After having announced the statistically significant observation (5.6σ) of the new exotic πK atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding ...atom lifetime, based on the full πK data sample: τ=(5.5−2.8+5.0)×10−15 s. By means of a precise relation (≈1%) between atom lifetime and scattering length, the following value for the S-wave isospin-odd πK scattering length a0−=13(a1/2−a3/2) has been derived: |a0−|=(0.072−0.020+0.031)Mπ−1.
We reanalize data collected with the DarkSide-50 experiment and recently used to set limits on the spin-independent interaction rate of weakly interacting massive particles (WIMPs) on argon nuclei ...with an effective field theory framework. The dataset corresponds to a total (16660 $\pm$ 270) kg d exposure using a target of low-radioactivity argon extracted from underground sources. We obtain upper limits on the effective couplings of the 12 leading operators in the nonrelativistic systematic expansion. For each effective coupling we set constraints on WIMP-nucleon cross sections, setting upper limits between $2.4 \times 10^{-45} \, \mathrm{cm}^2$ and $2.3 \times 10^{-42} \, \mathrm{cm}^2$ (8.9 $\times 10^{-45} \, \mathrm{cm}^2$ and 6.0 $\times 10^{-42} \, \mathrm{cm}^2$) for WIMPs of mass of 100 $\mathrm{GeV/c^2}$ (1000 $\mathrm{GeV/c^2}$) at 90\% confidence level.
The observation of hydrogenlike πK atoms, consisting of π^{-}K^{+} or π^{+}K^{-} mesons, is presented. The atoms are produced by 24 GeV/c protons from the CERN PS accelerator, interacting with ...platinum or nickel foil targets. The breakup (ionization) of πK atoms in the same targets yields characteristic πK pairs, called "atomic pairs," with small relative momenta Q in the pair center-of-mass system. The upgraded DIRAC experiment observed 349±62 such atomic πK pairs, corresponding to a signal of 5.6 standard deviations. This is the first statistically significant observation of the strange dimesonic πK atom.
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogenlike π^{+}π^{-} atoms, produced by protons hitting a beryllium target. A part of these atoms ...crossed the gap of 96 mm between the target and a 2.1 μm thick platinum foil, in which most of them dissociated. Analyzing the observed number of atomic pairs, n_{A}^{L}=436_{-61}^{+157}|_{tot}, the lifetime of the 2p state is found to be τ_{2p}=(0.45_{-0.30}^{+1.08}|_{tot})×10^{-11} s, not contradicting the corresponding QED 2p state lifetime τ_{2p}^{QED}=1.17×10^{-11} s. This lifetime value is three orders of magnitude larger than our previously measured value of the π^{+}π^{-} atom ground state lifetime τ=(3.15_{-0.26}^{+0.28}|_{tot})×10^{-15} s. Further studies of long-lived π^{+}π^{-} atoms will allow us to measure energy differences between p and s atomic states and so to discriminate between the isoscalar and isotensor ππ scattering lengths with the aim to check QCD predictions.
The results of a search for hydrogen-like atoms consisting of π∓K± mesons are presented. Evidence for πK atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been ...seen in terms of characteristic πK pairs from their breakup in the same target (178±49) as well as in terms of produced πK atoms (653±42). Using these results, the analysis yields a first value for the πK atom lifetime of τ=(2.5−1.8+3.0) fs and a first measurement of the S-wave isospin-odd πK scattering length |a0−|=13|a1/2−a3/2|=(0.11−0.04+0.09)Mπ−1 (aI for isospin I).
The DIRAC spectrometer installed at CERN PS was upgraded in order to study simultaneously A2π and AπK atoms, namely the bound states of two π mesons, and of π and K mesons, respectively. The detector ...system can now accept a high intensity beam of 2–6×1011 primary protons per second. The electronics and the data-acquisition system can handle a very large amount of data to identify π, K, p, e and µ, allowing the selection of ππ and πK pairs in the offline analysis. The resolution of the longitudinal and transverse components of the relative momentum Q of each meson pair in their center-of-mass system with respect to the direction of the pair was substantially improved. The analysis of their distributions allowed an reliable separation between the meson pairs originating from hadronic atoms and the backgrounds permitting the measurement of the lifetimes of hadronic atoms in the ground state and π–π, π–K s-wave scattering lengths. The upgraded setup also allowed the study of the long-lived excited states of ππ atoms.
We present new constraints on sub-GeV dark-matter particles scattering off electrons based on 6780.0 kg d of data collected with the DarkSide-50 dual-phase argon time projection chamber. This ...analysis uses electroluminescence signals due to ionized electrons extracted from the liquid argon target. The detector has a very high trigger probability for these signals, allowing for an analysis threshold of three extracted electrons, or approximately 0.05 keVee. We calculate the expected recoil spectra for dark matter- electron scattering in argon and, under the assumption of momentum-independent scattering, improve upon existing limits from XENON10 for dark-matter particles with masses between 30 and 100 MeV/c2.
Barkas effect for antiproton stopping in H2 Lodi Rizzini, E; Bianconi, A; Bussa, M P ...
Physical review letters,
2002-Oct-28, 20021028, Letnik:
89, Številka:
18
Journal Article
Recenzirano
We report the stopping power of molecular hydrogen for antiprotons of kinetic energy above the maximum (approximately 100 keV) with the purpose of comparing with the proton one. Our result is ...consistent with a positive difference in antiproton-proton stopping powers above approximately 250 keV and with a maximum difference between the stopping powers of 21%+/-3% at around 600 keV.
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