Annual Modulation Signal Research Articles

Results from the 1998–1999 runs of the cryogenic dark matter search

The Cryogenic Dark Matter Search (CDMS) uses low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interaction with atomic nuclei while discriminating against interactions of background particles. CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section are lower than those of any other experiment for WIMPs with masses between 10–70 GeV c −2. Under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit.

Searching for the dark universe by the DAMA experiment

DAMA is searching for rare processes by developing and using several kinds of radiopure scintillators. In particular, here the results released so far on the WIMP annual modulation signature are discussed and next perspectives are shortly addressed.

Dark Matter search

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.

Exclusion limits on the WIMP-nucleon cross section from the Cryogenic Dark Matter Search

The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si detectors to search for Weakly Interacting Massive Particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. For recoil energies above 10 keV, events due to background photons are rejected with >99.9% efficiency, and surface events are rejected with >95% efficiency. The estimate of the background due to neutrons is based primarily on the observation of multiple-scatter events that should all be neutrons. Data selection is determined primarily by examining calibration data and vetoed events. Resulting efficiencies should be accurate to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent with an earlier analysis with a more restrictive fiducial-volume cut. Twenty-three WIMP candidate events are observed, but these events are consistent with a background from neutrons in all ways tested. Resulting limits on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}. These limits border, but do not exclude, parameter space allowed by supersymmetry models and accelerator constraints. Results are compatible with some regions reported as allowed at 3-sigma by the annual-modulation measurement of the DAMA collaboration. However, under the assumptions of standard WIMP interactions and a standard halo, the results are incompatible with the DAMA most likely value at >99.9% CL, and are incompatible with the model-independent annual-modulation signal of DAMA at 99.99% CL in the asymptotic limit.

Mass and scalar cross sections for neutralino dark matter in the anomaly mediated supersymmetry breaking model

We consider the neutralino to be the lightest supersymmetric particle in the framework of the minimal anomaly mediated supersymmetry breaking (mAMSB) model. We have studied the variation of the neutralino mass with the supersymmetric parameters. Considering these neutralinos to be candidates for weakly interacting massive particles (WIMPs) or cold dark matter, we have calculated the neutralino nucleon scalar cross sections and compared them with the results of the DAMA-NaI neutralino direct detection search. From this study, we observe that the mAMSB model results cannot explain the allowed region in WIMP mass and WIMP–nucleon scalar cross-section space obtained from the annual modulation signature in the DAMA-NaI experiment.

Effect of the galactic halo modeling on the DAMA-NaI annual modulation result: An extended analysis of the data for weakly interacting massive particles with a purely spin-independent coupling

The DAMA-NaI Collaboration has observed a $4\ensuremath{\sigma}$ C.L. model-independent effect investigating the annual modulation signature in the counting rate of an NaI(Tl) setup (total exposure of 57986 kg day) and the implications of this effect have been studied under different model-dependent assumptions. In this paper we extend one of the previous analyses, the case of a WIMP with a purely spin-independent coupling, by discussing in detail the implications on the results of the uncertainties on the dark matter galactic velocity distribution. We study in a systematic way possible departures from the isothermal sphere model, which is the parametrization usually adopted to describe the halo. We specifically consider modifications arising from various matter density profiles, effects due to anisotropies of the velocity dispersion tensor and rotation of the galactic halo. The hypothesis of WIMP annual modulation, already favored in the previous analysis using an isothermal sphere, is confirmed in all the investigated scenarios, and the effects of the different halo models on the determination of the allowed maximum-likelihood region in the WIMP mass and WIMP-nucleon cross section are derived and discussed.

Results with the DAMA/NaI(Tl) experiment at LNGS

DAMA experiment is an observatory for rare events mainly devoted to WIMP search at the Gran Sasso National Laboratory of the I.N.F.N.. In this paper, the results obtained with the ⋍ 100 kg NaI(Tl) set-up will be summarized, pointing out in particular those regarding the investigation of the WIMP annual modulation signature.

Results of the DAMA experiment at LNGS

DAMA is searching for rare processes by developing and using several kinds of radiopure scintillators: in particular, NaI(Tl), liquid Xenon and CaF2(Eu). Here more recent results are summarized with particular attention to the investigation of the WIMP annual modulation signature.

Results of the DAMA experiment at LNGS

DAMA is searching for rare processes by developing and using several kinds of radiopure scintillators: in particular, NaI(Tl), liquid Xenon and CaF 2 (Eu). Here more recent results are summarized with particular attention to the investigation of the WIMP annual modulation signature.

GENIUS-TF: a test facility for the GENIUS project

GENIUS is a proposal for a large scale detector of rare events. As a first step of the experiment, a small test version, the Genius Test-Facility will be built at the Laboratori Nazionali del Gran Sasso. With about 40 kg of natural Ge detectors operated in liquid nitrogen, GENIUS-TF could exclude (or directly confirm) the DAMA annual modulation seasonal modulation signature within about 2 yr of measurement using both, signal and signature of the claimed WIMP Dark Matter. The construction of the experiment has already been started, and four 2.5 kg germanium detectors with an extreme low threshold of 500 eV have been produced.

Dark Matter search

Some general arguments on the particle Dark Matter search are addressed. The WIMP direct detection technique is mainly considered and recent results obtained by exploiting the annual modulation signature are summarized.

Investigating the DAMA annual modulation data in a mixed coupling framework

Abstract In this Letter the data, collected by the ≃100 kg NaI(Tl) DAMA set-up deep underground in the Gran Sasso National Laboratory of I.N.F.N. during four annual cycles (57986 kg day statistics), are analyzed in terms of WIMP annual modulation signature considering a candidate with mixed coupling to ordinary matter.

Nucleon scattering with Higgsino andW-ino cold dark matter

Neutralinos that are mostly wino or higgsino are shown to be compatible with the recent DAMA annual modulation signal. The nucleon scattering rates for these dark matter candidates are typically an order of magnitude above the oft-considered bino. Although thermal evolution of higgsino and wino number densities in the early universe implies that they are not viable dark matter candidates, non-thermal sources, such as from gravitino or moduli decay in anomaly mediated supersymmetry breaking, suggest that they can be the dominant source of cold dark matter. Their stealthiness at high energy colliders gives even more impetus to analyze nucleon scattering detection methods. We also present calculations for their predicted scattering rate with Germanium detectors, which have yet to see evidence of WIMP scattering.

Weakly interacting massive particle annual modulation signal and nonstandard halo models

Currently the best prospect for detecting weakly interacting massive particles (WIMPs) is via the annual modulation, which occurs due to the Earth's rotation around the Sun, of the direct detection signal. We investigate the effect of uncertainties in our knowledge of the structure of the galactic halo on the WIMP annual modulation signal. We compare the signal for three non-standard halo models: Evans' power-law halos, Michie models with an asymmetric velocity distribution and Maxwellian halos with bulk rotation. We then compare the theoretical predictions of these models with the experimental signal found by the DAMA experiment and investigate how the WIMP mass and interaction cross section determined depend on the halo model assumed. We find that the WIMP mass confidence limits are significantly extended to larger masses, with the shape of the allowed region in the mass--cross-section plane depending on the model.

Searching for signals from the dark universe by DAMA at Gran Sasso

The DAMA set-ups are running deep underground in the Gran Sasso National Laboratory of the I.N.F.N.. Results of various rare event searches have been achieved. In particular, the results obtained in the investigation of the WIMP annual modulation signature obtained in four annual cycles (total statistics: 57986 kg · day) are summarized.

On the investigation of possible systematics in WIMP annual modulation search

An investigation of the WIMP annual modulation signature is in progress at the Gran Sasso National Laboratory of the I.N.F.N. by means of the similar or equal to 100 kg NaI(TI) DAMA set-up; the results obtained during four annual cycles have already been published. In this paper we will further address in some details the main arguments, which have allowed us to exclude known systematic effects as a possible source of the annual modulation observed in the rate at very low energy. In particular. the (more recently released) data of the DAMA/NaI-3 and DAMA/NaI-4 running periods are considered as quantitative examples.

Sensitivity plots for WIMP direct detection using the annual modulation signature

Annual modulation due to the Earth's motion around the Sun is a well-known signature of the expected weakly interacting massive particle (WIMP) signal induced in a solid state underground detector. In the present paper, we discuss the prospects of this technique on statistical grounds, introducing annual-modulation sensitivity plots for the WIMP–nucleon scalar cross-section for different materials and experimental conditions. The highest sensitivity to modulation is found in the WIMP mass interval 10≲ m W≲130 GeV, the actual upper limit depends on the choice of the astrophysical parameters, while the lowest values of the explorable WIMP–nucleon elastic cross-sections fall in most cases within one order of magnitude of the sensitivities of the present direct detection WIMP searches.

Triaxial haloes and particle dark matter detection

This paper presents the properties of a family of scale-free triaxial haloes. We adduce arguments to suggest that the velocity ellipsoids of such models are aligned in conical coordinates. We provide an algorithm to find the set of conically aligned velocity second moments that support a given density against the gravity field of the halo. The case of the logarithmic ellipsoidal model –the simplest triaxial generalization of the familiar isothermal sphere– is examined in detail. The velocity dispersions required to hold up the self-consistent model are analytic. The velocity distribution of the dark matter can be approximated as a triaxial Gaussian with semiaxes equal to the velocity dispersions. There are roughly 20 experiments worldwide that are searching for evidence of scarce interactions between weakly interacting massive-particle dark matter (WIMP) and detector nuclei. The annual modulation signal, caused by the Earth's rotation around the Sun, is a crucial discriminant between WIMP events and the background. The greatest rate is in June, the least in December. We compute the differential detection rate for energy deposited by the rare WIMP–nucleus interactions in our logarithmic ellipsoidal halo models. Triaxiality and velocity anisotropy change the total rate by up to ∼40 per cent, and have a substantial effect on the amplitude of the annual modulation signal. The overall rate is greatest, but the amplitude of the modulation is weakest, in our radially anisotropic halo models. Even the sign of the signal can be changed. Restricting attention to low energy events, the models predict that the maximum rate occurs in December, and not in June.

Sensitivity plots for WIMP modulation searches

Prospects of WIMP searches using the annual modulation signature are discussed on statistical grounds, introducing sensitivity plots for the WIMP-nucleon scalar cross section.

Dark matter search with the DAMA experiments

DAMA experiments are running deep underground in the Gran Sasso National Laboratory of I.N.F.N. Results on various rare event searches and, in particular, on WIMP annual modulation signature have been achieved.