Bubble Chamber Experiment Research Articles

Micro-e+ dilepton production in charged-current nu micro interactions.

The production of ${\ensuremath{\mu}}^{\ensuremath{-}}{e}^{+}$ dileptons by muon neutrinos is studied in a high-statistics bubble-chamber experiment. The experiment consisted of exposing the Fermilab 15-ft bubble chamber filled with a heavy Ne-${\mathrm{H}}_{2}$ mix to a wideband neutrino beam. In a total sample of 146 700\ifmmode\pm\else\textpm\fi{}11 700 charged-current interactions, 461 events with an ${e}^{+}({P}_{{e}^{+}}>300 \mathrm{MeV}/c)$ and a ${\ensuremath{\mu}}^{\ensuremath{-}}$ are observed. The rate for ${\ensuremath{\mu}}^{\ensuremath{-}}{e}^{+}$ dilepton production in measured to be (0.42\ifmmode\pm\else\textpm\fi{}0.06)%. The energy dependence of this rate is presented. The kinematic distributions for the ${\ensuremath{\mu}}^{\ensuremath{-}}{e}^{+}$ events are consistent with charm production and subsequent semileptonic decay. A total of 60 ${K}_{S}^{0}$ and 31 ${\ensuremath{\Lambda}}^{0}$ decays were observed in the ${\ensuremath{\mu}}^{\ensuremath{-}}{e}^{+}$ event sample. The measured rates for neutral-strange-particle production are 0.78\ifmmode\pm\else\textpm\fi{}0.12 $\frac{{K}^{0}}{{\overline{K}}^{0}}'\mathrm{s}$ and 0.19\ifmmode\pm\else\textpm\fi{}0.04 ${\ensuremath{\Lambda}}^{0}'\mathrm{s}$ per ${\ensuremath{\mu}}^{\ensuremath{-}}{e}^{+}$ event. Finally, rates for ${\ensuremath{\Lambda}}_{c}^{+}$, ${D}^{0}$, and ${D}^{+}$ production in charged-current ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ interactions are derived. They are found to be (${4}_{\ensuremath{-}2}^{+10}$)%, (${1.7}_{\ensuremath{-}0.7}^{+0.5}$)%, and (${1.3}_{\ensuremath{-}0.5}^{+0.4}$)%, respectively.

W 2 andQ 2 dependence of charged hadron and pion multiplicities invp and $$\bar vp$$ charged current interactionscharged current interactions

Using data onvp and\(\bar vp\) charged current interactions from a bubble chamber experiment with BEBC at CERN, the average multiplicities of charged hadrons and pions are determined as functions ofW2 andQ2. The analysis is based on ∼20000 events with incidentv and ∼10000 events with incident\(\bar v\). In addition to the known dependence of the average multiplicity onW2 a weak dependence onQ2 for fixed intervals ofW is observed. ForW>2 GeV andQ2>0.1 GeV2 the average multiplicity of charged hadrons is well described by〈n〉=a1+a2ln(W2/GeV2)+a3ln(Q2/GeV2) witha1=0.465±0.053,a2=1.211±0.021,a3=0.103±0.014 for thevp anda1=−0.372±0.073,a2=1.245±0.028,a3=0.093±0.015 for the\(\bar vp\) reaction.

Experimental test of the PCAC hypothesis in the reactionsv ? p? ?? p?+ and $$ \bar v_\mu p \to \mu ^ + p\pi ^ - $$ in the?(1232) region

Data on the reactionsv μ p→ μ− pπ+ and\( \bar v_\mu p \to \mu ^ + p\pi ^ - \) in the Δ(1232) region are presented and a test of the PCAC hypothesis, using a modified version of the Adler model, is performed. The analysis is based on 1081 events in the neutrino and on 180 events in the antineutrino reaction, obtained in a bubble chamber experiment with BEBC at CERN. The experimental cross-sections for an invariant hadronic massW<1.4 GeV and an (anti-)neutrino energyE L v >10 GeV are determined to be (0.628±0.059)·10−38 cm2 for the neutrino and (0.168±0.023)·10−38 cm2 for the antineutrino reaction. TheQ 2 andW distributions, the density matrix elements of the Δ resonance, and moments of the pion angular distribution are discussed. The data are found to be in good agreement with the Adler model in theQ 2 region below 1 GeV2. A maximum likelihood fit for the axial massm A in the axial-vector form factor yields a value ofm A =1.31±0.12 GeV. At lowQ 2 the data confirm the PCAC hypothesis and the discrepancy, formerly observed between the experimental and theoretical cross-sections forv μ p→ μ− pπ+ at low momentum transfers (Q 2≲0.2 GeV2), is understood as being due to inadequate pion ‘off-mass-shell’ corrections.

Production ofρ +, −, 0 (770),η(550), ω(783) andf 2(1270) mesons in $$\bar v$$ neon and ν neon charged current interactions

The production of the meson resonances ϱ(770) (all three charge states), η(550), ω(783) andf 2(1270) in\(\bar v\) Ne and ν Ne charged current interactions is investigated in a bubble chamber experiment with BEBC at CERN. Except for thef 2, the main features of resonance production are reasonably well described by the Lund model, although the average resonance multiplicities are overestimated by the model by (67±30)%. The average multiplicities of all resonances, including thef 2, are well reproduced by a semiempirical model, whose parameters were determined from hadron interaction data.

Final results on μe-pair production in neutrino interactions in the SKAT freon bubble chamber experiment

We present the final results from the search for μe pairs produced in neutrino interactions using the freon filled bubble chamber SKAT. The rate of μ− e + pairs to charged current events above the charm threshold is $$R_{\mu ^ - e^ + } = (4.8 \pm 1.1)10^{ - 3} $$ . Assuming charm particle production to be the origin of the positron we calculate $$R_{\Lambda _c^ + } = (6.2 \pm 3.1)10^{ - 2} $$ andR D =(2.8±0.9)10−2. We observe no considerable μ− e − pair production above the background. In the regionE v >3 GeV,p μ,e >1.0 GeV/c andp μ>p e we find with a 90% confidence level the limit $$R_{\mu ^ - e^ - }< 1.7 10^{ - 4} $$ .

A study ofv e −v μ universality and search for neutrino oscillations

In the SKAT neutrino bubble chamber experiment at the Serpukhov accelerator we observe 83 events with electrons and no further lepton in the final state. Comparing the ratio of electron to muon charged current events at energies 3<E v <30 GeV with that expected fromv e -beam background assuming lepton universality we find $$R = (N_{e^ - } /N_{\mu ^ - } )_{\exp } /(N_{e^ - } /N_{\mu ^ - } )_{calc} = 0.98 \pm 0.15$$ . Furthermore we compare experimental observations and theoretical expectations for some differential distributions of the electron-neutrino charged current reaction. No significant deviation from lepton universality is found. Looking in the charged current reaction for oscillations of muon to electron type neutrinos we find no effect down to the 90% confidence limits Δm 2 =1.3 eV2 at sin22θ=1 and sin22θ=2.5·10−3 at Δm 2=60 eV2.

Coherent rho + production in neutrino-neon interactions.

Coherent ${\ensuremath{\rho}}^{+}$ production on neon nuclei has been observed in charged-current events in a neutrino bubble-chamber experiment. The incident neutrino energy was 10--320 GeV, with a median event energy of 80 GeV. The rate per charged-current event was (0.28\ifmmode\pm\else\textpm\fi{}0.10)%. Comparison was made to vector-meson-dominance predictions; agreement with the overall rate, but disagreement at high neutrino energies and at high ${Q}^{2}$, was found.

Strangeness production in Madron-nucleus reactions

Strange-particle production in hadron-nucleus reactions is discussed. Emphases are: (1) Although enhancements of strangeness production may be a good signature of exotic phenomena associated with highly-excited nuclear matter, one must carefully separate effects of secondary processes. An enhancement of Λ production in p̄-nucleus reactions observed in a KEK bubble-chamber experiment was explained by secondary processes. (2) Hyperon polarization provides a good tool to probe quark structures of hadrons and nuclei. A KEK experiment on hyperon-beam polarization indicated that the quark-diquark recombination model seemed to work not only at high energies but also at low energies. It is interesting to study possibilities and/or limitations of applying such parton-recombination pictures to low-energy phenomena in the target-rapidity region. (3) Hyperon polarization also provides a variety of applications to spin physics of hypernuclei.

The holographic bubble chamber experiment and the determination of the effective charmed quark mass and theK-factor for hadronic charm production

In the first holographic bubble chamber experiment — the HOBC experiment — we have accumulated a total of 40000 holograms with particle interactions. We have determined the total charm pair cross section inpN collisions to be 23.3−7.7+10 μb and 3.6−1.7+2.3 μb for 360 and 200 GeV/c incident protons respectively. We have assumed a linear dependence of the cross section on the atomic number of the target. This experiment has demonstrated the feasibility of holographic recording in small bubble chambers. Assuming that the charm cross section can be described by the standard QCD factorized expression with gluon fusion and quark-antiquark annihilation, we have used our measured charm cross sections with other measurements to determine the effective charmed quark mass to be 1.8−0.35+0.25 GeV/c2. TheK factor, which describes the importance of the higher order corrections, is calculated to be 9.8−6.9+12.5 (See noted added in proof.)

Rho and omega production in pi+p interactions at 15.7 GeV/c.

We report the results of a study of \ensuremath{\rho} and \ensuremath{\omega} production in ${\ensuremath{\pi}}^{+}$p interactions at 15.7 GeV/c. The SLAC hybrid bubble-chamber facility was used to study reactions in which neutral particles are produced. Three tantalum plates inside the 40-in. bubble chamber and a large array of lead glass downstream of the chamber provided photon detection over a large solid angle. Final states with two neutral particles have been isolated with kinematic fits in which neutral pions were reconstructed in the plates and lead glass. Data from an earlier untriggered ${\ensuremath{\pi}}^{+}$p bubble-chamber experiment at 15 GeV/c were used to obtain samples of events in channels which did not trigger the hybrid system. Cross sections for \ensuremath{\rho} and \ensuremath{\omega} production are given for several exclusive final states. Relative \ensuremath{\rho} and \ensuremath{\omega} production rates are studied. The ratio of nondiffractive \ensuremath{\omega} to ${\ensuremath{\rho}}^{0}$ production is measured to be \ensuremath{\omega}/${\ensuremath{\rho}}^{0}$=0.44\ifmmode\pm\else\textpm\fi{}0.07. We estimate the inclusive \ensuremath{\omega} cross section to be 1.9\ifmmode\pm\else\textpm\fi{}0.3 mb. The results are compared to the Lund model of low-${p}_{T}$ hadronic reactions.

Production ofμ − e + pairs in neutrino interactions in the SKAT bubble chamber experiment

The production of μe-pairs is studied in interactions of neutrinos with nuclei of heavy freon in the SKAT bubble chamber experiment. A rate of μ−e+ to charged current interactions above the charm threshold of\(R^{\mu ^ - e^ + } = (4.6 \pm 1.2) \cdot 10^{ - 3} \) is found. The properties of the observed μ−e+ events can be well described by assuming them to originate from the semileptonic decay of quasielastic produced charmed baryonsΛc and inclusive charmedD-meson production. The rates for these reactions are found to be (6.7±3.5)×10−2 and (2.5±0.9)×10−2, respectively. A total charmed particle production rate of (9.2±3.6)×10−2 is calculated.

New measurement of the asymmetry parameter for the Sigma +-->p gamma decay.

The asymmetry parameter ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$ for the ${\ensuremath{\Sigma}}^{+}$\ensuremath{\rightarrow}p\ensuremath{\gamma} decay has been measured with counter techniques. From a sample of about 190 ${\ensuremath{\Sigma}}^{+}$\ensuremath{\rightarrow}p\ensuremath{\gamma} decays, the asymmetry parameter is found to be ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$=-0.86\ifmmode\pm\else\textpm\fi{}0.13\ifmmode\pm\else\textpm\fi{}0.04, where the quoted errors are statistical and systematic, respectively. The present result confirms with better accuracy the large and negative value for ${\ensuremath{\alpha}}_{\ensuremath{\gamma}}$ measured by two previous bubble-chamber experiments. The branching ratio is also found to be (1.30\ifmmode\pm\else\textpm\fi{}0.15) \ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$, which is consistent with previous measurements.

Observation of μ−e− events in neutrino interactions at 3–30 GeV neutrino energy

The production of μ − e − pairs is studied in interactions of neutrinos with nuclei of heavy freon in the SKAT bubble chamber experiment. A rate of μ − e − pairs to charged current interactions of R μ − e − =(2.5± 1.4 4.3)×10 −4 is found at an average neutrino energy of 10 GeV. The ratio μ − e −/ μ − e + comes out to be μ − e −/ μ − e + = 0.12± 0.08 0.22.

Spin alignment of ρ 0 mesons produced in antineutrino and neutrino neon charged-current interactions

In a bubble chamber experiment with BEBC the spin alignment parameter η= 1 2 (2ϱ 00 − ϱ 11 − ϱ −1−1) is measured for ϱ 0 mesons produced in deep inelastic charged-current antineutrino and neutrono interactions on neon. In the current fragmentation region η is found to be η v =0.48±0.27 ( stat.)±0.15 ( syst.) for v Ne and η v =0.12±0.20 (stat.)±0.10 (syst.) for vNe interactions

Diffractive pion production in neutrino reactions

The hypothesis of a diffractive, PCAC-dominated description of high- W single pion production in neutrino and antineutrino reactions is confronted with recent data from a CERN bubble chamber experiment. Reasonable agreement is found.

Measurement of the antineutron mass

The mass of the antineutron has been measured in a bubble chamber experiment. A value of 939.568±0.039 MeV/ c 2 has been found.

Constraints on couplings of a fast decaying axion

Constraints are imposed on the couplings of an axion-like pseudoscalar particle φ that decays into e +e − and γγ. The electron g−2 sets a severe bound not only on the φe +e − coupling but also on the φγγ coupling. The most reliable bound on the φ coupling to the light quarks comes from the decay ∑ + → pe +e − which was measured in a hydrogen bubble-chamber experiment with good sensitivity and resolution covering the entire range of e +e − mass practically down to 2 m e. These upper bounds, together with a constraint from the decay K +→π +γγ, reinforce arguments against the particle-physics interpretation of the anomalous positrons in heavy-ion collisions, since the couplings are by orders of magnitude smaller than needed to produce e +e − pairs at the observed level by known mechanisms.

Deuteron and antideuteron identification with liquid Cherenkov counters in separated beams

Peculiarities in applying Cherenkov counters with a liquid radiator are discussed for the case of heavy loading conditions in a bunched beam (bunch duration − 30 ns). The design of the counter radiator, of the radiator dispersion compensator and general layout of the detector are presented. The measurement technique in the beam is described. The main results obtained in the separated particle beam in the bubble chamber experiment from the measurements of 12 GeV c deuterons and antideuterons are presented.

A Measurement of the Total Charm Cross Section in 200 and 360 GeV/c pN Interactions Using a Holographic Bubble Chamber

We present results from the first holographic bubble chamber experiment. Using topological information on the events observed in the heavy liquid bubble chamber HOBC, we have determined a total charm pair production cross section of (24.6-8.3+12.0) μb and (3.9-1.9+2.5) μb in 360 GeV/c and 200 GeV/c proton-nucleon interactions respectively. For these estimates we assumed a linear dependence of the charm cross section on the atomic number A.

Anomalous carbon nuclei

Results are presented from a bubble chamber experiment to search for anomalous mean free path (MFP) phenomena for secondary multicharged fragments (Zf=5 and 6) of a12C beam at 4.2 GeV/c per nucleon. A total of 50,000 primary interactions of carbon with propane (C3H8) were treated. Approximately 6,000 beam fragments with charges Zf=5 and 6 were analyzed in detail to search for an anomalous decrease of MFP. The anomaly is observed only for secondary carbon nuclei.