In the last 30 days

• Open/close Review of Particle Physics

  K Nakamura (Particle Data Group) 2010 J. Phys. G: Nucl. Part. Phys. 37 075021 Tag this article

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  This biennial Review summarizes much of particle physics. Using data from previous editions, plus 2158 new measurements from 551 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on neutrino mass, mixing, and oscillations, QCD, top quark, CKM quark-mixing matrix, V _ud & V _us, V _cb & V _ub, fragmentation functions, particle detectors for accelerator and non-accelerator physics, magnetic monopoles, cosmological parameters, and big bang cosmology.

  A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: pdg.lbl.gov.

• Open/close Review of Particle Physics

  W-M Yao et al 2006 J. Phys. G: Nucl. Part. Phys. 33 1 Tag this article

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  This biennial Review summarizes much of particle physics. Using data from previous editions, plus 2633 new measurements from 689 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors, probability, and statistics. Among the 110 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V _ud & V _us, V _cb & V _ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.
       A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.

• Open/close ALICE: Physics Performance Report, Volume II

  ALICE Collaboration et al 2006 J. Phys. G: Nucl. Part. Phys. 32 1295 Tag this article

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  ALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. It currently involves more than 900 physicists and senior engineers, from both the nuclear and high-energy physics sectors, from over 90 institutions in about 30 countries.

  The ALICE detector is designed to cope with the highest particle multiplicities above those anticipated for Pb–Pb collisions (d N _ch/d y up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and pA), which primarily provide reference data for the nucleus–nucleus collisions. In addition, the pp data will allow for a number of genuine pp physics studies.

  The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2004. The experiment is currently under construction and will be ready for data taking with both proton and heavy-ion beams at the start-up of the LHC.

  Since the comprehensive information on detector and physics performance was last published in the ALICE Technical Proposal in 1996, the detector, as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) provides an updated and comprehensive summary of the performance of the various ALICE subsystems, including updates to the Technical Design Reports, as appropriate.

  The PPR is divided into two volumes. Volume I, published in 2004 (CERN/LHCC 2003-049, ALICE Collaboration 2004 J. Phys. G: Nucl. Part. Phys. 30 1517–1763), contains in four chapters a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, the experimental conditions at the LHC, a short summary and update of the subsystem designs, and a description of the offline framework and Monte Carlo event generators.

  The present volume, Volume II, contains the majority of the information relevant to the physics performance in proton–proton, proton–nucleus, and nucleus–nucleus collisions. Following an introductory overview, Chapter 5 describes the combined detector performance and the event reconstruction procedures, based on detailed simulations of the individual subsystems. Chapter 6 describes the analysis and physics reach for a representative sample of physics observables, from global event characteristics to hard processes.

• Open/close Fragment mass distributions in the fission of heavy nuclei by intermediate- and high-energy probes

  E Andrade-II et al 2011 J. Phys. G: Nucl. Part. Phys. 38 085104 Tag this article

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  Recent experiments have shown that the multimode approach for describing the fission process is compatible with the observed results. A systematic analysis of the parameters obtained by fitting the fission-fragment mass distribution to the spontaneous and low-energy data has shown that the values for those parameters present a smooth dependence upon the nuclear mass number. In this work, a new methodology is introduced for studying fragment mass distributions through the multimode approach. It is shown that for fission induced by energetic probes ( E > 30 MeV) the mass distribution of the fissioning nuclei produced during the intranuclear cascade and evaporation processes must be considered in order to have a realistic description of the fission process. The method is applied to study ²⁰⁸Pb, ²³⁸U, ²³⁹Np and ²⁴¹Am fission induced by protons or photons.

• Open/close Structure of scalar mesons and the Higgs sector of strong interaction

  Martin Schumacher 2011 J. Phys. G: Nucl. Part. Phys. 38 083001 Tag this article

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  The scalar mesons σ(600), κ(800), f ₀(980) and a ₀(980) together with the pseudo Goldstone bosons π, K and η may be considered as the Higgs sector of strong interaction. After a long time of uncertainty about the internal structure of the scalar mesons there now seems to be consistency which is in line with the major parts of experimental observations. Great progress has been made by introducing the unified model of Close and Törnqvist. This model states that scalar mesons below 1 GeV may be understood as in S-wave with some in P-wave in the center, further out they rearrange as and finally as meson–meson states. The P-wave component inherent in the structure of the neutral scalar mesons can be understood as a doorway state for the formation of the scalar meson via two-photon fusion, whereas in nucleon Compton scattering these P-wave components serve as intermediate states. The masses of the scalar mesons are predicted in terms of spontaneous and explicit symmetry breaking.

• Open/close CMS Physics Technical Design Report, Volume II: Physics Performance

  The CMS Collaboration 2007 J. Phys. G: Nucl. Part. Phys. 34 995 Tag this article

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  CMS is a general purpose experiment, designed to study the physics of pp collisions at 14 TeV at the Large Hadron Collider (LHC). It currently involves more than 2000 physicists from more than 150 institutes and 37 countries. The LHC will provide extraordinary opportunities for particle physics based on its unprecedented collision energy and luminosity when it begins operation in 2007.

  The principal aim of this report is to present the strategy of CMS to explore the rich physics programme offered by the LHC. This volume demonstrates the physics capability of the CMS experiment. The prime goals of CMS are to explore physics at the TeV scale and to study the mechanism of electroweak symmetry breaking—through the discovery of the Higgs particle or otherwise. To carry out this task, CMS must be prepared to search for new particles, such as the Higgs boson or supersymmetric partners of the Standard Model particles, from the start-up of the LHC since new physics at the TeV scale may manifest itself with modest data samples of the order of a few fb ⁻¹ or less.

  The analysis tools that have been developed are applied to study in great detail and with all the methodology of performing an analysis on CMS data specific benchmark processes upon which to gauge the performance of CMS. These processes cover several Higgs boson decay channels, the production and decay of new particles such as Z' and supersymmetric particles, B _s production and processes in heavy ion collisions. The simulation of these benchmark processes includes subtle effects such as possible detector miscalibration and misalignment. Besides these benchmark processes, the physics reach of CMS is studied for a large number of signatures arising in the Standard Model and also in theories beyond the Standard Model for integrated luminosities ranging from 1 fb ⁻¹ to 30 fb ⁻¹. The Standard Model processes include QCD, B-physics, diffraction, detailed studies of the top quark properties, and electroweak physics topics such as the W and Z ⁰ boson properties. The production and decay of the Higgs particle is studied for many observable decays, and the precision with which the Higgs boson properties can be derived is determined. About ten different supersymmetry benchmark points are analysed using full simulation. The CMS discovery reach is evaluated in the SUSY parameter space covering a large variety of decay signatures. Furthermore, the discovery reach for a plethora of alternative models for new physics is explored, notably extra dimensions, new vector boson high mass states, little Higgs models, technicolour and others. Methods to discriminate between models have been investigated.

  This report is organized as follows. Chapter 1, the Introduction, describes the context of this document. Chapters 2–6 describe examples of full analyses, with photons, electrons, muons, jets, missing E _T, B-mesons and τ's, and for quarkonia in heavy ion collisions. Chapters 7–15 describe the physics reach for Standard Model processes, Higgs discovery and searches for new physics beyond the Standard Model.

• Open/close The cosmological constant puzzle

  Steven D Bass 2011 J. Phys. G: Nucl. Part. Phys. 38 043201 Tag this article

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  The accelerating expansion of the Universe points to a small positive vacuum energy density and negative vacuum pressure. A strong candidate is the cosmological constant in Einstein's equations of general relativity. Possible contributions are zero-point energies and the condensates associated with spontaneous symmetry breaking. The vacuum energy density extracted from astrophysics is 10 ⁵⁶ times smaller than the value expected from quantum fields and standard model particle physics. Is the vacuum energy density time dependent? We give an introduction to the cosmological constant puzzle and ideas how to solve it.

• Open/close Thermal properties of baryonic matter

  H R Moshfegh and M Ghazanfari Mojarrad 2011 J. Phys. G: Nucl. Part. Phys. 38 085102 Tag this article

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  On the basis of the Thomas–Fermi approximation as a semi-classical mean-field method, the equation of state at finite temperature for different structures of baryonic matter such as symmetric and asymmetric nuclear matter, pure neutron matter and beta stable matter is determined by using the extended phenomenological nucleon–nucleon interaction of Seyler and Blanchard, presented by Myers and Swiatecki (1990 Ann. Phys. 204 401; 1996 Nucl. Phys. A 601 141). By performing the functional variation of total free energy with respect to the occupancy distribution in phase space to reach the minimum conditions of total free energy, we have obtained expressions for effective mass which is only density dependent and effective one-body potential which has both density and temperature dependences. Accordingly, an explicit form of the distribution function can be derived. In our statistical approach, the thermal properties of these dense structures are studied. The quantities such as free energy, energy, entropy and the pressure are calculated as the functionals of the distribution function for given temperature and density. Special attention is also paid to the investigation of the critical behavior of these systems. As a result, the critical temperature and critical exponent of symmetric nuclear matter are found while there is no phase transition in the pure neutron matter and beta stable matter. Our results are in good agreement with experimental predictions and other theoretical investigations.

• Open/close On the chemical composition of cosmic rays of highest energy

  Grzegorz Wilk and Zbigniew Włodarczyk 2011 J. Phys. G: Nucl. Part. Phys. 38 085201 Tag this article

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  We present arguments aiming at reconciling apparently contradictory results concerning the chemical composition of cosmic rays (CRs) of highest energy, coming recently from the Auger and HiRes collaborations. In particular, we argue that the energy dependence of the mean value and root mean square fluctuation of shower maxima distributions observed by the Auger experiment are not necessarily caused by the change of the nuclear composition of primary CRs. They could also be caused by the change of distribution of the first interaction point in the cascade. A new observable, in which this influence is strongly suppressed, is proposed and tested.

• Open/close Study of the ¹¹C(p, γ) reaction via the indirect d(¹¹C,¹²N)n transfer reaction

  D W Lee et al 2011 J. Phys. G: Nucl. Part. Phys. 38 075201 Tag this article

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  The ¹¹C(p,γ) ¹²N reaction is expected to be an important branch point in supermassive low-metallicity stars because it could produce CNO seed nuclei before the traditional triple-α process turns on. In this work, the d( ¹¹C, ¹²N)n transfer reaction was employed to evaluate this reaction using a radioactive ion beam of 150 MeV ¹¹C with 6 × 10 ⁵ ions s ⁻¹ on target from the BEARS project at the 88 inch cyclotron at the Lawrence Berkeley National Laboratory. Excellent agreement was obtained between the experimental cross sections (θ _c.m. = 10.9–71.5°) and DWBA calculations. The asymptotic normalization coefficient was deduced to be .