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Status of the OPERA experiment

On behalf of the OPERA Collaboration Andrea Russo INFN - Napoli

1 QFTHEP 2010 1


OPERA: first direct detection of neutrino oscillations in appearance mode in the µ channel
following the Super- Kamiokande discovery of oscillations with atmospheric neutrinos and the confirmation obtained with accelerator beams.

OPERA main features: 1) long baseline, 2) high neutrino energy, 3) Kton detector mass, 5) detect short lived taus produced in tau neutrino interactions

L = 730 km

CERN

T

flight

= 2. 44 m s

LNGS

Expected neutrino interactions for 22.5x1019 pot: ~ 23600 µ CC + NC ~ 160 e + e CC ~ 115 CC (m2 = 2.5 x 10-3 eV2) 2


CNGS neutrino beam performances
2006 2007 2008 2009 2010 0.076x1019 pot 0.082x1019 pot 1.78x1019 pot 3.52x1019 pot 1.74x1019 pot (19 July) Commissioning Commissioning First physics run Physics run Physics run

2010
t eg a no s no o P rt tr

Improving features in 2010: beam close to nominal intensity; Aiming at higher intensity run in 2011

2009

2008
3
A. Ereditato - CERN - 4 June 2010

Days

3


Detecting leptons with ECC detectors
75.4mm 125mm
CS sheet

8.3kg 10X0

beam
100mm

OPERA emulsion film (Fuji Japan )

Lead plate (Goslar Germany)

4


Emulsion film scanning
EU: ESS (European Scanning System) Japan: SUTS (Super Ultra Track Selector)

· Scanning speed/system: 20cm2/h · Customized commercial optics and mechanics · Asynchronous DAQ software

· Scanning speed/system: 75cm2/h · High speed CCD camera (3 kHz), Piezo-controlled objective lens · FPGA Hard-coded algorithms

Similar performances · ~ 0.3 micron spatial resolution · ~ 2 mrad angular resolution

5


The target region of the OPERA detector
The OPERA detector is hybrid: bricks are organized in walls interleaved with scintillating strips Electronic detectors: Provide timing information on neutrino events Preselect the neutrino interaction point with cm accuracy



6


The OPERA detector
S M1 S M2

ECC target modules

ECC target modules

7

Target area

Muon spectrometer

Target area

Muon spectrometer


event reconstruction
Neutrino event reconstruction in tho phases: 1)Electronic detector reconstruction

20 m
8


2) emulsion analysis

ECC brick
1 mm

Electronic


trackers





Pb

emulsion layers

interface films (CS)
9
9


Kinematical measurements in event analysis
Important to achieve large signal/background ratio The use of a succession of lead plates as target allows: e/ identification and e/m shower calorimetry momemtum measurement for charged particles

10


Momentum measurement by Multiple Coulomb Scattering

test beams

Comparison with muon spectrometer measurements

p/p = (22±4)%

Pmcs error bar: 68% CL

11


detection and 0 mass reconstruction
2 EM showers give a reconstructed mass ~ 160 MeV

E = 8.1 GeV E = 0.5 GeV

EM shower energy measured by shower shape analysis and Multiple Coulomb Scattering method

12


0 mass resolution (data)

35 gamma pairs

1 mass resolution: ~ 45%

13


Detection of charmed particle produced in µ CC interactions

14


The study of charmed particles production in neutrino events in OPERA is important because of their short lifetime (similar to the ) and because they represent a background source to all tau decay channels

Charm candidate event (dimuon)
x-view

1ry muon 1ry vertex kink

flight length: 1330 microns kink angle: 209 mrad IP of daughter: 262 microns daughter muon: 2.2 GeV/c decay Pt: 0.46 GeV/c

daughter muon

1 . 3 mm

15


Charm candidate event (4-prong)

Flight lenght: 313.1 microns : 173.20 minimum invariant mass: 1.7 GeV

16


Event statistics

Total found neutrino vertices: 1617 Events with search of decay topologies completed: 1088 (current number is 1700) This is about 35% of the total 2008-2009 run statistics, corresponding to 1.85 x 1019 pot With the above statistics, and for m223 = 2.5 x10-3 eV2 and full mixing, 17 OPERA expects: ~ 0.5 events


A very interesting event

18


Muonless event 9234119599, taken on 22 August 2009, 19:27 (UTC) (as seen by the electronic detectors)

19


From CS to vertex location
Large area scanning
a kinkllisecoected ction of vertices and gammas Fu r det nstru

CS prrediictiions CS p ed ct ons
Scan-back in ECC

20


Event reconstruction (I)

gamma

gamma kink

careful visual inspection of the films behind/in front the secondary vertex: no "black" or "evaporation" tracks. Support to the topological hypothesis of a particle decay
21


Event reconstruction (II)
Zoom

gamma parent

daughter

22


Features of event tracks
TRACK NUMBER PID Probability

MEASUR EMENT 1
ta n tan P (GeV/c)

MEASUR EMENT 2
tan tan P (GeV/c)

X

Y

X

Y

1

HADRON range in Pb/emul=4.1/1.2 cm PROTON

Prob()10-

3

0. 17 7

0. 368

0.77 [0.66,0.93]

0.175

0. 35 7

0.80 [0.65,1.05]

2

range, scattering and dE/dx interaction seen

-0.646

-0.001 0.60 [0.55,0.65]

-0.653

0. 00 1

3 4 (PARENT) 5

HADRON

0. 10 5 -0.023

0. 113 0. 026 0. 275

2.16 [1.80,2.69] 1.33 [1.13,1.61]

0.110 -0.030 0.149

0. 11 3 0. 01 8 0. 25 9

1.71 [1.42,2.15] 1.23 [0.98,1.64]

HADRON: range in Pb/emul=9.5/2.8 cm HADRON: range in Pb/emul=1.6/0.5 cm From a prompt neutral particle HADRON

Prob()10-

3

0. 16 5

6

Prob()10-

3

0.334

-0.584

0.36 [0.27,0.54]

7 8

0. 43 0
interaction seen

0. 41 9 -0.008

0.34 [0.22,0.69] 12 [9,18]

0.445 -0.009

0. 41 9 -0.020

0.58 [0.39,1.16]

(DAUGHTER)

-0.004

Residual probability to be a µCC event (due to a possibly undetected large angle muon) ~1%. 23


detection
2

1

8 daughter

· length available for



detection downstream of the vertices: 6.5 X0

·2 gammas detected, both assumed to come from secondary vertex after impact parameter analysis
Distance from 2ry vertex (mm)

Energy (GeV)

1st 2 nd

2.2 12.6

5.6 ± 1.0 ± 1.7 1.2 ± 0.4 ± 0.4
24


Kinematical variables
VARIABLE AVERAGE

kink (mrad)

41 ± 2 1335 ± 35 12 470 570
+6 -3

The kinematical variables are computed averaging the two sets of track parameter measurements

decay length (µm) P daughter (GeV/c) Pt daughter (MeV/c) missing Pt (MeV/c) (deg)

+230 -120

+320 -170

173 ± 2

The average values are used in the following kinematical analysis Uncertainty on Pt due to the gamma attachment choice is smaller than 50 MeV
25


Topological and kinematical analysis
OPERA analysis flow (as defined in the experiment proposal) applied to this candidate event: · kink occurring within 2 lead plates downstream of the primary vertex · kink angle larger than 20 mrad · daughter momentum higher than 2 GeV/c · decay Pt higher than 600 MeV/c, 300 MeV/c if 1 gamma pointing to the decay vertex · missing Pt at primary vertex lower than 1 GeV/c · azimuth angle between the resulting hadron momentum direction and the parent track direction larger than /2 rad
26


Event interpretation and invariant mass analysis
· This event passes all cuts, with the presence of at least 1 gamma pointing to the secondary vertex ·This event is a candidate with the 1-prong hadron decay mode. · The invariant mass of the two detected gammas is consistent with the 0 mass value (see below). · The invariant mass of the (daughter++) system is compatible with that of the (770). The appears in about 25% of the decays: (- 0) .

(+) mass
120 ± 20 ± 35 MeV

(++daughter) mass
640
+125 +100 -80 -90

MeV
27


Background sources
· Prompt


~ 10-7/CC ~ 10-6/CC ~ 10-6/CC

· Decay of charmed particles produced in e interactions · Double charm production · Decay of charmed particles produced in µ interactions · Hadronic reinteractions

~ 10-5/CC ~ 10-5/CC

28


Statistical significance
1 candidate in the 1 prong decay channel observed. Given the statistics mentioned before, the background expectation is: Considering all decay channels: Considering only 1prong channel: 0.045 ± 0.020 (syst) BG events 0.018 ± 0.007 (syst) BG events

The probability to observe at least 1 BG event is (all decay channels) 4.5%. The probability to observe at least 1 BG event is (only t 1prong) 1.8%. The observation of 1 canditate event corresponds to a significance of 2.01 if we consider all dacay channels, 2.36 for the 1prong decay channel.
29


Outlook

At the present scanning speed we expect to complete the analysis of 2008+2009 runs by the end of 2010 (NB we expect about 2 taus in this sample)
30


Thank you for your attention!
31


SPARES

32


Impact parameter measurement
µm

IP distribution for: events (MC) NC+CC µ events (MC), NC+CC µ events (Data)
expanded scale

IP distribution for events (MC)

33


DATA/MC comparison: good agreement in normalization and shape (pion test-beam exposure)

1- pr ong

multi-prong

34


e candidate event
From a subsample of ~ 800 located events we detected 6 candidates
study µ-e oscillations
e

Additional physics subject:

35


Typical µCCand NC-like events
The measured ratio of NClike/CC-like events after muon ID and event location is ~20%, as expected from simulations

20 m

36

36


attachment to the vertices
Distance from IP to 1ry 2ry vertex (mm) vertex (µm) IP to 2ry vertex (µm) Prob. of Prob. of Attachment hypothesis attach. to 1ry attach. to 2ry vtx* vtx*

1st 2nd

2. 2 12. 6

45.0 <11> 85.6 <56>

7.5 <7> 22 <50>

<10

-3

0. 32 0. 82

2ry vertex 2ry vertex (favored)

0. 10

* probability to find an IP larger than the observed one

1ry vertex

2ry vertex

2

1
Pointing resolution (1) for a given gamma: function of scattering and distance
37


Kinematical cuts to be passed
Reject NC events with larger missing Pt (neutrino)
cu cutt

Blue: MC NC Black: MC -
Missing Pt at primary vertex

GeV/c

Pt at decay vertex

Reject hadron interactions

cut
38

GeV/c8 3


Signal :

X (hadron shower)

BG: small



=180

o

Azimuthal angle between the resulting hadron momentum direction and the parent track direction

-decay




kink

-

x -

-

N

-X µN



µ

µ-X

Blue: MC - NC Black: MC -

cut
39 r ad
39


Hadronic re-interaction studies for background evaluation
Search for hadronic interactions along a total of 9 m of hadron track measured for scanned events. This is about a factor 8 larger than the so far scanned track length for NC events (number of NC x hadron multiplicity x 2 mm decay length).
·

· Goal: ~100 m as needed to fully validate (eventually replace) the MC background prediction

40
1 cm


Hadronic re-interaction studies, present status

signal region

· no events in the signal region · 90% CL upper limit of 1.54 x 10-3 kinks/NC event · the number of events outside the signal region is confirmed by MC
41


Charm background
Charmed particles have similar decay topologies to the µ
,e

µ,e

-

primary lepton not identified

µ+

D+

e h

+ +

· charm production in CC events represents a background source to all tau decay channels · for the 1-prong hadronic channel 0.007±0.004 (syst) background events are expected for the analyzed statistics · further charm BG reduction is under evaluation by implementing the systematic follow-down of low energy tracks in the bricks and the inspection of their end-range, as done for the "interesting" event. For the latter we have 98-99% muon ID efficiency. · this background is suppressed by identifying the primary lepton with ~ 95% muon ID

Charm search: 20 candidate events selected by the kinematical cuts, Expected: (16.0 ± 2.9) + ~2 BG events
42