first results on appearance mode neutrino oscillations from opera

First results on appearance mode neutrino oscillations from OPERA

A. PastoreBari University and INFN, Italy

on behalf of the OPERA Collaboration

Lake Louise Winter Institute 201120-26 February 2011 – Lake Louise

BelgiumIIHE-ULB Brussels

CroatiaIRB Zagreb

FranceLAPP AnnecyIPHC StrasbourgIPNL Lyon

GermanyHamburgMünster

ItalyBariBolognaLNF FrascatiL’Aquila,LNGSNaplesPadovaRomeSalerno

JapanAichiTohoKobeNagoyaUtsunomiya

IsraelTechnion Haifa Korea

Jinju

RussiaINR RAS MoscowLPI RAS MoscowITEP MoscowSINP MSU MoscowJINR Dubna

SwitzerlandBernETH Zurich

TurkeyMETU Ankara

TunisiaCNSTN Tunis

180 physicists, 32 institutions in 12 countries

Feb 25, 2011 A. Pastore, LLWI 2011 2

Outline

• OPERA physics motivation

•The CERN Neutrinos to Gran Sasso project

• hunting

• OPERA at work

• Conclusions and outlook


Neutrino oscillations: fundamental achievement (I)

3 eigenstates of mass, flavor:

Unitary matrix UPMNS : 3 Euler rotation angles + 1 CP phase

Measured by atmosphericand accelerator experiments

Mainly constrained byreactor experiments

(CHOOZ, PaloVerde)

Measured bysolar experiments

& by KamLAND


• Super-K (1998): atmospheric neutrino

anomaly interpretable in terms of

oscillations

• CHOOZ: e oscillation excluded as

dominant process responsible for

atmospheric neutrino disappearance

• Super-K signal confirmed by K2K and

MINOS ( oscillation)

Direct observation of appearance

from oscillation at atmospheric scale still missing

CERN

LNGS

730 km

OPERA appearance in a beam

730 km

Neutrino oscillations: fundamental achievement (II)

A. Pastore, LLWI 2011 5

The CERN Neutrinos to Gran Sasso beam

- 400 GeV/c protons from the CERN SPS on a graphite target- 6 s cycle length, 2 extr. every 50 ms, 10.5 s pulse length- beam intensity 2.4 1013 pot/extr- average power at the target 510 kW - neutrinos from pions and kaons decaying in flight

400 GeV/c K+, π+

20–50 GeV

~ 1 km, 2.5 m

P+C (interactions) (decay in flight)

vacuum

diameter: 80cm & 115 cmcurrent: 150kA & 180 kA

conventional neutrino beam with a high intensity and high energy proton beam, intenseshort beam pulses and small beam spots (< 1 mm)

Feb 25, 2011 6

Pr( ) &CC convolution

maximized high E beam

(“appearance”- optimized)

L = 732 kmCERNLNGS

Shared SPS operation, 200 days/year

CC

CC

The CERN Neutrinos to Gran Sasso beam

Feb 25, 2011 7

~ 0.6

mm

- + X (17 %)

h-n((50 %)e-e(18 %)n(14 %)

“ “kink”kink”

topologiestopologies

detector requirements: large mass, high resolution (for signal selection and background rejection)

The Oscillation Project with Emulsion tRacking Apparatus experimental signature

@ 4.5·1019 p.o.t./year, 200 days/year

for OPERA (~1.25 Kton) detector:

~ 4700 CC+NC / year

~ 30 e + e CC / year

~ 25 CC / year (m2 = 2.5 x 10-3 eV2)

expected neutrino interactions

_

e h 3h total

signal(m2=2.5 10-3 eV2)

2.9 3.5 3.1 0.9 10.4

bkgd 0.17 0.17 0.24 0.17 0.75

@22.5 1019 pot


OPERA: nuclear emulsions + electronic detectors

OPERA: the hybrid solution

~ 150000 bricks in the OPERA target (~ 1.25 kton)

1 mm

Pb

Emulsion layers

8.3 Kg(10.2*12.5)cm2

1 emulsion film: 2 emulsion layers (44 m thick) poured on a 200 m plastic base

when electronic detectors enter the game:

trigger for a neutrino interaction muon identification and momentum/charge measurement

1 Changeable Sheet doublet (CS)/brick:two refreshed emulsion films,vacuum

packed and glued onto the downstream brick face

ECC brick: 57 emulsion films sandwiched between 1mm Pb

plates

physics in an ECC brick:

interactions and decay topology reconstruction measurement momenta by MCSeseparation electromagnetic calorimetry

CS

9

The OPERA detector@LNGS

Surface INFN laboratory 980 mthe underground lab is at about the same altitude

Laboratori Nazionali del Gran Sasso (Italy)

•1400 m rock overburden• cosmic µ reduction ~ 106 (1 /m2/h)

OPERA

low radioactivity rock

Feb 25, 2011 10

Veto (RPC)

High precision tracker Dipole magnet● 6 4-fold layers of ● 1.53 T

drift tubes ● 22 XY planes of RPC

muon spectrometer (8×10 m2)

Target + Target Tracker (6.7m)2

● target/SM: ~75000 bricks

(Pb – nuclear emulsions) Mass/SM 0.625 kt

● Target tracker : 31 doublets XY (256 plastic scintillator strip + WLS fibres+ multi-anodes PMT) for trigger, brick selection and calorimetry

SM1 SM2

The OPERA detector@LNGS[~3100 m.w.e. overburden, ~1 cosmic μ / m2 x hour]

[Ref. JINST 4 (2009) P04018]

Feb 25, 2011 11

Event analysis in OPERA

• on-line analysis of electronic data

• brick finding algorithm for events ‘on time’ with the beam

• remove brick and scan CS: the interface between brick and TT (pos ≈ 10 mm, ≈ 20 mrad)

• confirmation of the extracted brick

• development of the brick to be sent in a scanning Lab for ‘CS to brick connection’ (pos ≈ 70 m, ≈ 8 mrad), event location, decay search studies, etc ..

[200

9 J

INS

T 4

P

0401

8]


OPERA films data taking: automatic microscopes

~ 20 bricks daily extracted from the target analyzed using high-speed automated systems (≥ 20 cm2/h)

S-UTS (Japan)European Scanning System

Common Data Base for data sharing/publication

• Customized commercial optics and mechanics

• asynchronous DAQ software modular, de-

centralized, approach

High speed

CCD Camera (3 kHz)

Piezo-controlled

objective lens

• Synchronization of objective lens and

(constant speed) stage

• Hard-coded algorithms, custom electronics

~90% tracking efficiencyspatial resolution < 1 m and angular resolution < 2 mrad


Hadronic energy deposited in TTdensity x length of the muon track

Tranverse profile of hadronic showers Energy resolution

Total reconstructed energy in events with at least one identified muon

Momentum X charge for muons

Electronic detectors performances

Feb 25, 2011 14

ECC analysis performances (I)

IP distribution for events (MC)

IP distribution for: events (MC)NC+CC events (MC),

NC+CC events (Data)

expanded scale

mIp measurement:

particles momenta measurements by MCS

9

8

7

6

5

4

3

2

1

1 2 3 4 5 6 7 8

Pre

c (G

eV

)

Pbeam (GeV)

test beam

= (22±4)%

Measurements performed on several selected OPERA

soft muon events


detection and 0 mass reconstruction

E = 0.5 GeV

E = 8.1 GeV

2 em showers give a reconstructed mass 160±30

MeV/c2

EM shower energy measured by shower shape

analysis and Multiple Coulomb Scattering method

e-paire+ e-

70% of 1-prong hadronic decays

include one or more 0 importance of gamma detection

Gamma detection: how to…detection of showerdetection e-pair at start point

1 mass resolution: ~ 45%

ECC analysis performances (II)


CNGS physics runs

* nominal value: 4.5 1019 pot

2010

2009

2008

pot

days

In total 9639 events collected (within 1 w.r.t. expectation from pot)

2.1 nominal years in 3 years

yearbeam days

# p.o.t.*SPSeff.

events inthe bricks

run

2006 0.076×1019 no brick commissioning

2007 0.082×1019 38 commissioning

2008 123 1.78x1019 61% 1698 Physics runs

2009 155 3.52x1019 70% 3693 Physics runs

2010 187 4.04x1019 81% 4248 Physics runs


2889 neutrino interactions located, 95% of the 2008-09

expected yield.

Number of events for which the analysis is released: 1088 (187 NC)(1.85 × 1019 pot corresponding to 20% of the total statistics)

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

OPERA expects: ~ 0.5 events

OPERA data analysis status


charm decays inside the OPERA target

Decay search procedure defined (ip evaluation, small angle kink search, extra-tracks search)

Decay Search extensively applied to located interactions data sample

Charm topology analogous to : reference sample for the decay finding efficiency

4 m

m

kink

x-view

1ryvertex

1.3 mm

1ry

daughter

flight length: 1330 micronskink angle: 209 mradIP of daughter: 262 micronsdaughter muon: 2.2 GeV/cdecay Pt: 0.46 GeV/c

charm candidate (dimuon)

20 charm candidate

3 of them with 1-prong kink topology.

Expected: 16.0 ± 2.9 out of which 0.80 ± 0.22 with kink topologyExpected BG: ~ 2 events (loose cuts: work in progress to reduce BG)

D0 hypothesis:

F.L.: 313.1 m,

: 173.20,

invariant mass: 1.7 GeV

D0 hypothesis


Distance from 2ry vertex (mm)

Energy (GeV) 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 5.6 ± 1.0 ± 1.7 45.0 <11> 7.5 <7> <10-3 0.32 2ry vertex

2nd 12.6 1.2 ± 0.4 ± 0.4 85.6 <56> 22 <50> 0.10 0.82 2ry vertex (favoured)

the first candidate event (I)

•The primary neutrino interaction consists of 7 tracks of which one exhibits a visible kink•Two electromagnetic showers caused by -rays, associated with the event, have been located (total radiation length downstream the vertices: 6.5 X0)

* probability to find an IP larger than the observed one

• none of the tracks is compatible with being an electron track• for tracks 1, 5 and 6 P() < 10-3 (p-range consistency check) • remaining tracks are hadrons (interaction seen) • residual probability of CC event (possibly undetected large angle muon) is ≈ 1%. “Nominal” value of 5% assumed


the first candidate event (II)

Kinematical variables are satisfying all selection criteria for hadronic kink first candidate !defined in the proposal

candidate to the 1-prong hadron decay mode

• invariant mass of -rays 1 and 2: 120 ± 20 (stat)± 35(syst) MeV/c2

supporting the hypothesis 0

• assuming the charged decay product as -, the invariant mass of - and 2 gammas:

640 +125-80

+100-90 MeV/c2

compatible with the (770) mass

With the available statistics** (m232 = 2.5 x10-3 eV2 , full mixing) OPERA expected ~ 0.5 events

** at the time of observation

VARIABLE AVERAGE*

kink (mrad) 41 ± 2

decay length (m)

1335 ± 35

P daughter (GeV/c)

12 +6-3

Pt decay (MeV/c)

470 +230-120

missing Pt (MeV/c)

570 +320-170

ϕ (deg) 173 ± 2

*assuming both 1 and 2 attached to 2ry vertex(uncertainty on Pt due to the alternative 2 attachment is < 50 MeV/c )

2ry vtx compatible with hn


the first candidate event (III)

Evaluation of 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 (UPDATE wrt Proposal) ~ 10-5/CC

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

- Background evaluation by using state-of-the-art FLUKA code (upgrade wrt Proposal)- Kink probabilities integrated over the μ NC hadronic spectrum yield (same cuts as for the tau analysis) a BG probability of (3.8 ± 0.2) x 10-5 kinks/NC (2 mm Pb, cuts on event global kinematics applied) - First cross-checks of the simulation were performed on a scan-forth tracks sample and on dedicated test-beam data, showing a good agreement with the simulation, although still statistically limited


the first candidate event (IV)

Background expectations 1-prong hadron decay channel:(~ 50% syst. error for each component)

0.011 events (reinteractions)0.007 events (charm, assuming standard mu ID)

---------------------------------0.018 ± 0.007 (syst.) events 1-prong hadron

BCK for all decay modes: 1-prong hadron, 3-prongs + 1-prong μ + 1-prong e :0.045 ± 0.020 (syst.) events total BG

Background fluctuation probabilities to 1 event:

1-prong hadron channel only: P=1.8% 2.36 significanceAll tau decay modes included in search: P=4.5% 2.01 significance


10 electron neutrino interactions have been reconstructed in the OPERA target

eCC interactions


Conclusions and outlook

- The OPERA experiment is approaching its fourth physics run.

- the analysis of a sub-sample of the neutrino data taken in the CERN CNGS beam in the 2008-2009 runs lead to the reconstruction of a number of interesting topologies such as charm decays candidates and eCC interactions in agreement with the expectations.

- one muonless event showing a 1-prong hadron decay topology has been detected and studied in detail. It passes all kinematical cuts required to reduce the physics background. It is the first candidate event in OPERA, with statistical significance of 2.36 (1prong hadronic decay mode) and 2.01 (all decay modes).

- analysis on 2008+2009 full sample data will be finished in less than two months, according with the present scanning speed.

- analysis of 2010 events is being performed in parallel.

thank you for your attention!


backup


Expected neutrino flux @ LNGS

CC event rate@ 4.5 1019pot 600 CC/kt/ 1019pot5.5 e CC/kt/ 1019pot


OPERA sensitivity

OP

ER

A

Dis

cove

ry p

rob

ab

ility

(%

)

m2 (eV2)

4- evidence

3- evidence

MINOS 2008

5 years, nominal 4.5 1019 pot


Event tracks’ features TRACK

NUMBERPID Probability MEASUREMENT 1 MEASUREMENT 2

tan ΘX tan ΘY P (GeV/c) tan ΘX tan ΘY P (GeV/c)

1

HADRONrange in

Pb/emul=4.1/1.2 cm

Prob(μ)≈10-3 0.177 0.3680.77

[0.66,0.93]0.175 0.357

0.80 [0.65,1.05]

2 PROTONrange,

scattering and dE/dx

-0.646 -0.0010.60

[0.55,0.65]-0.653 0.001

3 HADRONinteraction

seen0.105 0.113

2.16 [1.80,2.69]

0.110 0.1131.71

[1.42,2.15]

4 (PARENT) -0.023 0.026 -0.030 0.018

5

HADRON:range in

Pb/emul=9.5/2.8 cm

Prob(μ)≈10-3 0.165 0.2751.33

[1.13,1.61]0.149 0.259

1.23 [0.98,1.64]

6

HADRON:range in

Pb/emul=1.6/0.5 cm

Prob(μ)≈10-3 0.334 -0.5840.36

[0.27,0.54]

7From a prompt neutral particle

0.430 0.4190.34

[0.22,0.69]0.445 0.419

0.58 [0.39,1.16]

8(DAUGHTER)

HADRONinteraction

seen -0.004 -0.008 12 [9,18] -0.009 -0.020

muonless event (favored hypothesis)


OPERA nominal analysis flow applied to the hadronic kink candidates:

(more refined selection criteria being developed were not considered here to not bias our analysis)

10 years old criteria (@Proposal) Blind analysis

• 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 thedecay vertex

• missing Pt at primary vertex lower than 1 GeV/c• azimuthal angle between the resulting hadron momentum direction and the parent track direction larger than π/2 rad

OPERA Kinematical analysis


Missing Pt at primary vertex

cut

32

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


Charmed particles have decay topologies similar to the ones

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

• 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.

,e

,e-

+

e+

h+D+

primary lepton not identified

OPERA: charm background


Simulation of the reinteraction BG with FLUKA…

…cross check I (scan-forth data)

signal region

• no events in the signal region

• 90% CL upper limit of 1.54 x 10-3 kinks/NC event

• nr of events outside the signal region

confirmed by MC (within the ~30% statistical

accuracy of the measurement)

…cross check II (4GeV test-beam data)

8 times track length of tau search

multi-prong1-prong

18 times track length of tau search

first results on appearance mode neutrino oscillations from opera

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