ALICE Upgrade

Quantum-ChromoDynamics (QCD) is the theory of the strong force and understanding its properties has been the focus of intense World-wide research over the past half century. QCD forms a major part of the Standard Model and its understanding is crucial in producing an overall theory to describe the properties of matter and the fundamental forces of nature including a grand unification theory to explain how the Universe evolved from the Big Bang.

The principal purpose of our research is to use ultra-relativistic heavy-ion interactions to study QCD at extreme energy densities. Theoretical models predict that under very extreme conditions of high energy densities the quarks, which are confined in normal nuclear matter, will be freed and nuclear matter will undergo a phase transition into a hot, dense plasma of free quarks and gluons known as a Quark-Gluon Plasma (QGP). It is thought that such a state of matter would have existed until about 10^-5 seconds after the Big Bang, after which time the Universe would have cooled sufficiently for protons and neutrons to form.

The physics aim of this research is to study the strong force under these extreme conditions and, in particular, explore the properties of this exotic state of matter. By studying the QGP, we hope to address the fundamental questions of quark confinement and how quarks gain a large effective mass in hadrons due to the strong force (accounting for 99% of atomic mass).

In order to create the conditions required to produce a QGP we must collide heavy nuclei together at the highest possible energies, creating tiny hot (~10^13K) and dense fireballs. As the resulting QGP will only last for about 10-22 seconds, before condensing in to thousands of elementary particles, we must also use the most sophisticated detectors to analyse these collisions.

The LHC collides lead ions at centre-of-mass energies of 2.76 TeV in ALICE. We also collide protons together as this forms an excellent reference data set. Moreover, the excellent particle identification and tracking make ALICE an ideal detector to study the global aspects of proton-proton collisions in their own right.

This field of research employs about two thousand physicists around the world and ALICE is the most sophisticated experiment ever built in the field, studying heavy-ion collisions at centre-of-mass energies over an order of magnitude greater than its nearest rival. It hence represents the pinnacle of research in this field.

The ALICE collaboration is now preparing for the second LHC upgrade scheduled to start in 2018. These upgrades are required to cope with the anticipated increase in lead beam luminosity which will increase beam intensities by an order of magnitude. The main motivation for the luminosity upgrade is to achieve a precise, quantitative understand of the properties of the QGP by focusing on rare probes both at low and high transverse momenta as well as on multi-dimensional analysis of such probes with respect to centrality, event plane, multi-particle correlations, etc.

The ALICE-UK Collaboration proposes to play a leading role in the ALICE Upgrade at the LHC (CERN), in particular the upgrades to the Central Trigger Processor (CTP) and the Inner Tracking System (ITS) where it has recognised international leadership. This will enable us to continue to be responsible for the vital CTP to bring our world-class expertise in Si Tracking Detector Systems to the ALICE ITS Upgrade Project. This will position us to play a leading role in the future, precision, measurements of heavy flavour probes of the partonic matter produced in Pb-Pb collisions at the LHC, building on the leading role we currently play in the measurements of light and heavy flavour probes with the exiting detector. This project will capitalise on the prior investment of STFC in the ALICE experiment by sustaining and enhancing the leadership role the UK plays.

The main beneficiaries of this upgrade will be experimentalists and theorists working in the field of hot Quantum Chromodynamics. They will directly benefit from the new insights that will arise out of the research, made possible by this upgrade. The results of the subsequent research will be disseminated in high impact journals, through conference talks and seminars so as to reach as wide an audience as possible. More broadly, both the technologies developed during the upgrade and the resulting research will also be of relevance to researchers in other fields, including other areas of nuclear physics, particle physics, astrophysics and cosmology. Some of the hardware developments related to the Birmingham design of the original ALICE trigger subsystem have already had impact, having being adopted by another experiment at CERN. Future developments that are foreseen in this proposal will potentially have relevance to a new generation of experiments planning to run in continuous data taking mode. The ITS upgrade project will develop MAPS technologies, an area where the UK is already considered to be a world leader. Such technologies will not only have applications for other particle detectors but are likely to have applications in the areas of medicine and security.

Another strand revolves around the public understanding of science. The research that is related to this proposal has the potential to capture the imagination and to inspire a new generation of scientists. The research programme which will arise from this upgrade is involved in studying matter as it would have existed a fraction of a second after the Big Bang. This aspect is relevant to the evolution of the Early Universe and the possible existence of (strange) quark matter stars. Members of the ALICE-UK collaboration have given over 70 public lectures over the past five years and been involved in many other public outreach event to school children, teachers, and members of the general public.