Evidence for the two-body charmless baryonic decay B+→pΛ‾ {B}^{+}\to p\overline{\varLambda}

See paper for full list of authors - All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-048.html - Submitted to JHEPInternational audienceA search for the rare two-body charmless baryonic decay $B^+ \to p \bar\Lambda$ is performed with $pp$ collision data, corresponding to an integrated luminosity of 3\mbox{\,fb}^{-1}, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of $B^+ \to p \bar\Lambda$ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the $B^+ \to K^0_{\mathrm S} \pi^+$ decay for normalisation, is \begin{eqnarray} \mathcal{B}(B^+ \to p \bar\Lambda) & = & ( 2.4 \,^{+1.0}_{-0.8} \pm 0.3 ) \times 10^{-7} \,, \nonumber \end{eqnarray} where the first uncertainty is statistical and the second systematic

USING FAST PROCESSES TO INVESTIGATE CLUSTER STATES AND NUCLEAR CORRELATIONS IN MEDIUM-HEAVY NUCLEI: SPECIFIC TOOLS AND NEW OPPORTUNITIES WITH RADIOACTIVE ION BEAMS

Clustering effects show up in several ways along the Nuclear Chart. While for light nuclei (A≤40) the existence of clusters has been directly linked to nuclear structure and reaction dynamics observations, this is less the case when moving towards medium-mass systems. Pre-equilibrium emission is a nice example of mechanism capable to fill this gap, linking structure with dynamics and, eventually, to clustering in medium-mass nuclei. For central collisions, cluster pre-formation probabilities can be derived by studying light particle production cross sections and multiplicities. Several theories have been developed in the framework of exciton models to describe pre-equilibrium processes and try to explain how these are influenced by the structure of the reacting nuclei. The forthcoming availability of intense radioactive ion beams will open new challenging scenarios in this field of study, allowing the comparison of new systems where projectiles exhibit extreme neutron to proton ratios, bringing to structural configurations where clusters may show up in a more evident way.status: publishe

The fission time scale measured with an atomic clock

We present a new direct method of measuring the fission absolute time scale using an atomic clock based on the lifetime of a vacancy in the atomic K-shell. We studied the reaction Ne-20 + Th-232 -&gt; O-16 + U-236* at 30 MeV/u. The excitation energy of about 115 MeV in such a reaction is in the range where a fission lifetime of the order of 10(-18) s has been suggested on basis of blocking experiments. The lifetime of the K-shell hole for U is about 6x10(-18) s. The reaction channel is detected by a forward hodoscope, operated in coincidence with detectors for fission fragments and with Germanium detectors. The latter detectors allow one to detect the characteristic K x rays. The K-shell ionization probability due to the projectile and the projectile-like fragment is about 2%. Depending on the fission lifetime of the U nuclei, either a continuum (short lifetimes) or an explicit characteristic K x-ray spectrum of U (long lifetimes) can be observed. First analysis indicates a x-ray yield in the U energy region.</p

Direct K-shell ionization probabilities in 30-MeV/u Ne- and 8.3-MeV/u C-induced reactions near zero impact parameter

Direct K-shell ionization probabilities were measured in coincidence with elastically scattered particles in 30-MeV/u Ne+Sn, Tb, Pb, Th and 8.3-MeV/u C+Zr, Ag, Sn, Sm, Au, Pb, Th reactions. Experimental data were compared with calculations in the semiclassical approximation. The transitional behavior at the reduced velocity xi(K)approximate to1, where the projectile velocity approaches the velocity of the K-shell electrons, is discussed

Isospin effects on two-particle correlation functions in E/A=61 MeV Ar-36+Sn-112,Sn-124 reactions

Small-angle, two-particle correlation functions have been measured for Ar-36+Sn-112,Sn-124 collisions at E/A=61 MeV. Total momentum gated neutron-proton (np) and proton-proton (pp) correlations are stronger for the Sn-124 target. Some of the correlation functions for particle pairs involving deuterons or tritons (nd, pt, and nt) also show a dependence on the isospin of the emitting source

Chronology of particle emission from the E/A=61 MeV Ar-36+Al-27 reaction

The emission time chronology of neutrons, protons, and deuterons from the E/A=61 MeV Ar-36+Al-27 reaction is deduced from two-particle correlation functions

Calibration of a neutron time-of-flight multidetector system for an intensity interferometry experiment

We present the details of an experiment on light particle interferometry. In particular, we focus on a time-of-flight technique which uses a cyclotron RF signal as a start and a liquid scintillator time signal as a stop, to measure neutron energy in the range of En approximate to 1.8-150 MeV. This dynamic range (up to 300 ns) is much larger than the beam bunch separation (54 ns) of the AGOR cyclotron (KVI). However, the problem of a short burst period is overcome by using the time information obtained from a fast projectile fragment phoswich detector. The complete analysis procedure to extract the final neutron kinetic energy spectra, is discussed. (C) 2003 Elsevier B.V. All rights reserved

16^{16}O Coulomb dissociation: towards a new means to determine the 12^{12}C+α\alpha fusion rate in stars

NESTERA feasibility study was made of an important aspect of the Coulomb-dissociation method, which has been proposed for the determination of the rate of the astrophysically important $^{12}C(\alpha, \gamma)^{16}O$ reaction. A crucial aspect is the disentanglement of nuclear and Coulomb interactions on one hand and the separation of dipole and quadrupole contributions on the other. As a first step the resonant breakup via two well-known 2$^+$ states of $^{16}O$ was measured. The differential cross section of $^{208}Pb(^{16}O, ^{16}O*)^{208}Pb$ and the angular correlations of the fragments $^{12}C$ and $\alpha$ in the center of mass were measured and compared to theoretical predictions calculated in DWBA and the coupled-channel method. The best agreement was found for the state at 11.52 MeV associated to a one-step excitation from the ground state, while the 9.84 MeV requires coupling to the first-excited 2$^+$ state and is not well described