Y. Goldschmidt-Clermont

Observation of direct soft photon production in K+p interactions at 70 GeV/c

Abstract The inclusive γ cross section in K + p interactions at 70 GeV/ c shows an excess of (4.5 ± 0.9) mb over the contributions arising from hadron decays. The excess consists of soft γs with −0.001 x p T c . The shape of this soft γ spectrum is consistent with that expected from QED inner bremsstrahlung, but the measured total cross section exceeds the QED expectation, indicating the presence of other source(s) of soft photons.

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*.

A fast on-line trigger for events with multiple high transverse momentum tracks

Abstract We present a fast (30 μs) on-line trigger that selects, from 300 GeV/ c π − interactions, events with three tracks of transverse momentum larger than 0.9 GeV/ c . The essential features of this trigger are a fast read-out (300 ns per cluster) of wire chambers, situated on the chamber frame, and a digital computation of transverse momenta that can cope with multiple hits in the detectors of the trigger tracks. The digital computation is done with standard MBNIM modules.

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.

Determination of the Masses of Charged Particles Observed in the Photographic Plate

A study has been made of scattering of 40 protons and 160 mesons in photographic emulsions in order to determine the mass of the individual particles. The spread in the values so obtained is large, but the evidence suggests that the majority of mesons recorded by the emulsion can be identified both with the mesons, of mass 200 me, commonly observed in cloud-chamber experiments and with counters, and with the μ-mesons observed in the photographic plates. The slow particles producing nuclear disintegrations, σ-mesons, appear to contain a large proportion of particles with a mass equal to that of the π-mesons.

HYPERON AND KAON PRODUCTION BY 16 Gev/c NEGATIVE PIONS ON PROTONS

SummaryStrange particle production by 16 GeV/c negative pions in hydrogen has been studied. 60 000 pictures were taken with the CERN 32 cm hydrogen bubble chamber. The cross sections found for associated and K-K pair production are σyk= 1.32±0.15 mb, σk-k=2.21±0.25 mb. The angular distributions of the Λ0 and Σ+ hyperons show a pronounced backward peaking in the pion-proton c.m.s. The backward peak is less pronounced for Σ(−. The ratio Σ+/Σ− is 1.3 ±0.3 at production. The neutral kaons are significantly peaked forward. The average longitudinal momentum in the c.m.s. is 0.26±0.05 GeV/c along the direction of the incident pion. The average transverse momentum is small, ∼ 0.5 GeV/c, and possibly independent of the kind of particle produced. Our results indicate a higher mean value for Σ± than for Λ0 and K0. The average pion multiplicities are: for Y + K production 4.9 ±0.1, for K + -K production 4.0±0.1. The kinetic energy distributions have been compared with the predictions of the statistical theory. The contribution of nonstatistical processes is important. Different estimates give 30% as a lower limit.RiassuntoSi è studiata la produzione di particelle strane con pioni negativi da 16 GeV/c in idrogeno. Si son prese 60 000 fotografie con la camera a bolle ad idrogeno da 32 cm del CERN. Le sezioni d’urto trovate per la produzione di YK associati e di coppie K-K sono σk-k = (1.32±0.15) mb, σYK= (2.21 ±0.25) mb. La distribuzione angolare degli iperoni Λ0 e Σ+ presenta un picco all’indietro nel sistema del centro di massa pioneprotone. Il picco all’indietro è meno pronunciato per i Σ-. Il rapporto Σ+/Σ- è 1.3±0.3 alla produzione. I kaoni neutri lianno un notevole picco in avanti. L’impulso longitudinale medio nel sistema del centro di massa è (0.26±0.05) GeV/c lungo la direzione del pione incidente. L’impulso trasversale medio è piccolo, ∼ 0.5 GeV/c, e forse indipendente dal tipo di particella prodotta. I nostri risultati indicano un valore medio più alto per Σ+- che per Λ0 e K0. Le molteplicità pioniche medie sono: perla produzione di Y+K 4.9±0.1, per la produzione di K+-K 4.0±0.1. Le distribuzioni della energia cinetica sono state confrontate con le predizioni della teoria statistica. Il contributo dei processi non statistici è importante. Valutazioni differenti danno 30% corne limite inferiore. ntίs|Traduzione a cura della Redazione.

A study of the inclusive reactions K+p → K∗(890) + X+and K+p → K∗(1420) + X+at 8.2 GeV/c

Abstract The K∗, very strongly produced in K+p collisions at 8.2 GeV/c, are separated out in an inclusive analysis. The key features of their missing mass and momentum transfer distributions are compared to those already seen in the K+p → Ko + anything, inclusive reaction and which are those expected from a simple Regge model. The K∗ results here reported are also compatible with such a model. An important contribution from pion exchange is required at small four-momentum transfers in contradistinction with what is found for quasi elastic production.

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