Results of a high-statistics study of π++p→ρ++p at 1.55-1.84 GeVc are consistent with dominance of π and ω exchange close to threshold. A pronounced dip in ρ00sdσdt at −t≃0.4 GeV2 may be attributed to pion exchange with strong absorption.
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Interactions initiated by 3-Bev protons of the Brookhaven Cosmotron were studied by photoemulsion technique. With appropriate criteria, 115 events are attributed to interactions of the incident beam protons with hydrogen nuclei (∼55%) and with bound protons of other nuclei (∼45%). A detailed analysis allowed the subdivision of the 115 events in categories, according to the number of π mesons (N>~0) produced in the collision. The ratio of elastic scattering to the total number of events was estimated to be σelσtotal=0.20−0.07+0.04. The observed cross section for pure elastic scattering is σel=8.9±1.0 mb. The percentages of single, double, triple, and quadruple π-meson production are respectively: 34−20+22; 35.6−23+20; 9.6−4+6; ∼1.0+3.5. Among the 20 most probable cases of single π-meson production—the estimated ratio of π+ to π0 is σπ+σπ0=5.3−1.4+0.3. The experimental results are not in agreement with the Fermi statistical-model theory (in particular the lower limit for the experimental ratio of triple to single production is given by σ3σ1>∼110 in contrast with the predicted ratio σ3σ1=167) but are not inconsistent with the Peaslee excited-state-model theory.
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Total and differential cross sections for π−p elastic scattering are presented at 35 energies between 1400 and 2000 MeV.
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The properties of events having the topology and kinematic features of double Pomeron exchange are described. The data were taken at the CERN pp¯ collider at s=0.63 TeV in the UA1 detector. A calorimeter trigger was used to isolate events in which a central cluster of particles was separated from forward particles by large rapidity gaps. The invariant mass M of the central cluster (possibly a colliding Pomeron-Pomeron system) covers the range 10-70 GeV/c2. The M dependence of charged particle multiplicity distributions in these double Pomeron events is strikingly different from their s dependence in pp and pp¯ interactions.
Pseudorapidity distribution for charged particle tracks in the DPE data.
Pseudorapidity distribution for charged particle tracks in the MB events.
Mean charged particle multiplicity as function of the invariant mass of the charged particles in DPE events.
Total and differential elastic cross-section data are presented at eight incident π+ momenta: 1.28, 1.34, 1.40, 1.43, 1.55, 1.68, 1.77, and 1.84 GeVc. These data were obtained from a hydrogen-bubble-chamber exposure at the Bevatron, and contain more than 65 000 events. This represents more than 1½ times the world's data hitherto available in this energy region.
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The strong coupling constant αs has been determined from a study of the reaction p¯p→W±X, W→eν at s of 630 GeV in the UA1 experiment at CERN. The measurement is based upon a study of jet production in association with W bosons. The result obtained is αs(MW2)=0.127±0.026(stat)±0.034(syst).
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Using new data from 100 GeV c π − interactions, we find the energy dependence of the invariant cross-section in the target fragmentation (central) region to be consistent with an A + Bs − 1 2 (C + Ds − 1 4 ) behavior. The leading particle peak near x = + 1 exhibits a width in x which becomes smaller with increasing energy and an integrated cross section which is approximately energy independent.
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p¯p elastic scattering at an incident beam momentum of 2.85 GeV/c is analyzed using 18 412 events. The simple exponential parametrization of the diffraction peak is found to be a poor representation of the data. Two other parametrizations are tried and the estimates of dσdt at t=0 and of the slope of the diffraction peak are found to differ significantly between various parametrizations. It is found that two coherent interfering exponentials are able to represent the differential cross section over the range 0.04≤|t|≤1.8 (GeV/c)2 with a χ2 probability of approximately 40%.
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The differential scattering cross section is presented for p¯p elastic scattering at an incident laboratory momentum of 2.33 GeV/c based upon 11 758 events. The experiment was performed at the Brookhaven National Laboratory using the 31-inch hydrogen bubble chamber and an electrostatically separated beam. The attempts to fit limited regions of the data are presented for different parametrizations. The parametrization which corresponds to two coherent interfering exponentials successfully reproduces a very large t region for the scattering.
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A search is presented for lepton-flavor violating decays of the Higgs boson to $\mu\tau$ and e$\tau$. The data set corresponds to an integrated luminosity of 137 fb$^{-1}$ collected at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. No significant excess has been found, and the results are interpreted in terms of upper limits on lepton-flavor violating branching fractions of the Higgs boson. The observed (expected) upper limits on the branching fractions are, respectively, $\mathcal{B}($H $\to\mu\tau)$$\lt$ 0.15 (0.15)% and $\mathcal{B}($H$\to$e$\tau)$ $\lt$ 0.22 (0.16)% at 95% confidence level.
Observed (expected) 95% CL upper limits on $B(H\to\mu\tau)$ for each individual category and combined
Observed (expected) 95% CL upper limits on $B(H\to e\tau)$ for each individual category and combined
Summary of observed and expected upper limits at 95% CL, best fit branching fractions and corresponding constraints on Yukawa couplings for the $H\to\mu\tau$ and $H\to e\tau$ channels
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