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)