Updated results of the OPERA long baseline neutrino experiment

Size: px

Start display at page:

Download "Updated results of the OPERA long baseline neutrino experiment"

Laurence Nicholson
5 years ago
Views:

1 Updated results of the OPERA long baseline neutrino experiment On behalf of the OPERA Collaboration S.Dusini INFN Padova EPS- HEP Grenoble S.Dusini - INFN Padova 1

OPERA experiment The aim of OPERA experiment is the direct detection of neutrino oscillation in appearance mode in the ν µ ν τ channel, an important missing tile in the neutrino oscillation physics.

2 OPERA experiment The aim of OPERA experiment is the direct detection of neutrino oscillation in appearance mode in the ν µ ν τ channel, an important missing tile in the neutrino oscillation physics. Requirment: 1) long baseline, 2) high neutrino energy, 3) high beam intensity, 4) large mass, 5) detect short lived τ s Requirements L = 730 km! CERN! T flight = 2.44 ms! LNGS! Expected neutrino interac@ons for 22.5x10 19 pot: ~ ν µ CC + NC ~ 520 an@- ν µ CC + NC ~ 160 ν e + an@- ν e CC ~ 115 ν τ CC (Δm 2 = 2.5 x 10-3 ev 2 ) EPS- HEP Grenoble S.Dusini - INFN Padova 2

How to detect a tau The separation of the ν τ CC from the dominant ν µ interactions is based on the identification, eventby-event, of the peculiar decay topology of the τ.

Cloud Chamber = sandwich of lead plate and Background components: emulsion films Production of charmed particles in CC interactions (all decay channels) ν µ,e Coulomb large angle scattering of

3 How to detect a tau The separation of the ν τ CC from the dominant ν µ interactions is based on the identification, eventby-event, of the peculiar decay topology of the τ. oscilla@on ν µ ν τ + N τ + X (35% of Non- Scaling QE and 65% DIS) ν µ Decay kink ν τ τ - µ - (cτ ~ 87 μm 600 μm of path) (11% of Non- Scaling QE and 89% DIS) µ - ν µ ν µ no- oscilla@on Emulsion Cloud Chamber = sandwich of lead plate and Background components: emulsion films Production of charmed particles in CC interactions (all decay channels) ν µ,e Coulomb large angle scattering of muons in lead Bck. to τ µ µ -,e - D + µ + e + h + ν µ µ - Hadronic interactions in lead: Bck. to τ h or to τ µ (if hadron misid or mismatched with muon) ν µ ν µ ν µ h µ --, ν µ h EPS- HEP Grenoble S.Dusini - INFN Padova 3

CNGS beam performance Year Beam days Protons on target SPS Eff. 2008 123 1.78x10 19 61% 1698 2009 155 3.52x10 19 70% 3693 2010 187 4.04x10 19 81% 4248 Events in the bricks 2011 Ongoing 2.

4 CNGS beam performance Year Beam days Protons on target SPS Eff x % x % x % 4248 Events in the bricks 2011 Ongoing 2.86x % 2858 pot In 2011 in dedicated mode (no other fixed target exp.) from March 18th to June 7th Expected to run for 223 days è 5x10 19 pot EPS- HEP Grenoble S.Dusini - INFN Padova 4

5 Observation of first ν τ candidate In spring 2010 OPERA present the first ν τ candidate base on the analysis of 35% of 08/ 09 statistics. Data selection was done using the cuts defined at the time experimental proposal (2001) Phys. LeZ. B 691 (2010) EPS- HEP Grenoble S.Dusini - INFN Padova 5

Update and improvements of the analysis Completed (92%) the 2008-2009 data analysis =

6 larger then previous publication Improvements in signal and background based on:

the emulsion to reduce charm background searching for muons not observed by the

simulation chain with emulsion off-line reconstruction.

6 Update and improvements of the analysis Completed (92%) the data analysis = pot Statistic 2.6 larger then previous publication Improvements in signal and background based on: Search of highly ionizing tracks in hadronic interactions Follow down of the tracks in the emulsion to reduce charm background searching for muons not observed by the Electronic Detector Hadronic background due to muon mis-matched to hadrons Full simulation chain with emulsion off-line reconstruction. Better knowledge of Charm production cross section from CHORUS. No new ν τ found Paper submitted to Physics Letter B, (arxiv: [hep-ex]). EPS- HEP Grenoble S.Dusini - INFN Padova 6

2008-2009 sample 85% are events induced by neutrino interaction outside OPERA target 0 mu 1 mu All Trigger 31576 Events predicted by the electronic

events This corresponds to the 92% of the expected sample that could be decay searched: 2978±75 OPERA data n Reconstructed MC Full simulation chain

7 sample 85% are events induced by neutrino interaction outside OPERA target 0 mu 1 mu All Trigger Events predicted by the electronic detector Located in dead material Interactions located in the ECC Decay search performed ν NC events This corresponds to the 92% of the expected sample that could be decay searched: 2978±75 OPERA data n Reconstructed MC Full simulation chain including newly developed off-line emulsion reconstruction software Location efficiency: 74% for CC 48% for NC EPS- HEP Grenoble S.Dusini - INFN Padova 7

Track follow down For the first ν τ candidate we followed down all the tracks to search for possible muon not identified by the Electronic Detector We can suppress backgrounds due to Charm Hadron

8 Track follow down For the first ν τ candidate we followed down all the tracks to search for possible muon not identified by the Electronic Detector We can suppress backgrounds due to Charm Hadron interactions in ν µ CC with misidentified µ (τ h channel) Hadron interactions in ν µ CC and NC (τ µ channel) Charm background µ -,e - ν µ,e D + µ + e + h + Hadron interactions background ν µ ν µ ν µ µ --, ν µ h h EPS- HEP Grenoble S.Dusini - INFN Padova 8

Classification of the tracks: Interaction visible in the brick Track Follow Down de/dx at end point of the track for π/µ separation Momentum/Range

path ρ lead = lead density p = momentum measured in the emulsion Hadrons and muon stopping in the brick Results: Mis-ID muons in Charm events: 3.

9 Classification of the tracks: Interaction visible in the brick Track Follow Down de/dx at end point of the track for π/µ separation Momentum/Range correlation Discriminating variable D = L R lead ( p) " lead " average L = track length R lead = moun range in lead ρ average = average density along the path ρ lead = lead density p = momentum measured in the emulsion Hadrons and muon stopping in the brick Results: Mis-ID muons in Charm events: 3.28% ( 34% reduc.) 2 orders of magnitude reduction of hadronic background to τ µ due to µ mismatch in CC and NC events EPS- HEP Grenoble S.Dusini - INFN Padova 9

Search for highly ionizing particles in hadron interactions

the detection efficiency of protons and nuclear fragments

nuclear evaporation process Found fragment 1 Found fragment 2

sample of hadronic interactions Ø No highly ionizing particle

10 Search for highly ionizing particles in hadron interactions Hadron interactions background can be reduced by increasing the detection efficiency of protons and nuclear fragments emitted in the cascade of intra-nuclear interactions and in nuclear evaporation process Found fragment 1 Found fragment 2 Ø Specific tool for scanning Ø Validation on the test-beam sample of hadronic interactions Ø No highly ionizing particle found in OPERA ν τ candidate EPS- HEP Grenoble S.Dusini - INFN Padova 10

1 mm 2 à Highly ionizing tracks detection in 57±7% of cases Expected from Fluka : 53% Forward-backward

11 Test beam for highly ionizing particles search Study of 64 interactions of 8 GeV π - beam Search of black tracks ( γβ < 0.5 ) in a large field of view 2.5x2.1 mm 2 à Highly ionizing tracks detection in 57±7% of cases Expected from Fluka : 53% Forward-backward asymmetry: 0.75 ± 0.15 Backward Forward Expected from Fluka simulation: 0.71 Test beam data n MC Fluka EPS- HEP Grenoble S.Dusini - INFN Padova 11

Taking into account the larger acceptance of the new scanning tool and the lower momentum threshold for additional protons and fragments the probability for a hadron to produce a single prong kink

12 Taking into account the larger acceptance of the new scanning tool and the lower momentum threshold for additional protons and fragments the probability for a hadron to produce a single prong kink with P > 2 GeV ( P t > 0.6 GeV ) or ( P t > 0.25 GeV + gamma ) over 2 mm of lead 1.53 x 10-4 / NC -20% previous estimation Kink probability Momentum GeV/c Momentum GeV/c Momentum GeV/c Pi+ K+ K- p Fluka simulation Momentum GeV/c Momentum GeV/c Pi- Probability in 10-4 units Old selec@on New selec@on EPS- HEP Grenoble S.Dusini - INFN Padova 12

13 Hadron tracks in OPERA neutrino interactions with kink topology far from primary vertex Pion interaction studies Hadron interactions search in 4 GeV π test beam Signal region Signal region 14 m, equivalent to 2300 NC events No events found in signal region, signal boundary region (Pt>200 MeV/c): à 10 events observed (10.8 events expected by updated simulation including black tracks search) EPS- HEP Grenoble S.Dusini - INFN Padova 13

14 Charm cross section and fragmentation Results recently published by CHORUS - arxiv: [hep-ex] scaled at OPERA energies CHORUS results OPERA [%] σ(charm) / σ(ν µ CC) 5.75 ± 0.32(stat) ± 0.30(sys) 4.46 f(d + ) 25.3 ± f(d 0 ) 43.7 ± f(l) 19.2 ± f(d s ) 11.8 ± Inclusive charm rate OLD NEW Increase σ(charm) / σ(ν µ CC) % Fragmentation OLD NEW Muonic BR OLD(1998) NEW(2010) The D + has the main background contribution to all channels due to the higher efficiency for the kinematical cuts. The charm background increase goes from x1.57 to x2.43 depending on channel (h-mu) EPS- HEP Grenoble S.Dusini - INFN Padova 14

2008-2009 charm sample Topology Observed events Expected events Charm Background Total Charged 1- prong 13 15.9 1.9 17.8 Neutral 2- prong 18 15.7 0.8 16.5 Charged 3- prong 5 5.5 0.3 5.

15 charm sample Topology Observed events Expected events Charm Background Total Charged 1- prong Neutral 2- prong Charged 3- prong Neutral 4- prong < Total ± ± ±8.3 Angle between the charmed particle and the primary µ in the transverse plane Decay length of charmed particles OPERA n MC OPERA n MC EPS- HEP Grenoble S.Dusini - INFN Padova 15

16 Updated OPERA sensitivity Including all the improvements in the analysis Decay channel Number of signal events expected for Dm 2 = ev p.o.t. Analysed sample τ µ τ e τ h τ 3h Total In the analyzed sample (92% of data) one ν τ observed in the τ h channel compatible with the expectation of 1.65 signal events. EPS- HEP Grenoble S.Dusini - INFN Padova 16

17 Summary of background Very clean channel Decay channel Number of background events for: p.o.t. Analysed sample Charm Hadron Muon Total Charm Hadron Muon Total τ µ ± ±0.01 τ e ± ±0.01 τ h ± ±0.01 τ 3h ± ±0.01 Total ± ±0.03 The expected background in the τ h channel is 0.05 ± 0.01 The probability of a background fluctuation up to at least one event is 5%. The total expected background is 0.16 ± 0.03 and the probability a background fluctuation is 15%. EPS- HEP Grenoble S.Dusini - INFN Padova 17

18 Outlook interactions located in the bricks, 3232 decay searched events EPS- HEP Grenoble S.Dusini - INFN Padova 18

19 Summary The analysis data sample has been completed (92%) and submitted to PLB, (arxiv: [hep-ex]). Analysed statistic 2.6 larger then previous publication. The signal and background expectations have been updated Full simulation chain with emulsion off-line reconstruction Track Follow Down technique hadronic background to τ µ killed Search for protons/fragments in hadronic interactions New charm cross section (CHORUS paper) One ν τ observed in the τ h channel compatible with the expectation of 1.65 signal events and a background of 0.05±0.01. Probability of a background fluctuation is 5% EPS- HEP Grenoble S.Dusini - INFN Padova 19

20 Thank you EPS- HEP Grenoble S.Dusini - INFN Padova 20

21 Muon reconstruction with ED ν τ signal in arbitrary units OPERA ( 08-09) - MC EPS- HEP Grenoble S.Dusini - INFN Padova 21

22 OPERA electronic detector performance OPERA ( 08-09) - MC OPERA ( 08-09) - MC EPS- HEP Grenoble S.Dusini - INFN Padova 22

23 Side view Event topological features γ2 γ daughter 6 EPS- HEP Grenoble S.Dusini - INFN Padova 23

24 Event tracks features TRACK NUMBER PID Probability MEASUREMENT 1 MEASUREMENT 2 tan Θ X tan Θ Y P (GeV/c) tan Θ X tan Θ Y P (GeV/c) 1 HADRON range in Pb/ emul=4.1/1.2 cm Prob(µ) [0.66,0.93] [0.65,1.05] 2 PROTON range, scattering and de/dx [0.55,0.65] HADRON interaction seen [1.80,2.69] [1.42,2.15] 4 (PARENT) HADRON: range in Pb/ emul=9.5/2.8 cm Prob(µ) [1.13,1.61] [0.98,1.64] 6 HADRON: range in Pb/ emul=1.6/0.5 cm Prob(µ) [0.27,0.54] 7 From a prompt neutral particle [0.22,0.69] [0.39,1.16] 8 (DAUGHTER) HADRON interaction seen [9,18] muonless event (favored hypothesis) EPS- HEP Grenoble S.Dusini - INFN Padova 24

25 Decay length Features of the decay topology red bands: values for the interesting event with uncertainties mm Kink angle Daughter momentum reject < 20 mrad cut 11 June 2010 A. Ereditato - LNGS - 31 May 2010 Stefano Dusini - ISTITUTO NAZIONALE di GeV/c FISICA NUCLEARE - Padova rad 25

26 Kinematical cuts to be passed Reject NC events with larger missing Pt (neutrino) Blue: MC NC Black: MC - τ Missing Pt at primary vertex cut GeV/c Reject hadron interactions Pt at decay vertex 11 June 2010 cut Stefano Dusini - ISTITUTO NAZIONALE di FISICA NUCLEARE - Padova 26 GeV/c 26

27 Signal : φ =180 o X (hadron shower) BG: small φ Azimuthal angle between the resulting hadron momentum direction and the parent track direction τ- decay ν τ τ - ν τ N φ π - τ - X kink x ν µ φ π - π - ν µ N ν µ π - X Blue: MC - NC Black: MC - τ cut 11 June 2010 Stefano Dusini - ISTITUTO NAZIONALE di FISICA NUCLEARE - Padova 27 rad 27

Detection of short lived particle with Emulsion Cloud Chamber (ECC) To accommodate Large Mass High Tracking Resolu@on we use thin metal plates (neutrino

ECC technique successful applied in DONUT experiment for the discovery of ν τ (2000) Iron 3D tracking: 32 grains/100µm 0.

28 Detection of short lived particle with Emulsion Cloud Chamber (ECC) To accommodate Large Mass High Tracking we use thin metal plates (neutrino target) interleaved with nuclear photographic emulsion on films. ECC technique successful applied in DONUT experiment for the discovery of ν τ (2000) Iron 3D tracking: 32 grains/100µm 0.3 µm accuracy Changeable Sheet (CS) removable emulsion sheets to interface electronic detector O(mm) with emulsion O(µm) DONUT ν τ event Use electronic detectors to to the emulsions and preselect the region EPS- HEP Grenoble S.Dusini - INFN Padova 28

29 SM1 OPERA detector Mechanical structure Changeable Sheet Doublet SM2 (CS) in separate envelope 20 m 6m ECC Brick Target: ~150,000 bricks (total ass ~interleaved 1.25 kt) Walls of target ECC bmrick plas@c arranged in 54 walls scin@llator tracker walls EPS- HEP Grenoble Brick: 57 nuclear emulsion ﬁlms interleaved with 56 lead plates (1mm thick)! Instrumented dipolar magnet f10.2cm or muon spectrometry 12.5cm! S.Dusini - INFN Padova 29

30 LNGS of INFN CERN LNGS Largest underground laboratory for astro-particle physics. underground area: m m rock coverage cosmic µ reduction= 10 6 (1/m2h) OPERA EPS- HEP Grenoble S.Dusini - INFN Padova 30

Oscilla@on Project with Emulsion tracking Apparatus Super Module 2 Super Module 1 Veto Target Muon ECCs scint. 10 m! Detector supermodules construction: Sept. 2003 spring 2007 20 m!

8 cm resol., ε 99% rate 20 Hz/pixel @1 p.e. EPS- HEP 2011 - Grenoble Drift tubes Spectrometer strips BRICK WALLS 2850 bricks/wall 53 walls RPC HIGH PRECISION TRACKERS 6 drift-tube layers/spectrometer spatial resolution < 0.

31 Project with Emulsion tracking Apparatus Super Module 2 Super Module 1 Veto Target Muon ECCs scint. 10 m! Detector supermodules construction: Sept spring m! BMS Brick Manipulator system TARGET TRACKERS 2x31 scintill. strips walls X-Y strips/wall WLS fiber readout Target Trackers 64-channel PMTs neutrino trigger channels brick localization 0.8 cm resol., ε 99% rate 20 p.e. EPS- HEP Grenoble Drift tubes Spectrometer strips BRICK WALLS 2850 bricks/wall 53 walls RPC HIGH PRECISION TRACKERS 6 drift-tube layers/spectrometer spatial resolution < 0.5 mm INNER TRACKERS 990-ton dipole magnets (B= 1.55 T) instrumented with 22 RPC planes 3050 m2, ~1.3 cm res. S.Dusini - INFN Padova RPC + drift tubes in spectrometers: muon ID, momentum, charge 31

Latest Results from the OPERA Experiment (and new Charge Reconstruction)

Latest Results from the OPERA Experiment (and new Charge Reconstruction) on behalf of the OPERA Collaboration University of Hamburg Institute for Experimental Physics Overview The OPERA Experiment Oscillation