The Study of High Energy Heavy Nucleus Interactions in Nuclear Emulsion Chambers Using Digital Image Processing.

Nuclear emulsion chambers with lead targets have been exposed to a 158 GeV per nucleon beam of \sp{208}pb nuclei, by far the heaviest ion accelerated to such a high energy to date. These interactions frequently produce more than 1000 charged particles. In order to measure multiplicities and secondary particle trajectories in these extremely large events, an automatic CCD-based microscope system has been developed to analyze images, count secondary tracks, measure their trajectories, and estimate their charge. Based on the analysis of 40 high-multiplicity Pb-Pb events measured using this system, we assess the degree to which these interactions can be described as a superposition of individual nucleon-nucleon interactions. The measured pseudorapidity distributions agree very well with the superposition-based FRITIOF parton model, although the actual multiplicities are somewhat lower than the calculated ones. The Pb-Pb pseudorapidity distributions are compared to those from emulsion exposures to other beams. At energies of 158-200 GeV per nucleon, the target and projectile tails of the pseudorapidity distributions are consistent with limiting fragmentation of the target and beam nucleons, supporting the wounded nucleon description of superposition. The variations in the central pseudorapidity regions can also be described as the sum of production from wounded target and projectile nucleons. In agreement with previous studies, we find that multiplicities of heavy nucleus interactions increase more rapidly with energy than in nucleon-nucleon interactions. However, the produced multiplicity per wounded nucleon in central Pb-Pb interactions is no greater than in central interactions of protons, oxygen, or sulfur on silver-bromine targets. This suggests that the increase in multiplicity may not be the effect of re-interaction of particles in large nuclei, as previously conjectured

X-ray polarimetry with an active-matrix pixel proportional counter

We report the first results from an X-ray polarimeter with a micropattern gas proportional counter using an amorphous silicon active matrix readout. With 100% polarized X-rays at 4.5 keV, we obtain a modulation factor of 0.33 +/- 0.03, confirming previous reports of the high polarization sensitivity of a finely segmented pixel proportional counter. The detector described here has a geometry suitable for the focal plane of an astronomical X-ray telescope. Amorphous silicon readout technology will enable additional extensions and improvements.Comment: 4 pages, 4 figures, 1 tabl

A burst chasing x-ray polarimeter

Gamma-ray bursts are one of the most powerful explosions in the universe and have been detected out to distances of almost 13 billion light years. The exact origin of these energetic explosions is still unknown but the resulting huge release of energy is thought to create a highly relativistic jet of material and a power-law distribution of electrons. There are several theories describing the origin of the prompt GRB emission that currently cannot be distinguished. Measurements of the linear polarization would provide unique and important constraints on the mechanisms thought to drive these powerful explosions. We present the design of a sensitive, and extremely versatile gamma-ray burst polarimeter. The instrument is a photoelectric polarimeter based on a time-projection chamber. The photoelectric time-projection technique combines high sensitivity with broad band-pass and is potentially the most powerful method between 2 and 100 keV where the photoelectric effect is the dominant interaction process. We present measurements of polarized and unpolarized X-rays obtained with a prototype detector and describe the two mission concepts; the Gamma-Ray Burst Polarimeter (GRBP) for the U.S. Naval Academy satellite MidSTAR-2, and the Low Energy Polarimeter (LEP) onboard POET, a broadband polarimetry concept for a small explorer mission

Charged particle production in the Pb+Pb system at 158 GeV/c per nucleon

Charged particle multiplicities from high multiplicity central interactions of 158 GeV/nucleon Pb ions with Pb target nuclei have been measured in the central and far forward projectile spectator regions using emulsion chambers. Multiplicities are significantly lower than predicted by Monte Carlo simulations. We examine the shape of the pseudorapidity distribution and its dependence on centrality in detail.Comment: 17 pages text plus 12 figures in postscript 12/23/99 -- Add TeX version of sourc

Imaging X-Ray Polarimeter for Solar Flares (IXPS)

We describe the design of a balloon-borne Imaging X-ray Polarimeter for Solar flares (IX PS). This novel instrument, a Time Projection Chamber (TPC) for photoelectric polarimetry, will be capable of measuring polarization at the few percent level in the 20-50 keV energy range during an M- or X class flare, and will provide imaging information at the approx.10 arcsec level. The primary objective of such observations is to determine the directivity of nonthermal high-energy electrons producing solar hard X-rays, and hence to learn about the particle acceleration and energy release processes in solar flares. Secondary objectives include the separation of the thermal and nonthermal components of the flare X-ray emissions and the separation of photospheric albedo fluxes from direct emissions

Automated track recognition and event reconstruction in nuclear emulsion

The major advantages of nuclear emulsion for detecting charged particles are its submicron position resolution and sensitivity to minimum ionizing particles. These must be balanced, however, against the difficult manual microscope measurement by skilled observers required for the analysis. We have developed an automated system to acquire and analyze the microscope images from emulsion chambers. Each emulsion plate is analyzed independently, allowing coincidence techniques to be used in order to reject background and estimate error rates. The system has been used to analyze a sample of high-multiplicity Pb-Pb interactions (charged particle multiplicities ∼1100) produced by the 158 GeV/c per nucleon 208Pb beam at CERN. Automatically measured events agree with our best manual measurements on 97% of all the tracks. We describe the image analysis and track reconstruction techniques, and discuss the measurement and reconstruction uncertainties

High-Multiplicity Lead-Lead Interactions at 158 GeV/c per nucleon

The Krakow-Louisiana-Minnesota-Moscow Collaboration (KLMM) has exposed a set of emulsion chambers with lead targets to a 158 GeV/c per nucleon beam of Pb-208 nuclei, and we report the initial analysis of 40 high-multiplicity Pb-Pb collisions. To test the validity of the superposition model of nucleus-nucleus interactions in this new regime, we compare the shapes of the pseudorapidity distributions with FRITIOF Monte Carlo model calculations, and find close agreement for even the most central events. We characterize head-on collisions as having a mean multiplicity of 1550 +/- 120 and a peak pseudorapidity density of 390 +/- 30. These estimates are significantly lower than our FRITIOF calculations