arXiv subjects

V. Marian

Publications and source records attributed to V. Marian.

5 recordsLinked to original sources

arXiv2026

Studies of Neutrino-Nucleus Elastic Scattering with Point-Contact Germanium Detectors at the Kuo-Sheng Reactor Neutrino Laboratory

The low energy and intense flux of electron anti-neutrinos from nuclear reactors provide the perfect stage to study elastic neutrino-nucleus scattering ($\nu A_{el}$) in the fully coherent regime. We report results from the TEXONO experiment using electro-cooled $p$-type point-contact Germanium detectors with masses of 523~g and 1434~g at the Kuo-Sheng Reactor Neutrino Laboratory. We report improved constraints on the $\nu A_{el}$ cross section with a combined exposure of 404(813.7)~kg-days of Reactor ON(OFF) data at an electron-equivalent threshold of 200~eV$_{ee}$. The Lindhard model, in which the quenching factor is parameterized by a single parameter k, is adopted to describe the suppression of ionization yield. At the benchmark value of k=0.162, a limit of $\rho<$2.0 at 90\% confidence level (CL) is derived, where $\rho$ represents the ratio of the observed to the predicted Standard Model cross section. Moreover the region k$>$0.205 is excluded at 90\% CL using the SM-predicted $\nu A_{el}$ rate. A bound on the neutrino magnetic moment from $\nu A_{el}$ at $\mu_{\nu} {<} 5.9 \times 10^{-10}~\mu_B$ at 90\% CL is also derived.

hep-ex↗

arXiv2021

Large-size sub-keV sensitive germanium detectors for the CONUS experiment

Intense fluxes of reactor antineutrinos offer a unique possibility to probe the fully coherent character of elastic neutrino scattering off atomic nuclei. In this regard, detectors face the challenge to register tiny recoil energies of a few keV at the maximum. The CONUS experiment was installed in 17.1 m distance from the reactor core of the nuclear power plant in Brokdorf, Germany, and was designed to detect this neutrino interaction channel by using four 1 kg-sized point contact germanium detectors with sub-keV energy thresholds. This report describes the unique specifications addressed to the design, the research and development, and the final production of these detectors. It demonstrates their excellent electronic performance obtained during commissioning under laboratory conditions as well as during the first two years of operation at the reactor site which started on April 1, 2018. It highlights the long-term stability of different detector parameters and the achieved background levels of the germanium detectors inside the CONUS shield setup.

physics.ins-det↗

arXiv2020

A significant excess in major merger rate for AGNs with the highest Eddington ratios at z<0.2

Observational studies are increasingly finding evidence against major mergers being the dominant mechanism responsible for triggering AGN. After studying the connection between major mergers and AGN with the highest Eddington ratios at z=2, we here expand our analysis to z<0.2, exploring the same AGN parameter space. Using ESO VLT/FORS2 B-, V- and color images, we examine the morphologies of 17 galaxies hosting AGNs with Eddington ratios >0.3, and 25 mass- and redshift-matched control galaxies. To match the appearance of the two samples, we add synthetic point sources to the inactive comparison galaxies. The combined sample of AGN and inactive galaxies was independently ranked by 19 experts with respect to the degree of morphological distortion. We combine the resulting individual rankings into multiple overall rankings, from which we derive the respective major merger fractions of the two samples. With a best estimate of 0.41 $\pm$ 0.12 for the AGN host galaxies and 0.08 $\pm$ 0.06 for the inactive galaxies our results imply that our AGN host galaxies have a significantly higher merger rate, regardless of the observed wavelength or applied methodology. We conclude that although major mergers are an essential mechanism to trigger local high Eddington ratio AGNs at z<0.2, the origin of >=50% of this specific AGN subpopulation still remains unclear.

astro-ph.GA↗

arXiv2019

Major mergers are not the dominant trigger for high-accretion AGNs at z = 2

Research over the past decade has shown diminishing empirical evidence for major galaxy mergers being a dominating or even important mechanism for the growth of supermassive black holes in galaxies and the triggering of optically or X-ray selected active galactic nuclei (AGN). We here for the first time test whether such a connection exists at least in the most plausible part of parameter space for this mechanism: the highest specific accretion rate broad-line AGNs at the peak epoch of black hole activity around z = 2. To that end we examine 21 galaxies hosting a high accreting black hole (L/Ledd > 0.7) observed with HST/WFC3 and 92 stellar mass- and redshift- matched inactive galaxies taken from the CANDELS survey. We removed the AGN point sources from their host galaxies and avoided bias in visual classification by adding and then subtracting mock point sources to and from the comparison galaxies, producing matched residual structures for both sets. The resulting samples were joined, randomized, and subsequently visually ranked with respect to perceived strength of structural distortions by 10 experts. The ensuing individual rankings were combined into a consensus sequence and from this we derived merger fractions for both samples. With the merger fractions f$_{m,agn}$ = 0.24 $\pm$ 0.09 for the AGN host galaxy sample and f$_{m,ina}$ = 0.19 $\pm$ 0.04 for the inactive galaxies, we find no significant difference between the AGN host galaxies and inactive galaxies. Also, both samples display comparable fractions of disk-dominated galaxies. These findings are consistent with previous studies for different AGN populations, and we conclude that even black hole growth at the highest specific accretion rates and at the peak of cosmic AGN activity is not predominantly caused by major mergers. (abriged)

astro-ph.GA↗

arXiv2016

Characterization and Performance of Germanium Detectors with sub-keV Sensitivities for Neutrino and Dark Matter Experiments

Germanium ionization detectors with sensitivities as low as 100 eVee (electron-equivalent energy) open new windows for studies on neutrino and dark matter physics. The relevant physics subjects are summarized. The detectors have to measure physics signals whose amplitude is comparable to that of pedestal electronic noise. To fully exploit this new detector technique, various experimental issues including quenching factors, energy reconstruction and calibration, signal triggering and selection as well as evaluation of their associated efficiencies have to be attended. The efforts and results of a research program to address these challenges are presented.

physics.ins-det↗