Programm für das Sommersemester 2019
Mittwochs, 13:00 Uhr s.t.
Kaffee und Tee ab 14:00 UhrOrt: Institut für Physik, Lorentz-Raum 05-127, Staudingerweg 7
|17.04.19||Chris Allton, Swansea University|
Although the strong interaction of particle physics normally confines quarks inside hadrons (with a force equivalent to 15 tonnes of weight!), at very high temperatures the interaction changes nature and quarks become essentially free. These conditions existed for the first few microseconds after the Big Bang and can be recreated in heavy-ion collision experiments. Studying these conditions is problematic for both experimentalists and theorists. This talk discusses the lattice approach to simulating quarks and hadrons at these temperatures using Bayesian and other approaches.
|08.05.19||Johannes Albrecht, TU Dortmund|
Precision measurements of decays of heavy mesons offer a unique lab to test the Standard Model of particle physics. Heavy, virtual particles in loop processes lead to quantum corrections that are measurable in the precision tests of flavour physics. Using this strategy, hints for postulated new particles can be found. The energy range tested here extends the range reachable in direct searches by about one order of magnitude. Historically, many discoveries in particle physics have first been seen in precision measurements. The talk will give a status of the current measurements in flavour physics with a focus on the recent measurements of the LHCb collaboration. Recently observed tensions between LHCb data and the Standard Model prediction will be discussed and perspectives to clarify these in the near future are given.
|22.05.19||Francesca Bellini, CERN|
The observation of anti-deuteron and anti-helium in cosmic rays has been suggested as a smoking gun in indirect searches for Dark Matter in the Galaxy, under the hypothesis that the background from secondary astrophysical production is negligible. Constraining predictions for the secondary cosmic-ray flux of anti-helium and anti-deuteron with data is therefore crucial to searches with space-based or balloon-based experiments such as AMS-02 and GAPS. To this end, the LHC can be used as anti-matter factory to measure the production of d, 3He and 4He in the laboratory. In proton-proton, proton-nucleus and nucleus-nucleus collisions at the TeV collision-energy scale, light nuclei and their anti-matter counterparts are produced in equal amounts for a given species. Not only accelerator data on light (anti-)nuclei provide unique information to characterise the system produced in high-energy collisions, but they can also be used to test and constrain coalescence production models widely employed in astrophysics. In this Seminar, I will present the most recent results on anti-nuclei production at the LHC and discuss their implications for cosmic ray physics and indirect dark matter searches. Finally, I will present perspectives for future precision measurements with the increased integrated luminosity foreseen for the upcoming High-Luminosity phase of the LHC in years 2021-2029. 1
|29.05.19||Adriana Palffy, MPI Heidelberg|
More than fifty years ago, it was the invention of the laser that revolutionized atomic physics and laid the foundations for quantum optics and coherent control. With only optical frequencies available, the interaction of coherent light with matter was for a long time mainly restricted to atomic transitions. Only recently have novel high-frequency light sources rendered possible the photo-excitation of low-lying nuclear states opening the new field of nuclear quantum optics and promising substantial progress in the field of metrology. These developments aim to exploit the fact that nuclei are very clean quantum systems, well isolated from the environment and benefiting from long coherence times. The lecture will follow these perspectives at the borderline between nuclear and atomic physics on the one hand side and metrology and quantum optics on the other hand side. First, the present status of the efforts to use the 229Th isomer at approx. 8 eV for a nuclear frequency standard will be discussed. Second, the lecture will follow the developments on the emerging field of x-ray quantum optics and focus on the mutual control of coherent x-ray radiation and nuclear transitions in this new regime of laser-matter interactions.
|12.06.19||Aurora Tumino, Kore University of Enna &INFN-LNS, CATANIA|
The source of energy that sustains burning stars for millions to billions of years is provided by nuclear reactions that are responsible also for the element nucleosynthesis inside them. Over the past forty years nuclear physicists have been trying to measure the rates of the most relevant reactions, but there is still considerable uncertainty about their values. Although the stellar temperatures are high, on the order of hundred million degrees, they correspond to sub-Coulomb energies. As a consequence, the Coulomb barrier causes a strong suppression of the cross-section, which drops exponentially with decreasing energy. Thus, the corresponding reaction rates are extremely small, making it difficult for them to be measured directly in the laboratory. In addition, the electron screening effect due to the electrons surrounding the interacting ions prevents one to measure the bare nucleus cross-section. Typically, the standard way to get the ultra-low energy bare nucleus cross-section consists in a simple extrapolation of available higher energy data. This is done by means of the definition of the astrophysical S(E) factor which represents essentially the cross-section free of Coulomb suppression. However, the extrapolation may introduce additional uncertainties due for instance to the presence of unexpected resonances or to high energy tails of sub-threshold resonances. A valid alternative approach is represented by the Trojan Horse Method (THM) that provides at present the only way to measure the bare nucleus S(E) factor of a relevant charged particle twobody reaction A + x → c + C in the Gamow energy window, overcoming the main problems of direct measurements. This is done by selecting the quasi-free (QF) contribution of an appropriate three-body reaction A + a → c + C + s, where a is described in terms of clusters x⊕ s. The QF reaction is performed at energies well above the Coulomb barrier, such that cluster x is brought already in the nuclear field of A, leaving s as spectator to the A+x interaction. The THM has been successfully applied to several reactions connected with fundamental astrophysical problems as well as with industrial energy production. I will recall the basic ideas of the THM and show some recent results. I will emphasis in particular those related to the 12C+12C fusion channel in stars, whose reaction rate was found to be strongly enhanced at the relevant temperatures.
|19.06.19||Florian Reindl, Institut für Hochenergiephysik, WIEN|
Today, the situation in direct dark matter detection is controversial: The DAMA/LIBRA experiment observes an annual modulation signal at high confidence. Furthermore, this signal is perfectly compatible in terms of period and phase with the expectation for a galactic halo of dark matter particles which interact in their NaI target crystals. However, in the so-called standard scenario on dark matter halo and dark matter interaction properties, the DAMA/LIBRA signal contradicts null-results of numerous other experiments. The new experiment COSINUS aims for a model-independent cross-check of the DAMA/LIBRA signal. Such a cross-check is absent up to now and necessarily requires the use of the same target material (NaI). While several experimental efforts are planned or already ongoing, COSINUS is the only experiment operating NaI as cryogenic detector which yields several distinctive advantages: Discrimination between electronic interactions and nuclear recoils off sodium and iodine on event-by-event basis, a lower nuclear recoil energy threshold and a better energy resolution. In this contribution we will review the prototype measurements performed so far, present the plans for the new underground facility foreseen to be installed at LNGS and give an outlook on the COSINUS timescale.
|10.07.19||Michael Spannowsky, Institute for Particle Physics, DURHAM|
The discovery of the Higgs boson has for the first time established an arguably elementary scalar sector at the electroweak scale. With a newly discovered and yet unexplored scalar sector novel opportunities arise to address fundamental questions in nature. To maximise our understanding of this sector a concerted effort between collider and non-collider experiments, as well as perturbative and non-perturbative methods is required. I will outline peculiarities of the Higgs sector and point towards possible future research directions to explore the electroweak symmetry breaking potential.
|Prof. Dr. Stefan Tapprogge|
Institut für Physik, ETAP