Phys. Lett. B

Jets in photoproduction events have been studied with the ZEUS detector for γp centre-of-mass energies ranging from 130 to 250 GeV. The inclusive jet distributions give evidence for the dominance of resolved photon interactions. In the di-jet sample the direct processes are for the first time clearly isolated. Di-jet cross sections for the resolved and direct processes are given in a restricted kinematic range.

10.2172/10158865

Phys. Lett. B

New experimental results for polarization transfer, κ 0 and the analyzing power, T 20 , in 12 C ( d , p ) X at 0° are present. The measurements have been performed at the Dubna polarized deuteron facility. At high intrinsic momenta of the proton in the deuteron ( k ⩾300 MeV/ c ) the behaviour of these observables is in disagreement with the impulse approximation predictions based on realistic NN-potentials. The data are compared with calculations of some other models predicting the high k behaviour of κ 0 and T 20 .

Z. Phys. C

The study of the properties of inclusive production ofDs mesons and of events in which a ϕ and a muon are present in the same jet provides two independent measurements of the probability,fsw, for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ0 decays. The combined value of these measurements isfsw=0.19±0.06±0.08. From the flight distance distributions ofDs and of (ϕ-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theBs0 meson lifetime. Combining these measurements with a previous result based on the study ofDs-μ events, theBs0 meson lifetime is measured to be: 0.96±0.37 ps.

Phys. Lett. B

An analysis of the production of the Λ baryon in the hadronic decays of the Z 0 is presented, based on about 993K multihadronic events collected by the DELPHI detector at LEP during 1991 and 1992. The differencial cross section of the Λ and the correlations between Λ and Λ produced in the same event are compared to current models, based both on string fragmentation and on cluster decay. The predictions of the string fragmentation model are found to give satisfactory agreements with the data, clearly better than those of the cluster model.

Nucl.Instrum.Meth.A

A calorimeter module was fabricated using profiled lead plates and scintillating fibers with diameter 1 mm and attenuation length about 80 cm. The absorber-to-fiber volume ratio was 1.17 and the module average radiation length X 0 ⋍ 1.05 cm . The energy resolution of the module was investigated using the electron beams of U-70 at Serpukhov and of the SPS at CERN in the energy range 5–70 GeV. The energy resolution at θ = 3° (the angle between the fiber axis and the beam direction) may be expressed by the formula σ E (\) = 13.1 E ⊕ 1.7 . The energy resolution was also simulated by Monte Carlo and good agreement with the experiment has been achieved.

Phys.Lett.B

This paper presents our first measurement of the F 2 structure function in neutral-current, deep inelastic scattering using the ZEUS detector at HERA, the ep colliding beam facility at DESY. The data correspond to an integrated luminosity of 24.7 nb −1 . Results are presented for data in range of Q 2 from 10 GeV 2 to 4700 GeV 2 and Bjorken x down to 3.0 × 10 −4 . The F 2 structure function increases rapidly as x decreases.

Phys. Lett. B

A search has been made for pairs and for single production of scalar leptoquarks of the first and second generations using a data sample of 392 000 Z 0 decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95% confidence level of 45.5 GeV/ c 2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit abd its results exclude first and second generation leptoquarks D 0 with masses below 65 GeV/ c 2 and 73 GeV/ c 2 respectively, at 95% confidence level, assuming that the D 0 lq Yukawa coupling α λ is equal to the electromagnetic one. An upper limit is also given on the coupling α λ as a function of the leptoquark mass m D

10.2172/10124115

Nuovo Cim.A

Experiment WA91 searches for non-$q\bar q$ mesons produced in the central region in the reaction pp→pf(X0)ps at 450 GeV/c using the CERN Omega Spectrometer. WA91 is a continuation of the WA76 experiment which has studied this reaction using beams of 85 and 300 GeV/c. Preliminary results from experiment WA91 are presented. In particular the X(1450) and X(1900) observed for the first time in the π+π-π+π- channel of the WA76 experiment at 300 GeV/c are confirmed by the WA91 data.

Phys.Lett.B

In deep inelastic, neutral current scattering of electrons and protons at s =296 GeV , we observe in the ZEUS detector events with a large rapidity gap in the hadronic final state. They occur in the region of small Bjorken x and are observed up to Q 2 of 100 GeV 2 . They account for about 5% of the events with Q 2 ⩾10 GeV 2 . Their general properties are inconsistent with the dominant mechanism of deep inelastic scattering, where color is transferred between the scattered quark and the proton remnant, and suggest that the underlying production mechanism is the diffractive dissociation of the virtual photon.

Phys. Lett. B

With a current-splitting technique, we calculate the gauge-invariant initial-state radiation to order \oalf\ with soft-photon exponentiation for on- and off-shell $W$-pair production. This result generalizes the convolution formula, which is known from the description of the $Z$ resonance, to the case of the production of two $W$-bosons. After up to eightfold analytical integrations, a sufficiently smooth integral over three invariant masses remains to be treated numerically. Including the Coulomb singularity, the largest corrections are covered. We discuss the corrections in a large energy range up to $\sqrt{s}$=1TeV and draw numerical conclusions on their influence on the $W$-mass determination at LEP200. Table1 and figure5 are revised after correcting the analytical formulae for the nonuniversal corrections.

Nucl. Instrum. Meth. A

A new method of function minimization is developed and a new code (called FUMIVI) is created. Its main features are: i) regular functions of arbitrary structure can be minimized, ii) when minimizing χ 2 -like functions or functionals of a more general case one can use the linearization method, and in case of degeneration FUMIVI may automatically switch to accurate calculation of the second derivatives matrix, iii) nonlinear regular constraints of arbitrary type can be used, iv) both analytical and numerical calculation of the derivatives are possible. The new code was extensively tested both with model and real events of the experiment on rare K-meson decays.

Nucl. Instrum. Meth. A

A number of long scintillator counters employing UPS 923A and NE 114 plastic scintillators seen by a single photomultiplier were tested using cosmic muons. These counters have suitable dimensions to be used in large arrays in a proton supercollider experiment. The efficiency for m.i.p. was excellent in all cases. The yield of UPS 923A was found to be by about 25% higher than NE 114, while the attenuation length was approximately the same.

Phys.Lett.B

A search for Ks0→e+e− decay was performed by means of a 624-channel lead glass shower hodoscope and a set of proportional chambers. Neutral kaons were obtained in the quasibinary charge exchange reaction. A new upper limit of 2.8×10 −6 at 90% C.L. for the branching ratio is obtained.

Phys. Lett. B

This paper reports a search for excited electrons at the HERA electron-proton collider. In a sample corresponding to an integrated luminosity of 26 nb − , no evidence was found for any resonant state decaying into e − γ , ν W − or e − Z 0 . Limits on the coupling strength of an excited electron have been determined for masses between 45 and 225 GeV. This study also reports the observation of the wide-angle e γ Compton scattering process.

J.Phys.A

Based on the Maslov complex germ theory, a method of constructing the quasi-classical spectral series for the Dirac operator is proposed. The case when the corresponding relativistic Hamiltonian system is non-integrable and it admits a family of invariant two-dimensional stable Lagrangian tori containing the focal points is considered. The resulting quantization conditions for the above family generalize the Bohr-Sommerfeld-Maslov conditions and include new additional characteristics. The quasi-classical asymptotics obtained are regular over the full classically allowed domain. They also form an asymptotically complete and orthonormal set. Examples which use the proposed technique of the quasi-classical quantization are analysed.

Z. Phys. C

This paper presents energy distributions of the hadronic system produced in neutral-current electron-proton deep-inelastic scattering at a centre of mass energy of 296 GeV. Comparison of the results with QCD Monte Carlo models shows that QCD radiation has a strong influence on the characteristics of the final state. The data are reasonably reproduced by the Lund model based on a matrix element calculation in first order ofαs, followed by appropriate parton showers, as well as by the colour dipole model. The HERWIG parton shower model also gives a reasonable representation of the data. Neither the first order matrix elements alone nor the Lund parton shower model, without the matrix element calculation, reproduce the data.

Mod.Phys.Lett.A

We present the first measurement of the left-right cross-section asymmetry (ALR) in Z-boson production observed at the SLAC Linear Collider. In 1992 the SLD detector recorded 10 224 Z events produced by the collision of longitudinally polarized electrons with an unpolarized positron beam at a center-of-mass energy of 91.55 GeV. The average electron beam polarization during the run was (22.4 ± 0.6)%. We measure ALR to be 0.100 ± 0.0440 (stat.) ±0.004 (syst.), which determines the effective weak mixing angle to be $\sin^2\theta_W^{\rm {eff}} = 0.2378\pm 0.0056\, ({\rm stat.})\pm 0.0005\, ({\rm syst.})$.

Phys.Lett.B

The decays of B -hadrons have been reconstructed using the charged particles recorded in the DELPHI silicon microstrip detector. The sum of the charges of the secondaries determines the charge of the B -hadron parent. Some 232 114 multihadronic Z 0 decays recorded during the 1991 run of LEP at centre-of-mass energies between 88.2 GeV and 94.2 GeV yield 253 B -hadron candidates with well-measured charge. From these the mean lifetimes of neutral and charged B -hadrons are found to be 1.44±0.21 (stat.)±0.14(syst.) ps and 1.56±0.19(stat.)±0.13(syst.) ps respectively. The ratio of their lifetimes is 1.09 −0.23 +0.28 (stat.) ± 0.11(syst.). Under some assumptions on the abundance and lifetime of the Λ b 0 and B s 0 states, the B 0 and B + lifetimes are inferred.

Nucl. Phys. B

Based on a sample equivalent to 365 000 hadronic Z 0 decays, the search in DELPHI data for pairs of leptons accompanied by a pair of charged particles is described. A total of 11 events were found in the electron channel, 9 in the muon channel and 7 in the tau channel. Results on lepton pairs with a radiated photon are also presented. The data from all channels are compatible with the expectations from standard processes. However, one event was found in the tau channel with an unusually high mass of the charged particle pair.

Phys.Lett.B

A determination of the hadronic fragmentation functions of the Z 0 boson is presented from a study of the inclusive hadron production with the DELPHI detector at LEP. These fragmentation functions were compared with the ones at lower energies, thus covering data in a large kinematic range: 196 ⩽ Q 2 ⩽ 8312 GeV 2 and x (= P h E beam ) > 0.08 . A large scaling violation was observed, which was used to extract the strong coupling constant in second order QCD: α s ( M Z ) = 0.118 ± 0.005. The corresponding QCD scale for five quark flavours is: Λ (5) MS = 230 ± 60 MeV .

Z.Phys.C

A study of the fragmentation properties of charm and bottom quarks intoD mesons is presented. From 263 700Z0 hadronic decays collected in 1991 with the DELPHI detector at the LEP collider,D0,D+ andD*+ are reconstructed in the modesK−π+,K−π+K+ andD0π+ followed byD0→K−π+, respectively. The fractional decay widthsParseError: KaTeX parse error: Invalid size: '-' at position 75: …} \right. \kern-̲\nulldelimiters… are determined, and first results are presented for the production ofD mesons from$c\bar c$ and$b\bar b$ events separately. The average energy fraction ofD*± in charm quark fragmentation is found to be 〈XE(D*)〉c=0.487±0.015 (stat)±0.005 (sys.). Assuming that the fraction ofDs and charm-baryons produced at LEP is similar to that around 10 GeV, theZ0 partial width into charm quark pairs is determined to beΓc/Γh=0.187±0.031 (stat)±0.023 (sys). The probability for ab quark to fragment into$\bar B_s$ orb-baryons is inferred to be 0.268±0.094 (stat)±0.100 (sys) from the measured probability that it fragments into a$\bar B^0$ orB−.

Nucl.Phys.A

The double strangeness production has been observed in two final states of annihilation of antiprotons at momentum less than 0.9 GeV/ c on Xe nuclei: K + K + X (8 events) and K + K 0 ΛX (6 events). The probabilities of the reaction p Xe → K + K + X vary from 2 · 10 −5 (at rest) up to 7 · 10 −5 (in flight). The reaction p Xe → K + K 0 ΛX is observed only in flight with probability 3 · 10 −4 . The properties of the observed reactions are similar to those resulting from the cascade process with production of Ξ hyperon: p N → K ∗ −K ∗ , K ∗ → Kπ, −K ∗ N → ΞK, ΞN → ΛΛ . The new upper limit on the production probability of the stable H ( S = −2) dibaryon in the reaction Xe → K + K + H(H → Σ − p)X was obtained to be < 2 · 10 − (90% C . L .).

Z.Phys.C

A new measurement of αs is obtained from the distributions in thrust, heavy jet mass, energy-energy correlation and two recently introduced jet broadening variables following a method proposed by Cata