B. Gottschalk

A model-independent partial-wave analysis of the π+π− system produced at low four-momentum transfer in the reaction π−p ↑ → π+π−n at 17.2 GeV/c

Abstract The π + π − partial waves are studied up to the F-wave in the mass region from 580 to 1780 MeV/ c 2 at low four-momentum transfer. The study is based on a previous hydrogen target experiment and a more recent polarized target experiment. Using the results of both experiments for 0.01 ⩽ | t | ⩽ 0.20 GeV 2 / c 2 , a partial-wave analysis is performed in each mass bin ( Δm = 40 MeV/ c 2 ) independently. For the first time a model-independent analysis has been possible, which enables us to check the assumptions made in previous studies. In general we find a unique solution determining the exact intensity of each partial wave. The uniqueness of our solution is related to the Barrelet zeros being real in the mass region where their imaginary part were supposed to produce ambiguities. We observe a non-π exchange contribution even in the helicity m = 0 amplitudes.

Measurement and analysis of the reaction π−p→ϱ0n on a polarized target

Abstract The reaction π − p→ π + π − n has been measured in a high-statistics experiment on a transversely polarized proton target at 17.2 GeV, and unexpectedly large nucleon polarization effects have been observed. Combining the results of this experiment with a measurement on a hydrogen target allows a model-independent partial-wave analysis in terms of the “nucleon transversity” amplitudes. Unique or at most twofold ambiguous solutions are obtained. In particular we find a high lower limit ( ⪆30% ) of the spin non-flip unnatural exchange amplitudes at low | t |. These amplitudes, interpreted as being due to the exchange of an object with the quantum numbers of the A 1 , have been assumed to be absent in previous analyses. In checking the consequences of this finding on the old results, we test the validity of the rank-two assumotions for the density matrix. We find a small but significant deviation, which shows the need for a new phase-shift analysis including the A 1 exchange contribution.

Experimental indications for a 2++ non-qq object

Abstract Using our high-statistics data from the πp → ππn reaction, we have remade a model-independent partial-wave analysis in finer mass bins at low four-momentum transfer. The Breit-Wigner fits to the leading waves yield mρ = (777.4 ± 2.0) MeV and Γρ = (160P+4.1−4.0) MeV, as well as mf = (1273.3 ± 2.3) MeV, Γ f = (179.2 +6.9 −6.6 ) MeV and xf = (84.9 ± 2.5)%. The last two parameters yield Γ(f → ππ) = (152.1 ± 7.3) MeV, a value which is higher than the one resulting from fits to the decays of the JPC = 2++ mesons. On the basis of a smaller discrepancy, Rosner has speculated about a non- q q admixture (possibly gg) in the f(1270), i.e. | f (1270)〉 = | q q 〉 cos θ + | gg 〉 sin θ . Repeating his fits with more recent data we obtain a considerably more significant effect with sin2θ = 0.18 ± 0.04. This sets a mass of an orthogonal state | f T 〉 = − | q q 〉 sin θ + | gg 〉 cos θ between 1420 and 1620 MeV. The fT could be identified with a 1440 MeV state seen in some K K experiments, A1 exchange being a possible production mechanism. A fit to our polarized target K+K− data at ∼ 18 GeV/c yields m(fT) = (1445 +20−19) MeV and Γ (fT = (81+52−25) MeV.

A partial-wave analysis of the reaction π−p → K+K−n measured on a polarized target at ∼18 GeV/c

Abstract The reaction π − p→K + K − n has been studied on a hydrogen target (27 000 events) at 18.4 GeV/ c and on a polarized target (54 000 events) at 17.2 GeV/ c . A combination of results of both experiments allows a partial-wave analysis of the K + K − system between 1.1 and 1.74 GeV mass without any model assumptions. In general our fits yield unique solutions. Using results of our previous analysis of π + π − final states and assuming the dominance of the positive G -parity states in the K + K − system, the branching ratios BR ( K K /ππ) of partial waves into K K and ππ are determined. The S-wave appears to be mainly a broad e (1300) with BR ( K K /ππ) = 0.068 −0.021 +0.017 . The weak P-wave can be described by a tail of the ϱ(770) with BR ( K K /ππ) = 0.081 −0.025 +0.029 . The D-wave is interpreted in terms of a superposition of f(1270) + A 2 (1310) + f′(1515) resonances. The fit yields BR ( K K /ππ) = 0.069 −0.031 +0.023 for the f(1270) and BR( ππ /all) = 0.027 −0.013 +0.071 for the f′(1515). The F-wave shows the g(1690) meson with BR ( K K /ππ) = 0.191 −0.037 +0.040 . All the above values refer to the t bin between 0.01 and 0.20 (GeV/ c ) 2 . Some results are also given for the high- t region.

Coherent A2− production of nuclei observed in the K−KS0 decay channel at 17.2 GeV/c

We have studied A2− production by π− on a nuclear target in the K−KS0 decay channel, where the A2− is observed above a small background at 17.2 GeV/c incident momentum. Direct confirmation of coherent A2 (JP = 2+) production has been found.

A model independent partial wave analysis of the π+π− system produced at low four‐momentum transfer in the reaction π−p↑→π+π−n at 17.2 GeV/c

Partial wave analysis is performed on a combined sample of 1,500,000 events with an average polarization of 68%. (AIP)

Measurement of diffractive 3π production on a polarized target at 17 GeV/c

Abstract The reaction π − p↑→ π − π + π − p has been measured at 17 GeV/ c using a polarized target. The data sample contains about 60 000 interactions on polarized protons. The nucleon polarization as a function of momentum transfer is very similar to elastic π − p scattering and is nearly independent of the π mass, except for a possible structure around 1.2 GeV. Using the isobar model, we have performed a partial-wave analysis and extracted the 3π amplitudes. The generalized 3π density matrix elements agree with earlier determinations. Relative phases obtained from density matrix elements agree well with the ones obtained from transversity amplitudes. This proves the validity of the coherence assumption made in the interpretation of unpolarized target results. Our results confirm the existence of an A 1 resonance in the region 1.2–1.3 GeV.

A Partial Wave Analysis of the K+K- System Produced in the Reaction π-p → K+K-n at 17.2 GeV/c using a Transversely Polarized Target

The reaction π-p → K+K-n has been studied on hydrogen (27 000 events) at 18.4 GeV/c and on a transversely polarized butanol target (54 000 events) at 17.2 GeV/c. A combination of results of both experiments allows to obtain unique solutions for a partial wave analysis of the K+K-system without any model assumptions. This analysis was performed at low four-momentum transfer 0.01 < |t| < 0.2 (GeV/c)2 and in the mass range between 1.10 and 1.74 GeV. Using results of our previous analysis of π+π- final states and assuming the dominance of the positive G-parity states in the K+K- system, the branching ratios BR(KK/ππ) of partial waves S,P,D and F into KK and ππ are determined.

A model independent partial wave analysis of the

Partial wave analysis is performed on a combined sample of 1,500,000 events with an average polarization of 68%. (AIP)