A search for direct electron production inpp interactions at 70GeV/c

A search for directly produced electrons in 70 GeV/cpp interactions has been performed using BEBC equipped with a hydrogen filled track sensitive target surrounded by a hydrogen/neon blanket. No candidates for single electron production with momentump _e >500 MeV/c were found in a sample of 66,000 primary interactions. This result places an upper limit of 2.5 μb on the cross section for singlee ^± production at the 90% confidence level. The corresponding upper limit on the charmed particle production cross section in 14 μb. From the observation of 7 events producing ane ⁺e^? pair with mass, \(m_{e^ + e^ - } > m_{\pi ^0 } \) thee ^±/π^± ratio from this source is estimated to be (0.7±0.2)×10^?4.     

Measurement ofR ine + e − annihilation for\sqrt s between 7.4 and 9.4 GeV

The rationR=σ(e ⁺ e ^?→hadrons)/σ(e ⁺ e ^?→ µ⁺ µ^?) was measured with the LENA detector at DORIS in a scan between 7.40 and 7.48 GeV and between 8.67 and 9.43 GeV center of mass energies. Corrected for QED radiative effects,R is found to be constant with an average value ofR=3.37 ±0.06_stat±0.23_syst. No narrow resonances withΓ _ee (Γ _had/Γ _tot)?0.30 keV (95% C.L.) and no steps have been observed. Based on this value ofR, revised values for υ(1S) resonance parameters are presented.     

Study of the charge-exchange reactions\pi ^ - p \to (\pi ^0 ,\eta ,\eta \prime )n at 63 GeV

Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π⁰ production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ _e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10^?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions.     

A study of e+e− pairs in the mass range 11 to 25 GeV/c2 at the CERN intersecting storage rings

A sample of 58e⁺e^? events with an invariant mass greater than 11 GeV/c² produced in pp collisions at a centre-of-mass energy of 62.3 GeV is discussed. The cross sections are presented as a function of the mass and transverse momentum. The electron pairs produced with a mean transverse momentum of 2.50 ± 0.25 GeV/c.     

Total cross section for hadron production bye + e − annihilation between 9.4 and 9.5 GeV

The total cross section fore ⁺ e ^? annihilation into hadrons for center of mass energies from 9.4 to 9.5 GeV has been measured with the nonmagnetic DESY-Heidelberg detector at DORIS. A value ofR=σ_had/σ_µµ=3.8±0.7 for the continuum region around the Υ (9.46) resonance has been determined. The ratioΓ _ee Γ _had/Γ _tot of electronic, hadronic and total widths has been reevaluated to be (1.00±0.23) keV for the Υ resonance and (0.37±0.16) keV for the Υ′. In addition, a search for directly produced pohotons from Υ decays of the type Υ→γ+gluon+gluon has been performed. The Υ decay into muon pairs has also been searched for.     

Diffraction dissociation at the CERN pulsedpp collider at c.m. Energies of 900 and 200 GeV

Cross-sections for diffractive particle production and pseudorapidity distributions of the decay products of diffractive states are presented. The data were obtained with the UA 5 streamer chamber detector at the CERNpp Collider operated in a new pulsed mode yieldingpp interactions at c.m. energies of 900 and 200 GeV. Data recorded with a special trigger designed to select a sample of events enriched in single-diffractive interactions clearly favour ap _t -limited fragmentation of diffractive states. The cross-section for single-diffractive particle production ? was found to be 7.8±0.5±1.1 mb at 900 GeV and 4.8±0.5±0.8 mb at 200 GeV (first error statistical, second systematic). From the pseudorapidity distribution of diffractive states we deduce the average number of charged particles to be 6.5±1.0 at 900 GeV and 4.1±1.1 at 200 GeV. Furthermore we report on our estimates for the cross-section of double-diffractive particle production at both Collider energies.     

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 baryonsΛ _c 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.     

Kaon production in\bar pp interactions at c.m. energies from 200 to 900 GeV

A detailed analysis ofK _s ⁰ production in \(\bar pp\) |<2.5 the average transverse momentum is found to be 0.53±0.07 GeV/c at 200 GeV and 0.62±0.08 GeV/c at 900 GeV, which is an increase with respect to data at c.m. energies below 60 GeV. TheK _s ⁰ production cross sections in inelastic collisions are 29±4 mb at 200 GeV and 63±6 mb at 900 GeV, showing an increase compared to lower energy data. The central kaon density is found to increase as a logarithmic function of energy. At 900 GeV, where statistics are sufficient to allow one to draw conclusions, the average transverse momentum is higher in events with large charged multiplicity than in events with low multiplicity.     

An analysis of the charged and neutral energy flow in e+e− hadronic annihilation at 34 GeV,and a determination of the QCD effective coupling constant

Using both charged and neutral components, 2600 multihadronic e⁺e^? annihilation events, recorded at 34 GeV by the CELLO detector at PETRA, have been analysed in a calometric approach. The fraction of energy carried by gamma rays is measured to be f_γ = (26.0 ± 0.4 (stat) ± 4.0 (syst)%. The neutral energy flow is seen to follow closely the overall energy flow. From the corrected oblateness distribution, a first order determination of α_s is performed. The result is α_s = 0.16 ± 0.01 (stat) ± 0.03 (syst).     

A precise determination of the τ-mass

The energy dependence of the cross sections for e⁺e^? → e^±(μ^±) + 1 charged track has been measured for centre of mass energies between 3.60 and 4.40 GeV. The pair production of the τ-lepton is observed at all energies and the τ-mass is determined to be 1.787_?0.018^+0.010 GeV from a fit to the energy dependence of the cross section.     

Observation of charmed baryon production in νp interactions in BEBC

Two examples of charmed baryon production by neutrinos have been observed in BEBC filled with hydrogen. Both events fit uniquely the reaction νp → μ^?pK^?π⁺π⁺ and thus apparently violate the ΔS = ΔQ rule. None of the appropriate mass combinations is consistent with the mass values of the D⁰ and D⁺ mesons. However, for the mass combinations of the pK^?π⁺ systems, values of (2.285 ± 0.005) GeV and (2.280 ± 0.003) GeV are found for event 1 and 2, respectively. These values agree with the mass of (2.285 ± 0.006) GeV for the Λ_c⁺ charmed baryon determined recently in e⁺e^? collisions at SLAC.     

Measurement of particle and antiparticle elastic scattering on protons between 6 and 14 GeV

Differential cross sections in the t-range between 0.02 and 1.5 GeV² have been measured for the elastic scattering of particles and antiparticles on protons at 6.4, 10.4 and 14 GeV for K^±p and 10.4 GeV for π^±p and p^±p. Large statistics have been achieved and systematic uncertainties have been minimized. The relative systematic uncertainty between particle and antiparticle data is less than 0.5%. Accurate measurements of the position of the first crossover between particle and antiparticle differential cross sections have been performed. As the energy increases from 6.4 to 14 GeV the K^±p crossover moves to smaller values by 0.010 GeV² with a statistical error of 0.006 GeV² and a systematic uncertainty of 0.005 GeV². The crossover positions at 10.4 GeV for π^±, K^± and p^± scale approximately with the interaction radii.     

Elastische Elektronenstreuung an14N,15N,16O und18O bei kleiner Impulsübertragung

Elastic electron scattering cross sections of¹⁴N and¹⁶O have been measured relative to the proton and of¹⁵N and¹⁸O relative to the lighter isotope (¹⁴N,¹⁶O resp.) using gas targets. The momentum transfer ranged from 0.22 to 0.48 fm^?1. The data were analyzed by phase shift calculations assuming harmonic oscillator shell model charge distributions. The following rms charge radii have been deduced: R_m(¹⁴N)=2.540±0.020 fm R_m(¹⁵N)=2.580±0.026 fm R_m(¹⁶O)=2.718±0.021 fm R_m(¹⁸O)=2.789±0.027 fm. The errors include statistical and systematic uncertainties and an estimate of effects due to the choice of the model. The radius differences of the isotopes are smaller than the values predicted by anA ^1/3 relation     

Justification of Landau Hydrodynamic-Tube model in central relativistic heavy-ion collisions

The statistical event-by-event analysis of inelastic interactions of ¹⁶O and ³²S nuclei in emulsion at 60 A?GeV/c and 200 A?GeV/c reveals the existence of groups of high multiplicity events belonging to very central nuclear interactions with Gaussian pseudorapidity distributions for produced particles as suggested by the original hydrodynamic-tube model. Characteristics of these events are presented. The experimental observations are interpreted as a result of quark-gluon plasma formation in the course of central nuclear interactions.     

Comparison of e+e− annihilation with QCD and determination of the strong coupling constant

We have analyzed 1113 events of the reaction e⁺e^? → hadrons at CM energies of 12 and 30 GeV in order to make a detailed comparison with QCD. Perturbative effects can be well separated from effects depending on the quark and gluon fragmentation parameters to yield a reliable measurement of the coupling constant α_S. At 30 GeV, the result is α_S = 0.17 ± 0.02 (statistical) ± 0.03 (systematic). QCD model predictions, using the fragmentation parameters determined along with α_S, agree with both gross properties of the final states and with detailed features of the three-jet states.     

Observation of a spin 4 neutral meson with 2 GeV mass decaying in π° π°

The invariant mass spectrum of neutral meson states from π^?p interactions at 40 GeV/c incident momentum has been investigated in a high statistics experiment performed at the 70 GeV IHEP accelerator. To detect the high energy photons coming from the produced neutral states, a hodoscope spectrometer with a computer on-line was used. A clear structure on the mass spectrum of dipions produced in the reaction π^?p→π°π°n is observed at 2 GeV. The decay angular distributions show in this mass region the variation with mass typical of a state with a spin J = 4. The mass of the observed meson is found to be M = (2020±30)MeV and the estimate of the full width is (180±60) MeV.     

Thermal emission of pions in antiproton-proton annihilation at 12 GeV/c

Using data of \(\bar pp\) annihilation at 12 GeV/c we have found that centrally-emitted pions follow a thermal energy spectrum with an inclusive temperature of 111±2 MeV, the same as has been found for pions produced in πp collisions at 16 GeV/c. An analysis of individual high-multiplicity events to search for fluctuations in the temperature parameter on an event-byevent basis has been made, using two different methods. We obtained the value 0.18±0.02 for the relative dispersion of the temperature fluctuations.     

Study of electron-positron collisions at the highest PETRA energy

We report on the results of the study of e⁺e^? collisions at the highest PETRA energy of √s = 31.57 GeV, using the 4π sr, electromagnetic and calorimetric detector Mark J. Based on 88 hadron events, and an integrated luminosity of 243 nb^?1 we obtain R = σ(e⁺e^? → hadrons)/σ(e⁺e^? → μ⁺μ^?) = 4.0 ± 0.5 (statistical) ± 6 (systematic). The R value, the measured thrust distribution and average spherocity show no evidence for the production of new quark flavors.     

Proof of comparable K-pair and π-pair production from time-like photons of 1.5, 1.6, and 1.7 GeV and determination of the K-meson electromagnetic form factor

The observation of 21 K⁺K^? pairs in 38 hadron pair events produced at 1.5, 1.6, and 1.7 GeV total centre-of-mass energies in e⁺e^? annihilations, establishes that time-like photons produce K pairs and π pairs with comparable rates in this energy range. The K-meson electromagnetic form factor at a mean s-value of 2.4 GeV² is measured to be |F_K| = 0.50±0.08. The number of e⁺e^? pairs observed in the same angular and energy range is 5148.     

Measurement of the lifetime of hadrons containing the b-quark

Data collected with the High Resolution Spectrometer at PEP, corresponding to an integrated luminosity of 200 pb⁻¹ of e⁺e⁻ annihilation at 29 GeV, were used to measure the mean lifetime of hadrons containing the bottom quark. The lifetime was determined using the impact parameter method on events containing a high-transverse-momentum electron. The result, based on a sample of 301 events, is τ_B = 1.02 ±_0.39^0.42 ps, where the indicated errors include both statistics and systematics.