Schwiening J.,Gesellschaft fur Schwerionenforschung MbH
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011
The P̄ANDA experiment at FAIR will perform high precision experiments in the charmed quark sector using cooled antiproton beams of unprecedented intensities of L=2×1032 cm-2 s-1 in the momentum range of 115 GeV/c. The charged particle identification in the barrel region needs a thin detector operating in a strong magnetic field. A ring imaging Cherenkov detector using the DIRC principle is an excellent match to those requirements. This article describes aspects of the design and R&D for the P̄ANDA barrel DIRC detector. The availability of highly pixelated fast photon detectors allows several key improvements compared to the successful BaBar-DIRC detector, some of which were tested in a proton beam at GSI. The optical properties of the radiator bars, made from synthetic fused silica, are critical to the success of the DIRC. Measurements of the attenuation length and reflection coefficient allow the determination of the surface roughness of prototype radiator bars. © 2010 Elsevier B.V. All rights reserved.
Pangon V.,Gesellschaft fur Schwerionenforschung MbH |
Pangon V.,Goethe University Frankfurt
International Journal of Modern Physics A | Year: 2012
We study in this paper the sine-Gordon model using functional renormalization group at local potential approximation using different renormalization group (RG) schemes. In d = 2, using WegnerHoughton RG we demonstrate that the location of the phase boundary is entirely driven by the relative position to the Coleman fixed point even for strongly coupled bare theories. We show the existence of a set of IR fixed points in the broken phase that are reached independently of the bare coupling. The bad convergence of the Fourier series in the broken phase is discussed and we demonstrate that these fixed points can be found only using a global resolution of the effective potential. We then introduce the methodology for the use of average action method where the regulator breaks periodicity and show that it provides the same conclusions for various regulators. The behavior of the model is then discussed in d≠2 and the absence of the previous fixed points is interpreted. © 2012 World Scientific Publishing Company.
Levai P.,KFKI Research Institute |
Skokov V.,Gesellschaft fur Schwerionenforschung MbH
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010
Nonperturbative charm and bottom quark-pair production is investigated in the early stage of heavy-ion collisions. The time-dependent study is based on a kinetic description of fermion-pair production in strong non-Abelian fields. We introduce a time-dependent chromo-electric external field with a pulselike time evolution to simulate the overlap of two colliding heavy ions. The calculations is performed in a SU(2) color model with finite current quark masses. Yields of heavy quark pairs are compared to the ones of light and strange quark pairs. We show that the small inverse duration time of the field pulse determines the efficiency of the quark-pair production. The expected suppression for heavy quark production, as follows from the Schwinger formula for a constant field, is not seen, but rather an enhanced heavy quark production appears at ultrarelativistic energies. © 2010 The American Physical Society.
Block M.,Gesellschaft fur Schwerionenforschung MbH
Springer Tracts in Modern Physics | Year: 2014
The mass of an atom is directly related to the binding energy of all its constituents. Thus, it provides information about all the interactions inside the atom. High-precision mass measurements hence allow studies of fundamental interactions and are of great importance in many different fields in physics. Themasses of radionuclides provide information on their stability and their structure and are therefore of particular interest for nuclear structure investigations and as input for nucleosynthesis models in nuclear astrophysics. Penning trap mass spectrometry provides masses of radionuclides with unprecedented accuracies on the order of 10-8 and can nowadays be applied even to nuclides with short half-lives and low production rates. Utilizing advanced ion manipulation techniques radionuclides from essentially all elements produced in a broad range of nuclear reactions can be accessed. In this chapter the standard procedures of on-line Penning trap mass spectrometry are introduced and some representative examples of recent mass measurements are given. © Springer-Verlag Berlin Heidelberg 2014.
Reifarth R.,Gesellschaft fur Schwerionenforschung MbH |
Reifarth R.,Goethe University Frankfurt
Journal of Physics: Conference Series | Year: 2010
Almost all of the heavy elements are produced via neutron capture reactions in a multitude of stellar production sites. The predictive power of the underlying stellar models is currently limited because they contain poorly constrained physics components such as convection, rotation or magnetic fields. Neutron captures measurements on heavy radioactive isotopes provide a unique opportunity to largely improve these physics components, and thereby address important questions of nuclear astrophysics. Such species are branch-points in the otherwise uniquely defined path of subsequent neutron captures along the s-process path in the valley of stability. These branch points reveal themselves through unmistakable signatures recovered from pre-solar meteoritic grains that originate in individual element producing stars. Measurements on radioactive isotopes for neutron energies in the keV region represent a stringent challenge for further improvements of experimental techniques. This holds true for the neutron sources, the detection systems and the technology to handle radioactive material. © 2010 IOP Publishing Ltd.