Regular Series


Vol. 29 (1998), No. 11, pp. 2963 – 3526


all authors

M. Andersson, Chr. Bargholtz, E. Fumero, K. Fransson, L. Holmberg, K. Lindh, L. Mårtensson, D. Protic, I. Sitnikova, P.-E. Tegnér, P. Thörngren Engblom, G. Weiss, K. Wilhelmsen Rolander

Isospin Resolved Double Pion Production at Celsius

abstract

Two-pion production close to threshold has been measured in d+d and p+d reactions at CELSIUS. The results are compared to results at higher energies.


all authors

M. Andersson, Chr. Bargholtz, E. Fumero, K. Fransson, L. Holmberg, K. Lindh, L. Mårtensson, I. Sitnikova, P.-E. Tegnér, P. Thörngren Engblom, G. Weiss, K. Wilhelmsen Rolander

Study of the \(p + d \rightarrow ^3\)He \(+ 2\pi \) Reaction at CELSIUS

abstract

The exclusive \(p + d \rightarrow ^3{\rm He} + 2\pi \) reaction has been studied at CELSIUS at a beam energy of 477 MeV. Preliminary results indicate that the two pions are created mainly in an isospin \(T=1\) state.


Near-Threshold Meson Production in \(pp\) Collisions

abstract

A program of near threshold investigations of meson production channels in \(\vec {p} + p\) collisions has been carried out by the DISTO collaboration. Preliminary results are given. The ability of the experimental apparatus to eventually determine total and differential cross-sections is demonstrated. A number a spin observables will also be evaluated. The potentialities of these measurements for the understanding of two leading problems in meson physics: OZI rule violation in \(\phi \) production and status of the \(\eta '\) meson, are discussed.


all authors

R. Bilger, A. Bondar, W. Brodowski, H. Calen, H. Clement, J. Dyring, C. Ekström, K. Fransson, L. Gustafsson, S. Häggström, B. Höistad, J. Johanson, A. Johansson, T. Johansson, K. Kilian, S. Kullander, A. Kupsc, A. Kuzmin, P. Marciniewski, B. Morosov, A. Mörtsell, W. Oelert, A. Povtorejko, R.J.M.Y. Ruber, U. Schuberth, T. Sefzick, V. Sidorov, B. Shwartz, V. Sopov, J. Stepaniak, A. Sukhanov, A. Sukhanov, V. Tchernychev, A. Turowiecki, G. Wagner, Z. Wilhelmi, J. Zabierowski, A. Zernov, J. Zlomanczuk

Threshold Eta Production in \(pN\) Reactions at CELSIUS

abstract

The quasi-free p+n\(\rightarrow \)d+\(\eta \) reaction cross section has been measured at threshold using 1295 MeV protons in the CELSIUS storage ring and an internal cluster-jet deuterium target [1]. Excess energies from threshold to 10 MeV in the center of mass of the final \(d\eta \) system were covered. Approaching the threshold the cross section is enhanced compared to phase-space expectations. This behaviour is typical for a strong final state interaction.


all authors

R. Bilger, W. Brodowski, H. Calen, H. Clement, J. Dyring, C. EkstrÖM, K. Fransson, J. Greiff, L. Gustafsson, S. Häggström, B. Höistad, J. Johanson, A. Johansson, T. Johansson, A. Khoukaz, K. Kilian, I. Koch, S. Kullander, A. Kupsc, P. Marciniewski, B. Morosov, A. Mörtsell, W. Oelert, R. Ruber, U. Schubert, B. Shwartz, J. Stepaniak, A. Sukhanov, P. Sundberg, A. Turowiecki, G. Wagner, Z. Wilhelmi, J. Zabierowski, A. Zernov, J. Zlomanczuk

Two-Pion Production in Proton–Proton Collisions Near Threshold at CELSIUS

abstract

Two-pion production reactions in proton-proton collisions near threshold are measured using an internal cluster-jet hydrogen target and the WASA/PROMICE detector at the CELSIUS storage ring. Four out of the five possible two-pion production reactions are measured simultaneously.


all authors

Kai-Thomas Brinkmann, R. Bilger, A. Böhm, H. Clement, H. Dennert, S. Dshemuchadse, H. Dutz, W. Eyrich, C. Fanara, D. Filges, A. Filippi, H. Freiesleben, M. Fritsch, R. Geyer, A. Hassan, J. Hauffe, P. Herrmann, D. Hesselbarth, B. Hübner, P. Jahn, K. Kilian, H. Koch, J. Kress, J. Krug, E. Kuhlmann, S. Marcello, S. Marwinski, A. Metzger, W. Meyer, P. Michel, K. Möller, H.P. Morsch, H. Nann, B. Naumann, L. Naumann, A. Raimondo, E. Roderburg, M. Rogge, A. Schamlott, P. Schönmeier, W. Schroeder, M. Schulte-Wissermann, M. Steinke, F. Stinzing, G.Y. Sun, J. Wächter, G.J. Wagner, M. Wagner, S. Wirth, U. Zielinski, M. Pfuff, B. Sanz, W. Scobel

Three-Particle Final States Measured at the Pion Threshold with the COSY–TOF Spectrometer

abstract

The production of pions in pp collisions at beam energies of \(\leq \) 300 MeV has been studied with the COSY-TOF spectrometer, which was recently extended to flight paths of \(\approx \) 3 m for charged particles through the addition of a barrel section. Together with the bremsstrahlung channel, which was investigated in an earlier experiment, pion production exhausts the inelastic pp cross section at these energies. TOF allows the simultaneous study of all channels, the measurement of \(pn\pi ^+\) being facilitated by the neutron detector COSYnus. In this contribution, preliminary results on the pionic three-body final states are discussed.


all authors

H. Clement, R. Bilger, A. Denig, K. Föhl, J. Gräter, W. Kluge, R. Meier, J. Pätzold, M.G. Schepkin, G.J. Wagner

Pionic Double Charge Exchange

abstract

The pionic double charge exchange reaction on nuclei is reviewed. The observed systematics in the data points to a large sensitivity to short-range nucleon-nucleon correlations in nuclei — as anticipated since long for this genuine two-nucleon process. This is particularly true for non-analog transitions, which do not contain the mean-field driven analog route. In non-analog transitions the resonant \({\mit \Delta }{\mit \Delta }\) process dominates at high energies, whereas at low energies another resonance-like narrow structure appears, which has led to the hypothesis of a very special correlation, the formation of a \(\pi NN\) resonance decoupled from the \(NN\)-channel, the so-called \(d'\) resonance.


all authors

R. Dahl, L. Farhi, W. Augustiniak, J.L. Boyard, M. Drews, C. Ellegaard, C. Gaarde, T. Hennino, J. Jensen, J.C. Jourdain, R. Kunne, J. Larsen, P. Radvanyi, B. Ramstein, M. Roy-Stephan, M. Skousen, P. Zupranski

Evidence of Coherent \(\pi ^+\) Production in \((^3{\rm He},t)\) Reactions

abstract

Experimental evidence for coherent \(\pi ^+\) production in \(^{12}{\rm C}(^3{\rm He},t \pi ^+)^{12}{\rm C}\) charge exchange reactions at 2 GeV is presented. The excited states of carbon are found to be suppressed relative to the ground state. Angular distributions show that the momentum of the coherent pions is directed along the momentum transfer.


Direct Determinations of the \(\pi NN\) Coupling Constants

abstract

A novel extrapolation method has been used to deduce directly the charged \(\pi N N\) coupling constant from backward \(np\) differential scattering cross sections. The extracted value, \(g^2_c = 14.52(0.26)\) is higher than the indirectly deduced values obtained in nucleon-nucleon energy-dependent partial-wave analyses. Our preliminary direct value from a reanalysis of the GMO sum-rule points to an intermediate value of \(g^2_c\) about 13.97(30).


all authors

W. Garske, M.G. Betigeri, J. Bojowald, A. Budzanowski, A. Chatterjee, M. Drochner, J. Ernst, S. Förtsch, L. Freindl, D. Frekers, W. Garske, K. Grewer, A. Hamacher, S. Igel, I. Ilieva, R. Jahn, L. Jarczyk, G. Kemmerling, K. Kilian, S. Kliczewski, W. Klimala, D. Kolev, T Kutsarova, B.J. Lieb, G. Lippert, H. Machner, A. Magiera, R. Maier, H. Nann, E. Pentchev, H.S. Plendl, D. Prasuhn, D. Protic, B. Razen, P. von Rossen, B. Roy, R. Siudak, J. Smyrski, A. Strzałkowski, R. Tsenov, P.A. Żołnierczuk, K. Zwoll

Meson Production Studied with the GEM Detector

abstract

Measurements of proton induced meson production on hydrogen and deuterium targets using the GEM-detector at COSY are described. Preliminary estimates of the total cross section are presented. Results of the \(pp\rightarrow d\pi ^+\) and \(pp\rightarrow pp{\pi ^0}\) cross section are in agreement with previous findings. The total cross section of \(pd\rightarrow {^3{\rm He}}\pi ^0\) is consistent with results from pion absorption but a surprisingly large value was found at a beam momentum of 750 MeV/\(c\). The reaction \(pd \rightarrow {^3{\rm He}} \eta \) was measured at two beam energies and was identified by missing mass technique.


all authors

A. Gillitzer, H. Geissel, H. Gilg, A. Gillitzer, R.S. Hayano, K. Itahashi, N. Iwasa, P. Kienle, M. Knülle, M. Münch, G. Münzenberg, K. Oyama, W. Schott, T. Yamazaki

Discovery of Deeply Bound \(\pi ^-\) States in the \(^{208}\)Pb(\(d,^3\)He) Reaction

abstract

In the \(^{208}\)Pb (\(d,^3\)He) reaction at 600 MeV the population of deeply bound pionic states was observed for the first time. The states were identified as the pionic 2\(p\) and 1\(s\) states, respectively. The \(\pi ^-\) binding energies have been determined to be \(B_{\pi }(2p) = 5.28\pm {}0.11\) MeV and \(B_{\pi }(1s) = 7.04\pm {}0.32\) MeV. Using these binding energies a \(\pi ^-\) mass shift of \(+20\pm {}4\)MeV in nuclear matter at saturation density with the neutron excess of \(^{207}\)Pb was deduced.


Pion Production from \(dp\rightarrow dN\pi \)-Reactions with Deuteron Beams at CELSIUS

abstract

The reactions \(dp\rightarrow dp\pi ^o\) and \(dp\rightarrow dn\pi ^+\) have been measured at CELSIUS with deuteron beam energies between 436 MeV and 558 MeV. The observed energy and angular distributions show contributions of comparable size from different production mechanisms like quasi-free \(NN\rightarrow d\pi \) and a 3-nucleon \(dN\rightarrow dN\pi \) production mechanism.


Pion Production in Proton–Proton Collisions

abstract

Based on well established models for nucleon–nucleon and pion–nucleon scattering a model for pion production in proton–proton collisions is developed. The \(\Delta (1232)\) is taken into account explicitly and is found to play an important role even at energies close to production threshold.


Eta Production in Heavy-Ion Collisions and the DLS Di-Electron Enhancement

abstract

The Dalitz-decay contribution of neutral mesons to the di-electron invariant-mass spectrum at 1 \(A\)GeV is deduced from a systematics of meson production cross sections measured with the photon spectrometer TAPS. A comparison with recently published di-electron mass spectra of the DLS collaboration shows that \(\eta \) Dalitz decay does not exhaust the \(e^+e^-\) yield in the mass range of 0.2–0.5 GeV/\(c^2\).


Scalar Meson Spectroscopy from Three Channel Model Analysis of Meson–Meson Scattering

abstract

New isoscalar \(S\)-wave \(\pi \pi \) phase shift solutions have been analysed. Separable potential model of three coupled channels \(\pi \pi \), \(K \bar K\) and an effective \(2\pi 2\pi \) has been used. Spectrum of scalar resonances up to 1600 MeV has been evaluated.


Reinvestigation of \(pp\rightarrow pp\pi ^0\) and \(pp\rightarrow pp\eta \) at Threshold

abstract

\(pp\rightarrow pp\pi ^0\) and \(pp\rightarrow pp\eta \) were considered close to threshold. The pion production was found not only to be dominated by IA and rescattering contributions, but also strongly by box-diagrams, resonances and heavy-meson exchanges. New relevant contributions for the IA were found. The role of the offshell behaviour of nucleon-resonance couplings (\(P_{11}(1440), S_{11}(1535)\)) and of interference effects for the eta production was investigated. The results opened a large door for microsopic understanding of short range physics. A covariant model for \(pp\rightarrow pp\eta \) being under construction is going to be finished.


Multinucleon Pion Absorption Cross Sections on N, Ar and Xe in the Delta Resonance Region

abstract

The pion absorption reaction \(\pi ^{+}\) on Ar was studied at pion energies of 70, 118, 162, 239 and 330 MeV, and on N and Xe at 239 MeV. Absorption reaction channels with at least two energetic charged particles in the final state have been identified. Partial cross sections split according to the number of protons, neutrons and deuterons in the final state have been determined.


\(\pi N \rightarrow \eta N\) Cross Sections and the Influence of Baryonic Resonances

abstract

We present a coupled channel meson exchange model for investigating the structure of the \(N^{\ast }(1535)\) resonance and the coupling between \(\pi N\) and \(\eta N\). The curvature of the differential \(\pi N \rightarrow \eta N\) cross sections calls for a coupling between \(\pi N\) and \(\eta N\) in the \(D_{13}\) partial wave.


The Absorptive \(\rho ^{2}\) Terms in the \(\eta \) Optical Potential

abstract

The two-nucleon absorptive optical potential for \(\eta \)-mesons is calculated on the basis of recent experiments of \(\eta \) production in two nucleon collisions. The mesons are most likely to be absorbed on \( NN \) pairs in the spin \( 1 \) state.


Symmetries in Low Energy Pion Physics and the \(\pi NN\) Coupling Constant

abstract

We use a new value for the s-wave matrix element at threshold for the \(pp\rightarrow d\pi ^+\) reaction to determine the isoscalar \(\pi N\) scattering length. This is done by invoking symmetries and three ratios. Two of the ratios are measured and the third one is obtained from a new calculation. This leads to a new value for the \(\pi NN\) coupling constant \(f^2/4\pi = 0.0760\pm 0.0011\).


The \(\Delta N\)-Interaction in Hadronic Reactions on a Deuteron Target

abstract

The \(\pi ^+ d\) scattering and the \(d(p,n)\) charge exchange reaction are used to study the \({\mit \Delta } N\) interaction in the \({\mit \Delta }\) resonance energy region. Various observables, such as inclusive and exclusive cross sections, angular distributions, and analyzing powers, are calculated in a coupled channel approach and shown to be influenced by the \({\mit \Delta } N\) potential.


Threshold \(K\), \(\eta \), and \(\eta ^{\prime }\) Mesons Production in \(pp\) Interaction

abstract

The near threshold total cross sections for the \(pp\rightarrow pp\eta ^{\prime }\) and \(pp\rightarrow pp K^{+}K^{-}\) reactions has been measured at the COSY–11 facility. Possible production mechanisms are discussed. The energy dependence of the total cross section for the both reactions disagrees with predictions based on the phase space volume and the proton–proton final state interaction.


Meson–Meson and Meson–Baryon Interactions in a Chiral Non-Perturbative Approach

abstract

A qualitative account of the meson-meson and meson-baryon interactions using chiral Lagrangians and the inverse amplitude method in coupled channels is done. The method, imposing exact unitarity, proves to be a very useful tool to extend the information contained in the chiral Lagrangians at energies beyond the realm of applicability of chiral perturbation theory.


Two-Spin Measurements of Pion Production Near Threshold

abstract

We have recently measured single pion production cross sections in proton-proton scattering with both beam and target polarized. These measurements were made at four beam energies between 325 and 400 MeV using the “Cooler” storage ring at IUCF in Bloomington, Indiana. This covers a region relatively close to threshold (\(\eta \lt 1\)) where only a few partial waves can contribute to the scattering. The spin dependence can be used to separate the contributions due to specific partial waves, even if angular distributions are statistically limited. Data have been taken for both the neutral and charged pion production, but only neutral pion data will be presented here, along with plans and prospects for the future.


all authors

B. Razen, M.G. Betigeri, J. Bojowald, A. Budzanowski, A. Chatterjee, M. Drochner, J. Ernst, S. Förtsch, L. Freindl, D. Frekers, W. Garske, K. Grewer, A. Hamacher, M. Hawash, S. Igel, I. Ilieva, R. Jahn, L. Jarczyk, G. Kemmerling, K. Kilian, S. Kliczewski, W. Klimala, D. Kolev, T. Kutsarova, B.J. Lieb, G. Lippert, H. Machner, A. Magiera, R. Maier, H. Nann, H.S. Plendl, D. Protic, B. Razen, P. von Rossen, B. Roy, R. Siudak, J. Smyrski, A. Strzałkowski, R. Tsenov, P.A. Żołnierczuk

Beam Energy Calibration with Meson Production

abstract

The magnetic spectrometer BIG KARL is used to get energy calibration fix-points for the external beam of COSY-Jülich. These fixpoints were obtained by measuring the meson-production reaction \(pp \rightarrow d\pi ^+ \) close to threshold and at the beam momentum, where the forward pions and the backward deuterons have the same momentum.


Final State Interaction in Near-Threshold Meson Production

abstract

It is discussed what kind of information other than the FSI parameters can be extracted from near-threshold meson production.


Application of \(\rho \)–\(\omega \) Mixing in CP Violating \(B\)-Decays

abstract

We show how \(\rho \)–\(\omega \) mixing can be exploited to constrain the strong phase difference between tree and penguin contributions to the decays \(B^\pm \rightarrow \pi ^+\pi ^-\rho ^\pm \) and to enhance the CP violation. The resulting CP violation is greater than 20% and very stable against theoretical uncertainties. Moreover, it should be possible to extract the sign of the CKM angle, \(\alpha \), unambiguously.


Isoscalar S-Wave \(\pi \)–\(\pi \) Interaction in the Nuclear Medium

abstract

The s-wave isoscalar \(\pi \pi \) scattering amplitude in a nuclear medium has been evaluated using a non-perturbative unitary coupled channels method and the standard chiral Lagrangians. The method is successful describing the \(\pi \pi \) properties in vacuum, in the scalar-isoscalar channel up to 1.2 GeV giving rise to poles in the \(T\) matrix for the \(f_0(980)\) and the \(\sigma \). The extension of the method to the nuclear medium implies the renormalization of the pions in the medium and also the introduction of interaction terms related to contact terms in the \(\pi N \rightarrow \pi \pi N\) reaction.


all authors

J. Złomańczuk, R. Bilger, W. Brodowski, H. Calén, H. Clement, J. Dyring, C. Ekström, G. Fäldt, K. Fransson, L. Gustafsson, S. Häggström, B. Höistad, M. Jacewicz, A. Johansson, J. Johansson, T. Johansson, A. Khoukaz, K. Kilian, I. Koch, S. Kullander, A. Kupsc, P. Marciniewski, B. Morosov, A. Mörtsell, W. Oelert, R.J.M.Y. Ruber, U. Schuberth, B. Shwartz, J. Stepaniak, A. Sukhanov, P. Sundberg, A. Turowiecki, G.J. Wagner, Z. Wilhelmi, C. Wilkin, J. Zabierowski, A. Zernov

Near-Threshold Pion Production in \(pN\) Collisions at CELSIUS

abstract

The \(pp\to pp\pi ^0\) and \(pn\to pp\pi ^-\) reactions have been measured at 310, 320 and 340 MeV using the CELSIUS proton beam and \(^1\)H and \(^2\)H internal cluster-jet targets. The \(\pi ^0\) production at 310 MeV has been fully analyzed and a significant deviation from isotropy found in the pion angular distributions. This increases at small excitation energies of the final proton pair, suggesting that d-wave pion production is important even close to threshold. Evidence is also found for some P-wave excitation in the final \(p\)–\(p\) system.


The \(\pi ^-p\rightarrow \gamma \gamma n\) Reaction and Pion Compton Scattering

abstract

We propose to measure the two-photon capture mode of pionic hydrogen using the RMC pair spectrometer at the TRIUMF cyclotron. Currently, only an experimental upper limit of B.R. \(\leq 5.5\times 10^{-4}\) is available for the \(\gamma \gamma \) capture mode Our new data will critically test the theoretical calculations and the intriguing predicted dominance of the \(\pi \pi \rightarrow \gamma \gamma \) annihilation graph. More speculatively, since crossing symmetry relates \(\pi \pi \rightarrow \gamma \gamma \) to \(\gamma \pi \rightarrow \gamma \pi \), this threshold reaction may be a novel probe of the pion’s electric polarizability. We show results of our 1997 engineering run and Monte Carlo studies for the two–photon capture mode of pionic hydrogen and carbon. We also present our preliminary upper limit for the B.R. \([\pi ^-p\rightarrow \gamma \gamma n] \leq 2.8\times 10^{-4}\).


Physics with the Upgraded CERES Detector

abstract

The possible occurance of a phase transition from hadronic to quark matter and a related restoration of chiral symmetry have been predicted within the framework of QCD. On the experimental side the investigation of dilepton production in heavy ion collisions is of particular interest, because electromagnetic radiation escapes the reaction volume without final state interactions and, therefore, provides information about the early hot and dense stage of the reaction. The significant enhancement of the dilepton yield observed in S+Au and Pb+Au collisions at SPS energies cannot be explained without the inclusion of non-trivial modifications of the in-medium properties of the vector mesons. To discriminate between different theoretical approaches, an improvement of the experimental data in terms of mass resolution and statistics is needed. For this purpose, the CERES detector at the CERN-SPS will be upgraded with a radial drift TPC located downstream of the existing spectrometer.


Status of Effective Field Theory of \(NN\) Scattering

abstract

I review recent progress in developing a systematic power counting scheme for scattering processes involving more than one nucleon.


all authors

W. Borgs, W. Cassing, M. Hartmann, H. Hodde, L. Jarczyk, B. Kamys, H.R. Koch, P. Kulessa, R. Maier, M. Matoba, H. Ohm, D. Prasuhn, K. Pysz, Z. Rudy, O.W.B. Schult, A. Strzałkowski, I. Zychor

\(K\)-\({\mit \Lambda }\) Production in \(p\)+Bi Interaction

abstract

The production of \({\mit \Lambda }\) hypernuclei was studied in p+Bi reaction. The lifetime of the produced heavy hypernuclei was measured by observation of delayed fission using the recoil shadow method. The measurements were performed at 1.9 GeV proton energy whereas the background was determined at 1.0 GeV. Upper limit for cross section for reported elsewhere component of a lifetime 2700 ps was estimated.


Meson Production and Meson Properties at Finite Nuclear Density

abstract

The properties of \(\pi , \eta , K^+\) and \(K^-\) mesons are studied in nuclear reactions from SIS to SPS energies within the covariant transport approach HSD in comparison to the experimental data. Whereas the pion, \(\eta \) and kaon abundancies and spectra indicate little or vanishing self energies for these mesons in the medium, antikaons (as well as antiprotons) are found to experience strong attractive potentials in nucleus–nucleus collisions at SIS energies. However, even when including these potentials the \(K^+\) and \(K^-\) spectra at AGS energies are noticeably underestimated showing an experimental excess of strangeness that points towards a nonhadronic phase in these reactions. On the other hand the \(K^+, K^-\) production at SPS energies is well described by the hadronic approach without incorporating any parton degrees of freedom.


\({K}^+\) Flow in Heavy Ion Collisions at SIS Energies

abstract

Experimental data on \({K}^+\) sideward flow measured with the FOPI detector at SIS/GSI in the reactions \({\rm Ni+Ni}\) at 1.93\(\cdot A\) GeV and \({\rm Ru+Ru}\) at 1.69\(\cdot A\) GeV are presented. They are compared to different transport model predictions investigating the effects of in-medium modification of kaon properties.


all authors

F. Dohrmann, K. Bethge, W. Enghardt, O. Fateev, C. Garabatos, E. Grosse, C. Müntz, W. Karig, W. Koenig, L. Smykov, M. Sobiella, A. Steigerwald, H. Stelzer, J. Stroth, J. Wüstenfeld, Y. Zanewsky, A. Zentek

A Low-Mass Drift Chamber System for the HADES-Spectrometer

abstract

A new high resolution (\(\Delta M/M\lt 1\%\)) and high acceptance (\(45~\%\)) di-electron spectrometer (HADES) has been designed to investigate in-medium properties of hadrons. For tracking of all charged particles (in particular with sufficient resolution for electrons) a system of 24 low-mass drift chambers (Helium based counting gas and Aluminum field and cathode wires), arranged in four tracking planes, is used. Design aspects of the chambers are reported. Results of performance optimization using various prototype detectors are discussed, including results of an ageing test. Stable operation in the high-multiplicity environment of heavy ion collisions, and a spatial resolution of \(70~\mu \rm m(\sigma )\) over 80 % of a cell have been demonstrated in two beam experiments.


Meson–Nucleon Scattering and Vector Mesons in Nuclear Matter

abstract

The properties of vector mesons in nuclear matter are discussed. I examine the constraints imposed by elementary processes on the widths of \(\rho \) and \(\omega \) mesons in nuclear matter. Furthermore, results for the \(\rho \)- and \(\omega \)-nucleon scattering amplitudes obtained by fitting meson-nucleon scattering data in a coupled-channel approach are presented.


Baryon–Baryon Mixing in Hypernuclei

abstract

Implications of few-body hypernuclei for our understanding of the baryon-baryon interaction are examined. Octet-octet coupling effects not present in conventional, non strange nuclei are the focus. The need to identify strangeness \(-2\) hypernuclei to test model predictions is emphasized.


On the Influence of Baryonic Resonances on the Dynamics of Kaons

abstract

The influence of the Delta lifetime to kaon flow is investigated within the framework of the QMD model.


Chiral Disorder and Diffusion of Light Quarks in the QCD Vacuum

abstract

We give a pedagogical introduction to the concept that light quarks diffuse in the QCD vacuum following the spontaneous breaking of chiral symmetry. By analogy with disordered electrons in metals, we show that the diffusion constant for light quarks in QCD is \(D=2F_{\pi }^2/|\left \lt \bar {q}q\right \gt |\) which is about \(0.22\) fm. We comment on the correspondence between the diffusive phase and the chiral phase as described by chiral perturbation theory, as well as the cross-over to the ergodic phase as described by random matrix theory. The cross-over is identified with the Thouless energy \(E_c=D/\sqrt {V_4}\) which is the inverse diffusion time in an Euclidean four-volume \(V_4\).


Chiral Dynamics in Dense Matter: In-Medium Meson Spectra

abstract

We summarize recent developments related to meson spectra in a dense nuclear medium. Our primary emphasis is on vector meson mass spectra in matter and their role as possible indicators of a tendency toward restoration of spontaneously broken chiral symmetry.


Dilepton Production in Relativistic Heavy Ion Collisions

abstract

In this contribution we will discuss the production of low mass dileptons. The current theoretical understanding will be briefly reviewed, emphasising possible in medium effects.


How to Trace Heating and Cooling of Nuclear Matter?

abstract

Selected studies of different phases of the violent collisions between heavy ions at the intermediate energies are reviewed.


Coulomb Effects in Charged Particle Spectra from Heavy Ion Collisions at AGS and SIS

abstract

Data from the AGS experiment E866 on charged particles emitted in central Au+Au collisions at 10.8 \(A\)GeV incident energy is reviewed. The study of spectral shapes indicates the presence of collective transverse flow and — in particular for charged pions — of Coulomb final state interaction between emitted particles and the nuclear charge distribution. The comparison to SIS pion data measured with KaoS elucidates the role of charged pions to probe nuclear reaction dynamics at lower incident energies.


Restoration of Chiral Symmetry in Nucleus–Nucleus Collisions Around 10 GeV/u

abstract

Using hadron phase-space distributions obtained with the quark-gluon string model, we have studied [1] the modification of the quark condensate \(\left \lt \bar {q}q\right \gt \) in relativistic nucleus–nucleus collisions and estimated the 4-volume, where the ratio of \(\left \lt \bar {q}q\right \gt \) over its vacuum value \(\left \lt \bar {q}q\right \gt _0\) is small (\(0.1 \lesssim \left \lt \bar {q}q\right \gt /\left \lt \bar {q} q\right \gt _0\lesssim 0.3\)) and the scalar baryon density exceeds its value for normal nuclear density by 50%. As a function of beam energy this 4-volume rises sharply in the region \(1\) GeV \(\lesssim E_{\rm lab}/A \lesssim 4\) GeV and decreases at higher energies. Based on this estimate it is concluded that moderate beam energies on the order of 10 GeV/u are favourable for studying the restoration of chiral symmetry in baryon-rich matter. At higher energies chiral symmetry restoration is dominated by mesons. Therefore a dedicated machine in the energy regime around 10 GeV/u is needed to study chiral symmetry restoration in baryon-rich matter. Such studies would be complementary to those at SPS-, RHIC- and LHC-energies on meson-dominated chiral-symmetry restoration.


Time Evolution of Pion Emission in Heavy Ion Collisions at SIS Energies

abstract

Using a magnetic spectrometer pions, kaons and protons were detected in mass-symmetric heavy ion reactions from C+C to Au+Au and at incident energies between 0.6 and 2.0 A\(\cdot \)GeV. The center-of-mass pion spectra deviate from a Boltzmann distribution for all collision systems. Results are presented indicating that high-energy pions are emitted at an early stage of the collision. This is based on (i) a comparison of \(\pi ^+\) and \(\pi ^-\) spectra and (ii) the shielding of pions by spectator matter in peripheral collisions.


Particle Production Systematics from SIS to SPS

abstract

The mean multiplicity of negatively charged hadrons per participant nucleon for central nucleus–nucleus collisions is lower than the corresponding multiplicity for nucleon–nucleon interactions for \(p_{\rm LAB} \le \) 15\( A\,\)GeV/\(c\), whereas the result at 158–200 \(A\,\)GeV/\(c\) is above the corresponding nucleon–nucleon multiplicity. The ratio of strange particle multiplicity to pion multiplicity is larger for central nucleus–nucleus collisions than for nucleon–nucleon interactions at all studied energies. Single particle momentum spectra and two particle correlations suggest a significant transverse flow at thermal freeze-out for central heavy ion collisions.


Kaon and Antikaon Production in Nucleus–Nucleus Collisions at SIS

abstract

The production and propagation of kaons and antikaons has been studied in symmetric nucleus–nucleus collisions in the SIS energy range. The \(K^+\) multiplicity was found to increase more than linearly with the mass number \(A\) of the collision system. This behaviour is due to collective effects such as multiple hadron–hadron interactions. In noncentral Au+Au collisions, the \(K^+\) mesons are preferentially emitted perpendicular to the reaction plane. The \(K^-/K^+\) ratio from \(A+A\) collisions at equivalent beam energies is found to be 1–2 orders of magnitude larger than the corresponding ratio from \(p+p\) collisions. This effect is an experimental signature for an enhanced \(K^-\) production in \(A+A\) collisions. In order to reproduce the data, transport models consider a reduction of the \(K^-\) mass in the dense nuclear medium.


Dilepton Measurements in Nucleon–Nucleon and Nucleus–Nucleus Interactions from E\(_{\rm beam}\)=1 to 5 GeV

abstract

Measurements of dileptons in nucleus–nucleus interactions at 1 GeV/\(A\) and in \(p+p\) and \(p+d\) interactions from 1 to 5 GeV are reviewed. The status of attempts to model dilepton production at these energies is briefly discussed. Current models are found to under-predict dilepton production in the invariant mass range between the \(\pi ^0\) and the \(\rho -\omega \) masses. Possible avenues for investigation of the experimental “excess” in dilepton production are discussed.


Photoproduction of Mesons in Nuclei

abstract

We calculate cross sections for inclusive pion and eta photoproduction in nuclei in the energy range from 300 to 800 MeV within the framework of a semi-classical BUU transport model. Our results are compared to existing experimental data.


all authors

C. Furget, D. Abbott, A. Ahmidouch, H. Anklin, J. Arvieux, J. Ball, S. Beedoe, E.J. Beise, L. Bimbot, W. Boeglin, H. Breuer, R. Carlini, N.S. Chant, S. Danagoulian, K. Dow, J.E. Ducret, J. Dunne, L. Ewell, L. Eyraud, M. Garçon, R. Gilman, C. Glashausser, P. Gueye, K. Gustafsson, K. Hafidi, A. Honneger, J. Jourdan, S. Kox, G. Kumbarski, L. Lu, A. Lung, D. Mack, P. Markowitz, J. McIntyre, D. Meekins, F. Merchez, J. Mitchell, S. Mtingwa, H. Mrktchyan, D. Pitz, L. Qin, R. Ransome, J.S. Real, P.G. Roos, P. Rutt, W. Schmidt, R. Sawafta, S. Stepanyan, E.J. Stephenson, R. Tieulent, E. Tomasi-Gustafsson, W. Turchinetz, K. Vansyoc, J. Volmer, E. Voutier, W. Vulcan, C. Williamson, S.A. Wood, C. Yan, J. Zhao, W. Zhao

Tensor Polarization Measurement in Elastic Electron–Deuteron Scattering at Large Momentum Transfer

abstract

The three tensor polarization components (t\(_{20}\), t\(_{21}\) and t\(_{22}\)) of the recoil deuteron in elastic electron-deuteron scattering have been measured in the range of 4-momentum transfer \(Q~=~4.1\)–\(6.8\) fm\(^{-1}\). The experiment was performed with the multi-GeV, high intensity electron beam available at the Jefferson Laboratory and using the tensor deuteron polarimeter POLDER. These new data are used to separate the charge \(G_C\) and quadrupole \(G_Q\) form factors at large momentum transfer and provide additional constraints on theoretical models.


The Radiative Muon Capture Program at TRIUMF

abstract

We describe recent measurements of radiative muon capture on hydrogen, \(^3\)He and \(^{58,60,62}\)Ni using the RMC pair spectrometer at the TRIUMF cyclotron laboratory. Our determinations of the induced pseudoscalar coupling of the nucleon’s weak current are discussed.


Electroproduction of Mesons in the First Resonance Region

abstract

An experimental programme has been carried out at ELSA (ELectron Stretcher Accelerator) to investigate the four momentum transfer dependence of the \(N\) to \({\mit \Delta }\) transition. In a series of electron scattering coincidence experiments on \(^1\)H and \(^2\)D the \(-K^2\)-range from \(0.04\,{\rm GeV}^2/c^2\) to \(0.8\,{\rm GeV}^2/c^2\) was sampled by measuring the \(\vartheta ^*_N\) and \(\varphi ^*_N\) angular distributions of the double differential pion production cross sections. The so-determined ratio of the structure functions \(R_{\rm LT}/R_{\rm TT}\) at a–\(K^2\!=\! 0.2\,{\rm GeV}^2\!/\!c^2\) is one of the first results obtained with the ELAN (Electron scattering collaboration at Bonn) time-of-flight spectrometer.


all authors

F. Klein, J. Barth, M. Bockhorst, W. Braun, R. Burgwinkel, K.H. Glander, S. Goers, J. Hannappel, N. Jöpen, U. Kirch, F. Klein, F.J. Klein, D. Menze, W. Neuerburg, E. Paul, W.J. Schwille, M.-Q. Tran, R. Wedemeyer, F. Wehnes, B. Wiegers, F.W. Wieland, J. Wißkirchen, J. Ernst, H.G. Jüngst, H. Kalinowsky, E. Klempt, J. Link, H.V. Pee, R. Plötzke, M. Schumacher, F. Smend, H.-N. Tran, C. Bennhold, A. Kozela, J. Smyrski

Recent Results on Meson Production from SAPHIR

abstract

The SAPHIR detector is a magnetic spectrometer for multiparticle final states attached to the 3.5 GeV electron accelerator ELSA. The experiments focus on the photoproduction of associated strangeness in \(\gamma \)p \(\rightarrow K^{+}{\mit \Lambda }\), \(K^{+}{\mit \Sigma }^{0}\) and \(K^{0}{\mit \Sigma }^{+}\) final states and the production of the lightest vector mesons \(\rho \), \(\omega \) and \(\phi \). In the \(K^{+}{\mit \Lambda }\) cross section a steep threshold behaviour is observed which is different in the case of \(K^{+}{\mit \Sigma }^0\) which is reflected in the differential cross section. Contrary, \({\mit \Lambda }\) and \({\mit \Sigma }\) polarizations show little variation with energy. A bump in the \(t\)-distribution for \(\omega \)-production for \(E_\gamma \simeq 1.5~\rm {GeV}\) could be an indication for a resonance while the production of \(\phi \)-mesons appears fully diffractive down to energies below 2 GeV.


Spin Self-Analysis of Photoproduced Meson and Baryon Resonances

abstract

Spin-1 mesons are self-analyzing with respect to their tensor polarization, and spin-2 mesons are self-analyzing with respect to their rank-2 and their rank-4 polarization. Also spin-\(3/2\) baryons are self-analyzing with respect to their rank-2 polarization. These properties make, for example, spin-correlations involving the vector-meson’s vector polarization inaccessible directly with present experimental techniques.


New Results from Meson Photoproduction Experiments with TAPS at MAMI

abstract

Some recent experimental results for the photoproduction of neutral mesons from the deuteron and the measurement of inclusive-, coherent-, and double-\(\pi ^0\)-photoproduction from heavy nuclei are disscussed. The results were obtained in a series of experiments carried out with the TAPS-detector at the Mainz MAMI accelerator in 1992. Some first preliminary results from a second experimental campaign with TAPS at MAMI in 1996 are presented.


Photoproduction of \({\pi }{\pi }\) and \(K\overline {K}\) Pairs

abstract

\(S\)-wave photoproduction of \(\pi ^+\pi ^-\) and \(K^+K^-\) pairs on hydrogen is studied. Coupled channel final state interactions between different pseudoscalar mesons are included. Effective mass and momentum transfer distributions as well as total cross sections are calculated. Effective mass distributions in the Born approximation are structureless but the final state interactions produce peaks and dips near the energies corresponding to the scalar resonances \(f_0\)(980) and \(f_0\)(1400). Calculations are performed in the effective mass region between the \(\pi \pi \) threshold and 1.6 GeV in the range of the momentum transfer squared up to 2 (GeV/\(c)^2\). The photon energy dependence of the total cross sections is studied between 2 and 15 GeV. Valuable information on the \(f_0\)(980) resonance structure can be extracted from data. These calculations are closely related to the experimental program of the CEBAF accelerator in USA.


Photoproduction of \(\eta ^{\prime }\)-Mesons with SAPHIR

abstract

The \(\eta ^{\prime }\) production was studied by searching for 5-track events from the decay chain \(\gamma {\rm p} \rightarrow {\rm p}\eta ^{\prime }\;\rightarrow {\rm p}\pi ^+\pi ^-\eta \;(43.7\%)\; \rightarrow {\rm p}2\pi ^+ 2\pi ^- \pi ^0/\gamma (23.2\%/4.78\%)\) having a total decay probability of 10.1% for the \(\pi ^0\) branch. From this decay with only one neutral particle much less background is expected than from the 3-track decays of the \(\gamma {\rm p} \rightarrow {\rm p} \eta ^{\prime }\) reaction, namely \(\rightarrow {\rm p}\pi ^+\pi ^-\eta (\rightarrow 2\pi ^0/2\gamma )\) or the decay \({\rm p}\eta ^{\prime } \rightarrow {\rm p}\rho \gamma \; \rightarrow {\rm p}\pi ^+\pi ^-\gamma \).


Evidence for a Glueball — \(q\overline {q}\) Filter

abstract

QCD predicts that particles composed of bound states of gluons should exist. Experiments WA76, WA91 and WA102 have performed a dedicated search for these states using the CERN Omega Spectrometer. Evidence for a glueball — \(q\overline {q}\) filter is presented based upon a kinematical cut on the difference in transverse momentum of the exchanged particles, \(dP_{T}\). It is shown that at small \(dP_{T}\) undisputed \(q\overline {q}\) mesons are suppressed, whereas glueball candidates are enhanced.


Pseudoscalar Meson-Photon Transition Form Factors

abstract

I discuss the perturbative calculation of \(P\gamma \) transition form factors, with \(P=\pi ^0,\eta ,\eta ',\eta _c\).


Mixing Angles and Electromagnetic Properties of Ground State Pseudoscalar and Vector Meson Nonets in the Light-Cone Quark Model

abstract

Both the mass spectra and the wave functions of the light pseudoscalar (\(\pi ,K,\eta ,\eta '\)) and vector(\(\rho ,K^{*},\omega ,\phi \)) mesons are analyzed within the framework of the light-cone constituent quark model. A gaussian radial wave function is used as a trial function of the variational principle for a QCD motivated Hamiltonian which includes not only the Coulomb plus confining potential but also the hyperfine interaction to obtain the correct \(\rho -\pi \) splitting. The mixing angles of \(\omega -\phi \) and \(\eta -\eta '\) are predicted and various physical observables such as decay constants, charge radii, and radiative decay rates etc. are calculated. Our numerical results have a good agreement with the available experimental data.


The Status of Scalar Mesons: Evidence for Glueballs

abstract

A series of new scalar and tensor mesons has been discovered at LEAR, mostly in the Crystal Barrel experiment. One of these states, the \(f_0(1500)\), has unusual properties: a comparatively narrow width and a decay pattern which seems incompatible with SU(3) relations based on the OZI rule. In a naive quark model a \(s\bar s\) state should be expected at this mass but the \(f_0(1500)\) partial decay width to \(\bar {{K}}{K}\) is small. This leads to the conclusion that the state is supernumerous and must interpreted as the ground-state scalar glueball mixing with nearby quarkonia. Alternative interpretations are however not yet ruled out.


On Self-Consistency in the Theory of Finite Fermi Systems

abstract

It is shown how single-particle and collective excitations can be treated consistently in the framework of an extended Landau–Migdal theory.


\(B\) Meson Spectroscopy

abstract

A review of recent experimental progress in the \(B\) meson spectroscopy is given. The results concerning the masses, production rates at \(Z^0\) energy and helicity of beauty mesons are presented and compared with theoretical predictions.


Gluonic Excitations in Mesons

abstract

We report on some interesting recent theoretical and experimental advances on \(J^{PC}\) exotics and hybrid mesons. These are the decay selection rules governing \(J^{PC}\) exotic decay, the experimental evidence for a \(J^{PC} = 1^{-+}\) exotic in \(\eta \pi \) and \(\rho \pi \), and the production of charmonium hybrids at forthcoming \(B\)-factories.


Diffractive Production of Vector Mesons at HERA

abstract

Recent measurements of the diffractive production of neutral vector mesons at HERA are reviewed. The issue of transition between ‘soft’ and ‘hard’ underlying production mechanism is discussed in context of the phenomenology of Regge theory and the predictions of the perturbative QCD.


Meson Formation in Photon-Photon Collisions at LEP with the L3 Detector

abstract

We report on the study of several meson resonances and on \(\rho ^{0} \rho ^{0}\) production in photon–photon collisions with the L3 detector at LEP. The \(\eta '(958)\) and its form factor are studied in the \(\pi ^{+} \pi ^{-} \gamma \) final state. The \(\pi ^{+} \pi ^{-} \pi ^{0}\) final state shows evidence for the formation of the \(a_{2}(1320)\) and its radial recurrence around 1750 MeV. The formation of the \(f_{2}'(1525)\) is studied in the \(K^{0}_{s} K^{0}_{s}\) final state. The \(\chi _{c2}\) is observed in its decay to \(\gamma {\rm J}/\psi \). The observation of diffractive \(\rho ^{0} \rho ^{0}\) events is compared with MC predictions for \(W_{\gamma \gamma }\geq 3\) GeV.


Production of c and b Flavored Mesons and Their Decays at LEP

abstract

The production rates of D\(^0\), D\(^+\), D\(_s^+\), \(\Lambda _c\), D\(^{*+}\), D\(^{*0}\), D\(_s^{*+}\), D\(^{**}\) and D\(_s^{**}\) hadrons in Z\(^0\rightarrow c\overline {c}\) and Z\(^0\rightarrow b\overline {b}\) measured by the LEP collaborations are presented. The measurements of the number of produced charm quarks in \(b\)-hadron decays and the partial width of the Z\(^0\) going into a charm quark pair \({\mit \Gamma }_{c\overline {c}}\,/{\mit \Gamma }_{\rm had}\) derived from charm production rates are discussed. The LEP measurements of the semileptonic branching ratio Br(B\(\rightarrow l\)) are compared with results from CLEO and with recent theoretical calculations. From the production rates of pseudoscalar and vector mesons the ratio V/(V+P) in the D and the D\(_s\) sectors are determined and the results are compared with simple spin counting predictions. Finally the first observation of the radially excited D\(^{*'}\) meson is discussed.


Experimental Results on Polarized Nucleon Structure Functions

abstract

Experimental results of deep inelastic scattering of polarized leptons from polarized target nucleons are reviewed. Accurate values of the spin dependent structure function \(g_1(x)\) were obtained in those experiments covering a large kinematic range. The combination of all experimental results confirms the validity of the Bjorken sum rule.


Exotic Mesons and Structure of Soft Glue

abstract

Hybrid meson phenomenology is reviewed and models of soft gluons are discussed in the context of heavy quarkonia.


Consequences of Nonperturbative Nucleon Structure at High Energies

abstract

I briefly review some consequences of the meson cloud in the nucleon for high-energy nucleon-nucleon and nucleon-antinucleon scattering. The discussion includes the analysis of the production of W and Z bosons and dijets in proton-antiproton collisions. A consistent analysis of deep-inelastic data and the gauge boson production data shows that the concept of virtual mesons in the nucleon is very useful in understanding the charged lepton asymmetry measured by the CDF collaboration at Fermilab. I discuss a possibility to test the \(\bar d\)–\(\bar u\) asymmetry in the nucleon by the analysis of some asymmetries possible to measure in principle at RHIC. I discuss some selected effects which may potentially be responsible for an enhancement of the large-\(E_{T}\) inclusive jet production observed by the CDF collaboration at Fermilab. It is shown that target mass corrections in lepton DIS and effect of the pion cloud in the nucleon may be very important for a proper understanding of the experimental jet data.


Hadron Radii and the Origin of Chiral Singularities

abstract

Hadron radii are discussed with particular emphasis on chiral singularities \(m_{P S}^{-1}\) and log \(m_{P S}\); those result from the photon coupling to the \((PS+PS)\) continuum and are, therefore, most visible in isovector electromagnetic radii. It is shown that OZI rule violation leads to \(m_K^{-1}\) and log \(m_K\)-terms in the isoscalar radii as well. The \(\gamma \pi \pi \pi \) vertex function is free of chiral singularities and so are all quark core contributions. The \({\mit \Delta }(1232)\) contribution is particularly important for the subleading log \(m_{\pi }\)-terms, where a delicate cancellation occurs with pion loop contributions of the same order.


Associated Hyperon Production at COSY

abstract

At the new COSY cooler synchrotron several experimental facilities are in operation at internal and external target stations. One main topic of the present experiments is strangeness production with emphasis to the threshold region. The combination of a high quality low emittance proton beam with high acceptance detector systems allows precise and complete experiments.


Search for Neutrino Oscillations

abstract

Neutrino oscillations provide the most sensitive method to explore the mass of neutrinos. Within the two component mixing scheme the current status of the search for neutrino oscillations is presented. Claimed evidence for oscillations of atmospheric and solar neutrinos need further experimental confirmation. An oscillation \(\bar {\nu }_{\mu } \rightarrow \bar {\nu }_{e}\) as found by the LSND experiment could not be confirmed by the KARMEN experiment.


Relativistic Theory of Drip-Line Nuclei

abstract

Relativistic Mean Field (RMF) theory is used for an investigation or nuclei in the vicinity of the drip-lines Pairing correlations are taken into account by Hartree-Bogoliubov theory based on \(pp\)-interaction of finite range. Phenomena as neutron skin and neutron halo are discussed within a self-consistent framework.


Phase Transitions at High Level Density and Giant Resonances in Hot Nuclei

abstract

The properties of highly excited states embedded in the continuum of decay channels are investigated. First some general properties of open quantum systems are discussed. Especially, the restructuring taking place at high level density is considered and shown to be, in many cases, a second-order phase transition. The characteristic features of the phase transition are formulated. Then, the formalism is applied to giant resonances. The interferences of the resonance states via the continuum lead to a redistribution of the transition strength under critical conditions. Calculations for the ISMGR in \(^{208}\)Pb are performed in the continuum-RPA. Narrow resonances at about 30 MeV excitation energy are shown to arise from resonance trapping. These resonance states have an almost pure 1p-1h structure.


all authors

F.-K. Thielemann, C. Freiburghaus, T. Rauscher, F. Rembges, S. Rosswog, B. Pfeiffer, K.-L. Kratz, H. Schatz, M.C. Wiescher

Explosive Nucleosynthesis Close to the Drip Lines

abstract

We give an overview of explosive burning and the role which neutron and/or proton separation energies play. We focus then on the rapid neutron capture process (r-process) which encounters unstable nuclei with neutron separation energies in the range 1–4 MeV, and the rapid proton capture process (rp-process), operating close to the proton drip-line. The site of the rp-process is related to hydrogen accreting neutron stars in binary stellar systems. Explosive H-burning produces nuclei as heavy as A=100, powering events observable as X-ray bursts. The r-process abundances witness nuclear structure far from beta-stability as well as the conditions in the appropriate astrophysical environment. But there is a remaining lack in the full understanding of its astrophysical origin, ranging from the high entropy neutrino wind, blown from hot neutron star surfaces after a supernova explosion, to low entropy “cold decompresssion” of neutron star matter ejected in mergers of binary neutron star systems.


Relating Microscopic Results to Semiclassical Models of Collective Excitations

abstract

The interpretation of the low energy orbital magnetic dipole excitations of nonspherical nuclei, commonly called scissors modes, is examined. It is demonstrated that the “fluid dynamical model” which evolves from the Bohr–Mottelson collective model when the nuclear fluid is treated in Thomas–Fermi approximation, agrees much closer with microscopic calculations than other semiclassical models. This allows to interpret the microscopic results in more detail than usually done, and sheds light on the origin of the apparent discrepancies between semiclassical theory and experiment.


Summary of Meson ’98 Workshop

abstract

One never quite knows what to say in a summary. If you were at the sessions, you heard the same talks I did. Perhaps the purpose is to summarize the parallel sessions, but like you, I can only attend one of these sessions. In addition, the time is short, so that this cannot be a real summary. What I will present are impressions of the past two days, and these will certainly be colored by my own views. Thus at the outset, let me apologize for any and all omissions and distortions. I will cover primarily the plenary session talks, but will organize this summary along the following lines:

  1. vector (V) mesons;
  2. pseudoscalar mesons, and
  3. other subjects, notably with electrons.
This afternoon’s talks are so close in time to this summary that I shall omit them.


top

ver. 2024.03.17 • we use cookies and MathJax