arXiv subjects

Stephan Paul

Publications and source records attributed to Stephan Paul.

31 records · Page 2Linked to original sources

arXiv2015

A z-Vertex Trigger for Belle II

The Belle II experiment will go into operation at the upgraded SuperKEKB collider in 2016. SuperKEKB is designed to deliver an instantaneous luminosity $\mathcal{L}=8\times10^{35}\,\mathrm{cm}^{-2}\,\mathrm{s}^{-1}$. The experiment will therefore have to cope with a much larger machine background than its predecessor Belle, in particular from events outside of the interaction region. We present the concept of a track trigger, based on a neural network approach, that is able to suppress a large fraction of this background by reconstructing the $z$ (longitudinal) position of the event vertex within the latency of the first level trigger. The trigger uses the hit information from the Central Drift Chamber (CDC) of Belle II within narrow cones in polar and azimuthal angle as well as in transverse momentum ("sectors"), and estimates the $z$-vertex without explicit track reconstruction. The preprocessing for the track trigger is based on the track information provided by the standard CDC trigger. It takes input from the 2D track finder, adds information from the stereo wires of the CDC, and finds the appropriate sectors in the CDC for each track. Within the sector, the $z$-vertex is estimated by a specialized neural network, with the drift times from the CDC as input and a continuous output corresponding to the scaled $z$-vertex. The neural algorithm will be implemented in programmable hardware. To this end a Virtex 7 FPGA board will be used, which provides at present the most promising solution for a fully parallelized implementation of neural networks or alternative multivariate methods. A high speed interface for external memory will be integrated into the platform, to be able to store the $\mathcal{O}(10^9)$ parameters required. The contribution presents the results of our feasibility studies and discusses the details of the envisaged hardware solution.

physics.ins-det↗

arXiv2015

A neural network z-vertex trigger for Belle II

We present the concept of a track trigger for the Belle II experiment, based on a neural network approach, that is able to reconstruct the z (longitudinal) position of the event vertex within the latency of the first level trigger. The trigger will thus be able to suppress a large fraction of the dominating background from events outside of the interaction region. The trigger uses the drift time information of the hits from the Central Drift Chamber (CDC) of Belle II within narrow cones in polar and azimuthal angle as well as in transverse momentum (sectors), and estimates the z-vertex without explicit track reconstruction. The preprocessing for the track trigger is based on the track information provided by the standard CDC trigger. It takes input from the 2D ($r - φ$) track finder, adds information from the stereo wires of the CDC, and finds the appropriate sectors in the CDC for each track in a given event. Within each sector, the z-vertex of the associated track is estimated by a specialized neural network, with a continuous output corresponding to the scaled z-vertex. The input values for the neural network are calculated from the wire hits of the CDC.

physics.ins-det↗

arXiv2014

FPGA Based Data Read-Out System of the Belle 2 Pixel Detector

The upgrades of the Belle experiment and the KEKB accelerator aim to increase the data set of the experiment by the factor 50. This will be achieved by increasing the luminosity of the accelerator which requires a significant upgrade of the detector. A new pixel detector based on DEPFET technology will be installed to handle the increased reaction rate and provide better vertex resolution. One of the features of the DEPFET detector is a long integration time of 20 μs, which increases detector occupancy up to 3 %. The detector will generate about 2 GB/s of data. An FPGA-based two-level read-out system, the Data Handling Hybrid, was developed for the Belle 2 pixel detector. The system consists of 40 read-out and 8 controller modules. All modules are built in μTCA form factor using Xilinx Virtex-6 FPGA and can utilize up to 4 GB DDR3 RAM. The system was successfully tested in the beam test at DESY in January 2014. The functionality and the architecture of the Belle 2 Data Handling Hybrid system as well as the performance of the system during the beam test are presented in the paper.

physics.ins-det↗

arXiv2013

Precision spectroscopy with COMPASS and the observation of a new iso-vector resonance

We report on the results of a novel partial-wave analysis based on $50\cdot 10^6$ events from the reaction $π^- + p \to π^-π-^π^+ + p_\text{recoil}$ at 190 $\text{GeV/c}$ incoming beam momentum using the COMPASS spectrometer. A separated analysis in bins of $m_{3π}$ and four-momentum transfer $t'$ reveals the interference of resonant and non-resonant particle production and allows their spectral separation. Besides well known resonances we observe a new iso-vector meson $a_1(1420)$ at a mass of 1420 $\text{MEV\c}^2$ in the $f_0(980)π$ final state only, the origin of which is unclear. We have also examined the structure of the $0^{++}$ $ππ$-isobar in the $J^{PC}=0^{-+}, 1^{++}, 2^{-+}$ three pion waves. This clearly reveals the various $0^{++}$ $ππ$-isobar components and its correlation to the decay of light mesons.

hep-ex↗

arXiv2013

First Results of the PixelGEM Central Tracking System for COMPASS

For its physics program with a high-intensity hadron beam of up to 2e7 particles/s, the COMPASS experiment at CERN requires tracking of charged particles scattered by very small angles with respect to the incident beam direction. While good resolution in time and space is mandatory, the challenge is imposed by the high beam intensity, requiring radiation-hard detectors which add very little material to the beam path in order to minimize secondary interactions. To this end, a set of triple-GEM detectors with a hybrid readout structure consisting of pixels in the beam region and 2-D strips in the periphery was designed and built. Successful prototype tests proved the performance of this new detector type, showing both extraordinary high rate capability and detection efficiency. The amplitude information allowed to achieve spatial resolutions about a factor of 10 smaller than the pitch and a time resolution close to the theoretical limit imposed by the layout. The PixelGEM central tracking system consisting of five detectors, slightly improved with respect to the prototype, was completely installed in the COMPASS spectrometer in spring 2008.

physics.ins-det↗

arXiv2012

The Neutron and the Universe - History of a Relationship

We discuss selected topics in the field of particle- and astrophysics with neutrons. They have a direct link with our understanding of the history of the Universe and are related to recent, ongoing or future measurements. They deal with the structure of space-time (tests of gravitation at small distance scales), search for an electric dipole moment of the neutron (CP-violation and the origin of matter in the Universe), the neutron lifetime (rate of primordial nucleosynthesis) and the two-body decay of the neutron testing the V--A structure of weak interaction (right-handed neutrinos and the very early Universe). We describe the status, measurement methods and highlight experimental challenges.

hep-ex↗

arXiv2009

Development of a GEM-TPC prototype

The use of GEM foils for the amplification stage of a TPC instead of a con- ventional MWPC allows one to bypass the necessity of gating, as the backdrift is suppressed thanks to the asymmetric field configuration. This way, a novel continuously running TPC, which represents one option for the PANDA central tracker, can be realized. A medium sized prototype with a diameter of 300 mm and a length of 600 mm will be tested inside the FOPI spectrometer at GSI using a carbon or lithium beam at intermediate energies (E = 1-3AGeV). This detector test under realistic experimental conditions should allow us to verify the spatial resolution for single tracks and the reconstruction capability for displaced vertexes. A series of physics measurement implying pion beams is scheduled with the FOPI spectrometer together with the GEM-TPC as well.

physics.ins-det↗

arXiv2009

The Puzzle of Neutron Lifetime

In this paper we review the role of the neutron lifetime and discuss the present status of measurements. In view of the large discrepancy observed by the two most precise individual measurements so far we describe the different techniques and point out principle strengths and weaknesses. In particular we discuss the estimation of systematic uncertainties and its correlation to the statistical ones. In order to solve the present puzzle, many new experiments are either ongoing or being proposed. An overview on their possible contribution to this field will be given.

hep-ex↗

arXiv2009

Test of Symmetries with Neutrons and Nuclei

Precision experiments at low energies probing weak interaction are a very promising and complementary tool for investigating the structure of the electro-weak sector of the standard model, and for searching for new phenomena revealing signs for an underlaying new symmetry. With the advent of new technologies in particle trapping and production of beams for exotic nuclei as well as ultracold neutrons, we expect one or two orders of magnitude gain in precision. This corresponds to the progress expected by new high luminosity B-factories or the LHC. Domains studied are $β$-decays where decay correlations, partial or total decay rates may reveal the nature of the left-right structure of the interaction and the investigation of discrete symmetries. Here the search for a finite electric dipole moment which, due to its CP-violating nature were sensational by itself, could shed light on the structure of the vacuum at very small distances. Last but not least ideas of a mirror world can be extended to the sector of baryons which can be studied with neutrons.

hep-ex↗

arXiv2005

Recent Physics results with the COMPASS Experiment

The COMPASS experiment has obtained first physics results in the field of polarized distribution functions for quarks and gluons using muon scattering off polarized deuterons. The analysis using open charm production and pairs of high $p_T$ hadrons is presented. We also have used a transversely polarized target to address transverse information for quarks inside the nucleon. In addition, a pilot run with incoming pions taken late 2004 will give first information on the pion polarizabilities and hadron resonances. The physics prospects from this run as well as from future data taking in this field are also outlined.

hep-ex↗

arXiv2005

Selected Aspects of Neutron Decay

Precision measurements of neutron decay offer complementary access to particle physics at small distance scales or high energies. In particular they allow tests of the V-A structure of the weak interaction. Among many experimental activities which are ongoing around the world we present two new experiments which are planned or studied for the near future. While the neutron lifetime still bears significant experimental uncertainties and thus has to be studied with greatest precision the two-body decay ($n\to H\barν$) of the neutron has not yet been observed. Despite its small branching fraction it offers many possibilities in the framework of particle physics. Both cases are addressed in this contribution.

hep-ex↗

arXiv1999

Strangeness in Hadronic Systems

This paper reviews different aspects of hadronic systems with strange quarks. It reviews production, spectroscopy and decay of baryons and hypernuclei with emphasis on recent results obtained in this field. It includes a comparison of different systems doped with strange (or heavy) quarks, emphasizing the single particle nature which can be observed in baryons and nuclei.

hep-ph↗

arXiv1999

Heavy Baryons - Different Facets of Experimental results

This paper reviews the experimental status of heavy baryons. It covers the aspec ts of production, spectroscopy and decay presenting recent results obtained in this fi eld. It closes with an outlook on further work on and with heavy baryons and their po ssible role for other measurements.

hep-ph↗