Earth’s Minerals as time-integrated detectors for Axions. Anastasios Liolios Physics Department Aristotle University of Thessaloniki K. Zioutas G.Kitis G.Polymeris N.Tsirliganis. Overview. Axions what are they? sources Dose Rate in matter from natural sources from axions
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what are they?
from natural sources
excellent candidate for dark matter
Axion phenomenology is determined by its mass ma, which in turn is fixed by the scalefa of the Peccei-Quinn symmetry breaking:
A combination of cosmological, astrophysical and nuclear physics constraints, restricts the allowed range of viable axion masses into:
10-6 eV < ma < 10-2 eV
This range suggests a range for the coupling constant, gaγγ, which is proportional to ma :
gaγγ(GeV -1) = 10-10·ma(eV)
The axion-photon-photon coupling constant gαγγ is the same for both types
Axions is expectedto be produced in the core of the stars via the Primakoff effect which converts the blackbody photons into axions in the electric field of the plasma constituents.
When the Galaxy was formed, cold dark matter clustered with luminous matter.
Halo contains the most of the mass of the Milky Way, presumably in the form of cold dark matter.
Rotation curve of a spiral galaxy.
Density → ρDM ~ 0.3 GeV/cm3
Dark Matter candidates beyond the SM:
WIMPs (SS)&Axions (QCD, CP)
Φsolar = 3.5·1011 ·(1010·gaγγ)2 =
= 3.5·1011·ma2 (cm-2 s-1)
A method for setting boundson dark matter particle characteristicsby using natural dosimeters.
Estimation of bounds
for the axion coupling constantgaγγ,
as time-integrating luminescence detectors.
DR = 1,6·10-16Φ·σ·Ν·Ε (Gy/sec) (1 Gy = 1 J/kg)
Φi (cm-2s-1) is total flux of particles at earth,
σ (cm2) is the total cross section of their interaction with ordinary matter,
E (eV) is the energy of the particles, N ~ 1023 is the number of atoms/gr of earth’s matter
axion to photon conversion
dose accumulated in a material
(Creswick et al., Phys.Lett. B 427(1998)235)
Total cross section for elastic axion to photon conversionin the presence of a nucleus with charge Z:
where n = r0k, (r0 the screening length of atoms, k the photon-axion momentum).
The first bracket is proportional to Z2 and (gaγγ)2 αnd for gaγγ= 10-8 GeV-1
it takes the values of ~2∙10-45 cm2for Z = 14 (Si) and ~0.7∙10-45 cm2for Z = 8 (O) .
The values of the second bracket (the coherence term) change from 1 to 10 for energy in the range above 1 keV. On the contrary, it goes down very fast for energies below 1 keV, reaching 10-9 for the energy of 1 keV.
The cross section (per atom) integrated over the energy range 0 to 12 keV is:
σ ≈ (10-28 cm2)∙g2aγγ ≈ (10-48 cm2)∙ma2
or (for gaγγ = 10-8GeV-1):σ ≈ (10-44 cm2)∙
The associated Dose Rate from axions is a function of axion's coupling constant gaγγ or, alternatively, of its rest mass. Since DR is proportional to Φ and to σ (~ ma2) :
DR ~ Φ·σ
it will be proportional to ma4 in the case of solar axions (Φ ~ ma2) and proportional to ma in the case of galactic axions(Φ ~ 1/ma).
Dose Rate from solar axions:
DR≈ 10-14 ma4Gy/year
Dose Rate from relic axions:
DR = 5·10-18 ·maGy/year
with a mean energy of ~0.25 MeV.
σ ≈ 10-47cm2Ev / MeV
for νen→e-p or anti-νe p→e+p , . . ., inelastic (charged-current events)
DRv≈ 10-24(Gy/sec) ≈ 3·10-17(Gy/yr)
This is lower than the DR from solar axions for ma above ~ 0.1 eV.
the proposed method is applicable for ma> 0.1 eV gaγγ > 10-11 GeV-1
Geologicalmaterials receive a total dose from:
Apossible dose excess could be attributed to axions
estimation of gaγγ limits
The dose is measured by
Thermoluminescence and Optically Stimulated Luminescence.
Thermoluminescence (TL) or Optically Stimulated Luminescence (OSL) techniques measure the accumulated dose in a material which was exposed to radiation.
As the material is heated or exposed to light,
a light signal, proportional to the dose, is produced.
Natural TL/OSL dosimeters
problems: signal fading and high dose thresholds
(Dose Rate)·(Stability Time Period of the TL/OSL)>(Lowest Detectable Dose Limit)
DR·P > LDDL
andStability Time Period of the TL/OSL signal: P < 5·108 yr
This corresponds to a solar axion mass: mα > 2.5 eV →gaγγ> 2.5·10-10 GeV-1
The method could detect doses from solar axions
with mass ma > 1 eV →gaγγ > 10-10 GeV-1
Assumption: ideal TL/OSL samples
no contribution from natural radioactivity
no contribution from cosmic rays
For solar axions:
gaγγ = 10-10 GeV-1 using natural CaF2
gaγγ = 2.5·10-10 GeV-1 using SiO2
gaγγ= 4·10-8 GeV-1 (KOUPA samples)
gaγγ= 7·10-8 GeV-1 (NESTOR samples)
“Minerals as Time-Integrating Luminescence Detector for setting bounds on Dark Matter Particles Characteristics” NIM A in print