Ultra-relativistic heavy ion collisions - Application for bridging support

Most of the visible mass of the universe is in the form of protons and neutrons that make up the everday nuclei found within the elements we see around us. This might suggest that protons and neutrons are the fundamental building blocks of matter, but, in fact, protons and neutrons are themselves composed of more fundamental particles known as quarks. Quarks are strongly attracted to each other and are never seen in isolation. They owe their attraction to gluons, which are force particles that stick quarks together. What makes this attraction different from other types of forces is that the gluons attract each other too. It is this interaction amongst the force particles that makes the nuclear force so strong. It also has a rather surprising effect: the strength of the interaction decreases with distance. This suggests that at high enough densities quarks and gluons behave as if they are free particles. In this case protons and neutrons would not exist at all. Instead matter would be comprised of a plasma of quarks and gluons. This would have been what matter was like during the first fraction of a second after the Big Bang. Attempts are now underway to recreate the conditions of the Big Bang in the laboratory, albeit on a much smaller scale, by colliding heavy nuclei at very high energies. In a head-on collision between two nuclei a significant amount of kinetic energy is converted into new particles, producing matter which is both extremely dense and extremely hot. What is needed is an experimental probe that can tell us exactly how dense and how hot it really is. One way to do this is to study jets. Jets occur when quarks and gluons collide head-on and are scattered sideways. As free quarks and gluons are not observed, they shower into a jet of hadrons. This is a rare process, but sufficient numbers are produced to make them a powerful diagnostic tool. The key to their usefulness lies in the fact that they can be absorbed in the hot dense medium that is the quark-gluon plasma, making them an ideal tool for studying the properties of this new state of matter. This proposal seeks to unite two experimental groups at Birmingham University to study jets, amongst other observables, in heavy-ion collisions at the Large Hadron Collider (LHC), which is situtated at the European Centre for Nuclear Research (CERN) in Switzerland. The LHC will start colliding protons in late 2007 and the first heavy-ion beams are expected at the end of 2008. Compared to previous studies at the Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC), near New York, the LHC will achieve collision energies 30 times higher than seen before. It is expected that the initial temperature will be 4-5 times higher than the critical temperature required to observe a transition to quark deconfined matter. One of the groups at Birmingham is already heavily involved in preparations for the first collisions to be seen in the ALICE experiment. The other group has been involved in an experiment called STAR at the RHIC facility and bring with them experience of data analysis using a similar detector system. Together, it is hoped that the two groups will make a major impact on an international quest to discover what matter was like a fraction of a second after the Big Bang.