searching for cosmic sources of neutrinos with antaresaart heijboer, fermilab june 25 2004 searching...
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Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Searching for cosmic sources of neutrinos with ANTARES
Aart HeijboerNIKHEF/University of Amsterdam
outline:neutrino astronomycosmic rays, gammas and neutrinosANTARES
statusreconstructionpoint source searches
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Solar neutrinosSN1987a (12+6 's)neutrino oscillations
atmosphericSolar
The birth of neutrino astronomy
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
MeV neutrinos (SNO, SK):produced in nuclear reactionsdetected from Sun and Supernova fluxes from other stars or extra-galactic SN
(probably) too low
TeV neutrinos:produced in collisions of high energy
hadrons (or decay of massive particles)observational advantages
neutrino cross-section rises with Esmall scattering angle (due to large
boost)allows for pointing accuracyenergetic reaction products: can use
sparse detector to monitor large volume cost effectively
through-going muon in SK
Going to TeV energies
put PMTs furhter apart!
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
PhotonsProtons Neutrinos
High energy multi-messenger astronomy
Need stable particles
SatellitesBalloons
Air shower arrays
GeV: satellitesTeV: Air Cherenkov
Water Cherenkov(+radio+air showers)
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Cosmic Rays
Fermi acceleration probableSources still unknown, due to deflection my magnetic fields
The existence of (ultra) high energy cosmic rays is a major motivation for high energy gamma and neutrino astronomy
light elementsdisappear first?
SNR standard candidate for acceleration uptoZ 1015 eV
Highest energies:AGN, GRB?
microquasar
??
?
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
0accp (p) X
ee
ee
Cosmic ray interactions, photons and neutrinos
straight propagation reprocessed to low E in (opaque) source absorbed on extra-galactic photon background alternative production mechanism: electrons > 100 GeV air-Cherenkov technique
straight propagationsources transparent to neutrinosno absorption while propagatingsmoking gun for hadronshard to detect
Photons and neutrinos are produced in ~equal amounts by CR interactions
cosmic ray proton(or nucleus)
photons neutrinos
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
The Sky in TeV Photons
H. Völk, TAUP 2003
many types of Galactic and extra-Galactic sources
up to 70 TeV
evidence forhadrons?
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Evidence for hadrons?
Recently:Cangaroo galactic centerastro-ph/0403592well fitted with protons
Enomoto et al. (Cangaroo), Nature 2002Reimer et al., 2002
inverseCompton
0
RX J1713.7-3946
detection neutrinos would provide direct proof of hadron component
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Other signals in neutrino telescopes
GZK neutrinosUHECR+cmbX
Dark matterWimps can be gravitationally bound to heavy objects
(Earth, Sun, Galactic center). Neutralinos can annihilate e.g. W+W-+X
Decay of very massive, long lived particlestopological defects, GUT particles
Magnetic Monopolesdirect detection when traversing detector
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
●Use the Earth as target and the sea as detector●reconstruct muon trajectory from arrival times of Cherenkov photons on PMTs (ns precision)
Water/ice Cherenkov: Detection principle
Cherenkov Photons
43o
p
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Water/ice Cherenkov: Backgrounds
p
p
p
backgrounds:atmospheric atmospheric
backgroundsatmospheric :reject by looking for up-going muonsbeware of mis-reconstructed atm. muons (need factor 107 rejection)
atmospheric :largely irreducible, butisotropic with steeply falling (soft) energy spectrumrejection:
energy (look for hard, diffuse fluxes)direction (look for point sources).....time (transients (GRB), correlate to other
detectors)
need accurate muon reconstruction
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
AMANDA
Dumand
Baikal
SNO
SuperK
MACRO
taking data at South Polenext step: IceCube
pioneering experimentin good, deep waterfunding stopped in 1995
ANTARES
NEMO NESTOR
Mediterranean Sea:deep, clear water
DUMANDBAIKAL
running since 1996at shallow depth.
Cherenkov telescopes around the world
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
ANTARES
NEMONESTOR
Three projects in Mediterranean
KM3NeTJoint initiative for km3-scaledetector somewhere in Med.
NEMOR&D for km3 scale detector in Italy
NESTORplanning detector in Pylos, Greece
ANTARESbuilding 0.1 km2 scale detector
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
The ANTARES collaboration
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
The ANTARES detector
floors consisting of 3 PMTs,with electronics fordigitisation, local clock
40 km electro-opticalcable to the shore
buoy
60 m string spacing
14.5 m floor spacing
junction box
bottom 100m not instrumented
depth =2.4 km12 strings x 25 floors x 3 = 900 PMTs
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Site of Detector and shore station
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Offset of ~110 ns between adjacent floors due to difference in fibre length,
Check of internal clock-system calibrationTiming resolution of 2.0/21.4 ns.
dominated by TTS of the PMT
Deliver simultaneous laser pulses to OMsTake data with full DAQ systemMeasure time differences between hits
on different OMs
Prototype Sector Line: in the lab
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Movie of sector line connection
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
screenshot ofonline monitoring
period of highoptical backgroundbackground related
to sea currents
Prototype Sector Line: in the water
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Reconstruction of muondirection (and position)based on hit-timesv=cstraight line (multiple
scattering very small)beware of background
photonsmuon does not go 'through'
the hits (non-linear problem)
Energy reconstruction basedon amount of light emitted
Muon Track Reconstruction
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
theoretical arrival time
residual w.r.t actual hit time
˜d
Find track parameters so that residuals are 'small'
Muon Track Reconstruction
v
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
●MC simulation ●simulation of water propertiestaking in situ measurementsinto account.
● PDF strongly peaked despite●light scattering●secondary electrons (pair production and bremsstrahlung)●optical background
E = TeV
residual (ns)
nu
mb
er o
f h
its
(a.u
.)
total
electrons & scatteredmuon
Optical background due to decaying 40Kand bioluminescence.
Distribution of residuals
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
time residuallo
g(P
)0
background hits (flat)signal hits (peaked with tail)
Amplitude of hitdistance track-PMTangle between PMT and photon
For each hit, the signal and backgroundPDFs are weighed differently
Gives very accurate reconstruction....but there is a problem
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Finding the maximum of the likelihood function
scan of -likelihood aroundtrue direction (position fixed to true)
zenith angle (deg)azi
muth angle
(deg)
-log
(L)
+ C
onst
ant
Problem: likelihood function is 'flat' whentrack parameters far from true values. Due to flat PDFfor large residuals.
Fitting algorithms rely onderivatives of PDF.
Scanning unfeasible in 5-dim parameter space
Need good starting pointfor the fit (1o accurate)
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
linear 2 fit yieldingdx/dt, dy/dt, dz/dt
and x0, y
0, z
0
linear prefit
hit time t
PM
pos
ition
x
roughly 10o accuratenot good enough, but it's a start
Step 1: Linear prefit
linear prefit
hit time t
PM
pos
ition
x linear prefit
hit time t
PM
pos
ition
x
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Fitting technique that is resistant to 'outliers', but still is able to find the global minimum byminimising a 'modified least squares': called M
hit residual (ns)
rises only linearly:outliers are notso important
r2
ri2
M = g(ri)
buzzword: robust estimation(see e.g. numerical recipes)Trade-off needed between accurate PDF of residualsproviding gradient to the true minimum
many events withfew degree accuarcy
Step 2: M-estimator
M-estimatorleast
squares
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
multiple stages with increasing accuracy
linear prefit
fit with M-estimator
final fit with full likelihood
try a few different starting points
hit selection
hit selection
Full reconstruction algorithm
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Value of likelihood is used to select well-reconstructed events
-log(L)/ndof
1.0o
0.1o
0.01o
10o
Also rejects atmospheric muons whichare mis-reconstructed as upward-going.
log
10 (
reco
nst
ruct
ion
err
or
/deg
)
Event selection
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
angular resolutionbelow 0.2o for high energiesdominated by physics
below ~3 TEV
Effective area
cut on MC truth: known sources
Detector Performance
up
hor
Absoption in Earth
Aeff= Rdet /
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
(simulation of)One year of atmospheric neutrinos
seen by ANTARES
Excess of events:Discovery?
no excess:Upper limit
Point Source Searches
ra
celestial coordinatesdeclination () and right
ascension (ra)
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
cone method
grid method
for both methods
clusters are built by selecting all events in a cone
count events fallingin square-like bins
only event countingbin/cone size chosen to give
constant backgroundoptimal bin/cone sizes found
for exclusion and discoverysignificances can be calculated
analytically from the dataresults for both methods are
largely similar
but......
Conventional methods
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Idea: use all available informationprecise configuration of the eventsenergy of the eventsdetailed knowledge of angular
resolution
signal like not so signal like
2 clusters with 5 events
optimal observable (test statistic) = likelihood ratio
hypothesis that there is only background
hypothesis that, in addition to the background,there is a point source of neutrinos.
Likelihood ratio method
how to calculateP(data|s+b) ?
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
point spread function
effective area forneutrinos
probability of gettingreconstructed muon energy
neutrino energyunknown: integrate
probability of the data can be expressed as a sum over the events
signal hypothesis
angle betweensource position and reconstructed muon direction
spectrum
ra
Likelihood calculation
source position: ra, fluxdsig/dE
unknown parameters in sig
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
background like signal like
fit source positionand spectrum, maximising
P(data| ra, , sig)
Cluster with the highest likelihood
corresponds to best source candidate
ra
preselection:clustering
(large cone size)
likelihood P(data|ra, , sig) takesinto account: energy of the eventspoint spread function
Likelihood ratio is observablediscriminating between signal+bgand bg-only hypotheses
all events
Likelihood ratio method
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Discovery: finding a cluster that is so signal-like that the probability for the background to produce it is very small (i.e. 2.7•10-3/ 5.7•10-7, for 3/5 )
Three rare examples of 'best candidate' clusters:
signal eventbackground event
true source positionfitted source position
Likelihood ratio method
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
=-80o
LR method can discover a source at 5 CL, which is only a 3 excess in grid methodAlternatively: grid method needs ~40% stronger flux to reach same CL
Likelihood ratio method
optimized grid method
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
As an extra, we get a ML estimate of the source position
6 events seen from source
single-evt resolution/Ns
For pinpointing a source, ANTARES has a resolution < 0.1o !
E-2 spectrum
Likelihood ratio method
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
AMANDA-II:197 days in 2000
2009
2001
90% CL averageexclusion limit
discoverableat 5 CL
detect in specialisedanalysis
Point source sensitivity of ANTARES
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Motivation for high energy neutrino astronomyCosmic ray origin?Do TeV gamma rays show evidence of hadrons?
Neutrino telescopes in MediterraneanANTARES 0.1 km2 is under constructionJoint effort with NESTOR and NEMO for KM3NeT
ReconstructionTake into account optical backgroundReaches 0.2o accuracy
Point source searchesProfit from accurate reconstructionLikelihood ratio method to improve discovery potential (3)2007 (hopefully): observe southern sky
improve existing limits by factor 10 in 1 yearcomplement AMANDA, which studies northern hemisphere
Future km3-scale detector in the Mediterranean
Summary
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
In ice: (Wiebush, vlvnt)
but no background
fit = 1.09
error estimates from thefit describes the actual errorto within ~10%.
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
RICE AGASA
Amanda, Baikal2002
2004
2007
AUGER Anita
AABN
2012 km3
EUSOAugerSalsa
GLUE
C. Spiering
water/iceCherenkov
(radio) detectionof -induced showers
Water/ice Cherenkovbest for E<107 GeVgood angular resolution
beat the backgroundidentify the source
Neutrino telescopes up to very high E
Air showerneutrinos produce deep,
horizontal showers
Radio detectionUHE showers emit
coherent radiation inradio frequencies.very cost effective
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
1.0
0.1
0.01
10
Event selection
Also rejects background from atmospheric muons whichare mis-reconstructed as upward-going.
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
ANTARES History and future
cable to shoredeployed
ANTARES 0.1 km2
data taking
sector line builtand deployed
2000 20022001 2003 2004 2007+20062005
line 12deployment
junction boxdeployment
sector lineconnected
sector linerecovered
first linedeployment
October 2001:Deployment of 40 kmcable to detector site
2002:Building of the 'sector line'detector
prototype line consistingof 5 floors (15 PMTs),final electronics.connected via final
junciton box and cable
SEPT 20022002:September 2002:deployment of sector lineMarch 2003
Connecting sector lineto junction box
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Prototype Sector Line: in the waterba
seli
ne (
kHz)
burs
t fra
ctio
n
median of countrate in15 min. intervals
fraction of time the rateexceeds 1.2 x baseline
periods of high activity, partially correlated with sea currentimpact on detector performance under study
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
atmospheric neutrino background
Events
above E
(y
ear-1
)
atm 's have diffuse, steeply falling spectrumrejection:
energy (look for hard, diffuse fluxes)direction (look for point sources).....time (transients (GRB), correlate to other detectors)
astrophysical diffuseflux shows up above atm. neutrino background
uncertainty on contributionfrom charmed meson decay(Costa, Astroparticle phys 16,2001)
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
NC and CC e and
t produce showers.
Still focus on muons:good direction reconstructionincrease effective volume
oscillations: e ≈ 1:1:1 for astrophysical source
NC and CC e and
t produce showers.
Still focus on muons:good direction reconstructionincrease effective volume
oscillations: e ≈ 1:1:1 for astrophysical source
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
Select events with >5.3:~1 atmospheric muon/day 10.0 atmospheric neutrinos /day74% efficient for E
-2 signal events with an error < 1o
Contribution of mis-reconstructed atm.muons must be estimated fromextrapolation :-(
Atmospheric muon background rejection
log(L)/Ndof
full simulationof 8 hours ofatmospheric
showers
Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Fermilab June 25 2004
AMANDA-II 197 days
1555 events,667 up-going