Heavy Liquid Bubble Chamber Research Articles

Observation of (μ¯e + ) pairs associated with strange particles in neutrino interactions in Gargamelle

This experiment is being carried out in the heavy liquid bubble chamber Gargamelle with a filling of freon (CF 3 Br, ρ = 1.5g/cm 3 , X 0 =11 cm). The chamber has been operated in the neutrino beam at CERN in a series of runs terminating in November 1975. The exposures carred out before 1975 had resulted in a total of 500 000 photos and one event containing a (μ¯e+V 0 ) was found and has been reported (Deden et al . (1975). In September 1975 an exposure of 70 000 pictures was made with an average p. s. intensity of 5 x 10 12 protons per pulse and in November 1975 an exposure of 160 000 pictures with an intensity of 8 x 10 12 protons per pulse. The September run is completely analysed and yielded one further event (μ¯e+V 0 ) and the analysis of the November run is in progress and so far one additional event has been found. The observation of events containing a (μ¯e+V 0 ) indicates the existence of some new phenomenon. A possible explanation is that these events arise from the production and subsequent semi-leptonic decay of some new particle, for example a charmed particle. In the charm scheme decay of the new particles into strange particles is favoured. Thus a possible production and decay chain is: v + N→µ¯ + C + X ↳e + + v e + ( S = -1 state)

The hybrid gas-liquid chamber - a new combined track detector

A 51 cloud chamber has been placed into the volume of a 130 1 heavy-liquid bubble chamber. The new combined track device is designed to study multi-prong events.

Correction of effects due to reactions on complex nuclei in a sample of hydrogen-like [formula omitted] annihilations from a heavy liquid bubble chamber experiment

A method is presented, which has been used to determine the pion multiplicity distributions for p annihilations on free protons from a sample of events obtained in a heavy liquid bubble chamber experiment. The method uses data obtained in the experiment in question together with the usual invariance principles satisfied by strong interactions. Furthermore no particular nuclear model is assumed.

Study of the reactions π+p → π+p π0π0 and π+p → π+p π0π0π0 at 3.5 GeV

We study the reactions π +p → π +p nπ 0 ( n = 2, 3) at 3.5 GeV/ c, with 940 and 143 events, respectively. Complete final states are recorded and measured in a heavy liquid bubble chamber. We find the cross sections: sigma;(π + p → π + p 2π 0) = 1300 ± 210 μ b, σ(π + p → π + p 3π 0) = 320 ± 70 μ b , below the values predicted by statistical models from charged pion data. The mass spectra are given and channel separations are performed using Van Hove variables. Our results are in agreement with charged pion experiments. We present a description of the 3 π 0 system, with 61 events. Under certain hypotheses a spin-parity analysis favours 0 − at low mass and 1 − at high mass.

The External Proton Beam Lines and the Splitter Systems of the CERN SPS

The exploitation of the CERN Super Proton Synchrotron (SPS) is based on two experimental areas, the West Area and the North Area. The West Area consists of the West Experimental Hall, fed by a slow ejected proton beam of 200 GeV/c maximum momentum and a Neutrino Facility which is fed by protons of 400 GeV/c. Several important detectors are installed in the West Area, the Omega spectrometer, the Big European Bubble Chamber (BEBC) and the heavy liquid bubble chamber Gargamelle. The North area has been built for physics at 400 GeV/c. At present it consists of two experimental halls, a large multipurpose hall (EHN1) and a smaller hall (EHN1) dedicated to muon physics. The protons are extracted from the SPS in two of the six long straight sections (LSS) and are transported from the underground machine through a system of tunnels to the external targets. The beam lines have a combined length of approximately 2.7 km. Both the beam lines to the West and North Area contain beam splitting stations which divide the slow extracted proton beam into three branches. The beam line to the West Area also contains a switchyard which can deflect the fast ejected proton beam eithermore » onto a target for an rf separated beam or into an underground cave where the production targets for the neutrino beams are placed.« less

K−-meson absorptions at rest in carbon nuclei leading to final states containing a Λ-hyperon

A study has been made of K--meson interactions at rest in the CERN 1.1 m3 heavy-liquid bubble chamber filled with a mixture of hydrocarbons. The emission frequency of Λ0-hyperons following K--meson absorptions in carbon nuclei is determined to be 0.68 ± 0.02. A detailed study of the (Λ0π-) final state has allowed an estimate to be made of the internal-conversion probability C(Σ+) of {perspective}+-hyperons produced in association with π--mesons. The result is C(Σ+)=0.62 ± 0.02. The contribution of the direct channel to the (Λ0π-) final state is found to be 0.23 ± 0.01. The results are compared with those obtained for other absorbing media. © 1977 Societa Italiana di Fisica.

S-wave ππ scattering from the reaction π+p → π+p π0π0 at 3.5 GeV/c

We have studied the 2π 0 system produced in the reaction π +p → π +p π 0 π 0 at 3.5 GeV/ c, using the heavy-liquid bubble chamber technique. The cross section of the reaction π + π − → π 0 π 0 saturates the S-wave unitarity limit around 750 MeV/ c 2 and near threshold is indicative of an I=0 S-wave scaterring length larger than expected.

Experimental study of the energy spectrum of theπ+inK+→π+π0π0decay

A sample of 5635 ${\ensuremath{\pi}}^{+}$ with kinetic energies between 8 and 50 MeV was obtained from ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ decays in the ANL-Michigan 40-in. heavy liquid bubble chamber filled with propane. For these the energy dependence was well described by a linear spectrum of the form ${|M|}^{2}=1+g[\frac{({s}_{3}\ensuremath{-}{s}_{0})}{{m}_{\ensuremath{\pi}+}^{2}}]$, where $g=0.602\ifmmode\pm\else\textpm\fi{}0.021$. No evidence was found for a quadratic term significantly different from 0. When the five conventional test quantities for the isospin selection rules were formed using the value of $g$ from this experiment and current world averages for the other $K\ensuremath{\rightarrow}3\ensuremath{\pi}$ decay parameters, it was found that there was significant evidence for $|\ensuremath{\Delta}I|=\frac{3}{2}$ amplitudes into both $I=2$ and $I=1$ final states. These experimental values are in good agreement with theoretical predictions for them obtained in models which satisfy the current-algebra relation at the soft-pion points and include $|\ensuremath{\Delta}I|=\frac{3}{2}$ as well as $|\ensuremath{\Delta}I|=\frac{1}{2}$ amplitudes.

An experimental study of the production of neutral pions in p̄p annihilations at 1.6 GeV/ c

The heavy liquid bubble chamber Garamelle has been used to study the rate of production of neutral pions in the pionic annihilation of 1.6 GeV/ c antiprotons on free protons. Preliminary results are presented on the relative cross-sections for most channels together with the mean π 0 multiplicity and the first moments for annihilation into 0-prongs, 2-prongs, 4-prongs and 6-prongs.

Search for electromagnetic decays of neutral hyperons in the 1210–1500 MeV range and of neutral mesons in the 150–600 MeV mass range

K − interactions in a heavy liquid bubble chamber have been analysed to extract proton interactions of the following types: K −p→ Λ 0 γγ, Λ 0 γγγ, Λ 0 π 0 γ, Λ 0 π 0 γγ. A comparison has been made with K −p→ Λ 0 π 0, Σ 0 π 0and Λ 0 π 0 π 0 reactions, and a systematic search has been made for γγ, π 0γ, π 02γ structures in the 150–600 MeV mass range and Λ 0γ, Σ 0γ structures in the 1210–1500 MeV mass range. Limits for Σ 0 → Λ 0 γγ and Σ 0(1385) → Λ 0 γ or Σ 0 γ have been obtained, and a direct measurement of the mass Σ 0 → Λ 0 γ has been achieved. No resonance Λ 0 (1327) → Λ 0 γ or Σ 0 γ was observed at a level of (K −p → Λ 0 (1327) π 0) / (K −p → Σ 0 π 0) < 3%.

Search for neutrino-produced magnetic monopoles in a bubble chamber exposure

J. Schwinger has suggested that magnetically charged particles could be produced via a magnetically charged intermediate boson process similar to the mechanism sometimes envisioned for double muon production by neutrinos. A search for magnetic monopole production by neutrinos has been made by reexamining the CERN heavy liquid bubble chamber pictures obtained during the neutrino exposures of 1963 and 1967. Five different searches were made for events which contained a free monopole with and without target nucleus excitation, and for bound monopoles which deexcited by photon emission. No events were found. Neutrino monopole production cross-section limits are given.

A study of the semi-leptonic decays of K + mesons

The form factors of the semi-leptonic decays K +→ π 0e + ν and K +→ π 0 μ + ν have been investigated using a sample of events detected in the CERN 1.1 m 3 heavy liquid bubble chamber. Analyses have been carried out using methods independent of any assumption of the q 2 dependence of the form factors in addition to the usual linear parametrizations. Consistent results have been obtained from separate studies of both Dalitz plot density distributions and the branching ratio. A parametrized global analysis of both decay modes gives the values ξ(0) = -1.3 ± 0.7 and ξ(4.4 M π 2) = -0.45 ± 0.13, or λ 0 = - 0.017 ± 0.011 both for a fitted value of λ + = 0.025 ± 0.007.

The conversion probability and emission ratio of charged Σ-hyperons following k− meson capture at rest in carbon

Abstract A study has been made of K − meson interactions at rest in the CERN 1.1 m 3 heavy liquid bubble chamber filled with a mixture of hydrocarbons. The data are used to determine (i) the internal conversion probability, C ( Σ − ), of Σ − hyperons produced in association with π + mesons by K − meson interactions in carbon nuclei, (ii) the relative emission frequencies of ( Σ + π − ) and ( Σ − π + ) pairs, E ( Σ + π − / Σ − π + ), and the emission frequency E ( Σ ± π ∓ /K − ), of ( Σ ± π ∓ ) pairs per K − meson absorption in carbon, (iii) the branching fraction, P ( Σ − π + /K − ), for the primary process K − + p → Σ − + π + in carbon and (iv) the trapping probability, T ( Λ °), for Λ ° hyperons produced by Σ − hyperon interactions in carbon nuclei. The results are: C ( Σ − ) = 0.38 ± 0.03, E ( Σ + π − / gS − π + ) = 1.25 +- 0.09, E ( Σ ± π −+ /K − ) = 0.164 ± 0.006, P ( Σ − π + /K − ) = 0.127 ± 0.004 and T ( Λ °) = 0.13 ± 0.04, where the errors quoted are statistical and correspond to one standard deviation. Possible systematic errors were estimated to be at most of the same order of magnitude as the statistical uncertainties.

Study of the reactions K −p → Λ0+ neutrals in the C.M. energy range from 1580 to 1750 MeV

Results on the channels K −p → Λ 0 η 0, Λ 0 π 0, Σ 0 π 0, Λ 0 π 0 π 0 and Σ 0 π 0 π 0 are obtained in a K −p formation experiment using 1 million photographs taken in a heavy liquid bubble chamber filled with a CF 3BrC 3H 8 mixture. The results are compared with hydrogen bubble chamber (HBC) experiments and with experiments having full or partial gamma-ray detection. Our Λ 0 π 0 and Λ 0 + neutral cross section agree with HBC results. Our Σ 0 π 0 cross section does not exhibit a bump at 1670 MeV as previously seen in HBC experiments. Our Λ 0 π 0 π 0 data are dominated by a Σ(1385) π 0 production. Our Σ 0 π 0 π 0 data is consistent with the presence of some Σ(1405) π 0 production.

Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment

Events induced by neutral particles and producing only hadrons, but no muon or electron, have been observed in the heavy liquid bubble chamber Gargamelle exposed to neutrino ( v) and antineutrino ( v) beams at CERN. A study of the various sources which could give rise to such events reveals that less than 20% could be attributed to neutrons or K L°. The events behave as expected if they arise from neutral current processes induced by neutrinos and antineutrinos. The ratio of the number of these events to the number of corresponding events with charged lepton is 0.22 ± 0.04 for v and 0.43 ± 0.12 for v .

Channel cross sections for K −p → Λ0 + neutrals between 0.525 and 0.820 GeV/c

A study has been made of the individual channels that contribute to the reaction K −p → Λ 0 + neutrals in the K − momentum range from 525 to 820 MeV/ c. Total cross sections are presented for the K −p → Λ 0 η 0, Σ 0 Σ 0 π 0, Λ 0 π 0, Σ 0 π 0 and Σ 0 π 0 π 0 channels and differential cross sections for K −p → Λ 0 π 0. The data were obtained in a heavy liquid bubble chamber experiment with an average gamma detection efficiency of 70%. Only events with all decay gammas detected were used for analysis. This is the first of a series of papers on this subject and presents the experimental technique in detail.

An experimental study of the form factor in the decay K+ → πoe+ν

The q 2 variation of the factor ƒ +(q 2) in the decay K +→ π 0e + ν has been studied using a sample of even detected in the CERN 1.1 m 3 heavy-liquid bubble chamber. The data are consistent with a linear development ƒ +(q 2)=ƒ +(0) (1+λ +q/m 2 π) with λ +=0.027±0.008.

An experimental study of the K+ → πoμ+ν decay dalitz plot

A sample of K + μ3 events, detected in the CERN 1.1 m 3 heavy-liquid bubble chamber, has been used to investigate the q 2 dependence of the form factors, giving ξ(0) = −1.1 ± 1.0 and ξ(6.6 m 2 π ) = −0.34 ± 0.20, for λ + = 0.027. A three parameter fit gives a value for λ + = 0.025 ± 0.017 in good agreement with the preceding K e3 analysis.

Coherent production of 2, 3, 4 and 5 π-mesons by π+-Nuclei interactions at 11.7 GeV/cinteractions at 11.7 GeV/c

π+-Nuclei coherent interactions with 2, 3, 4 and 5 pions in the final state have been looked for in a heavy-liquid bubble chamber experiment with direct detection of π0,s. Abundant coherent production has been found in the three-pion channels π+π+π− and π+π0π0, essentially in the A1 mass region, but the available statistics did not allow to put in evidence coherence in the 2, 4 and 5π channels, for which upper limits of cross-sections are given. The branching ratioR=Γ(A1→+ρ0)/Γ(A1→0ρ+) was found to beR=0.67±0.22.

Experimental Study of the RareK+Decay Modes:K+→π+π0γ,K+→μ+π0νγ,K+→π+γγ,K+→π+νν¯,K+→π0π0e+ν, andK+→e+π0νγ

Six rare stopped-${K}^{+}$ decays have been studied in the 40-inch heavy-liquid bubble chamber at Argonne National Laboratory. The chamber was filled with C${\mathrm{F}}_{3}$Br. Twenty-two radiative ${K}_{\ensuremath{\pi}2}$ events with three converted $\ensuremath{\gamma}$ rays were analyzed. The experiment was sensitive to positive pions with kinetic energy 55 to 102 MeV. The strengths ($\ensuremath{\gamma}$ and $\ensuremath{\beta}$) of the direct processes in the decay were determined to be $\ensuremath{\gamma}=\ensuremath{-}{0.02}_{\ensuremath{-}0.43}^{+0.17}$, $\ensuremath{\beta}=0.0\ifmmode\pm\else\textpm\fi{}0.3$, and the branching ratio is (${1.5}_{\ensuremath{-}0.6}^{+1.1}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$ for $55l{T}_{{\ensuremath{\pi}}^{+}}l80$ MeV. These results are consistent with assuming the decay is dominated by internal bremsstrahlung. No events were found in the search for ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\pi}}^{0}\ensuremath{\nu}\ensuremath{\gamma}$, and the upper limit on the branching ratio is reported as 6.1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ for $\ensuremath{\gamma}$ energies greater than 30 MeV. No examples of the ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\gamma}\ensuremath{\gamma}$ decay mode were found. The experiment was sensitive to pions with kinetic energy 6 to 102 and 114 to 127 MeV. The null result allowed us to discard several theoretical models which made branching-ratio predictions for this decay. Assuming a phase-space model for the pion spectrum, the upper limit is 3.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$. The upper limit on the neutral current decay ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ is reported as 5.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ assuming a vector interaction. The decay ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}{e}^{+}\ensuremath{\nu}$ was observed for the first time. Two events were found in which all four converted $\ensuremath{\gamma}'\mathrm{s}$ were seen. These two events give a branching ratio of (${1.8}_{\ensuremath{-}0.6}^{+2.4}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}5}$ for this decay. The form factor ${f}_{1}$ for the decay is $|{f}_{1}|={0.97}_{\ensuremath{-}0.19}^{+0.50}$. These results are in good agreement with $\ensuremath{\Delta}I=\frac{1}{2}$ rule predictions. Seventeen ${K}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\pi}}^{0}\ensuremath{\nu}\ensuremath{\gamma}$ events were observed. The branching ratio is reported as $\frac{\ensuremath{\Gamma}({K}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\pi}}^{0}\ensuremath{\nu}\ensuremath{\gamma})}{\ensuremath{\Gamma}({K}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\pi}}^{0}\ensuremath{\nu})}=(0.48\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ for ${E}_{\ensuremath{\gamma}}g30$ MeV and ${cos\ensuremath{\theta}}_{e\ensuremath{\gamma}}l0.9$.