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A significant drop of the vector meson masses in nuclear matter is observed in a chiral SU(3) model due to the e ects of the baryon Dirac sea. This is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation. The appreciable decrease of the in-medium vector meson masses is due to the vacuum polarisation e ects from the nucleon sector and is not observed in the mean field approximation.
We introduce a model for the real-time evolution of a relativistic fluid of quarks coupled to non-equilibrium dynamics of the long wavelength (classical) modes of the chiral condensate. We solve the equations of motion numerically in 3+1 spacetime dimensions. Starting the evolution at high temperature in the symmetric phase, we study dynamical trajectories that either cross the line of first-order phase transitions or evolve through its critical endpoint. For those cases, we predict the behavior of the azimuthal momentum asymmetry for highenergy heavy-ion collisions at nonzero impact parameter.
The J/psi yield at midrapidity at the top RHIC (relativistic heavy ion collider) energy is calculated within the statistical coalescence model, which assumes charmonium formation at the late stage of the reaction from the charm quarks and antiquarks created earlier in hard parton collisions. The results are compared to the new PHENIX data and to predictions of the standard models, which assume formation of charmonia exclusively at the initial stage of the reaction and their subsequent suppression. Two versions of the suppression scenario are considered. One of them assumes gradual charmonium suppression by comovers, while the other one supposes that the suppression sets in abruptly due to quark-gluon plasma formation. Surprisingly, both versions give very similar results. In contrast, the statistical coalescence model predicts a few times larger J/psi yield in the most central collisions.
The SENECA model, a new hybrid approach to air shower simulations, is presented. It combines the use of efficient cascade equations in the energy range where a shower can be treated as one-dimensional, with a traditional Monte Carlo method which traces individual particles. This allows one to reproduce natural fluctuations of individual showers as well as the lateral spread of low energy particles. The model is quite efficient in computation time. As an application of the new approach, the influence of the low energy hadronic models on shower properties for AUGER energies is studied. We conclude that these models have a significant impact on the tails of lateral distribution functions, and deserve therefore more attention.
Im Rahmen dieser Arbeit wurden Zellulare Neuronale Netzwerke (CNN) zur nichtlinearen Signalanalyse bei der Prädiktion hirnelektrischer Signale bei Epilepsie herangezogen. Die invasiven Aufnahmen hirnelektrischer Aktivität liegen zeitlich diskretisiert vor, sodaß ein zeitdiskretes Netzwerk (DTCNN) eingesetzt werden konnte. Die parallele Struktur von CNN konnte zur simultanen Untersuchung von sechs Elektroden genutzt werden, mit denen die hirnelektrische Aktivität aufgenommen wurde. Insbesondere ist die direkte Wechselwirkung der einzelnen Zellen untereinander durch eine lokale Nachbarschaft gegeben. In den durchgeführten Untersuchungen wurde zunächst festgestellt, daß für ein DTCNN, das ausgehend vom aktuellen Zeitpunkt den Signalwert des nächsten Zeitpunktes prädizieren soll, eine Prädiktionsordnung größer als zwei keine wesentliche Minimierung des Prädiktionsfehlers nach sich zieht. Daher wurde ein DTCNN mit zeitlich verzögerten Zellzuständen eingesetzt, wobei die Definitionsweise von Roska und Chua [21] im Rahmen dieser Arbeit für beliebige Prädiktionsordnungen erweitert wurde. Da bei einer Prädiktionsschrittweite größer als eins eine deutliche Erhöhung des Prädiktionsfehlers festgestellt werden konnte, wurde diese im folgenden gleich eins gewählt. Weiterhin wurde festgestellt, daß bei Verwendung polynomialer Kopplungsfunktionen der Grad der Nichtlinearität gleich drei gewählt werden kann, da eine weitere Erhöhung des Grades der Nichtlinearität zu keineren weiteren Minimierung des Prädiktionsfehlers geführt hat. Im Rahmen dieser Arbeit wurde ein Programm entwickelt, das aus den Aufnahmen der hirnelektrischen Aktivität einzelne Elektroden extrahieren kann, sodaß die Meßwerte dem DTCNN präsentiert werden konnten. Mit Hilfe des zugrundegelegten DTCNN konnte der zeitliche Verlauf der hirnelektrischen Aktivität von sechs Elektroden simultan prädiziert werden. Eine Analyse des zeitlichen Verlaufes des Prädiktionsfehlers ließ vor einem epileptischen Anfall keine signifikanten Änderungen erkennen. Daher wurde ein Programm entwickelt, mit dessen Hilfe der zeitliche Verlauf der Parameter des verwendeten DTCNN analysiert und deutliche Änderungen aufgezeigt werden können. Es konnten Berechnungsmethoden, hier die lokale Mittelwertbildung und die Gradientenberechnung, gefunden und an den jeweils untersuchten Patienten angepaßt werden, sodaß diese Änderungen der Parameter deutlicher hervorgehoben wurden. Bei zwei der vier Patienten konnten signifikante Änderungen des zeitlichen Verlaufes der Parameter des untersuchten DTCNN festgestellt werden, die vor dem Auftreten des epileptischen Anfalls liegen und somit als Vorläufer eines epileptischen Anfalls betrachtet werden können. Die Untersuchung eines dritten Patienten zeigte deutliche Änderungen der analysierten Parameter, die zeitlich mit dem Beginn des epileptischen Anfalls übereinstimmen. Bei einem vierten Patienten konnten signifikante Änderungen des zeitlichen Verlaufes der Parameter vor dem epileptischen Anfall nur dann festgestellt werden, wenn der betrachtete Datensatz hirnelektrischer Aktivität während des Auftretens eines Anfalls aufgenommen wurde. Wurde stattdessen die Aufnahme von zwei epileptischen Anfällen, die kurz hintereinander auftraten, analysiert, so konnten keine signifikanten Änderungen des Verlaufes der Parameter gefunden werden.
Das in der Plasmamembran tierischer Zellen vorkommende Enzym "Na+/K+-ATPase" setzt katalytisch ATP in ADP um. Als transmembranes Protein vollführt es während der Katalyse einen elektrogenen Zyklus von Konformationsänderungen, wobei 3 intrazelluläre Na+ gegen 2 extrazelluläre K+ ausgetauscht werden, und besitzt damit die Funktion eines primär aktiven Ionentransporters. Bisherige Aktivitätsmessungen, z.B. von B. Vilsen (Vilsen, 1994), an dem in Lösung befindlichen Enzym ergaben deutliche pH-Abhängigkeiten der Aktivität, die auf eine intrazelluläre Wechselwirkung des Protons mit der ATPase zurückgeführt wurden. Im Rahmen der hier vorliegenden Arbeit war nun die Frage zu klären, inwieweit der extrazelluläre pH-Wert auf die Transportfunktion der in der Membran liegenden Na+/K+-ATPase einen Einfluß ausübt. Es wurden daher elektrophysiologische Messungen mit dem Two-Elektrode-Voltage-Clamp-Verfahren und dem Giant-Patch-Clamp-Verfahren an der Zellmembran von Oozyten des Xenopus laevis durchgeführt und die pH-Abhängigkeit von durch die Na+/K+-ATPase verursachten transmembranen stationären als auch transienten Ionenströmen analysiert. Die stationären (steady-state) Ströme sind ein Maß für die Pumpaktivität, während die transienten auf Partialreaktionen des Enzyms schließen lassen. Die elektrophysiologischen Messungen wurden an der ouabainsensitiven und der ouabainresistenten Na+/K+-ATPase des Torpedo californica durchgeführt. Als Expressionssystem diente die Oozyte des Xenopus laevis. Die Messungen wurden mit Hilfe des Two-Elektrode-Voltage-Clamp-Verfahrens sowie des Giant-Patch-Clamp-Verfahrens durchgeführt. Um eine pH-Abhängigkeit zu untersuchen, wurden steady-state- als auch transiente Ströme bei den pH-Werten pH6, pH7,5 und pH9 gemessen. Als Pumenströme wurden die K+-aktivierbaren oder Ouabain-inhibierbaren Stromkomponenten betrachtet. Zunächst wurde die pH-Abhängigkeit von Pumpenströmen der im normalen Modus arbeitenden, ouabainsensitiven Na+/K+-ATPase untersucht. Die Pumpenströme wurden durch [K+]a=5mM aktiviert und durch [K+]a=0mM inhibiert. Die Messungen in einem natriumfreien extrazellulären Medium ergaben eine ausgeprägte pH-Abhängigkeit der Strom-Spannungskennlinien der Pumpenströme. Dieser Effekt wurde zum großen Teil auf einen, bei J.Rettinger (Rettinger, 1996) beschriebenen, Protonen-Einwärtsstrom zurückgeführt. Durch eine Korrektur konnten die vom Protoneneinwärtsstrom unbeeinflußten Pumpenströme analysiert werden, und es zeigte sich Potentialunabhängigkeit der Strom-Spannungskennlinien bei pH6 und pH9, während bei pH7,5 Potentialabhängigkeit (positive Steigung im negativen Potentialbereich) zu erkennen war. Dies wurde auf eine protonierbare im "access-channel" angenommene Stelle zurückgeführt, welche dann einen Einfluß auf die Affinität der Kationenbindung ausüben könnte. In hochnatriumhaltigem extrazellulären Medium (100mM) war dieser pH abhängige Effekt nicht nachweisbar, die Strom-Spannungskennlinien folgten dem schon bekannten Verlauf (Rakowski et al., 1997) mit einer positiven Steigung im negativen Potentialbereich. Weiterhin wurden transiente Ströme des Na/Na-Austausches sowohl an der ouabainsensitiven (OS) als auch an der ouabainresistenen (OR) Na+/K+-ATPase untersucht. Hierfür wurde in hochnatriumhaltigem (100mM) und kaliumfreiem extrazellulären Medium gemessen. Der Na/Na-Austausch der OS Pumpe wurde extrazellulär mit 100:M Ouabain inhibiert, während der der OR Pumpe mit 10mM Ouabain inhibiert wurde. Messungen mit dem Two-Elektrode-Voltag-Clamp-Verfahren ergaben auf Grund der zu geringen Zeitauflösung keine analysierbare pH-Abhängigkeit. Für die bei diesen Messungen festgestellte Ladungsverschiebung konnte eine effektive Wertigkeit von zq=0,80±0,02 ermittelt werden, was mit den Angaben von J. Rettinger et. al. (Rettinger et al., 1994) vergleichbar ist. Die Messungen mit dem Giant-Patch-Clamp-Verfahren an der OR und OS Pumpe ergaben für transiente Ströme einen relaxierenden Strom-Zeitverlauf, der einer Linearkombination aus drei unterschiedlich schnell relaxierenden Exponentialfunktionen mit verschiedenen Amplituden entspricht. Die Zeitkonstanten ließen keine signifikante pHAbhängigkeit erkennen. Ihre Werte lagen in den Bereichen 10-10 :s, 1-5ms und 10-200ms, wobei die am schnellsten relaxierende Funktion nicht analysiert werden konnten. Die langsam relaxierende Exponentialfunktion ließ sich der Konformationsänderung zuordnen, die mittelschnell relaxierende der extrazellulären Wechselwirkung mit den Na+-Ionen. Die Amplituden hingegen zeigten eine pH-Abhängigkeit. Im depolaren Potentialbereich hatten die Amplituden der mittelschnell relaxierenden Funktion bei pH6 eine größere Potentialabhängigkeit als bei pH9. Die Amplituden der langsam relaxierenden Funktion hatten im hyperpolaren Potentialbereich bei pH6 eine geringere Potentialabhängigkeit als bei höheren pH-Werten. Im ersten Fall könnte eine Protonierung an einer Stelle der ATPase die Potentialabhänigkeit über eine Veränderung des "accesschannels" verstärken, im zweiten Fall könnte diese in die Konformationsänderung eingebunden sein.
Accelerating cavities exchange HOM power through interconnecting beam pipes in case of signal frequencies above the cut-off of their propagating waveguide modes. This may lead either to improved HOM damping or - in the case most severe - to unwanted phase coherence of fields to the beam. Therefore the knowledge of the scattering properties of a cavity as a line element is needed to analyse all kinds of RF cavity-cavity interaction. Since there is a lack of measurement tools capable to provide a multidimensional scattering matrix at a given frequency point, we have been developing a method for this purpose. It uses a set of 2-port S-parameters of the device under test, embedded in a number of geometrically different RF environments. The application of the method is demonstrated with copper models of TESLA cavities.
A new method for the determination of S-matrices of devices in multimoded waveguides and first experimental experiences are presented. The theoretical foundations are given. The scattering matrix of a TESLA copper cavity at a frequency above the cut-off of the second waveguide mode has been measured.
The influence of high and low energy hadronic models on lateral distribution functions of cosmic ray air showers for Auger energies is explored. A large variety of presently used high and low energy hadron interaction models are analysed and the resulting lateral distribution functions are compared. We show that the slope depends on both the high and low energy hadronic model used. The models are confronted with available hadron-nucleus data from accelerator experiments.
We discuss the new data for the production of the psi meson in pA collisions at 450 GeV at CERNSPS (of the NA50-collaboration) [1]. We extract from the CERN data sigma(psi'N) 8 mb under the assumption that the psi is produced as a result of the space-time evolution of a point-like c¯c pair which expands with time to the full size of the charmonium state. In the analysis we assume the existence of a relationship between the distribution of color in a hadron and the cross section of its interaction with a nucleon. However, our result is rather sensitive to the pattern of the expansion of the wave packet and significantly larger values of sigma(psi'N)are not ruled out by the data. We show that recent CERN data confirm the suggestion of ref. [2] that color fluctuations of the strengths in charmonium-nucleon interaction are the major source of suppression of the J/psi yield as observed at CERN in both pA and AA collisions.
We evaluate the in-medium D and -meson masses in hot hadronic matter induced by interactions with the light hadron sector described in a chiral SU(3) model. The e ective Lagrangian approach is generalized to SU(4) to include charmed mesons. We find that the D-mass drops substantially at finite temperatures and densities, which open the channels of the decay of the charmonium states ( 2, c, J/ ) to D pairs in the thermal medium. The e ects of vacuum polarisations from the baryon sector on the medium modification of the D-meson mass relative to those obtained in the mean field approximation are investigated. The results of the present work are compared to calculations based on the QCD sum-rule approach, the quark-meson coupling model, chiral perturbation theory, as well as to studies of quarkonium dissociation using heavy quark potential from lattice QCD.
Abstract: The e ect of vacuum fluctuations on the in-medium hadronic properties is investigated using a chiral SU(3) model in the nonlinear realization. The e ect of the baryon Dirac sea is seen to modify hadronic properties and in contrast to a calculation in mean field approximation it is seen to give rise to a significant drop of the vector meson masses in hot and dense matter. This e ect is taken into account through the summation of baryonic tadpole diagrams in the relativistic Hartree approximation (RHA), where the baryon self energy is modified due to interactions with both the non-strange ( ) and the strange ( ) scalar fields.
The N/Z ratio of free nucleons from collisions of neutron-rich nuclei as a function of their momentum is studied by means of Isospin dependent Quantum Molecular Dynamics. We find that this ratio is not only sensitive to the form of the density dependence of the symmetry potential energy but also its strength determined by the symmetry energy coe cient. The uncertainties about the symmetry energy coe cient influence the accuracy of probing the density dependence of the symmetry energy by means of the N/Z ratio of free nucleons of neutron-rich nuclei.
Dynamics of strange, charm and high momentum hadrons in relativistic nucleus nucleus collisions
(2003)
We investigate hadron production and attenuation of hadrons with strange and charm quarks (or antiquarks) as well as high transverse momentum hadrons in relativistic nucleus-nucleus col- lisions from 2 A·GeV to 21.3 A·TeV within two independent transport approaches (UrQMD and HSD). Both transport models are based on quark, diquark, string and hadronic degrees of freedom, but do not include any explicit phase transition to a quark-gluon plasma. From our dynamical calculations we find that both models do not describe the maximum in the K+/ + ratio at 20 - 30 A·GeV in central Au+Au collisions found experimentally, though the excitation functions of strange mesons are reproduced well in HSD and UrQMD. Furthermore, the transport calculations show that the charmonium recreation by D + J/ + meson reactions is comparable to the dissociation by comoving mesons at RHIC energies contrary to SPS energies. This leads to the final result that the total J/ suppression as a function of centrality at RHIC should be less than the suppression seen at SPS energies where the comover dissociation is substantial and the backward channels play no role. Furthermore, our transport calculations in comparison to exper- imental data on transverse momentum spectra from pp, d+Au and Au+Au reactions show that pre-hadronic e ects are responsible for both the hardening of the hadron spectra for low transverse momenta (Cronin e ect) as well as the suppression of high pT hadrons. The mutual interactions of formed hadrons are found to be negligible in central Au+Au collisions at s = 200 GeV for pT e 6 GeV/c and the sizeable suppression seen experimentally is attributed to a large extent to the interactions of leading pre-hadrons with the dense environment.
Abstract: The measured particle ratios in central heavy-ion collisions at RHIC-BNL are investigated within a chemical and thermal equilibrium chiral SU(3) Ã É approach. The commonly adopted non-interacting gas calculations yield temperatures close to or above the critical temperature for the chiral phase transition, but without taking into account any interactions. In contrast, the chiral SU(3) model predicts temperature and density dependent effective hadron masses and effective chemical potentials in the medium and a transition to a chirally restored phase at high temperatures or chemical potentials. Three different parametrizations of the model, which show different types of phase transition behaviour, are investigated. We show that if a chiral phase transition occured in those collisions, freezing of the relative hadron abundances in the symmetric phase is excluded by the data. Therefore, either very rapid chemical equilibration must occur in the broken phase, or the measured hadron ratios are the outcome of the dynamical symmetry breaking. Furthermore, the extracted chemical freeze-out parameters differ considerably from those obtained in simple non-interacting gas calculations. In particular, the three models yield up to 35 MeV lower temperatures than the free gas approximation. The inmedium masses turn out to differ up to 150 MeV from their vacuum values.
Abstract: The medium modification of kaon and antikaon masses, compatible with low energy KN scattering data, are studied in a chiral SU(3) model. The mutual interactions with baryons in hot hadronic matter and the e ects from the baryonic Dirac sea on the K( ¯K ) masses are examined. The in-medium masses from the chiral SU(3) e ective model are compared to those from chiral perturbation theory. Furthermore, the influence of these in-medium e ects on kaon rapidity distributions and transverse energy spectra as well as the K, ¯K flow pattern in heavy-ion collision experiments at 1.5 to 2 A·GeV are investigated within the HSD transport approach. Detailed predictions on the transverse momentum and rapidity dependence of directed flow v1 and the elliptic flow v2 are provided for Ni+Ni at 1.93 A·GeV within the various models, that can be used to determine the in-medium K± properties from the experimental side in the near future.
Charmonium production and suppression in heavy-ion collisions at relativistic energies is investigated within di erent models, i.e. the comover absorption model, the threshold suppression model, the statistical coalescence model and the HSD transport approach. In HSD the charmonium dissociation cross sections with mesons are described by a simple phase-space parametrization including an e ective coupling strength |Mi|2 for the charmonium states i =Xc,J/psi, psi'. This allows to include the backward channels for charmonium reproduction by DD channels which are missed in the comover absorption and threshold suppression model employing detailed balance without introducing any new parameters. It is found that all approaches yield a reasonable description of J/psi suppression in S+U and Pb+Pb collisions at SPS energies. However, they di er significantly in the psi'/J/psi ratio versus centrality at SPS and especially at RHIC energies. These pronounced differences can be exploited in future measurements at RHIC to distinguish the hadronic rescattering scenarios from quark coalescence close to the QGP phase boundary.
By replacing the irises in an electron linac by a slit one gets a structure capable of focussing/defocussing an electron beam (rf-quadrupoles). Therefore one can think of a combination of rf- and conventional magnetic quadrupoles for transversal focussing in linear-colliders. Furthermore they can meet the demands of BNS-damping without initial energy spread. Considering multibunch-operation of a collider, the long-range wake behaviour of this kind of structure has to be investigated. A three-cell structure has been built and investigated for dipole-type transversal long-range wakes. The experimental results are compared to numerical simulations done with MAFIA.
The effect of a single HOM-damper cell within a channel of undamped cells is described theoretically using an equivalent circuit model. From this a simple equation can be derived which relates the Q-value of the single damping-cell, the bandwidth of the passband under consideration, and the additional phase shift which is introduced by the damper cell to provide energy flow into the damper cell. This equation immediately shows the limitations of such single cell damping systems. Comparisons with experimental results are shown.
Damping cells for the higher order modes are necessary for the S-band linear collider to minimize BBU (Beam-Break-Up). The construction of the damper cells has to take into account the different field geometries of the higher order modes. So two different types of dampers have been designed: a wall slotted an an iris slotted cell. In order to optimize the two types of damping cells with respect to damping strength, impedance matching between coupling system and waveguide dampers and between damping cell and undamped cells and the tuning system, damping cells of both types have been built and examinated.
Antibaryons bound in nuclei
(2004)
We study the possibility of producing a new kind of nuclear systems which in addition to ordinary nucleons contain a few antibaryons (B = p, , etc.). The properties of such systems are described within the relativistic mean field model by employing G parity transformed interactions for antibaryons. Calculations are first done for infinite systems and then for finite nuclei from 4He to 208Pb. It is demonstrated that the presence of a real antibaryon leads to a strong rearrangement of a target nucleus resulting in a significant increase of its binding energy and local compression. Noticeable e ects remain even after the antibaryon coupling constants are reduced by factor 3 4 compared to G parity motivated values. We have performed detailed calculations of the antibaryon annihilation rates in the nuclear environment by applying a kinetic approach. It is shown that due to significant reduction of the reaction Q values, the in medium annihilation rates should be strongly suppressed leading to relatively long lived antibaryon nucleus systems. Multi nucleon annihilation channels are analyzed too. We have also estimated formation probabilities of bound B + A systems in pA reactions and have found that their observation will be feasible at the future GSI antiproton facility. Several observable signatures are proposed. The possibility of producing multi quark antiquark clusters is discussed. PACS numbers: 25.43.+t, 21.10.-k, 21.30.Fe, 21.80.+a
A new method for measuring quality factors in cavities is presented. This method is capable of measuring Q-factors in heavily damped as well as in undamped cavities. In addition, the possibility of separating overlapping modes and measuring their Q-factors is provided. Measurements on HOM (higher order mode) damped cavities for the DESY/THD linear collider project are presented
We study the phase diagram of a generalized chiral SU(3)-flavor model in mean-field approxi- mation. In particular, the influence of the baryon resonances, and their couplings to the scalar and vector fields, on the characteristics of the chiral phase transition as a function of temperature and baryon-chemical potential is investigated. Present and future finite-density lattice calculations might constrain the couplings of the fields to the baryons. The results are compared to recent lattice QCD calculations and it is shown that it is non-trivial to obtain, simultaneously, stable cold nuclear matter.
A critical discussion of the present status of the CERN experiments on charm dynamics and hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A·GeV: here the hydrodynamic model has predicted the collapse of the v1-flow and of the v2-flow at 10 A·GeV; at 40 A·GeV it has been recently observed by the NA49 collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as potential evidence for a first order phase transition at high baryon density B. A detailed discussion of the collective flow as a barometer for the equation of state (EoS) of hot dense matter at RHIC follows. Here, hadronic rescattering models can explain < 30% of the observed elliptic flow, v2, for pT > 2 GeV/c. This is interpreted as evidence for the production of superdense matter at RHIC with initial pressure far above hadronic pressure, p > 1 GeV/fm3. We suggest that the fluctuations in the flow, v1 and v2, should be measured in future since ideal hydrodynamics predicts that they are larger than 50 % due to initial state fluctuations. Furthermore, the QGP coe cient of viscosity may be determined experimentally from the fluctuations observed. The connection of v2 to jet suppression is examined. It is proven experimentally that the collective flow is not faked by minijet fragmentation. Additionally, detailed transport studies show that the awayside jet suppression can only partially (< 50%) be due to hadronic rescattering. We, finally, propose upgrades and second generation experiments at RHIC which inspect the first order phase transition in the fragmentation region, i.e. at µB 400 MeV (y 4 5), where the collapse of the proton flow should be seen in analogy to the 40 A·GeV data. The study of Jet-Wake-riding potentials and Bow shocks caused by jets in the QGP formed at RHIC can give further information on the equation of state (EoS) and transport coe cients of the Quark Gluon Plasma (QGP).
We study the collective flow of open charm mesons and charmonia in Au + Au collisions at s = 200 GeV within the hadron-string-dynamics (HSD) transport approach. The detailed studies show that the coupling of D, mesons to the light hadrons leads to comparable directed and elliptic flow as for the light mesons. This also holds approximately for J/ mesons since more than 50% of the final charmonia for central and midcentral collisions stem from D + induced reactions in the transport calculations. The transverse momentum spectra of D, mesons and J/ s are only very moderately changed by the (pre-)hadronic interactions in HSD, which can be traced back to the collective flow generated by elastic interactions with the light hadrons. PACS-Nr. 25.75.-q, 13.60.Le, 14.40.Lb, 14.65.Dw
A scenario of heavy resonances, called massive Hagedorn states, is proposed which exhibits a fast (t H 1 fm/c) chemical equilibration of (strange) baryons and anti-baryons at the QCD critical temperature Tc. For relativistic heavy ion collisions this scenario predicts that hadronization is followed by a brief expansion phase during which the equilibration rate is higher than the expansion rate, so that baryons and antibaryons reach chemical equilibrium before chemical freeze-out occurs. PACS-Nr.: 12.38.Mh
To reach high luminosities in future linear colliders short range wakes havea to be controlled in the range of X-band frequencies or higher. Rectangular irises can be used to introduce strong focusing quadrupole-like rf-fields. Even circular irises in iris-loaded accelarator structures have the capability of focusing if the particle velocity differs from phase velocity. Theoretical investigations concerning the focusing strength to be expected are presented. Their applicability for linear colliders is discussed.
Mode propagation in an iris type accelerator section loaded with single heavily HOM-damped cells
(1994)
The wakefield effects in accelerator sections for future linear colliders will be reduced either by damping by detuning or by a combination of both. For the DESY/THD linac [1] it is forseen to employ heavily HOM-damped cells to provide a strong coupling to the TE/TM11-dipole passband as well as to the TM/TE11-dipole passband. For our experiments we have used wall-slotted damping cells. This leads to several problems concerning the propagation of fundamental and HOM-modes. Experimental investigations have been done. Results are presented.
A new method of measuring quality factors in cavities is presented. This method is well suited to measure quality factors in undamped cavities as well as in heavily damped cavities, and in addition this method provides a possibility of separating modes and measuring quality factors especially in cases of overlapping modes. Measurements have been carried out on HOM-damped cavities for the DESY/THD linear collider project. Results are presented.
Due to the additional need of very short bunches for the FEL operation with the TESLA-machine strong wakefield effects are expected. One third of the total wakefield energy per bunch is radiated into the frequency region above the energy gap of Cooper pairs in superconducting niobium. The energy of the cooper pairs in superconducting niobium at 2 K corresponds to a frequency of 700 GHz. An analytical and experimental estimation for the overall energy loss of the FEL bunch above energy gap is presented. The analytical method is based on a study from R. B. Palmer [1]. The results of the wakefield estimations are used to calculate possible quality factor reduction of the TESLA cavities during FEL operation. Results are presented.
The operation of a Free Electron Laser (FEL) in the ultraviolet or in the X-ray regime requires the acceleration of electron bunches with an rms length of 25 to 50 mikrometer. The wakefields generated by these sub picosecond bunches extend into the frequency range well beyond the threshold for Cooper pair breakup (about 750 GHz) in superconducting niobium at 2 K. It is shown, that the superconducting cavities can indeed be operated with 25 mikrometer bunches without suffering a breakdown of superconductivity (quench), however at the price of a reduced quality factor and an increased heat transfer to the superfluid helium bath. This was first shown by wakefield calculations based on the diffraction model [1]. In the meantime a more conventional method of computing wake fields in the time domain by numerical methods was developed and used for the wakefield calculations [2]. Both methods lead to comparable results: the operation of TESLA with 25 mikrometer bunches is possible but leads to an additional heat load due to the higher order modes (HOMs). Therefore HOM dampers for these high frequencies are under construction [3]. These dampers are located in the beam pipes between the 9-cell cavities. So it is of interest, if there are trapped modes in the cavity due to closed photon orbits. In this paper we investigate the existence of trapped modes and the distribution of heat load over the surface of the TESLA cavity by numerical photon tracking.
The study of hidden charm production is an important part of the heavy ion program. The standard approach to this problem [1] assumes that c¯c bound states are created only at the initial stage of the reaction and then partially destroyed at later stages due to interactions with the medium [2, 3, 4].
Nuclear collisions at intermediate, relativistic, and ultra-relativistic energies offer unique opportunities to study in detail manifold fragmentation and clustering phenomena in dense nuclear matter. At intermediate energies, the well known processes of nuclear multifragmentation -- the disintegration of bulk nuclear matter in clusters of a wide range of sizes and masses -- allow the study of the critical point of the equation of state of nuclear matter. At very high energies, ultra-relativistic heavy-ion collisions offer a glimpse at the substructure of hadronic matter by crossing the phase boundary to the quark-gluon plasma. The hadronization of the quark-gluon plasma created in the fireball of a ultra-relativistic heavy-ion collision can be considered, again, as a clustering process. We will present two models which allow the simulation of nuclear multifragmentation and the hadronization via the formation of clusters in an interacting gas of quarks, and will discuss the importance of clustering to our understanding of hadronization in ultra-relativistic heavy-ion collisions.
Entropy production in the compression stage of heavy ion collisions is discussed within three distinct macroscopic models (i.e. generalized RHTA, geometrical overlap model and three-fluid hydrodynamics). We find that within these models \sim 80% or more of the experimentally observed final-state entropy is created in the early stage. It is thus likely followed by a nearly isentropic expansion. We employ an equation of state with a first-order phase transition. For low net baryon density, the entropy density exhibits a jump at the phase boundary. However, the excitation function of the specific entropy per net baryon, S/A, does not reflect this jump. This is due to the fact that for final states (of the compression) in the mixed phase, the baryon density \rho_B increases with \sqrt{s}, but not the temperature T. Calculations within the three-fluid model show that a large fraction of the entropy is produced by nuclear shockwaves in the projectile and target. With increasing beam energy, this fraction of S/A decreases. At \sqrt{s}=20 AGeV it is on the order of the entropy of the newly produced particles around midrapidity. Hadron ratios are calculated for the entropy values produced initially at beam energies from 2 to 200 AGeV.
Impact parameter dependencies in Pb(160 AGeV)+Pb reactions : hydrodynamical vs. cascade calculations
(1999)
We investigate the impact parameter dependence of the specific entropy S/A in relativistic heavy ion collisions. Especially the anti-Lambda/anti-proton ratio is found to be a useful tool to distinguish between chemical equilibrium assumptions assumed in hydrodynamics (here: the 3-fluid model) and the chemical non-equilibrium scenario like in microscopic models as the UrQMD model.
Entropy production in the initial compression stage of relativistic heavy-ion collisions from AGS to SPS energies is calculated within a three-fluid hydrodynamical model. The entropy per participating net baryon is found to increase smoothly and does not exhibit a jump or a plateau as in the 1-dimensional one-fluid shock model. Therefore, the excess of pions per participating net baryon in nucleus-nucleus collisions as compared to proton-proton reactions also increases smoothly with beam energy.
The isospin and strangeness dimensions of the Equation of State are explored. RIA and the SIS200 accelerator at GSI will allow to explore these regions in compressed baryonic matter. 132 Sn + 132 Sn and 100 Sn + 100 Sn collisions as well as the excitation functions of K/pi, Lambda/pi and the centrality dependence of charmonium suppression from the UrQMD and HSD transport models are presented and compared to data. Unambiguous proof for the creation of a 'novel phase of matter' from strangeness and charm yields is not in sight.
We study Mach shocks generated by fast partonic jets propagating through a deconfined strongly-interacting matter. Our main goal is to take into account different types of collective motion during the formation and evolution of this matter. We predict a significant deformation of Mach shocks in central Au+Au collisions at RHIC and LHC energies as compared to the case of jet propagation in a static medium. The observed broadening of the near-side two-particle correlations in pseudorapidity space is explained by the Bjorken-like longitudinal expansion. Three-particle correlation measurements are proposed for a more detailed study of the Mach shock waves.
Nonequilibrium models (three-fluid hydrodynamics, UrQMD, and quark molecular dynamics) are used to discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions from the SPS via RHIC to LHC. It is demonstrated that these models - although they do treat the most interesting early phase of the collisions quite differently (thermalizing QGP vs. coherent color fields with virtual particles) -- all yield a reasonable agreement with a large variety of the available heavy ion data. Hadron/hyperon yields, including J/Psi meson production/suppression, strange matter formation, dileptons, and directed flow (bounce-off and squeeze-out) are investigated. Observations of interesting phenomena in dense matter are reported. However, we emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data. The role of future experiments with the STAR and ALICE detectors is pointed out.
We study the effects of isovector-scalar meson delta on the equation of state (EOS) of neutron star matter in strong magnetic fields. The EOS of neutron-star matter and nucleon effective masses are calculated in the framework of Lagrangian field theory, which is solved within the mean-field approximation. From the numerical results one can find that the delta-field leads to a remarkable splitting of proton and neutron effective masses. The strength of delta-field decreases with the increasing of the magnetic field and is little at ultrastrong field. The proton effective mass is highly influenced by magnetic fields, while the effect of magnetic fields on the neutron effective mass is negligible. The EOS turns out to be stiffer at B < 10^15G but becomes softer at stronger magnetic field after including the delta-field. The AMM terms can affect the system merely at ultrastrong magnetic field(B > 10^19G). In the range of 10^15 G - 10^18 G the properties of neutron-star matter are found to be similar with those without magnetic fields.
A strong interest is currently going on in the physics of high intensity and high energy beams: intense proton or deuteron beams are required in various fields of science and industry, including sources of neutrons for research experiments and material processing, nuclear physics experiments, tritium production and nuclear waste transmutation. High current heavy ion beams are envisaged for power production facilities (inertial fusion). Several projects presently under study are based on rf linacs as driver, sometimes followed by accumulation and/or compressor rings [Acc98]. The critical issue for all of them is to be operated in a low loss regime, because of activation problems in the structure. For this reason careful investigations have to be performed in order to understand and control the beam behaviour, aiming at conserving the beam quality, reducing the emittance growth and filamentation and avoiding the formation of halo. The beam current to be accelerated is actually limited by the amount of beam losses, which depends upon the beam halo: in order to reduce induced radioactivity and to allow for hands-on maintenance, normally losses <1 W/m are considered as acceptable [Sto96]. One of the major facilities under study is the European Spallation Source (ESS), a project based on a H- linac accelerating a 107 mA peak current beam (360 ns pulse in the DTL) and on two compressor rings, producing 5 MW average beam power [ESS]. Also the USA are developing a proposal for a Spallation Neutron Source (SNS), providing a short pulse H- beam with average power of 1÷2 MW; a 30 mA linac is required [SNS]. The Accelerator for Production of Tritium (APT), studied at Los Alamos, requires a 100 mA proton beam current (cw) to produce a power of 130÷170 MW [APT]. A similar but smaller accelerator (40 mA, 40 MW beam power) would serve as driver for the Accelerator Driven Transmutation of Waste (ADTW) system [ATW]. The accelerator system for the International Fusion Material Irradiation Facility (IFMIF) will test the behaviour of materials to be used for magnetic fusion (e.g. ITER); it consists of two 125 mA deuteron beams in parallel, to generate a fusion-like neutron spectrum with 10 MW cw [IFM]. In the field of heavy ions, for about 20 years scientists have been working on inertial confinement fusion, as an alternative to magnetic confinement one, to find a practical and cleaner method for producing energy. Nuclear fusion occurs when the nuclei of lighter elements (in a state of matter called "plasma") merge to form heavier elements; the extremely high temperatures and densities needed to get the nuclei to collide in the proper way and release big amounts of energy are obtained in a small "pellet" of fusion fuel, which receives energy from laser or ion beams, implodes and its inertia compresses it hard enough to hold together the plasma until it reaches ignition. Both laser and accelerator facilities have been investigated as drivers, since a demonstration of ignition at low gains is more easily accessible by lasers, whereas the intrinsic properties of accelerators -efficiency and repetition rate- will be essential for a medium-gain power plant. One study for a fusion power system driven by heavy ion beams (HIBALL) was completed in Europe already in 1982 [Bad81]. When the USA declassified essential information on pellet design, "indirect drive" targets have been considered openly, where the pellet is hit by X-rays generated from laser or ion beams rather than directly from the beams. Main progress has been achieved during the latest years in the understanding of pellet dynamics after ignition, i.e. in plasma physics [Sym1][Sym2][Sym3][Bas97][Lut97], imposing also new requirements on the layout of the driver accelerator facilities. In 1994-95 Frankfurt University and several other European laboratories (leaded by GSI) started a new collaboration called HIDIF (Heavy Ion Driven Ignition Facility) in order to simplify the accelerator plant design owing to the new technique of indirectly driven targets and to some technological improvements. First studies were oriented towards the conceptual goal of a facility providing just enough beam energy for the ignition of fusion reactions at very low gain (a "proof of principle") [Hof98]. In a recent phase of the study, it was realized that the proposed concept would make this scheme a more appropriate choice for energy production rather than for ignition; the acronym HIDIF was therefore intended as Heavy Ion Driven Inertial Fusion, and the parameters are going to be modified accordingly [Hof96][Hof97][Hof98]. The scenario presently discussed by this group proposes the formation and acceleration of an intense beam (400 mA) of singly charged heavy ions of three different atomic species, with mass differences of about 10% (the reference one is 209Bi+) in a main rf linac; they are then injected into some storage rings at an energy of 50 MeV/u, bunched in induction linacs and finally transported to a target with different velocities in such a way that the three species merge on the pellet ("telescoping") at 500 TW peak power. In this thesis the main linac of the HIDIF proposal is extensively investigated as an example of a high intensity heavy ion linac. Results are presented from numerical simulations of multi-particle beam dynamics carried out for the first time in this context. After a short presentation of the HIDIF reference scenario (Ignition Facility), including a discussion of the motivations for a high current heavy ion linac, some elements of the theory of beam transport and acceleration are recalled [Con91][Hof82][Kap85] [Lap87][Law88][Mit78][Rei94][Str83]. Then the used simulation programs are described, and a particle dynamics layout of a conventional 200 MHz Alvarez DTL is discussed with respect to low emittance growth at high transmission, including large space-charge effects, taking into account the influence of different kinds of statistical errors and of input mismatch on the beam dynamics. The modifications needed for "telescoping" are investigated with simulations for the nominal mass difference (10%) and for a smaller one (5%); finally the transfer line between DTL and rings is discussed and studied both analytically and by numerical calculations. The large mass number (A= 209) helps to reduce the space-charge effects with respect to protons, therefore the behaviour of the beam is not space-charge dominated. Nevertheless the tune depression values (similar to those of the ESS linac e.g.) indicate that these effects cannot be neglected. For a linac with low duty cycle, as in the case of an ignition facility, the results from particle dynamics calculations can be considered as a reliable guideline for the DTL layout, since they indicate that such a high intensity linac can fulfill the requirements on smooth beam behaviour and low losses.
The D-meson spectral density at finite temperature is obtained within a self-consistent coupled-channel approach. For the bare meson-baryon interaction, a separable potential is taken, whose parameters are fixed by the position and width of the Lambda_c (2593) resonance. The quasiparticle peak stays close to the free D-meson mass, indicating a small change in the effective mass for finite density and temperature. However, the considerable width of the spectral density implies physics beyond the quasiparticle approach. Our results indicate that the medium modifications for the D-mesons in nucleus-nucleus collisions at FAIR (GSI) will be dominantly on the width and not, as previously expected, on the mass.
We study properties of compact stars with the deconfinement phase transition in their interiors. The equation of state of cold baryon-rich matter is constructed by combining a relativistic mean-field model for the hadronic phase and the MIT Bag model for the deconfined phase. In a narrow parameter range two sequences of compact stars (twin stars), which differ by the size of the quark core, have been found. We demonstrate the possibility of a rapid transition between the twin stars with the energy release of about 10 ^52 ergs. This transition should be accompanied by the prompt neutrino burst and the delayed gamma-ray burst.