV
(e+e)/ 0.87%
/ 2.1%
prompt negligible
“off peak”
Limiting for → ee
searches
Event rate for OPERA (~1.3kton) with 4.5·1019 pot (200 days/year)~ 6200 (CC + NC) / year
~ 25 CC/year for ∆m2 = 2.4·10-3 eV2
CERN LNGS730 km
OPERA
Laboratori Nazionali del Gran Sasso - INFN
• 1400 m rock coverage• cosmic µ reduction factor = 10–6 → 1/m2 h• underground area: 18 000 m2
• 756 scientists from 25 countries
• Neutrino physics (mass, oscillations, stellar physics)• Dark matter• Nuclear reactions of astrophysics interest • Gravitational waves• Geophysics• Biology
Roma
To identify leptons, “see” their decay “kink”
decay kink
~ 0.6 mm
Lead – nuclear emulsion sandwich
“Emulsion Cloud Chamber” ( ECC)
AND see the decay m resolutionrare process massive target
The challenge
The Emulsion Cloud Chamber (ECC)
• Emulsions for tracking, passive material as target
–Established technique • charmed “X-particle” first observed in cosmic rays (1971)
• DONUT/FNAL beam-dump experiment: observed (2000)
< m space res. mass
Pb
1 mm
Emulsion layers
track segments• m2 = O (10-3 eV2 ) Mtarget ~ O (kton)
–modular structure (“bricks”): basic performance is preserved–large detector sensitivity, complexity–required: “industrial” emulsions, fast automatic scanning
• The dense lead-emulsion sandwich allows
–electron identification by showering –momentum measurement by Multiple Coulomb Scattering
36 INSTITUTIONS, ~160 PHYSICISTS
IPNL, IPHC, LAPP
INR ITEP, MSU, LPI
JINR, Obninsk
Zagreb
L’Aquila, Bari, Bologna, Napoli, Padova, Roma,
Salerno, LNF, LNGS
BernNeuchatelETH Zurich
Brussels
Hamburg, Münster,Rostock
Sofia
Aichi, TohoKobe, NagoyaUtsunomiya
Technion Haifa
METU Ankara
Tunis
Gyeongsang University
The OPERA Collaboration
20m20m
10m10m
10m10m
SM1SM2
Target• lead/emulsion ECC bricks
• emulsion tracking resolution: x< 1μm1mrad
• 154,750 “bricks” ~ 1.3 kton
• planes of scintillator strips
Pb
Emulsion layers
1 mm
Muon Spectrometers•Magnetized iron slabs.
•Vertical drift tubes for momentum measurement from deflection through 24 magnet instrumented with 22 RPC planes
•∆p/p~20% up to 50 GeV
The OPERA ”hybrid” detector
1 brick: 8.3 kg
Lead – Emulsion target Brick (basic module) 56 Pb 1 mm thick plates
57 emulsions films
Emulsion film (Fuji-Nagoya)
emulsion layers (43 m thick)
on both sides of a 200 m thick plastic base
12.5cm
10.2cm
8.3 kg
10 X0 wall 52 x 64 bricks
Bricks assembled in wallsTotal target mass : 1300t
Changeable Sheet (CS)Doublet of emulsion films with very low background,
attached to the brick, as interface to electronic detectors
Brick Assembly Machine (BAM) at LNGS
Robots produce bricks at a rate of 700 bricks / day
Brick Manipulator System (BMS)
Ventouse Vehicle
Brick
Carousel mechanism
Robot for brick insertion (target filling)
and removal (during run)
An event in OPERA
Electronic detectors select νinteraction brick and
CS μ ID, charge and p
Target Trackers
Pb/Em. target
μ spectrometer
8 cm
Pb/Em. brick
Extract selected brick
with CS
Emulsion analysis vertex search decay search e/μ ID, kinematics
Pb 1 mm
Basic “cell”
Emulsion
ντ
Automated Emulsion Scanning Started with the pioneering work in Nagoya
~ 30 bricks will be daily extracted from the target and analyzed quasi-online using high-speed automatic systems in Several labs in Europe and Japan
Customized commercial optics and mechanics + asynchronous DAQ software
Hardware-coded algorithmsContinuous movement of emulsion
High speed CCD Camera (3 kHz)
Piezo-controlled objective lens
Constant speed stage
Synchronization of objective lens and stage
S-UTS (Japan)European Scanning System
Track segments found in 8
consecutive films
Passing-through tracks rejection
Vertex reconstruction
3D reconstruction of particle tracks
16 tomographic images
200 m
Microscope field of viewMicroscope field of view
43 m emulsion sheet
Automaticmicroscopy: from a microscope field of view to a reconstructed vertex
Search for oscillation:expected number of events
decay channels
SignalBackground
m2 = 2.4 x 10-3 eV2 m2 = 3.0 x 10-3 eV2
µ 2.9 4.2 0.17
e 3.5 5.0 0.17
h 3.1 4.4 0.24
3h 0.9 1.3 0.17
ALL 10.4 15.90 0.76
full mixing, 5 years run @ 4.5x1019 pot / year
Main background sources: - charm production and decays- hadron re-interactions in lead- large-angle muon scattering in lead
OPERA sensitivityD
iscovery
pro
bab
ilit
y
(%)
Discovery probability vs m2
m eV 2 3 210
4- evidence
3- evidence
Exclusion plot at 90% C.L
•A short run: 0.0824*1019 protons on target with 1.8*1013
p/extraction3.6 effective days at nominal proton intensity
4.5*1013
•On October 3rd observed the first event in the target
•365 events in the whole detector selected and analyzed 331 events passed through the analysis cuts (303 expected)
•38 events (31.5 expected) in the neutrino target Their study is ongoing
First OPERA Physics RunSept. 24 - Oct. 22, 2007
Time Selection of Beam Events
GPS
TCERN
SPS extraction
TOPERA
Event Time
Tflight = 2.44 ms
TOPERA - TCERN resolution ~ 100 ns Cosmic ray background
Beam
22MIAMI 2007
In target events in the electronic detectors(top: display in the whole detector; bottom: display in the target)
EVENT 179673325 in el. det. and ECC
quasi-elastic-like topology
IP = 0.33 m
SlopeX=-0.040 SlopeY=0.014
IPh = 4.50 m
SlopeX=-0.380 SlopeY=-0.602
(by ionization)
ECC
6 prongs a
b
e
d
cf
Track Slope CS track
Stop film
IP (m)
A -0.028, 0.095-0.028, 0.095 6 57 5.2
B -0.114 ,0.143-0.114 ,0.143 (7?) 57 0.3
C 0.091, 0.0090.091, 0.009 57 6.2
D -0.166,-0.342-0.166,-0.342 32 21.4
E 0.127, 0.0750.127, 0.075 35 16.4
F -0.370, 0.430-0.370, 0.430 28 15.3
Shower 0.019, -0.0060.019, -0.006 2,8 38 -
EVENT 178969961 in el. det. and ECC
ECC
Track SlopeX SlopeY Length IP
1 0.026 -0.097 30-33 5.7
2() -0.024 0.019 30-56 1.2
3 0.045 0.197 30-52 1.7
4 0.024 0.203 30-52 2.6
5 0.100 0.151 30-51 7.9
6 -0.047 0.199 31-45 2.9
7 0.073 0.152 31-45 8.8
8 0.085 0.254 31-43 10.3
9 0.074 0.201 30-33 4.6
Track 1: kink between plates 33 and 34
Flight length of parent track 5 mm
Kink attributed to hadronic interaction
EVENT 180400976 in el. det. and ECC
ECC
Conclusions
Main aim: prove the → interpretation of the atmospheric disappearance, by observing → appearance
First physics run 24 Sept. - 22 Oct. 2007
The whole chain from data acquisition to event analysis has been tested
The studies on the acquired events are ongoing
Wait for the 2008 physics run and the 1st appearance !
“Neutrino oscillations” Pontecorvo, 1957 Maki, Nakagawa and Sakata, 1962 Pontecorvo and Gribov, 1969
• A phenomenon induced by m > 0• Implies the apparent “metamorphosis” of a into a different one (e.g. )• A very sensitive method to measure m
2
The PMNS matrixThe PMNS matrix
3
2
1
321
321
321
UUU
UUU
UUU eeee
100
0cossin
0sincos
cos0sin
010
sin0cos
cossin0
sincos0
001
1212
1212
1313
1313
2323
2323
CPCP ii ee
Atmospheric
Terms probed by next experiments
Solar, reactor analysis
CP violation phase
September 24th to October 22nd 2007: first OPERA Physics Run
On October 3rd OPERA observed
the first event in the target
SPS super-cycle with 3 CNGS cycles every 39.6s
During the run we have accumulated 0.0824*1019 pot onto the target with a mean value of 1.8*1013 proton per extraction: this represents effective days for the run!
CNGS run parameters
Data are extracted from the DAQ data base every 12 hours and processed with the OPERA reconstruction package.
In time events are selected and stored on a dedicated file.
Then in time events are scanned visually and stored by categories:• magnet interaction• rock muon• in target CC and NC like (according to the muon id)
The interactions in the material surrounding OPERA target are analysed separately and are used for the monitoring on the CNGS beam and of the OPERA detector
Data analysis and event selection
Beam events
CC event originated upstream of the detector (BOREXINO, rocks)
CC event originated in the first magnet
Data analysis and event selection
Main physical distribution for the selected events
The vertical angle of the track. Fit: 3.4±0.2 degree
The Vertex location is defined as the first hit of the 3D reconstructed track
The Energy of the muon as measured with the RPC of the spectrometer
In target events analysis
We have observed 38 events (31.5 expected) in the emulsion target area
• 22 charged current• 9 neutral current
compatible with the relative cross sections
The events are analysed through the brick finding package: • a neural network for the wall finding • the hadronic shower parametrization• the exact configuration and alignment of the target at the time of the
event taking into account the wall elongation as a function of the filling• the probability estimate for the vertex location in each brick
35
Target Tracker
7 m
7 m
6.9m
1.7m
Plastic scintillator strips (AMCRYS-H, 6.7m x 2.6cm x 1cm)readout by Kuraray WLS fibres +Hamamatsu PMT’s (64 channels)
Target Tracker tasks
● Trigger: > 99%● Initiate muon tagging 31 walls
Alberto Marotta - INFN NapoliMIAMI 2007
• Beam events are
selected correlating
events GPS time
information with CERN
beam spill time• 319 events on time
selected
Events Time Structure
OPERA
Cosmic ray background
Extraction length = 10.5 sec
OPERA
Angular distribution of all events
Angle w.r.t. horizontal
Azimuth angle
Cosmic µ: mountain rock structure asymmetry
coherently with previous MACRO observation
Zoom on Beam eventsComing 3.5° from below