W.B. Johnson

A study of K−π+ scattering in the reaction K−p→K−π+n at 11 GeV/c

Results from a high statistics study of the reaction K−p→K−π+n are presented. These results are based on data obtained with an 11 GeV/c beam using the LASS spectrometer at SLAC. The mass dependence of the spherical harmonic moments provides clear evidence for the production of the complete leading orbitally excited K∗ series up through JP = 5−. These moments are used to perform an energy independent partial wave analysis of the K−π+ system from threshold to 2.6 GeV/c2 using a t-dependent parametrization of the production amplitudes. The amplitudes corroborate the leading K∗(892), K2∗(1430), K3∗(1780), K4∗(2060), and K5∗(2380) resonances observed directly in the moments, and also provide new evidence for underlying states. The 0+ amplitude contains the K0∗(1350) and a second 0+K∗(1950) at higher mass. The 1−K∗(1790) seen earlier two and three-body analyses is confirmed, and evidence is provided for suppressed K−π+ decay mode of a second 1− state, the K∗(1410), which has been seen in earlier three-body analyses.

A study of the Ks0Ks0 system in the reaction K−p→Ks0Ks0Λ at 11 GeV/c

Abstract A 4.1 event/nb sample of 11 GeV/c K−p interactions in the LASS spectrometer at SLAC has been used in an analysis of the exclusive Ks0Ks0Λ final state. The Ks0Ks0 mass distribution exhibits a small cluster of events near threshold, but the mass spectrum is dominated by the f2′(1525), which an amplitude analysis shows to be produced by both natural and unnatural parity exchange. This analysis also provides evidence for an S-wave state in the f2′(1525) region, while production of the f2(1720) is not observed. However, there is structure at ∼ 2.2 GeV/c2 which is similar in shape to that observed in the region of the X(2220) in radiative J/ψ decay; an analysis of the angular distribution indicates a spin of at least 2 in this region. This, together with results from other analyses, indicates that the X(2220) may be the 2++ or 4++, mainly s s , state expected near this mass in the conventional quark model.

Evidence for two strangeonium resonances with JPC=1++ and 1+− in K−p interactions at 11 GeV/c☆

Abstract The results of a partial wave analysis of the low mass KKπ system produced in the reactions K − p →K 0 s K ± π ± Λ at 11 GeV/ c using the LASS spectrometer are presented. Evidence is given for two ss axial-vector meson states: one with quantum numbers J PC = 1 ++ , mass ∼ 1530 MeV/ c 2 , and width ∼ 100 MeV/ c 2 , and the other with quantum numbers J PC =1 +− , mass ∼ 1380 MeV/ c 2 , and width ∼ 80 MeV/ c 2 . These states are good candidates to be the mostly strangeonium members of the ground state 1 ++ and 1 +− nonets predicted by the quark model.

The strange meson resonances observed in the reaction K−p → K0π+π−n at GeV/c

Abstract A model incorporating K ∗ resonance contributions and simple backgrounds is shown to quantitatively reproduce the mass dependence of the partial wave amplitudes governing the production and decay of the K 0 π + π − system. A fit of this model to these amplitudes confirms the resonance interpretations of the well-established 1 + K 1 (1400), the 2 + K 2 ∗ (1430), the 3 − K 3 ∗ (1780), and the less well-known 1 − states, the K ∗ (1410) and the K ∗ (1790). The 4 + amplitudes are shown to be consistent with the production and decay of the 4 + K 4 ∗ (2060). A second 2 + enhancement at a mass of ∼ 1.95 GeV/ c 2 can be interpreted as resonant and may be the radial excitation of the K 2 ∗ (1430) or the triplet partner of the K 4 ∗ (2060). New measurements of the masses, widths and branching ratios of these states are given, and the implications of these data for the spectroscopy of the non-strange meson sector are discussed.

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

Evidence for A JPC=4++ KK state at ∼2.2 GeV/c2 from K−p interactions at 11 GeV/c

Abstract Data from the reaction K − p→K − K + Λ at 11 GeV/ c have been obtained in the LASS spectrometer at SLAC. A spherical harmonic moments analysis of the K − K + system provides evidence for a rather narrow J PC =4 ++ state at ∼2.2 GeV/ c 2 . Relevant data from the reaction K − p →K 0 s K 0 s Λ in the present experiment are shown also, and comparisons made to results from MARK III and GAMS in this mass region.

Observation of the selective coupling of K* states to the K−η channel☆

Abstract The K−η effective mass spectrum in the reaction K−p→K−π+π−π0p at 11 GeV/c has a prominent peak at ≈1.75 GeV/c2, which is shown to be due to the K3∗(1780) by a spherical harmonic moments analysis and amplitude decomposition; there is no significant signal for K2∗(1430). The measured branching fractions for the leading L=1 and L=2 K∗,s, [BF(K2∗ (1430)→Kη) BF ( K 3 ∗ (1780)→ Kη )=9.4±3.4%] confirm the SU(3) prediction that the Kη channel couples preferentially to odd spin K*,s.

A study of the reaction π−p → π−π+n at 16 GeV/c

Abstract We present the analysis of the reaction π−p →π−π+n at 16 GeV/c. The total cross section for this channel was measured to be 0.40 ± 0.08 mb and production cross sections of 52 ± 13 ωb and 38 ± 9 ωb were determined for the ϱo and fo resonances, respectively. A comparison with the one-pion-exchange model of Wolf shows good agreement with our data.

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−.

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).