Possible merits of high pressure Xe gas for dark matter detection C J Martoff (Temple) & P F Smith...
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Transcript of Possible merits of high pressure Xe gas for dark matter detection C J Martoff (Temple) & P F Smith...
Possible merits of high pressure Xe gas for dark matter detection
C J Martoff (Temple) & P F Smith (RAL, Temple)
• most dark matter experiments use cryogenic solid or liquid targets
semiconductors
crystals
noble liquids
phonons
ionisation
scintillation
• Ionization & scintillation signals available also from gases at normal temperature. • Could provide reasonable size competitive detectors at 5-10 bar
Brief history of dark matter detectors
<-- 1986 --> 1990 2000
Bolometers for Cabrera, Fiorini, Stodolski, vonFeilitzsch, Seidel, Pretzl…
Semiconductors for Avignone, Caldwell, Boehm…
Crystal scintillators forparticle detection Owen (1959), Doll….
Liquid Ar &Xe studies for solar & rare events Rubbia, Cline, Aprile…..
Noble gas studies forcharged particles & M Suzuki, Saito, Flaks….. Edberg, Sadoulet……
Ionizaton/ bolometers
NaI, CsI pulse shape
Liquid Xe ioniz’n/scint’n
Liquid Ar ioniz’n/scint’n
Suggested high pressure noble gas DM exptsRAL, RAL/Ohio, HELLAZ, SIGN Funding for r&d relatively small
Balloon Xe gas X-ray telescopes SIGHT, AXEL
Low bkgrd Ge
scintillation
Signal options
pmts
electric field
electric field
ionization
both
Field reduces recombination scintillation output, but more measurements needed.
target gas
Assume scintillation only
Scintillation pulse shape discrimination in Xe gas(zero electric field)
0.001
0.01
0.1
0 500 1000 1500 2000 2500
time ns
light output/ns normalised to 1
gamma pulse
alpha pulse
M Suzuki 1982 NIM 192, 623
0.1
1
10
100
1000
10000
100000
1000000
0 1000 2000 3000
time cut t = t1 ns
number of events for t > t1
1000000 background gammas
20 nuclear recoils
Signal sensitivity versus total background
Thus nuclear recoil population of 20 recoils/year detectable for background 1E6 gammas/year
1.0
10.0
100.0
1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10
total background gamma events
significant number of recoils
90% significant number of recoils
Possible module sizes
R8778 pmts inside vessel 0.6m
copper vessel
Xe gas @ 10 bar = 34kg
2 m
2.5 m
0.75m
Xe gas @ 5 bar = 34kg
Neutron & Gamma/beta Backgrounds
muonmuon
rock U/Th/K
n
n
pmts U/Th
n,
n,
Cu detector vessel U/Th
Kr85 in Xe
water /n shield
n,
Low energy background levels
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
1.0E+04
1.0E+05
1.0E+06
0 200 400 600
Water thickness cm
Events/kg/day
gammas from rock
neutrons from rock U/Th
neutrons from rock muons
neutrons from water muons
DM sensitivity 1E-8 pb
DM sensitivity 1E-10 pb
<------ gammas from Cu vessel 0.1ppb U/Th
<------ gammas from pmts 2 inch R8778
<------ n from metal vessel 0.1ppb U/Th-------
<----------- n from R8778 PMTs
possible WIMP sensitivity
Example 1 2m x 0.6m module at 10 bar (34kg) with 3m water shieldLight collection estimate gives energy threshold 2-3 keV
Total gamma background < 40 keV = 70/kg/d = 8E5/yearTotal neutron background < 40 keV = 4E-4/kg/d = 5/year
90% Poisson recoil limit / efficiency = (20+5)/year = 2E-3/kg/d
Equivalent WIMP proton cross section in 360 days = 2E-9pb
Example 212 modules (400kg) with n backgrounds reduced 1/10 by veto
90% Poisson recoil limit / efficiency = (28 +6)/year = 2.4E-4/kg/d
Equivalent WIMP proton cross section in 360 days = < 3E-10pb
Illustrative 1000 kg gas detector systemBased on individual Xe modules with local pmts
Some modules with Ar or Ar/Xe to confirm A2 dependence
water shield
30 x 2m x 0.6m (34kg) modules
End planes of pmts
Alternative large scale configuration suggested by F Calaprice (Princeton) - based on Borexino principles
Target vessels with transparent silica walls + wavelength shifters
water shield
surrounding water-shielded pmt array
optional scintillator veto region
Preliminary conclusions
• If nuclear recoils give pulse shapes similar to alphas then DM sensitivity levels in range 1E-8 - 1E-9pb possible for gas target masses 30-100kg, using scintillation only.
• Assessment of simultaneous ionization/scintillation signals requires new measurements.
• Sensitivity 1E-9 - 1E-10pb possible with 100-1000kg and existing pmt backgrounds. Target sizes reasonable for 5-10 bar gas pressure.
• Different gases easily compared for A-dependence.
• Room temperature simplifies design and operation. Large mass gas experiments could be lower-cost than mK bolometers and noble liquids for same sensitivity.