2008 European School of High-Energy Physics - Trest,  Czech Republic - 19 August - 1st September

Target Tracker Data Analysis In OPERA ExperimentS. Dmitrievsky, S. Zemskova - JINR

OPERA Experiment

The OPERA experiment is designed for direct observation of appearance in the CNGS long baseline beam (from CERN to Gran Sasso Laboratory) as a result of oscillation.

OPERA exploits nuclear emulsions as very high resolution tracking devices for the direct detection of tau leptons produced in the charge current (CC) interaction of the with matter of the detector.

OPERA ECC BrickLead plate(1mm) / Emulsion Film (OPERA film) Sandwich

125mm

100mm

Lead Plate Emuslion Film (OPERA Film)

125mm

100mm

PbEmulsion layers

1 mm

CNGS Beam

Beam optimized to have the maximal number of Charged Current interactions (given the baseline L=730 km)

productionthreshold

3.9% /

negligible prompt

17 GeV<E>

0.73%(e+e)/

L/E ~ 43 km/GeV, not optimal for Posc

Beam energy and contamination

Signal and background eventsnm -nt oscillation channel

0.174.22.9 - µ-

0.175.03.5 - e-

0.244.43.1 - h-

0.171.30.9 - 3h

Background:

Charm

Hadron interaction

Muon scatteringm2 = 3.0 x 10-3 eV2

m2 = 2.5 x 10-3 eV2

- decay

channels

15.0 0.76 ALL

Signal ÷ (m2)2 – Full mixing

10.4

Preliminary

OPERA subsidiary physics programme includes

measurement of upper limit of at level

The first CNGS neutrino test run took place in August 2006.

.

Alignment of TT with the help of muon tracks

Alignment of the TT is essential for track reconstruction and the brick finding. Making use of straight cosmic muon tracks we clarify a geometrical position of the TT modules (the angles of rotation around of coordinate axes and displacement along the axes).We need to set local coordinate systems of modules to general system of coordinates of the experiment.

We can see summary difference between experimental points and calculated tracks before alignment and after 3 iteration on these pictures.

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:Target Tracker tasks:

● ● Trigger: Trigger: > 99% > 99%● ● Brick finding : Brick finding : 707080%80%● ● Initiate muon taggingInitiate muon tagging

31 walls

Detection of the appearance signal

Two conflicting requirements: Large mass low Xsection High granularity

signal selection background rejection

Target:1800 tons, 5 years running

• 30 000 neutrino interactions• ~150 interactions• ~15 identified• < 1 event of background

Toplogy selection:

Kink signature

The challenge is to identify interactions from interactions

-

Decay “kink”

-

~1 mm

oscillation

-

Autumn 2007 CNGS Commissioning and Physics RUN

• If intensity as in August 2006 : 1.7 1013 pot/extraction (70% nominal)• If extraction scheme as in November 2006: 3 double fast extraction per 36 s SPS cycle • If typical 70 % efficiency of the machines complex • If target filling programme as scheduled

Target mass 505(37%) → 615(46%) tons

Beam intensity 0.43 1019 pot

≈ 10% nominal year

≈ 10 × flux in 2006

Events in bricks 180

Charm events 10

3 weeks of CNGS commissioning run + 3 weeks of physics run following June CERN SPSC recommendation

OPERA detector : 2 identical super-modules (target, TT, Spectrometer) + veto system

Target and Target Tracker (6.7m)2

● Target : 77500 bricks, 29 walls

● Target tracker : 31 XY doublets of 256 scintillator strips + WLS fibres + multi-anodes PMT for

• Brick selection• Calorimetry

Veto plane (RPC)High precision tracker Instrumented dipole magnet

● 6 4-fold layers of ● 1.53 T drift tubes ● 22 XY planes of RPC in

both arms

Muon spectrometer (8×10 m2)

SM1 SM2

ID, charge, pp/p < 25%Wrong charge < 0.3%

ID, charge, p

0.68 kton 0.68 kton

Brick Finding

An essential issue in OPERA is finding of a target brick where the neutrino interaction took place. For this purpose the OpBrickFinder program was developed that performs the vertex brick identification using the information from the target tracker and spectrometer.

Our brick finding (BF) strategy includes the following steps: - event cleaning; - muon track identificatin and reconstruction; - hadron shower axis reconstruction;

- the most probable vertex wall determination:

For a vertex wall determination we use a multilayer perceptron (MLP) with standard back propagation training algorithm.

Expected BF Efficiency:

1 brick extraction: ~70%2 bricks extraction: ~85%3 bricks extraction: ~90%

Output variables of the neural network are probabilities of each wall to be a vertex wall. The wall finding efficiency achieved so far is ~85% for events

- localization of the most probobal vertex bricks:

After the vertex wall is selected by the NN, we use its position, a muon track, and/or a shower axis parameters to determine x-y coordinates of the vertex brick in the wall.

CC

5 years of data taking Nominal beam intensity 4.5*10^19 p.o.t./year1.35 kton target mass (25% reduction w.r.t. proposal)

2305.006.0

223

132

232

22232

232

132

105.2

14.02sin

5.0sin

27.1sinsin2sin)(

eVm

GeVE

kmLeVmP e

06.02sin 132

Neutrino int. in TT

100

0cossin

0sincos

cos0sin

010

sin0cos

cossin0

sincos0

001

zyx RRRR

13