First evidence for the two-proton decay of 45Fe

Decays of five ⁴⁵Fe atoms have been observed at the fragment separator of GSI. Whereas one event is consistent with the β-decay of ⁴⁵Fe accompanied by the emission of a 10 MeV proton, four decays are consistent with the emission of particle(s) of total energy 1.1±0.1 MeV. This observation represents the first evidence for two-proton ground-state radioactivity, a decay mode predicted for ⁴⁵Fe. The time distribution of the observed decay events corresponds to a half-life of 3.2^+2.6 _-1.0 ms. Received: 17 May 2002 / Accepted: 28 May 2002     

Two-proton correlations in the decay of 45Fe

The decay of extremely neutron-deficient 45Fe has been studied in detail by means of a novel type of a gaseous detector employing digital imaging to record tracks of charged particles. The two-proton radioactivity channel was clearly identified. For the first time, the angular and energy correlations between two protons emitted from the nuclear ground state were determined, indicating the genuine three-body character of this decay. The half-life of 45Fe was found to be 2.6+/-0.2 ms and the observed 2p decay branching ratio is 70+/-4%.     

Observation of a narrow charm-strange meson D(+)(sJ)(2632)-->D(+)(s)eta and D(0)K(+)

We report the first observation of a charm-strange meson D(+)(sJ)(2632) at a mass of 2632.5+/-1.7 MeV/c(2) in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D(+)(s)eta and D0K+. In the D(+)(s)eta decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4+/-3.3 MeV/c(2). There is a corresponding peak of 21 events over a background of 6.9 at 2631.5+/-2.0 MeV/c(2) in the decay mode D0K+. The decay width of this state is <17 MeV/c(2) at 90% confidence level. The relative branching ratio Gamma(D0K+)/Gamma(D(+)(s)eta) is 0.14+/-0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D(+)(s)eta decay mode.     

Measurement of the pseudoscalar decay constant fDs using charm-tagged events in e+e- collisions at square root s=10.58 GeV

Using 230.2 fb-1 of e+e- annihilation data collected with the BABAR detector at and near the peak of the Upsilon(4S) resonance, 489+/-55 events containing the pure leptonic decay Ds+-->micro;+numicro have been isolated in charm-tagged events. The ratio of partial widths Gamma(D+-->micro+numicro)/Gamma(Ds+-->phipi+) is measured to be 0.143+/-0.018+/-0.006 allowing a determination of the pseudoscalar decay constant fDs=(283+/-17+/-7+/-14) MeV. The errors are statistical, systematic, and from the Ds+-->phipi+ branching ratio, respectively.     

Studies with one- and two-proton drip line nuclei

In recent experiments at GANIL, we studied nuclei at the one- and two-proton drip line. The production rates allowed to search for direct 2p emission in the drip line nuclei ⁴²Cr, ⁴⁵Fe, and ⁴⁹Ni. No evidence for this decay mode was found in ⁴²Cr and ⁴⁹Ni, whereas the situation stays unclear for ⁴⁵Fe due to the limited statistics. In the medium-mass region ( A = 50-70), the half-life was measured for all proton-rich nuclei in the range T _z = 0 to T _z = - 1 between Z = 27 and Z = 36. First half-lives were determined for ⁶⁰Ga, ⁶²Ge, ⁶⁴As and ⁶⁶Se. Finally, β-decay studies of the 0⁺ → 0⁺ decay of ⁶²Ga have been performed at IGISOL in Jyv?skyl?. Non-analog transitions have been observed and are compared to theoretical predictions. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: blank@cenbg.in2p3.fr     

Angular distributions of light projectile fragments in deep inelastic Pb + Em interactions at 160 A GeV

The nuclear emulsion was exposed at CERN by the lead projectile at 160 A GeV. The angles between any pair of fragments with Z = 2-4 have been measured in the emulsion plane for the events which did not contain heavy fragments. The constant characterizing the normal angle (J) distribution of the fragment momentum projection onto the emulsion plane with respect to initial projectile momentum p₀ is found to be C_J = (0.37 - 0.02) mrad. Corresponding value C₀ = (121 - 6) MeV/c of nucleon momentum distribution in the lead nucleus coincides with that expected from Fermi momentum distribution for this nucleus. The peak in the pair-angle distribution of double-charged fragments, ⁸Be M 2!, is presented for the region of small angles (<0.1 mrad). The fraction of !-particles coming from the decay of the ground state ⁸Be is found to be (13 - 2)% of their whole number.     

Prompt alpha decay of a well-deformed band in (58)Ni

Two excited well-deformed bands have been observed in the semi-magic nucleus (58)Ni. One of the bands was observed to partially decay by emission of a prompt discrete alpha particle that feeds the 2949 keV 6(+) spherical yrast state in the daughter nucleus (54)Fe. This constitutes the first observation of prompt alpha emission from states lying in the deformed secondary minimum of the nuclear potential. gamma-ray linking transitions via several parallel paths establish the spin, parity, and excitation energy of this deformed band in (58)Ni.     

First observation of 54Zn and its decay by two-proton emission

The nucleus 54Zn has been observed for the first time in an experiment at the SISSI/LISE3 facility of GANIL in the quasifragmentation of a 58Ni beam at 74.5 MeV/nucleon in a (nat)Ni target. The fragments were analyzed by means of the ALPHA-LISE3 separator and implanted in a silicon-strip detector where correlations in space and time between implantation and subsequent decay events allowed us to generate almost background free decay spectra for about 25 different nuclei at the same time. Eight 54Zn implantation events were observed. From the correlated decay events, the half-life of 54Zn is determined to be 3.2(+1.8)(-0.8) ms. Seven of the eight implantations are followed by two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and the partial half-life are compared to model predictions and allow for a test of these two-proton decay models.     

Measurement of the B0-B-0 oscillation frequency with inclusive dilepton events

The B0-B-0 oscillation frequency has been measured with a sample of 23 x 10(6) BB- pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives deltamd = 0.493+/-0.012(stat)+/-0.009(syst) ps-1.     

Systematic studies on α-decay half-lives for super heavy nuclei

Radioactive decay of super heavy nuclei via the emission of α-particles has been studied theoretically in the preformed cluster model (PCM). The nucleus-nucleus (NN) potential is obtained by double folding the density distributions of the α-particle and the daughter nucleus with a realistic effective interaction. The M3Y effective interaction, supplemented by a zero-range pseudo-potential for exchange term, is used to calculate the NN potential. The α decay half-lives for 317 nuclei at Z=102–120 are performed in the PCM framework with the theoretical Q values extracted from the Mller-Nix-Kratz and Liran-Marinov-Zeldes mass tables and are compared with the experimental data. The calculated results are also compared with those obtained by using Q values from the Muntian-Hofmann-Patyk-Sobiczewski and Myers-Swiatecki mass estimates.     

The reaction 48Ca + 238U → 286112* studied at the GSI-SHIP

The fusion reaction of ⁴⁸Ca projectiles with ²³⁸U target nuclei was studied at the velocity filter SHIP of GSI in Darmstadt. Two decay chains were measured, which fully confirm data that were previously assigned to the isotope ²⁸³112 in experiments at the Flerov Laboratory in Dubna. Two other events are consistent with a 50% spontaneous-fission (SF) branch of this isotope. The mean value obtained for the half-life of ²⁸³112 is (6.9 ^+6.9 _-2.3 s, the α energy is (9.520±0.015) MeV, and the total kinetic energy (TKE) of SF is (238±14) MeV. The half-life of the α decay daughter nucleus ²⁷⁹Ds is (0.18 ^+0.32 _-0.07 s, and the TKE of SF is (210 ⁺³² _-11 MeV. The cross-section deduced from all four events is (0.72 ^+0.58 _-0.35 pb , measured at an excitation energy of 34.6MeV of the compound nucleus ²⁸⁶112.     

Evidence for the exclusive decay B(c)+- --> J/psi pi+- and measurement of the mass of the B(c)+- meson

We report the first evidence for a fully reconstructed decay mode of the B(c)+- meson in the channel B(c)+- --> J/psi pi+-, with J/psi --> mu+ mu-. The analysis is based on an integrated luminosity of 360 pb(-1) in pp collisions at 1.96 TeV center of mass energy collected by the Collider Detector at Fermilab. We observe 14.6 +/- 4.6 signal events with a background of 7.1 +/- 0.9 events, and a fit to the J/psi pi+-mass spectrum yields a B(c)+- mass of 6285.7 +/- 5.3(stat) +/- 1.2(syst) MeV/c2. The probability of a peak of this magnitude occurring by random fluctuation in the search region is estimated as 0.012%.     

Direct observation of two protons in the decay of 54Zn

The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.     

Observation of the decay xi0 --> sigma+ mu- nu(mu)

The xi0 muon semileptonic decay has been observed for the first time with nine identified events using the KTeV beam line and detector at Fermilab. The decay is normalized to the xi0 beta decay mode and yields a value for the ratio of decay rates gamma(xi0 --> sigma+ mu- nu(mu))/gamma(xi0 --> sigma+ e- nu(e)) of [1.8(-0.5)(+0.7)(stat) +/- 0.2(syst)] x 10(-2). This is in agreement with the SU(3) flavor symmetric quark model.     

Two-proton radioactivity search

Two-proton radioactivity, a spontaneous breakup of elements with emission of two protons, was predicted to exist near the proton drip line by V.I. Goldansky long time ago. The recent theoretical and experimental progress in a search for such an exotic nuclear decay is reviewed. In theory, the new three-body model which treats two-proton radioactivity as a genuine three-particle nuclear decay is considered. In experiment, the first evidence for two-proton decay of ⁴⁵Fe is described. Four atoms of ⁴⁵Fe, produced at the fragment separator of GSI, decayed via particle emission with a total energy of 1.1(1) MeV and a half-life of 3.2 _?1.0 ^+2.6 ms. A possible experiment for a direct observation of two-proton emission from the ground state of ¹⁹Mg is considered for its decay in-flight. The half-life of ¹⁹Mg, as well as proton-proton correlations, might be derived from the distribution of the ¹⁹Mg decay vertices extrapolated from the measured trajectories of all fragments.     

On the applicability of the model of competing acceptors to Fe1+ in 57Co:ZnSe

Mössbauer emission spectra of a ⁵⁷Co:ZnSe powder source at low temperature exhibit the overcompensated Fe¹⁺ state of the nucleogenic daughter ion generated as an after effect of the ⁵⁷Co(EC)⁵⁷Fe decay. We analyse to what extent the model of competing acceptors is able to account for the formation and fraction of Fe¹⁺ and present evidence for the role of hole trapping by zinc vacancies.     

Comparison ofβ-decay and Charge-exchange Reactions in Mirror T =2 Nuclei and Isospin Mixing

We have carried out β decay studies of proton rich nuclei in the fp shell at different laboratories.Here we present our recent results on the decay of Tz =-2 nuclei performed at GANIL and compare them with the Charge Exchange reactions on their stable, mirror-partner targets, performed at RCNP. In one of the cases, the 56Zn - 56Fe pair, a strong isospin mixing has been observed. The results are well reproduced in the framework of Shell Model calculations     

Role of the cluster deformations in explaining the exotic decay half-lives

We investigate the influence of nuclear deformations of the cluster and daughter nuclei on the exotic cluster decay half-lives of $\ensuremath 221\leq A \leq 242$ for the favored cluster decay of the radioactive nuclei by using the semiclassical WKB method and the Bohr-Sommerfeld quantization condition. The results have also been presented for the spherical nuclei case in order to show clearly the effects of the deformations on the exotic decay half-lives. The half-lives become close to the experimental data when both the deformation of daughter and cluster nuclei are taken into account in the calculations. Furthermore, considering cluster deformations together with the orientation angles of daughter and cluster also provides positive contributions to the results.     

Search for lepton-flavor violation in the decay tau- --> l- l+ l-

A search for the lepton-flavor-violating decay of the tau into three charged leptons has been performed using 91.5 fb(-1) of data collected at an e(+)e(-)center-of-mass energy around 10.58 GeV with the BABAR detector at the SLAC storage ring PEP-II. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (1-3)x10(-7) at 90% confidence level.