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A widely recognized paper by Colin Mayer (1988) has led to a profound revision of academic thinking about financing patterns of corporations in different countries. Using flow-of-funds data instead of balance sheet data, Mayer and others who followed his lead found that internal financing is the dominant mode of financing in all countries, that therefore financial patterns do not differ very much between countries and that those differences which still seem to exist are not at all consistent with the common conviction that financial systems can be classified as being either bank-based or capital market-based. This leads to a puzzle insofar as it calls into question the empirical foundation of the widely held belief that there is a correspondence between the financing patterns of corporations on the one side, and the structure of the financial sector and the prevailing corporate governance system in a given country on the other side. The present paper addresses this puzzle on a methodological and an empirical basis. It starts by demonstrating that the surprising empirical results found by Mayer et al. are due to a hidden assumption underlying their methodology. It then derives an alternative method of measuring financing patterns, which also uses flow-of-funds data, but avoids the questionable assumption. This measurement concept is then applied to patterns of corporate financing in Germany, Japan and the United States. The empirical results are very much in line with the commonly held belief prior to Mayer’s influential contribution and indicate that the financial systems of the three countries do indeed differ from one another in a substantial way.
The paper is a follow-up to an article published in Technique Financière et Developpement in 2000 (see the appendix to the hardcopy version), which portrayed the first results of a new strategy in the field of development finance implemented in South-East Europe. This strategy consists in creating microfinance banks as greenfield investments, that is, of building up new banks which specialise in providing credit and other financial services to micro and small enterprises, instead of transforming existing credit-granting NGOs into formal banks, which had been the dominant approach in the 1990s. The present paper shows that this strategy has, in the course of the last five years, led to the emergence of a network of microfinance banks operating in several parts of the world. After discussing why financial sector development is a crucial determinant of general social and economic development and contrasting the new strategy to former approaches in the area of development finance, the paper provides information about the shareholder composition and the investment portfolio of what is at present the world's largest and most successful network of microfinance banks. This network is a good example of a well-functioning "private public partnership". The paper then provides performance figures and discusses why the creation of such a network seems to be a particularly promising approach to the creation of financially self-sustaining financial institutions with a clear developmental objective.
This paper provides an in-depth analysis of the properties of popular tests for the existence and the sign of the market price of volatility risk. These tests are frequently based on the fact that for some option pricing models under continuous hedging the sign of the market price of volatility risk coincides with the sign of the mean hedging error. Empirically, however, these tests suffer from both discretization error and model mis-specification. We show that these two problems may cause the test to be either no longer able to detect additional priced risk factors or to be unable to identify the sign of their market prices of risk correctly. Our analysis is performed for the model of Black and Scholes (1973) (BS) and the stochastic volatility (SV) model of Heston (1993). In the model of BS, the expected hedging error for a discrete hedge is positive, leading to the wrong conclusion that the stock is not the only priced risk factor. In the model of Heston, the expected hedging error for a hedge in discrete time is positive when the true market price of volatility risk is zero, leading to the wrong conclusion that the market price of volatility risk is positive. If we further introduce model mis-specification by using the BS delta in a Heston world we find that the mean hedging error also depends on the slope of the implied volatility curve and on the equity risk premium. Under parameter scenarios which are similar to those reported in many empirical studies the test statistics tend to be biased upwards. The test often does not detect negative volatility risk premia, or it signals a positive risk premium when it is truly zero. The properties of this test furthermore strongly depend on the location of current volatility relative to its long-term mean, and on the degree of moneyness of the option. As a consequence tests reported in the literature may suffer from the problem that in a time-series framework the researcher cannot draw the hedging errors from the same distribution repeatedly. This implies that there is no guarantee that the empirically computed t-statistic has the assumed distribution. JEL: G12, G13 Keywords: Stochastic Volatility, Volatility Risk Premium, Discretization Error, Model Error
This study contributes to the valuation of employee stock options (ESO) in two ways: First, a new pricing model is presented, admitting a major part of calculations to be solved in closed form. Designed with a focus on good replication of empirics, the model fits with publicly observable exercise characteristics better than earlier models. In particular, it is able to account for the correlation of the time of exercise and the stock price at exercise, suspected of being crucial for the option value. The impact of correlation is weak, however, whereas cancellations play a central role. The second contribution of this paper is an examination to what extent the ESO pricing method of SFAS 123 is subject to discretion of the accountant. Given my model were true, the SFAS price would be a good proxy. Yet, outside shareholders usually cannot observe one of the SFAS input parameters. On behalf of an example I show that there is wide latitude left to the accountant.
This study contributes to the valuation of employee stock options (ESO) in two ways: First, a new pricing model is presented, admitting a major part of calculations to be solved in closed form. Designed with a focus on good replication of empirics, the model fits with publicly observable exercise characteristics better than earlier models. In particular, it is able to account for the correlation of the time of exercise and the stock price at exercise, suspected of being crucial for the option value. The impact of correlation is weak, however, whereas cancellations play a central role. The second contribution of this paper is an examination to what extent the ESO pricing method of SFAS 123 is subject to discretion of the accountant. Given my model were true, the SFAS price would be a good proxy. Yet, outside shareholders usually cannot observe one of the SFAS input parameters. On behalf of an example I show that there is wide latitude left to the accountant.
In a framework closely related to Diamond and Rajan (2001) we characterize different financial systems and analyze the welfare implications of different LOLR-policies in these financial systems. We show that in a bank-dominated financial system it is less likely that a LOLR-policy that follows the Bagehot rules is preferable. In financial systems with rather illiquid assets a discretionary individual liquidity assistance might be welfare improving, while in market-based financial systems, with rather liquid assets in the banks' balance sheets, emergency liquidity assistance provided freely to the market at a penalty rate is likely to be efficient. Thus, a "one size fits all"-approach that does not take the differences of financial systems into account is misguiding. JEL - Klassifikation: D52 , E44 , G21 , E52 , E58
When options are traded, one can use their prices and price changes to draw inference about the set of risk factors and their risk premia. We analyze tests for the existence and the sign of the market prices of jump risk that are based on option hedging errors. We derive a closed-form solution for the option hedging error and its expectation in a stochastic jump model under continuous trading and correct model specification. Jump risk is structurally different from, e.g., stochastic volatility: there is one market price of risk for each jump size (and not just \emph{the} market price of jump risk). Thus, the expected hedging error cannot identify the exact structure of the compensation for jump risk. Furthermore, we derive closed form solutions for the expected option hedging error under discrete trading and model mis-specification. Compared to the ideal case, the sign of the expected hedging error can change, so that empirical tests based on simplifying assumptions about trading frequency and the model may lead to incorrect conclusions.
This paper deals with the superhedging of derivatives and with the corresponding price bounds. A static superhedge results in trivial and fully nonparametric price bounds, which can be tightened if there exists a cheaper superhedge in the class of dynamic trading strategies. We focus on European path-independent claims and show under which conditions such an improvement is possible. For a stochastic volatility model with unbounded volatility, we show that a static superhedge is always optimal, and that, additionally, there may be infinitely many dynamic superhedges with the same initial capital. The trivial price bounds are thus the tightest ones. In a model with stochastic jumps or non-negative stochastic interest rates either a static or a dynamic superhedge is optimal. Finally, in a model with unbounded short rates, only a static superhedge is possible.
Empirical evidence suggests that even those firms presumably most in need of monitoringintensive financing (young, small, and innovative firms) have a multitude of bank lenders, where one may be special in the sense of relationship lending. However, theory does not tell us a lot about the economic rationale for relationship lending in the context of multiple bank financing. To fill this gap, we analyze the optimal debt structure in a model that allows for multiple but asymmetric bank financing. The optimal debt structure balances the risk of lender coordination failure from multiple lending and the bargaining power of a pivotal relationship bank. We show that firms with low expected cash-flows or low interim liquidation values of assets prefer asymmetric financing, while firms with high expected cash-flow or high interim liquidation values of assets tend to finance without a relationship bank. JEL - Klassifikation: G21 , G78 , G33
This paper suggests a motive for bank mergers that goes beyond alleged and typically unverifiable scale economies: preemtive resolution of banks´ financial distress. Such "distress mergers" can be a significant motivation for mergers because they can foster reorganizations, realize diversification gains, and avoid public attention. However, since none of these potential benefits comes without a cost, the overall assessment of distress mergers is unclear. We conduct an empirical analysis to provide evidence on consequences of distress mergers. The analysis is based on comprehensive data from Germany´s savings and cooperatives banks sectors over the period 1993 to 2001. During this period both sectors faced significant structural problems and superordinate institutions (associations) presumably have engaged in coordinated actions to manage distress mergers. The data comprise 3640 banks and 1484 mergers. Our results suggest that bank mergers as a means of preemtive distress resolution have moderate costs in terms of the economic impact on performance. We do find strong evidence consistent with diversification gains. Thus, distress mergers seem to have benefits without affecting systematic stability adversely.
Tests for the existence and the sign of the volatility risk premium are often based on expected option hedging errors. When the hedge is performed under the ideal conditions of continuous trading and correct model specification, the sign of the premium is the same as the sign of the mean hedging error for a large class of stochastic volatility option pricing models. We show, however, that the problems of discrete trading and model mis-specification, which are necessarily present in any empirical study, may cause the standard test to yield unreliable results.
The question whether the adoption of International Financial Reporting Standards (IFRS) will result in measurable economic benefits is of special policy relevance in particular given the European Union’s decision to require the application of IFRS by listed companies from 2005/2007. In this paper, I investigate the common con-jecture that internationally recognized high quality reporting standards (IAS/IFRS or US-GAAP) reduce the cost of capital of adopting firms (e.g. Levitt 1998; IASB 2002). Building on Leuz/Verrecchia (2000), I use a set of German firms which pre-adopted such standards before 2005, but investigate the potential economic benefits by analyzing their expected cost of equity capital utilizing and customizing avail-able implied estimation methods (e.g. Gebhardt/Lee/Swaminathan 2001, Easton/Taylor/Shroff/Sougiannis 2002, Easton 2004). Evidence from a sample of about 13,000 HGB, 4,500 IAS/IFRS and 3,000 US-GAAP firm-month observations in the period 1993-2002 generally fails to document lower expected cost of equity capital and therefore measurable economic benefits for firms applying IAS/IFRS or US-GAAP. Accordingly, I caution to state that reporting under internationally accepted standards, per se, lowers the cost of equity capital of adopting firms.
The GPS recorder consists of a GPS receiver board, a logging facility, an antenna, a power supply, a DC-DC converter and a casing. Currently, it has a weight of 33 g. The recorder works reliably with a sampling rate of 1/s and with an operation time of about 3 h, providing time-indexed data on geographic positions and ground speed. The data are downloaded when the animal is recaptured. Prototypes were tested on homing pigeons. The records of complete flight paths with surprising details illustrate the potential of this new method that can be used on a variety of medium-sized and large vertebrates.
In this study, we develop a technique for estimating a firm’s expected cost of equity capital derived from analyst consensus forecasts and stock prices. Building on the work of Gebhardt/Lee/-Swaminathan (2001) and Easton/Taylor/Shroff/Sougiannis (2002), our approach allows daily estimation, using only publicly available information at that date. We then estimate the expected cost of equity capital at the market, industry and individual firm level using historical German data from 1989-2002 and examine firm characteristics which are systematically related to these estimates. Finally, we demonstrate the applicability of the concept in a contemporary case study for DaimlerChrysler and the European automobile industry.
Empirical evidence suggests that even those firms presumably most in need of monitoring-intensive financing (young, small, and innovative firms) have a multitude of bank lenders, where one may be special in the sense of relationship lending. However, theory does not tell us a lot about the economic rationale for relationship lending in the context of multiple bank financing. To fill this gap, we analyze the optimal debt structure in a model that allows for multiple but asymmetric bank financing. The optimal debt structure balances the risk of lender coordination failure from multiple lending and the bargaining power of a pivotal relationship bank. We show that firms with low expected cash-flows or low interim liquidation values of assets prefer asymmetric financing, while firms with high expected cash-flow or high interim liquidation values of assets tend to finance without a relationship bank.
We investigate the connection between corporate governance system configurations and the role of intermediaries in the respective systems from a informational perspective. Building on the economics of information we show that it is meaningful to distinguish between internalisation and externalisation as two fundamentally different ways of dealing with information in corporate governance systems. This lays the groundwork for a description of two types of corporate governance systems, i.e. insider control system and outsider control system, in which we focus on the distinctive role of intermediaries in the production and use of information. It will be argued that internalisation is the prevailing mode of information processing in insider control system while externalisation dominates in outsider control system. We also discuss shortly the interrelations between the prevailing corporate governance system and types of activities or industry structures supported.
The paper is a follow-up to an article published in Technique Financière et Developpement in 2000 (see the appendix to the hardcopy version), which portrayed the first results of a new strategy in the field of development finance implemented in South-East Europe. This strategy consists in creating microfinance banks as greenfield investments, that is, of building up new banks which specialise in providing credit and other financial services to micro and small enterprises, instead of transforming existing credit-granting NGOs into formal banks, which had been the dominant approach in the 1990s. The present paper shows that this strategy has, in the course of the last five years, led to the emergence of a network of microfinance banks operating in several parts of the world. After discussing why financial sector development is a crucial determinant of general social and economic development and contrasting the new strategy to former approaches in the area of development finance, the paper provides information about the shareholder composition and the investment portfolio of what is at present the world's largest and most successful network of microfinance banks. This network is a good example of a well-functioning "private public partnership". The paper then provides performance figures and discusses why the creation of such a network seems to be a particularly promising approach to the creation of financially self-sustaining financial institutions with a clear developmental objective.
EU financial integration : is there a 'Core Europe'? ; evidence from a cluster-based approach
(2005)
Numerous recent studies, e.g. EU Commission (2004a), Baele et al. (2004), Adam et al.(2002), and the research pooled in ECB-CFS (2005), Gaspar, Hartmann, and Sleijpen(2003), have documented progress in EU financial integration from a micro-level view.This paper contributes to this research by identifying groups of financially integratedcountries from a holistic, macro-level view. It calculates cross-sectional dispersions, andinnovates by applying an inter-temporal cluster analysis to eight euro area countries for the period 1995-2002. The indicators employed represent the money, government bond and credit markets. Our results show that euro countries were divided into two stable groups of financially more closely integrated countries in the pre-EMU period. Back then, geographic proximity and country size might have played a role. This situation has changed remarkably with the euro's introduction. EMU has led to a shake-up both in the number and composition of groups. The evidence puts a question mark behin d using Germany as a benchmark in the post-EMU period. The ¯ndings suggest as well that ¯nancial integration takes place in waves. Stable periods and periods of intense transition alternate. Based on the notion of 'maximum similarity', the results suggest that there exist 'maximum similarity barriers'. It takes extraordinary events, such as EMU, to push the degree of ¯nancial integration beyond these barriers. The research encourages policymakers to move forward courageously in the post-FSAP era, and provides comfort that the substantial di®erences between the current and potentially new euro states can be overcome. The analysis could be extended to the new EU member countries, to the global level, and to additional indicators.
Tractable hedging - an implementation of robust hedging strategies : [This Version: March 30, 2004]
(2004)
This paper provides a theoretical and numerical analysis of robust hedging strategies in diffusion–type models including stochastic volatility models. A robust hedging strategy avoids any losses as long as the realised volatility stays within a given interval. We focus on the effects of restricting the set of admissible strategies to tractable strategies which are defined as the sum over Gaussian strategies. Although a trivial Gaussian hedge is either not robust or prohibitively expensive, this is not the case for the cheapest tractable robust hedge which consists of two Gaussian hedges for one long and one short position in convex claims which have to be chosen optimally.
The German corporate governance system has long been cited as the standard example of an insider-controlled and stakeholder-oriented system. We argue that despite important reforms and substantial changes of individual elements of the German corporate governance system the main characteristics of the traditional German system as a whole are still in place. However, in our opinion the changing role of the big universal banks in the governance undermines the stability of the corporate governance system in Germany. Therefore a breakdown of the traditional system leading to a control vacuum or a fundamental change to a capital market-based system could be in the offing.
Small and medium-sized firms typically obtain capital via bank financing. They often rely on a mixture of relationship and arm’s-length banking. This paper explores the reasons for the dominance of heterogeneous multiple banking systems. We show that the incidence of inefficient credit termination and subsequent firm liquidation is contingent on the borrower’s quality and on the relationship bank’s information precision. Generally, heterogeneous multiple banking leads to fewer inefficient credit decisions than monopoly relationship lending or homogeneous multiple banking, provided that the relationship bank’s fraction of total firm debt is not too large.
Small and medium-sized firms typically obtain capital via bank financing. They often rely on a mixture of relationship and arm’s-length banking. This paper explores the reasons for the dominance of heterogeneous multiple banking systems. We show that the incidence of inefficient credit termination and subsequent firm liquidation is contingent on the borrower’s quality and on the relationship bank’s information precision. Generally, heterogeneous multiple banking leads to fewer inefficient credit decisions than monopoly relationship lending or homogeneous multiple banking, provided that the relationship bank’s fraction of total firm debt is not too large.
This paper makes an attempt to present the economics of credit securitisation in a non-technical way, starting from the description and the analysis of a typical securitisation transaction. The paper sketches a theoretical explanation for why tranching, or nonproportional risk sharing, which is at the heart of securitisation transactions, may allow commercial banks to maximize their shareholder value. However, the analysis makes also clear that the conditions under which credit securitisation enhances welfare, are fairly restrictive, and require not only an active role of the banking supervisory authorities, but also a price tag on the implicit insurance currently provided by the lender of last resort.
We derive the effects of credit risk transfer (CRT) markets on real sector productivity and on the volume of financial intermediation in a model where banks choose their optimal degree of CRT and monitoring. We find that CRT increases productivity in the up-market real sector but decreases it in the low-end segment. If optimal, CRT unambiguously fosters financial deepening, i.e., it reduces credit-rationing in the economy. These effects rely upon the ability of banks to commit to the optimal CRT at the funding stage. The optimal degree of CRT depends on the combination of moral hazard, general riskiness, and the cost of monitoring in non-monotonic ways.
We provide insights into determinants of the rating level of 371 issuers which defaulted in the years 1999 to 2003, and into the leader-follower relationship between Moody’s and S&P. The evidence for the rating level suggests that Moody’s assigns lower ratings than S&P for all observed periods before the default event. Furthermore, we observe two-way Granger causal-ity, which signifies information flow between the two rating agencies. Since lagged rating changes influence the magnitude of the agencies’ own rating changes it would appear that the two rating agencies apply a policy of taking a severe downgrade through several mild down-grades. Further, our analysis of rating changes shows that issuers with headquarters in the US are less sharply downgraded than non-US issuers. For rating changes by Moody’s we also find that larger issuers seem to be downgraded less severely than smaller issuers.
This article presents an overview of the contemporary German insurance market, its structure, players, and development trends. First, brief information about the history of the insurance industry in Germany is provided. Second, the contemporary market is analyzed in terms of its legal and economic structure, with statistics on the number of companies, insurance density and penetration, the role of insurers in the capital markets, premiums split, and main market players and their market shares. Furthermore, the three biggest insurance lines—life, health, and property and casualty—are considered in more detail, such as product range, country specifics, and insurance and investment results. A section on regulation outlines its implementation in the insurance sector, offering information on the underlying legislative basis, supervisory body, technical procedures, expected developments, and sources of more detailed information.
Charged-particle exclusive data for Ar+Pb collisions at 0.772 GeV/u are analyzed in terms of collective variables for the event shapes in momentum space. Semicentral collisions lead to sidewards flow whereas nearly head-on collisions have spherical shapes in the c.m. frame, resulting from complete stopping of projectile motion. The hydrodynamical model predictions agree qualitatively with the data whereas the standard cascade model disagrees, lacking in stopping power and collective flow.
Nuclear resonance fluorescence measurements with linearly polarized bremsstrahlung were performed to determine parities of bound dipole transitions in 206Pb. A new 1+ level at 5800 keV was found, which has almost the same strength as the isoscalar M1 transition in 208Pb. Twenty-four further dipole states in 206Pb below 7.6 MeV possess negative parity.
Pion and proton production are measured to investigate thermal equilibrium in central collisions of 40Ar+KCl at 1.8 GeV/nucleon. The bulk of the pion yield is isotropic in the c.m. system, with an apparent temperature of 58±3 MeV, much lower than the 118±2 MeV of the protons. It is shown that the low pion "temperature" can be explained by the decay kinematics of delta resonances in thermal equilibrium. A (5±1)% component in the pion spectrum is, however, found to have a temperature of 110±10 MeV. The effect on the spectra of possible contributions from collective radial flow is discussed.
An event by event analysis is carried out for all charged particles observed in central collisions of 40Ar + KCl and 40Ar + Pb at 1.808 and 0.772 GeV/nucleon, respectively. Total transverse energy is used for impact parameter selection within the central trigger condition. The central Ar + KCl reaction exhibits a forward-backward oriented momentum flux. The flux distribution of the most central Ar + Pb events is approximately isotropic in the fireball center of mass.
Triple differential cross sections d3 sigma /dp3 for charged pions produced in symmetric heavy-ion collisions were measured with the KaoS magnetic spectrometer at the heavy-ion synchrotron facility SIS at GSI. The correlations between the momentum vectors of charged pions and the reaction plane in 197Au+197Au collisions at an incident energy of 1 GeV/nucleon were determined. We observe, for the first time, an azimuthally anisotropic distribution of pions, with enhanced emission perpendicular to the reaction plane. The anisotropy is most pronounced for pions of high transverse momentum in semicentral collisions.
Nuclear resonance fluorescence experiments with linearly polarized bremsstrahlung were performed to determine parities of strong dipole transitions in 40Ar. A total of 14 transitions—ten of them previously unknown—in the energy range from 4.7 to 10.2 MeV could be identified. From this experiment it is evident that the main dipole strength to bound states is due to E1 excitations. An upper limit of B(M1) [up arrow] <0.5 µN2 was found for individual magnetic dipole excitations in 40Ar in the energy region below neutron threshold.
Electric charge correlations were studied for p+p, C+C, Si+Si, and centrality selected Pb+Pb collisions at sqrt[sNN]=17.2 GeV with the NA49 large acceptance detector at the CERN SPS. In particular, long-range pseudorapidity correlations of oppositely charged particles were measured using the balance function method. The width of the balance function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions.
The properties of two measures of charge fluctuations D-tilde and DeltaPhiq are discussed within several toy models of nuclear collisions. In particular their dependence on mean particle multiplicity, multiplicity fluctuations, and net electric charge are studied. It is shown that the measure DeltaPhiq is less sensitive to these trivial biasing effects than the originally proposed measure D-tilde. Furthermore the influence of resonance decay kinematics is analyzed and it is shown that it is likely to shadow a possible reduction of fluctuations due to QGP creation.
Dt. Fassung: Der Umgang mit Rechtsparadoxien: Derrida, Luhmann, Wiethölter. In: Christian Joerges und Gunther Teubner (Hg.) Rechtsverfassungsrecht: Recht-Fertigungen zwischen Sozialtheorie und Privatrechtsdogmatik. Nomos, Baden-Baden 2003, 249-272.
Analysis of Lambda and associative pion production in relativistic nucleus-nucleus collisions
(1984)
The transverse momentum and rapidity distributions of negative hadrons and participant protons have been measured for central 32S+ 32S collisions at plab=200 GeV/c per nucleon. The proton mean rapidity shift < Delta y>~1.6 and mean transverse momentum <pT>~0.6 GeV/c are much higher than in pp or peripheral AA collisions and indicate an increase in the nuclear stopping power. All pT spectra exhibit similar source temperatures. Including previous results for K0s Lambda , and Lambda -bar, we account for all important contributions to particle production.
The NA35 experiment has collected a high statistics set of momentum analyzed negative hadrons near and forward of midrapidity for central collisions of 200A GeV/c 32S+S, Cu, Ag, and Au. Using momentum space correlations to study the size of the source of particle production, the transverse source radii are found to decrease by ~40% at midrapidity and ~20% at forward rapidity while the longitudinal radius RL is found to decrease by ~50% as pT increases over the interval 50<pT<600 MeV/c. Calculations using a microscopic phase space approach (relativistic quantum molecular dynamics) reproduce the observed trends of the data. PACS: 25.75.+r
Transverse momenta and rapidities of Lambda 's produced in central nucleus-nucleus collisions at 4.5 GeV/c·u (C-C,...,O-Pb) were studied and compared with those from inelastic He-Li interactions at the same incident momentum. Polarization of the Lambda hyperons was found to be consistent with zero ( alpha P=-0.06=0.11 for Lambda 's from central collisions). An upper limit of the Lambda -bar / Lambda production ratio was estimated to be less than 4.5 x 10-3. The experiment was performed in a triggered streamer chamber.
Difficulties of the thermodynamical model approach to pion production in relativistic ion collisions
(1983)
Thermodynamical models with various forms of partial transparency of nuclear matter are considered. It is shown that the introduction of transparency, however, significantly improves agreement with pion data concerning multiplicities and transverse momenta leads to a serious discrepancy with average rapidities of pions. Qualitative arguments are given that difficulties of the thermodynamical approach can be overcome if one assumes hydrodynamical expansion in the first stage of nuclear interactions.
A detailed study of pion production in inelastic and central nucleus-nucleus collisions was carried out using a 2 m streamer spectrometer. Nuclear targets mounted inside the streamer chamber were exposed to nuclear beams of 4.5 GeV/c/nucleon momentum. A systematic study of the influence of the central trigger on observed data is performed. The data on multiplicities, rapidities, transverse momenta, and emission angles of negative pions are presented for various pairs of colliding nuclei. Intercorrelations between various characteristics are studied and discussed. The results are compared with predictions of some theoretical models. It is shown that the main features of the pion production in nuclear collisions can be satisfactorily described by a model assuming independent nucleon-nucleon collisions with subsequent cascading process. However, the observed correlation between Lambda and pion characteristics seems to be unexplained by this picture.
We argue that the recent analysis of strangeness production in nuclear collisions at 200 A GeV/c performed by Topor Pop et al. is flawed. The conclusions are based on an erroneous interpretation of the data and the numerical model results. The term "strangeness enhancement" is used in a misleading way.
Pion and strangeness puzzles
(1996)
Data on the mean multiplicity of strange hadrons produced in minimum bias proton--proton and central nucleus--nucleus collisions at momenta between 2.8 and 400 GeV/c per nucleon have been compiled. The multiplicities for nucleon--nucleon interactions were constructed. The ratios of strange particle multiplicity to participant nucleon as well as to pion multiplicity are larger for central nucleus--nucleus collisions than for nucleon--nucleon interactions at all studied energies. The data at AGS energies suggest that the latter ratio saturates with increasing masses of the colliding nuclei. The strangeness to pion multiplicity ratio observed in nucleon--nucleon interactions increases with collision energy in the whole energy range studied. A qualitatively different behaviour is observed for central nucleus--nucleus collisions: the ratio rapidly increases when going from Dubna to AGS energies and changes little between AGS and SPS energies. This change in the behaviour can be related to the increase in the entropy production observed in central nucleus-nucleus collisions at the same energy range. The results are interpreted within a statistical approach. They are consistent with the hypothesis that the Quark Gluon Plasma is created at SPS energies, the critical collision energy being between AGS and SPS energies.