The search of dark matter with ArDM detector

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The search of dark matter with ArDM detector
CRACOW EPIPHANY CONFERENCE ON NEUTRINOS AND DARK
MATTER5 - 8 January 2006, Cracow, Poland

• Piotr Mijakowski
• The Andrzej Soltan Institute For Nuclear Studies
  (IPJ), Warsaw, Swierk

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OUTLINE

• I ArDM (Argon Dark Matter)
• II Neutron background in dark matter underground
  searches
• III Geant4 neutron background studies

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part I ArDM
http//neutrino.ethz.ch/ArDM
A.Badertscher, R.Chandrasekharan, L.Kaufmann,
A.Knecht, L.Knecht, M.Laffranchi, M.Messina,
G.Natterer, P.Otiougova, A.Rubbia, J.Ulbricht ETH
Zurich, Switzerland C.Amsler, C.Regenfus,
A.Buechler-Germann Zurich University,
Switzerland A.Bueno, M.C.Carmona-Benitez,
J.Lozano-Bahilo, S.Navas-Concha University of
Granada, Spain I.Gil-Botella, P.Ladron de
Guevara, L.Romero CIEMAT, Spain T.Kozlowski,
P.Mijakowski, E.Rondio Soltan Institute (IPJ)
Warsaw-Swierk, Poland H.Chagani, E.Daw, 
P.Majewski, V.Kudryavtsev, N.SpoonerUniversity
of Sheffield, England
ArDM a proposed ton-scale liquid Argon
experiment for direct detection of Dark Matter as
WIMPs (Weakly Interacting Massive Particle, c)
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ArDM (cont.)
Elastic scattering reaction c Arat rest ? c
Arrecoil

• Measurement of the recoils of target nuclei
  10-100 keV.
• Recoil energy ? scintillation ionization of
  ArgonGOAL independently detect the light
  (PMTs) and the charge (Large Electron
  Multiplier)
• light/charge ratio allows to discriminate
  background events (e/g vs. nuclear recoils)

ArDM_at_CERN
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ArDM status

• RD _at_ CERN (1 ton prototype)
• High voltage system
• LEM based charge readout
• Light detection system (PMTs VUV reflecting
  mirrors)
• CAD design and assemby of the detector
• KEY POINT UNDERSTAND THE DETECTOR PERFORMANCE
• FIRST GOAL proof of principle 39Ar rejection
  (intrinsic background, beta-emitter with decay
  rate of 1 kHz in a 1 ton detector)
• Simulations full detector geom., experimental
  background

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ArDM prospects

• TIME SCALE
• 2006 assembly of detector at CERN test on
  surface
• 2007 transport to the Underground Laboratory
  (Canfranc, Spain) installation in experimental
  hall and mounting of infrastructure neutron
  shield
• 2007 first data taking

CANFRANC LAB (2450 m w.e.)
pictures E.Coccia_at_TAUP05
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Estimated event rates
100 event/ton/day
Assuming 30 keV recoil energy threshold, Mc
100 GeV/c2
1 event/ton/day
for s 10-46 1 event/ton/100 day
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part II Neutron background
Background events

• the same signal from WIMP neutron
  interactions !!!
• only possible way to distinguish neutron
  multiple scattering

e-like eventspossible to discriminate
nuclear events
MOTIVATION neutron background limits detector
sensitivity to WIMPs

• NEUTRON BACKGROUND SOURCES
• local radioactivity (surrounding rock, detector
  components)
• muon-induced neutrons

• spontaneous fission 238U
• (a,n) reactions as from radioactive chains of
  U/Th

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Neutron background sources

• 1 neutrons from surrounding rock - 238U and
  (a,n) reactionsflux Frock 3.8 10-6
  n/(s?cm2) _at_ CANFRANC ArDM input (preliminary)
  13200 n/day
• supression neutron shielding
• 2 neutrons from det. components - 238U and (a,n)
  reactions flux detector dependent ArDM input
  (preliminary) 74 n/daysupression high-purity
  materials
• 3 muon-induced neutrons production in hadronic
  e-m cascades init. by ms flux Fm-ind 1.7
  10-9 n/(s?cm2) _at_ CANFRANCArDM input
  (preliminary) 6 n/day
• supression active veto

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Neutron background energy spectra
1 rock
3 m-ind
2 detector components
only fission spectrum
plots 1 3 M.J. Carson, J.C. Davies et al.,
Astroparticle Physics 21(2004) 667-687
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part III Geant4 neutron background studies
How many neutron recoils we will have in our
experiment? (how many neutrons will enter the
detector? what energy spectrum? how many would
interact and produce visible recoils? how many
would undergo multiple scattering?)
full detector sim. (GRANADA)

• ArDM simulation tasks
• detailed detector geom. (Geant4)
• verifiaction of sim. processes (elastic
  scattering, neutron capture)
• rock neutrons
• neutrons from det. components
• muon-induced neutrons
• other background sources gs, 39Ar

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Geant4 neutron background studies elastic
scattering in liquid Argon
Argon recoil spectra from G4 simulation
Tn 2 MeV
Tn 5 keV
Tn 15 MeV
TnltltMnnon relativistic
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Geant4 neutron background studies rock
neutrons analysis example
SIMULATION - neutron source placed randomly on
the walls of fiducial volume - neutrons going out
of the detector are neglected
Fn 3.810-6 n/(s?cm2) assumed total neutron
flux at the walls of fiducial volume
OUTPUT
IN OUR GEOMETRY1 neutron per 6.5 sec.13200
neutrons per day
10 keV threshold
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Geant4 neutron background studies rock
neutrons analysis example
no of incoming neutrons 13200 n/day
- correction for interacting neutrons Pint 577500 n/day
- correction for multiplicity Pmulti 537500 4000 3500 n/day
correction for spatial resolution (2 cm) 3700n/day
Pinter57
Pmulti53
assumed 2cm spatial resolution
visible95
- shielding (CH2) reduction factor 104-106 1-135 events per year
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Summary Outlook

• ArDM a new project aiming at developing and
  operating a 1 ton-scale liquid Argon detector
  for direct detection of WIMPs
• With a 1 ton prototype we want to show the
  validity of this design (in particular 39Ar
  rejection)
• Neutron shieldings will be addressed in a second
  phase
• Investigations on neutron background sources and
  their interactions inside the detector are also
  performed (simulations in Geant4)
• evaluation of expected number of neutron events
  (data analysis)
• simulations will help to specify requirements for
  detector veto and shielding
• SIMULATIONS OUTLOOK
• Energy spectra and flux of incoming neutrons
• Detailed detector geometry in Geant4

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BACKUP
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Geant4 neutron background studies neutron
capture in liquid Argon
capture on natural Argon(40Ar - 99,6, 36Ar -
0.337, 38Ar - 0.063)
6.099 MeV
Initial neutron energy 10 eV
6.598 MeV
8.788 MeV
Average number of gs produced 3.5