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Register a new userThe first search for bosonic super-WIMPs with masses up to 1 MeV/c$^2$ with GERDA
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We present the first search for bosonic super-WIMPs as keV-scale dark matter candidates performed with the GERDA experiment. GERDA is a neutrinoless double-beta decay experiment which operates high-purity germanium detectors enriched in $^{76}$Ge in an ultra-low background environment at the Laboratori Nazionali del Gran Sasso (LNGS) of INFN in Italy. Searches were performed for pseudoscalar and vector particles in the mass region from 60 keV/c$^2$ to 1 MeV/c$^2$. No evidence for a dark matter signal was observed, and the most stringent constraints on the couplings of super-WIMPs with masses above 120 keV/c$^2$ have been set. As an example, at a mass of 150 keV/c$^2$ the most stringent direct limits on the dimensionless couplings of axion-like particles and dark photons to electrons of $g_{ae} < 3 cdot 10^{-12}$ and ${alpha}/{alpha} < 6.5 cdot 10^{-24}$ at 90% credible interval, respectively, were obtained.
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Bosonic super-WIMPs, including pseudoscalar and vector particles, are dark matter candidates. Until now, many underground experiments searches for super-WIMPs have been performed in the mass range of a few $rm keV/c^2$ to 1 $rm MeV/c^2$. All these searches utilize the absorption process of a super-WIMP by a target atom in the detector, which is similar to the photoelectric effect. In this study, we consider another process, namely, a Compton-like process. As an example, we compare the cross-section of a germanium atom for the absorption process with that of a Compton-like process. Our findings indicate that the cross-section for the Compton-like process becomes dominant, compared to that for the absorption process for mass above approximately 150 $rm keV/c^2$ for both pseudoscalar and vector super-WIMPs. In particular, the cross-section for the Compton-like process for a vector super-WIMP becomes increasingly greater than that for the absorption process by an order of magnitude to two orders of magnitude in the 400 $rm keV/c^2$ to 1 $rm MeV/c^2$ mass range, respectively. By including the Compton-like process, which has not been used in any other super-WIMP search experiment, the experimental upper limits can be improved.
We report a first search for weakly interacting massive particles (WIMPs) using the background rejection capabilities of SuperCDMS. An exposure of 577 kg-days was analyzed for WIMPs with mass < 30 GeV/c2, with the signal region blinded. Eleven events were observed after unblinding. We set an upper limit on the spin-independent WIMP-nucleon cross section of 1.2e-42 cm2 at 8 GeV/c2. This result is in tension with WIMP interpretations of recent experiments and probes new parameter space for WIMP-nucleon scattering for WIMP masses < 6 GeV/c2.
Two neutrino double beta decay of $^{76}$Ge to excited states of $^{76}$Se has been studied using data from Phase I of the GERDA experiment. An array composed of up to 14 germanium detectors including detectors that have been isotopically enriched in $^{76}$Ge was deployed in liquid argon. The analysis of various possible transitions to excited final states is based on coincidence events between pairs of detectors where a de-excitation $gamma$ ray is detected in one detector and the two electrons in the other. No signal has been observed and an event counting profile likelihood analysis has been used to determine Frequentist 90,% C.L. bounds for three transitions: ${0^+_{rm g.s.}-2^+_1}$: $T^{2 u}_{1/2}>$1.6$cdot10^{23}$ yr, ${0^+_{rm g.s.}-0^+_1}$: $T^{2 u}_{1/2}>$3.7$cdot10^{23}$ yr and ${0^+_{rm g.s.}-2^+_2}$: $T^{2 u}_{1/2}>$2.3$cdot10^{23}$ yr. These bounds are more than two orders of magnitude larger than those reported previously. Bayesian 90,% credibility bounds were extracted and used to exclude several models for the ${0^+_{rm g.s.}-0^+_1}$ transition.
We present results of searches for vector and pseudo-scalar bosonic super-WIMPs, which are dark matter candidates with masses at the keV-scale, with the XENON100 experiment. XENON100 is a dual-phase xenon time projection chamber operated at the Laboratori Nazionali del Gran Sasso. A profile likelihood analysis of data with an exposure of 224.6 live days $times$ 34,kg showed no evidence for a signal above the expected background. We thus obtain new and stringent upper limits in the $(8-125)$,keV/c$^2$ mass range, excluding couplings to electrons with coupling constants of $g_{ae} > 3times10^{-13}$ for pseudo-scalar and $alpha/alpha > 2times10^{-28}$ for vector super-WIMPs, respectively. These limits are derived under the assumption that super-WIMPs constitute all of the dark matter in our galaxy.
New Crystal Barrel data are reported for pbar-p -> omega-pizero and pbar-p -> omega eta-pizero with omega decaying to piplus-piminus-pizero. The shapes of angular distributions agree well with those for data where omega -> pizero-gamma; this is a valuable cross-check on systematic errors. The new data provide good measurements of vector and tensor polarisations P_y, T20, T21 and T22 of the omega. These lead to significant improvements in parameters of several resonances reported earlier. New values of masses and widths (in Mev) are: J^PC = 5^-- (2300+-45, 260+-75), J^PC = 3^-- (2260+-20, 160+-25), J^PC = 1^+- (2240+-35, 320+-85), and J^PC = 1^-- (2110+-35, 230+-50). A remarkable feature of the data is that vector polarisation P_y is close to zero everywhere. It follows that all interfering amplitudes have relative phases close to 0 or 180 deg. Tensor polarisations are large.
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