Virtual bremsstrahlung from pions and quarks in thermalized hadronic matter

A soft photon approximation is used to calculate the rates of lepton pair production through virtual bremsstrahlung from both pions and quarks. Standard assumptions about the evolution of a nuclear system under collision allow pion and quark driven total production to be calculated. Comparisons are made with Dalitz decay of light mesons. These mechanisms are expected to be significant contributors to the soft dilepton mass spectra one might observe in heavy ion collisions at RHIC and LHC energies.Comment: 9 page

Meson Mixing and Dilepton Production in Heavy Ion Collisions

We study the possibility of $\rho-a_0$ mixing via N-N excitations in dense nuclear matter. This mixing is found to induce a peak in the dilepton spectra at an invariant mass equal to that of the $a_0$. We calculate the cross section for dilepton production through mixing and we compare its size with that of $\pi-\pi$ annihilation. In-medium masses and mixing angles are also calculated. Some preliminary results of the mixing effect on the dilepton production rates at finite temperature are also presented.Comment: To be published in the proceedings of CIPANP 200

A unique parametrization of the shapes of secondary dilepton spectra observed in central heavy-ion collisions at CERN-SPS energies

A unique parametrization of secondary (thermal) dilepton yields in heavy-ion experiments at CERN-SPS is proposed. This parametrization resembles a thermal $q \bar q$ annihilation rate. This is inspired by the observation that lepton pair production rates are quantitatively similar, whether expressed in a hadronic or partonic basis. Adding the thermal yield and the background contributions (hadronic cocktail, Drell-Yan, correlated semileptonic decays of open charm) the spectral shapes of the CERES/NA45, NA38, NA50 and HELIOS/3 data from experiments with lead and sulfur beams can be well described.Comment: 23 pages including figures (new version: only new output format

An evaluation of staff engagement programmes in four National Health Service Acute Trusts

Purpose – The purpose of this paper is to report the findings from an evaluation project conducted to investigate the impact of two staff engagement programmes introduced to four National Health Service (NHS) hospital Trusts in England. It seeks to examine this development in the context of current policy initiatives aimed at increasing the level of staff involvement in decision-making, and the related literature. \ud \ud Design/methodology/approach – A mixed-methods approach incorporating document analysis, interviews, a survey and appreciative inquiry, informed by the principles of impact evaluation design, was used. \ud \ud Findings – The main finding to emerge was that leadership was crucial if widespread staff engagement was to be achieved. Indeed, in some of the trusts the staff engagement programmes were seen as mechanisms for developing leadership capability. The programmes had greater impact when they were “championed” by the Chief Executive. Effective communication throughout the organisations was reported to be a prerequisite for staff engagement. Problems were identified at the level of middle management where the lack of confidence in engaging with staff was a barrier to implementation. \ud \ud Practical implications – The nature of the particular organisational context is crucial to the success of efforts to increase levels of staff engagement. The measures that were found to work in the trusts would need to be adapted and applied to best meet the needs of other organisations. \ud \ud Originality/value – Many health care organisations in England will need to harness the efforts of their workforce if they are to meet the significant challenges of dealing with financial restraint and increasing patient demand. This paper provides some insights on how this can be done

Soft dilepton production in relativistic heavy ion collisions

Production of electron-positron pairs with invariant masses less than 300 MeV from thermalized hadronic matter in relativistic heavy ion collisions is calculated using a soft virtual photon approximation. The general theoretical framework is reviewed and extended to include arbitrarily massed and charged reaction partners, which we apply to pions and quarks. This result, exact within the soft photon approximation, is compared with a widely used approximate result which uses an electromagnetic amplitude limited in validity to momentum transfers less than $4m_{\pi(q)}^{2}$. A comparison is made between the rate of production of zero total momentum soft dileptons obtained using resummation techniques in QCD perturbation theory to that which we calculate using this soft photon approximation.Comment: 29 pages typed in revtex, 13 figures (not included), hardcopy available by regular mail upon request, McGill/92-3

Dilepton Yield in Heavy-Ion Collisions with Bose Enhancement of Decay Width

The excess of low invariant mass dilepton yield in heavy ion collisions arising from reduction in the rho meson mass at finite temperatures is partially suppressed because of the effect on the width of the rho meson induced by Bose enhancement, essentially due to emission of pions in a medium of the pion gas in the central rapidity region. The sensitivity of the effect on the initial temperature of the hadronic phase is also examined.Comment: Plain latex fil

Pion and Quark Annihilation Mechanisms of Dilepton Production in Relativistic Heavy-Ion Collisions

We revise the pion-pion and quark-quark annihilation mechanisms of dilepton production during relativistic heavy-ion collisions. We focus on the modifications caused by the specific features of intramedium pion states rather than by medium modification of the rho-meson spectral density. The main ingredient emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, "connects" the 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the dilepton production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant masses below two masses of the annihilating particles.Comment: 6 pages, 6 figures, LaTex; to appear in Mod. Phys. Lett.