The low-energyD(α, γ)6Li and6Li+208Pb→D+α+208Pb cross sections

We have calculated theE1 andE2 contributions to the low-energyD(,)⁶Li fusion and to the⁶Li+²⁰⁸Pb D++²⁰⁸Pb Coulomb dissociation cross sections within a multichannel Resonating Group calculation based on many-body deuteron+ configurations and pseudo-states. For both reactions experimentally determined cross sections are reasonably well reproduced. We find that dipole capture contributes noticeably to the fusion cross sections atE500 keV, while it is negligible in the Coulomb dissociation data.     

The contrast gain in a guest-host nematic display due to a periodic boundary condition

The mean square tilt angle of a nematic slab with finite anchoring energy and periodic boundary conditions has been theoretically investigated, as a function of the slab geometry and of the reduced extrapolation length. If the anchoring strength is free-surfacelike, the contrast is affected by a loss 10% at room temperature if the ratio between the anchoring pitch and the cell thickness is 0.5.Glossary anchoring pitch - h cell thickness - /h - ( = x/, = y/h) reduced coordinates - (, ) local tilt angle - elastic constant - w_a anchoring energy anisotropy - b=/w _a de Gennes-Kleman extrapolation length - B=b/h reduced extrapolation length - T _NI nematic-isotropic transition temperature - :=(T/T _NI ) – 1 reduced temperature - easy axis direction - _MAX - _± ² mean square tilt angle along the boundary - () absorbance coefficients of the p-dye - r /: dichroic ratio - c contrast - G contrast gain - S order parameter     

Study of coherent diffractive production reactions ofp+C→[Y 0 K +]+C type and observation of narrow structures in ∑ (1385)0 K + and ∑0 K + effective mass spectra

In the experiments at the SPHINX facility in 70 GeV proton beam of the IHEP accelerator the coherent diffractive production reactions on carbon nucleip+C [(1385)⁰ K ⁺+C andp+C[⁰ K ⁺]+C were investigated. The evidences for new baryon states were obtained in the study of hyperon-kaon effective mass spectra in these two reactions:X (2050) with massM=(2052±6) MeV and width =(35 _–35 ⁺²² ) MeV inM[(1385)⁰ K ⁺] andX(2000) withM=1999±6 MeV and =91±17 MeV inM[⁰ K ⁺]. The unusual features of these massive states (small enough decay widths, anomalously large branching ratios for decays with strange particles emission) make them very serious candidates for cryptoexotic pentaquark baryons with hidden strangeness.     

The proton g9/2 isomer in theN=50 nucleus87Rb and M2 transition rates in85,87Rb

Low-lying states of theN=50 nucleus⁸⁷Rb have been investigated in the (, ') reaction measuring- and delayed-rf-coincidences. A half-life ofT _1/2=6(1) ns was obtained for the level at 1578.1 keV. This experimental result confirms the 9/2⁺ assignment and the proton 1g_9/2 single-particle character of this state. Experimental M2 transition strengths in^85,87Rb are compared with predictions of the shell model and the particle-core coupling model.This work was partly supported by the Bulgarian National Research Foundation.     

The decay of spin-isospin modes in a semi-infinite slab

The surface response for charge exchange (p, n) and (³He, T) reactions is studied in the-region using the semi-infinite slab model. The contribution to the total response from different decay channels, (NN, N, ), is calculated. These decay channels corresponds to the exclusive channels, (pp, p ⁺, ⁺), measured in recent (p, n) and (³He, T) experiments. The in-medium properties of the-resonance is taken into account by using microscopic calculations of the-width in nuclear matter. From the-width in nuclear matter a non-local imaginary-potential, as well as a local potential, is constructed for the semi-infinite slab model. The results in the semi-infinite slab model gives a qualitative understanding of the exclusive experiments. The exclusive (NN, N, ) channels are more sensitive, than the total response, tog-correlation parameters,-width and the absorption function used at the external vertex. Our calculations suggest low values of theg-correlation parametersg _N andg , (0.3). The results with the-width represented as a non-local or a local-potential are very similar, with only minor differences in the exclusive channels.Supported in part by the Swedish Natural Science Research Council and by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Nuclear Physics Division of the U.S. Department of Energy under Contract No. DE-ACO3-76SF00098     

Pion production in heavy ion reactions induced by16O and84Kr beams at 60 MeV per nucleon

Low energy ⁺ and ^– production cross sections have been measured in¹⁶O at 65 MeV/u and⁸⁴Kr at 60 MeV/u induced reactions on⁷Li,¹²C,²⁷Al,¹⁰⁸Ag and¹⁹⁷Au. The results are compared with a previous measurement obtained with¹⁶O at 93 MeV/u. Large deviations are observed between light and heavy ion data. At variance with¹⁶O, the ratios ^–/ ⁺ are independent of the target in the Krypton case. A change in the regime of the projectile-target mass scaling of cross-sections is observed with the heaviest projectile.Experiments performed at GANIL facility, F-14032 Caen, France     

The\bar pp \to e^ + e^ - reaction at rest and the hierarchy of the annihilation ranges

A new procedure is devised to evaluate the proton form-factor at the ¯pp threshold from experimental data on ¯ppe ⁺ e ^– annihilation at rest. Comparison of the ¯ppe ⁺ e ^– and¯pp ^+– processes reveals that annihilation ranges for various channels are ranked in line with quark dynamics.This work has been funded in part by the German Federal Minister for Research and Technology (BMFT) under the contract number 06HD756     

Spin and parity of isomeric and ground states of the doubly-odd nucleus184Au

Low-spin states in doubly-odd¹⁸⁴Au have been populated in the ⁺/EC decay of¹⁸⁴Hg produced by bombarding¹⁸⁴Sm targets with an 185 MeV⁴⁰Ar beam. Radioactive Hg nuclei were transported by a He jet system. A new level scheme has been established from --t and X--t coincidence measurements. Spin and parity values I=5⁺, I =2⁺ and I=3^– were assigned to the ground state and the two isomeric states of¹⁸⁴Au, respectively. The structure of these states is discussed using B(E1) values.     

Search for an enhanced production of low energy pions in C(p, π+)X,Cu(p, π+)X,and Cu(p, π∘)X reactions for 300 MeV≦Tp≦400 MeV

The observation of an enhancement in the production of low energy pions in the Cu(p, ⁺)X reaction is confirmed. The width of the bump is about 5 MeV around 350 MeV. A similar enhancement appears at 330 MeV for C(p, ⁺)X but the width has not been measured. An attempt to observe this behaviour in Cu(p, )X is described. From the data one cannot conclude about the existence of a structure around 350 MeV proton energy. The lack of resolution in the spectrometer may have washed out the small effect expected from ⁺ measurements.     

Nuclear structure calculation ofβ + β +,β +/EC and EC/EC decay matrix elements

Nuclear matrix elements for double positron emisson ( ^{+ +}), positron emission/electron capture ( ⁺/ EC) and double electron capture (EC/EC) in the 2 decay mode and for ^{+ +} and ⁺/EC decay in the 0 mode are calculated for the experimentally most promising isotopes⁵⁸Ni,⁷⁸Kr,⁹⁶Ru,¹⁰⁶Cd,¹²⁴Xe,¹³⁰Ba and¹³⁶Ce within pn-QRPA. We point out that the matrix element for the 2 ⁺/EC decay differs from the 2 ^{+ +} matrix element, an effect not considered previously. For the neutrino accompanied decays our calculation predicts for the ⁺/EC and the EC/EC mode half lives which are shorter typically by 4–7 orders of magnitude than those for the double positron emission. However, even for the best candidates typical values for 2 ⁺/EC (2 EC/EC) are still in the range of 10²² ((some) 10²¹) years. For 0 decay we have calculated all matrix elements relevant for both, the mass mechanism and the right-handed currents for the first time complete. A detailed discussion of the differences between the 0 ⁺⁺, the 0 ⁺/EC and 0 ^{– –} decay is given.This work is supported in part by a Grant-in-Aid for Scientific Research (05243204) from the Ministry of Education, Science and Culture. One of us (M.H.) would like to thank the Japanese Ministry of Education, Science and Culture (Monbusho) for financial support. He also acknowledges valuable discussions with S.S.     

Triple Regge analysis of inclusiveΛ production inK + p and π+ p interactions at 250 GeV/c

A triple Regge analysis is performedof inclusive production in the proton fragmentation region ofK ⁺+X and ⁺+X at 250 GeV/c. Slope and intercept of the leading strange meson trajectory are determined. The results obtained here are compared with those of other experiments.Partially supported by grants from CPBP 01.06 and 01.09.     

Measurement of the reaction γp → K0Σat photon energies up to 2.6 GeV⋆

The reaction p K⁰⁺ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the ⁺ as a function of the kaon production angle in the centre-of-mass system, cos^c.m._K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of p K⁺⁰. The ⁺ is polarized predominantly at cos^c.m._K 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.     

Measurement of γp→K + Λ and γp→K + Σ 0 at photon energies up to 1.47 GeV

The reactions pK ⁺ and pK ^{+ 0} have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the ⁰ polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and ⁰ is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I     

Partition temperatures ofK 0 andΛ 0 fromπ + p collisions

The rapidity distributions of inclusive ⁺ p ^–,K ⁰, ⁰ andK ^* (892) atP _1ab=16 GeV/c of CERN experiments, are analyzed using the covariant partition temperatureT _p model. In the fireball system, apart fromK ^* (892),T _p ^* m, no indication of thermal equilibrium, the average momentum ofK ⁰ and ⁰ being approximately equal and in the opposite direction, the entropy density is practically the same forK ⁰ and ⁰ but less than that of ^–. It is found that the principle of equipartition holds rather for the momenta of ,K, and in the fireball system.     

Observing b → s μ+μ− decays at hadron colliders

We examine the prospects for observing weak flavour-changing neutral current (FCNC) decays ofB mesons at hadron colliders, including effects of anomalousWWZ vertices. Since it is very difficult to measure the inclusive rate B X_s ^+– one should consider exclusive modes such as BK^{* + –} and B K^{+ –}. Even though this requires one to compute hadronic matrix elements, we show that experimentally observable quantities (ratios of decay rates) are not strongly parametrisation dependent. Some possibilities for reducing the theoretical uncertainties from other experimental data are discussed.     

A Rigorous Derivation of a Linear Kinetic Equation of Fokker–Planck Type in the Limit of Grazing Collisions

We rigorously derive a linear kinetic equation of Fokker–Planck type for a 2-D Lorentz gas in which the obstacles are randomly distributed. Each obstacle of the Lorentz gas generates a potential V( ), where V is a smooth radially symmetric function with compact support, and >0. The density of obstacles diverges as ^– , where >0. We prove that when 0< <1/8 and =2+1, the probability density of a test particle converges as 0 to a solution of our kinetic equation.     

Investigation of the fusion reaction27Al+236U→263105 at excitation energies of 57 MeV and 65 MeV

The neutron-deficient isotopes^257,258105 were produced in the reaction²⁷Al+²³⁶u in 6n and 5n evaporation channels, respectively. The evaporation residues emerging from the target were separated in-flight from the projectiles and from products of different nuclear reactions by the electrostatic separator VASSILISSA [1]. The isotopes were then implanted into position-sensitive silicon detectors and identified using the --correlation method. The measured production cross-section is (5n)=(0.45±0.20)nb atE _P =154 MeV and (6n)=(0.075±0.055) nb atE _P =163 MeV. These cross-sections are compared with data measured for the same isotopes in the more symmetrical reaction⁵⁰Ti+²⁰⁹Bi.     

Excitations in208Pb nearE x=5683 keV

A search for the recently proposed two-phonon octupole vibrational (2-POV) 4⁺ or 6⁺ state in²⁰⁸Pb at an excitation energy of 5683 keV has been performed using the²⁰⁷Pb(d,p),²⁰⁸Pb (p,p) and (,) reactions at high energy resolution. No evidence for a two-phonon excitation at this energy is found.This work was supported in part by the DFG under contract nr. II C4-Gr 894/2-1 and by the DFG-Graduiertenkolleg Struktur der Hadronen und Kerne under contract nr. Mu 705/3-1.     

Shell model yrast states in the many-particle nucleus 72 157 Hf85

In-beam- andn-measurements have for the first time identified excited states in the ₇₂ ¹⁵⁷ Hf₈₅ nucleus and have established its yrast levels up to 6.5 MeV and I=(51/2). The results of parameter-free 11-particle recoupling calculations in the framework of the shell model for the configurationsh ₁₁ ^2/8 f ₇ ^2/3 andh ₁₁ ^2/8 f ₇ ^2/2 h_9/2 are in excellent agreement with the observed levels up to 39/2 at 4.758 MeV. A weakly populated 52 ns 29/2⁺ yrast isomer at 2.876 MeV is assigned as the three-neutron configurationf_7/2h_9/2i_13/2.