UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-23 18:26
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Conference: Bucharest University Faculty of Physics 2014 Meeting


Section: Theoretical Physics and Applied Mathematics


Title:
The pi-/pi+ multiplicity ratio in heavy-ion collisions and the conservation of energy


Authors:
D. COZMA


Affiliation:
IFIN-HH, Reactorului 30, 077125 Magurele, Romania


E-mail
dan.cozma@theory.nipne.ro


Keywords:
heavy-ion collisions, equation of state of nuclear matter, symmetry energy, transport models


Abstract:
The multiplicity ratio of pi-/pi+ meson in heavy-ion collisions at few-hundred MeV impact energy has been proven to be an observable sensitive to the isovector part of the equation of state of nuclear matter (asy-EoS). However, constraints for the stiffness of the asy-EoS extracted using this observable are extremely model dependent and additionally are often in contradiction with those extracted from elliptic flow observables. The present study focuses on an upgrade of the Tuebingen QMD transport model, achieved by enforcing the conservation of energy at a local (LEC) or global (GEC) level in collision, decay and absorption processes by including contributions due to in-medium density, isospin asymmetry and momentum dependent baryon potential energies for both nucleons and baryonic resonances, which has as an effect the in-medium modification of particle production thresholds. It is shown that compatible constraints for asy-EoS stiffness from pi-/pi+ multiplicity ratio and elliptic flow can be extracted only within the GEC scenario. However, an important dependence of the pi-/pi+ observable on the strength of the isovector part of the Delta(1232) isobar potential is also demonstrated. The lack of information on this quantity prevents at present a precise extraction of the value for the asy-EoS stiffness employing the mentioned observable. A remedy of this situation will however make experimental information on pi-/pi+ multiplicity ratio in heavy-ion collisions close to or below pion production threshold extremely valuable.