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Heavy Ion Collisions and Strings at CERN

Final Report Summary - HICSCERN (Heavy Ion Collisions and Strings at CERN)

One of the main objectives of the Large Hadron Collider (LHC) is the study of the properties of matter at the largest temperatures ever achieved in a laboratory. This is pursued by colliding lead nuclei at extremely high energy and observing the many particles produced in the collision. The temperatures reached by this method are so high that the protons and neutrons that form the colliding nuclei melt liberating the quarks and gluons they are made off. For a short period of time these partons form a new state of matter, the Quark Gluon Plasma (QGP), with very interesting and unusual properties, such as very low viscosity and extreme opacities. One of the most fascinating of those properties is that in the plasma the quarks and gluons, instead of behaving as (quasi) particles that scatter scarcely, they interact so much that they loose their identity and they cannot be told apart from one another.
The description of plasma with no (quasi) particles poses a big theoretical problem. The standard theoretical tools available for analyzing the interactions amongst quarks and gluons, which are described by Quantum Chromo Dynamics (QCD), are not suitable for this problem. As a step towards developing those tools, there has been a lot of effort in understanding the dynamics of other theories different from QCD but for which techniques able to address this physical regime are available. These techniques, which originate from string theory, are known under the generic name of gauge/gravity duality and relate, in a mathematical way, complicated field theories which govern interactions among particles with much simpler gravitational theories. However, since these tools are not available for QCD itself, but only for theories alike, it is important to design tests, both theoretical and experimental, which can address how reliable the studies based on the gauge/gravity duality can be. Developing some of these tests has been the major objective of this project.
The work in this project has concentrated mainly in the way the heavier quarks produced in energetic collisions interact with the rest of the formed QCD matter. The reason for this is two-fold: first of all, the theoretical treatment of those quarks within the gauge/gravity duality is well understood; secondly, unlike previous experiments, at the LHC heavy quarks will be produced copiously allowing both their unambiguous identification and detailed experimental studies.