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ANTARES a Neutrino Telescopein the Mediterranean Sea
31/01/2014
Salvatore Mangano
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Outline
IntroductionResearch Projects ▪ Measurements - Shower reconstruction along muon - Velocity of light - Optical properties ▪ Searches - Gravitational lensing and neutrinos
Achievements/Conclusion
Salvatore Mangano
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2000 - 2001
OPERA
Oscillation Project with
Emulsion-tRacking Apparatus
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2001 - 2005
HERA (H1)
Hadron-Electron
Ring Accelerator
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2006 - 2013
ANTARES
Astronomy with a Neutrino Telescope and
Abyssal environmental RESearch
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ANTARES Collaboration
8 countries31 institutes~150 scientists
X ANTARES site
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ANTARES Detector
In Mediterranean Sea
40 km from Toulon 2.5 km under water
12 Lines (885 PMTs)
Line length ~450 m
Optimized for muonsat TeV energies
Taking high quality data since 2007
450
m
60 m
14.
5 m
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Neutrino Astronomy
Photon: Absorbed by interstellar medium and extragalactic background light (ɣ + ɣ ↔ e + e)
Proton:Deflected by magnetic field (E<1019 eV)and interact with CMB (E>1019 eV → 30 Mpc)
Neutrino: Interact weak (travel cosmological distances)Point back to source emissionSignature of hadronic processesDisadvantage → need large detector volume
Photon
Proton
Neutrino
Main Goal: Find cosmic neutrino sources
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Neutrino Detection
Neutrino
Charged CurrentInteraction
Muon
Cherenkov lightfrom muon
Detection lineswith PMTs
Reconstruction of muon trajectory from timing and positionof PMT hits
Cheap high quality sea water
Sea floor
Earth shielding rejects atmospheric muonsUpward going muon → neutrino candidate from Southern hemisphere
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ANTARES Basics
Detector
108 atmospheric muons per year
103 atmosphericneutrinos per year
??? cosmicneutrinos per year
??? exotic neutrinos per year
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Electromagnetic Showers along Muon Tracks
Salvatore Mangano
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Muon Energy Loss
Energy loss ~ (a + bE)
Below 1 TeV:
Continuous energy loss
Above 1 TeV:
Discrete energy loss
Large energy fluctuation Electromagnetic showers
waterwater
total
ionisation
pair production bremsstrahlungphotonuclear
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Shower Identification Method
Muon emits: continuously Cherenkov photons and sometimes discrete electromagnetic showers
Project photons onto reconstructed muon track
=>Search for clusters/peaks
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Algorithm
1. Reconstruct muon track
2. Calculate photon emission positions
Photons with early arrival times (|20 ns|):
Calculate photon vertex assuming emission underCherenkov angle
Photons with late arrival times (20-250 ns):
Calculate photon vertex assuming spherical emission
3. Search shower candidates with a peak finding algorithm
Data
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Photon Emission along MC Muon Track
all reconstructed emission points of the photons on muon trajectory
hits selected by the algorithm
positions of generated showers along the muon direction
Use MC to quantify performance of shower reconstruction
MC
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Vertical Downgoing Track
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Atmospheric Muon with Two Electromagnetic Showers
Idea: 1. Reconstruct muon trajectory 2. Project photons onto muon track 3. Peak signals shower position
Photon (+)Muon track (black line)Shower (red line)
Photon for track (■)Photon for shower (○)
Photons along track
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Shower Multiplicity
MC shows (Horandel):
Shower energy 0.5TeVMuon energy with shower 3.7TeVPosition resolution 5mShower Efficiency 5%Shower Purity 70%
No reconstruction efficiency used
Main systematic errors:Water absorption lengthPMT acceptance
Published inNIM A675 (2012) 56
Applications: Energy estimator, variable for cosmic-ray composition
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Velocity of Light
Salvatore Mangano
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Method
Pulse width 4 ns for LED and 0.8 ns for LaserFlash at a frequency of 330 Hz
1. Flash light with fixed λ from a given position2. Measure time when light reaches PMT → group velocity of light, refractive indexImportant for timing resolution (Angular resolution)
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Wavelength Spectra of Light Sources
Measured
Simulated at 120 m
Difference between spectra are due to variation of absorption length as a function of wavelength
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Fit Arrival Time at Photomultiplier
Arrival time distribution of each PMT fitted with functionwhich is a convolution of a Gaussian and an exponential.
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Arrival Time as Function of Distance
For one run wavelength = 469 nm
42 runs (data period 2008-2011)
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Velocity of Light in Sea Water
Published inAP 35 (2012) 9
Group velocity of light measured at eight different wavelengths in Mediterranean Sea at a depth of 2.2 km
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Optical Properties
Salvatore Mangano
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Absorption and Scattering Lengthas Function of Wavelength of Light
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Various models exist for absorption and scattering length.Crucial for detector performance.
Smith&Baker
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Method1. Take data with flashing optical beacon
- Plot the hit arrival time distributions for all OMs
2. Simulate many MC samples with different input values: λa and λs
3. Compare hit arrival time distributions from MC samples and data
4. Choose MC with λa and λs which describes best data
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Monte Carlo Samples • Simulation depends on two parameters: s and a
• Generate different MC input parameters, for example:a = 35, 40, 45, 50, 55, 60, 65, 70, 75 m 9 valuess = 35, 40, 45, 50, 55, 60, 65, 70, 75 m 9 values
9 times 9 = 81 MC samples for each data run
• Each generated MC run has his:– detector geometry– charge calibration – background noise – all OMs corrected by efficiency
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Histogram Comparison Compare time distributions from data and MC for many different OMs Calculate χ2 to quantify agreement between data and MC histograms
Data
λ_a = 55 m and λ_s = 50 m
MC describes better data
λ_a = 70 m and λ_s = 80 m
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Absorption vs. Scattering for Line 2
Calculate chi2 for each line and each MC template(in this case for Line 2 for 81 MCs)
Numbers give normalized chi2
Select MC model with minimal chi2
Cross check MC with MC
Errors are to small
Scattering length [m]35 75
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75
Abs
orpt
ion
leng
th [
m]
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Results
Take from lines the simulation with smallest chi2
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Gravitational Lensing and Neutrinos
Salvatore Mangano
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Full-Sky Point Source Search
Published inApJ 760 (2012) 53
ANTARES 2007-2010 data~3000 neutrino candidates (85 % purity)Angular resolution 0.5 +/- 0.1 degrees
No statistical significant signalBest cluster with 2.2σat (-46.5o, -65.0o)
Do we see neutrinos from space?
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Search from Selected Candidates
Gravitational lensing- Well-known prediction
of Einstein´s relativity (with many observations)
- Magnification of cosmic signals (higher fluxes)
- Same geodesic for photons and neutrinos
Advantage: Neutrinos not absorbed by lens
• Look at promising sources → Limit region of sky - Less general than full-sky → Improve sensitivity• Select galactic and extragalactic sources - Consider strong gamma-ray fluxes • Select neutrino sources behind powerful gravitational lens - Consider strong lenses with large magnification
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Galaxy and Quasar Lensed by Galaxy Cluster
Multiple images
Magnification for light between 1 and 100
Lens z= 0.68
Lens mass ~ 1014 Msun
Gravitational light deflection order of tenth of arcsec
Field of view: arcminAngular resolution → Point like for us → No multiple images, but magnification
Gamma emissionPKS1830, JVAS B0218
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Cosmic Neutrino SearchHow to tell there are cosmic neutrinos?(Likelihood ratio, calculate statistics from data)
Hypotheses: All neutrinos are atmospheric
Statistics
If you get this result=>Probably atmospheric neutrinos
Statistics
4 σ
If you get this result=>Cosmic neutrinos
If cosmic neutrinos exist
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Large separation quasar SDSS J1004+4112 is lensed by a galaxy cluster
Gravitational Lens: Best Cluster
X-ray image from Chandra project
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Neutrino Sky Map in Galactic Coordinates51 strong gamma-ray sources and 11 strong lenses
Data unblinding → no significant excess → set upper limits
▪ Neutrino event Strong ɣ-flux Strong lens
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Upper Limits on Neutrino Flux
Limits of ANTARES compared with other experiments
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Achievements/Conclusion• Experience in experimental neutrino astronomy and particle physics (OPERA, H1, ANTARES)
• Co-author of 70 publications
• Main author of two publications
• 15 presentations at international conferences PPC2013 (USA), Moriond 2013 (Italy), ICRC2013, ….
• 50 presentations at ANTARES meeting
• Develop innovative research lines
Salvatore Mangano
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Backup
Salvatore Mangano
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Cosmic “Neutrino” Acceleration• Photon astronomy exists with sources with E > TeV• Neutrinos possibly produced in interactions of high energy nucleons with matter or radiation
• If hadron acceleration: high energy nucleons + hadrons → mesons + hadrons → neutrinos and photons + hadrons
Photon energy ≈ Neutrino energy Photon flux ≈ 2 x Neutrino flux
• Neutrino sky has so far only 2 objects (MeV): 1. Sun 2. SN1987A (few seconds)
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Neutrino flux on Earth
(SN 1987A)
= measured
Water-Cherenkov Detectors in natural environments
Alternative techniques
Solar neutrino experiments
(other components arehypothetical)
Energy range ofNeutrino telescopes {
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Pure Proton Primaries or Pure Iron Primaries versus Data
No way to explain data with onlyproton or iron primaries
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Fit light and heavy nuclei to data
• High shower multiplicity dominated by heavy nuclei• Low shower multiplicity dominated by light nuclei• Fits says data contains 91% light and 9% heavy nuclei
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Gravitational Lens List
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Maximum likelihood search method:
A likelihood ratio is used as test statistics (λ):
Search method uses:1. event direction 2. number of hits in track fit 3. angular error estimate
Search Method
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P-value Calculation for Most Significant Event
Unblind => λobs
Compare λobs with λ distribution of only background case
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Skymap in Equatorial Coordinates of Selected Sources
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Upper Limits for Gravitational Lens Sources
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Upward Going Muons from Charged Current Neutrino Interactions
Cumulative distribution of reconstruction quality variablefor upgoing tracks (2007-2010)
Distribution of zenith angle withquality variable > -5.2 → ~3000 neutrino candidates
Tracks reconstructed by maximization of track likelihoodLikelihood = probability density of observed hit time residualsTime residuals = difference between observed and expected time
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Cosmic Point Source SearchAlgorithm for cluster search usesunbinned maximum likelihood method
In neutrino sky distinguish: - atmospheric neutrinos (background)
isotropic event distribution
- from cosmic neutrinos (signal)
event accumulation
Factor ~3 improved sensitivitycompared to previous result (2007+8 data) ApJL 743 (2011) L14 Main criteria for improvement:• More than twice the statistics• Energy information (gain of 20%)
Probability of discovering a source as a function of signal events (E-2)
For 5σ discovery:~9 events per source
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Full-Sky Hot-Spot
1o
3o
Most signal-like clusterin full-sky search:9 neutrino events in 3o
5 neutrino events in 1o
Likelihood fit assigns:5.1 signal events
Pseudo-Experiments:p-value 2.6%significance = 2.2σ
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Simulation of Gravitational LensingAnimation takenfrom Wikimedia
Simulation of gravitational lensingcaused by massiveobject going pastbackground galaxy
If background source, massive lensing object and observer aligned → Einstein ring