Silica aerogel; synthesis, properties and characterization

R-Parity-violating supersymmetry

We review the data and models describing the production of the electrons, termed secondary electrons, that initiate the secondary and subsequent feedback avalanches required for the growth of current during breakdown and for the maintenance of low-current, cold-cathode discharges in argon First we correlate measurements of the production of secondary electrons at metallic cathodes, ie the yields of electrons induced by Ar+ ions, fast Ar atoms, metastable atoms and vuv photons The yields of electrons per ion, fast atom and photon vary greatly with particle energy and surface condition Then models of electron, ion, fast atom, excited atom and photon transport and kinetics are fitted to electrical-breakdown and low-current, discharge-maintenance data to determine the contributions of various cathode-directed species to the secondary electron production Our model explains measured breakdown and low-current discharge voltages for Ar over a very wide range of electric field to gas density ratios E/n, ie 15 Td to 100 kTd We review corrections for nonequilibrium electron motion near the cathode that apply to our local-field model of these discharges Analytic expressions for the cross sections and reaction coefficients used by this and related models are summarized

https://iopscience.iop.org/article/10.1088/0963-0252/8/3/201/pdf

Cold-cathode discharges and breakdown in argon: surface and gas phase production of secondary electrons

The XENON1T experiment is currently in the commissioning phase at the Laboratori Nazionali del Gran Sasso, Italy. In this article we study the experiment's expected sensitivity to the spin-independent WIMP-nucleon interaction cross section, based on Monte Carlo predictions of the electronic and nuclear recoil backgrounds. The total electronic recoil background in 1 tonne fiducial volume and (1, 12) keV electronic recoil equivalent energy region, before applying any selection to discriminate between electronic and nuclear recoils, is (1.80 ± 0.15) · 10(−)(4) (kg·day·keV)(−)(1), mainly due to the decay of (222)Rn daughters inside the xenon target. The nuclear recoil background in the corresponding nuclear recoil equivalent energy region (4, 50) keV, is composed of (0.6 ± 0.1) (t·y)(−)(1) from radiogenic neutrons, (1.8 ± 0.3) · 10(−)(2) (t·y)(−)(1) from coherent scattering of neutrinos, and less than 0.01 (t·y)(−)(1) from muon-induced neutrons. The sensitivity of XENON1T is calculated with the Profile Likelihood Ratio method, after converting the deposited energy of electronic and nuclear recoils into the scintillation and ionization signals seen in the detector. We take into account the systematic uncertainties on the photon and electron emission model, and on the estimation of the backgrounds, treated as nuisance parameters. The main contribution comes from the relative scintillation efficiency Script L(eff), which affects both the signal from WIMPs and the nuclear recoil backgrounds. After a 2 y measurement in 1 t fiducial volume, the sensitivity reaches a minimum cross section of 1.6 · 10(−)(47) cm(2) at m(χ) = 50 GeV/c(2).

/pdf/physics-reach-of-the-xenon1t-dark-matter-experiment-4nlp7ku3x2.pdf

Physics reach of the XENON1T dark matter experiment

We present the state of the art regarding the relation between the physics of Quantum Black Holes and Noncommutative Geometry. We start with a review of models proposed in the literature for describing deformations of General Relativity in the presence of noncommutativity, seen as an effective theory of Quantum Gravity. We study the resulting metrics, proposed to replace or at least to improve the conventional black hole solutions of Einstein's equation. In particular, we analyze noncommutative-inspired solutions obtained in terms of quasi-classical noncommutative coordinates: indeed because of their surprising new features, these solutions enable us to circumvent long standing problems with Quantum Field Theory in Curved Space and to cure the singular behavior of gravity at the centers of black holes. As a consequence, for the first time, we get a complete description of what we may call the black hole SCRAM, the shut down of the emission of thermal radiation from the black hole: in place of the conventional scenario of runaway evaporation in the Planck phase, we find a zero temperature final state, a stable black hole remnant, whose size and mass are determined uniquely in terms of the noncommutative parameter $\theta$. This result turns out to be of vital importance for the physics of the forthcoming experiments at the LHC, where mini black hole production is foreseen in extreme energy hadron collisions. Because of this, we devote the final part of this review to higher dimensional solutions and their phenomenological implications for TeV Gravity.

Noncommutative Black Holes, The Final Appeal To Quantum Gravity: A Review

The photoemission quantum efficiency of reflective photocathodes in methane gas has been investigated in the spectral range between 140 and 250 nm. The spectral response of solid metals and CsI, as well as of liquid and solid TMAE film, have been measured. The high quantum efficiency of CsI (35% at 170 nm) makes it attractive for BaF 2 or xenon scintillation detection. A BaF 2 crystal coupled to an ionization chamber with a reflective CsI photocathode has been successfully tested. Adsorbed TMAE films can significantly increase the quantum yields of metal and CsI (to 46% at 170 nm), making them suitable for fast RICH and other applications.

/pdf/reflective-uv-photocathodes-with-gas-phase-electron-10lpyz5t34.pdf

Reflective UV photocathodes with gas-phase electron extraction: solid, liquid, and adsorbed thin films

A short review of Cherenkov radiation and its use for particle identification with threshold and differential counters is presented. The focusing principles of Ring Imaging Cherenkov (RICH) counters are then developed and applied successively to gas and liquid radiators. An analysis of proximity focused images from liquid or solid radiators follows. A method to reconstruct the Cherenkov angle from the experimental data is developed for spherical as well as for flat detector surfaces. These formulas define the Cherenkov angle sensitivity due to intrinsic as well as extrinsic (measurement) errors. Particle identification limits are then given for each of the different imaging methods.

Theory of ring imaging Cherenkov counters

In this survey we discuss the development of Ring Imaging Cherenkov (RICH) counters for particle identification. Since 1977, it has been based on the use of gaseous photosensors in detectors with gaseous amplification (MWPC and MSAC) and sensitive to single UV photons. The detectors are classified into three groups, each developed over the last sixteen years, but based on different techniques and readout methods. The main developments, and the principal operating RICH detectors, are described and critically analyzed in order to compare their respective absolute performances. The newer detector designs and photosensors are also discussed. The aim of this historical survey is to give an overview of the technique, even if not completely exhaustive, in order to help in understanding RICH counters, their problems and their possibilities.

A historical survey of ring imaging Cherenkov counters

Detection of far-ultraviolet photons with the multistep avalanche chamber. Application to Cherenkov light imaging and to some problems in high-energy physics

The International Conference on the History of Original Ideas and Basic Discoveries, held at the "Ettore Majorana" Centre for Scientific Culture in Erice, Sicily, July 27-August 4, 1994, brought together sixty of the leading scientists including many Nobel Laureates in high energy physics, principal contributors in other fields of physics such as high T_c superconductivity, particle accelerators and detector instrumentation, and thirty-six talented younger physicists selected from candidates throughout the world.

T. Ypsilantis

Papers

Reflective UV photocathodes with gas-phase electron extraction: solid, liquid, and adsorbed thin films

Theory of ring imaging Cherenkov counters

A historical survey of ring imaging Cherenkov counters

Detection of far-ultraviolet photons with the multistep avalanche chamber. Application to Cherenkov light imaging and to some problems in high-energy physics

History of original ideas and basic discoveries in particle physics