J. Ballam

Determination of ±s from a differential-jet-multiplicity distribution in e+e- collisions at ss =29 and 91 GeV

We measured the differential jet-multiplicity distribution in {ital e}{sup +}{ital e}{sup {minus}} annihilation with the Mark II detector. This distribution is compared with the second-order QCD prediction and {alpha}{sub {ital s}} is determined to be 0.123{plus minus}0.009{plus minus}0.005 at {radical}{ital s}{approx}{ital M}{sub {ital Z}} (at the SLAC Linear Collider) and 0.149{plus minus}0.002{plus minus}0.007 at {radical}{ital s}=29 GeV (at the SLAC storage ring PEP). The running of {alpha}{sub {ital s}} between these two center-of-mass energies is consistent with the QCD prediction.

A search for B and ϱ′(1250) production in the reaction γp → pπ+π− + neutrals at 2.8, 4.7 and 9.3 GeV☆

Abstract We have studied the reaction γ p → p π + π − + neutrals in the LBL-SLAC 82″ hydrogen bubble chamber exposed to a linearly polarized photon beam at 2.8., 4.7 and 9.3. GeV. We observe an enhancement at 1.24 GeV in the mesonic mass recoiling against the proton. The enhancement is produced peripherally with slopes of 5−7 GeV −2 and cross sections of 1−3 μb. We show that ωπ o is likely to be the major decay mode and give upper limits for other decay modes. The enhancement can be either the J P = 1 + B meson, a yet unestablished J P = 1 − meson decaying via ωπ o , or a diffractively produced Deck-type background. The observed decay correlations are compatible with an s -channel helicity conserving production process. Our data at higher masses are consistent with a ϱϵ decay of the ϱ′(1600) and we obtain an upper limit of 4±1 μ b for ϱ′(1600) production in the final state p π + π − + neutrals at 9.3 GeV.

γp interactions at 5.25 GeV

Abstract Photoproduction of resonances has been studied using positron annihilation radiation at 5.25 GeV in the SLAC 40-inch hydrogen bubble chamber. Results are presented on the nonstrange particle events and related to the vector dominance model.

Polarization Measurement of theΣ+Produced in the Line-Reversed Reactionsπ+p→K+Σ+andK−p→π−Σ+at 7 and 11.6 GeV/c

The polarization of the ..sigma../sup +/ has been measured for the line-reversed reactions ..pi../sup +/p ..-->.. K/sup +/..sigma../sup +/ and K/sup -/p ..-->.. ..pi../sup -/..sigma../sup +/ at 7 and 11.6 GeV/c using the SLAC Hybrid Facility. Since the ..sigma../sup +/ decay is observed in the bubble chamber, the trigger of the flash lamps on a fast K/sup +/(..pi../sup +/) did not bias the polarization measurements. We find that the ..sigma../sup +/ polarizations from the two reactions have opposite signs but similar magnitude and are in much better agreement with the predictions of weak exchange degeneracy than previous lower-energy comparisons.

Inclusive ϱ0 production in γp interactions at 2.8, 4.7, and 9.3 GeV☆

Abstract Inclusive ϱ 0 production in γ p → ϱ 0 + anything is studied at 2.8, 4.7, and 9.3 GeV, using the SLAC linearly polarized backscattered laser photon beam and the 82 inch hydrogen bubble chamber. Over this energy range the inclusive inelastic ϱ 0 cross section rises from 6.0 μb to 20.5 μb. The multiplicity, i.e. the average number of μ 0 mesons per inelastic hadronic event, has an energy dependence consistent with 1n s . The inclusive cross section is studied as a function of Feynman x , c.m. rapidity, and p T 2 variables, and is also broken down into exclusive channels. At 9.3 GeV a forward inelastic peak is observed in the x distribution, containing mainly polarized ϱ 0 mesons. The cross section for this inealastic diffractive component is 2.7 ± 0.6 μ b. The p T 2 distributions are exponential with a slope of 3 − 4 (GeV/ c ) −2 , similar to that found in inclusive ϱ 0 production in pp and μ p reactions.

Photoproduction of ω - mesons from 1.2 to 8.2 GeV

Abstract The reaction γ p→ ω p was studied between 1.2 and 8.2 GeV using positron annihilation radiation. Assuming σ ∝ C OPE · E γ −2 + C DIFF we obtain for the Pomeron exchange cross section (1.5 ± 0.3) μb.

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.

Spin and parity of the diffractively produced Nπ system from its interference with the Δ(1236) isobar

We perform an isospin and partial-wave analysis of the low-mass Nπ system in πN → π(Nπ) using new data at 14 GeV/c in the interval 0.02 < tππ < 0.5 GeV2. We study the diffractive background by means of its interference with the Δ and find that a considerable fraction of this background has spin-parity 12− and does not obey the Gribov-Morrison rule. Using a model for Δ production the helicity amplitudes for diffractive production and their phases can be estimated.

Observation of a four-pion vector-meson state of mass ≈ 1.5 GeV produced by linearly polarized 9.3 GeV photons

Abstract From a study of γp → 2 π + 2 π − p using 9.3 GeV linearly polarized photons, evidence is found for a J P = 1 − , I G = 1 + four pion enhancement of mass ∼ 1.5 GeV with a production cross section of 1.6 ± 0.4 μb .

Charged hadron multiplicities and topologies in inelastic μ−p scattering☆

Abstract We report the final state charged-hadron multiplicities and topological cross sections for inelastic scattering of 16 GeV μ −, s from hydrogen in the SLAC 40-inch bubble chamber. We find that for 1.8 ⩽ W ⩽ 5.0 GeV the charged hadron multiplicity is generally lower at Q 2 = 1.5 GeV 2 than for photoproduction.