How to Test the Existence of the Early Parton Cascade Using Photon HBT Correlations?

We report on a possible application of the HBT phenomenon in testing the existence of two hypothetical phenomena. First, it is argued that the existence of a rapidly developing parton cascade in the earliest stages of a high energy nuclear collision process can be tested by studying two-photon HBT correlations over a wide longitudinal momentum scale - corresponding to the early photon emission time from the hypothetical parton system. This method provides the needed selectivity for the early emitted photons, since the photons emitted at later times correlate over progressively narrower momentum scales. Second, in a similar way we argue that the existence of a hypothetic dark matter candidate, the Weakly Interacting Massive Particle (WIMP), may be tested by studying HBT correlations of cosmic gamma rays at a relatively long detection time scale - corresponding to the very narrow spectral line of the photons emerging from WIMP annihilations. Background photons leave no signature since they essentially do not correlate.Comment: Presented at the 2nd Catania Relativistic Ion Studies, CRIS'98, Catania, Sicily, Italy, June 8-12, 1998. To appear in the Proceedings, Worl Scientifi

Electric potential and field calculation of charged BEM triangles and rectangles by Gaussian cubature

It is a widely held view that analytical integration is more accurate than the numerical one. In some special cases, however, numerical integration can be more advantageous than analytical integration. In our paper we show this benefit for the case of electric potential and field computation of charged triangles and rectangles applied in the boundary element method (BEM). Analytical potential and field formulas are rather complicated (even in the simplest case of constant charge densities), they have usually large computation times, and at field points far from the elements they suffer from large rounding errors. On the other hand, Gaussian cubature, which is an efficient numerical integration method, yields simple and fast potential and field formulas that are very accurate far from the elements. The simplicity of the method is demonstrated by the physical picture: the triangles and rectangles with their continuous charge distributions are replaced by discrete point charges, whose simple potential and field formulas explain the higher accuracy and speed of this method. We implemented the Gaussian cubature method for the purpose of BEM computations both with CPU and GPU, and we compare its performance with two different analytical integration methods. The ten different Gaussian cubature formulas presented in our paper can be used for arbitrary high-precision and fast integrations over triangles and rectangles.Comment: 28 pages, 13 figure

Intrinsic volumes of random polytopes with vertices on the boundary of a convex body

Let $K$ be a convex body in $\R^d$, let $j\in\{1, ..., d-1\}$, and let $\varrho$ be a positive and continuous probability density function with respect to the $(d-1)$-dimensional Hausdorff measure on the boundary $\partial K$ of $K$. Denote by $K_n$ the convex hull of $n$ points chosen randomly and independently from $\partial K$ according to the probability distribution determined by $\varrho$. For the case when $\partial K$ is a $C^2$ submanifold of $\R^d$ with everywhere positive Gauss curvature, M. Reitzner proved an asymptotic formula for the expectation of the difference of the $j$th intrinsic volumes of $K$ and $K_n$, as $n\to\infty$. In this article, we extend this result to the case when the only condition on $K$ is that a ball rolls freely in $K$

New Developments in Hybrid Photon Detectors

New developments in HPD design are presented, triggered by applications in high energy physics and astrophysics. The presented HPD designs are based on three innovations. (i) In order to achieve the highest possible surface coverage in a RICH detector, we introduced a photoelectron focussing method which is efficient to the periphery of the photocathode. (ii) To prevent positive ion feedback in HPDs, we introduced a permanent potential barrier in front of the anode. (iii) To replace a transmittive by a reflective photocathode, we arrived at a conceptually new HPD design with surprisingly good imaging characteristics, high quantum efficiency and low cost

Solution to the ion feedback problem in Hybrid Photon Detectors and Photo Multiplier Tubes

A general solution to the positive ion feedback problem in Hybrid Photon Detectors (HPD), photo multipliers (PM) and other similar detectors was found in the insertion of a permanent electrostatic potential barrier which prevents drift of positive ions from the anode, or the first dynode, towards the photocathode. In this paper we present the method as applied to the Intevac HPD.Comment: 9 pages, 7 figures, accepted for publication in Nucl. Inst. Meth.

Imaging Hybrid Photon Detectors with Minimized Dead Area and Protection Against Positive Ion Feedback

Imaging Hybrid Photon Detectors (HPD) have been developed for integration in large area Cherenkov detectors for high energy physics and astrophysics. The presented designs - developed particularly for the experiments MAGIC, LHCb and AQUA-RICH - comprise very good imaging properties, protection against positive ion feedback and(or) minimum dead area. The underlying innovations are discussed in some detail.Comment: 29 pages, 20 figures, submitted to Nucl. Inst. Meth.