M.J. Counihan

ϱ0 and f production in π+p interactions

Abstract Inclusive ϱ 0 and f(1270) production are analysed in π + p collisions at 8, 16 and 23 GeV/ c . The ϱ 0 cross section increases with energy such that the ϱ 0 /π − ratio remains constant. Emphasis is laid on cross sections as a function of the transverse momentum and of the Feynman x variable. The ϱ 0 s can be attributed to two sources: some ϱ 0 s are centrally produced, but there is a pronounced forward peak. The distribution of leptons coming from ϱ 0 decay is discussed.

Partial-wave analysis of the 3π system produced in the reaction π+p → (π+π+π−)p at 8, 16 and 23 GeV/c

Abstract A partial-wave analysis has been made of the (3π) system produced in the reaction π + p → ( π + π + π − )p at 8, 16 and 23 GeV/ c using the Illinois partial-wave analysis program. The (3π) systems is in about 93% of the cases in the unnatural spin-parity states 0 − , 1 + , 2 − and 3 + and is produced in about 100% of the cases by natural parity exchange. For all J P states, the differential cross section d σ /d t ′ peaks at small tt ′, except for 2 + D which has a dip at t ′ ≈ 0. The cross sections for J P = 1 + , 2 + and 2 − in the A 1 , A 2 and A 3 regions, respectively, all have similar energy dependence, p lab − n , with n = 0.3 ± 0.2. The weak variation of the 1 + S phase across the 1.0–1.2 GeV mass region, suggests that A 1 cannot be considered as a single resonance, while the phase variation of 2 + D (ϱπ) in the A 2 mass region is consistent with resonance behaviour. In the A 3 region, the behaviour of the 2 − S and 2 − P phases is complex and further work is needed to understand the mechanisms involved there.

A study of direct and indirect pion production in π+p interactions at 16 GeV/c

Abstract The sources of negative pions are analysed in π+p interactions at 16 GeV/c. It is shown that the kinematics of resonance decay is crucial in determining the pions′ longitudinal and transverse momentum spectra. The identifiable meson resonances, of which η, ω, ϱ0 and f are the dominant ones, account for about 50% of all π−s produced. The “direct” pions, i.e. those that are primary products of the π+p interactions, appear to constitute 10 to 30% of the total π− yield.

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.

Determination of the fire-ball dimensions from second-order interference between two pions

Abstract Positive correlations are observed for pion pairs of equal charge and similar momentum vectors, produced in the reactions π p→p+5 π and π p→p + 7 π at 4 to 25 GeV/ c . The results are consistent with being due to the second-order interference effects expected for pairs of identical bosons and lead to the determination of the average dimension of the “fire-ball’ from which the pions are emitted (〈 R 〉 = 1.0 ± −0.2 +0.4 fm). Attempts are made to study the fire-ball shape by selecting pions pair emitted in various polar and azimuthal directions.

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.

Multiplicity cross sections for 100 GeV/c π−p interactions

Abstract Charged particle multiplicity cross sections for 100 GeV/ c π − p inelastic interactions are presented and compared with results at other energies. The results for multiplicities n ⪖ 4 show a consistent trend in their energy dependence. The two-prong cross section curve differs as it tends to flatten off at the higher energies. The zero-prong cross section values decrease steeply as p lab −1.1 . The results for n ⩾ 2 for π − p and pp reactions appear to lie on a “universal” curve if nσ n / σ inel is plotted against 〈 n 〉/ n . This “scaling” rule is equivalent to KNO scaling, but the plot suggested here is more useful in studying low multiplicities. An interpretation in terms of a two-component model and a possible extrapolation to higher energies are proposed.

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.

An impact parameter analysis of multiparticle production in medium-energy meson-proton interactions

Abstract Lower bounds can be calculated for the root-mean-square impact parameter b , in any exclusive reaction. These lower bounds, b L , have been calculated for 9 exclusive π − p reactions at 16 GeV/ c and for 24 exclusive K − p reactions at 10 and 16 GeV/ c . It is found that b L decreases with increasing multiplicity, but is larger at higher energy. The values of b L are larger for diffractive than for non-diffractive channels of the same multiplicity.

Charge exchange and charge distributions in K−p interactions at 10 and 16 GeV/c

Abstract For each K − p event, the charge exchange, ΔQ , is calculated, as the difference between the total charge of the forward going particles and of the incident K-meson. Taking all inelastic events, it is found that zero charge exchange does not dominate, occuring in only 40% of the cases. The proportion of ΔQ = + 1 is also 40%, while ΔQ = − 1 and ΔQ = + 2 both represent about 10% of the events and other values of ΔQ are not important. The average charge exchange and the dispersion of ΔQ values are compared with the predictions of the multiperipheral and fragmentation models.