M. Markytan

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/c π+p and K−p interactions (2 × 106 and 106 pion pair combinations, respectively) and in a smaller sample of pp annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.

Inclusive production of K̄∗(890) and K̄∗(1420) in K̄−p interactions at 10 and 16 GeV/c

Abstract The inclusive production of K∗(890) and K∗(1420) is studied in K−p interactions at 10 and 16 GeV/c. At 10 GeV/c an enhancement in the ( K 0 π − ) mass distribution is found at 1.74 GeV, but no clear signal is seen at 16 GeV/c. The fraction of K 0 s coming from decay of the K ∗ (890) or K ∗ (1420) is large, being (50 ± 6)% and (45 ± 5)% at 10 and 16 GeV/c, respectively. The inclusive cross sections for K∗−(890) and K ∗0 (890) production are almost constant with energy from 8 to 32 GeV/c with values of 3.5 and 3.3 mb, respectively. The K ∗ (890) production cross section is studied as a function of transverse and longitudinal variables and found to derive mainly from fragmentation of the incident K− meson. The spectra of K 0 s resulting from the decay of K ∗ (890) are studied.

K∗(890) and K∗(1420) production in quasi two-body K−p reactions at 10 GeV/c

Abstract Results are presented for six reactions induced by K−p collisions at 10 GeV/c, where K∗(890) and K∗(1420) resonances are produced in association with a proton, a neutron, a Δ+(1236) or ΔO(1236) isobar. Partial and differential cross sections as well as density matrix elements are compared to one another and to previous results at lower energies. The following observations are made: (i) There is a first indication of a difference in the energy dependence of the pK∗− and nK∗O cross sections. (ii) In the pK∗−(890) channel the ratio of π to ω exchange decreases with increasing energy. (iii) The ratio of π to ω exchange increases with the mass produced, the pion exchange contribution to the pK∗−(1420) channel being larger than that to the pK∗−(890) channel. (iv) Natural spin-parity exchange dominates in the pK∗−(890) channel, but there are significant contributions of both natural and unnatural parity exchanges in the nK∗O(890) channel. (v) There exists a clear hierarchy of exchanges such that when ω or fO-exchanges are possible, they dominate over pion-exchange; pion exchange dominates over ϱ or A2-exchange in ΔQ = 1 or ΔI = 1 reactions, at least up to 10 GeV/c. (vi) Differential cross sections dσ/dt′ of reactions dominated by pion exchange are better fitted by a two-exponential formula of the type P[exp (−Qt′)+R exp (−St′)], than by the pion propagator. (vii) At least ≈ 25% of the unnatural exchange in the nK∗O(890) channel at 4–10 GeV/c must be due to mechanisms other than simple pion exchange.

A comparison of πππ, Kππ, πKKKK system produced in the reactions meson +p→3 mesons + p

Abstract A comparison is made of the low-mass three-meson systems (πππ), (Kππ), (π K K ) and ( K K K ) diffractively produced in the reaction meson + proton → three mesons + proton. Several striking similarities and a few important differences are observed: (i) the reactions are consistent with the assumption that the three mesons decay entirely into a 0− meson and a 0+, 1− or 2+ resonance; (ii) the three-meson mass spectra have a peak ≈ 250 MeV above the effective threshold Meff of the dominant decay mode and then fall off approximately as (mass)−3;(iii) the average spin 〈J〉 = 0.55 + 1.1 Qeff, where Qeff = M - Meff; (iv) the average orbital angular momentum 〈l〉 increases according to 〈l〉 = 0.75 Qeff; (v) the three-meson states are produced dominantly in unnatural spin-parity states and no evidence for their being resonant is found; (vi) the only natural spin-parity states found are the well-established 2+ resonances A2 and K∗ (1420); they have similar properties to the non-resonant unnatural parity states except for a dip at t = 0 in the dσ/dt distributions; (vii) both the unnatural and natural spin-parity states are produced mostly by an exchange of natural parity; (viii) there is evidence for two types of production mechanism with different polarization properties, one approximately conserving helicity in the t-channel and the other in the s-channel.

Study of lambda production in 10 GeV/c K−p interactions

Lambda production is studied in K−p interactions at 10.1 GeV/c, where the dominant reaction is K−p → Λ + pions. General characteristics such as the distributions of the double differential cross section in the lab system, of the variable x = pL∗pmax∗, of p⊥2 and of the missing mass to the lambda are presented. Total cross sections for Λ production and for the various channels are given. Differential cross sections dσdt, dσdt′ and dσdu′ are presented. Forward and backward peaks are observed in the dσdt′ and dσdu′ distributions, respectively. It is found that the exponential slope of these distributions decreases with increasing missing mass to the lambda and, for dσdt′, also for increasing multiplicity in the final state. The polarization of the lambdas is studied as a function of multiplicity, pL∗, (Λπ±) effective mass, t′ and u′. The forward lambdas show

Inclusive production of γ, Kn, Λ0 and Λ0 in K−p interactions at 110 GeV/c

Abstract Results on inclusive production of γ,K n , Λ 0 and Λ 0 in K − p interactions at 110 GeV/ c are presented. Total cross sections, and differential cross sections in terms of Feynman x , rapidity and p T 2 are given. It is found that about 40% of K n s are produced together with a strange particle pair, and that 80% of Λ 0 s are produced together with a K K pair. These Λ 0, s are produced predominantly in the backward direction. Fits to the form (1−| x |) n to the x F distributions of K n and Λ 0 in the fragmentation regions are found to be in general agreement with quark counting rule predictions.

Eta and omega meson production in medium energy π+-p and K−p interactions

The production of η(550) and ω(780) mesons is studied in π±p interactions at 16 GeV/c and K−p interactions at 10 and 16 GeV/c. Cross sections for exclusive channels are presented, and for the π+p data differential cross sections are given for quasi-inclusive production where the η or ω is required to be accompanied by charged particles only. Close similarities are observed between η, ω and also ϱ0(770) production in terms of longitudinal and transverse variables. By a rough estimate, the η, ω and ϱ0 inclusive yields are found to be in the ratio 0.32 : 0.85 : 1, respectively, for 16 GeV/c π+p collisions. For non-peripheral production we estimate this same ratio to be 0.34 : 0.9 : 1.

Tests of s-and t-channel helicity conservation in pπ+ π−, K−π+π− and π±π+π− production in 16 GeV/c π±p and 10 GeV/c K−p interactions

Abstract Necessary conditions for s-and t-channel helicity conservation are tested for pπ+π−, K−π+π− and π±π+π− states produced in 16 GeV/c π±p and 10 GeV/c K−p interactions by means of a method which is independent of specific spin-parity assignments to these states. It is found that the production of pπ+π− states is generally consistent with t-channel helicity conservation for masses up to 2.4 GeV, but that for π±π+π− and K−π+π− some inconsistency with t-channel helicity conservation is found, primarily in the A1± and Q− mass regions. s-channel helicity conservation is excluded for all states.

Comparison of π±p and K−p reactions with a multiperipheral model using the Van Hove hexagon and cuboctahedron plots

Abstract Several reactions of 8 ifGeV/ cπ + p , 10 GeV/ c K − p and 16 GeV/ c π − p have been compared with the multiperipheral Regge-pole model of chan, Łoskiewicz and Allison, using the technique of longitudinal phase-space plots introduced by Van Hove, to investigate the relative importance of the various exchange diagrams. While the gross features of the data are satisfactorily reproduced at all

Evidence for unnatural spin-parity states of (Kππ)0 in the charge-exchange reaction K−p→(K0π+π−)n

Abstract A partial-wave analysis of the (Kππ)0 system produced in the charge exchange reaction K − p →( K 0 π + π − ) n has been made in the mass range 1.04 ⩽ M (Kππ) 2 3 of the cases, the (Kππ)0 system is produced in states of unnatural spin-parity, namely JP = 0− and 1+; the rest is in the natural spin-parity state JP = 2+ state is consistent with being all K∗ (1420). The unnatural spin-parity states are produced mostly (∼ 80% of the events) by natural parity exchange. The facts that unnatural spin-parity states are produced in this non-diffractive channel, with JP = 1+ dominant, and that the exchange responsible for their production is mostly of natural parity, are similar to what was found for the charged (Kππ)− system in the diffractive reaction K−p→(Kππ)−p. However, the absolute value and the energy dependence of the cross sections are very different in the two cases.