Results from the OPERA experiment in the CNGS beam

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Linda Grace Baker
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1 Results from the OPERA experiment in the CNGS beam A. Paoloni (INFN LNF) on behalf of the OPERA collaboration NUFACT 16 Quy Nhon, 3 August physicists, 11 countries, 8 institutions

The OPERA project 1 8 9 9 val o r p Ap l ivi c of d En 4 6 ng ion t c ru ng t i s n con sio s f i m do m n o E C ri e e in g n e 8 Verify the μ oscillation at e det e El the atmospheric m scale.

2 The OPERA project val o r p Ap l ivi c of d En 4 6 ng ion t c ru ng t i s n con sio s f i m do m n o E C ri e e in g n e 8 Verify the μ oscillation at e det e El the atmospheric m scale. CNGS RUN ro cto 6 9 n ly k ric b s 15 cks i r b appearance event-by-event L = 73 km in an artificial μ beam. 1 Decommissioning Gran Sasso CNGS RUN st 1 τ h nd τ 3h rd 3 τ μ th 4 τ h th 5 τ h

of Emulsion Cloud Chambers (or bricks) Reconciles the needs for: the brick kink the

3 The detection technique long decays: kink Detect a few CC from ~. 6 kink mm 17 % e - e 18 % h n( ) multi-prong - 5 % n( ) 14 % Modular detector of Emulsion Cloud Chambers (or bricks) Reconciles the needs for: the brick kink the bulk of CC Large mass N ( m) M target Extreme granularity m space resolution 1 X short decays: I.P. Pb

The OPERA experiment ~3o electronics racks

Drift tubes Spectrometer m Hybrid apparatus:

+ several ancillary facilities off-site :

Manipulator System (LNGS) Labelling and X ray

4 The OPERA experiment ~3o electronics racks BOREXINO Super Module 1 Veto Super Module Target 15k bricks 31 scintill. planes Brick Manipulator System RPC 35 m Muon 1 m Drift tubes Spectrometer m Hybrid apparatus: Emulsions + electronic detectors ``Brick-finding'' + several ancillary facilities off-site : Assembly/disassembly of bricks (LNGS) Brick Manipulator System (LNGS) Labelling and X ray marking (LNGS) Automatised development (LNGS) Scanning of CS doublets (LNGS+JP) Scanning bricks (Europe + JP)

5 CERN Neutrinos to Gran Sasso The oscillation peak for L= 73 km at ~ 1.5 GeV (similar to NuMI) but the beam is designed to observe leptons: < E > 17 GeV L / < E > 43 km/gev N( )~ Pr( ) x CC(E) x flux Fluxes: ( e+ e ) /.9 % /.1 % prompt (from Ds) negligible Interaction rates (1.8 x 1 pot ): ~ k CC+NC 66.4 CC (not efficiency corrected) Threshold for at ~ 3.5 GeV.

6 Collected data samples The 5 year long CNGS run has ended in x 1 p.o.t. collected 8% of the design (.5 x 1) 1.5 kton initial target mass (15 k bricks) 1955 neutrino interactions in the emulsion targets. Year Days p.o.t. (119) interactions tot Spectrum of muons from CC events measured in the spectrometers

7 Brick finding OPERA is a hybrid apparatus. Electronic detectors predictions to locate bricks with neutrino interactions. candidate event Accuracy of predictions by the electronic detectors: position: 1 cm slope: 3 mrad

Electronic detector predictions to be confirmed by scanning of CS

8 Brick finding Changeable Sheets: the bridge from the cm scale of electronics detectors to m scale of emulsions. Electronic detector predictions to be confirmed by scanning of CS doublet. Up to 4 bricks ranked in probability are considered for research. candidate event

9 Vertex location and topology decay search in the brick Tracks in the CS are followed upstream until a stopping point is found. Vertex reconstruction by apposite algorithms. Search of decay topologies (e.g. large impact parameters IP). JHEP 11 (13) 36 Full MC simulation of and 1 samples. Data/MonteCarlo in reasonable agreement.

10 Validation with the CNGS charm events sample Charmed hadrons produced in CC events ( at the primary vertex) Charm and decays are topologically similar. Test for: reconstruction efficiencies, description of kinematic variables, charm background. 8-1 data sample: 54 ± 4 expected events 5 observed events Eur.Phys.J. C74 (14) 8, 986

candidate identification The brick is a complete stand-alone detector: Neutrino interaction vertex and decay topology reconstruction Measurement of charged particles' momenta by Multiple Coulomb

11 candidate identification The brick is a complete stand-alone detector: Neutrino interaction vertex and decay topology reconstruction Measurement of charged particles' momenta by Multiple Coulomb Scattering (-3% resolution) e/ separation and energy measurement Kinematical cuts to increase S/B ratio:.3 GeV/c in presence of in the decay vertex For candidate events, Track Follow Down (TFD) procedure: All reconstructed event tracks followed from brick to brick, to enhance -identification (99%) improve /h discrimination (range measurement and nuclear interaction detection)

12 background characterization Monte Carlo simulation benchmarked on control samples. In order of decreasing relevance CC with charm production (all channels) IF the primary lepton is not identified and the daughter charge is not (or incorrectly) measured Hadronic interactions Background for h -,e-,e + e+ h+ + D h Large angle muon scattering Background for MC tuned on CHORUS data (cross section and fragmentation functions), validated with measured OPERA charm events. Reduced by ''track follow down'' procedure and large angle scanning FLUKA + pion test beam data Reduced by large angle scanning and nuclear fragment search Measurements in the literature (Lead form factor), improved MC simulations

13 events observed in OPERA

14 Fifth candidate: discovery of appearance OPERA - h- Phys. Rev. Lett. 115 (15) 118 VARIABLE VALUE Kink angle (mrad) 9 ± decay length (μm) 634 ± 3 Pry (GeV/c) Pmisst (GeV/c).3±.1 ϕ (degrees) 151 ± 1

15 νµ ντ oscillation analysis results Decay channel 1h 3h µ e Total Expected background Charm Had. Re-interaction Large scattering Total.17±.3.17±.3.4±.1.3±.1.±.4.±.6.3±.1.±.1.±.1.±.1.4±.1.17±.3.4±.1.3±.1.5±.5 psum : scalar sum of the momenta of all particles measured in the emulsion films 1, 4, 5: 1h : 3h 3: expected signal events m = ev Observed events.5±.1.73±.14.61±.1.78±.16.64± Probability to be explained by background fluctuation p = 1.1x1-7 No oscillation hypothesis excluded at 5.1 m3 = 3.3 x 1-3 ev with a 9% confidence interval [., 5.] x 1-3 ev (assuming full mixing) Probability of observing 5 candidates (.9 S+B events expected): 17% Frequency of configurations being less probable than the observed one: 6.4%

16 event with 3 vertices: description Muonless event A primary and two secondary vertices found in emulsion, Electromagnetic activity ( s) at the kink point. Flight lengths: II: 13 m III: 116 m Invariant masses at both secondary vertices larger than 1 GeV.

Dedicated simulations and Artificial Neural Network (ANN) analysis have been performed.

17 event with 3 vertices: analysis Vertex can be a charmed particle decay. Vertex III not classified as interaction by standard selection cuts. Dedicated simulations and Artificial Neural Network (ANN) analysis have been performed. Event classified as interaction with charm production (first topology of this kind). 3.5 CL with respect to bkg only hypothesis. In total, less than.1 expected event. More details at ICNFP 16 17

18 disappearance OPERA Full data sample (8-1) Use of electronic detector data only and separation between CC and NC like events Fit using NC-like/CC-like ratio in which all mixing parameters are fixed to the PDG values but m3 energy deposited in the scintillator planes reweighting MC according to oscillation probability and minimizing between MC and data To reduce systematic effects coming from the beam uncertainty (no near detector), NC like over CC like ratio is used systematics under study Preliminary measurement of m3 consistent with the world average and the internal OPERA appearance results

19 e oscillation analysis 8-1 Fulls sample (17.97 x 119 p.o.t.): 34 e events observed. Expected number of events: oscillation:.9 ±.4 e A candidate e beam contamination: 36.7 ± 5 Other backgrounds ( e and mis-id): 1. ±.1 preliminary To increase signal/bkg ratio, E<3 GeV cut: 13 observed events for 1.4 ±. events from oscillation e 9. ± 1 events from background Work in progress to extract exclusion limits on sterile neutrino according to 3+1 model.

: preliminary results on sterile 3+1 model standard m41 vs 4 U 4 U 4 = sin ( ) Δ 31 P( )=4 U 3 U 3 sin (normal hierarchy) Δ 41 + 4 U 4 U 4 sin exotic + ℜ [U 4 U 4 U 3 U 3 ]sin Δ 31 sin Δ41 Δ31 4 ℑ[U

20 : preliminary results on sterile 3+1 model standard m41 vs 4 U 4 U 4 = sin ( ) Δ 31 P( )=4 U 3 U 3 sin (normal hierarchy) Δ U 4 U 4 sin exotic + ℜ [U 4 U 4 U 3 U 3 ]sin Δ 31 sin Δ41 Δ31 4 ℑ[U 4 U 4 U 3 U 3 ]sin sin Δ41 Δ41 Δ ℜ[U 4 U 4 U 3 U 3 ]sin sin Δ ℑ[U 4 U 4 U 3 U 3 ]sin Δ 31 sin Interference term Δ m ij L Δ = ij E - 9% CL exclusion limit on m41 lowered down to 1- ev for sin(θ ) >.5 - At large m41 : sin(θ ) <.119 at 9% CL Update of JHEP 156 (15) 69

single 1 Multi- Results compatible with a simple π-k model No significant contribution of the prompt component up to

21 Cosmic rays: R = N /N Highest-E region reached! opposite magnet polarities runs lower systematics Strong reduction of the charge ratio for multiple muon events single 1 Multi- Results compatible with a simple π-k model No significant contribution of the prompt component up to Eμ cos θ * 1 TeV Validity of Feynman scaling in the fragmentation region up to Eμ TeV (EΝ TeV) arxiv.org/abs/ (accepted by Eur. Phys. J. C) Eur. Phys. J. C (14) 74, arxiv.org/abs/143.44

22 Conclusions 1.8 x 1 pot by CNGS from 8-1 (8% of design). 5 candidates so far with.5 expected background events. No oscillation hypothesis excluded at 5.1 σ. In addition to the standard analysis, observed also a neutrino interaction with charm production. Study on μ e sub-dominant oscillation channel in progress. First results from disappearance analysis shown. Sterile neutrino: limits on Uμ4 Uτ4 from appearance results. Cosmic ray physics: atmospheric in the highest energy region to date.

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