Observation of ν μ → ν τ oscillations in the CNGS beam with the OPERA experiment M. De Serio University of Bari & INFN Bari On behalf of the OPERA Collaboration 3 rd International Conference of New Frontiers in Physics - Kolymbari, Crete

M. De Serio - ICNFP Observation of ν μ → ν τ oscillations in the CNGS beam with the OPERA experiment  The OPERA experiment  Physics motivation   detection principle  Detector  Analysis chain  Status of data analysis  ν μ → ν τ oscillation results  Other physics results

The OPERA Collaboration M. De Serio - ICNFP About 140 physicists from 28 institutions Belgium IIHE-ULB Brussels Croatia IRB Zagreb France LAPP Annecy IPHC Strasbourg Germany Hamburg Israel Technion Haifa Italy Bari Bologna Frascati L’Aquila LNGS Naples Padova Rome Salerno Japan Aichi Toho Kobe Nagoya Utsunomiya Russia INR RAS Moscow LPI RAS Moscow ITEP Moscow SINP MSU Moscow JINR Dubna Switzerland Bern Turkey METU Ankara Korea Jinju

M. De Serio - ICNFP 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

M. De Serio - ICNFP Oscillation Project with Emulsion tRacking Apparatus L = 732 km CERN LNGS Cern Neutrinos to Gran Sasso beam High-energy beam ( ) optimised to maximise  interactions at LNGS Gran Sasso National Laboratory: 1400 m rock shield (cosmic  flux reduction ~ )

M. De Serio - ICNFP Decay kink --  oscillation  -, h -, e - (+ 3h)    -- ν τ 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

M. De Serio - ICNFP OPERA detector SUPERMODULE 1SUPERMODULE 2 Hall C Laboratori Nazionali Gran Sasso CNGS Beam Muon spectrometer dipolar magnet instrumented with RPCs and drift tubes Target section walls 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

M. De Serio - ICNFP OPERA detector SUPERMODULE 1SUPERMODULE 2 Hall C Laboratori Nazionali Gran Sasso CNGS Beam Muon spectrometer dipolar magnet instrumented with RPCs and drift tubes Target section walls 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 :   60  80%

M. De Serio - ICNFP OPERA detector 6 m 150,000 bricks (total target mass ~ 1.25 kt) arranged in 62 walls Changeable Sheets (CS) Changeable Sheets (CS): 2 nuclear emulsion films in a removable box glued on the downstream face of the brick acting as an interface between TT and brick 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

M. De Serio - ICNFP 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

M. De Serio - ICNFP 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 energy Impact parameter of tracks w.r.t. reconstructed interaction vertices

M. De Serio - ICNFP 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

M. De Serio - ICNFP Search for short-lived particle decays: charmed hadrons as control sample Charmed hadrons have masses and lifetimes similar to those of the  lepton: powerful tool to directly test  detection efficiency 50 events observed in the sample 2008   4 events expected arXiv Accepted for publication in EPJC Details will be given in A. Pastore’s talk this afternoon

M. De Serio - ICNFP Runp.o.t. (10 19 ) SPS efficiency Beam days ν interactions % % % % % Total % Status of the analysis 1.18 kt on average  80% of the expected intensity Analysis strategy  Runs 2008 – 2009: 1 st and 2 nd most probable bricks analysed  Runs 2010  2012: 1 st brick only analysed so far. Extension to less probable bricks in progress.

M. De Serio - ICNFP ν μ → ν τ oscillation analysis Data sample: 4685 located and fully analysed interactions Expected  events: 2.1  0.4 (  m 2 = 2.32 x eV 2,  23 =  /4 ) Observed  events: 4

M. De Serio - ICNFP The first  candidate event Physics Letters B 691 (2010) 138 First direct detection of    oscillations in appearance mode VariableValue Kink angle (mrad)41 ± 2 Decay length (µm)1335 ± 35 P daughter (GeV/c) Pt (MeV/c) Missing Pt at 1ry vertex (MeV/c) ϕ (deg) 173 ± 2 τ − → ρ − ν τ ρ − → π 0 π- π 0 → γ γ

2000  m M. De Serio - ICNFP The second  candidate event Journal of High Energy Physics 11 (2013) 036  -  h - h - h +   candidate decay in plastic base Flight length: 1.54 mm

M. De Serio - ICNFP The third  candidate event First measurement of the lepton charge in appearance mode Phys. Rev. D 89 (2014) (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

M. De Serio - ICNFP The fourth  candidate event arXiv Submitted to PTEP

The fourth  candidate event M. De Serio - ICNFP 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

M. De Serio - ICNFP The fourth  candidate event

Expected events after completion of 2 nd bricks for 2010  2012 runs: 3.2 events M. De Serio - ICNFP ν μ → ν τ 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 1 st candidate 3 rd candidate 4 th candidate 2 nd candidate

Expected events after completion of 2 nd bricks for 2010  2012 runs: 3.2 events M. De Serio - ICNFP ν μ → ν τ 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 Δm 23 2 = 2.32 meV 2 Total background Observed  h 0.41 ± ±  3h 0.57 ± ±  0.52 ± ±  e 0.62 ± ± Total2.11 ± ± Two statistical methods  Fisher combination of single channel p-values  Likelihood ratio 4.2  significance of null observation Observation of  appearance

M. De Serio - ICNFP ν μ → ν τ 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  m 2 23 with  appearance 90% CL intervals on Δm 2 32 assuming sin 2 (2θ 23 ) = 1 Feldman & Cousin [1.8 – 5] x eV 2 Bayesian [1.9 – 5] x eV 2 OPERA Off-peak L/ ~ 43 Km/GeV (L/ ) peak ~ 500 Km/GeV

M. De Serio - ICNFP ν μ → ν e oscillation results ν e events searched for in a sample of 505 neutrino interactions without muon in the final state (runs ). 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: sin 2 (2θ new ) < 7.2 x for large  m 2 Details in V. Tioukov’s talk

M. De Serio - ICNFP 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 = N μ+ / N μ- in the TeV region Complete data-sample analysed: ~2.22 M μ events during 2008  2011 runs, days of livetime in Standard Magnet Polarity ~823 k μ events during 2012 run, 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 accepted for publication in EPJC R μ as a function of the vertical surface muon energy Details in L. Consiglio’s poster

M. De Serio - ICNFP Conclusions and Outlooks  Successful data taking from 2008 to 2012, x p.o.t. integrated  Oscillation analysis results: 4685 located and fully analysed interactions 4  candidate events observed 2.1  0.4 expected events Observation of ν μ  ν τ oscillation in appearance mode (significance 4.2  )  Other physics results: Measurement of the atmospheric muon charge ratio in the TeV region   e oscillation  ν τ search now being extended to other bricks of the probability map  Improvements in the statistical analysis under study

M. De Serio - ICNFP Thank you Image taken using OPERA emulsion film with pinhole hand made camera Courtesy by D.onato Di Ferdinando

M. De Serio - ICNFP ν μ → ν τ oscillation: background