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