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Topic 2: "Cosmic Matter in the Laboratory

Helmholtz-Institute Mainz

The Helmholtz-Institute Mainz (HIM) has been founded in 2009 as the first institute of its kind after the evaluation of a strategic research proposal by an international committee. It comprises an outpost of GSI on the campus of the Johannes Gutenberg-Universität Mainz (JGU). Its budget of 5.5 million € p.a. is complemented by infrastructure measures by JGU amounting to a similar sum. Its structure is based on the one hand on long standing collaborations between JGU-groups and GSI. On the other hand, the local expertise of research groups complements in an ideal way the demands of the new FAIR facility, since JGU operates the 1.6 GeV electron accelerator MAMI and the research reactor TRIGA on the campus in Mainz. The scientific programm of the institute is focused on FAIR in the area of hadron physics, nuclear physics with superheavy elements, and atomic physics with antiprotons. A theory floor works in close collaboration with all experimental sections. The section on accelerator research and developpement works on developments for the FAIR HESR and a superconducting CW-linac for superheavy element synthesis. The HIM is part of the excellence cluster PRISMA, which has recently been established within the framework of the German excellence initiative. The HIM management receives advice in scientific and strategic questions by a scientific council. There is a large overlap between the members of the HIM and the GSI scientific council. HIM has an active guest scientist program for distinguished researchers and (co-)organises a number of workshops and conferences.

 

JGU and GSI have created 2 new full professor positions each, of which one has been filled recently, for two others offers have been made.The institute is organised in 6 research sections and has in the past been successful in two Helmholtz-Young-Investigator Group proposals. The university has been successfull in the application for a research building for HIM, which had been very positively evaluated by the German "Wissenschaftsrat" in a highly competitive process. The total cost of the building will be about 35 million €. It will provide office space for about 150 people on about 1800 m2 and in addition about 1800 m2 of laboratory space, including an experimental hall for the mounting of larger scale detector systems, a cleanroom for the mounting of superconducting cavities as well as a compute center for the operation of high performance compute clusters with installed cooling power of 750 kW.

 

HIM is making leading contributions to the construction of PANDA , the preparation of its physics program as well as the PANDA online and offline software packages. The experimental activities are carried out in two research sections: section SPECF (Spectroscopy and Flavor) and section EMP (Electromagnetic Processes).

 

 

Section Electromagnetic Processes (EMP)

explores the measurement of nucleon structure observables in the nonperturbative regime of Quantum Chromo Dynamics with antiproton annihilation reactions. The electromagnetic probe has the advantage that due to the small electromagnetic coupling αEM one photon exchange allows a clean separation between the structure observables like for example electromagnetic form factors in the time like regime and kinematics. The knowledge of the modulus of the time like electromagnetic form factors for example can be brought from a statistical error of at present 20% - 40% to a level of a few percent up to a four momentum transfer of 16 GeV/c2. Other examples of time like nucleon structure observables comprise the time like analogon of the Generalized Parton Distributions accessible in wide angle Compton scattering as well as the so called Transisition Distribution Amplitudes (TDAs). The detection of Drell-Yan-processes for the extraction of the transverse spin structure of the nucleon seams feasible and will be studied during the coming funding period. The measurement of the imaginary part of the time like electromagnetic form factors will be possible with a transversely polarized target in PANDA.

 

The section EMP is performing detailed and large statistics physics simulations in order to determine the possible precision in the extraction of nucleon structure observables from antiproton annihilation reactions. So far the measurement of the modulus of the time like electromagnetic form factors has been explored as well as a possible extraction of the transition distribution amplitude. An extension to the Drell Yan processes involving electrons in the final state as well as other physics processes is foreseen for the coming funding period.

 

The electromagnetic calorimeter of the PANDA experiment is here of special interest due to its importance for a precision energy measurement of final state electrons and photons as well as for particle identification. The Section EMP has taken full system responsibility for the backward end-cap of the electromagnetic calorimeter. While many aspects of the barrel and forward end cap part of the electromagnetic calorimeter can just be copied, the special constraints concerning the extremely tight space make special developments, like an improved thermal shield for the PWO-crystals necessary, which will be operated at –25°C. HIM is together with GSI developing the planar GEM-tracker in PANDA.

 

The section EMP is developing a superconducting Meissner-shield in order to suppress the longitudinal 2T field of the PANDA solenoid. This would enable the operation of a polarized hydrogen target for the extraction of the imaginary part of the time like electromagnetic form factors, for access to additional single spin asymmetries connected to transverse spin structure observables and other single spin observables in spectroscopy as well.

 

Researchers from HIM are driving the extraction of time-like electromagnetic form factors from data of the BES-II experiments. This will on the one hand allow to enhance the precision of the world data from the present level by a factor two through the analysis of initial state radiation events. On the other hand, many aspects like the threshold behavior of electromagnetic form factors and radiative quantum corrections like the two-photon exchange amplitude in the time-like region can be implemented and tested with BES-III data and will be an important intermediate step to reach the high precision aimed for the extraction of the time-like form factors at PANDA.

 

 

Section Spectroscopy and Flavor (SPECF)

is focusing on future analyses of charmonium and charmonium-like resonances with the overall goal to arrive at a detailed and quantitative understanding of quark binding in the non-perturbative regime of strong interactions. Proton-antiproton annihilation with a state-of-the art detector system as PANDA offers unique possibilities in the field of charmonium spectroscopy and furthermore has the potential to discover states, which are made of gluonic excitations such as glueballs or hybrids. To optimize the sensitivity of the PANDA detector in view of these spectroscopy projects defines the hardware and software developments of the research section. SPECF has for instance taken the responsibility for the design and construction of the PANDA luminosity detector, which will consist of four layers of Si pixel detectors and will be located 12 meters downstream the target. From the rate of elastically scattered antiproton events at low polar angles, the luminosity will be determined with few percent accuracy. Such a precision is of utmost importance for the lineshape measurements of charmonium resonances which are foreseen at PANDA. The design and construction of the PANDA-DIRC detector is pursued in close collaboration with GSI and will provide high-resolution PID information. The Mainz group is involved in all aspects regarding the readout of the detector including the design of FPGA-based TDCs. The event trigger is a challenge in the high-rate environment of PANDA. Moreover, there are many final state of interest, which have an event topology similar to background or continuum events. This requires innovative approaches, which go beyond the present technology of hardware triggers as a suppression rate of 1:1000 is requested while keeping a high detection efficiency for many signal processes. PANDA has decided to develop a purely software-based event trigger for which FPGAs, GPUs or big conventional computer farms are possible options. HIM researchers are also developing highly sophisticated tools to analyze the intrinsic structure of the signal distributions which will be measured by PANDA. An efficient Partial Wave Analysis (PWA) is the key to eventually determine the quantum numbers of the states and to arrive at a physics interpretations. Presently, a versatile PWA package is developed within SPECF. To train such a package with real data, Mainz researchers have joined the BESIII collaboration, where these tools can be tested and where results in electron-positron experiments are obtained. At BESIII exciting results recently have been obtained regarding socalled XYZ states, i.e. regarding charmonium resonances which are known to be possibly of exotic nature. Most recently, charged states with a mass of approximately 4 GeV were discovered, which unambiguously proves that those states must have a quark content beyond purely charm and anticharm. The participation in BESIII allows Mainz researchers to design and optimize future measurements at PANDA. Finally, SPECF researchers are preparing a setup for dedicated PANDA runs to search for double-hypernuclei states. This setup consists of a primary wire target and a secondary active target, in which the hypernuclei will be produced. The hypernuclear runs require not only a modification to the target, but also to the vertex detector.

 

 

Section Matter-Antimatter Symmetry (MAM)

At the heart of the research section MAM there are precision experiments to test the fundamental symmetry between ordinary matter and antimatter. This symmetry is called CPT symmetry and is inherent to relativistic quantum field theories and thus the present Standard Model of particle physics. In the Universe, however, no such symmetry is observed and the hadronic antimatter is just missing. This baryon asymmetry of the Universe is a puzzle if one assumes that the Big Bang has produced equal amounts of matter and antimatter. One experimental approach to this fundamental question is to compare properties of matter and antimatter at ever increasing levels of experimental precision.

 

Both ultrahigh-resolution laser-spectroscopy of antihydrogen and the measurement of the magnetic moment of the antiproton have the potential to test CPT symmetry at unprecedented levels of experimental precision. The Facility for Low-Energy Antiproton and Ion Research (FLAIR) at FAIR and the availibility of the CRYring will start a new era in this field of precision experiments with antimatter at very low temperatures. Many of the experimental techniques are presently being developed at CERN's Antiproton Decelerator, the only existing source of low-energy antiprotons.

 

One important requirement for precision experiments with antihydrogen is to cool the atoms as much as possible. Laser-cooling of antihydrogen can be done using radiation at 122 nm wavelength in the Vacuum Ultraviolet (Lyman-alpha). The only continuous laser source at Lyman-alpha exists within HIM/MAM. Ongoing work on the Lyman-alpha source aims at improving the yield and the reliability for experiments with antihydrogen.

 

Another goal in MAM is to develop techniques to measure the magnetic moment of both the proton and the antiproton at unprecedented precision. The experiment is located at Mainz and is a collaboration between HIM/MAM, Univ. Mainz, GSI at Darmstadt, the MPI for nuclear physics at Heidelberg, and Riken/Japan. The experiment uses just one single isolated particle which can be stored for arbitrarily long times (many months) in cryogenic Penning traps. The crucial element of the experiment is the detection of spin-flips of one single proton, which has been pioneered by the Mainz experiment. This is the first time that spin-flips of a magnetic moment on the order of a nuclear magneton have been observed with a single isolated particle. The present experimental value of the magnetic moment of the proton comes from a measurement of the hyperfine splitting of hydrogen in a magnetic field using a MASER. This value has stood up for more than 40 years. Work is now ongoing in MAM to improve the precision with which the proton magnetic moment is known using the new method.

 

Ultraprecise magnetometry is yet another important activity in MAM. This is needed for the next generation of ultra-precise mass and g-factor measurements with Penning traps. The characteristic time constant for the free induction decay of Helium-3 nuclear spins even in high magnetic fields beyond 1 Tesla can reach time-scales as long as ten seconds. The Larmor precession frequency in the 100 MHz range can thus be measured with great precision. An ultra-sensitive Helium-3 magnetometer for particle trap experiments will be developed in MAM which has the potential to provide an independent measure for the stabilization of magnetic fields at the ppb level and better.

 

 

Section Superheavy Elements (SHE)

GSI Darmstadt provides intense stable beams of nearly all elements and features a worldwide unique set of experimental facilities for superheavy element (SHE) research. It comprises the velocity filter SHIP, the gas-filled separator TASCA, the chemistry beam-line ARTESIA, and the Penning trap mass spectrometer SHIPTRAP along with their ancillary systems. At Mainz University, the TRIGA research reactor and the TRIGA-SPEC setup are installed. The outlined research programme is focused on using the GSI/HIM experimental facilities in Darmstadt and Mainz, which are ideally suited for the proposed projects. The realization of the programme depends strongly on the availability of UNILAC beamtime for experiments in 2015-19. If conditions are unfavourable, part of the programme will have to be realized at foreign institutes to ensure readiness for GSI flagship experiments after 2019.

 

Recently, the synthesis and decay properties of the superheavy elements Z = 114, 115, 116 and 117 were studied. Search experiments for new elements with Z=119 and 120 in different reactions were performed. Despite a very high sensitivity - as low as 70 fb for one event - only upper limits were obtained. In light of such low cross sections for new elements and the reduced availability of beamtime, no search experiments for new elements will be performed in PoF 3. Rather, experiments focusing on the study of the production mechanism, on nuclear, atomic and chemical properties will be performed. Missing nuclei in the gap between the regions of isotopes produced in cold and in 48Ca-induced hot fusion reactions will be synthesized. The atomic number of nuclei produced in 48Ca+actinide reactions will be determined by measuring characteristic X rays. A recent first experiment on this topic yielded promising indications in decay chains assigned to element 115. Entrance channel studies to help selecting optimum reactions for the search for new elements in the PoF 4 period, as well as transfer and non-equilibrium reactions to investigate possible alternative production mechanisms for SHE will be performed.

 

Continuation of decay spectroscopy of SHE isotopes aims at exploring shell strengths along N = 152 and around Z = 108, N = 162. Accessing very short-lived nuclides and isomers is possible by using digital signal processing. Long-lived isotopes will be studied using pure samples after chemical separation.

 

High precision mass measurements of transuranium isotopes near N=152 were performed in the region of Pu-Cf (TRIGA-SPEC) and 255No, 255;256Lr (SHIPTRAP). Combined with spectroscopic data, a first direct mapping of a shell closure in the heaviest elements was achieved. This will be extended towards higher atomic numbers (SHIPTRAP) and towards a more detailed mapping along N=152 in the region of lighter actinides (TRIGA-TRAP).

Laser spectroscopic studies on nobelium will be performed, representing the first optical spectroscopy beyond Fm. In agreement with state-of-the-art fully-relativistic quantum chemical calculations, chemical studies established element 114 to be a volatile metal, forming metallic bonds in contact with metal surfaces. Detailed studies of the volatility and reactivity of elements 113 - never studied chemically to date - and 114 will be performed. New compound classes of lighter transactinides (Z = 106-109) will be studied, significantly broadening the scope of chemical studies of SHE. In a pioneering experiment Sg(CO)6 - featuring a carbon-metal bond characteristic of organometallic compounds - was recently synthesized, and its volatility and interaction with quartz surfaces was studied. Such compounds became accessible only thanks to the combination of recoil separator and chemistry setups. To keep the highly visible SHE program competitive in the long-term, the availability of 10 to 20 times higher beam intensities is crucial. For this, a superconducting continuous-wave linear accelerator in combination with an upgraded High Charge Injector (HLI) is currently under development by HIM in the program Matter and Technology, sub-topic Superconducting RF-Technology. It will operate at markedly reduced operational costs in comparison with the existing GSI accelerator. Generic R&D investigating a complete multi-cell CH-cavity string is foreseen in the program Matter and Technology, sub-topic Superconducting RF-Technology. This will pave the way for the synthesis of new elements in the PoF 4 period.

 

 

Section Accelerators and integrated detectors (ACID)

During the PoF 3 period ACID will concentrate on two main topics. The first one, the development of a multi-cavity superconducting cryo-module for heavy ion acceleration, is located in the program Matter and Technology, sub-topic Superconducting RF-Technology. The second main work package for ACID is electron cooling at the HESR. Within the HESR consortium, ACID operates in close collaboration with Forschungszentrum Jülich and GSI.

 

The availability of a very intense cooler electron beam with relativistic energies is mandatory for the PANDA experiment if the ultimate energy resolution of the experiment is to be reached. This demand, however, creates several challenges. Electron cooling was not included the first modularized start version (MSV 0-3) of FAIR mainly because critical issues were pending and therefore a realistic prediction of cooler performance (and costs) was impossible. During the PoF 3 period ACID will find solutions for these problems and demonstrate their feasibility.

 

A first work package deals with the magnetization of the beam. This property requires that the electron beam is continuously immersed in a longitudinal magnetic field during its electrostatic acceleration towards relativistic energies up to 4.5 MeV (γ = 10). The solenoids which generate the field in the acceleration stage have to be powered by floating supplies. Conventional means of powering (i.e. insulating transfomers, rotating shafts) are not efficient in the multi-MV regime. Very recently, gas expansion turbines have been commercialized by a German company (with development support given by HIM/ACID) for green energy applications (Energiewende). Based on this concept, ACID will build a prototype of an innovative floating power supply which operates on the 10% scale (0.5 MV) of the device needed for HESR. This eliminates the main technological problem for the cooler and therefore forms the basis for its realization which can take place immediately after the POFthree period.

 

Within a collaboration with FZJ, ACID pursues a second cooler problem, which lies in the fact that diagnostics while cooling antiprotons is more difficult due to the missing H0 signal. ACID researchers have suggested to use an innovative minimal invasive device for the diagnostics which is based on Laser-Thomson scattering. A demonstration set-up has already been realized. During PoF 3, this method will first be verified in the test-labs at Mainz and can also be utilized at the existing 2MV cooler system at COSY.

 

 

Section Theory Floor (THFL)

THFL provides the theoretical foundations for all sections of HIM. The main focus lies on the theoretical understanding of the strong interaction at low energies in terms of the underlying gauge theory of Quantum Chromodynamics (QCD). While perturbation theory in the strong coupling constant successfully describes processes involving quarks and gluons at very high energies, a nonperturbative treatment must be employed at typical hadronic scales. Theoretical approaches in the low-energy regime include effective field theories, QCD factorization and simulations of QCD on a space-time lattice. These techniques are being applied in order to make predictions for the FAIR experiments and to pursue a broad research program in hadron spectroscopy, hadron structure, as well as studies of matter under extreme conditions.

 

The PANDA experiment at FAIR will provide detailed information on the internal structure of the nucleon. Of particular interest is the ability to study nucleon form factors for time-like momentum transfers (section EMP). Perturbative QCD can be used for a systematic treatment of quarkgluon dynamics at short distances. From this point of view, the region of large momentum transfers Q >> ΛQCD , where the process can be described as a superposition of hard and soft subprocesses, is especially interesting. Many phenomenological investigations suggest that the correct description should include the so-called soft-overlap contribution which is missing in the collinear factorization. Substantial progress in a model-independent description can be achieved with the help of the Soft Collinear Effective Theory (SCET), and is a major activity in the THFL.

 

Lattice QCD has emerged as a versatile tool for tackling a wide range of topics in strong interaction physics. By applying the latest algorithmic improvements, the lattice group of HIMTHFL will continue to generate state-of-the-art gauge ensembles with dynamical quarks and exploit them for an extensive research program in hadron spectroscopy, hadron structure and QCD thermodynamics. In the area of hadron spectroscopy activities will be focussed on computing the excitation spectrum in various mesonic and baryonic channels. Charmonium spectroscopy is of particular interest, also because of the rich experimental data expected from PANDA. HIM-THFL and collaborators from DESY-Zeuthen are key participants in a European effort for generating a new set of gauge ensembles with 2+1 dynamical quarks for a wide range of lattice spacings. The technical and algorithmic improvements applied in the generation of the new gauge ensembles are a key advantage for detailed calculations of the charmonium spectrum with controlled systematic errors. Another major activity of THFL is the calculation of observables which encode structural properties such as hadronic form factors, moments of parton distribution functions and, eventually, generalized parton distributions. The THFL section has led efforts to eliminate a systematic bias in lattice results for nucleon form factors arising from excited state contributions in Euclidean correlation functions. The use of summed operator insertions offers a handle to reduce these contributions, which has already produced a precise lattice estimate which is compatible with experiment. These activities will be continued and extended when the newly generated gauge ensembles become available.

 

Lattice QCD has been very successful in providing the equation of state of strongly interacting matter at finite temperature. A full investigation of the QCD phase diagram as a function of the baryon chemical potential (as will be probed by the HADES experiment at GSI) is impeded by the notorious sign problem. The THFL section has investigated the nature of the transition from the hadronic to the deconfined phase in the theory with two light quarks at vanishing baryon chemical potential. The nature of this transition in the massless limit constrains the phase diagram of QCD as a whole. As a byproduct of these simulations over a wide range of temperatures, the THFL section has investigated the real-time properties of the medium by constraining the ρ channel spectral function. The latter is key to understand the ρ melting and to make a theoretical prediction of the dilepton spectrum measured in heavy-ion collisions. More work is planned in this direction, including the use of exact QCD sum rules as further constraint on the spectral functions.