Strangeness Production in pp,pA,AA Interactions at SPS Energies.HIJING Approach

In this report we have made a systematic study of strangeness production in proton-proton(pp),proton-nucleus(pA) and nucleus- nucleus(AA) collisions at CERN Super Proton Synchroton energies, using$\,\,\, HIJING\,\,\, MONTE \,\,\,CARLO \,\,\,MODEL$ \\ (version $HIJ.01$). Numerical results for mean multiplicities of neutral strange particles ,as well as their ratios to negatives hadrons($$) for p-p,nucleon-nucleon(N-N),\,\,p-S,\,\,p-Ag,\,\,p-Au('min. bias')collisions and p-Au,\,\,S-S,\,\,S-Ag,\,\,S-Au ('central')collisions are compared to experimental data available from CERN experiments and also with recent theoretical estimations given by others models. Neutral strange particle abundances are quite well described for p-p,N-N and p-A interactions ,but are underpredicted by a factor of two in A-A interactions for $\Lambda,\bar{\Lambda}, K^{0}_{S}$ in symmetric collisions(S-S,\,\,Pb-Pb)and for $\Lambda,\bar{\Lambda}\,\,$in asymmetric ones(S-Ag,\,\,S-Au,\,\,S-W). A qualitative prediction for rapidity, transverse kinetic energy and transverse momenta normalized distributions are performed at 200 GeV/Nucleon in p-S,S-S,S-Ag and S-Au collisions in comparison with recent experimental data. HIJING model predictions for coming experiments at CERN for S-Au, S-W and Pb-Pb interactions are given. The theoretical calculations are estimated in a full phase space.Comment: 33 pages(LATEX),18 figures not included,available in hard copy upon request , Dipartamento di Fisica Padova,report DFPD-94-NP-4

Variational principles for involutive systems of vector fields

In many relevant cases -- e.g., in hamiltonian dynamics -- a given vector field can be characterized by means of a variational principle based on a one-form. We discuss how a vector field on a manifold can also be characterized in a similar way by means of an higher order variational principle, and how this extends to involutive systems of vector fields.Comment: 31 pages. To appear in International Journal of Geometric Methods in Modern Physics (IJGMMP

NHS commissioning practice and health system governance: a mixed-methods realistic evaluation

Background By 2010 English health policy-makers had concluded that the main NHS commissioners [primary care trusts (PCTs)] did not sufficiently control provider costs and performance. After the 2010 general election, they decided to replace PCTs with general practitioner (GP)-controlled Clinical Commissioning Groups (CCGs). Health-care commissioners have six main media of power for exercising control over providers, which can be used in different combinations (‘modes of commissioning’). Objectives To: elicit the programme theory of NHS commissioning policy and empirically test its assumptions; explain what shaped NHS commissioning structures; examine how far current commissioning practice allowed commissioners to exercise governance over providers; examine how commissioning practices differ in different types of commissioning organisation and for specific care groups; and explain what factors influenced commissioning practice and the relationships between commissioners and providers. Design Mixed-methods realistic evaluation, comprising: Leximancer and cognitive frame analyses of policy statements to elicit the programme theory of NHS commissioning policy; exploratory cross-sectional analysis of publicly available managerial data about PCTs; systematic comparison of case studies of commissioning in four English sites – including commissioning for older people at risk of unplanned hospital admission; mental health; public health; and planned orthopaedic surgery – and of English NHS commissioning practice with that of a German sick-fund and an Italian region (Lombardy); action learning sets, to validate the findings and draw out practical implications; and two framework analyses synthesising the findings and testing the programme theory empirically. Results In the four English case study sites, CCGs were formed by recycling former commissioning structures, relying on and maintaining the existing GP commissioning leaderships. The stability of distributed commissioning depended on the convergence of commissioners’ interests. Joint NHS and local government commissioning was more co-ordinated at strategic than operational level. NHS providers’ responsiveness to commissioners reflected how far their interests converged, but also providers’ own internal ability to implement agreements. Commissioning for mental health services and to prevent recurrent unplanned hospital readmissions relied more on local ‘micro-commissioning’ (collaborative care pathway design) than on competition. Service commissioning was irrelevant to intersectoral health promotion, but not clinical prevention work. On balance, the possibility of competition did not affect service outcomes in the ways that English NHS commissioning policies assumed. ‘Commodified’ planned orthopaedic surgery most lent itself to provider competition. In all three countries, tariff payments increased provider activity and commissioners’ costs. To contain costs, commissioners bundled tariff payments into blocks, agreed prospective case loads with providers and paid below-tariff rates for additional cases. Managerial performance, negotiated order and discursive control were the predominant media of power used by English, German and Italian commissioners. Conclusions Commissioning practice worked in certain respects differently from what NHS commissioning policy assumed. It was often laborious and uncertain. In the four English case study sites financial and ‘real-side’ contract negotiations were partly decoupled, clinician involvement being least on the financial side. Tariff systems weakened commissioners’ capacity to choose providers and control costs. Commissioners adapted the systems to solve this problem. Our findings suggest a need for further research into whether or not differently owned providers (corporate, third sector, public, professional partnership, etc.) respond differently to health-care commissioners and, if so, what specific implications for commissioning practice follow. They also suggest that further work is needed to assess how commissioning practices impact on health system integration when care pathways have to be constructed across multiple providers that must tender competitively for work, perhaps against each other. Funding The National Institute for Health Research Health Services and Delivery Research programme

Reduction and reconstruction of stochastic differential equations via symmetries

An algorithmic method to exploit a general class of infinitesimal symmetries for reducing stochastic differential equations is presented and a natural definition of reconstruction, inspired by the classical reconstruction by quadratures, is proposed. As a side result the well-known solution formula for linear one-dimensional stochastic differential equations is obtained within this symmetry approach. The complete procedure is applied to several examples with both theoretical and applied relevance

Stratification of the orbit space in gauge theories. The role of nongeneric strata

Gauge theory is a theory with constraints and, for that reason, the space of physical states is not a manifold but a stratified space (orbifold) with singularities. The classification of strata for smooth (and generalized) connections is reviewed as well as the formulation of the physical space as the zero set of a momentum map. Several important features of nongeneric strata are discussed and new results are presented suggesting an important role for these strata as concentrators of the measure in ground state functionals and as a source of multiple structures in low-lying excitations.Comment: 22 pages Latex, 1 figur

On the relation between standard and μ\mu-symmetries for PDEs

We give a geometrical interpretation of the notion of $\mu$-prolongations of vector fields and of the related concept of $\mu$-symmetry for partial differential equations (extending to PDEs the notion of $\lambda$-symmetry for ODEs). We give in particular a result concerning the relationship between $\mu$-symmetries and standard exact symmetries. The notion is also extended to the case of conditional and partial symmetries, and we analyze the relation between local $\mu$-symmetries and nonlocal standard symmetries.Comment: 25 pages, no figures, latex. to be published in J. Phys.

Rapidity distributions around mid-rapidity of strange particles in Pb-Pb collisions at 158 AA GeV/c

The production at central rapidity of K0s, Lambda, Xi and Omega particles in Pb-Pb collisions at 158 A GeV/c has been measured by the NA57 experiment over a centrality range corresponding to the most central 53% of the inelastic Pb-Pb cross section. In this paper we present the rapidity distribution of each particle in the central rapidity unit as a function of the event centrality. The distributions are analyzed based on hydrodynamical models of the collisions.Comment: 15 pages, 10 figure

Strangeness enhancements at central rapidity in 40 A GeV/c Pb-Pb collisions

Results are presented on neutral kaon, hyperon and antihyperon production in Pb-Pb and p-Be interactions at 40 GeV/c per nucleon. The enhancement pattern follows the same hierarchy as seen in the higher energy data - the enhancement increases with the strangeness content of the hyperons and with the centrality of collision. The centrality dependence of the Pb-Pb yields and enhancements is steeper at 40 than at 158 A GeV/c. The energy dependence of strangeness enhancements at mid-rapidity is discussed.Comment: 15 pages, 10 figures and 3 tables. Presented at International Conference on Strangeness in Quark Matter (SQM2009), Buzios, Rio de Janeiro, Brazil, 27 Sept - 2 Oct 2009. Submitted to J.Phys.G: Nucl.Part.Phys, one reference adde

Strange particle production in 158 and 40 AA GeV/cc Pb-Pb and p-Be collisions

Results on strange particle production in Pb-Pb collisions at 158 and 40 $A$ GeV/$c$ beam momentum from the NA57 experiment at CERN SPS are presented. Particle yields and ratios are compared with those measured at RHIC. Strangeness enhancements with respect to p-Be reactions at the same beam momenta have been also measured: results about their dependence on centrality and collision energy are reported and discussed.Comment: Contribution to the proceedings of the "Hot Quarks 2004" Conference, July 18-24 2004, New Mexico, USA, submitted to Journal of Physics G 7 pages, 5 figure

Strangeness Enhancement in p+Ap+A and S+AS+A Interactions at SPS Energies

The systematics of strangeness enhancement is calculated using the HIJING and VENUS models and compared to recent data on $\,pp\,$, $\,pA\,$ and $\,AA\,$ collisions at CERN/SPS energies ($200A\,\, GeV\,$). The HIJING model is used to perform a {\em linear} extrapolation from $pp$ to $AA$. VENUS is used to estimate the effects of final state cascading and possible non-conventional production mechanisms. This comparison shows that the large enhancement of strangeness observed in $S+Au$ collisions, interpreted previously as possible evidence for quark-gluon plasma formation, has its origins in non-equilibrium dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced back to the change in the production dynamics %from $pp$ to minimum bias $pS$ and central $SS$ collisions. A factor of two enhancement of $\Lambda^{0}$ at mid-rapidity is indicated by recent $pS$ data, where on the average {\em one} projectile nucleon interacts with only {\em two} target nucleons. There appears to be another factor of two enhancement in the light ion reaction $SS$ relative to $pS$, when on the average only two projectile nucleons interact with two target ones.Comment: 29 pages, 8 figures in uuencoded postscript fil