arXiv subjects

J. Va'vra

Publications and source records attributed to J. Va'vra.

11 recordsLinked to original sources

arXiv2026

A new way to explain the 511 keV signal from the center of the Galaxy and experimental search for small hydrogen

The first detected gamma-ray line originating from outside the solar system is the 511 keV emission from the center of our Galaxy. The widely accepted explanation attributes this signal to electron-positron annihilation. However, despite over 30 years of extensive theoretical and observational research, the primary sources of these positrons remain unidentified. In this paper, we propose an alternative explanation: the observed signal arises from atomic transitions involving a small hydrogen atom, where an electron is captured into a tightly bound orbit around a proton. We review the current status of experimental searches for small hydrogen, both in astrophysical data and laboratory experiments, and propose new methods for its direct detection in the lab. Additionally, we explore whether small hydrogen could be a candidate for dark matter.

astro-ph.IM↗

arXiv2025

Electron Emissions and Hot spots in Dual-Phase LXe TPCs

Persistent photon and single-electron emissions - in the form of "electron trains" and localized "hot spots" - have been observed in multiple dual-phase liquid xenon (LXe) time projection chambers (TPCs), often persisting long after ionizing events. We show that these phenomena are naturally explained by photon-triggered single-electron emission from resistive mixed-oxide films on stainless-steel wires, which behave as leaky capacitors with long RC time constants at LXe temperature. Positive ions landing on these oxides can further enhance local fields and drive Malter-like electron emission. We outline the materials physics (Cr2O3 / Cr2O3-x / Cr(OH)3 mosaics), quantify expected time scales (~1 second under illumination), and demonstrate how small damaged regions with enhanced QE can produce persistent hot spots.

physics.ins-det↗

arXiv2021

Design and production of the high voltage electrode grids and electron extraction region for the LZ dual-phase xenon time projection chamber

The dual-phase xenon time projection chamber (TPC) is a powerful tool for direct-detection experiments searching for WIMP dark matter, other dark matter models, and neutrinoless double-beta decay. Successful operation of such a TPC is critically dependent on the ability to hold high electric fields in the bulk liquid, across the liquid surface, and in the gas. Careful design and construction of the electrodes used to establish these fields is therefore required. We present the design and production of the LUX-ZEPLIN (LZ) experiment's high-voltage electrodes, a set of four woven mesh wire grids. Grid design drivers are discussed, with emphasis placed on design of the electron extraction region. We follow this with a description of the grid production process and a discussion of steps taken to validate the LZ grids prior to integration into the TPC.

physics.ins-det↗

arXiv2020

High precision time measurements in future experiments

Detector examples discussed: MRPCs, MCP-PMTs, Diamond detectors, SiPMTs, Low and high gain Avalanche diodes (LGADs) and Micromegas. We specifically discuss issues such as single pixel vs. multi-pixel tests, small test vs. large physics system results and hidden problems people usually do not want to talk about.

physics.ins-det↗

arXiv2017

Small FDIRC Designs

In this article we explore the angular resolution limits attainable in small FDIRC designs taking advantage of the new highly pixelated detectors that are now available. Since the basic FDIRC design concept attains its particle separation performance mostly in the angular domain as measured by two-dimensional pixels, this paper relies primarily on a pixel-based analysis, with additional chromatic corrections using the time domain, requiring single photon timing resolution at a level of 100-200ps only. This approach differs from other modern DIRC design concepts such as TOP or TORCH detectors, whose separation performances rely more strongly on time-dependent analyses. We find excellent single photon resolution with a geometry where individual bars are coupled to a single plate, which is coupled in turn to a cylindrical lens focusing camera.

physics.ins-det↗

arXiv2014

Design and performance of the Focusing DIRC detector

We present the final results from a novel Cherenkov imaging detector called the Focusing DIRC (FDIRC). This detector was designed as a full-scale prototype of the particle identification system for the SuperB experiment [1], and comprises 1/12 of the SuperB barrel azimuthal coverage, with partial photodetector and electronics implementation. The prototype was tested in the SLAC Cosmic Ray Telescope which provided 3-D tracking of cosmic muons with an angular resolution of ~1.5 mrad, a position resolution of 4-5 mm, a start time resolution of 70 ps, and muon tracks above ~2 GeV tagged using an iron range stack. The fused silica focusing photon camera was coupled to a full-size BaBar DIRC bar box and was read out, over part of the full coverage, by 12 Hamamatsu H8500 multi-anode photomultipliers (MaPMTs) providing 768 pixels. We used waveform digitizing electronics to read out the MaPMTs. We give a detailed description of our data analysis methods and point out limitations on the present performance. We present results that demonstrate some basic performance characteristics of this design, including: (a) single photon Cherenkov angle resolutions with and without chromatic corrections, (b) signal-to-noise (S/N) ratio between the Cherenkov peak and background, which primarily consists of ambiguities of the possible photon paths from emission along the track to a given pixel, (c) dTOP = TOP_measured - TOP_expected resolutions (with TOP being the photon Time-of-Propagation in fused silica), and (d) performance of the detector in the presence of high-rate backgrounds.

physics.ins-det↗

arXiv2014

Molecular excitations: a new way to detect Dark matter

We believe that the Dark Matter (DM) search should be expanded into the domain of detectors sensitive to molecular excitations, and so that we should create detectors which are more sensitive to collisions with very light WIMPs. In this paper we investigate in detail di-atomic molecules, such as Fused Silica material with large OH-molecule content, and water molecules. Presently, we do not have suitable low cost IR detectors to observe single photons, however some OH-molecular excitations extend to visible and UV wavelengths, and can be measured by Bialkali photocathodes. There are many other chemical substances with di-atomic molecules, or more complex oil molecules, which could be investigated also. This idea invites searches in experiments having large target volumes of such materials coupled to a large array of single-photon detectors with Bialkali or infrared-sensitive photocathodes.

astro-ph.IM↗

arXiv2014

A New Possible Way to Explain the DAMA Results

At present there is an effort to reconcile the results of the DAMA experiment with those from other Dark Matter experiments such as CoGeNT, CRESST, CDMS, and all LXe experiments. The author suggests a new model describing the Dark Matter signal as the result of collisions of very light (1-to-few GeV/c^2) WIMPs with hydrogen, and compares it with currently accepted models of collisions with heavy nuclei (Na, Ge or Xe). The hydrogen target would come from H-contamination of NaI(Tl), Ge and CaWO4 crystals. Initial tuning indicates that one can explain the modulation amplitude of DAMA and CoGeNT with this model, assuming a WIMP-proton cross section between 10^33 and 10^32 cm^2. This paper should be considered to be a new idea which will need substantial new experimental input from all involved experiments.

astro-ph.GA↗

arXiv2014

High Voltage in Noble Liquids for High Energy Physics

A workshop was held at Fermilab November 8-9, 2013 to discuss the challenges of using high voltage in noble liquids. The participants spanned the fields of neutrino, dark matter, and electric dipole moment physics. All presentations at the workshop were made in plenary sessions. This document summarizes the experiences and lessons learned from experiments in these fields at developing high voltage systems in noble liquids.

physics.ins-det↗

arXiv2014

What is needed to accept the new explanation of DAMA results

The DAMA experiment clearly observes a small oscillatory signal. The observed yearly modulation is in phase with the Earth's motion around the Sun. Recent reference [Vavra, 2014] suggested that the DAMA experiment observes a WIMP of much smaller mass than what Xenon 10, Xenon 100, LUX and CDMS experiments can possibly reach. Scattering would occur on proton or oxygen target present in the NaI(Tl) crystal as OH-contamination at a few ppm level. This paper elaborates further on the idea that the OH-molecule could act as a very sensitive detection mechanism for neutrons or WIMPs, and suggests a calibration procedure to prove this idea. We also propose a new detector concept to detect a low mass WIMP.

astro-ph.IM↗

arXiv2003

Optical Properties of the DIRC Fused Silica Cherenkov Radiator

The DIRC is a new type of Cherenkov detector that is successfully operating as the hadronic particle identification system for the BABAR experiment at SLAC. The fused silica bars that serve as the DIRC's Cherenkov radiators must transmit the light over long optical pathlengths with a large number of internal reflections. This imposes a number of stringent and novel requirements on the bar properties. This note summarizes a large amount of R&D that was performed both to develop specifications and production methods and to determine whether commercially produced bars could meet the requirements. One of the major outcomes of this R&D work is an understanding of methods to select radiation hard and optically uniform fused silica material. Others include measurement of the wavelength dependency of the internal reflection coefficient, and its sensitivity to surface contaminants, development of radiator support methods, and selection of good optical glue.

hep-ex↗