observation of ν μ → ν τ oscillations in the cngs beam with the opera experiment m. de serio...
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Observation of νμ → ντ oscillations in the CNGS beam with the OPERA experiment
M. De Serio University of Bari & INFN Bari
On behalf of the OPERA Collaboration
3rd International Conference of New Frontiers in Physics - Kolymbari, Crete
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Observation of νμ → ντ oscillations in the CNGS beam with the OPERA experiment
The OPERA experiment
Physics motivation detection principle Detector Analysis chain Status of data analysis
νμ → ντ oscillation results
Other physics results
The OPERA Collaboration
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About 140 physicists from 28 institutions
http://operaweb.lngs.infn.it
BelgiumIIHE-ULB Brussels
CroatiaIRB Zagreb
FranceLAPP Annecy
IPHC Strasbourg
GermanyHamburg
IsraelTechnion Haifa
ItalyBari
BolognaFrascatiL’Aquila
LNGSNaplesPadova
RomeSalerno
JapanAichiTohoKobe
NagoyaUtsunomiya
RussiaINR RAS MoscowLPI RAS Moscow
ITEP MoscowSINP MSU Moscow
JINR Dubna
SwitzerlandBern
TurkeyMETU Ankara
KoreaJinju
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Neutrino oscillation appearance
Neutrino oscillation in the atmospheric sector established in 1998 in disappearance mode (SuperKamiokande, MACRO, …)
Oscillation mechanism later confirmed by accelerator experiments (K2K, MINOS) as well as solar neutrino experiments (KamLAND, SNO, Borexino, …)
Oscillated neutrino appearance: a missing tile in the picture.
OPERA designed to observe appearance in a pure beam.
Requirements:
High neutrino energy High beam intensity Large target mass Long baseline Detector capability to identify short-lived
lepton
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Oscillation Project with Emulsion tRacking Apparatus
L = 732 kmCERNLNGS
Cern Neutrinos to Gran Sasso beam
High-energy beam (<E 17 GeV>) optimised to maximise interactions at LNGS
Gran Sasso National Laboratory:1400 m rock shield
(cosmic flux reduction ~ 10-6)
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Decay kink
t-nm oscillation
-, h-, e-
(+ 3h)nt
n
nm
-
ντ detection signature
Detection of ’s from oscillation in a sea of interactions through the observation of decays into muon, electron and hadron(s):
• Target mass O(kt) (small interaction cross-section)• High granularity detector ( decay detection, background rejection)
appearance on event-by-event basis
)4/(sincos)2(sin 223
213
423
2 ELmP
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OPERA detector
SUPERMODULE 1 SUPERMODULE 2
Hall C Laboratori Nazionali Gran Sasso
CNGS Beam
Muon spectrometerdipolar magnet instrumented
with RPCs and drift tubes
Target sectionwalls of lead – nuclear
emulsion bricks interfaced with planes of plastic
scintillator strips (Target Tracker, TT)
Veto
Muon ID, momentum and charge measurement Event trigger and brick
finding
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OPERA detector
SUPERMODULE 1 SUPERMODULE 2
Hall C Laboratori Nazionali Gran Sasso
CNGS Beam
Muon spectrometerdipolar magnet instrumented
with RPCs and drift tubes
Target sectionwalls of lead – nuclear
emulsion bricks interfaced with planes of plastic
scintillator strips (Target Trackers, TT)
Veto
id efficiency 95% (with TT)
p/p < 20% , p < 50 GeV/c
misidentified charge prob. : 1.2%
● Trigger efficiency > 99% ● Brick finding : 6080%
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OPERA detector
6 m
150,000 bricks (total target mass ~ 1.25 kt)
arranged in 62 walls Changeable Sheets (CS):
2 nuclear emulsion films in a removable
box glued on the downstream face of
the brickacting as an interface between TT and brick
Brick:57 nuclear emulsion films interleaved with 56 lead
plates (1mm thick)
12.5cm
10.2cm
10 mm
25 mrad
TT - CS
60 m
10 mrad
CS - brick
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From ED data analysis, a brick probability map is built.
The brick with the highest probability is extracted from the target.
First interaction reconstructed in OPERA target (2007)
Event location strategy
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Event location strategy• Analysis of CS confirmation of interaction, predictions for brick analysis
• Track following in the brick film by film up to disappearance point
• High-energy cosmic rays used for film inter-calibration
Micrometric resolution achieved in track and vertex reconstruction
JHEP 11 (2013) 036
Location efficiency vs event energyImpact parameter of tracks w.r.t.
reconstructed interaction vertices
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Decay search strategy
Decay confirmation benefits of :
• Momentum measurement by Multiple Coulomb Scattering
• E.m. shower detection and energy measurement
• Detection of highly-ionizing nuclear fragments
(discrimination between interactions and decays)
Impact parameter crucial to detect decay daughters
Details will be given in A. Pastore’s talk this afternoon
Impact parameter vs. longitudinal distance from reconstructed interaction vertex
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Search for short-lived particle decays: charmed hadrons as control sample
Charmed hadrons have masses and lifetimessimilar to those of the lepton:
powerful tool to directly test detection efficiency
50 events observed in the sample 2008 2010 54 4 events expected
arXiv1404.4357 Accepted for publication in EPJC
Details will be given in A. Pastore’s talk this afternoon
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Run p.o.t.(1019)
SPSefficienc
y
Beamdays
ν interaction
s
2008
1.7 61% 123 1931
2009
3.53 73% 155 4005
2010
4.09 80% 187 4515
2011
4.75 79% 243 5131
2012
3.86 82% 257 3923
Total
17.97 77% 965 19505
Status of the analysis
1.18 kt on average
80% of the expected intensity
Analysis strategy Runs 2008 – 2009:
1st and 2nd most probable bricks analysed Runs 2010 2012:
1st brick only analysed so far. Extension to less probable bricks in progress.
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νμ → ντ oscillation analysis
Data sample: 4685 located and fully analysed interactions
Expected events: 2.1 0.4 (m2 = 2.32 x 10-3 eV2, 23 = /4 )
Observed events: 4
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The first candidate event
Physics Letters B 691 (2010) 138
First direct detection of oscillations in appearance mode
Variable Value
Kink angle (mrad)
41 ± 2
Decay length (µm)
1335 ± 35
P daughter (GeV/c)
12 +6-3
Pt (MeV/c)470 +230
-
120
Missing Pt at 1ry vertex (MeV/c)
570 +320-
170
ϕ (deg) 173 ± 2
τ−→ρ− ντ
ρ−→π0 π- π0 → γ γ
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2000 m
The second candidate event
Journal of High Energy Physics 11 (2013) 036
- h- h- h+
candidate decay in plastic baseFlight length: 1.54 mm
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The third candidate event
𝑩→
First measurement of the lepton charge
in appearance mode
Phys. Rev. D 89 (2014) 051102(R)
- -
Muon momentum: by range (electronic detectors) 2.8 0.2 GeV/c
by MCS in emulsion 3.1 [2.6, 4.0] GeV/c
The fourth candidate event
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All tracks attached to the reconstructed interaction have been followed in downstream bricks in order to check the compatibility
with the muon hypothesis.
Track 2 crosses 9 wall and stops in the spectrometer;not compatible with hypothesis based on
momentum – range correlation
Track 3: visible interaction in downstream brick #2
Track 4 crosses 1 wall; identified as a proton based on its ionization
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Expected events after completion of 2nd bricks for 2010 2012 runs: 3.2 events
νμ → ντ oscillation analysis summary
Not yet accounted for: foreseen extension of the analysis
to 3rd and 4th bricks in the probability map (~ 20% effect )
Visible energy in emulsion
1st candidate3rd candidate
4th candidate
2nd candidate
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Expected events after completion of 2nd bricks for 2010 2012 runs: 3.2 events
νμ → ντ oscillation analysis summary
Not yet accounted for: foreseen extension of the analysis
to 3rd and 4th bricks in the probability map (~ 20% effect )
Decay channel
Expected signal
Δm232 = 2.32
meV2
Total backgroun
d
Observed
h 0.41 ± 0.08 0.033 ± 0.006
2
3h 0.57 ± 0.11 0.155 ± 0.030
1
0.52 ± 0.10 0.018 ± 0.007
1
e 0.62 ± 0.12 0.027 ± 0.005
0
Total 2.11 ± 0.42 0.233 ± 0.041 4
Two statistical methods Fisher combination of single channel p-values Likelihood ratio
4.2 significance of null observationObservation of appearance
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νμ → ντ oscillation analysis
OPERA Preliminary (tau appearance)
ANTARES (atm. neutrino)
MINOS (pure atm. anti-nu)
MINOS (anti-nu beam)
MINOS (pure atm. nu)
MINOS (atmospheric)
T2K
MINOS (2ν, maximal mixing)
First measurement of m223
with appearance
90% CL intervals on Δm232
assuming sin2(2θ23) = 1
Feldman & Cousin [1.8 – 5] x 10-3 eV2
Bayesian [1.9 – 5] x 10-3 eV2
OPERA Off-peak L/<E> ~ 43 Km/GeV
(L/<E>)peak ~ 500 Km/GeV
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νμ → νe oscillation results
νe events searched for in a sample of 505 neutrino interactions without muon in the final state (runs 2008-
2009) .Extension to full statistics in progress.
19 (4) events observed, 19.8 2.8 (4.6) events expected (E<20GeV)
JHEP 1307 (2013) 004
Non standard oscillation limit: sin2(2θnew) < 7.2 x 10-3 for large m2
Details in V. Tioukov’s talk
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Cosmic ray physics results
OPERA: a deep underground detector with charge and momentum reconstruction and excellent timing capabilities (~10 ns)Measurement of the atmospheric muon charge ratio Rμ = Nμ+ / Nμ- in the TeV region
Complete data-sample analysed:~2.22 M μ events during 20082011 runs, 625.0 days of livetime in Standard Magnet Polarity ~823 k μ events during 2012 run, 234.8 days of livetime in Inverted Magnet Polarity Misalignment systematics reduced at the level of 0.1 mrad
Compatible with the expectation from a simple π-K model; no significant contribution
of the prompt component up to Eμ cos θ* ∼ 10 TeV
arXiv 1403.0244 - accepted for publication in EPJC
Rμ as a function of the vertical surface muon energy
Details in L. Consiglio’s poster
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Conclusions and Outlooks
Successful data taking from 2008 to 2012, 17.97 x 1019 p.o.t. integrated
Oscillation analysis results: 4685 located and fully analysed interactions4 candidate events observed 2.1 0.4 expected events
Observation of νμ ντ oscillation in appearance mode (significance 4.2 )
Other physics results:• Measurement of the atmospheric muon charge ratio in the TeV region • e oscillation
ντ search now being extended to other bricks of the probability map
Improvements in the statistical analysis under study
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Thank you
Image taken using OPERA emulsion film with pinhole hand made cameraCourtesy by D.onato Di Ferdinando
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