Search

Most currently, viable double beta decay experiments require highly enriched isotopic sources. These sources must be extraordinarily free of radioactive contamination. The double beta decay experiment NEMO 3 will study 100Mo, for which physical and chemical purification techniques have been investigated. The success of the chemical purification process is discussed in the context of ultra-low background, high-purity germanium spectrometer measurements.

To be sensitive to an effective Majorana neutrino mass, 〈 m ν 〉, on the order of 0.1 eV, the NEMO 3 double beta (ββ(0ν)) decay experiment requires precise knowledge and control of the backgrounds. The effect of neutrons and γ-rays from the Frejus underground laboratory (LSM, Laboratoire Souterrain de Modane) has been studied during 10 700 h of data collection. The data were taken with a NEMO 2 prototype detector using different shield configurations. Monte Carlo calculations with GEANT/MICAP code and a new library of γ-rays from neutron captures are presented. The implied consequences for the NEMO 3 detector which is under construction are discussed. The neutrinoless double beta decay background induced by neutrons and γ-rays within the LSM will be suppressed to the very suitable level of 0.1 event in a live time of five years given the appropriate shield and magnetic field.

The total cross section of the pd→pdη reaction has been measured at two energies near threshold by detecting the final proton and deuteron in a magnetic spectrometer. The values are somewhat larger than expected on the basis of two simple theoretical estimates.

The total cross section for $\ensuremath{\omega}$ production in the $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}\ensuremath{\omega}$ reaction has been measured at 5 c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong proton-proton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold $\ensuremath{\varphi}$ and $\ensuremath{\omega}$ production is, to within relatively large uncertainties, consistent with the predictions of a simple one-pion-exchange model. The degree of violation of the Okubo-Zweig-Iizuka rule is similar to that found in the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}n\ensuremath{\omega}/\ensuremath{\varphi}$ reactions.

The polarized d d -> alpha X reaction at beam energies close to the eta threshold shows very strong structure in the missing mass corresponding to the ABC enhancement. The deuteron tensor analysing power A_yy, and the slope of the vector analysing power A_y with respect to angle, have been measured for this reaction around the forward direction. Both signals are small, and their variations with the alpha-particle momentum are in broad agreement with a theoretical model in which each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -> d pi reaction.

The total cross section of the pp -> pp eta' reaction has been measured at two energies near threshold by detecting the final protons in a magnetic spectrometer. The values obtained are about a factor of 70 less than for the corresponding eta production, in good agreement with the predictions of a one-pion-exchange model.

In the framework of the RD-17 project at CERN an extensive work is in progress on the development of scintillating-fibre detectors using position-sensitive photomultipliers. With 0.5 mm diameter fibres a spatial resolution of about 125 μm was obtained with a detection efficiency higher than 95%. The time resolution of the detector is about 600 ps, and the track position is properly digitised in real time in less than 10 ns by a peak sensing circuit. A simulation, based on experimental data, has also been performed to compare different types of front-end electronics.

Fast and precise readout of scintillating fibres (SciFi) has a great potential for fast tracking and triggering at high-luminosity particle physics experiments. In the framework of the RD-17 experiment at CERN (FAROS) significant milestones in the development of SciFi detectors using position-sensitive photomultipliers have been achieved. Results obtained with a weak cross-talk multi-anode photomultiplier, Philips XP1724, and a parallel readout of the anodes are reported. With 0.5 mm diameter fibres a spatial resolution of about 125 μm and a detection efficiency in excess of 95% have been obtained. The time dispersion of signals from individual photomultiplier channels has been estimated to be about 1 ns. The possibility of digitising the track position in real time by a peak-sensing circuit is studied for the first time

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He., LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters B

We present some of the recent results of an R&D program on scintillating fibers readout by position-sensitive photomultiplier tubes. Considerable improvements have been achieved compared to the previous studies, in particular in detection efficiency (> 95%) and linearity. In addition, a detailed study on two-hit resolution enabled us to confirm the possibility of reconstructing double-hit events in real-time by using the delay-line method.

The [ital pp][r arrow][ital pp][eta] reaction is studied at energies near the [eta] production threshold. The total cross sections at nominal machine energies of 1260, 1265, and 1300 MeV are 90[plus minus]15, 790[plus minus]120, and 3460[plus minus]690 nb, respectively. None of the existing perturbative model calculations reproduces the energy dependence, which deviates strongly from phase space. This suggests that the cross section is enhanced in the near vicinity of the production threshold by a large [eta]-[ital pp] scattering length.

The reaction p + d → π − + X has been studied at Saturne at 1.45, 2.10 and 2.70 GeV, using the spectrometer SPES III. The analysing power and the differential cross sections show no evidence for narrow structures which could be interpreted as a resonance in the three baryon system. At the lowest incident energy, the shapes of the experimental cross sections are well reproduced by phase-space distributions.

The background induced by radioactive impurities of $^{208}\rm Tl$ and $^{214}\rm Bi$ in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which decrease the background from the above mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons., 15 pages, 13 figures, accepted in the Nuclear Instruments and Methods A

The analyzing powers of the {sup 1}H({ital {rvec d}},{ital pp}){ital X} reaction have been measured using polarized deuteron beams at {ital T}{sub {ital d}}=2.1 GeV, {theta}=17{degree} and {ital T}{sub {ital d}}=1.722 GeV, {theta}=0{degree}. In both cases a small oscillatory pattern has been observed in the tensor analyzing power at the same two-proton invariant mass and width {ital M}{sub {ital p}{ital p}}=1.945 GeV, {Gamma}{sub 1/2}{approx}8 MeV. The number of standard deviations are equal to 2.5 and 3.9, respectively.

Experimental results obtained with commercially available PSPMs coupled to 0.5-mm diameter scintillating fiber arrays show space resolution of < 200 ?m and time resolution better than 1 ns with a detection efficiency of about 90%. In addition, the preliminary studies indicate the feasibility of separating double-tracks with a minimum distance of 3 mm using this technology.

In order to search for isospin-2 dibaryons and to study the inelastic nucleon-nucleon channels producing at least two pions, the differential cross sections and analyzing powers have been measured for the {ital p}({ital {rvec p}},{pi}{sup {minus}}){ital X} reaction with polarized proton beams of 1.45, 2.1, and 2.7 GeV. The pions were detected at an angle of 13.8{degree} by the SPESIII spectrometer located at Laboratoire National Saturne. No statistically significant evidence for structures corresponding to {pi}{ital NN} bound states or six-quark states could be established. However, upper limits to the cross section for such processes are deduced. The data analysis in terms of phase space has shown that as the bombarding energy increases, {ital N}{sup *}{ital N} final states have to be taken into account besides the usual {ital N}{Delta} and {Delta}{Delta} processes in order to adequately describe our results.

For masses larger than 2 % + MT, narrow peaks in two proton invariant (missing) masses spectra : M (M ) are now well established. The existence of such PP x narrow peaks is not so unquestionable below 2 $ + Mr. Tensor analyzing power T20 + of the invariant mass M has been studied using the p(d,pp)~ reaction. Depending PP on the assumption done for background substraction -a hble or an oscillation mayappear at M = 1941 MeV. Additional data are under analysis and will improve the statistics. PP It is well known that narrow structures have been obsenred in two nucleon invariant masses, or missing mass experiments/l/. These structures have been tentatively attributed to isovector dibaryons although no proof has been advanced to associate them with quark degrees of freedom. This assumption relies only on the fact that such structures are not present in classical nuclear physics using meson exchanges and nucleon or delta degrees of freedom. The experimental certainty depends mainly on the quantum numbers and the mass of studied dibaryons. Up to now, none has been observed in T = 0/2/ or T = 2/31 isospin states. In case of T = 1 isospin, for the range of masses larger than 2 $ + M* (M > 2.016 GeV) there is a good agreement for narrow peaks between results obtained at Saturnel41 : measurement of d2a/dQdMx for 38e(p,d)~ reaction, and Lanpf/5/ where Ay was measured. These data correspond to the second generation of experiments, since they have used electronical detectors. ('1 Present address : Ben Gourion University of the Negev, P.O. Box 653 84105Beer Sheva, Israel. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990631 C6-372 COLLOQUE DE PHYSIQUE Below 2.016 GeV, many structures have been presented, corresponding usually -but not alwaysto the first generation of experiments studying bubble chamber pictures. Here the masses of experimentally observed structures do not concentrate around a few values, but are more or less distributed from 2 % to 2 % + M?/1/. The necessity of a precise second generation experiment close to the two nucleon mass appears then naturally. 3 Such an experiment has been carried out at SATURNE with the p(d,pp)X reaction. Tensor polarized deuteron beam of 1.722 GeV has been used and the two protons detected at 0" using the SPES3 facility. The properties of the spectrometer : pmax/pmin z 2.5, and As2 = sr allow the study of the following two proton invariant mass range : 2 % < M < 1.963 GeV, PP the counting rate decreasing regularly from small to larger masses M . This result is mainPP ly due to pp FSI giving rise to a narrow maximum a few MeV above 2 M . Due to the granulaP rity of the detection, when two trajectories intercept a same scintillator of one among the two major trigger detection plans or give rise to two mixing tracks on the focal pla~e, the event is lost. This produces a loss of efficiency in the first three MeV of the spectra.This explains that our FSI is located around 1880.7 MeV, that is ?. 3 MeV higher than the peak maximum from low energy experiments. The detection has been described elsewhere/3/. The empty target accounts for about 5 % of the counting rate. The FWHM of the experimental wcdth for M is 1.2 MeV. The data have been therefore binned into 2 MeV intervals. The M hisPP PP togram presented in Fig. 1 is quite continuous, without any discontinuity having a number of standard deviations (S .D .) larger than 2.2. id = 1.722 GeV epp =0° 0.2 188

A search for isoscalar dibaryonic resonances by means of missing-mass spectra in the d + d → d + X reaction has been attempted using deuteron beams of T = 2.29,2.00 and 1.65 GeV. The results do not show any evidence for a narrow peak with a limit of 30 nb GeV 2 for a 15 MeV width or a broad enhancement which could be unambiguously attributed to a dibaryonic resonance.

The differential cross section and analyzing power have been measured for the p( p , π − )X reaction at an incident energy of 1450 MeV and a pion angle of 13.8° in order to study eventual dibaryonic T =2 structures in the vicinity of the πNN threshold. No statistically significant evidence for such structures corresponding to πNN bound states or six-quark states could be established. Upper limits to the cross section are deduced. Analyzing power data are discussed.

Neutron hole states in the 1s shell have been studied in the n(K−, π−)Λ strangeness-exchange reaction on 6Li, 7Li, 9Be, and 12C targets at the CERN Proton Synchrotron. The excitation energy and the width of the states as well as the differential cross section have been determined. The clear similarity with the 1s proton hole states observed in (p, 2p) reactions indicates that the presence of the Λ-particle can be taken into account within the weak-coupling model. In this way the (K−, π−) reaction can be used for the study of Λ -states as well as for the investigation of neutron hole states produced at very low momentum transfer.

Differential cross sections have been measured for (t, d) reactions on 45 Sc, 52 Cr and 60 Ni near the Coulomb barrier at beam energies from 2.2 to 3.5 MeV. From the DWBA sub-Coulomb analysis, the normalization coefficient D 2 of (t, d) reactions was extracted to within 7% accuracy. The spectroscopic factors of some low-lying 46 Sc levels were deduced. Discussion is given to the sensitivity of the results to variations in the optical model parameters, the bound state neutron description and the approximations in the analysis.

Differential cross sections of elastic and inelastic scattering of 1.37 GeV α-particles from 40, 42, 44, 48Ca have been measured. The angular distributions show that the scattering process is quite diffractive. Glauber's nucleus-nucleus scattering theory for elastic scattering has been examined in two approximate ways. The method in which the projectile is assumed not to be excited internally in the course of multiple scattering, reproduces reasonably well the experimental angular distributions. The trend of the root-mean-square radii of the neutron densities of the four calcium isotopes has been found to be in agreement with the recent results from proton scattering measurements at 1.04 GeV.

We have studied (p, p) reactions on 12 C , 63 Cu, and 209 Bi to search for possible nuclear states formed ny antiprotons and nuclei. The experiments used the 180 MeV antiproton beam from LEAR, and the high-resolution magnetic spectrometer, SPES II, to detect the outgoing protons. No evidence of antiproton-nucleus states was found. The gross features of the proton spectra are reasonably well described by intranuclear cascade model calculations, which consider proton emission following antiproton annihilations in the target nucleus.

Cross sections for the production of hypernuclei were measured in the reaction A(K − , π − ) Λ A. on light and heavy nuclear targets, using a separated K − beam at the CERN Proton Synchrotron. The pions were detected in the forward direction. The results are compared with cross sections calculated under the assumption that the reaction took place on a single neutron. The good agreement between the measured and the calculated cross sections justifies the use of the (K − , π − ) reaction in order to obtain spectroscopic information on hypernuclei.

The knock-out reaction A( p , p)X has been used to search for narrow p -nucleus states. The experiment was performed using the 600 MeV/ c antiproton beam at LEAR and the high-resolution and large-acceptance magnetic spectrometer SPES II. The A -dependence of the annihilation-induced proton spectra has been studied on 2 H, 6 Li, 12 C, 63 Cu, 208 Pb and 209 Bi. The quasi-free elastic p p scattering observed in the lighter targets, and the comparison with the free p p scattering, also observed in this experiment, determine an effective proton number N eff for 1s- and 1p-shell protons. No evidence for narrow bound or resonant p -nucleus states could be found. Upper limits for their production are one order of magnitude lower than certain theoretical predictions, but consistent with the properties of the p -nucleus interaction, as established from recent elastic and inelastic scattering as well as from studies of antiprotonic atoms.

Proton-induced pion production at intermediate energies, leaving the final nucleus in discrete, resolved states, has been measured at the Saclay Synchrotron Saturne I, using the high resolution spectrometer facility SPES I. The (p, π+) reaction has been investigated on 9Be at proton energies of 410 and 605 MeV, and on 10B at incident energies of 320,410, 483 and 605 MeV. These data are presented and analysed in a coherent way, together with previous results at intermediate energies, by means of a pion exchange model. It is found that all the characteristic features of the data are reproduced satisfactorily.

The angular distributions of the inelastic scattering of antiprotons for a few collective states of 12C and 18O have been measured. They exhibit a diffractive pattern, typical of strong absorption. Coupled channel analysis of these data has been carried out. The derived multipole moments agree fairly well with those obtained with other probes. Microscopic calculations performed in the framework of the DWIA formalism, using either the Paris or the Dover-Richard NN interaction are in good agreement with the data for the low-lying collective states. The present status of the experimental study of the unnatural parity levels is discussed.

Angular distributions for elastic scattering of antiprotons from nuclei are analyzed in terms of a fuzzy black disk model. Data from /sup 12/C, /sup 16/O, /sup 18/O, and /sup 40/Ca at incident antiproton energies of 47 and 180 MeV are analyzed. The obtained fits are qualitatively good concerning the slope and position of the extrema, but are too deep in the minima.

The angular distribution for elastic scattering of 179.3 MeV antiprotons by deuterium has been measured. The data should provide further constraints on the elementary p-n amplitudes.

In the strangeness exchange reaction (K − , π − ) on 12 C and 16 O the most prominent transitions to hypernuclear states produced in recoilless and quasi-free Λ production have been identified. The analysis of the spectra shows that in the Λ-nucleus interaction the spin-orbit coupling is at least one order of magnitude smaller than for the nucleon-nucleus interaction.

The production of Σ particles in the (K−, π−) on 9Be at 720 MeV/c has been studied at the CERN proton synchrotron (PS). The missing-mass spectrum shows structures in the Σ region, which have been interpreted as belonging to hypernuclei with sigma particles. An upper limit of 8 MeV for the width of these states has been estimated.

Antiproton-carbon elastic and inelastic scattering cross sections have been measured at 46.8 MeV over an angular range 6° ⩽ θ ⩽ 59° with a magnetic spectrometer. Fits to the elastic and inelastic 4.44 MeV excited state cross sections put realistic limits on the strengths of the real and imaginary parts of the antiproton-carbon optical potential. The continuum cross section due to carbon break-up appears to be smaller than it is for corresponding proton data.

Angular distributions for elastic scattering of 180 MeV antiprotons from 12C, 40Ca, and 208Pb have been measured over a wide angular range with a magnetic spectrometer. In general, microscopic calculations agree fairly well with the data. Optical-model fits with Woods-Saxon parametrization determine the magnitude and the relative strength of the real and imaginary potentials at the nuclear surface. When the shape of the potentials is derived from that of the charge distribution, the depth of the real potential is found to be shallow (30 MeV < V0 < 70 MeV). These results are in some disagreement with several models and predictions, but are consistent with the results of p-12C scattering at 46.8 MeV and with a recent a analysis of p-atom data.

Elastic scattering of 178.4 MeV p has been measured on 16 O and 18 O isotopes. Both macroscopic and microscopic analyses of the data show differences which can be related to the neutron excess in 18 O

Energy excitation spectra have been obtained for hypernuclei in the s‐d shell from (K−,π−) reaction in flight on 32ΛS and 40ΛCa. The analysis is carried out in a simple particle hole model and leads to the results that the Λ behaves in the nucleus like an independant particle in a harmonic oscillator potential well with no significant spin orbit term.

Scintillating fibre technology has made substantial progress, and has demonstrated great potential for fast tracking and triggering at high luminosity experiments in Particle Physics. This talk presents some recent issues of the RD-17 project at CERN for fast and precise readout of scintillating fibre arrays, as well as for upgrade of position-sensitive photomultipliers. Excellent matching of scintillating fibre and position-sensitive photomultiplier, in particular in time characteristics, allowed to realise high detector performances, typically represented by spatial resolution of similar to 125 mu m as well as time resolution better than 1 ns with detection efficiency greater than 95 %.