W. Dunwoodie

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.

Observation of new resonant structures in the natural spin-parity strange meson system

Abstract High statistics data for the reaction K−p→K−π+n have been obatined using the LASS spectrometer at SLAC. An energy independent partial wave analysis of these data yields unique K−π+ elastic scatering partila wave amplitudes in the Kπ invariant mass region from 0.7 GeV to 1.8 GeV, and two distinguishable sets of amplitudes between 1.8 GeV and 2.3 GeV. Besides the three “old” K∗ resonances [J P = 1 − K ∗ (892), 2 + K ∗ (1430), 3 − K ∗ (1780)] these partial waves display evidence for a K∗ resonance with JP=4+ near 2.07 GeV. The energy dependence of the S wave amplitude confirms the existence of a resonant 0+ state in the 1.4 GeV region [the k(1500)], and provides evidence for a new high-mass S wave resonance [′(1850)] near 1.85 GeV. Resonant behavior is also observed in the P wave amplitude around 1.7 GeV.

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 − .

Observation of the leading K∗L-excitation series from JP = 1− through 5− in the reaction K− p → K− π+ n AT 11 GeV/c

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 moments analysis provides clear evidence for the production of the complete leading orbitally excited K∗ series up through JP = 5−. New measurements are made of the masses and widths of the 1−K∗(892), 2+K∗(1430 ), 3− K∗(1780), and 4+ K∗(2060), and evidence is presented for the production of a new K∗ state at 2382 MeV/c2 with spin-parity 5−.

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.

Study of K−p→K∗(890)n at 13 GeV

The results of a wire chamber spectrometer experiment studying K∗ (890) production in the reaction K−p→ K−π+n at 13 GeV are presented. Strong forward structure is observed for |t|< m2π in the s-channel density matrix elements and differential cross section. These features are similar to those observed in π−p→ϱ0n data and are characteristics of π exchange. In contrast in the intermediate, |t| ∼ 0.2 GeV2, and large momentum transfer regions K∗ (890) production is demonstrated by the natural parity ϱ−A2 exchange contribution.