Annual Review of Nuclear and Particle Science - Volume 73, 2023
Volume 73, 2023
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Lepton Flavor Violation and Lepton Flavor Universality Violation in b and c Decays
Vol. 73 (2023), pp. 1–21More LessTwo topics have recently risen to prominence within the ongoing searches of beyond–Standard Model effects in b and c decays: observables that test lepton flavor universality (LFU) and those that test lepton flavor violation (LFV). A coherent set of measurements suggests nonstandard LFU effects. General arguments relate LFU to LFV, and the observed size of the former gives hope of observable signals for the latter. We attempt a comprehensive discussion of both theoretical and experimental aspects of these tests. The main final message is that all the instruments necessary to fully establish the putative new effects are at hand, thanks to running experiments and their upgrades. Therefore, this subject stands a concrete chance of ushering in genuinely unexpected discoveries.
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New Solutions to the Gauge Hierarchy Problem
Vol. 73 (2023), pp. 23–39More LessApplying dimensional analysis to the Higgs mass leads one to predict new physics interactions that generate this mass at a scale of the order of 1 TeV. The question of what these interactions could be is known as the gauge hierarchy problem. Resolving this question has been a central aim of particle physics for the past few decades. Traditional solutions introduce new particles with masses below 1 TeV, but that prediction is now challenged by experiment. In this article, I review recent new approaches to the problem that do not require new particles at the TeV mass scale. I first discuss the relaxation approach, whereby the Higgs mass is made dynamical and is small at the absolute minimum of its potential. I then discuss the historical approach, whereby details about inflation and/or reheating after inflation cause the Higgs mass to be smaller than otherwise expected. Finally, I discuss solutions that use conditional probability, whereby conditioning on the fact that the cosmological constant is small automatically leads one to select vacua where the Higgs mass is also small.
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COHERENT at the Spallation Neutron Source
Vol. 73 (2023), pp. 41–68More LessThe Spallation Neutron Source (SNS) at Oak Ridge National Laboratory provides an intense, high-quality source of neutrinos from pion decay at rest. This source was recently used for the first measurements of coherent elastic neutrino–nucleus scattering (CEvNS) by the COHERENT Collaboration, which resulted in new constraints of physics beyond the Standard Model. The SNS neutrino source will enable further CEvNS measurements, exploration of inelastic neutrino–nucleus interactions of particular relevance for understanding supernova neutrinos, and searches for accelerator-produced sub-GeV dark matter. Taking advantage of this unique facility, COHERENT's suite of detectors in Neutrino Alley at the SNS is accumulating more data to address a broad physics program at the intersection of particle physics, nuclear physics, and astrophysics. This review describes COHERENT's first two CEvNS measurements, their interpretation, and the potential of a future physics program at the SNS.
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Experimental Considerations in Long-Baseline Neutrino Oscillation Measurements
Vol. 73 (2023), pp. 69–93More LessLong-baseline neutrino oscillation experiments, which are among the largest neutrino experiments in the world, have extensive physics programs to make precision measurements of three-flavor oscillation parameters, search for physics beyond the Standard Model, and study neutrinos from astrophysical sources. In this article, experimental considerations, including oscillation phenomenology, detector and experiment design, and analysis strategies, are described, with a focus on the three-flavor oscillation measurements. Current and future experiments are discussed, and significant sources of systematic uncertainty, along with mitigation strategies, are emphasized as control of systematic uncertainty is critical for success in precise measurement of long-baseline oscillation parameters. This article is structured as a primer for those new to this area of experimental work.
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Detection and Calibration of Low-Energy Nuclear Recoils for Dark Matter and Neutrino Scattering Experiments
Jingke Xu, P.S. Barbeau, and Ziqing HongVol. 73 (2023), pp. 95–121More LessDetection of low-energy nuclear recoil events plays a central role in searches for particle dark matter interactions with atomic matter and studies of coherent neutrino scatters. Precise nuclear recoil calibration data allow the responses of these dark matter and neutrino detectors to be characterized and enable in situ evaluation of an experiment's sensitivity to anticipated signals. This article reviews the common methods for detection of nuclear recoil events and the wide variety of techniques that have been developed to calibrate detector response to nuclear recoils. We summarize the main experimental factors that are critical for accurate nuclear recoil calibrations, investigate mitigation strategies for different backgrounds and biases, and discuss how the presentation of calibration results can facilitate comparison between experiments. Lastly, we discuss the challenges for future nuclear recoil calibration efforts and the physics opportunities they may enable.
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Implications of Large-Nc QCD for the NN Interaction
Vol. 73 (2023), pp. 123–152More LessWe present a method for ordering two-nucleon interactions based upon their scaling with the number of QCD colors, Nc, in the limit that Nc becomes large. Available data in the two-nucleon sector show general agreement with this ordering, indicating that the method may be useful in other contexts where data are less readily available. However, several caveats and potential pitfalls can make the large-Nc ordering fragile and/or vulnerable to misinterpretation. We discuss the application of the large-Nc analysis to two- and three-nucleon interactions, including those originating from weak and BSM (beyond the Standard Model) interactions, as well as two-nucleon external currents. Finally, we discuss some open questions in the field.
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The Hubble Tension and Early Dark Energy
Vol. 73 (2023), pp. 153–180More LessOver the past decade, the disparity between the value of the cosmic expansion rate determined directly from measurements of distance and redshift and that determined instead from the standard Lambda cold dark matter (ΛCDM) cosmological model, calibrated by measurements from the early Universe, has grown to a level of significance requiring a solution. Proposed systematic errors are not supported by the breadth of available data (and unknown errors are untestable by lack of definition). Simple theoretical explanations for this Hubble tension that are consistent with the majority of the data have been surprisingly hard to come by, but in recent years, attention has focused increasingly on models that alter the early or pre-recombination physics of ΛCDM as the most feasible. Here, we describe the nature of this tension and emphasize recent developments on the observational side. We then explain why early-Universe solutions are currently favored and the constraints that any such model must satisfy. We discuss one workable example, early dark energy, and describe how it can be tested with future measurements. Given an assortment of more extended recent reviews on specific aspects of the problem, the discussion is intended to be fairly general and understandable to a broad audience.
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High-Energy to Ultrahigh-Energy Neutrino Interactions
Vol. 73 (2023), pp. 181–204More LessThe cross sections for neutrino interactions with nucleons have been measured directly in accelerator experiments and through the zenith-angle and energy dependence of neutrino events at the IceCube Neutrino Observatory. Fluxes of high-energy neutrinos are produced at the Large Hadron Collider and by cosmic rays in the atmosphere. High-energy neutrinos also come from astrophysical and cosmic sources. The theory of neutrino interactions is reviewed. Current cross-section measurements and prospects for the future are discussed. The focus here is on neutrino interactions for energies larger than 1 TeV.
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Medium Response and Jet–Hadron Correlations in Relativistic Heavy-Ion Collisions
Vol. 73 (2023), pp. 205–229More LessThe study of high-energy heavy-ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider has evolved from a qualitative understanding to the precise extraction of the properties of the quantum chromodynamics medium at extremely high temperatures. Jet quenching has offered unique insights into the transport properties of the quark–gluon plasma (QGP) created in these energetic collisions. Apart from medium modification of jets, jet-induced medium excitation constitutes another crucial aspect of jet–QGP interaction and is indispensable in understanding the soft components of jets. We review recent theoretical and phenomenological developments regarding medium response to jet energy loss, including an overview of both weakly and strongly coupled approaches for describing the thermalization and propagation of energy deposition from jets, effects of medium response on jet observables, and exploration of its unique signatures in jet–hadron correlations. Jet-induced medium excitation is shown to be an essential component in probing the in-medium dynamics of jets and a critical step toward precise extraction of the QGP properties.
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Boson–Boson Interactions at the LHC
Vol. 73 (2023), pp. 231–253More LessVector boson scattering is a key production process to probe the electroweak symmetry breaking of the Standard Model and is one of the most important topics of the physics program for the HL-LHC since it involves both self-couplings of vector bosons and their coupling with the Higgs boson. If the Higgs mechanism is not the sole source of electroweak symmetry breaking, the scattering amplitude deviates from the Standard Model prediction at high scattering energy. Moreover, deviations may be detectable even if a New Physics scale is higher than the reach of direct searches. In this review, the most recent experimental measurements of the production cross sections of vector boson pairs in association with two jets in proton–proton collisions at
TeV at the LHC are reported, using data sets recorded by the ATLAS and CMS detectors. Applications to searches for New Physics, as well as prospects for measuring the electroweak vector boson scattering processes with larger data samples, are also summarized.
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Physics of the Top Quark at the LHC: An Appraisal and Outlook of the Road Ahead
Vol. 73 (2023), pp. 255–284More LessSince its start, the Large Hadron Collider (LHC) has helped advance both theory and experiment on the production and properties of the heaviest fundamental particle, the top quark. This review focuses on a selected set of measurements and associated searches for new physics, which have opened the door for unprecedented precision in this area of high-energy physics. Fundamental parameters of the theory such as mt, αS, Vtb, and yt are measured from top quark events with relative uncertainties that are smaller than 0.5%, 1.8%, 2%, and 10%, respectively, and that are expected to improve with more data, better experimental methods, and more accurate theory predictions. Several results, even if statistically limited, already significantly constrain the phase space of new physics: measurements of associated production with bosons, processes with four top quarks, and searches for rare decays, among others. It is expected that until the completion of the LHC program, top quark physics will keep providing unique insights regarding the consistency of the Standard Model and the energy scale of new physics.
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Recent Progress in Leptonic and Semileptonic Decays of Charmed Hadrons
Vol. 73 (2023), pp. 285–314More LessWe present a comprehensive review of purely leptonic and semileptonic decays of D0(+),
, and charmed baryons (including
, Ξc, and Ωc). The precise studies of these decays help deepen our understanding and knowledge of quantum chromodynamics via measuring decay constants and form factors, and test the Standard Model through examining the unitarity of the Cabibbo–Kobayashi–Maskawa matrix and lepton flavor universality. We give an overview of the theoretical and experimental tools before discussing the recent progress. The data sets collected by the Beijing Spectrometer III (BESIII) near the production thresholds of
,
, and
offer important opportunities for studies of charm physics.
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The s Process and Beyond
Vol. 73 (2023), pp. 315–340More LessNeutron captures produce the vast majority of abundances of elements heavier than iron in the Universe. Beyond the classical slow (s) and rapid (r) processes, there is observational evidence for neutron-capture processes that operate at neutron densities in between, at different distances from the valley of β stability. Here, we review the main properties of the s process within the general context of neutron-capture processes and the nuclear physics input required to investigate it. We describe massive stars and asymptotic giant branch stars as the s-process astrophysical sites and discuss the related physical uncertainties. We also present current observational evidence for the s process and beyond, which ranges from stellar spectroscopic observations to laboratory analysis of meteorites.
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Ultra-High-Energy Gamma-Ray Astronomy
Vol. 73 (2023), pp. 341–363More LessUltra-high-energy (UHE, >0.1 PeV) γ-ray astronomy is rapidly evolving into an expanding branch of γ-ray astronomy with the surprising discovery of 12 PeVatrons and the detection of a handful of photons above 1 PeV. Nearly all known celestial object types that have emissions in the TeV band are found also to emit UHE photons. UHE γ-rays have a well-defined horizon inside our Galaxy due to the absorption of infrared and cosmic microwave backgrounds in the Universe. In the last 30 years, traditional cosmic ray (CR) measurement techniques have enabled the detection of UHE γ-rays and opened the last observation window. For leptonic sources, UHE radiation is in the deep Klein–Nishina regime, which is largely suppressed. Therefore, UHE γ-ray detection will be helpful in locating and identifying hadronic radiation sources, tracing the historic pursuit for the origin of CRs around the knee of the spectrum. The Crab Nebula is the focus of attention with measured photon emissions up to 1 PeV. In the absence of hadronic processes, these emissions may indicate the existence of an extreme accelerator of e+e−. Use of CR extensive air shower detection techniques broadens the field of view of the source observations, enabling measurement of UHE radiation surrounding the sources. These observations can probe the particle propagation inside and outside the accelerators and the subsequent injection/escape into the interstellar medium.
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Deep-Sea and Lunar Radioisotopes from Nearby Astrophysical Explosions
Vol. 73 (2023), pp. 365–395More LessLive (not decayed) radioisotopes on the Earth and Moon are messengers from recent nearby astrophysical explosions. Measurements of 60Fe in deep-sea samples, Antarctic snow, and lunar regolith reveal two pulses about 3 Myr and 7 Myr ago. Detection of 244Pu in a deep-sea crust indicates a recent r-process event. We review the ultrasensitive accelerator mass spectrometry techniques that enable these findings. We then explore the implications for astrophysics, including supernova nucleosynthesis, particularly the r-process, as well as supernova dust production and the formation of the Local Bubble that envelops the Solar System. The implications go beyond nuclear physics and astrophysics to include studies of heliophysics, astrobiology, geology, and evolutionary biology.
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Physics Beyond the Standard Model Associated with the Top Quark
Vol. 73 (2023), pp. 397–420More LessIn this article, I review scenarios of physics beyond the Standard Model in which the top quark plays a special role. Models that aim at the stabilization of the weak scale are presented together with the specific phenomenology of partner states that are characteristic of this type of model. Further, I present models of flavor in which the top quark is singled out as a special flavor in the Standard Model. The flavor and collider phenomenology of these models is broadly presented. Finally, I discuss the possibility that dark matter interacts preferably with the top quark flavor and give an overview of the dark matter phenomenology of these scenarios, as well as collider and flavor signals.
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A Guide to Hunting Long-Lived Particles at the LHC
Vol. 73 (2023), pp. 421–449More LessThis article is a pedagogical review of searches for long-lived particles at the LHC. It is primarily aimed at experimentalists and theorists seeking to initiate and/or deepen their research in this field. We cover the general theoretical motivation and some example models, the main experimental techniques employed in searches for long-lived particles, and some of the important subtleties involved in estimating signal efficiencies and background rates.
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Previous Volumes
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Volume 74 (2024)
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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)