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The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,143 new measurements from 709 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 120 reviews are many that are new or heavily revised, including a new review on Machine Learning, and one on Spectroscopy of Light Meson Resonances. The Review is divided into two volumes. Volume 1 includes the Summary Tables and 97 review articles. Volume 2 consists of the Particle Listings and contains also 23 reviews that address specific aspects of the data presented in the Listings. The complete Review (both volumes) is published online on the website of the Particle Data Group (pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version optimized for use on phones, and as an Android app.

The inclusive charged-hadron momentum spectra from the psi and psi' decays produced in e/sup +/e/sup -/ collisions at SPEAR are presented. The data were obtained with a small solid-angle, single-arm magnetic spectrometer with good particle-identification abilities centered at 90 degrees with respect to the beams. The particle-separated invariant cross sections are compared with data from e/sup +/e/sup -/ collisions at ..sqrt..s-bar = 4.8 and 7.3 GeV, obtained with the same spectrometer, in order to observe the difference between hadron production at the resonances and in the continuum.

We report on inclusive hadron production in e/sup +/e/sup -/ annihilation at < s < or = = 53 GeV/sup 2/, using a small solid-angle magnetic spectrometer with good particle identification at 90/sup 0/ to the beams at SPEAR II. The cross sections of ..pi../sup + -/ and K/sup + -/ when compared with data at s = 23 GeV/sup 2/ exhibit scaling in (s/..beta..) dsigma/dx with x = 2E/s/sup 1/2/. The invariant cross section depends on the momentum as p/sup -4/.

Following reports of anomalous dielectron prediction in the mass region near 6 GeV at 400 GeV, we searched for an enhancement in the reaction e/sup +/e/sup -/ hadrons and e/sup +/e/sup -/ ..-->.. e/sup +/e/sup -/ at SPEAR in the center-of-mass energy range 5.67--6.43 GeV. The leptonic and hadronic cross sections show no statistically significant peaks. In this mass range, 95% confidence level upper limits for the decay width into electron pairs are less than 200 eV for a narrow resonance which decays predominantly either into hadrons or into electron pairs.

We present results on charged multiplicity ${n}_{\mathrm{ch}}=2$ and ${n}_{\mathrm{ch}}g2$ muon events produced in ${e}^{+}{e}^{\ensuremath{-}}$ collisions with $〈{s}^{\frac{1}{2}}〉=7.3$ GeV at 90\ifmmode^\circ\else\textdegree\fi{} to the beams. The background-subtracted inclusive cross section for the ${n}_{\mathrm{ch}}=2$ events is 10.2\ifmmode\pm\else\textpm\fi{}5.4 pb/sr, in agreement with the expected contribution from the heavy lepton $\ensuremath{\tau}$. The cross section for the ${n}_{\mathrm{ch}}g2$ events is 19.0\ifmmode\pm\else\textpm\fi{}6.5 pb/sr whereas we expect only 2.9 pb/sr from the $\ensuremath{\tau}$, indicating that we may be seeing the weak decays of charmed mesons.

Pulse height spectra in a sandwich of three thick plastic scintillators in which protons stopped with an approximately uniform range distribution were sensitive to the relationship between energy loss and light output. Although the response observed was definitely non-linear, the saturation was not as extreme as expected. If the relationship between rate of energy loss and rate of light output is taken to be of the form d L /d x = ( C / α ) ln {1 + α (d E /d x )}, then our data are consistent with a value for α between 0.007 and 0.015 (MeV/g·cm 2 ) −1 , but are difficult to reconcile with previously published values.

Large area directional Cherenkov detectors have been economically constructed at the University of Utah to provide a highly efficient trigger for a hodoscope of sonic ranging cylindrical spark counters. The detectors are water-filled concrete tanks having inside dimensions of 3 ft × 33 ft × 20 ft high, whose two large walls support an array of light collecting elements. A new type of highly efficient light collector which provides a wall coverage of about 70% has been developed and is now in use. Ultraviolet Cherenkov light generated by a relativistic muon passing through a tank is picked up and waveshifted to the visible by the light collectors. The visible light is then viewed by a photomultiplier tube located at one end of each collector. The output from the array on a wall corresponds to ≈ 13 photoelectrons with an average triggering efficiency of about 92%. The angular dependence of the triggering efficiency as well as the technology of operating phototubes underwater is discussed. Four Cherenkov tanks operated in coincidence incorrectly determine the directionality of a passing muon about once in 10 10 transversals.

A range telescope consisting of 22 plastic scintillators was constructed to aid in the identification of photoproduced K mesons with energies between 175 and 300 MeV. Extensive use of the correlation between pulse heights helped establish the particle identification. After preselection of a fairly standard nature, pulse heights from 18 scintillators were digitized and punched onto paper tape for subsequent computer analysis. Data from the last few counters were used to establish a range for the particle under a particular mass hypothesis, and it was required that these data represent a reasonable behavior for the stopping particle. Using this range and mass, a parameter similar to χ 2 was then computed from the data from the remaining counters. From the distribution of this variable, backgrounds and efficiencies were estimated. The method permitted a gain of about a hundred in rejection efficiency over pure electronic selection. Various backgrounds, phototube instabilities and computing difficulties limited the technique, but it was successful for this experiment and may have other uses.

Cross sections for π − p→n π o at 5.9, 10.1 and 13.8 GeV/ c incident momentum are presented in the angular region from 180 o to u , the crossed four-momentum transfer squared, of −2(GeV) 2 and the energy dependence is discussed. The cross section for π − p→n η o integrated over the same angular region at 5.9 GeV/ c is also presented.

The radiation environment in a typical SSC detector has been evaluated using the best available particle production models coupled with Monte Carlo simulations of hadronic and electromagnetic cascades. The problems studied include direct charged particle dose, dose inside a calorimeter from the cascades produced by incident photons and hadrons, the flux of neutrons and photons backscattered from the calorimeter into a central cavity, and neutron flux in the calorimeter. The luminosity lifetime at the SSC is dominated by collision losses in the interaction regions, where the luminosity is equivalent to losing an entire full-energy proton beam into the apparatus every six days. The result of an average p-p collision can be described quite simply. The mean charged multiplicity is about 110, and the particles are distributed nearly uniformly in pseudorapidity ({eta}) over all the angles of interest. The transverse momentum distribution is independent of angle, and for our purposes may be written as p{perpendicular}exp(-p{perpendicular}/{beta}). The mean value of p{perpendicular} may be as high as 0.6 GeV/c. Most of the radiation is produced by the very abundant low-p{perpendicular} particles. The dose or neutron fluence produced by individual particles in this energy region are simulated over a wide variety of conditions, and several measurements serve to confirm the simulation results. In general, the response (a dose, fluence, the number of backscattered neutrons, etc.) for an incident particle of momentum p can be parameterized in the form Np{sup {alpha}}, where 0.5 < {alpha}< 1.0. The authors believe most of their results to be accurate to within a factor of two or three, sufficiently precise to serve as the basis for detailed designs.

The NA34 (HELIOS) calorimeter has measured e/{pi} {congruent} 1.1 in a uranium/liquid argon calorimeter with a shaping time of 135 nsec. Lead may be a viable alternative, but e/{pi} must first be measured at fast shaping times in lead. We re preparing to measure e/{pi} at momenta ranging from 0.5 to 20 GeV/c and with shaping times of 50, 100 and 150 nsec.