Dark Matter search

TL;DR

The WIMP direct detection technique is mainly considered and recent results obtained by exploiting the annual modulation signature are summarized.

Abstract

Main arguments on the Dark Matter particle direct detection approach are addressed on the basis of the work and of the results of the about 100 kg highly radiopure NaI(Tl) DAMA experiment (DAMA/NaI), which has been operative at the Gran Sasso National Laboratory of the I.N.F.N. for more than one decade, including the preparation. The effectiveness of the WIMP model independent annual modulation signature is pointed out by discussing the results obtained over 7 annual cycles (107731 kg day total exposure); the WIMP presence in the galactic halo is strongly supported at 6.3 standard deviation C.L. The complexity of the corollary model dependent quests for a candidate particle is also addressed and several of the many possible scenarios are examined.

Figures (32)

• Figure 1: Exclusion plot in the plane axion to photon coupling constant, $g_{a \gamma \gamma}$, versus axion mass, $m_a$, achieved by DAMA/NaI in ref. Dax. The limit quoted in the paper ($g_{a \gamma \gamma}\le 1.7 \times 10^{-9} GeV^{-1}$ at 90% C.L.) is shown together with the expectations of the KSVZ and DFSZ models; see ref.Dax for details.
• Figure 2: Relic abundance of an heavy neutrino as a function of its mass according to the calculation of ref. Fa95; masses above the $Z_0$ pole are considered.
• Figure 3: Example of the effects due to the uncertainties in a given model framework when calculating exclusion plots. Here the simple case for the halo local velocity, $v_0$, and the escape velocity, $v_{esc}$, is shown in case of spin-dependent coupled WIMPs as from ref. Caf94. The top curve for each nucleus has been calculated -- in a given model framework -- assuming $v_0 = 180$ km/s and $v_{esc} = 500$ km/s, while the lower one has been calculated assuming $v_0 = 250$ km/s and $v_{esc} = 1000$ km/s; all the considered values are possible at present stage of knowledge. Analogous effects will be found for every kind of experimental result when varying experimental/theoretical parameters/assumption for whatever target-nucleus.
• Figure 4: Left: schematic representation of the experimental approach considered in ref. anisotr to investigate the correlation between the recoil direction and the Earth velocity direction by using anisotropic scintillators. The anisotropic scintillator is placed ideally at LNGS with $c'$ axis in the vertical direction and $b$ axis pointing to the North. The area in the sky from which the WIMPs are preferentially expected is highlighted. Right: expected rate, in the 3-4 keV energy window, versus the detector (or Earth) possible velocity directions. This example refers to the particular assumptions of a WIMP mass equal to 50 GeV, a WIMP-proton cross section equal to $3\cdot 10^{-6}$ pb and to the model framework of ref. anisotr. The dependence on the "polar-azimuth" angle ($\phi_{pa}$) induces a diurnal variation of the rate.
• Figure 5: Schematic description of the approach which correlates the time occurrence of each event with the diurnal rotation of the Earth. Left: the $\theta$ angle (defined by the Earth velocity in the Galactic frame with the vector joining the center of the Earth to the position of the laboratory) as a function of the sidereal time; here the case for the Gran Sasso National Laboratory of the I.N.F.N. is considered. Right: signal rate expected in the 2--6 keV energy interval when assuming a 60 GeV WIMP mass, a WIMP-proton cross section equal to: a) $7.0\cdot 10^{-6}$ pb, b) $5\cdot 10^{-2}$ pb, c) $10^{-1}$ pb, d) $1.0$ pb, and the model framework of ref. Diu99.