Search for Dark Matter with ANTARES

Holger Motz

Erlangen Centre for Astroparticle Physics

Experiental Particle Physics Seminar

Kyushu University, Fukuoka 2011.10.31

Neutrino Telescope: Detection Principle

• neutrinos can penetrate Earth

• CC interaction in the vicinity of

the detector → muon with

(almost) same trajectory

• muon emits Cerenkov light

when traversing water

• position and time of Cerenkov

photons detected allow

reconstruction of muon path

The ANTARES Collaboration and Site

24 Institutes from 7 Countries

Detector located in Mediterranean near

Toulon at 2475 m depth (to shield from

atmospheric muons)

40 km submarine cable

Depth: 2475 m

Toulon

The ANTARES Collaboration and Site

Shore Station “Michel Pacha” in

La Seyne sûr Mer

40km electro-optical cable for power

and data transmission

40 km submarine cable

Depth: 2475 m

Toulon

The ANTARES Detector

• 12 Lines + IL, ~0.1km² geometric area

• each line: 25 storeys with 3 PMTs per storey

• 885 PMTs total (one sector acoustic particle detection)

Junction Box

40 km electro-optical cable to shore

~70m

~450m

Detection and Calibration Elements

Hydrophonestorey position by

acoustic triangulation(5 per line)

Optical Module(10” PMT in 17” glass sphere)

photon detection

Local Control Module (in Titanium container)

front-end ASIC, Clock, DAQ/SC,compass and tiltmeter for

measuring storey orientation

Optical Beaconwith blue LEDstiming calibration

(4 per line)

Position Calibration

lineshape formula derived from drag and buoyancy of line components fitted to data. => position and orientation of all Optical Modules at ~cm precision

triangulation of the position forfive hydrophones per line with signal from emitters at Bottom String Socket (BSS)

orientation of each storey by compass and tiltmeters

Dominated by two effects:

1. β – decay of 40 K

2. Bioluminescent organisms:

e.g.

40 K

40 Ca

e-

γ

γ

Optical Background

March 2006 – May 2008

Event Reconstruction Basics

• track hypothesis described by x, y, z, t,

zenith and azimuth varied to minimize

time residuals

• time residuals of true track not zero

due to time smearing, light scattering

etc. → PDF

• background hits should either be

included in PDF or removed by hit

selection algorithms

p

Δt

Muon Event in 12-Line Detector

Hei

ght

o f h

it O

M

Time of hit

One plot per line

Neutrino Candidate Event

Hei

ght

o f h

it O

M

Time of hit

One plot per line

Triggering and Hit Selection

Online Trigger

• “all data to shore” concept – L0 hits with threshold 0.3 pe

• 104ms timeslices distributed among datafilters

• L1 hits: one 3 pe hit or 2 hits on storey with Δt <20ns

Standard trigger algorithms

• 3D Scan: 5 L1 hits causally connected + compatible with any track from

direction scan

• 2T3: 2 clusters of 2 L1 hits on adjacent storeys with Δt <100ns or on next to

adjacent storeys with Δt <200ns

Triggered HIts

• L2 hits: Hits that are part of the triggering pattern

Cluster Hit Selection

• select all hits within a window in

time and space from a primary hit

(loop over all hits)

• calculate slopes of lines connecting

primary hit with other selected hits

in z vs t

• calculate RMS of slope distribution

• if RMS worse than user defined

upper threshold, remove worst hit

• continue until RMS good or number

of hits drops below given minimum

• applied selection combines several

cluster sizes with different hit

amplitude cuts

Hei

ght

o f h

it O

M

Time of hit

Cluster Hit Selection Efficiency and Purity

average efficiency (fraction of selected signal hits in all signal hits) for cluster: 0.78, L1: 0.30, L2: 0.60

average purity (fraction of signal hits in selected hit sample) for cluster: 0.86, L1: 0.56, L2: 0.97

ν

µνpp

quality cuts required to remove atmospheric muon background

Background from Cosmic Radiation

badly reconstructed atmospheric muon events

Aart Strategy Reconstruction

• developed for point source search – good angular resolution (0.3°)

Reconstruction steps

• linear prefit as starting point

• several prefits starting from shifted positions and directions

• final fit with full likelihood including background hits

Qualtity Cut Λ

• Λ = log(likelihood)/ndof+0.1*(number of prefits deviating <1°)

• cut depends on background rate

• Λ > -5.3 at 60 kHz → 10% additional background from

misreconstructed atmospheric muons

ANTARES Low-Energy Effective Area

60 kHz background rate from K-40 decay and

bioluminescence

Indirect Search for Dark Matter

• Dark Matter Particle: WIMP, self annihilating (e.g. SUSY Neutralino χ)

• elastic scattering → bound to massive stellar objects (Sun, Earth)

• increase of Neutralino density → Annihilation rate enhanced

• primary annihilation products (quarks, gauge bosons, leptons) decay into

neutrinos

Sensitivity to mSugra Dark Matter

•flux prediction based on a random walk scan of mSugra Parameter Space

guided by the relic density compared to WMAP prediction

•mSugra parameters: m0, m

1/2, A

0 on GUT scale as well as tan(β) and μ

•RGE code ISASUGRA calculates masses on weak scale

•cross sections, relic density, fluxes from annihilation etc. from DarkSUSY

•neutrino oscillation effects for neutrinos from the centre of the Sun

calculated using path-ordered propagators to include matter effects (MSW)

•galactic Dark Matter halo model: Navarro-Frenk-White profile (0.3GeV/cm³)

•renormalisation dependent on top quark mass: mt set to 172.5 GeV

•Integrated νμ and νμ flux

above 10 GeV threshold

energy plotted against

neutralino mass

Neutrino Flux from mSugra Dark Matter Annihilation in the Sun

•sensitivity calculated for five

years of taking data

•unified approach by Feldman-

Cousins used

•background from atmospheric

neutrinos plus 10% more from

misreconstructed atmospheric

muons

•3° radius search cone

Detection Rate from mSugra Dark Matter Annihilation in the Sun

mSugra Parameter Space Regions

Focus Point Region

regions where relic density close tovalue predicted by WMAP

Exclusion Capabilities of ANTARES for the mSugra Parameter Space

Excludable in 3 years at 90% CL: all some none (A

0 varied between -3m

0 and +3m

0 and tan(β) within indicated slice)

Direct Detection

•comparison to direct

detection experiments

sensitive to spin

independent WIMP-

nucleon cross section

Direct Detection

•comparison to direct

detection experiments

sensitive to spin-dependent

WIMP-nucleon cross

section and other neutrino

experiments

•Sun consists mostly of

hydrogen → spin

dependent scattering

dominant for capture →

direct relation with

annihilation rate in, and

neutrino flux from Sun

Analysing the Flux from Earth's Centre

• data from December 2010 analysed

• searching for Dark Matter annihilations in Earth

• model independent limits for various annihilation

channels and WIMP masses

• only Zenith angle needs to be reconstructed →

higher efficiency and lower energy threshold

• no off-source region → background estimation

from MC only → improvements on MC

Monte Carlo Improvements

• background and OM-

Condition from Minimum

Bias Events (MBE) – data

snapshots taken every 10

seconds

• triggering on and

misreconstruction of pure

background also simulated

using MBE

• PMT gain spread for

simulated signal hits

randomized according to

MBE amplitude distribution

t

Simulated Event

MBE4400 ns

MBE4400 ns

MBE4400 ns

TriggeredHits

Trigger Snapshot +- 2200 ns

Use this MBE'sOM Condition

OM Condition in Data and MC

black: datared: MCblue: pure bkg MC

Average Rate per OM in Data and MC

black: datared: MCblue: pure bkg MC

Hit Amplitude Distribution (good OM)

Hit Amplitude Distribution (bad OM)

Global Hit Amplitude Distribution

Global Hit Amplitude Distribution

BBFit Reconstruction

Fit Procedure

• χ² fit on time residuals

• additional term: hit amplitude * Cerenkov light travel distance

• ROOT Minuit minimizer

• single line (zenith angle) and multi line version

• track and shower version (better χ² selected)

Initial hit selection

• large hits (>2.5 pe)

• coincidences on a storey (Δt <20ns)

• hits recursively connected by the T3 cluster definition

• all hits on a storey merged (time from first hit on storey)

Zenith Angle Distribution before Cuts

BBFit X²-Cuts

• separate cuts for single line, two and three line fits

• cut defined at 100% additional background from misrecontructed atmospheric muons

1 Line

2 Line3 Line

Zenith Angle Distribution after Cuts

Data / MC Events after Cuts over zenith

Simulated Annealing Fit

Time consuming fit for low energies

• used on events for which BBFit failed and reconstructed energy < 600 GeV

Simulated annealing minimizer

• random walk with decreasing step size (analogous to cooling metal)

3 Prefits

• PDF fitted from MC track and Cluster hit selection

• wide gaussian PDF (50ns) and all Hits

• narrow gaussian PDF (5ns) and Cluster Hits merged with time of first hit on

each storey

Final Fit

• only if no prefit reconstructed events as downgoing

• 10° zenith around best prefit

Simulated Annealing Fit Quality Cut

• Δt < 15 ns:direct hit

• >4 direct hits

• ω = reconstructed energy / number of direct hits

Zenith Angle Resolution

red: Simulated Annealing Fit avg. 5.6° green: BBFit 3-Line avg. 0.9°turquoise: BBFit 2-Line avg. 1.3°blue: BBFit 1-Line avg. 5.1°

Efficiency (Zenith Angle)

red: Simulated Annealing Fitgreen: BBFit 3-Lineturquoise: BBFit 2-Lineblue: BBFit 1-Line

Efficiency (Low Energy)

red: Simulated Annealing Fitgreen: BBFit 3-Lineturquoise: BBFit 2-Lineblue: BBFit 1-Line

Expected Signal Event Calculation

• additional weights for atm. neutrino Monte Carlo Simulation

• flux calculated for 200 annihilations per ns purely into one channel

• fluxtables from WIMPSIM homepage

• absorption to Earth surface negligible

• WIMP masses [GeV]: 25, 50, 80.3, 91.2, 100, 150, 176, 200, 250,

350, 500, 750, 1000, 1500, 3000, 5000

• annihilation channels:

Best Search Cone Calculation

• model rejection factor minimized (average upper limit / exp. events)

• for each channel and WIMP mass

W-channel, 100 GeV

Expected Signal Events (best cone)

Model Rejection Factor

Limit on the Number of Signal Events

black: datared: MCblue: limit

Feldman-Cousins90% CL limit

used cone cutsoptimized from MC beforehand

Limit on the Annihilation Rate

theoretical capture rate for a 10 ³ cm² spin independent x-section⁻⁴

Limit on the Neutrino Flux

•10 GeV neutrino energy threshold•used WIMPSIM tables again

events x 60, assume to measure expected background

5-year Sensitivity

Summary

Sensitivity of ANTARES to mSugra for annihilations in the Sun

• 5 year sensitivity reaches parameter space

• complimentary to direct detection and collider approach

Analysis of neutrino flux from Earth's centre

• prototype analysis with improvements on data selection and MC

simulation

• Simulated Annealing Fit allows to reconstruct extra events

especially at low energies

• limits set for annihilation rate and neutrino flux from WIMPs

annihilating into a single channel for various WIMP masses