After observing and investigating the double-exotic (a double-exotic atom is a bound system, in which both oppositely charged components are unstable particles like μ,π,K,…) π+π− atom with the ground ...state lifetime τ of about 3×10−15 s, the upgraded DIRAC experiment at the CERN PS accelerator observes for the first time long-lived states of the same atom with lifetimes of about 10−11 s and more. The number of characteristic pion pairs resulting from the breakup (ionisation) of long-lived π+π− atoms amounts to 436±61, corresponding to a signal-to-error ratio of better than 7 standard deviations. This observation opens a new possibility to measure energy differences between p and s atomic states and so to determine ππ scattering lengths.
The basic goal of this work is the development of investigation technique of space-time parameters of broadband oscillator of the powerful Luch Facility of the Russian Federal Nuclear Center designed ...to smooth radiation profile during passage of fiber optical line. The smoothing is achieved by means of modes mixing because of wave length dispersion in fiber optics, as a result the speckled radiation structure is removed. The optical scheme for recording radiation and the photochronograph with slot scan have been prepared to carry out measurements. The measurements of duration, impulse shape and space-time heterogeneity of laser radiation at output of formation system of reference radiation with fiber optical smoothing were carried out using that developed technique.
Selenium is an essential component of more than two dozen enzymes and other selenoproteins that play critical roles in reproduction, DNA synthesis, thyroid hormone metabolism, and protection from ...oxidative damage and infection. Selenium has a protective action against some forms of cancer and cardiovascular diseases, modulates levels of inflammatory mediators, promotes to maintain bone homeostasis and protects against bone loss. Selenium significance as a cardioprotective agent may be associated not only with its antioxidant properties, but also with its ability to prevent inflammation, autophagy, as well as the intrinsic and extrinsic apoptosis pathways. Signaling pathways, such as p-AMPK, PARP, Nrf2, STAT, are involved in the protective effects of selenium. Selenium protects against cardiovascular damage by increasing the survival rate of cardiomyocytes, including a mitochondria-dependent pathway and autophagy through peroxisome proliferator-activated receptors. Research demonstrating neuroprotective and cardioprotective effects of selenium preparations – selenoline, selenocysteine and selenomethionine – is growing at a rapid rate. It has been established that these compounds are able to normalize the levels of heat shock proteins (HSP70), which limit the cytotoxic effects of free radicals, produce energotropic action, prevent a decrease in the membrane mitochondria charge, and the opening of the mitochondrial pore. Also regulate the expression of transmembrane factors NF-kB, c-fos, which is associated with their main biological function of chaperone proteins, providing protection of neurons from damage. In this review, we want to emphasize pharmacological role of Selenium and its derivatives on human health is very complex and has yet to be fully understood.
The goal of the DIRAC experiment at CERN (PS212) is to measure the π+π− atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the S-wave ππ scattering ...lengths combination |a0−a2|. Based on part of the collected data we present a first result on the lifetime, τ=2.91−0.62+0.49×10−15 s, and discuss the major systematic errors. This lifetime corresponds to |a0−a2|=0.264−0.020+0.033mπ−1.
The DarkSide-50 direct-detection dark matter experiment is a dual-phase argon time projection chamber operating at Laboratori Nazionali del Gran Sasso. This paper reports on the blind analysis of a ...(16 660±270) kg d exposure using a target of low-radioactivity argon extracted from underground sources. We find no events in the dark matter selection box and set a 90% C.L. upper limit on the dark matter–nucleon spin-independent cross section of 1.14×10−44 cm2 (3.78×10−44 cm2, 3.43×10−43 cm2) for a WIMP mass of 100 GeV/c2 (1 TeV/c2, 10 TeV/c2).
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/c^{2}.
The Obelix experiment at CERN collected samples of antiproton annihilations at rest in different gaseous targets, such as hydrogen, deuterium and helium. We analyze a set of the Obelix data using a ...new technique for measuring, for the first time, the cascade times independent of the capture energy and of the antiproton stopping power. We report on measurements of the cascade times for hydrogen at 3.4, 5.8, 9.8 and 150 mbar and for helium at 8.2, 50 and 150 mbar pressure. An estimate of the antiproton capture energy in hydrogen is also presented.
DarkSide-50 has demonstrated the high potential of dual-phase liquid argon time projection chambers in exploring interactions of WIMPs in the GeV/c2 mass range. The technique, based on the detection ...of the ionization signal amplified via electroluminescence in the gas phase, allows us to explore recoil energies down to the sub-keV range. We report here on the DarkSide-50 measurement of the ionization yield of electronic recoils down to ~ 180 eVer, exploiting 37Ar and 39Ar decays, and extrapolated to a few ionization electrons with the Thomas-Imel box model. Moreover, we present a model-dependent determination of the ionization response to nuclear recoils down to ~ 500 eVnr, the lowest ever achieved in liquid argon, using in situ neutron calibration sources and external datasets from neutron beam experiments.
We reanalyze 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 ± 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 × 10−45 cm2 and 2.3 × 10−42 cm2 ( 8.9 × 10−45 cm2 and 6.0 × 10−42 cm2 ) for WIMPs of mass of 100 GeV/c2 ( 1000 GeV/c2) at 90% confidence level.
Finding unequivocal evidence of dark matter interactions in a particle detector is a major goal of research in physics. Liquid argon time projection chambers offer a path to probe Weakly Interacting ...Massive Particles scattering cross sections on nuclei down to the so-called neutrino floor, in a mass range from a few GeV to hundreds of TeV. Based on the successful operation of the DarkSide-50 detector at LNGS, a new and more sensitive experiment, DarkSide-20k, has been designed and is now under construction. A thorough understanding of the DarkSide-50 detector response and, therefore, of all types of events observed in the detector, is essential for the optimal design of the new experiment. In this article, we report on a specific set of events, namely, standard two-pulse scintillation–ionization signals with a third small amplitude pulse, occurring within the 440μs data acquisition window of standard events. Some of these events are due to the photoionization of the TPC cathode. We compare our results with those published by collaborations using liquid xenon time projection chambers, which observed a similar phenomenon, and, in particular, with a recent paper by the LUX Collaboration (D.S. Akerib et al. Phys.Rev.D 102, 092004 (2020)) From the measured rate of these events, we estimate for the first time the quantum efficiency of the tetraphenyl butadiene deposited on the DarkSide-50 cathode at wavelengths of around 128 nm, in liquid argon. Also, both experiments observe events likely related to the photoionization of impurities in the liquid. The probability of photoelectron emission per unit length turns out to be an order of magnitude lower in DarkSide-50 than in LUX.
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