status and the preliminary results of the opera experiment v.tioukov (infn, napoli) on behalf of the...

Status and the Status and the preliminary results of the preliminary results of the

OPERA experimentOPERA experiment

V.Tioukov (INFN, Napoli)V.Tioukov (INFN, Napoli)

on behalf of the OPERA collaborationon behalf of the OPERA collaboration

V. Tioukov QFTHEP11, SochiV. 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


OPERA

CNGS neutrino beam

Detection principle

● The detection of the 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)

e-, , h

3h

e (17.8%)(17.4%)h (49.5%)

3h (15.2%)


CNGS CNGS appearance potential 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<Eμ> 17 Gev

eeμ0.87%

μμ4 %

prompt negligible

Total p.o.t 22.5x 1019

μ CC + NC ~23600

ee CC ~160

~115



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

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 OPERAIn 2008-2011

OPERA layout 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


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%


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 sheets57 (300m) FUJI emulsion layers 2 (300m) changeable sheets

Long decay

Short decay

10.3 cm

12.8 cm7.5 cm = 10 X

0


Emulsion/lead target

8.3kg

10 X0

10.2 x 12.7 x 7.5 cm

• Brick filling is finished in July 2008

• 146621 bricks with ~ 8 millions of nuclear emulsions plates

Bricks assembling was technologically challengingThe small mechanical industry installedunderground and worked in the red-light dark room



Changeable sheet (interface films) Changeable sheet (interface films)

600 microns

160m

icro

n

muon track

Side view of a CS doublet

Hybrid target structure.Hybrid target structure.

Neutrino

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

Muon

Other products

No cosmic rays in CS!

The automatic emulsion scanningThe automatic emulsion scanning

Developedgrains

frame

2-3 m

15-16 frames/45 microns

The European Scanning System. About 30 of them installed in the European labs


UTS, S-UTS automatic microscopes generation (Japan)

•75 cm2/hour scanning performance

•High speed CCD Camera (3 KHz)

•Objective lens moved by piezo-element

•Dedicated hardware for the reconstruction algorithms

S-UTS:


OPERA emulsion targetOPERA emulsion target

Pb

Emulsion layers

1 mm • 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 schemeECC 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 photonsECC Technique validated by the direct observation of : DONUT 2000 V. Tioukov QFTHEP11, SochiV. Tioukov QFTHEP11, Sochi


Some numbers concerning the OPERA Some numbers concerning the OPERA scanningscanning

• 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

Emulsion data reconstructionEmulsion 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

Vertex found


• In spring 2010 OPERA present the first 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)

The first tau candidate


beam

Event ECC pink color

The viewer of scintillation Target Tracker

1919


• 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.

Work of the last year (after the candidate detection)


-,e-,e

D+

+

e+

h+

h

--,

h

BG reduction by the systematical tracks follow down for the candidate events to improve the muons id

Charm background Hadrons re-interaction background

• Momentum range correlation: tested for the first candidate event

•  Misidentified muons from charm events: 3.28 % (was 5%) •  Factor 100 reduction of the BG for the τ -> µ channel: golden channel!

In 95 % of cases the muon should be identified by the electronic detectorBut when it missed or misidentified with hadron the following topologies becomes the background:


Hadron tracks in OPERA neutrino interactions with kink topology far from primary vertex

Hadron interactions search in 4 GeV π test beam

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)

Signal region Signal region

Hadron re-interaction studies using the Pions test-beam data and real OPERA data


Decay channel Number of signal events expected for m2 = 2.5×10-3 eV2

22.5×1019 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 ‘08+’09 data) one

observed in the h channel compatible with the expectation of 1.65 signal events.

Including all the improvements in the analysis

Expected OPERA signal


Decaychannel

Number of background events for:

22.5×1019 p.o.t. Analysed sample

Charm Hadron Muon Total Charm Hadron Muon Total

→ µ 0.025 0.00 0.07 0.09±0.04 0.00 0.00 0.02 0.02±0.01

→ e0.22 0 0 0.22±0.05 0.05 0 0 0.05±0.01

→ h 0.14 0.11 0 0.24±0.06 0.03 0.02 0 0.05±0.01

→ 3h0.18 0 0 0.18±0.04 0.04 0 0 0.04±0.01

Total 0.55 0.11 0.07 0.73±0.15 0.12 0.02 0.02 0.16±0.03

Background summary

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


3765 interactions located, 3289 “decay searched” events

OPERA events interaction, bricks extraction and processing rates

2008

2009

2010

2011


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


Summary for the peculiar topologies found Summary for the peculiar topologies found

Events

Located

Decay search

Charm

Candidates

e

candidates

Total 3765 3289 52 20 1


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.

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


Summary of the principle for the TOF measurement

Measure t =TOFc - TOF

31

z

y x


Time-link created between Tx LNGS and Tx CERN updated every second

GPS and common view modeData 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)


• 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.



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 → 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 candidate event is compatible with the expectation of 1.65 signal events. The significance of the observation of one decay in the →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 - flavor transition, as well as of the study of the sub-leading -ee oscillation

•In the coming months will be done the extensive campaign for crosschecking and additional systematic errors study for the neutrino velocity measurement

status and the preliminary results of the opera experiment v.tioukov (infn, napoli) on behalf of the...

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