Search

The reaction π−p → K+K− π− p at 16 GeV/c was studied in the CERN OMEGA spectrometer and a partial-wave analysis (PWA) of the low-mass (K+K−π−) system (1.3–2.0 GeV) was performed. Only states in the unnatural spin-parity series produced by natural parity exchange are important and they approximately conserve t-channel helicity. The 1+S K∗K wave dominates the low-mass (K+K−π−) region. We observe an enhancement in 2−P K∗K wave at a mass of 1.7 GeV, consistent with the decay of the A3 resonance.

The final states\(\bar p\)pω and\(\Delta ^{ + + } \bar \Delta ^{ - - } \pi ^0 \), produced in the reaction\(\bar p\)p →\(\bar p\)pπ+π−π0 (6435 events) at 5.7 GeV/c, are studied. Cross-sections are presented, and general features of the resonances produced are investigated. Spin alignment of the ω’s, reported earlier, is studied. An enhancement is observed in the ωp (ω\(\bar p\)) mass plot of mass (1810±15) MeV and width (87 ± 20) MeV.

Plastic scintillator counters made of long slabs (200×20 cm 2 ) of different thickness have been tested with 120 cm long plexiglas light guides coupled to 58 AVP photomultipliers. The accuracies achieved in measuring the time of flight of 600 MeV/ c protons, which hit the counter at different distances from the photo-multiplier, range from 350 to 450 ps fwhh. The impact position of the particles is determined along the counter by the time difference, as measured from the two opposite ends, with an accuracy ranging from 4.5 to 5.5 cm fwhh.

An experiment has been undertaken at the CERN SPS, using the Omega spectrometer, aimed at confirming the enhancement observed in a p p φ − mass spectrum at 2.95 GeV [1]. With statistics of twelve times the original experiment no signal is seen. In the reaction φ − p → p p φ − p , the upper limit (four standard deviations) for the production of a resonance in the p p φ − system at 2.95 GeV, with a width ⩽ 30 MeV, is 50 nb.

Results are presented of a spin-parity analysis on a sample of ∼ 1000 E mesons centrally produced in the reactions (π+/p) p → (π+/p) (K01K±π∓) p at 85 GeV/c. The E quantum numbers are determined to be JPC = 1++. Its decay in this channel is consistent with being 100% into K∗K + c.c. and no evidenceis seen for a δ π decay mode where δ → KK. The mass and width were determined to be M = (1425 ± 2) MeV and Γ = (62 ± 5) MeV.

From 63 760 four pronged events we have selected 10 960 events of the p p π + π − final state. We have studied baryon resonances production and the associated production of Δ(1236) Δ (1236) isobars. We find (48.5 ± 2.6)% of Δ ++ Δ ++ and (4.5 ± 0.5)% of Δ 0 Δ 0 . Study of the various mass spectra shows that they are essentially described by the introduction of Δ ++ ( Δ ++ ) production. Introduction of the strong t dependence of the Δ ++ ( Δ ++ ) changes this description only slightly. A study of the interaction radius of the pπ system reveals a best value of r = 1.6 ± 0.4 fm. Bumps observed in the pπ+π− + c.c. system at 1450 and 1690 MeV when treated as resonances give rates of (4.0 ± 0.4)% and (4.5 ± 0.4)% respectively. We arrive at the conclusion that the reaction p p → p p π + π − at 5.7 GeV/c proceeds almost entirely via the production of baryon resonances.

Performing a PWA of the π − π − π + system over the −t p/p range 0.2 to 0.4 GeV 2 we find evidence for a J P = 0 − , J G =1 − meson of mass 1342 ± 20 MeV and width 220 ±70 MeV decaying into ϵπ. This state is produced by natural parity exchange with a slope similar to that of elastic scattering. It can be interpreted as a radial excitation of the π meson (π′).

The reaction π − p → φφ n has been isolated at 16 GeV/ c and its cross section determined to be 40 ± 10 nb. The φφ mass spectrum shows a threshold enhancement between 2.1 and 2.5 GeV. A successful description of the angular content of the φφ system requires two interferingss J P = 2 + states.

Results are presented on the properties of the pp interactions at 3.6 GeV/c leading to a hyperon or an antihyperon in final states with ⩾3 particles from an experiment of 35 eV/μb sensitivity. Results of amultidimensional mass fit to each final state are given along with the cross sections, differential cross sections and polarization, where possible, for the hypercharge exchange reactions pp→ΛY∗(1385), ΛY∗(1520), ΣY∗(1385) and ΣY∗(1520).

Inclusive φφ production has been studied in π−Be interactions at 85 GeV/c incident momentum, and a signal of 4327 φφ events was found in a sample of data recorded with the aim of studying the low mass φφ system. We estimate that ∼ 75% of this signal can be attributed to the correlated production of two φ′s. A search for narrow enhancements leads to upper limits at the 99.7% confidence level for σ(X) × BR(X → φφ) varying from ⩽ 562 nb/Be nucleus at a mass of 2.1 GeV/c2 to ⩽ 221 nb/Be nucleus at 3.1 GeV/c2, where X represents a possible narrow state. These upper limits represent an increase in sensitivity by a factor 3 to 5 when compared to currently available data.

We have analyzed theK10K± π∓ system in the reactions π+/pp→π+/p(K10K± π∓)p. A spin-parity analysis of theK10K± π∓ system in the “4C” channel confirms the existence of the 1++E meson which decays mainly throughK*\(\bar K\). The data allow the presence of a 0−+ wave at a level of 14% of theE/ι signal. The production ofD andE mesons in the channels where theK10K± π∓ system is produced along with a π0 or π+π− system is suppressed.

The nucleon isobars\({\mathcal{N}}^* (1518)\) and\({\mathcal{N}}^* (1688)\) are observed in inelastic interactions of 5.7 GeV/c antiprotons in hydrogen. The widths of both of them are found to be small ((55±15) MeV and (70±20) MeV respectively), in agreement with recent phase-shift data. The 2-body to 3-body branching ratios are estimated (being 1.25−0.71+0.44 in the case of the\({\mathcal{N}}^* (1518)\) and less than 1.26 with 95% confidence for the\({\mathcal{N}}^* (1688)\) and show that the inelasticities of both resonances in π−p scattering are high. A detailed study of the 3-body\({\mathcal{N}}\pi \pi \) decays provides no evidence in either case for the cascade decay into\(\mathcal{N}^* (1238) + \pi \). Deviations from uniform population of the Dalitz plots for the 3-body decays are observed and are studied in terms of the 3-body decay matrix elements. Upper limits for decay of the\({\mathcal{N}}^* (1688)\) into\({\mathcal{N}}\eta \) and ΛK final states are estimated.

In the π+π−π± systems of the reactions p p → K K mπ (m=4,5) two narrow peaks are observed at the positions of the δ and A1 mesons. The measured masses and widths are: M= (956±7)MeV, Γ=(46±22) MeV for the δ and M=(1076±5)MeV, Γ=(36−15+20)MeV, for the A1. Their decay modes and spin-parities are shown to be mainly 3π, JP=0− and ϱπ, JP=1+ (D-wave) respectively.

117 interactions of cosmic ray particles with aluminium nuclei have been studied. 101 showers containing no apparent unstable particles yielded the following multiplicities: $$\left\langle {n_s } \right\rangle = 7.3; \left\langle {n_s^ + } \right\rangle = 3.9; \left\langle {n_s^ - } \right\rangle = 2.7; \left\langle {n_s^ \pm } \right\rangle = 0.6.$$ . The momentum and angular distributions of the secondary particles were examined, and an attempt was made to study the momentum-angle correlation. The mean transverse momentum was 0.31 GeV/c, the RMS deviation about this mean being 0.23 GeV/c. A quantity related to the (U−pL) of the recoil nucleon was also investigated. 12 showers containing one V0 each and 1 shower containing two V0 particles were studied; this showed that the 117 showers contained; 29.5−11.0+14.0 Λ0 and 18.0−10.0+15.0 ϑ0 particles. 3 showers containing V± particles were also studied; one of them was probably a Ξ− particle.

A study of 3638 events of the reaction\(p\bar p \to p\bar p\pi ^ + \pi ^ - \) at 5.7 GeV/c in the 81 cm Saclay hydrogen bubble chamber is reported. The measurements were made with the CERN HPD system. The cross-section for the channel\(p\bar p \to p\bar p\pi ^ + \pi ^ - \) was found to be (3.31±0.16) mb. Abundant associated production ofN\(_{33}^* \)(1238)N\(_{33}^* \)(1238) has been observed; the cross-section for the process\(p\bar p \to \)N\(_{33}^* \)N\(_{33}^* \) is (2.08±0.14) mb which corresponds to (63±3)% of the total cross section for the studied channel. The production mecanism ofN\(_{33}^* \)N\(_{33}^* \) has been investigated and the experimental results compared with various predictions of the one-pion exchange model modified to take into account absorption in the initial and final states (absorption model). The slope of the differential cross-section is rather well reproduced by this mode, the experimental value is however exceeded by a factor of about three. The decay parameters of the joint decay distribution have been measured and found to be in reasonable agreement with the theoretical predictions. A small correlation between the decay angles of theN\(_{33}^* \) andN\(_{33}^* \) respectively of 0.10±0.04 has been found and is in agreement with the prediction of 0.05 from the absorption model.

A bubble chamber investigation of π−p interactions has been carried out at a momentum of 4 GeV/c. Analysis is limited to 3 828 events with two charged secondaries. Cross-sections, angular distributions and momentum distributions for the different reactions are presented. Four-momentum transfer distributions for elastic scattering and single-pion production are discussed. The production of pion resonant states is investigated.

The reaction\(\bar pp \to \bar pp\pi ^ - \pi ^ + \pi ^0 \) has been studied at 5.7 GeV/c in the 81 cm Saclay hydrogen bubble chamber. Production of ω0 and η0 mesons has been observed. The ω0 mesons are collimated in the forward and backward directions in the c.m.s. The decay angular distribution of the ω0 indicates that it is produced with the spin aligned in the plane perpendicular to the incident\(\bar p\) (or p) momentum transformed to the ω0 rest frame, an effect which is enhanced when the four-momentum transfert is limited to |t

We report a study of the reactions\(\bar pp \to n\pi ^ + + n\pi ^ - + m\pi ^0 \) at 3.0 GeV/c and 3.6 GeV/c (Ec.m.s. is equal to 2.77 GeV and 2.96 GeV respectively) wheren=3, 4 or 5 andm≥0. The sample contains 1988 six-prong events at 3.0 GeV/c, 440 eight-prong events at 3.0 and 3.6 GeV/c and 10 ten-prong events at 3.0 and 3.6 GeV/c. The cross-sections for various processes observed are compared with the cross-sections obtained in other experiments at different incident antiproton momenta. A maximum in the 7π annihilation cross-section is seen at a c.m.s. energy of about 2.7 GeV. Appreciable production of ρ0 in the six-pion events and of\(\rho ^{\begin{array}{*{20}c} \pm \\ 0 \\ \end{array} } \) and ω0 mesons in the seven-pion events is observed. In the six-pion events the 2π+2π− mass distribution and the ρ0π+π− mass distribution show evidence of structure with peaks at (1704±10) MeV and (1834±10) MeV. In the seven-pion events selected to contain a π+π− and π+π−π0 mass combination in the ρ0 and ω0 regions respectively, the ρ0π± mass distribution shows peaks in the mass regions corresponding to the A1 and A2 mesons with masses of (1054±7) MeV and (1269±9) MeV respectively, the width of the peak in the region of the A2 being smaller, (38±19) Mev, than that usually observed in bubble chambers but is compatible with the lower-mass peak of the split A2 as observed by Levratet al. The ρ0ω0 mass distribution shows two peaks at masses of (1689±10) MeV and (1848±11) MeV. The angular distributions of pions are slightly collimated along the direction of the incident particles, this collimation being an increasing function of pion momentum in the c.m.s. The ρ0 and ω0 mesons also have anisotropic distributions in the c.m.s. A strong angular correlation is observed between pairs of pions of opposite charge. This correlation decreases with increasing energy of the c.m.s. or when the number of π0 produced in the annihilation increases.

12357 events from antiproton-proton annihilations into kaons and pions have been analysed. Partial cross sections are determined for various K K + nπ(n = 0,1,2…) final states and the total cross section is found to be (3.5 ± 0.3) mb. The angular and the momentum distributions are presented and compared with the predictions of theoretical models. Strong production of K∗(890) ( K ∗± favoured ) is observed (0.7 K∗/event). In the c.m., the K∗+(K∗−) are collimated along the incident proton (antiproton) direction.

Data are presented which firmly establish the existence of the double charge exchange reaction p p → Σ − Σ − at 3.6 GeV/ c . The forward cross section was found to be (5.9 ± 1.1) μb and the ratio of the “forbidden” to “allowed” forward cross section is R = σ( Σ − Σ − σ( Σ + Σ + ) = 0.09 ± 0.02 .

From a bubble chamber exposure in an antiproton beam at 5.7 GeV/c yielding 13 events/μb, the final states p p → Y 1 ∗+ (1385)Λ, Y 1 ∗+ (1385)Σ + , Y 1 ∗+ (1385) Y 1 ∗+ (1385) have been isolated. We have measured the total cross section, dσ/dt, and the complete density matrix of the Y∗ for these processes. Upper limits have been set to the forbidden reactions p p → Y 1 ∗− (1385)Σ − , Y 1 ∗− (1385) Y 1 ∗− (1385) . The comparison of our results with other hypercharge reactions indicates the failure of factorisation predicted by exchange degeneracy and strongly suggests the presence of two reaction mechanisms.

A total of 1121 unambiguously identified events of the type $$\bar pp \to \bar KKn\pi $$ (n=1÷5) at momentum 3.0, 3.6 and 4.0 GeV/c have been analysed, and partial cross-section for the various channels are given. The total cross-sections for annihilation into two kaons with pions is estimated to be (5.1±0.4) mb or 14% of all annihilations. The amounts of resonant K*(890), ρ, ω and associated K*K* production in the various channels are determined. Evidence for the E-meson, a KKπ resonance at 1700 MeV, and a K*π resonance at 1265 MeV is presented. Study of 955 unfitted events containing two charged particles, a K 1 0 and ≥2 neutral secondaries gives rise to a four-standard-deviation peak in a strangeness-zero mass spectrum at (1820±12) MeV with a width (Γ) of (50±23) MeV. The angular distributions favour a peripheral rather than a statistical or core-core model of the annihilation process. The possible usefulness of weighting the various combinations in accord with this observation, to accentuate enhancements in the invariant-mass distribution, is discussed. A method of separating each annihilation into its most likely two-body final-state configuration based on maximizing the four-momentum transfer (u) in the cross-channel is presented as well as some examples of the enhancements in mass spectra obtained using this method.

The reactions pp→ΛΛ, ΛΣ0 or Σ0Λ, Σ+Σ+ are studied at an incident momentum of 3.6 GeV/c in a 35.4 event/μb experiment performed in the CERN 2m HBC. Total and differential cross sections are presented. The polarization of the hyperons is measured as a function of t and for the reaction pp→ΛΛ the complete spin correlation matrix is given.

A study has been made of the properties of 250 interactions produced by negative pions of 16 GeV/c momentum in the liquid hydrogen of the 30 cm diameter bubble chamber at C.E.R.N. The results are presented and discussed.

Total and differential cross sections are presented on the reactions: p p → Λ Λ, ΛΣ 0 + c.c. , Σ + Σ + at an incident momentum of 5.7 GeV/ c , from 200 000 photographs (13 events/ Σ b) of the CERN 2 metre hydrogen bubble chamber. The “forbidden” reaction p p → Σ − Σ − is also observed and its cross section is 1.3 ± 0.4 μ b. Polarization and correlation of polarizations are presented for the reaction p p → Λ Λ .

Photons produced in pp interactions at 450 GeV/ c were detected by reconstructing the e + e − pairs of photon conversions in a 1 mm thick lead sheet placed in front of the MWPCs of the OMEGA spectrometer at CERN. A soft photon signal 4.1±0.8 times the inner bremsstrahlung prediction was observed in the forward rapidity region ( y c.m.s. ⩾1.2), thus extending the domain of the anomalous soft photon effect seen already in K + p , π + p and π − p interactions.

We have observed φ production in π − p interactions at 19 GeV/ c with (44±10) events in the final state φπ + π − π − p and (45±9) events in φ K + K − π − p. The production ratios φπ + π − π − p/ ωπ + π − π − p ≈ 0.005 and φ K + K − π − p/ ϱ °K + K − π − p ≈ 0.45 agree with Zweig-rule expectations.

Annihilations of 5.7 GeV/c antiprotons in hydrogen into four charged pions have been studied. Production of ϱo and fo mesons and a possible enhancement in both π±π± and π+π− mass distributions at 1.54 GeV is seen. Upper limits for quasi 2-body annihilations are given.

The production of glueball candidates ι and Θ in hadronic interactions is investigated at high transverse momenta. The data come from a sample of π − interactions at 300 GeV/ c on a beryllium target, obtained at the CERN Omega Spectrometer using a trigger and off-line selection requiring a system of charged particles with p T >2 GeV/ c recoiling against an opposite particle with p T >0.9 GeV/ c . Cross sections are given for known resonances (ϱ 0 , φ, f 0 ) and upper limits for the ι(1440) and Θ(1720). A co mparison is made with recent theoretical calculations.

We report results on hadroproduction of charm based on a sample of {similar to}750 {ital D} mesons. Charmed particles, produced in a thin segmented target of Si and W by a 340 GeV/c {pi}{sup {minus}} beam and selected by a novel trigger with an enrichment factor of {similar to}15, are identified by the invariant mass of secondary vertices. Data were collected with the {Omega}{prime} spectrometer at the CERN SPS supplemented by a silicon microstrip vertex detector. Assuming the parameterization {sigma}({pi}{sup {minus}}{ital N}{r arrow}{ital DX}){similar to}{ital A{alpha}} where {ital A} is the atomic number, we find {alpha}=0.89{plus minus}0.05{plus minus}0.05 for a data sample with an average x{sub F} of 0.2. The x{sub F} and {ital p}{sub {perpendicular}} distributions of the charged {ital D} mesons are also described and the possibility of a leading effect is investigated.

Inclusive φ production is studied in π − p collisions at 16 GeV/ c . The φ cross section for Feynman variable x φ > 0.2 is found to be (15.5 ± 3.6) μb. This leads to an extrapolated cross section of (29.9 ± 7.0) μb for x φ > 0.0. Fitting the momentum transfer squared distribution of the φ to the form e −bp 2 T gives an average slope of b = (2.4 ± 0.3) (GeV/ c −2 for x φ > 0.5.

We present the results on a new trigger scheme for the selection of short lived particles. These results were obtained in a test run of the WA82 experiment at the CERN Omega spectrometer. We have measured, for charmed particles, an enrichment factor of ∼ 15 over an interaction trigger.

The implementation of a trigger aimed at selecting those nuclear interactions which contain a charm particle is described. The trigger uses a fast emulator of the PDP-11 which calculates the impact parameter of the decaying charged tracks originating from the charm decay. An enrichment factor of 15 is thereby obtained. The results obtained show that, in its present implementation, this trigger, while giving a good enrichment factor, performs a correct rejection, since it does not eliminate many good events that would have been retained by the more sophisticated selection of the offline programs. >

Mass spectra from two−body final state production due to pi−p, Kp, and pp annihilation at 85 GeV/c has been measured. Bumps in pi−plus−pi−minus spectra peak at ‐934 MeV with width of ‐77 MeV. Interesting features are present in K−plus−K−minus and K1−neutral−K1−neutral spectra.

A study of the reaction π − p → X − p based on 1.27 × 10 6 events, corresponding to a mean sensitivity of 200 events/μb, is presented. Properties of the exclusive channels π − p → π − π 0 p, π + π − π − p, π + π − π − π 0 p, π + π + π − π − π − p and π + π + π − π − π − π 0 p are discussed.

The aim of this experiment is to search for gluonic mesons in the reaction pp → pf(X0)ps at 300 GeV/c incident momentum, where the X0 system is a centrally produced meson. Preliminary results are presented on the two‐body (π+π−, K+K−, K0SK0S, pp), three body (K0SK±π±) and four‐body (2π+2π−) decays of the X0 system.

The WA76 experiment performed at the Ω facility at CERN required a high precision measurement of the forward produced particle whose momentum was close to 300 GeV/c. A telescope made of 12 silicon microstrip detectors has been built and operated for such a purpose.

A sample of 56 909 events of the reaction π−p→K+K−n at 10 GeV/c has been measured in the Omega Spectrometer at CERN. In the K+K− system, besides production of mesons in the S ∗ /φ, f 0 / A 2 , g /ω ∗ and h regions we observe a new structure at 2.20 GeV with a width of the order of 200 MeV.

The relative production yields and transverse mass spectra for Λ, Λ , Ξ− and Ξ + hyperons in proton-tungsten interactions are presented and compared with the WA85 results from central sulphur-tungsten interactions. A study of the negative particle yield has also been undertaken and the ratio of Λ hyperons to negative particles has been calculated.

Using a sample of $10^8$ triggered events, produced in $350\, \hbox{GeV}/c$ $\pi^-$ interactions in a copper target, we have identified $26$ b\=b events. These include $13$ events where the decays of both $B$ and $\overline{B}$ are well reconstructed. We measure the azimuthal \hbox{correlation} between beauty particles, and compare our result with predictions based on perturbative QCD.

This report describes the WA92 trigger system which has been designed to collect beauty decays from fixedtarget hadronic interactions. It incorporates muon and high P t triggers, and a novel pixel processor that searches for secondary vertices downstream of the target.

Using a sample of 26 bb events, produced in 350 GeV /c π − interactions in a copper target, which includes 13 events where the decays of both B and B are well reconstructed, we measure the differential distributions with respect to x F and p T 2 as well as some two-particle kinematic variables. We also compare our results with a previous experiment and with predictions based on perturbative QCD.

Evidence is presented for the production in antiproton-proton annihilations of mesons with masses (1717 ± ± 7) MeV and (1832 ± 6) MeV with narrow widths decaying to four charged pions in a neutral mode.