Search

The NA60 experiment has measured the production of muon pairs and charged particles in In+In collisions at a beam energy of 158 AGeV. For invariant dimuon masses below the , the spacetime averaged ? spectral function was isolated by a novel procedure. It shows a strong broadening but essentially no shift in mass. The production of J/? was measured as a function of the collision centrality. As in previous experiments studying Pb+Pb collisions an anomalous suppression is observed, setting in at approximately 90 participant nucleons. Using the charged particles, the reaction plane was reconstructed. The elliptic flow of charged particles increases with ptshowing a saturation for pt> 2 GeV/c. For the first time, azimuthal distributions for J/? are shown.

AbstractThis article presents a simple method of analysing speech test scores which are biased through ceiling effects. Eighty postlingually deafened adults implanted with a MED-EL COMBI 40/40+ cochlear implant (CI) were administered a numbers test and a sentence test at initial device activation and at 1, 3, 6, 12 and 24 months thereafter. As a measure for speech recognition performance, the number of patients who scored at the ‘ceiling level’ (i.e. at least 95% correct answers) was counted at each test interval. Results showed a quick increase in this number soon after device activation as well as a continuous improvement over time (numbers test: 1 month: 51%; 6 months: 73%; 24 months: 88%; sentence test: 1 month: 33%; 6 months: 49%; 24 months: 64%). The new method allows for the detection of speech recognition progress in CI patient samples even at late test intervals, where improvement curves based on averaged scores are usually assuming a flat shape.Copyright © 2004 S. Karger AG, Basel

The HELIOS experiment has measured inclusivep⊥ spectra of negative particles in the rapidity region 1.0⊥ spectra in p +W, O+W and S+W is similar, but cannot be described by a single exponential. Compared to p+p collisions, an excess is observed for low and highp⊥. This effect increases with the projectile mass. Except for very lowE⊥, the average transverse momentum ⊥> is found to be approximately constant up to the highest accessible values ofE⊥.

We present stdies of events triggered on two high-pT jets, produced inpp collisions at the CERN Intersecting Storage Rings (ISR) at =63 GeV, using a large solid angle calorimeter. The cross-section for producing two jets is measured in the dijet mass range 17–50 GeV/c2. A high-statistics sample of dijet events, where each jet has transverse energy above 10 GeV, is used to study the structure of jets and the associated event. We find the longitudinal fragmentation function to be similar to that of jets emerging frome+e− collisions but considerably harder than that observed at the Super Proton Synchrotron (SPS) Collider. A steepening of the fragmentation function is observed when increasing the jet energy. Studies of the charge distribution in jets show that these predominantly originate from fragmenting valence quarks. The transverse energy and particle flows are presented as functions of the azimuthal distance from the jet axis.

Aberrant 131I orthoiodohippurate renal plasma flow values were obtained when our image-based method was moved from an old to a new gamma camera. We suspected inadequate collimation as the reason for this problem because we observed increased septal penetration and scatter. Camera effects were largely eliminated because both our old and new cameras had W thick crystals. We report here the effects of two high and three medium energy collimators upon the fraction of syringe image count beyond the syringe image, and upon the correlation of these non-image count fractions with geometric collimator parameters. We also report the effects of these same collimators upon kidney-to-background count ratios, using patient relevant abdominal phantoms. The percentage counts beyond the syringe image varied from 33 to 57. The phantom kidney-to-background ratios varied from 3.7 to 2.0. We conclude that image-based quantitative measurements are strongly dependent on collimator selection. The data also provide a user basis for collimator evaluation, selection and design, and have implications for 131I and 111In antibody imaging.

We have studied the processpp???+X at GeV in the central rapidity region. We report a positive signal at 96% C.L., a ratio ??/e+e-=4.0±3.0 when the transverse momentum of each photon is above 2 GeV/c, and a cross-sectionds/dydM??=(5.5±2.7)×10-34 cm2/GeV when |y|<0.5,4??<6 GeV.

Diffractive dissociation of nuclei (Be, Al, W) in collisions with 450 GeV/c protons,pA?pX, has been measured with the HELIOS spectrometer at the CERN Super Proton synchrotron. The dependence of the single-diffraction cross-section on the nuclear massA can be parametrized as sSD mb×A0.35±0.02, showing the peripheral nature of the process. The differential cross-section dsSD=(3.8±0.3)mb ×A0.35±0.02, is exponential with the slope parameter, increasing from 6.2±0.4 (GeV/c)-2 for beryllium to 7.9±0.5 (GeV/c)-2 for tungsten. The slope parameter also increases with increasing massMX of the diffractively produced state. The rapidity, multiplicity, and transverse-momentum distributions of the particles of the diffractively produced stateX show a longitudinal phase-space population and are remarkably insensitive to the nuclear mass. This, together with theA1/3 dependence of sSD, suggests that the dominant process of nuclear diffractive excitation is the dissociation of single nucleons.

We have measured the inclusivepT spectra of soft photons produced at central and backward rapidities in 450 GeV/cp-Be collisions down to 1 MeV/c in transverse momentum. In the region 1T<20 MeV/c an excess of photons over those expected from hadronic decays is observed. This excess is comparable, within systematic errors, with estimates of direct photons produced via hadronic bremsstrahlung. An upper limit is derived on the presence of additional sources of direct photons at small transverse momentum.

Transverse-energy distributions have been measured in the pseudorapidity region -0.1lab<2.9 for oxygen-nucleus collisions at incident energies of 60 and 200 GeV per nucleon for Al, Ag, and W target nuclei. The cross-section for the heaviest target nuclei at the highest incident energy is measured over 5 orders of magnitude and out to a maximumET of 200 GeV. Measurements of the differential densitydET/d?lab as a function of?lab are presented. In the pseudorapidity region -0.1lab<2.9 the transverse energy for an average central collision is proportional to ˜A0.5, while the fraction of the total transverse energy measured in an extended region of?lab>2.9 decreases with increasingA. The distributions are compared with the predictions of a dual parton model. Finally the question of the energy density is addressed.

The transverse energy cross-sectionds/dET has been measured in the pseudorapidity region 0.6T distribution extends to 40 GeV, which is twice the kinematic limit forp-p collisions at the same incident beam momentum. The distribution ofET is found to shift towards low pseudorapidities with increasing total transverse energy.

Transverse-energy distributions have been measured in the pseudo-rapidity region -0.1 >?lab <2.9 for oxygen-nucleus collisions of incident energies of 60 and 200 GeV per nucleon for Al, Ag, and W target nuclei. We present a summary of the results and a comparison to theoretical model descriptions.

We report on the production of low-mass electron pairs and muon pairs in p-Be collisions at 450 GeV/c at the CERN SPS. For both electron and muon pairs the low-mass spectrum can be explained satisfactorily by lepton pairs from hadronic decays, and there is no need to invoke any “unconventional” source. The normalisation of the major hadronic sources is set by the data. The upper limit, at 90% confidence level, on any new source of lepton pairs is ~20% of the hadronic decay contribution for muons, and ~40% for electrons.

One-particle-inclusive measurements have been performed for the charge, kinetic energy and angular distributions of reaction products from238U +238U at 1 766MeV (7.42MeV/u) incident energy. The deep inelastic products exhibit features similar to those seen in reactions induced by medium heavy nuclei: increasing particle transfer is observed with increasing energy damping, the angular distributions are peaked near the grazing angle, they broaden significantly with increasing energy loss and/or charge transfer. The dominant reaction mechanism, however, is found to be sequential fission of one or both primary reaction products. The reconstructed primaryZ- andQ-value distributions show more particle transfer at a given energy loss than in other systems, i.e. the diffusion process seems to proceed colder in this system. This is confirmed by relatively large cross sections for surviving deep inelastic reaction products belowZ=92. A direct search fora-decay or fission of superheavy nuclei being produced in a deep inelastic reaction and being implanted in a surface barrier detector resulted in an upper cross section limit of 2 ×10-32cm2.

The results of two sets of transverse energy measurements, performed with incident proton beams of 200 and 450 GeV/c momentum on several nuclear targets, are presented. The transverse energy cross sections ds/dET are measured in a pseudorapidity range including the target fragmentation region (-0.1T/d? distributions shifts towards the target fragmentation region as the atomic mass number of the target increases or a selection of high transverse energy events is made. A parametrization based on a simple geometrical nucleonnucleon scattering approach was found to be inadequate to describe all features of the transverse energy distributions. Finally, the VENUS model is compared with the experimental data.

With age regular changes take place in the latent periods of spikes of the slow auditory evoked potential. In particular, the latencies of the comparatively early waves (P1, N1, and P2) become progressively shortened. Between 3–7 and 8–13 years the decrease is 50–60 msec, and later it is 25–35 msec. The latencies of the latest waves, especially P3, N3, and P4, increase from 3–7 to 8–13 years by 35–65 msec. Later the latent period of the P3 spike remains unchanged but the N3 and P4 waves disappear completely. Of all the components of the slow auditory evoked potential the most stable is the N2 wave, the latent period of which decreases only very slightly with age. In children aged 3–7 years two wave complexes (P1N1P2 and P2N2P3) overlap frequently to form a single undifferentiated wave. This splits up into its components by 8 years of age. Long age changes in the shape and parameters of the slow auditory evoked potential are examined from the standpoint of the predominantly extralemniscal origin of this potential. On the basis of correlation discovered between the late waves of the evoked potential and the level of EEG synchronization it is postulated that the late waves of the slow evoked potential are formed with the participation of the nonspecific synchronizing system.

Kinematically complete experiments have been performed on the two- and three-body exit channels in the reactions84Kr+166Er and129Xe+122Sn at 12.5 MeV/u. Three-body events occur with an unusually high probability. They arise from a fast two-step mechanism where a sequential fission-like process follows a deep inelastic collision with preferentially very large energy losses. Strong Coulomb proximity effects are observed in the three-body final state which, treated quantitatively in Coulomb trajectory calculations, establish a time-scale of 1·10-21 s between the consecutive scission acts. The angular distribution of fission fragments is consistent with an orientation of the fission axis approximately collinear with the axis of the first scission, and the mass distribution of the fission is asymmetric with the heavier mass emitted preferentially opposite to the direction of the third particle. The high fission probability, the short time-scale, the near collinear orientation and the fission mass asymmetry together present consistent evidence for a new phenomenon of non-equilibrium fission.

K-vacancy production probabilitiesPK(b) were measured with gas and solid targets byK-x-ray particle coincidences (impact parameterb is determined by the particle detection angle) in the region of light (ZP?ZT?10) up to intermediate heavy (ZP?ZT?36) collision systems. The measuredPK(b) reveal a very strong difference in shape between solid and gas targets independent ofZ. Only thePK(b) measured with gas targets and those measured with solid targets at very small impact parameters show reasonable good agreement with the 2ppx-2ps rotational coupling model. At largeb thePK(b) from solid targets are strongly influenced by a multiple collision effect, where projectileL-vacancies seem to be produced in collisions beforeK-vacancy production. However, this effect cannot be understood just by a two collision process whereL-vacancy production and 2ppx-2ps rotational coupling occurs in consecutive collisions.