Ebook: From the Big Bang to the Nucleosynthesis

The CLXXVIII Course of the International School of Physics “Enrico Fermi”, entitled “From the Big Bang to the Nucleosynthesis”, held in Varenna from July 19 to 24, 2010, was devoted to the present understanding of the primordial universe and of the origin of the elements as achieved by studying nuclei and their constituents in extreme regimes of energy and composition. In the quest to work out a comprehensive theory of the appearance and evolution of nuclear matter, physicists have so far made a great effort in reproducing in laboratory the conditions which characterized the Big Bang and the various nucleosynthesis mechanisms occurring in the stars. In particular, by colliding heavy ions at ultrarelativistic energies, one tries to recreate the predicted primordial state of high-energy density matter in which quarks and gluons are effectively deconfined, the so-called Quark Gluon Plasma (QGP), whereas the knowledge of the present-day abundances of heavy elements requires the exploration of the structure and reaction properties of very unstable nuclei as carried out by experiments with radioactive beams.

The actual high-energy frontier of relativistic heavy-ion physics has moved in the last few years from RHIC at BNL to the LHC at CERN, where ALICE is the experiment specifically designed to provide unambiguous evidence of the QGP formation and to characterize its properties. The physics programme underlying this experiment was illustrated by the two world-recognized experts in the field: F. Antinori and U. Wiedemann.

Nuclei far from stability are presently studied in various laboratories and new facilities featuring high-intensity beams are either just completed, under construction or in the planning stage. The main objective is to move further away from stability thus producing, in the most effective way, the relevant unstable nuclei involved in the nucleosynthesis stages and to understand how a many-body nuclear system can be described in conditions very much different from those we find on Earth. The different techniques needed to produce exotic nuclei and to study their degrees of freedom from the ground state and the properties of the excited states have been presented and pedagogically discussed in several lectures by renowned physicists, namely T. Aumann, P. Butler, M. Lewitowicz, T. Motobayshi. In connection with these lectures they gave very focused overviews of the major facilities (GSI-FAIR, CERN-ISOLDE and EURISOL, GANIL-SPIRAL2, RIKEN-RIBF) and their planned experimental programmes.

The complex but appealing theory describing the supernovae explosion and neutron stars was presented by the experts M. Baldo and K. Langanke, who clearly showed that, in addition to the very important role played by the radioactive beams, one also needs precise measurements of the Gamow-Teller strength in stable nuclei and exclusive measurements carried out in heavy-ion collisions around the Fermi energy. These experiments and their associated techniques were the subject of the lectures of M. Harakeh and W. Lynch, pioneers in this field and of the seminar of B. Tsang. The theoretical description of neutron stars as presented in this school pointed out the need of the combined information from ALICE and exotic-nuclei experiments. In addition, exciting lectures on dark energy and matter were given by A. Masiero.

The main lectures were complemented by seminars on issues of current interest and on their future prospect. These concerned the Big Bang nucleosynthesis and energy and solar neutrino production (A. Guglielmetti and C. Spitaleri) and the nuclear cosmochronology (P. Milazzo), which are among the most interesting topics in nuclear astrophysics addressed at the INFN LNS and LNGS laboratories and at CERN by the n_TOF experiment. Beta and gamma decay relevant for nucleosynthesis of heavy nuclei was also presented (G. Benzoni).

The students had the opportunity to compete in a poster session devoted to their activities, the authors of the best posters were selected to illustrate their main achievements in dedicated talks. The atmosphere of the conference was very pleasant and all the participants enjoyed of the presence, for the entire Course, of Prof. R. A. Ricci (honorary President of SIF), who provided a warm welcome and an appreciated concluding talk. The President of CNR, Prof. L. Maiani, honored us with a short visit in which he shared with all the participants his thoughts about the future of nuclear and particle physics. The Course also benefited from the unexpected visit of the former student, Prof. Uri Haber-Schaim, who attended the second course directed by Prof. G. Puppi, 56 years ago.

We are particularly indebted to Prof. L. Cifarelli, President of SIF, for having given us the opportunity to organize such an inspiring Course, and to all the lecturers, who greatly contributed to the scientific programme. We gratefully acknowledge the financial support of the Istituto Nazionale di Fisica Nucleare (INFN) and the technical support of INFN-CNAF, which allowed the lectures to be broadcasted via web. We express our heartfelt gratitude to Ms B. Alzani, Ms G. Bianchi Bazzi and Dr. A. Di Giuseppe for their very professional and efficient help before and during the School. A special thank to Dr. B. Million, scientific secretary of the Course, who played a key role towards the success of this Course. The continuous and invaluable support provided by the Varenna School staff together with the enthusiastic and active participation of the attendees have made this Course an unforgettable experience for us on both scientific and human aspects.

A. Bracco and E. Nappi

These lectures discuss selected topics in nuclear astrophysics. They include hydrogen burning, solar neutrinos, advanced stellar burning stages, the final fate of massive stars as core-collapse supernovae and the associated explosive nucleosynthesis. The emphasis is on the nuclear ingredients, which determine the evolution and dynamics of the astrophysical objects.

In the three lectures that I delivered at the School I tried to introduce some of the main topics in the theory of Neutron Stars where Nuclear Physics plays a major role. In the first part of these lecture notes the structure of (isolated) Neutron Stars is described briefly. The physics of the crust is first developed at basic level, with a short discussion about the properties of the Coulomb lattice of nuclei that is present both in the outer and in the inner crust. The relevance of very asymmetric nuclei is stressed, in relation with the facilities that are developing and planned throughout the world to study exotic nuclei. The many-body theory of nuclear matter is then developed, including the comparison among the different methods. Special attention is payed to neutron matter at low density, as it is present in the outer crust of Neutron Stars. Applications are developed to the theory of nuclei, by means of the energy density functional method with a microscopic basis. The many-body theory is then systematically applied to the structure of Neutron Stars. The structure of nuclei present in the lattice that forms the crust is illustrated in some detail, and a discussion is devoted to the degree of uncertainty that is present in the theory of (non-homogeneous) low density asymmetric nuclear matter. The nuclear matter EoS at higher density is discussed in relation not only to the astrophysical observations, but also to the data on heavy ion collisions at intermediate energy. The complementarity of the laboratory experiments and astrophysical observations is especially emphasized and the fruitful link between the two fields is illustrated. The problem of the maximum mass of Neutron Stars and the transition to quark matter is then introduced, and the latest observational data and their fundamental relevance are briefly discussed. It is shown that it is likely that transition to quark matter occurs at the center of massive Neutron Stars, but the overall content of quark matter is quite uncertain and model dependent. Despite these difficulties, from the latest observations it seems to emerge clearly that the quark matter EoS is more repulsive than in the simplest versions of the quark matter models usually employed to describe the high density deconfined phase. The presentation is kept at the basic level, while the more advanced developments are illustrated with specific examples. The researches that are at the frontier of the theory of Neutron Star structure are sketched, leaving to the references the detail of the theoretical developments. Unfortunately, due to the lack of time (and space) some issues, like superfluidity, are not even touched. Despite that, I hope that the present notes can stimulate the interest on these research lines and be of help to the beginners, entering this wide research field, that is promising new discoveries both at phenomenological and fundamental levels.

The study of giant resonances has been very fruitful in understanding the structure of these modes of excitation of the nucleus and also in helping to shed light onto certain astrophysical phenomena. For example, the compression modes, the isoscalar giant monopole (ISGMR) and dipole (ISGDR) resonances, were extensively studied because of their importance for the determination of the nuclear matter incompressibility and consequently their implications for the equation of state (EoS) of nuclear matter. Gamow-Teller (GT) transitions, on the other hand, play very important roles in various phenomena in nature. In nucleosynthesis, the β-decay of nuclei in the s- and r-processes determines the paths that these processes follow and the abundances of the elements synthesized. In supernova collisions, GT transitions are of paramount importance in the pre-supernova phase where electron capture occurs on neutron-rich fp-shell nuclei at the high temperatures reached in giant stars. Electron capture, which is mediated by GT transitions, removes the electron pressure that keeps the star from collapsing precipitating a cataclysmic implosion followed by a huge explosion throwing much of the star material into space leaving a neutron star or black hole behind.

Experiments with high-energy radioactive beams for nuclear astrophysics are discussed. Emphasis is paid to measurements of masses of exotic nuclei relevant for nucleosynthesis processes and the determination of dipole strength functions for neutron-rich nuclei relevant for both the r-process nucleosynthesis and neutron-star matter. Finally, an outlook is given on the experimental program planned at the radioactive-beam facility NuSTAR at the accelerator facility for anti-proton and ion research FAIR.

New facility of RIBF, Radioactive Isotope Beam Factory, at RIKEN started operation in 2007. It is designed to have capability of accessing 1000 more nuclei compared with the currently known 3000 isotopes by the projectile-fragmentation scheme. One of the advantages of the RIBF new facility, as well as of the old facility, is the availability of fast beams of nuclei far from the stability regardless of chemical property of the element of interest. Some recent studies with these fast beams and development of new devices to fully exploit the capability of the RIBF new facility are presented.

These lectures describe the key elements of ISOL technology and the production of accelerated radioactive ions beams (RIB). A brief history of the ISOL technique is given and current ISOL RIB facilities are described. New developments in ion guide and gas catcher technology are also presented. The second-generation ISOL facilities in Europe and the ultimate EURISOL facility are also described.

The SPIRAL 2 project, an important extension of the GANIL facility which has recently entered in the construction phase is shortly presented. The physics case of the facility based is on the use of high-intensity stable and radioactive beams. Expected performances and main technical parameters of the facility are introduced. Examples of physics topics and related measurements are discussed in the context of new experimental halls and devices to be constructed in order to fully explore the possibilities offered by this advanced Radioactive Ion Beam facility.

We discuss selected topics of the physics of heavy-ion collisions.

In high-energy Pb-Pb collisions at LHC, a deconfined QCD medium is expected to be produced. The open charm and beauty mesons are a powerful probe to investigate the medium properties and its effects on particle production since they experience all the deconfined phase. The ALICE experiment is well suited to perform open-charm analysis thanks to the excellent tracking system, its high-resolution secondary vertex reconstruction capabilities and particle identification performance. In this proceeding the status of the analysis of p-p collisions at = 7 TeV and the perspectives for Pb-Pb measurements will be presented.

The coming decade will have a main goal for particle physics: discovery and understanding of the alleged new physics beyond the Standard Model (SM) which has to be present at the TeV scale if it is to provide the needed ultraviolet completion of the SM for the stabilisation of its electroweak breaking energy scale. In these lectures I discuss why the dark matter issue represents the best hope we have to shed light on such TeV new physics among the various items (neutrino masses, cosmic matter-antimatter asymmetry, inflation, dark energy) of the astroparticle road to new physics. In particular, I will emphasize the complementary role of the LHC physics and the dark matter searches in our thirty-year old quest for low-energy supersymmetry signals.

The primordial nucleosynthesis process has been studied in cosmology since the forties, when Alpher, Bethe and Gamov described the reactions that could take place in the expanding universe represented by FRW metric. From this moment, the computations of light nuclei abundances have been improved with numerical techniques but also with astrophysical developments. However, it is imperative to upgrade the calculated abundances. In this work, we consider the influence of sterile neutrinos, as a contribution of dark matter in radiation domination and their effects in the Hubble factor H, through relativistic degrees of freedom, to compute the relative abundances of primordial nuclei that were produced in cosmological nucleosynthesis by solving the Boltzmann equation. In addition, we make a comparison between our results and the WMAP values for ²H, ³He, ⁴He and ⁷Li abundances.

At astrophysically relevant temperatures, nuclear cross-sections are extremely small and experimental measurements in a laboratory at the Earth's surface are hampered by the cosmic background. The LUNA Collaboration has exploited the unique features of the rock cover offered by the LNGS underground laboratory in terms of background reduction, to study very important H-burning reactions at astrophysically relevant energies. After a general introduction on the LUNA experiment, the most important results and their astrophysical consequences will be reviewed. On-going and future measurements will also be presented.

Because of the Coulomb barrier, reaction cross-sections in astrophysics cannot be accessed directly at the relevant Gamow energies, unless very favorable conditions are met. Theoretical extrapolations of available data are then needed to derive the astrophysical S(0)-factor. Various indirect technique have been used in order to obtain additional information on the parameters entering these extrapolations. The Trojan Horse Method is an indirect method which might help to bypass some of the problems typically encountered in direct measurements, namely the presence of the Coulomb barrier and electron screening between the interacting nuclei.

Nuclear astrophysics, advanced nuclear technology and nuclear structure physics present many cases that require neutron capture reaction data with high precision. In particular, focusing on nuclear astrophysics, refined data are needed for stellar nucleosynthesis, investigation of stellar physical conditions and applications to evaluations of the age of the Universe. New neutron capture measurements were performed at the pulsed neutron time-of-flight n_TOF facility at CERN, where the white neutron energy spectrum ranges from thermal to hundreds of MeV, covering the full energy range of interest for nuclear astrophysics. Moreover, the high instantaneous neutron flux, and the favourable background conditions in the experimental area make this facility unique for high-resolution time-of-flight measurements of neutron-induced reaction cross-sections. The n_TOF Collaboration is presently operating two different experimental set-ups. The first consists of two low-neutron sensitivity C₆D₆ detectors with the analysis relying on the pulse height weighting technique. In addition, a total absorption calorimeter, consisting of 40 BaF₂ crystals covering the whole solid angle, was used. A review of the astrophysical program made at the n_TOF facility, results on selected stable and unstable samples and implications are presented.

Neutron-rich nuclei beyond N = 126 in the lead region were populated by fragmenting a ²³⁸U beam at 1 GeV A on a Be target and then separated by the Fragment Separator at GSI. Their isomeric and beta-decays were observed, enabling the study of the shell structure of neutron-rich nuclei around Z = 82 shell closure. Preliminary results of the analysis are hereby reported.

Spectroscopic factors are fundamental quantities in nuclear physics. They have been extensively used in understanding the single-particle properties of nuclear structures and astrophysical network calculations. Neutron spectroscopic factors of 88 ground state and 565 excited states for Z=3−28 stable nuclei from (d, p) and (p, d) transfer reactions have been extracted using a systematic approach with minimum assumptions. This extensive set of data suggests that the extracted spectroscopic factors are in good agreement with the predictions of the large-basis shell-model predictions. We have extended the analysis to the experimental data obtained from inverse neutron transfer reaction of proton-rich ³⁴Ar and neutron-rich ⁴⁶Ar. The experimental results show little reduction of the ground-state neutron spectroscopic factor of the proton-rich nucleus ³⁴Ar compared to that of ⁴⁶Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions and the dispersive-optical model analysis, but are inconsistent with the trends observed in knockout reaction measurements.

Isospin mixing induced by Coulomb interaction has been measured in the compound nucleus ⁸⁰Zr^* with Z = N = 40 at T ~ 2 MeV produced in a fusion-evaporation reaction. The observable sensitive to the isospin purity of the compound nucleus is the giant dipole resonance γ decay. The Coulomb spreading width of the I = I₀ + 1 state and the degree of isospin mixing of the compound nucleus has been obtained via statistical model analysis of the measured γ spectrum.

The LHC physics programme envisages to collide lead ions with the aim to recreate the conditions just after the Big Bang under laboratory conditions. ALICE features an experimental layout optimized to study this physics topic. The ALICE-HMPID detector has been designed to identify charged hadrons (π, K, p) in the momentum range 1 ≤ p ≤ 5 GeV/c. Preliminary HMPID results from p-p collisions at = 7 TeV will be presented.