Status and results from the OPERA experiment

Tsutomu FUKUDA ( Nagoya University )

On behalf of the OPERA Collaboration

NNN10 , 14 Dec 2010, Toyama International Conference Center in Toyama, JAPAN

Oscillation Project with Emulsion-tRacking Apparatus

First direct detection of neutrino oscillations in appearance mode through the channel.

oscillation

-

decay “kink”

~1 mm

- ,h-,e-

Requirements : high neutrino energy & intensity & long base line & large target mass & detect short lived ’s

2 important experimental results for OPERA design

Neutrino oscillation (disappearance)Result from SK in 1998

Direct observation of events Result of DONuT in 2001

OPERA start !!

Flight Length： 280um

DONuT event

1mmIron

BelgiumIIHE-ULB Brussels

CroatiaIRB Zagreb

FranceLAPP AnnecyIPNL LyonIPHC Strasbourg

GermanyHamburgMünsterRostock

ItalyBariBolognaLNF FrascatiL’AquilaLNGSNaplesPadovaRomeSalerno

JapanAichiTohoKobeNagoyaUtsunomiya

IsraelTechnion Haifa

KoreaJinju

RussiaINR RAS MoscowNPI RAS MoscowITEP MoscowSINP MSU MoscowJINR Dubna

SwitzerlandBernETH Zurich

TurkeyMETU Ankara

180 physicists, 33 institutions in 12 countries

TunisiaCNSTN Tunis

The OPERA CollaborationThe OPERA Collaboration

Our philosophy

following the Super- Kamiokande discovery ofoscillations with atmospheric neutrinos and theconfirmation obtained with solar neutrinos and accelerator beams. Important, missing tile in the oscillation picture.

Full mixing and ∆m223 ~ 2.4 x 10-3 eV2

The light blue band indicates the OPERA allowed region (90% CL) for the above parameter values for 22.5 x 1019 pot

•　 OPERA give a clear and strong evidence for the existence of neutrino oscillation.

•　 OPERA is also searching for first direct observation of Lepton Flavor Violation.

CNGS beam line

CERN

LNGS

732km

conventional beam

< E > ( GeV ) 17 (e + e) / 0.87 %* / 2.1 %* prompt Negligible*

Expected interactions for 22.5x1019 pot (nominal pot in 5 years for 1.25kton target):

~23600 CC + NC ~160 e + e CC ~115 CC (m2 = 2.5 x 10-3 eV2)

~10 CC identified (BG<1)

* Interaction rate at LNGS

The OPERA target – ECC brick –

50 micron

Microscopic Image

Recorded as silver grains along the line where a charged particle passed through

Resolution of 0.3 micron

OPERA emulsion film

Lead plate : 1mm

57 OPERA films and 56 lead plates piled up.

125mm

100mm

75.4mm

8.3kg10X0

Neutrino Beam

Emulsion Cloud Chamber (ECC)

The OPERA detector

OPERA emulsion film

Emulsion + Target Tracker

Muon spectrometer

Emulsion + Target Tracker

Muon spectrometer

Typical CC-like and NC-like events

20 m

CC-like event

NC-like event

Emulsion Scanning for CS

• CS Scan & analysis NAGOYA : LNGS = 50:50

ECC brick

CS

Changeable Sheets (CS), two OPERA films fixed downstream of the ECC bricks, are used as interfaces between the electronic trackers and the ECC bricks.

When a neutrino interaction is detected by the electronic detectors, the most probable brick is extracted and the CS are developed and analyzed.

If one or more predicted tracks are found, the brick films are developed. If not, the brick is returned back to the detector with new CS and the next brick is extracted.

By using CS, emulsion analysis speed become about 10 times faster.

Emulsion Scanning for ECC brick

• ECC brick Scan & analysis JP : EU = 50:50

To Japan

PadovaBern

Bologna

RomaLNF

NapoliSalerno

Bari

LNGS

After tracks are found on CS, ECC brick films are developed and sent to scanning labs along with the CS information.

Neutrino event location

5 mm

CSECC brick

CS ~100cm2 large area scanECC ~100100m2 point scan

How to locate1. Connect track CS to ECC brick.2. Follow up track in ECC brick.

(Scan Back method)3. Confirm the stop plate.4. Scan around stop plate.

The Plate changer system for Scan Back in Japan.

Films of ECC brick are glued on a sheet for changing plates easily.

STOP

1 cm

Scan about 10 plates around stop plate by follow up from down stream.

Located neutrino interaction in ECC brick

1 cm

Reject passing trough track and only few plates connect track.

Located neutrino interaction in ECC brick

1 cm

Search tracks making vertex by neutrino interaction .

Located neutrino interaction in ECC brick

2010

2009

2008 Days

POT

Year Days beam

POT Events Run

2006 0.076×1019 no bricks Commissioning

2007 0.082×1019 38 Commissioning

2008 123 1.78×1019 1698 First physics run

2009 155 3.52×1019 3693 Physics run

2010 187 4.04×1019 4248 Physics run

• 9639 events collected (within 1 in agreement with expectations from pot) → 2.1 nominal years in 3 years.

• POT of 2010: 90% of nominal year

Progress of CNGS runs

Location Status

• Event location is going well. 2779 events are already located.• Based on the 2008 run efficiencies, about 5650 events to be located

in ( 2008 + 2009 + 2010 run ).

Interaction in the target

Events with at least 1 brick extracted

Events with a positive CS result

Interactions located in the bricks

Decay Search completed

Decay topology search

IP distribution for events (MC)

IP distribution for:

events (MC)

NC+CC events (MC),

NC+CC events (Data)

A Charm event (dimuon event)

Kink angle = 209mrad

Flight Length= 1330micron

Decay Pt ~ 460MeV/c

1ry

Charm

+

In 901 sub-sample events,20 charm events were found. (expected : 16.0±2.9)

The analysis of a sub-sample of the data taken in the 2008-2009 runs was completed.

Number of events completed: 1088 (187 NC)

This is ~20% of the total 2008-2010 run statistics, corresponding to 1.85 x 1019 pot

With the above statistics, and for m223 = 2.5 x10-3 eV2 and full mixing, OPERA expects:

~ 0.5 events

Event statistics for Decay search

The first candidate event was found

This result is opened at June/2010.

Event number 9234119599,taken on 22 August 2009, 19:27 (UTC)

2

1

3

2

75

1

6

8 (daughter)

4 (cand)

track # tan x tan y p [GeV/c]

1 0.176 0.363 0.78 +0.13-0.10

2 -0.650 0.000 0.32 +0.31-0.11

3 0.108 0.113 1.97 +0.33-0.25

4（ parent） -0.027 0.022

5 0.157 0.267 1.30 +0.22-0.16

6 0.334 -0.584 0.36 +0.18-0.09

7(from neutral track)

0.438 0.419 0.49 +0.29--0.13

8（ daughter） -0.007 -0.014 12 +6

-3

1 radiation length0.033 interaction length

primary vertex

kink point

Event topological features (Side view)

beam

top

view

side

vie

w

Event ECC pink color

The viewer of scintillation Target Tracker

primary vertex

kink point

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

γattachment to the vertices

Distance from 2ry vertex (mm)

IP to 1ry vertex (m)<resolution>

IP to 2ry vertex (m)<resolution>

Prob. of attach. to 1ry vtx*

Prob. of attach. to 2ry vtx*

Attachment hypothesis

1st 2.2 45.0 <11> 7.5 <7> <10-3 0.32 2ry vertex

2nd 12.6 85.6 <56> 22 <50> 0.10 0.82 2ry vertex (favored)

* probability to find an IP larger than the observed one

The invariant mass of 1 2 is consistent with 0.The invariant mass of 1 2 and (8) is consistent with

120 ± 20 ± 35 MeV 640 +125-80

+100-90 MeV

Kinematical variables

The event passes all the kinematical cuts required.

The uncertainty on Pt due to the alternative attachment is < 50 MeV.

VARIABLE MeasuredSelection

criteria

Kink (mrad)

41 ± 2 >20

Decay length (m)

1335 ± 35Within 2 plates

P daughter (GeV/c)

12 +6-3 >2

Pt daughter (MeV/c)

470 +230-120

>300 ( attached)

Missing Pt (MeV/c)

570 +320-170 <1000

ϕ (deg) 173 ± 2 >90

(Animation)

Missing Pt at primary vertex

cut

Pt at decay vertex

cut

GeV/c

Blue: MC NC Black: MC -

GeV/c

Missing Pt at primary vertex

cut

Features of the decay topology…red bands: values for the “interesting” event

with uncertainties

mm

Decay length

GeV/c

cut

Daughter momentum

1335 ± 35 m

12 +6-3 GeV

rad

Accepted kinks > 20 mrad

Kink angle41 ± 2 mrad

..and kinematical cuts to be passed

Reject NC events withlarger missing Pt (neutrino)

Reject hadron interactions 470 +230

-120 MeV

570 +320-170 MeV

Background sources

• Prompt ~ 10-7/CC• Decay of charmed particles produced in e interactions ~ 10-6/CC • Double charm production ~ 10-6/CC

• Decay of charmed particles produced in interactions ~ 10-5/CC

• Hadronic reinteractions ~ 10-5/CC

Main Background

Hadronic reinteraction background

cross check ① (4GeV test-beam data)

multi-prong1-prong

18 times track length of tau search

The number of estimated hadronic reinteraction BG is 0.011±0.006 by using FLUKA simulation code.

cross check ② (scan-forth data)

signal region

• no event 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 (within the ~30% statistical accuracy of the measurement)

8 times track length of tau search

Charmed particles have similar decay topologies to the

• charm production in CC events represents a background source to all tau decay channels

• this background can be suppressed by identifying the primary lepton ~ 95% muon ID

• for the 1-prong hadronic channel 0.007±0.004 (syst) background events are expected for the analyzed statistics

,e

,e-

+

e+

h+D+

primary lepton not identified

Charm background

We observe 1 event in the 1-prong hadron decay channel,with a background expectation (estimating a ~ 50% error for each component) of:

0.011 events (reinteraction)0.007 events (charm)

0.018 ± 0.007 (syst) events 1-prong hadron

all decay modes: 1-prong hadron, 3-prongs + 1-prong μ + 1-prong e :

0.045 ± 0.020 (syst) events total BG By considering the 1-prong hadron channel only, the probability to observe 1 event due to a background fluctuation is 1.8%, for a statistical significance of 2.36 on themeasurement of a first candidate event in OPERA.

If one considers all decay modes which were included in the search, the probability to observe 1 event for a background fluctuation is 4.5%. This corresponds to a significance of 2.01 .

Statistical significance

• The OPERA experiment is aimed at the first direct detection of neutrino oscillations in appearance mode through the study of the channel.

• In 2008 – 2010, data has been taken corresponding to 2.1 nominal years. In 2010, beam intensity has reached 90% nominal.

• One muon-less event showing a 1-prong hadron decay topology has been detected and studied in a subsample of 20% of the accumulated data.

• It passes all kinematical cuts required to reduce the physics background. It is the first candidate event in OPERA. The expected number of events in the analysed subsample is 0.54 ± 0.13 (syst.)

The statistical significance of 2.01 on the measurement of a first candidate event in OPERA when considering all tau decays is relevant.

Conclusions

• In 2011, 6 extra weeks of beam in dedicated mode have been attributed corresponding to 1.2 nominal years. If 2012 (or 2013) is like 2011: Data on ~ 19.7×1019 POT or ~ 87% of Proposal beam intensity collected

• Analysis of 2008/2009 events will be closed in Feb/2011 and new results on oscillations will be released in spring 2011.

Outlook

Thank you for your attention !

Tsutomu FUKUDA ( Nagoya University )

NNN10 , 14 Dec 2010, Toyama International Conference Center in Toyama, JAPAN