A measurement of novel event shapes quantifying the isotropy of collider events is performed in 140 fb$^{-1}$ of proton-proton collisions with $\sqrt s=13$ TeV centre-of-mass energy recorded with the ATLAS detector at CERN's Large Hadron Collider. These event shapes are defined as the Wasserstein distance between collider events and isotropic reference geometries. This distance is evaluated by solving optimal transport problems, using the 'Energy-Mover's Distance'. Isotropic references with cylindrical and circular symmetries are studied, to probe the symmetries of interest at hadron colliders. The novel event-shape observables defined in this way are infrared- and collinear-safe, have improved dynamic range and have greater sensitivity to isotropic radiation patterns than other event shapes. The measured event-shape variables are corrected for detector effects, and presented in inclusive bins of jet multiplicity and the scalar sum of the two leading jets' transverse momenta. The measured distributions are provided as inputs to future Monte Carlo tuning campaigns and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.
IRing2 for HT2>=500 GeV, NJets>=2
IRing2 for HT2>=500 GeV, NJets>=3
IRing2 for HT2>=500 GeV, NJets>=4
Results from a high-statistics experiment involving an exposure of the SLAC 82-in. hydrogen bubble chamber to a beam of 8-GeV/c π− yielding a final state of π−π+π−p are presented. Copious production of ρ, Δ++, and f is found. Considerable quasi-two-body production in which one particle decays to one of the above resonances is also observed. Some double-resonance production involving baryon and meson resonances is also seen. The production properties of ρ, Δ++, and f mesons are well described by a double-Regge model.
TOPOLOGICAL CROSS SECTIONS. FIRST 2 PRONG VALUE CONTAINS ELASTIC. 0PRONG IS TAKEN FROM A SMALLER AND DIFFERENT PARTIAL SAMPLE.
CROSS SECTION CALCULATED VIA THE OPTICAL THEOREM AS A CROSS CHECK.
SPECIFIC CHANNEL CROSS SECTIONS.
We have measured the polarization of the Λ hyperon produced in the reaction π−p→K0Λ at 3 and 5 GeV/c, for four-momentum transfers t′ out to 1.6 GeV2, by observing the parity-violating decay Λ→pπ−. With an increase in statistical power by a factor of 3 to 4 over the best previous experiments in this energy range, we confirm earlier observations that the polarization is small and positive below t′=0.4 GeV2, becoming large and positive for larger values of t′. In particular, at 5 GeV/c for all t′ between 0.8 and 1.6 GeV2 the polarization is consistent with a value of - 1.
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From 2728 events of 205-GeV pp interactions found in 15 000 pictures taken with the 30-in. hydrogen bubble chamber at the National Accelerator Laboratory, a total cross section of 39.5±1.1 mb was measured. The mean charged-particle multiplicity for inelastic pp collisions was measured to be 7.65±0.17. The prong distribution from 2 to 22 prongs is broader than a Poisson distribution and has a width parameter f2−=〈n−(n−−1)〉−〈n−〉2=0.95±0.21.
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This paper gives a detailed description of an experiment which studies the interactions of muon-type neutrinos in hydrogen and deuterium. The experiment was performed at the Zero Gradient Synchrotron using the wide-band neutrino beam incident on the Argonne 12-foot bubble chamber filled with hydrogen and deuterium. The neutrino energy spectrum peaks at 0.5 GeV and has a tail extending to 6 GeV. The shape and intensity of the flux is determined using measurements of pion yields from beryllium. The produced pions are focused by one or (for the latter part of the experiment) two magnetic horns. A total of 364000 pictures were taken with a hydrogen filling of the bubble chamber and 903 000 with a deuterium filling. The scanning and other analyses of the events are described. The most abundant reaction occurs off neutrons and is quasi-elastic scattering νd→μ−pps. The separation of these events from background channels is discussed. The total and differential cross sections are analyzed to obtain the axial-vector form factor of the nucleon. Our result, expressed in terms of a dipole form factor, gives an axial-vector mass of 0.95±0.09 GeV. A comparison is made to previous measurements using neutrino beams, and also to determinations based upon threshold pion electroproduction experiments. In addition, the data are used to measure the weak vector form factor and so check the conserved-vector-current hypothesis.
Measured Quasi-Elastic total cross section.
We have measured the differential cross sections and Λ polarizations in the reactions π−p→ΛK0 and π−p→ΛK*0 (890) near the backward direction, at 3, 4, 5, and 6 GeV/c. Data equal to several times the world's total sample above 2 GeV/c were recorded. Both reactions are characterized by cross sections falling rapidly with beam momentum, and by large positive Λ polarizations for u′ between 0.0 and 0.6 GeV2. Analysis of π−p→ΛK0 yields an effective Regge trajectory consistent with antishrinkage of the backward peak. Separation into amplitudes of definite-parity-naturality exchange shows the reaction to be dominated by unnatural-parity exchange. The energy behavior of this exchange is, however, not consistent with a single linear baryon Regge trajectory or exchange-degenerate pair of trajectories. An apparent normalization discrepancy between data on π−p→ΛK0 of a CERN-ETH group and other high-statistics data including that of this experiment is discussed.
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The charged-particle multiplicity distribution in 205−GeVc proton-proton interactions is presented. In addition, the total diffractive contributions to each charged multiplicity are estimated assuming a factorizable Pomeron.
THE TOTAL CROSS SECTION NORMALIZATION COMES FROM THIS AND OTHER EXPERIMENTS.
We present results of complete measurements of the two-prong events observed in a 50 000-picture exposure of the 30-in. hydrogen bubble chamber to a 205−GeVc proton beam at the National Accelerator Laboratory. Using kinematic fitting, elastic and inelastic events are separated and cross sections are obtained. The total two-prong cross section is measured to be 9.77 ± 0.40 mb, of which 2.85 ± 0.26 mb represents the inelastic contribution. The total elastic cross section is measured to be 6.92 ± 0.44 mb. Our data are consistent with the break in dσdt at |t|∼0.1−0.2 (GeVc)2 observed at the CERN ISR. A prominent low-mass enhancement is observed in the distribution of missing mass squared from the slow proton for the inelastic events. An analysis based on the missing-mass spectrum and the particle rapidities shows that this low-mass enhancement accounts for about 77% of the total inelastic two-prong cross section. The diffractive cross section in the two-prong events is 2.20 ± 0.25 mb, in agreement with certain two-component models.
USING A TOTAL CROSS SECTION OF 39.0 +- 1.0 MB.
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From a study of 8-GeV/c π−p interactions, the various two-pion and four-pion decay channels available to the g− meson have been investigated. Our results indicate that the dominant 4π decay modes involve intermediate ρ and ω production without significant A2 formation.
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Results of a high-statistics study of elastic scattering and meson resonances produced by π−p interactions at 8 GeV/c are presented. Large statistics and small systematic errors permit examination of the complete kinematic region. Total differential cross sections are given for ρ0,−, f0, g0,−, Δ±, Δ0, and N* resonances. Spin-density matrix elements and Legendre-polynomial moments are given for ρ, f, and Δ resonances. The results for ρ0 and f0 resonances are compared with the predictions of a Regge-pole-exchange model. Properties of the above resonances are compared and discussed. In particular, we present evidence that the ρ0 and f0 production mechanisms are similar. The similarity of the g0 t distribution to that of the ρ0 and f0 suggests a common production mechanism for all three resonances.
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SLOPE REFERS TO EXPONENTIAL FIT IN U.
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