Searching for cosmic sources of neutrinos with ANTARES Aart Heijboer

Searching for cosmic sources of neutrinos with ANTARESAart Heijboer, Philadelphia June 22 2004

Searching for cosmic sources of neutrinos with ANTARES

Aart HeijboerNIKHEF/University of Amsterdam

outline:neutrino astronomycosmic rays, gamma's and neutrinosANTARES

statusreconstructionpoint source searches


Solar neutrinosSN1987a (12+6 's)neutrino oscillations

atmosphericSolar

The birth of neutrino astronomy


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!


PhotonsProtons Neutrinos

High energy multi-messenger astronomy

Need stable particles

SatellitesBalloons

Air shower arrays

GeV: satellitesTeV: Air Cherenkov

Water Cherenkov(air) shower detection


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


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


The Sky in TeV Photons

H. Völk, TAUP 2003

many types of Galactic and extra-Galactic sources

up to 70 TeV

evidence forhadrons?


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


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


●Use the Earth as target and the sea as detector●reconstruct muon trajectory from arrival times of Cherenkov photons on PMTs

Water/ice Cherenkov: Detection principle

Cherenkov Photons

43o

p


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


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


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


The ANTARES collaboration


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


Site of Detector and shore station


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


Movie of sector line connection


screenshot ofonline monitoring

period of highoptical backgroundbackground related

to sea currents

Prototype Sector Line: in the water


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


theoretical arrival time

residual w.r.t actual hit time

˜d

Find track parameters so that residuals are 'small'

Muon Track Reconstruction

v


●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)

num

ber

of h

its

(a.u

.)

total

electrons & scatteredmuon

Optical background due to decaying 40Kand bioluminescence.

Distribution of residuals


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

.... but there is a problem


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: PDF is 'flat' forsmall or very large residuals

Fitting algorithms rely onderivatives of PDF.

Scanning unfeasible in 5-dim parameter space

Need good starting pointfor the fit (1o accurate)


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


Fitting technique that is resistant to 'outliers', but still is able to find the global minimum byminimising a 'modified 2': 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


Full reconstruction algorithmmultiple 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


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 /


(simulation of)

One year of atmospheric neutrinosseen by ANTARES

AMANDA-II 197 days

1555 events,667 up-going

Excess of events:Discovery?

no excess:Upper limit

Point Source Searches


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


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) ?


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


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



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



=-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


optimised grid method


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



AMANDA-II:197 days in 2000

2009

2001

90% CL averageexclusion limit

discoverableat 5 CL

detect in specialisedanalysis

Point source sensitivity of ANTARES


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


In ice: (Wiebush, vlvnt)

but no background

fit = 1.09

error estimates from thefit describes the actual errorto within ~10%.


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


1.0

0.1

0.01

10

well reconstructedevents are selectedby cutting on the valueof the likelihood

log 10

(re

cons

truc

tion

err

or /d

eg)

-log(L)/ndof

Event selection

Also rejects background from atmospheric muons whichare mis-reconstructed as upward-going.


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


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


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)


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


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 ANTARES Aart Heijboer

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