Dedicated to Professor Apolodor Aristotel Raduta’s 70th Anniversary

FAIR - THE FACILITY FOR ANTIPROTON AND ION RESEARCH

H. STOECKER1,2,3, C. STURM1

1GSI Helmholtzzentrum fur Schwerionenforschung GmbH,Planckstr. 1, D-64291 Darmstadt, Germany

2Institut fur Theoretische Physik, Goethe Universitat Frankfurt,Max-von-Laue Str. 1, D-60438 Frankfurt Main, Germany

3Frankfurt Institute for Advanced Studies, Ruth-Moufang-Str. 1,D-60438 Frankfurt am Main, Germany

Received June 17, 2013

In 2018 a broad spectrum of unprecedented fore-front research becomes avail-able at the Facility for Antiproton and Ion Research, FAIR. The new facility is beingconstructed within the next five years adjacent to the existing accelerator complex ofthe GSI Helmholtz Centre for Heavy Ion Research at Darmstadt/Germany, expandingthe research goals and technical possibilities substantially. At worldwide unique ac-celerator and experimental facilities, FAIR will open the way for a large variety ofexperiments in hadron, nuclear, atomic and plasma physics as well as applied scienceswhich will be briefly described in this article∗.

Key words: GSI; FAIR; strong electromagnetic fields; high energy density mat-ter; plasma; biological effectiveness; radiation damage; material re-search; relativistic nucleus-nucleus collisions; CBM; HADES; neu-tron star; QCD phase diagram first order phase transition; QCDcritical endpoint; charm; open-charm; multi-strange baryon; rareisotope beam; Super-FRS; supernova; nucleosynthesis; antiprotonbeam; PANDA; high precision spectroscopy; charmonium; hybridmeson; glueball; XYZ state; hypernuclei.

1. INTRODUCTION

The Facility for Antiproton and Ion Research, FAIR [1–3], will provide anextensive range of particle beams from protons and their antimatter partners, antipro-tons to ion beams of all chemical elements up to the heaviest one, uranium, with inmany respects world record intensities. As a joint effort of 16 countries † the newfacility builds, and substantially expands, on the present accelerator system at GSIHelmholtz Centre for Heavy Ion Research, both in its research goals and its tech-nical possibilities. Compared to the present GSI facility, an increase of a factor of100 in primary beam intensities, and up to a factor of 10000 in secondary radioactive∗This article bases upon the FAIR Green Paper [4] and updates our former publications [5–8].†In alphabetical order: Austria, China, Finland, France, Germany, Greece, India, Italy, Poland,

Romania, Russia, Slovenia, Slovakia, Spain, Sweden, and the United Kingdom

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beam intensities, will be a technical property of FAIR. Other characteristics will beexcellent beam qualities of both primary and secondary beams. This will be achievedthrough innovative beam handling techniques, many aspects of which hav e been de-veloped at GSI over recent years with the present system. This includes in particularelectron-beam cooling of high-energy, high-charge state ion beams in storage ringsand bunch compression techniques.

After the official launch of the project on November 7th, 2007, on October 4th,2010, nine countries‡ signed the international agreement on the construction of FAIR.Because of the long lead times for civil-construction planning, civil work for the firstbuildings of FAIR has started in 2012 and first beams will be delivered in 2018. Torealize a high degree of truly parallel operation of the different research programsthe design of FAIR includes the superconducting double-ring synchrotrons SIS100and SIS300 with a circumference of 1100 meters and a magnetic rigidity of 100 and300 Tm, respectively. Since a key feature of the new facility will be the generationof intense, high-quality secondary beams, the facility design contains a system ofassociated storage rings for beam collection, cooling, phase space optimization andexperimentation (Fig. 1).

The start version of FAIR, the so-called Modularized Start Version [4–8], con-sists of a basic module 0, the SIS100 accelerator, as well as three experimental mod-ules (module 1-3) as it is color-coded illustrated in Fig. 1. Following an upgrade forhigh intensities, the existing GSI accelerators UNILAC and SIS18 will serve as aninjector. Adjacent to the SIS100 synchrotron are two storage-cooler rings and experi-ment stations, including a superconducting nuclear fragment separator (Super-FRS)and an antiproton production target. The Modularized Start Version secures an out-standing science potential for all scientific pillars of FAIR within the current fund-ing commitments. Moreover, after the start phase and as additional funds becomeavailable the facility will be accomplished by experimental storage rings enhancingcapabilities of secondary beams and by the SIS300 providing parallel operation ofthe experimental programs as well as particle energies 20-fold higher compared tothose achieved so far at GSI.

2. THE EXPERIMENTAL PROGRAM OF FAIR

The main thrust of FAIR research focuses on the structure and evolution ofmatter on both a microscopic and on a cosmic scale – deepening our understandingof fundamental questions such as : How does the complex structure of matter atall levels arise from the basic constituents and the fundamental interactions ? How‡In alphabetical order: Finland, France, Germany, India, Poland, Romania, Russia, Slovenia and

Sweden

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Fig. 1 – On the left the existing GSI facility is shown. Displayed in color is the so called Modular-ized Start Version of FAIR including module 0, 1, 2 and 3 . Coloring: the 100 Tm super conductingsynchrotron SIS100 (module 0) - green; the experimental area for CBM/HADES (module 1) - red; theNuSTAR facility including the Super-FRS (module 2) - yellow; The Antiproton facility including thePANDA experiment (module 3) - orange. Not shown is the additional experimental area above groundfor the APPA community (module 1). These colored parts are financed within the presently availablefirm funding commitments of the partner countries.

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can the structure of hadronic matter be deduced from the strong interaction ? Inparticular, what is the origin of hadron masses ? What is the structure of matter underthe extreme conditions of temperature and density found in astrophysical objects ?What was the evolution and the composition of matter in the early Universe ? Whatis the origin of the elements in the Universe ?

The approved FAIR research program embraces 14 experiments. These formthe four scientific pillars of FAIR and offer a large variety of unprecedented forefrontresearch in hadron, nuclear, atomic and plasma physics as well as applied sciences.Already today, over 2500 scientists and engineers are involved in the design andpreparation of the FAIR experiments. The four scientific pillars are APPA, CBM,NuSTAR, and PANDA.

2.1. APPA – ATOMIC PHYSICS, PLASMA PHYSICS AND APPLICATIONS

Atomic physics with highly charged ions [9,10] will concentrate on two centralresearch themes: (i) the correlated electron dynamics in strong, ultra-short electro-magnetic fields including the production of electron-positron pairs and (ii) funda-mental interactions between electrons and heavy nuclei, in particular the interactionsdescribed by Quantum Electrodynamics, QED. Here bound-state QED in criticaland supercritical fields is the focus of the research programme. In addition, atomicphysics techniques will be used to determine properties of stable and unstable nu-clei and to perform tests of predictions of fundamental theories besides QED. SinceFAIR is promising the highest intensities for relativistic beams of stable and unsta-ble heavy nuclei, combined with the strongest available electromagnetic fields, for abroad range of experiments. This will then allow the extension of atomic physics re-search across virtually the full range of atomic matter, i.e. concerning the accessibleionic charge states as well as beam energies.

For Plasma physics the availability of high-energy, high-intensity ion-beamsenables the investigation of high energy density matter in regimes of temperature,density and pressure not accessible so far [11]. It will allow probing new areas in thephase diagram and long-standing open questions of basic equation-of-state researchcan be addressed.

FAIR will provide beams of high energy and very high intensity, whose biolog-ical effectiveness was never studied in the past, but whose contribution to the doseequivalent in space is very significant. It will be possible to investigate the radiationdamage induced by cosmic rays and protection issues for Moon and Mars missions.Furthermore, the intense ion-matter interactions with projectiles of energies above 1GeV/u will enable systematic studies of material modifications.

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2.2. CBM/HADES – COMPRESSED BARYONIC MATTER

Violent collisions between heavy nuclei promise insight into an unusual statein nature, that of highly compressed nuclear matter. In addition to its relevance forunderstanding fundamental aspects of the strong interaction, this form of matter mayexist in various so far unexplored phases in the interior of neutron stars and in thecore of supernovae. The mission of high-energy nucleus-nucleus collision experi-ments worldwide is to investigate the properties of strongly interacting matter underthese extreme conditions. At very high collision energies, as available at RHIC andLHC, the measurements concentrate on the study of the properties of deconfinedQCD matter at very high temperatures and almost zero net baryon densities. Resultsfrom lattice QCD indicate that the transition from confined to deconfined matter atvanishing net baryon density is a smooth crossover, whereas in the region of highnet baryon densities, accessible with heavy-ion reactions at lower beam energi es, afirst-order phase transition is expected [12]. Its experimental confirmation would bea substantial progress in the understanding of the properties of strongly interactingmatter.

Complementarily to high-energy nucleus-nucleus collision experiments at RHICand LHC, the CBM experiment [13–15] as well as HADES [16–21] at SIS100/300will explore the QCD phase diagram in the region of very high baryon densitiesand moderate temperatures by investigating heavy-ion collision in the beam energyrange 2–35 AGeV. This approach includes the study of the nuclear matter equation-of-state, the search for new forms of matter, the search for the predicted first orderphase transition to the deconfinement phase at high baryon densities, the QCD criti-cal endpoint, and the chiral phase transition, which is related to the origin of hadronmasses. In the case of the predicted first order phase transition, basically one has tosearch for non-monotonic behaviour of observables as function of collision energyand system size. The CBM experiment at FAIR is being designed to perform thissearch with a large range of observ ables, including very rare probes at these energyregime like charmed hadrons. Produced near threshold, their measurement might bewell suited to discriminate hadronic from partonic production scenarios. The for-mer requires pairwise creation of charmed hadrons, the latter the recombination ofc-quarks created in first chance collisions of the nucleus-nucleus reaction. Ratios ofhadrons containing charm quarks as a function of the available energy may providedirect evidence for a deconfinement phase.

The properties of hadrons are expected to be modified in a dense hadronic en-vironment which is eventually linked to the onset of chiral symmetry restoration athigh baryon densities and/or high temperatures. The experimental verification of thistheoretical prediction is one of the most challenging questions in modern stronglyinteracting matter physics. The dileptonic decays of light vector mesons (ρ,ω,φ) pro-

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vide the tool to study such modifications since the lepton daughters do not undergostrong interactions and can therefore leave the dense hadronic medium essentiallyundistorted by final-state interaction. For these investigations the ρ meson plays animportant role since it has a short lifetime and through this a large probability todecay inside the reaction zone when created in a nucleus-nucleus collision. As a de-tector system dedicated to high-precision di-electron spectroscopy at beam energiesof 1 – 2 AGeV, the modified HADES detector at SIS1 00 will measure e+e− decaychannels as well as hadrons [19–21] in collisions of light nuclei up to 10 AGeV beamenergy. Complementarily, the CBM experiment will cover the complete FAIR energyrange in collisions of heavy nuclei by measuring both the e+e− and the µ+µ− decaychannels.

Most of the rare probes like lepton pairs, multi-strange hyperons and charmwill be measured for the first time in the FAIR energy range. The goal of the CBMexperiment as well as HADES is to study rare and bulk particles including theirphase-space distributions, correlations and fluctuations with unprecedented precisionand statistics. These measurements will be performed in nucleus–nucleus, proton–nucleus, and proton–proton collisions at various beam energies. The unprecedentedbeam intensities will allow studying extremely rare probes with high precision whichhave not been accessible by previous heavy-ion experiments at the AGS and the SPS.

2.3. NuSTAR – NUCLEAR STRUCTURE, ASTROPHYSICS AND REACTIONS

The main scientific thrusts in the study of nuclei far from stability are aimedat three areas of research: (i) the structure of nuclei, the quantal many-body systemsbuilt by protons and neutrons and governed by the strong force, towards the limits ofstability, where nuclei become unbound, (ii) nuclear astrophysics delineating the de-tailed paths of element formation in stars and explosive nucleosynthesis that involveshort-lived nuclei, (iii) and the study of fundamental interactions and symmetriesexploiting the properties of specific radioactive nuclei.

The central part of the NuSTAR programme at FAIR [22, 23] is the high ac-ceptance Super-FRS with its multi-stage separation that will provide high intensitymono-isotopic radioactive ion beams of bare and highly-ionized exotic nuclei at andclose to the driplines. This separator, in conjunction with high intensity primarybeams with energies up to 1.5 AGeV, is the keystone for a competitive NuSTARphysics programme. This opens the unique opportunity to study the evolution of nu-clear structure into the yet unexplored territory of the nuclear chart and to determinethe properties of many short-lived nuclei which are produced in explosive astrophys-ical events and crucially influence their dynamics and associated nucleosynthesisprocesses.

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2.4. PANDA – ANTIPROTON ANNIHILATION IN DARMSTADT

The big challenge in hadron physics is to achieve a quantitative understandingof strongly interacting complex systems at the level of quarks and gluons. In pp-annihilation, particles with gluonic degrees of freedom as well as particle-antiparticlepairs are copiously produced, allowing spectroscopic studies with unprecedentedstatistics and precision. The PANDA experiment at FAIR [24–26] will bring newfundamental knowledge in hadron physics by pushing the precision barrier towardsnew limits. The charmonium (cc) spectroscopy will take advantage of high-precisionmeasurements of mass, width and decay branches. Particular emphasis is placedon mesons with open and hidden charm, which extends ongoing studies in the lightquark sector to heavy quarks, and adds information on contributions of the gluondynamics to hadron masses. The search for exotic hadronic matter such as hybridmesons or heavy glueballs gains enormously by precise scanning of resonance curvesof narrow states as well. Recently, this field has attracted much attention with thesurprise observation at electron-positron colliders of the new X, Y and Z states withmasses around 4 GeV. These heavy particles show very unusual properties, whosetheoretical interpretation is entirely open. Additionally, the precision gamma-rayspectroscopy of single and double hypernuclei will allow extracting information ontheir structure and on the hyperon-nucleon and hyperon-hyperon interaction.

3. CONCLUSION

On October 4th, 2010, and after about ten years of negotiations, R&D and writ-ing reports, nine countries signed the international agreement on the construction ofthe Facility for Antiproton and Ion Research FAIR. Construction of the first FAIRbuildings has started in 2013, so that the first beams will be delivered in 2018. Thestart version of FAIR, the so-called Modularized Start Version, includes the super-conducting synchrotron SIS100 as well as three experimental modules to performexperiments for all research pillars. It will allow to carry out an outstanding andworld-leading research programme in hadron, nuclear, atomic and plasma physicsas well as applied sciences. Due to the high luminosity which exceeds current fa-cilities by orders of magnitude, experiments will be feasible that could not be doneelsewhere. FAIR will expand the knowledge in various scientific fields beyond cur-rent frontiers. Moreover, the exploitation of exiting strong cross-topical synergiespromise novel insights.

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