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Register a new userAnnual and Diurnal Modulations of the Angular Distribution of the 3-D WIMP Velocity Observed at an Underground Laboratory
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Chung-Lin Shan
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In this article, I present our (Monte Carlo) simulation results of the angular distribution of the 3-dimensional WIMP velocity, in particular, a possible annual modulation and the diurnal modulation proposed in literature, for different underground laboratories.
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Various dark matter models predict annual and diurnal modulations of dark matter interaction rates in Earth-based experiments as a result of the Earths motion in the halo. Observation of such features can provide generic evidence for detection of dark matter interactions. This paper reports a search for both annual and diurnal rate modulations in the LUX dark matter experiment using over 20 calendar months of data acquired between 2013 and 2016. This search focuses on electron recoil events at low energies, where leptophilic dark matter interactions are expected to occur and where the DAMA experiment has observed a strong rate modulation for over two decades. By using the innermost volume of the LUX detector and developing robust cuts and corrections, we obtained a stable event rate of 2.3$pm$0.2~cpd/keV$_{text{ee}}$/tonne, which is among the lowest in all dark matter experiments. No statistically significant annual modulation was observed in energy windows up to 26~keV$_{text{ee}}$. Between 2 and 6~keV$_{text{ee}}$, this analysis demonstrates the most sensitive annual modulation search up to date, with 9.2$sigma$ tension with the DAMA/LIBRA result. We also report no observation of diurnal modulations above 0.2~cpd/keV$_{text{ee}}$/tonne amplitude between 2 and 6~keV$_{text{ee}}$.
In this article, we study in a little more detail the angular kinetic-energy distribution of halo Weakly Interacting Massive Particles (WIMPs) and consider two simple modifications with the Solar Galactic orbital velocity in our Monte Carlo simulations of the 3-dimensional WIMP velocity as the first trial of future investigations on distinguishing models of the Galactic structure of Dark Matter particles by using directional direct detection data.
Among the direct search experiments for WIMP dark matter, the DAMA experiment observed an annual modulation signal interpreted as WIMP interactions with 9.2$sigma$ significance. However, this result is contradictory with other direct search experiments reporting null signals in the same parameter space allowed by the DAMA observation, necessitating clarification of the origin of the modulation signal observed using the NaI(Tl) crystals of the DAMA experiment independently. Here, we report the first results of NaI(Tl) crystal measurement at the Yangyang Underground Laboratory to grow ultra-low-background NaI(Tl) crystal detectors.
We argue that comparison with observations of theoretical models for the velocity distribution of pulsars must be done directly with the observed quantities, i.e. parallax and the two components of proper motion. We develop a formalism to do so, and apply it to pulsars with accurate VLBI measurements. We find that a distribution with two maxwellians improves significantly on a single maxwellian. The `mixed model takes into account that pulsars move away from their place of birth, a narrow region around the galactic plane. The best model has 42% of the pulsars in a maxwellian with average velocity sigma sqrt{8/pi}=120 km/s, and 58% in a maxwellian with average velocity 540 km/s. About 5% of the pulsars has a velocity at birth less than 60,km/s. For the youngest pulsars (tau_c<10 Myr), these numbers are 32% with 130 km/s, 68% with 520 km/s, and 3%, with appreciable uncertainties.
We analyze the temporal variation of the diurnal anisotropy of sub-TeV cosmic ray intensity observed with the Matsushiro (Japan) underground muon detector over two full solar activity cycles in 1985-2008. The average sidereal amplitude over the entire period is 0.034+-0.003 %, which is roughly one third of the amplitude reported from AS and deep-underground muon experiments monitoring multi-TeV GCR intensity suggesting a significant attenuation of the anisotropy due to the solar modulation. We find, on the other hand, only weak correlations either with the solar activity- or magnetic-cycles. We examine the temporal variation of the single-band valley depth (SBVD) quoted by the Milagro experiment and, by contrast with recent Milagro reports, we find no steady increase in the Matsushiro observations in a 7-year period between 2000 and 2007. We suggest, therefore, that the steady increase of the SBVD reported by the Milagro experiment is not caused by the decreasing solar modulation in the declining phase of the 23rd solar activity cycle.
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