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Chemical equilibrium study in nucleus-nucleus collisions at relativistic energies (2004)

Francesco Becattini Marek Gazdzicki Antti Keränen Jaakko Manninen Reinhard Stock

We present a detailed study of chemical freeze-out in nucleus-nucleus collisions at beam energies of 11.6, 30, 40, 80 and 158A GeV. By analyzing hadronic multiplicities within the statistical hadronization approach, we have studied the strangeness production as a function of centre of mass energy and of the parameters of the source. We have tested and compared different versions of the statistical model, with special emphasis on possible explanations of the observed strangeness hadronic phase space under-saturation. We show that, in this energy range, the use of hadron yields at midrapidity instead of in full phase space artificially enhances strangeness production and could lead to incorrect conclusions as far as the occurrence of full chemical equilibrium is concerned. In addition to the basic model with an extra strange quark non-equilibrium parameter, we have tested three more schemes: a two-component model superimposing hadrons coming out of single nucleon-nucleon interactions to those emerging from large fireballs at equilibrium, a model with local strangeness neutrality and a model with strange and light quark non-equilibrium parameters. The behaviour of the source parameters as a function of colliding system and collision energy is studied. The description of strangeness production entails a non-monotonic energy dependence of strangeness saturation parameter gamma_S with a maximum around 30A GeV. We also present predictions of the production rates of still unmeasured hadrons including the newly discovered Theta^+(1540) pentaquark baryon.

Bose-Einstein correlations of charged kaons in central Pb+Pb collisions at E_beam = 158 AGeV (2002)

S. V. Afanasiev NA49 Collaboration

Bose-Einstein correlations of charged kaons were measured near mid-rapidity in central Pb+Pb collisions at 158 A GeV by the NA49 experiment at the CERN SPS. Source radii were extracted using the Yano-Koonin-Podgoretsky and Bertsch-Pratt parameterizations. The results are compared to published pion data. The measured m_perp dependence for kaons and pions is consistent with collective transverse expansion of the source and a freeze-out time of about 9.5 fm.

Incident-energy dependence of the effective temperature in heavy-ion collisions (2003)

Marek Gazdzicki Mark I. Gorenstein Frederique Grassi Yogiro Hama Takeshi Kodama Otavio Jr. Socolowski

We study the behaviour of the effective temperature for K+ in several energy domains. For this purpose, we apply the recently developed SPheRIO code for hydrodynamics in 3+1 dimensions, using both Landau-type compact initial conditions and spatially more spread ones. We show that initial conditions given in small volume, like Landau-type ones, are unable to reproduce the effective temperature together with other data (multiplicities and rapidity distributions). These quantities can be reproduced altogether only when using a large initial volume with an appropriate velocity distribution.

Fluctuations of strangeness and deconfinement phase transition in nucleus-nucleus collisions (2004)

Mark I. Gorenstein Marek Gazdzicki O. S. Zozulya

We suggest that the fluctuations of strange hadron multiplicity could be sensitive to the equation of state and microscopic structure of strongly interacting matter created at the early stage of high energy nucleus-nucleus collisions. They may serve as an important tool in the study of the deconfinement phase transition. We predict, within the statistical model of the early stage, that the ratio of properly filtered fluctuations of strange to non-strange hadron multiplicities should have a non-monotonic energy dependence with a minimum in the mixed phase region.

Energy dependence of transverse mass spectra of kaons produced in p+p and p+pbar interactions : a compilation (2003)

Michael Kliemant Benjamin Lungwitz Marek Gazdzicki

The data on mT spectra of K0S K+ and K- mesons produced in all inelastic p + p and p + pbar interactions in the energy range sqrt(s)NN=4.7-1800GeV are compiled and analyzed. The spectra are parameterized by a single exponential function, dN/(m_T*dm_T)=C exp(-m_T/T), and the inverse slope parameter T is the main object of study. The T parameter is found to be similar for K0S, K+ and K- mesons. It increases monotonically with collision energy from T~30MeV at sqrt(s)NN=4.7GeV to T~220MeV at sqrt(s)NN=1800GeV. The T parameter measured in p+p and p+pbar interactions is significantly lower than the corresponding parameter obtained for central Pb+Pb collisions at all studied energies. Also the shape of the energy dependence of T is different for central Pb+Pb collisions and p+p(pbar) interactions.

Energy scan program at the Cern SPS and an observation of the deconfinement phase transition in nucleus-nucleus collisions (2003)

Marek Gazdzicki

The history and the main results of the energy scan program at the CERN SPS are reviewed. Several anomalies in energy dependence of hadron production predicted as signals of deconfinement phase transition are observed and they indicate that the onset of deconfinement is located at about 30 A GeV. For the first time we seem to have clear evidence for the existence of a deconfined state of matter in nature.

Fluctuations and deconfinement phase transition in nucleus-nucleus collisions (2004)

Marek Gazdzicki Mark I. Gorenstein Stanislaw Mrowczynski

We propose a method to experimentally study the equation of state of strongly interacting matter created at the early stage of nucleus--nucleus collisions. The method exploits the relation between relative entropy and energy fluctuations and equation of state. As a measurable quantity, the ratio of properly filtered multiplicity to energy fluctuations is proposed. Within a statistical approach to the early stage of nucleus-nucleus collisions, the fluctuation ratio manifests a non--monotonic collision energy dependence with a maximum in the domain where the onset of deconfinement occurs.

Transverse activity of kaons and the deconfinement phase transition in nucleus-nucleus collisions (2003)

Mark I. Gorenstein Marek Gazdzicki Kyrill A. Bugaev

We found that the experimental results on transverse mass spectra of kaons produced in central Pb+Pb (Au+Au) interactions show an anomalous dependence on the collision energy. The inverse slopes of the spectra increase with energy in the low (AGS) and high (RHIC) energy domains, whereas they are constant in the intermediate (SPS) energy range. We argue that this anomaly is probably caused by a modification of the equation of state in the transition region between confined and deconfined matter. This observation may be considered as a new signal, in addition to the previously reported anomalies in the pion and strangeness production, of the onset of deconfinement located in the low SPS energy domain.

Correlation, price discovery and co-movement of ABS and equity (2005)

Andreas A. Jobst

Asset-backed securitization (ABS) has become a viable and increasingly attractive risk management and refinancing method either as a standalone form of structured finance or as securitized debt in Collateralized Debt Obligations (CDO). However, the absence of industry standardization has prevented rising investment demand from translating into market liquidity comparable to traditional fixed income instruments, in all but a few selected market segments. Particularly low financial transparency and complex security designs inhibits profound analysis of secondary market pricing and how it relates to established forms of external finance. This paper represents the first attempt to measure the intertemporal, bivariate causal relationship between matched price series of equity and ABS issued by the same entity. In a two-dimensional linear system of simultaneous equations we investigate the short-term dynamics and long-term consistency of daily secondary market data from the U.K. Sterling ABS/MBS market and exchange traded shares between 1998 and 2004 with and without the presence of cointegration. Our causality framework delivers compelling empirical support for a strong co-movement between matched price series of ABS-equity pairs, where ABS markets seem to contribute more to price discovery over the long run. Controlling for cointegration, risk-free interest and average market risk of corporate debt hardly alters our results. However, once we qualify the magnitude and direction of price discovery on various security characteristics, such as the ABS asset class, we find that ABS-equity pairs with large-scale CMBS/RMBS and credit card/student loan ABS reveal stronger lead-lag relationships and joint price dynamics than whole business ABS. JEL Classifications: G10, G12, G24

Security issuance and investor information (2005)

Andreas A. Jobst

Although the commoditisation of illiquid asset exposures through securitisation facilitates the disciplining effect of capital markets on the risk management, private information about securitised debt as well as complex transaction structures could possibly impair the fair market valuation. In a simple issue design model without intermediaries we maximise issuer proceeds over a positive measure of issue quality, where a direct revelation mechanism (DRM) by profitable informed investors engages endogenous price discovery through auction-style allocation preference as a continuous function of perceived issue quality. We derive an optimal allocation schedule for maximum issuer payoffs under different pricing regimes if asymmetric information requires underpricing. In particular, we study how the incidence of uninformed investors at varying levels of valuation uncertainty and their function of clearing the market effects profitable informed investment. We find that the issuer optimises own payoffs at each valuation irrespective of the applicable pricing mechanism by awarding informed investors the lowest possible allocation (and attendant underpricing) that still guarantees profitable informed investment. Under uniform pricing the composition of the investor pool ensures that informed investors appropriate higher profit than uninformed types. Any reservation utility by issuers lowers the probability of information disclosure by informed investors and the scope of issuers to curtail profitable informed investment. JEL Classifications: D82, G12, G14, G23

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