Annual Review of Nuclear and Particle Science - Volume 66, 2016
Volume 66, 2016
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The Multiverse and Particle Physics
Vol. 66 (2016), pp. 1–21More LessThe possibility of fundamental theories with very many ground states, each with different physical parameters, changes the way that we approach the major questions of particle physics. Most importantly, it raises the possibility that these different parameters could be realized in different domains in the larger universe. In this review, I survey the motivations for the multiverse and the impact of the idea of the multiverse on the search for new physics beyond the Standard Model.
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Electromagnetic Signatures of Neutron Star Mergers in the Advanced LIGO Era
Vol. 66 (2016), pp. 23–45More LessThe mergers of binaries containing neutron stars and stellar-mass black holes are among the most promising sources for direct detection in gravitational waves by the interferometers Advanced LIGO and Virgo over the next few years. The concurrent detection of electromagnetic emission from these events would greatly enhance the scientific return of these discoveries. We review the state of the art in modeling the electromagnetic signal of neutron star binary mergers across different phases of the merger and multiple wavelengths. We focus on those observables that provide the most sensitive diagnostics of the merger physics and the contribution to the synthesis of rapid neutron capture (r-process) elements in the Galaxy. We also outline expected future developments on the observational and theoretical sides of this rapidly evolving field.
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Long-Baseline Neutrino Experiments
M.V. Diwan, V. Galymov, X. Qian, and A. RubbiaVol. 66 (2016), pp. 47–71More LessWe review long-baseline neutrino experiments in which neutrinos are detected after traversing macroscopic distances. Over such distances neutrinos have been found to oscillate among flavor states. Experiments with solar, atmospheric, reactor, and accelerator neutrinos have resulted in a coherent picture of neutrino masses and mixing of the three known flavor states. We summarize the current best knowledge of neutrino parameters and phenomenology, with a focus on the evolution of the experimental technique. We proceed from the first evidence produced by astrophysical neutrino sources to the current open questions and the goals of future research.
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Initial-State Quantum Fluctuations in the Little Bang
Vol. 66 (2016), pp. 73–94More LessWe review recent developments in the ab initio theoretical description of the initial state in heavy-ion collisions. We emphasize the importance of fluctuations, both for the phenomenological description of experimental data from the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) and for the theoretical understanding of the nonequilibrium early-time dynamics and thermalization of the medium.
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Dark Energy Versus Modified Gravity
Vol. 66 (2016), pp. 95–122More LessUnderstanding the reason for the observed accelerated expansion of the Universe represents one of the fundamental open questions in physics. In cosmology, a classification has emerged among physical models for this acceleration, distinguishing between dark energy and modified gravity. In this review, we provide a brief overview of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology. We also introduce a rigorous distinction between dark energy and modified gravity based on the strong and weak equivalence principles.
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Triggering at the LHC
Vol. 66 (2016), pp. 123–141More LessThe trigger systems of the ALICE, ATLAS, CMS, and LHCb experiments overcame substantial challenges to successfully take data and produce historically significant results from the first run of the LHC. This review describes the challenges, requirements, architecture, design, algorithms, technologies, operation, and performance of the LHC experiment trigger systems during the first LHC run.
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Physics Accomplishments and Future Prospects of the BES Experiments at the Beijing Electron--Positron Collider
Vol. 66 (2016), pp. 143–170More LessThe cornerstone of the Chinese experimental particle physics program is a series of experiments performed in the τ-charm energy region. China began building e+e− colliders at the Institute for High Energy Physics in Beijing more than three decades ago. Beijing Electron Spectrometer (BES) is the common root name for the particle physics detectors operated at these machines. We summarize the development of the BES program and highlight the physics results across several topical areas.
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Neutrino Interactions with Nucleons and Nuclei: Importance for Long-Baseline Experiments
Vol. 66 (2016), pp. 171–195More LessThis article reviews our present knowledge of neutrino interactions with nucleons and discusses the interactions with nuclei, the target material of all presently running and planned long-baseline experiments. I emphasize descriptions of semi-inclusive reactions and full descriptions of the final state; the latter are needed to reconstruct the incoming neutrino energy from final-state observations. I then discuss Monte Carlo generator and more advanced transport-theoretical approaches in connection with experimental results on various reaction mechanisms. Finally, I describe the effects of uncertainties in the reconstruction of the incoming neutrino energy on oscillation parameters. The review argues that the precision era of neutrino physics also needs precision-era generators.
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Neutrino Mass Models
Vol. 66 (2016), pp. 197–217More LessThe discovery of nonzero neutrino masses is among the most important particle physics results of the last two decades: It indicates that the Standard Model of particle physics is incomplete. After 20 years of intense experimental and theoretical research, we still do not know the physics that leads to nonzero neutrino masses. The purpose of this review is to discuss the different models for nonzero neutrino masses. In doing so, I describe the differences between the models, how they connect to other aspects of particle physics, and whether or how one can hope to establish which model—if any—is a faithful description of nature.
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Reactor Neutrino Spectra
Anna C. Hayes, and Petr VogelVol. 66 (2016), pp. 219–244More LessWe present a review of the antineutrino spectra emitted from reactors. Knowledge of these spectra and their associated uncertainties is crucial for neutrino oscillation studies. The spectra used to date have been determined either by converting measured electron spectra to antineutrino spectra or by summing over all of the thousands of transitions that make up the spectra, using modern databases as input. The uncertainties in the subdominant corrections to β-decay plague both methods, and we provide estimates of these uncertainties. Improving on current knowledge of the antineutrino spectra from reactors will require new experiments. Such experiments would also address the so-called reactor neutrino anomaly and the possible origin of the shoulder observed in the antineutrino spectra measured in recent high-statistics reactor neutrino experiments.
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New Nonperturbative Methods in Quantum Field Theory: From Large-N Orbifold Equivalence to Bions and Resurgence
Vol. 66 (2016), pp. 245–272More LessWe present a broad conceptual introduction to some new ideas in nonperturbative quantum field theory (QFT) that have led to progress toward an understanding of quark confinement in gauge theories and, more broadly, toward a nonperturbative continuum definition of QFTs. We first present exact orbifold equivalences of supersymmetric and nonsupersymmetric QFTs in the large-N limit and exact equivalences of large-N theories in infinite volume to large-N theories in finite volume, or even at a single point. We discuss principles by which calculable QFTs are continuously connected to strong-coupling QFTs, allowing understanding of the physics of confinement or the absence thereof. We discuss the role of particular saddle solutions, termed bions, in weak-coupling calculable regimes. The properties of bions motivate an extension of semiclassical methods used to evaluate functional integrals to include families of complex saddles (Picard–Lefschetz theory). This analysis leads us to the resurgence program, which may provide a framework for combining divergent perturbation series with semiclassical instanton and bion/renormalon contributions. This program could provide a nonperturbative definition of the path integral.
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Physics Goals and Experimental Challenges of the Proton–Proton High-Luminosity Operation of the LHC
P. Campana, M. Klute, and P.S. WellsVol. 66 (2016), pp. 273–295More LessThe completion of Run 1 of the Large Hadron Collider (LHC) at CERN has seen the discovery of the Higgs boson and an unprecedented number of precise measurements of the Standard Model, and Run 2 has begun to provide the first data at higher energy. The high-luminosity upgrade of the LHC (HL-LHC) and the four experiments (ATLAS, CMS, ALICE, and LHCb) will exploit the full potential of the collider to discover and explore new physics beyond the Standard Model. We review the experimental challenges and the physics opportunities in proton–proton collisions at the HL-LHC.
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Positrons and Antiprotons in Galactic Cosmic Rays
Vol. 66 (2016), pp. 297–319More LessI consider the impact of recent measurements of positron and antiproton spectra in cosmic rays on our understanding of the origins and propagation of cosmic rays, as well as on the annihilation and decay characteristics of particles of Galactic dark matter, from the perspective of current models postulating energy-dependent leakage of cosmic rays from the Galaxy and of the nested leaky-box model, in which the leakage from the Galaxy is independent of energy. The nested leaky-box model provides a straightforward and consistent explanation of the observed spectral intensities, and finds no compelling need for a contribution from the annihilation or decay of Galactic dark matter. Improved observations and modeling efforts are needed to probe the properties of dark matter deeply enough to be significant to particle physics and cosmology.
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GRETINA and Its Early Science
Vol. 66 (2016), pp. 321–339More Lessγ-Ray spectroscopy continues to be an important tool for the study of nuclei. Excitation energies can be measured directly and in model-independent ways, and thus are among the key observables that can guide our understanding of atomic nuclei. With the availability of short-lived rare-isotope beams, the development of position sensitivity of γ-ray detection systems has been crucial in combating the Doppler broadening encountered for the energies of γ-rays emitted in flight, which are necessary to obtain good energy resolution while maintaining high efficiency. The advanced γ-ray tracking array GRETINA began its science mission at the National Superconducting Cyclotron Laboratory (NSCL), where rare-isotope beams are produced at velocities exceeding 30% of the speed of light. With selected examples from nuclear structure physics and nuclear astrophysics, we show the breadth and reach of the science program afforded by GRETINA and provide an outlook for what can be accomplished with the full 4π array GRETA at the Facility for Rare Isotope Beams (FRIB).
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Physics of Core-Collapse Supernovae in Three Dimensions: A Sneak Preview
Vol. 66 (2016), pp. 341–375More LessNonspherical mass motions are a generic feature of core-collapse supernovae, and hydrodynamic instabilities play a crucial role in the explosion mechanism. The first successful neutrino-driven explosions could be obtained with self-consistent, first-principles simulations in three spatial dimensions. But three-dimensional (3D) models tend to be less prone to explosion than the corresponding axisymmetric two-dimensional (2D) ones. The reason is that 3D turbulence leads to energy cascading from large to small spatial scales, the inverse of the 2D case, thus disfavoring the growth of buoyant plumes on the largest scales. Unless the inertia to explode simply reflects a lack of sufficient resolution in relevant regions, some important component of robust and sufficiently energetic neutrino-powered explosions may still be missing. Such a deficit could be associated with progenitor properties such as rotation, magnetic fields, or precollapse perturbations, or with microphysics that could cause enhancement of neutrino heating behind the shock. 3D simulations have also revealed new phenomena that are not present in 2D ones, such as spiral modes of the standing accretion shock instability (SASI) and a stunning dipolar lepton-number emission self-sustained asymmetry (LESA). Both impose time- and direction-dependent variations on the detectable neutrino signal. The understanding of these effects and of their consequences is still in its infancy.
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The Proton as Seen by the HERA Collider
Vol. 66 (2016), pp. 377–399More LessDeep-inelastic electron–proton (ep) scattering at the HERA collider has been very important in the investigation of the partonic structure of the proton. The neutral- and charged-current cross sections, measured over a large kinematic range, are one of the legacies of the first and so far only ep collider. Here I discuss the combination of H1 and ZEUS data. The HERA data alone can provide parton distribution functions (PDFs) within the framework of perturbative QCD. I also discuss the family of sets of PDFs called HERAPDF2.0 as well as the interpretation of such proton PDFs that characterize proton interactions in momentum space. I then introduce other possible applications of the precision cross sections. In addition, some measurements at HERA provide hints about spatial aspects of the proton. Finally, I present a brief discussion of the connection to nuclear physics.
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Neutrino Physics from the Cosmic Microwave Background and Large-Scale Structure
Vol. 66 (2016), pp. 401–420More LessCosmology and neutrino physics have converged into a recent discovery era. The success of the standard model of cosmology in explaining the cosmic microwave background and cosmological large-scale structure data allows for the possibility of measuring the absolute neutrino mass and providing exquisite constraints on the number of light degrees of freedom, including neutrinos. This sensitivity to neutrino physics requires the validity of some of the assumptions, including general relativity, inflationary cosmology, and standard thermal history, many of which can be tested with cosmological data. This sensitivity is also predicated on the robust handling of systematic uncertainties associated with different cosmological observables. We review several past, current, and future measurements of the cosmic microwave background and cosmological large-scale structure that allow us to do fundamental neutrino physics with cosmology.
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Electromagnetic Structure of Two- and Three-Nucleon Systems: An Effective Field Theory Description
Vol. 66 (2016), pp. 421–447More LessI discuss the use of chiral effective field theory (χEFT) to describe electromagnetic reactions in the two- and three-nucleon systems. I review the results of χEFT power counting for charge and current operators up to relative to leading order, before showing that renormalization-group arguments imply that short-distance electromagnetic operators play a larger role than suggested by this standard counting. A detailed examination of χEFT's predictions for the electromagnetic form factors of deuterium and the trinucleons, and for the threshold captures np→dγ and nd→tγ, enables a critical appraisal of the theory's performance in these contexts. Recent χEFT calculations using the chiral perturbation theory (χPT) potential yielded both form factors that agree with experimental data for Q2<0.25 GeV2 and an excellent description of the challenging threshold captures. Short-distance M1 operators are essential to this success, and the addition of a short-distance part of the nucleon–nucleon charge operator produces precise predictions of the deuteron charge and quadrupole form factors in this kinematic domain.
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Proton–Lead Collisions at the CERN LHC
Vol. 66 (2016), pp. 449–473More LessThe single proton–lead collision run performed at the LHC has had profound consequences for the entire field of hot and dense QCD. The prior, 20-year-long experimental exploration of high-energy nucleus–nucleus collisions indicated that a hot QCD medium is created in a very short time, a fast equilibration. The striking similarities found in these nucleus–nucleus data and the a priori simpler proton–lead collisions, where no hot medium was expected, are refining our understanding of the whole process of thermalization at the most fundamental level. We review the most relevant sets of data taken during the proton–lead collisions of Run 1 at the LHC and the implications they have for our understanding of the underlying physical mechanisms and characterization of hot and dense QCD systems.
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Previous Volumes
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Volume 73 (2023)
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Volume 72 (2022)
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Volume 71 (2021)
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Volume 70 (2020)
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Volume 69 (2019)
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Volume 68 (2018)
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Volume 67 (2017)
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Volume 66 (2016)
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Volume 65 (2015)
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Volume 64 (2014)
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Volume 63 (2013)
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Volume 62 (2012)
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Volume 61 (2011)
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Volume 60 (2010)
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Volume 59 (2009)
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Volume 58 (2008)
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Volume 57 (2007)
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Volume 56 (2006)
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Volume 55 (2005)
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Volume 54 (2004)
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Volume 53 (2003)
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Volume 52 (2002)
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Volume 51 (2001)
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Volume 50 (2000)
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Volume 49 (1999)
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Volume 48 (1998)
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Volume 47 (1997)
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Volume 46 (1996)
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Volume 45 (1995)
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Volume 44 (1994)
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Volume 43 (1993)
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Volume 42 (1992)
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Volume 41 (1991)
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Volume 40 (1990)
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Volume 39 (1989)
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Volume 38 (1988)
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Volume 37 (1987)
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Volume 36 (1986)
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Volume 35 (1985)
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Volume 34 (1984)
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Volume 33 (1983)
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Volume 32 (1982)
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Volume 31 (1981)
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Volume 30 (1980)
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Volume 29 (1979)
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Volume 28 (1978)
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Volume 27 (1977)
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Volume 26 (1976)
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Volume 25 (1975)
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Volume 24 (1974)
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Volume 23 (1973)
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Volume 22 (1972)
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Volume 21 (1971)
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Volume 20 (1970)
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Volume 19 (1969)
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Volume 18 (1968)
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Volume 17 (1967)
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Volume 16 (1966)
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Volume 15 (1965)
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Volume 14 (1964)
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Volume 13 (1963)
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Volume 12 (1962)
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Volume 11 (1961)
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Volume 10 (1960)
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Volume 9 (1959)
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Volume 8 (1958)
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Volume 7 (1957)
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Volume 6 (1956)
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Volume 5 (1955)
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Volume 4 (1954)
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Volume 3 (1953)
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Volume 2 (1953)
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Volume 1 (1952)
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Volume 0 (1932)