T.A. Lasinski

Q1 (1290) and Q2 (1400) Decay Rates and their SU(3) Implications

Abstract We summarize and combine the known information on the decay rates of the strangeness-one axial vector mesons, Q 1 and Q 2 . From this information and the rate for B→ωπ, we determine the Q A −Q B mixing angle and the S -wave, symmetric and antisymmetric octet couplings for vector-pseudoscalar decays of axial vector mesons. If we assume the D(1285) and the E(1420) belong to the J PC =1 ++ nonet, we find the A 1 to have a mass of ∼1.47 GeV and a large (>0.3 GeV) width.

Analysis of K−K+ and π−π+ final states in 13 GeV K−p interactions☆

Abstract The differential cross sections and density matrix elements for the φ and ϱ0 mesons have been measured in the reactions K−p → K−K+ (Λ, Σ0) and K−p → π−π+ (Λ, Σ0) at 13 GeV using a wire chamber spectrometer. The analysis shows that while the vector meson production is dominated by the natural parity exchange amplitude, some unnatural parity exchange is also required. Furthermore the φ and ϱ natural exchange cross sections are identical in shape and have the 2:1 relative strength expected in the quark model with K∗ and K∗∗ exchange degeneracy. The analysis of the clear peak-dip ϱ0−ω interference pattern observed in the π−π+ data indicates that the ω production is in phase with the ϱ and of similar magnitude. Both the S∗ and f′ meson are clearly observed in this experiment. The S∗ data are found to be consistent with S∗ parameters deduced from ππ scattering analyses. The f′ density matrix elements and a new limit of the f′ → π−π+ branching ratio are presented.

Direct electron pair production in π−p interactions at 16 GeV/c and a model for direct lepton and photon production at low pT☆

Abstract The production of prompt electron-positron pairs in 16 GeV/c π−p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contributions of direct and Dalitz decay of known resonances in the kinematic range defined by 0.1⩽x⩽0.45, 0⩽pT⩽0.8 GeV/c and 0.2⩽M(e+e−)⩽0.7 GeV/c2. The excess signal decreases slowly with increasing M, but exhibits very steep x and pT2 dependence. The contribution of this signal to the e+e− and γ/π ratios is discussed. Detailed comparisons are made between e+e− distributions and the corresponding low-mass μ+μ− distributions, and a simple production mechanism is proposed which describes the 16 GeV/c data well. The implications for direct photon production are presented, and it is shown that the model provides simultaneously a good description of the experimental data on the (e/π) and (μ/π) ratios for pT

A simple description of the JP = 1+K±π+π− system in the reactions K±p→K±π+π−p

A model in which Q1 and Q2 resonance contributions add coherently to a Gaussian background is shown to reproduce the mass dependence of the JP = 1+K∗π and ϱK partial waves in K±p→K±π+π− at 13 GeV/c. Through a fit to the data, the mass and total width for Q1 are found to be m = 1289 ± 3 ± (25) MeV, Λ = 150 ± 9 (±70) MeV and for Q2, m = 1404 ± 3 (±10) MeV, Λ = 142 ± 4 (±15) MeV, where estimated systematic errors are given in parentheses. While a significant background is required for the 1+K∗π system, none is needed for the 1+ϱK system.

Determination of the K∗(1800) spin parity

Abstract A spherical harmonic moment analysis of the reactions K − p → K − π + n and K + p → K + π − Δ ++ at 13 GeV/ c demonstrates the existence of a broad K ∗ state with mass in the vicinity of 1800 MeV and spin parity 3 − .

A study of K∗(890) and K∗(1420) production mechanisms in K+p → K+π−Δ++ at 13 GeV/c

Abstract Amplitudes for K∗(890) and K∗(1420) production, and their lower spin background, are determined from an analysis of the Kπ angular distribution observed in K+p → K+π−Δ++ at 13 GeV/c. The exchange mechanisms responsible for K∗Δ production are studied, and a simple model is introduced which describes all features of the data.

Partial wave analysis of the K°π+π− system produced in K−p interactions at 11 GeV/c☆

Abstract We have performed a partial wave analysis of the K °π + π − system produced in the reaction K − p → K °π + π − n at 11 GeV /c and detected in the LASS spectrometer at SLAC. Results from an analysis of ≈7600 events in the K °π + π − mass range from 1090 to 2290 MeV/c2 produced at low t(∥t′∥ The JP = 2+, 3− and 4+ amplitudes show the behavior expected of the leading K∗(1430), K∗(1780) and K∗(2060) respectively. The behavior of the JP = 1+ and 2− amplitudes can be associated with the Q2(1400) and the L(1770). The 1− amplitudes exhibit behavior which indicates the existence of two resonant states, one near 1400 MeV/c2 and the other near 1800 MeV/c2. A simple Breit-Wigner model is used to fit the leading partial wave amplitudes and to compute branching ratios for the K∗(1430) and the K∗(1780).

Observation of a spin-parity 4+ K∗(2090)

Abstract High statistics data for the reaction K − p → K − π + n at 11 GeV c have been obtained in the LASS spectrometer at SLAC. A spherical harmonic moment analysis of the Kπ angular distribution displays evidence for a new K ∗ state at 2086 MeV c 2 with the spin-parity assignment, J P = 4 + .

Observation of a direct low-mass e+e− continuum in π-p interactions at 16 GeV/c☆

Abstract The production of prompt electron-positron pairs in 16 GeV/c π-p collisions has been measured using the LASS spectrometer at SLAC. An excess of events is observed above the estimated contribution of direct and Dalitz decays of known resonances in the kinematic range defined by 0.1⩽χ⩽0.45, 0⩽p T ⩽0.8 GeV c and 0.2⩽M(e + e − )⩽0.7 GeV c 2 . The excess signal decreases slowly with increasing M, but exhibits very steep χ and pT2 dependence.

Amplitudes and exchange mechanisms for K∗(890) and K∗(1420) production

Abstract The K ∗ (890) and K ∗ (1420) production amplitudes are determined using data on the reaction K − p → K − π + n at 13 GeV/ c . The energy dependence of K ∗ (890) production is investigated by using in addition the corresponding data at 4 GeV/ c . A simple model, based on exchange degenerate Regge poles together with non-evasive ‘cut’ contributions is found to provide a good description of all features of the data.