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Dan Akerib

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CDMS II 100x improvement over present limits. Larger array & longer exposure ... Instrument the rock with 2.5 m streamer tubes. ... – PowerPoint PPT presentation

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Title: Dan Akerib


1
Instrumented Rock as Fast-Neutron Veto
  • Dan Akerib
  • Case Western Reserve University
  • with Moshe Katz-Hyman,
  • Thushara Perera, Richard Schnee
  • 10 July 2001
  • Snowmass, Colorado
  • E6.2 Working Group

2
CDMS II
  • CDMS II 100x improvement over present limits
  • Larger array longer exposure
  • Second generation detectors with event positions
  • Ge (WIMP n) and Si (WIMP/10 n)
  • (per unit volume)
  • Deeper site for further reduction in cosmic-ray
    background

Soudan Mine, Northern Minnesota 2300 depth
MINOS
CDMS II
Soudan II
3
CDMS II goals _at_ Soudan (2070 mwe depth)
  • Goal 0.01 evt/kg/day 0.0003 evt/kg/keV/day

99.5 ? rejection
95 ? rejection
0.01 /kg /day
Units /kg/keV/day at 15 keV (5kg Ge, 2kg Si -
2500 kg-days in Ge)
1 per 0.25-kg detector per year
4
Fast Neutron in CDMSII CryoArray
  • Expect dominant component from muon interactions
    in rock
  • Veto in cavity difficult neutrons from 2 3
    meters in
  • Polyethylene shield transparent above 50 MeV
  • Fast neutrons w/present simulations uncertain by
    factor of 10
  • Could be the limiting background in CDMSII
  • For CyroArray, need factor 20 reduction in
    neutron rate relative to CDMSII at Soudan
  • 1000-kg experiment based on CDMS detectors
  • Goal of 100 event sample at 10-46 cm2, with lt100
    background events

5
Neutron Production
  • Use Soudan as Test Case
  • Muon avg energy is 250 GeV
  • Fast neutron production
  • Photonuclear production via muon-induced
    electromagnetic showers
  • nuclear (hadron) cascades via direct
    muon-nucleus interactions
  • Neutron multiplicity number of showers versus
    number of detected neutrons. The curves are Monte
    Carlo simulations, the histograms are
    experimental data at 250-344 GeV from F.F.
    Kalchukov et. al. Hadrons and Other Secondaries
    Generated by Cosmic-Ray Muons Underground. Il
    Nuovo Cimento, Vol. 18 C, N. 5, 1995.

EM
Hadronic
6
Hadron sampling/detection
  • Throw 250GeV muons (vertical, monenergetic) in
    rock w/Soudan size Cavity. Tag as hadron or EM

EM
Hadronic
neutron multiplicty
Mean size (cm)
7
Theres hope
Hadron cascades account for most of the neutrons
entering the cavity
EM
Hadronic
Depth into wall
Mean size (cm)
8
75 of neutrons gt20MeV have gt50cm spread
9
Conclusions etc
  • Common veto signal
  • Experimental hall at National Underground
    Facility with common signal available to
    different experiments
  • Future work
  • More realistic muon distribution
  • Charge particles from ceiling can an umbrella
    boost rejection to 90 or better?
  • Charged particles from the walls?
  • Full simulation including
  • Tubes detectors
  • Wall detectors
  • DM experiment, eg, CDMS II or CryoArray

10
Anatomy of Penetrating Neutron Event
(v)Higher energy (30 MeV) neutron traverses
poly m.f.p 100 cm
(i) 100 GeV µ interacts in rock of tunnel
generating neutron
(iv)Lower energy neutrons moderate in
polyethylene m.f.p 3 cm_at_1 MeV
(ii) 330 MeV neutron from rock
(vi)Following 12 scatters in Cu/poly neutron
(now T100 keV) (vi) scatters in two Ge
detectors (Er5 keV), and then (vii) ultimately
captures on H in poly.
(iii)Pb nucleus shattered9 n (T 0.1-50 MeV)9 g
(E 0.1-2.5 MeV)
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