V.P. Henri

Measurement of the total and partial p̄p cross section between 1901 and 1950 MeV

Abstract The presence of a structure in the pp total cross section at 1930–1940 MeV, with a narrow width of 9 MeV is confirmed. The interpretation of the effect as a single, non interfering, resonance is made difficult by the comparison of the elastic scattering with the charge exchange cross sections.

Inclusive Production Cross-Sections of Resonances in 32-GeV/c K+ p Interactions

Abstract The inclusive production of resonances is systematically studied in K + p interactions at 32 GeV/ c . Total production cross sections are given for three baryon resonances, five vector and three 2 + tensor mesons. We also compare the central and fragmentation components of the total production cross sections with quark model predictions.

The reaction K+p → K0pπ+ at 3 GeV/c

SummaryThe reaction K+p → K0pπ+ has been studied at 3.0 GeV/c. The two dominant reactions in this final state are K+p → K*p, K* →c K0π+ and K+p →N*K0,N* → pπ+ accounting each for (38±3)% of the events and corresponding to a cross-section of (0.8±0.1) mb. The production angular distributions for both K* andN* are suggestive of a peripheral mechanism of production. Within the framework of a simple one-mesonexchange model, the decay angular distributions for K* are consistent with the assumption that these events are predominantly produced by the exchange of a vector meson with only (7±6)% of the events being produced by the exchange of a pion. TheN* decay distributions agree with the prediction of the model of Stodolsky and Sakurai. For both K* andN*, a form factor of the type exp [-δ2/t2], witht equal to about 0.6 GeV/c, is needed to fit the very sharply peaked production distributions. A modified one-meson-exchange model, taking into account absorption effects due to competing processes, derived by Gottfried, Jackson and Svensson, gives a reasonable account of the production angular distribution and of the decay correlations for both K* andN*.RiassuntoLa reazione K+p → K0pπ+ è stata studiata a 3 GeV/c. Le due reazioni dominanti nello stato finale sono K+p → K*p, K* → K0π+ e K+p →N*K0,N* → pπ+. Queste due reazioni sono prodotte nel (38±3)% dei casi e corrispondono ciascuna ad una sezione d’urto di (0.8±0.1) mb. Le distribuzioni angolari di produzione sia per il K* che per l’N* suggeriscono un meccanismo di produzione di tipo « periferico ». Nel limite di un semplice modello a scambio di un solo mesone, le distribuzioni angolari di decadimento del K* sono in accordo con l’ipotesi che questi eventi sono prodotti prevalentemente tramite lo scambio di un mesone vettore; solo il (7±6)% degli eventi possono essere attribuiti allo scambio di un pione. Le distribuzioni angolari di decadimento dell’ N* sono in accordo con le predizioni del modello di Stodolsky e Sakurai. Le distribuzioni angolari di produzione sia del K* che dell’N* presentano un forte picco ed è necessario fare uso di un fattore di forma del tipo exp [-δ2/t2] cont ⇏ 0.6 GeV/c per poterie deserivere. Usando un modello di scambio di un solo mesone modificato da Gottfried, Jackson e Svensson per tenere conto dei processi di assorbimento doTuti a reazioni in eompetizione, è possibile ottenere un buon accordo fra le distribuzioni angolari di produzione e le correlazioni di decadimento del K* e dell’N*.

K+p elastic scattering at 3.0 GeV/c

SummaryIn the course of a systematic study of K+p interactions at 3.0 GeV/c, the elastic-scattering reaction has been investigated. A total of 1720 events were identified as elastic scatters, giving a cross-section of (4.8±0.4) mb. The angular distribution shows characteristic diffraction peaking and was fitted using dσ/d|t|=(dσ/d|t|)0 exp [αt+βt2], in the momentum-transfer region (0.05÷1.14) (GeV/c)2. The best fit gaveα=(4.55±0.39) (GeV/c)−2 andβ=(0.64±0.42)(GeV/c)−4. The extrapolated experimental cross-section at 0°, (dσ/dt)0, is found to be (19.5±2.3) mb/(GeV/c)2, and exceeds the optical-theorem prediction by (3.8±2.3) mb/(GeV/c)2, implying that there is a contribution from the real part of the K+p scattering amplitude at 3.0 GeV/c.RiassuntoNel corso di uno studio sistematico delle interazioni K+p di 3.0 GeV/c si è esaminata la reazione di scattering elastico. Un totale di 1720 eventi è stato identificato come scattering elastici che danno una sezione d’urto di (4.8±0.4) mb. La distribuzione angolare presenta un caratteristico picco di diffrazione ed è stata approssimata da dσ/d|t|=(dσ/d|t|)0 exp[αt+βt2] nella regione dei momenti trasferiti (0.05÷1.14)(GeV/c)2. Un calcolo di « best fit » dàα=(4.55±0.39)(GeV/c)−2 eβ=(0.64±0.42)(GeV)−4. Si trova che la sezione d’urto sperimentale estrapolata a 0°, (dσ/d)0, è (19.5±2.5) mb/(GeV/c)2, e supera le predizioni del teorema ottico di (3.8±2.3) mb/(GeV/c)2, implicando che si ha un contributo della parte reale dell’ampiezza di scattering K+p a 3.0 GeV/c.

The reactionππ at 3 GeV/c and the production mechanism of

SummaryIn a study of the four-particle states K+p→ππ at 3 GeV/c, it is found that the quasi-two-body process K+p→* occurs in large proportion. The cross-sections for the various charge and decay modes of K** are in good agreement with the predictions based on isotopic-spin invariance. The sharply peaked c.m. production angular distribution suggests peripheralism. Within the framework of a simple one-meson-exchange model the decay angular distributions of K* and* are consistent with the assumption that the reaction proceeds predominantly through the exchange of a single pion. Such a model is unable to explain the nonzero value of the « interference » parameter Reϱ1, 0 (−0.13±0.02). In addition, the model requires the inclusion of a drasticad-hoc form factor, similar to the one used at 1.96 GeV/c, in order to fit the observed production angular distribution. A modified one-meson-exchange model taking into account the absorption due to competing processes and developped by Jackson, Donohue, Gottfried, Keyser and Svensson, does not explain the absolute value of the cross-section, but predicts, with a minimum of assumptions, a production angular distribution and decay correlations in reasonable accord with experiment.RiassuntoIn uno studio degli stati a quattro particelle K+ → a 3 GeV/c si è trovato che il processo di due quasi-corpi K+p→* avviene in grande proporzione. Le sezioni d’urto per i vari modi di carica e di decadimento del K** sono in buon accordo con le predizioni basate sull’invarianza dello spin isotopico. Il forte picco della distribuzione angolare della produzione nel centro di massa suggerisce il periferalismo. Entro lo schema di un semplice modello a scambio di un mesone le distribuzioni angolari del decadimento del K* e del* sono in accordo con l’ipotesi che la reazione proced a tramite lo scambio di un solo pione. Tale modello non è in grado di spiegare il valore non nullo del parametro di « interferenza » Reϱ1,0 (−0.13±0.02). Inoltre il modello esige che siano introdotti drastici fattori di formaad hoc, simili a quello usato a 1.96 GeV/c per approssimare la distribuzione angolare di produzione osservata. Un modello modificato a scambio di un mesone che tiene conto dell’assorbimento dovuto a processi in competizione, sviluppato da Jackson, Donhue, Gottfried, Keyser e Svensson, non spiega il valore assoluto della sezione d’urto, ma predice, con un minimo di ipotesi, una distribuzione angolare di produzione e delle correlazioni di decadimento in ragionevole accordo con l’esperienza.

Tests of large Čerenkov detectors with silica aerogel as radiator

Abstract Cerenkov detectors with silica aerogel as radiator, and a detector surface of about 18 × 52 cm 2 , have been tested in a particle beam at the CERN Proton Synchrotron. For 9 cm thickness of silica aerogel the number of photoelectrons for β = 1 particles was found to be 4.6 and 5.5 respectively, depending on the light collection system used.

Multiplicity of charged particles in 800 GeV p-p interactions

Abstract Results are reported concerning the charged-particle multiplicity distribution obtained in an exposure of the high-resolution hydrogen bubble chamber LEBC to a beam of 800 GeV protons at the Fermilab MPS. This is the first time that such data have been available at this energy. The distribution of the number n ch of charged particles produced in inelastic interactions obeys KNO-scaling. The average multiplicity is 〈 n ch 〉 = 10.26±0.15. For n ch ⩾8 the data can be well fitted to a negative binomial. The difference between the overall experimental multiplicity distribution and that resulting from the latter fit is in agreement with the contribution expected from diffractive processes.

Inclusive V0 production in pp interactions at 12 GeV/c

Results are presented on the inclusive reactions pp → K0X, pp → ΛX and pp → ΛX at an incident antiproton momentum of 12 GeV/c in BEBC. The cross sections are studied as functions of the Feynman scaling variable x, the rapidity, the transverse momentum of the V0 and the missing mass squared. The dependence of the Λ and Λ polarization on x are also studied. Comparisons with proton-proton data at 12 GeV/c are also made. Finally, events with two detected V0 are analyzed in order to study correlations arising from the production of two strange neutral particles.

The reactions K+ m̊p → ΛX++ and K+ p → ΛX++ at incident momenta of 8.2 and 16.0 GeV/c

Inclusive production of Λ and Λ in K+ p interactions is studied at incident momenta of 8.2 and 16.0 GeV/c. Cross sections and single-particle distributions are presented, the correlation between longitudinal and transverse momentum is investigated, and the dependence of average charge multiplicity on missing mass measured. For Λ production, early scaling is observed in the target fragmentation region when the data are presented in terms of (M2-Mth2)/s and t, where Mth is the threshold value of the missing mass M. Furthermore, a triple-Regge analysis in these variable yields an effective exchange trajectory which passes through the K, Q and L mesons. There is evidence for beam fragmentation in Λ and Λ production, but the contributions seem not to be dominant in the fragmentation region. Nevertheless, the parameter values in a triple-Regge description are estimated, and together with those for target fragmentation in Λ production, provide a complete description of the fragmentation contributions to the two reactions. Integration of the resultant distribution functions over the complete Chew-Low plot yields fragmentation cross sections increasing approximately as log s; in addition the observed features of the x, pL and pT2 projections and of the pL-pT correlation are well-described in the fragmentation regions. Central production contributions are isolated by subtracting the calculated fragmentation distributions

Production of K∗ (892) and K∗ (1420) in the reaction K+d→KπN(Ns) at 4.6 GeV/c

In a bubble-chamber experiment with the CERN 2 m chamber the reactions (i) K+d→K+π−pp, (ii) K+d→K0π0pp, and (iii) K+d→ K0π+ pn have been studied at a primary K+ momentum of 4.6 GeV/c. There is abundant production of K∗ (892) in reactions (i), (ii) and (iii), of K∗0(1420) in reactions (i) and (ii) and of Δ++ (1236) in reaction (iii). In reaction (i) backward production of K∗0 (892) is observed. Reaction and resonance-production cross sections are presented and their energy dependence is investigated. Production and decay angular distributions for the resonance bands are analyzed and compared to the results at other energies. In particular the data pertaining to the reaction K+n→K∗0p are compared in some detail with those for the reaction K−p→K∗0 (892) n. Finally, the evidence from reaction (i) for the existence of KN resonances other than K∗ (892) and K∗ (1420) is discussed.