AssociateJ/ψ+γ production: a clean probe of gluon densities

Production of strange and charm particles by hadron-proton collisions is analyzed in terms of a fire-ball (FB) model assuming the multiplicity of secondaries of a given massm, to be proportional to the FB mass: n(m)M ^*, the FB kinematics being determined by the Feynman-Yang scaling, as in the case of production. It is found that (m)1/m ² and that, using this property together with the scaling, no-free-parameter fits to currently available data of strange and charm particles frompp and p collisions are satisfactory, as well as for the photoproduction of charm mesonD and charm hyperon _c .     

Hard form factors for meson-baryon strong couplings as derived from deep inelastic lepton scattering

As stimulated by earlier attempts for obtaining theNN andN form factors from the deep inelastic lepton scattering data, we extend the analysis by taking into account effects of additional mesons including, , ,K, andK ^*, with the coupling constants fixed by the lowenergy nucleon-nucleon and hyperon-nucleon scattering data. Contrary to an earlier claim that the NN andN form factor must be very soft (e.g., with the cutoff mass less than 500 MeV in the monopole form), we find, for example, that with all form factors parametrized in the dipole form, a universal cutoff mass of 1150 MeV in the/N sector and 1400 MeV in the/ sector yields predictions in excellent agreement with recently published neutrino data on the momentum fractions carried by thes, , and¯d quarks, as well as consistent with the sea-to-valence ratio extracted from the CDHS data and the Femilab E615 experiment. Similar results can also be obtained by using exponential cutoffs for all couplings, or by using monopole forms for some vertices while retaining dipole forms for the rest. The success of the mesonexchange picture in generating the strangeness content in a proton suggests an alternative understanding of the origin of sea quarks in the proton.We wish to thank G. Garvey, K. Holinde, L.-C. Liu, M. B. Johnson, M. Strikman, A. W. Thomas and Jochen Wambach for helpful conversations. W-Y. P. Hwang wishes to acknowledge the Alexander von Humboldt Foundation for a fellowship to visit Jülich for conducting research. His research works was also supported in part by the National Science Council of the Republic of China. The work of G. E. Brown is supported in part by a Humboldt award, in part by NATO Grant RG85/0093, and in part by the U.S. Department of Energy.     

Coulomb corrections to Delbrück scattering

The emission of high-energy-rays in the deexcitation of hot⁴⁰Ca and³⁹K nuclei formed in heavy-ion fusion reactions at excitation energyE _x 90 MeV has been studied. The high energy-rays were measured in coincidence with evaporation residues or light charged particles. The spectrum from the self-conjugated compound nucleus⁴⁰Ca shows an appreciable yield suppression in the Giant Dipole Resonance (GDR) energy region with respect to the³⁹K, due to isospin selection rules in the dipole-decay. The spectral line shapes of the spectra are well reproduced by using a statistical code which treats explicitly the isospin quantum number in evaluating level densities and transmission coefficients. The GDR parameters determined from the present coincidence measurements are in good agreement with the systematic in theA 40 mass region at lower bombarding energy based on the analysis of inclusive spectra.We thank M. Caldogno for technical support in the development of evaporation residues detectors. We acknowledge the participation of M. Anghinolfi, P. Corvisiero, M. Taiuti and A. Zucchiatti in the early stages of this work. Thanks are due to M. Kicinska-Habior for providing the isospin-dependent code. Discussions with B. Fornal are also gratefully acknowledged.     

Nuclear and electromagnetic fragmentation of 2.25-TeV197Au nuclei

We report the first measurement of the total charge-loss cross section _tot=_em+_nuc and partial cross sections (for Z=1, 2, ..., 9) of 11.4 A GeV¹⁹⁷Au nuclei in various targets. The large Coulomb barrier for Au reduces the electromagnetic contribution _em in a Pb target to only 18% of _nuc, compared with 70% for 14.5 A GeV²⁸Si and 120% for 200 A GeV³²S. With _em taken to be Z _T ^1.8 , _nuc can be fitted with _nuc=(A _P ^1/3 +A _T ^1/3 –b)², with b=0.83 and =59 mb, essentially the same as found at energies of 1 to 2 A GeV. Electromagnetic partial cross sections for Z=1 exceed 40 mb in the Pb, Sn, Cu, and Fe targets and are substantial for larger values ofZ in the heavier targets.We are indebted to D. Beavis and the staff of the Alternating Gradient Synchrotron at Brookhaven National Laboratory for producing the beam of 11.4 A GeV Au ions, to D. Snowden-Ifft for his efforts in developing the automated scanning system, and to S. Hirzebruch for a useful discussion. This work was supported in part by the Office of Energy Research, Office of High Energy and Nuclear Physics, Division of High Energy Physics, of the Department of Energy under contract No. DEAC03-76SF00098.     

Lifetime measurements and particle-rotor calculations for 42 105 Mo63

The half-lives of seven levels in¹⁰⁵Mo have been determined with high precision at the fission-product separator Josef. The-- triple coincidence method with plastic and BaF₂ scintillators was used for a determination of the time between the _q feeding of a level of interest and its depopulation. A value of _q =0.38 (1) for the deformation parameter has been deduced from the half-lives of the first and second excited states. The results of Particle-Rotor model-calculations with the Nilsson parameters=0.084 and=0.28 support the assignment of the Nilsson orbital [532] 5/2^– to the ground state of¹⁰⁵Mo.The authors acknowledge with pleasure fruitful discussions with Profs. W.R. Phillips, I. Ragnarsson and O.W.B. Schult.     

Excitation functions and isomeric ratios in the reaction130Te (α,xpyn) for α-particle energies between 15 and 37 MeV

The¹³⁰Te(,n)¹³³Xe,¹³⁰Te(,p)¹³³I,¹³⁰Te(,pn)¹³²I and¹³⁰Te(, n)¹²⁹Te excitation functions for alpha particle energies between 14.7 and 36.5 MeV are presented. Excitation functions for the last three reactions are measured for the first time and more consistent results for (, n) are obtained. The isomeric ratios for the ( n), (, pn) and (, n) reactions were deduced. Calculations based on different theoretical models of equilibrium and preequilibrium decay are compared with the experimental results and discussed. Acceptable presentation of the energy behavior of the measured isomeric ratios was obtained when higher angular momentum depletion for preequilibrium emitted particles was included. The absolute values of the isomeric ratios however remain overestimated.We want to express our gratitude to Prof. Ts. Vylov and Dr. V. Brudanin (Dubna) who supplied us with measurement equipment, to Dr. Chr. Necheva for taking part in the experiments, to the U-200 cyclotron staff and to the direction of the Laboratory of Nuclear Reactions (JINR) for making the irradiation possible and to Dr. E. Dobreva (Sofia) for fruitful discussion of the experimental method. We wish to express our gratitude also to Prof. M. Uhl and the NEA data bank for making the computer code STAPRE available to us and to Prof. J. Ernst (Bonn) for fruitful discussions. This project has been completed with the financial support of the Committee for Science at the Council of Ministers under contract No. 644.     

The new element 111

In an experiment carried out to identify element 110, we have observed an-decay chain, that can be unambiguously assigned to²⁶⁹110. In a scries of preexperiments the excitation functions of the fusion reactions⁵⁰Ti +²⁰⁸Pb²⁵⁸104^* and⁵⁸Fe +²⁰⁸Pb²⁶⁶108^* were measured with high precision in order to get the optimum projectile energies for the production of these heavy elements. The cross-section maxima of the 1n evaporation channels were observed at excitation energies of 15.6 MeV and 13.4 MeV, respectively. These data result in an optimum excitation energy of 12.3 MeV of the compound nucleus for the production of²⁶⁹110 in the reaction⁶²Ni +²⁰⁸Pb²⁶⁹110 + 1n. In irradiations at the corresponding beam energy of 311 MeV we have observed a decay chain of 4 subsequent a decays. This can be assigned to the isotope with the mass number 269 of the element 110 on the basis of delayed - coincidences. The accurately measured decay data of the daughter isotopes of the elements 108 to 102, obtained in the previous experiments, were used. The isotope²⁶⁹110 decays with a hair-life of (270 _-120 ⁺¹³⁰⁰ ) s by emission of (11.132±0.020) MeV alpha particles. The production cross-section is (3.3 _-2.7 ^+6.2 ) pb.     

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.     

Production of isomeric44V and42Sc in high energy heavy ion reactions

Beta-coincident-rays were measured from implanted⁴⁴V and⁴²Sc nuclei. These were selected after⁵⁸Ni+nickel reactions by means of the LISE3 spectrometer at GANIL. The production of the isomeric states was identified by detecting their typical-delayed-ray cascades. From the intensities of the detected-lines the ratio between isomer and ground-state production of⁴⁴V follows to be 1 to 3.0(4).on leave of absence from GSI Darmstadt.     

γ-decay of the particle-hole states with the highest spins in208Pb

²⁰⁸Pb has been excited with inelastic heavy ion scattering of 350 MeV⁶⁴Ni and 420 MeV⁸²Se on a thick²⁰⁸Pb target. With - coincidence measurements 2 new decays of the 10⁺ isomer, namely a 34.5 keVE2-transition to 8 ₂ ⁺ and a 857.7 keVE3 transition to 7^– have been found and the wavefunctions of the participating levels deduced. An observed gamma cascade of 295.3, 348.0, 865.4 and 340.2 keV on top of the 10⁺ isomer is assigned to the particle-hole states with the highest spins 14^– 6744.1 keV13^– 6448.9 keV12⁺ 6100.9 keV11⁺ 5235.6 keV10⁺ 4895.4 keV.This work has been supported in part through the agreement on scientific cooperation between Poland and Germany.     

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     

Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions

The total photofission cross section _,F for²³⁵U and²³⁸U has been measured in the energy range 50E 800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4 arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section _F , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections _,F normalized to the atomic numberA for both isotopes coincide, and agree in the-resonance region, within the systematic errors, with the socalledUniversal Curve _,T /A of the total photon absorption cross section _,T . At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D₁₃ resonance (at 710 MeV) as observed for the free proton. This complete suppression of the D₁₃ resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.Excerpt from D26 Supported by the Deutsche Forschungsgemeinschaft, SFB 201 Mainz     

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     

Maximum excitation energy in fusion-evaporation reactions from light particle multiplicity measurements in32S+58Ni at 25 MeV/A

By using two 4 detector systems for charged particles and neutrons, we measured the evaporated light particles emitted in coincidence with evaporation residues (ER) produced in the reaction³²S+⁵⁸Ni atE(³²S) 820 MeV. From the analysis of the light particle multiplicities as a function of the ER velocity, we extracted the maximum excitation energy reached in fusion evaporation reactions for the studied system.Supported by the European Community Programme Human Capital and Mobility     

Complete spectroscopy of51,52V via the50,51V(n, γ) reactions

The gamma-ray spectra emitted after thermal neutron capture in highly enriched⁵⁰V and^natV targets have been studied using in-pile targets at the ILL high flux reactor and pair and germanium detectors. The neutron binding energies in⁵¹V and⁵²V were determined to beB _n (⁵¹V)=11051.11(17) keV andB _n (⁵²V)=7311.22(26) keV. The thermal neutron capture cross-section in⁵⁰V was measured to be 21 _–2 ⁺⁴ b. From 724 lines attributed to⁵¹V, 330 transitions, comprising 90% of the-ray flux, were placed into the level scheme. Fifty-nine primary dipole transitions from the 11/2⁺ or 13/2⁺ capture states in⁵¹V were established from which the E1 strength distribution was deduced. The energy scaling of these primary transitions was found to follow the E1-giant dipole resonance dominance. Many new levels were established; a number of states proposed in previous (d,p) and (n,) work were confirmed from their primary population and decaying secondary radiations. The density of levels in the high spin (9/2I15/2) region was parametrized with the Fermi gas model. The spin distributions of⁵¹V were analyzed and a spin cut-off parameter =2.8 (3) was deduced. — A nearly complete level scheme of⁵²V up to 3.5 MeV excitation and similar results concerning the level density and the primary -ray spectrum were obtained in the⁵¹V (n, )⁵²V study.Supported by Deutsches BMFT under contract 06GÖ141     

Identification of beta-decay of150La

The -decay of¹⁵⁰La, the heaviest isotope of lanthanum, has been identified by observing -rays from mass separated activities obtained at KUR-ISOL. From the decay curves of 97.0 and 208.7 keV -rays in¹⁵⁰Ce and of Ce-K X-ray, the half-life of¹⁵⁰La has been determined as 0.51(3) s. This value is in agreement with theoretical predictions from microscopic theory.     

Excited states of111I and the observation of a 21 ns isomer

Proton rich nuclei close to ¹⁰⁰ Sn have been investigated inbeam using the NORDBALL detector array. A beam of 270 MeV⁵⁸ Ni was used to bombard a ⁵⁴ Fe target. Reaction channel separation was achieved with a 4 charged particle multi-detector set-up together with a 1 neutron detector wall placed in the forward direction. Gamma-ray transitions belonging to the ¹¹¹ I nucleus were identified for the first time. A level scheme constructed from --particle-coincidence analysis is proposed. The level structure is discussed within the framework of the shell model and the systematics of the heavier odd iodine nuclei.     

Total decay-energy measurement in the fusion reactions90Zr(89Y,p)178Pt and90Zr(89Y, α)175Ir

In the fusion reactions⁹⁰Zr(⁸⁹Y,p)¹⁷⁸Pt and⁹⁰Zr(⁸⁹Y,)¹⁷⁵Ir the sum energy of all emitted rays as well as the energy of the promptly emitted charged particle were measured. From these data the mass-excess values for the evaporation residues¹⁷⁸Pt and¹⁷⁵Ir were extracted to be(¹⁷⁸Pt)=(–32.4±1.1)MeV/c² and(¹⁷⁵Ir)=(–32.0±1.2) MeV/c². The method provides absolute mass values for nuclides far from stability which can be produced in fusion reactions as evaporation residues in the 1p or 1 channel. The sources of the experimental uncertainties of the method are discussed, and the potential for considerable improvements is outlined.Dedicated to P. Armbruster on the occasion of his 60th birthday     

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.     

Pre-equilibrium γ-ray emission in dissipative heavy-ion collisions

-rays are measured in coincidence with the dissipative complex fragments from the³⁵Cl +⁶⁴Ni reaction at 7.7 A MeV. Theoretical -ray coincidence spectra are determined through a fitting procedure using the contribution of the excited fragment statistical -decay calculated by means of the CASCADE code. Whereas the expected statistical spectra fit very well the data in the energy regionE =2 to 8 MeV, above this energy another emission mechanism in addition to the statistical decay has to be considered in order to reproduce the experimental spectra. Simulations based on the Vlasov equation suggest that this emission could come from the decay of dipole strength excited in the intermediate dinuclear system.The authors are greatly indebted with A. Boiano, A. Buccheri, M. Cipriano, F. Pagano and R. Rocco for their assistance during the set up of the experimental apparatus. Dr. J. Girard and the technical staff of the CEA/DAPNIA-DPhN are acknowledged for the valuable operation of the accelerator.