W. Rühmer

Evidence for planar events in e+e− annihilation at high energies

Abstract Hadron jets produced in e+e− annihilation between 13 GeV and 31.6 GeV in c.m. at PETRA are analyzed. The transverse momentum of the jets is found to increase strongly with c.m. energy. The broadening of the jets is not uniform in azimuthal angle around the quark direction but tends to yield planar events with large and growing transverse momenta in the plane and smaller transverse momenta normal to the plane. The simple q q collinear jet picture is ruled out. The observation of planar events shows that there are three basic particles in the final state. Indeed, several events with three well-separated jets of hadrons are observed at the highest energies. This occurs naturally when the outgoing quark radiates a hard noncollinear gluon, i.e., e + e − → q q g with the quarks and the gluons fragmenting into hadrons with limited transverse momenta.

Properties of hadron final states in e+e− annihilation at 13 GeV and 17 GeV center of mass energies

Abstract We have observed e + e − hadrons at C.M. energies of 13 GeV and 17 GeV at PETRA using the TASSO detector. We find R (13 GeV) = 5.6 ± 0.7 and R (17 GeV) = 4.0 ± 0.7. The additional systematic uncertainty is 20%. Comparing inclusive charged hadron spectra we observe scaling between 5 GeV and 17 GeV for x = p / p beam > 0.2; however the 13 GeV cross section is above the 17 GeV cross section for smaller x . This may be due to copious bb production. The events become increasingly jet like at high energies as evidenced by a shrinking sphericity distribution with increasing energy.

Evidence for a narrow width boson of mass 2.95 GeV

Abstract In a search for resonances coupled to the p pπ − system, we have studied π − p interactions at 16 GeV/ c giving a forward antiproton, using the Omega spectrometer at CERN. In the final states involving a p , p and π − we observe a 5.6 (6.3) standard deviation enhancement in the p pπ − mass spectrum at (2.95 ± 0.01) GeV with a width consistent with the resolution ( σ = 15 MeV). The production cross section × branching ratio is estimated to be of the order 1 μb. The data are consistent with a resonance decaying partly via intermediate p p final states.

Inclusive φ production in π− p interactions at 16 GeV/c

Abstract Inclusive φ production is studied in π − p collisions at 16 GeV/ c . The φ cross section for Feynman variable x φ > 0.2 is found to be (15.5 ± 3.6) μb. This leads to an extrapolated cross section of (29.9 ± 7.0) μb for x φ > 0.0. Fitting the momentum transfer squared distribution of the φ to the form e −bp 2 T gives an average slope of b = (2.4 ± 0.3) (GeV/ c −2 for x φ > 0.5.

Results from a π−p slow proton trigger experiment at 12 GeV/c

Abstract A study of the reaction π − p → X − p based on 1.27 × 10 6 events, corresponding to a mean sensitivity of 200 events/μb, is presented. Properties of the exclusive channels π − p → π − π 0 p, π + π − π − p, π + π − π − π 0 p, π + π + π − π − π − p and π + π + π − π − π − π 0 p are discussed.

Observation in the K+K− system of a new structure at 2.20 GeV

Abstract A sample of 56 909 events of the reaction π − p→K + K − n at 10 GeV/ c has been measured in the Omega Spectrometer at CERN. In the K + K − system, besides production of mesons in the S ∗ /φ, f 0 / A 2 , g /ω ∗ and h regions we observe a new structure at 2.20 GeV with a width of the order of 200 MeV.

Analysis of the reaction π−p→ppn at 10 and 16 GeV/c

Abstract Antiproton-proton pairs and antiproton-neutron pairs produced in the reaction π − p → p pn , were studied in the mass range from threshold to 2.6 GeV on the basis of 4 · 104 events at 10 GeV/c and 2 · 104 events at 16 GeV/c incident momentum. The cross section for peripheral production of p n pairs is significantly larger than for p p pairs. The p p production mechanism is consistent with the predictions of the one-pion exchange model, whereas the p n production cannot be sufficiently described by that model. A partial-wave analysis of the p p system, assuming pure one-pion exchange, shows that we need for a reasonable description of our data in addition to the JP = 3− resonance at 2.11 GeV and the 4+ resonance at 2.26 GeV found in an analysis of a formation experiment ( p p → π + π − ), two further resonances: a 1− state at 1.92 GeV and a 2+ state at 2.02 GeV.

K∗0(890) polarization measurements in the hypercharge exchange reaction π−p→K∗0(890) Λ0Σ0 at 10 GeV/c

K∗0(890) production in the hyperchange exchange reaction π−p→K∗0(890) Λ0Σ0 at 10 GeV/c (28 448 events) is discussed. An amplitude analysis in the t′ range up to 1 GeV2 shows that the production mechanism is dominated by natural parity exchange (∼84%). Comparisons are made with predictions from a Regge model and a quark model.

Inclusive production in π−p interactions at 16 GeV/c

Abstract Inclusive K ∗0 production is studied in π − p interactions at 16 GeV/ c with x ϝ > 0.2. The K ∗0 is found to be pre-dominantly centrally produced with cross section σ( K ∗0 ) = (72 ± 12) μb for x ϝ > 0.2 and compares closely to data on K ∗0 production in π + p interactions at the same energy.

Inclusive K∗0(890) production in π−p interactions at 16 GeV/c

Abstract Inclusive K ∗0 production is studied in π − p interactions at 16 GeV/ c with x ϝ > 0.2. The K ∗0 is found to be pre-dominantly centrally produced with cross section σ( K ∗0 ) = (72 ± 12) μb for x ϝ > 0.2 and compares closely to data on K ∗0 production in π + p interactions at the same energy.