Elastic scattering of 32.1 GeV/ c K + on protons has been measured in a bubble chamber experiment. Results are presented in the momentum transfer interval 0.06–1.40 GeV 2 and compared with data at different energies. An effective Regge trajectory is calculated using K + p elastic data from 10 to 175 GeV/ c .
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At 3 GeV/ c , the total and differential cross sections of the reactions K − n → Y π − have been determined for nine S = −1 baryonic states. Backward peaks associated with a dip near u = −0.2 are observed in many cases. They have been interpreted, for the isospin-zero Y-states, in terms of a proton-exchange mechanism. The backward peaks in the reactions K − n → Λπ − and K − n → Σ o π − have been more quantitatively related to the backward π N → N π differential cross sections at the same energy. This comparison leads to the conclusion, that the first reaction is dominated by nucleon exchange, whereas the second one requires a more complex exchange mechanism.
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The inclusive production of resonances is systematically studied in K + p interactions at 32 GeV/ c . Total production cross sections are given for three baryon resonances, five vector and three 2 + tensor mesons. We also compare the central and fragmentation components of the total production cross sections with quark model predictions.
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In an analysis of the reaction K − n →Λ4π at 3 GeV c we find evidence for the production of the B(1220) resonance, mainly decaying in ωπ. For the mass and width we find (1236 ± 15) MeV c 2 and (132±20) MeV c 2 respectively. The cross section for the reaction K − n→ Λ +B(1220) is found to be (102±26) μ b.
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A systematic search for exotic states produced in K − d interactions at 3 GeV/ c is reported. From the analysis of the mass spectra of strange mesons, non-strange mesons, hyperons with S = −1 and S = −2, upper limits for the production cross sections of exotic resonances may be placed at one or two orders of magnitude smaller than for the production of normal resonances of same strangeness and baryon number.
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We employ data taken by the JADE and OPAL experiments for an integrated QCD study in hadronic e+e- annihilations at c.m.s. energies ranging from 35 GeV through 189 GeV. The study is based on jet-multiplicity related observables. The observables are obtained to high jet resolution scales with the JADE, Durham, Cambridge and cone jet finders, and compared with the predictions of various QCD and Monte Carlo models. The strong coupling strength, alpha_s, is determined at each energy by fits of O(alpha_s^2) calculations, as well as matched O(alpha_s^2) and NLLA predictions, to the data. Matching schemes are compared, and the dependence of the results on the choice of the renormalization scale is investigated. The combination of the results using matched predictions gives alpha_s(MZ)=0.1187+{0.0034}-{0.0019}. The strong coupling is also obtained, at lower precision, from O(alpha_s^2) fits of the c.m.s. energy evolution of some of the observables. A qualitative comparison is made between the data and a recent MLLA prediction for mean jet multiplicities.
Overall result for ALPHAS at the Z0 mass from the combination of the ln R-matching results from the observables evolved using a three-loop running expression. The errors shown are total errors and contain all the statistics and systematics.
Weighted mean for ALPHAS at the Z0 mass determined from the energy evolutions of the mean values of the 2-jet cross sections obtained with the JADE and DURHAMschemes and the 3-jet fraction for the JADE, DURHAM and CAMBRIDGE schemes evaluted at a fixed YCUT.. The errors shown are total errors and contain all the statistics and systematics.
Combined results for ALPHA_S from fits of matched predicitions. The first systematic (DSYS) error is the experimental systematic, the second DSYS error isthe hadronization systematic and the third is the QCD scale error. The values of ALPHAS evolved to the Z0 mass using a three-loop evolution are also given.
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
The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $\rho$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $\rho(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$.
Spin-density matrix elements for the photoproduction of $\rho(770)$ in the helicity system. The first uncertainty is statistical, the second systematic. The systematic uncertainties for the polarized SDMEs $\rho^1_{ij}$ and $\rho^2_{ij}$ contain an overall relative normalization uncertainty of 2.1% which is fully correlated for all values of $-t$.
Spin-density matrix elements for the photoproduction of $\rho(770)$ in the helicity system. The first uncertainty is statistical, the second systematic. The systematic uncertainties for the polarized SDMEs $\rho^1_{ij}$ and $\rho^2_{ij}$ contain an overall relative normalization uncertainty of 2.1% which is fully correlated for all values of $-t$.
We measure the spin-density matrix elements (SDMEs) of the $\Delta^{++}(1232)$ in the photoproduction reaction $\gamma p \to \pi^-\Delta^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson Lab. The measurement uses a linearly--polarized photon beam with energies from $8.2$ to $8.8$~GeV and the statistical precision of the SDMEs exceeds the previous measurement by three orders of magnitude for the momentum transfer squared region below $1.4$ GeV$^2$. The data are sensitive to the previously undetermined relative sign between couplings in existing Regge-exchange models. Linear combinations of the extracted SDMEs allow for a decomposition into natural and unnatural--exchange amplitudes. We find that the unnatural exchange plays an important role in the low momentum transfer region.
Spin-density matrix elements for the photoproduction of $\Delta(1232)^{++}$ in the Gottfried-Jackson system. The first uncertainty is statistical, the second systematic. The systematic uncertainties for the polarized SDMEs $\rho^1_{ij}$ and $\rho^2_{ij}$ contain an overall relative normalization uncertainty of 2.1% which is fully correlated for all values of $-t$.
Spin-density matrix elements for the photoproduction of $\Delta(1232)^{++}$ in the Gottfried-Jackson system. The first uncertainty is statistical, the second systematic.
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