Heavy Ion physics with the ALICE experiment at the CERN LHC

After close to 20 years of preparation, the dedicated heavy ion experiment ALICE took first data at the CERN LHC accelerator with proton collisions at the end of 2009 and with lead nuclei at the end of 2010. After a short introduction into the physics of ultra-relativistic heavy ion collisions, this article recalls the main design choices made for the detector and summarizes the initial operation and performance of ALICE. Physics results from this first year of operation concentrate on characterizing the global properties of typical, average collisions, both in pp and nucleus-nucleus reactions, in the new energy regime of LHC. The pp results differ, to a varying degree, from most QCD inspired phenomenological models and provide the input needed to fine-tune their parameters. First results from Pb-Pb are broadly consistent with expectations based on lower energy data, indicating that high density matter created at LHC, while much hotter and larger, still behaves like a very strongly interacting, almost perfect liquid.Comment: Talk given at Royal Society meeting on "Physics at the high energy frontier - the Large Hadron Collider project", London, 16 - 17 May 2011, to be published in "Philosophical Transactions of the Royal Society A

Heavy Ion Physics at the LHC: What's new ? What's next ?

Towards the end of 2010, some 25 years after the very first collisions of ultra-relativistic heavy ions at fixed target energies, and some 10 years after the start of operation of the Relativistic Heavy Ion Collider (RHIC), the LHC opened a new era in heavy ion physics with lead on lead collisions at $\sqrt{s_{NN}} = 2.76$ TeV. After a short reminder of the main results from lower energies, this review highlights a few selected areas where significant progress has been made during the first three years of ion operation at the LHC.Comment: Talk given at the 'Nobel Symposium on LHC results', Krusenberg, Sweden, 13 - 17 May 2013, to be published in Physica Script

QM2017: Status and Key open Questions in Ultra-Relativistic Heavy-Ion Physics

Almost exactly 3 decades ago, in the fall of 1986, the era of experimental ultra-relativistic (\emph{E/m $\gg 1$}) heavy ion physics started simultaneously at the SPS at CERN and the AGS at Brookhaven with first beams of light Oxygen ions at fixed target energies of 200 GeV/A and 14.6 GeV/A, respectively. The event was announced by CERN \cite{cernpress1,cernpress2} with the usual superlatives "Break new ground.., World Record Energy ..", but also with the information that "up to 400 particles were created per collision" and that "over 300 physicists .. analyzing the data .. [try] to find out whether the famous quark-gluon plasma really has been achieved". One would have thought that with almost one physicist per particle, this would have been figured out rather quickly. However, as we know today, 30 years and 21 Quark Matter conferences later, the study of dense and hot matter, of the strong interaction in the non-perturbative regime, has been a long and winding road. The journey was much more difficult and time consuming, but also much more interesting and rewarding, than anyone could have anticipated, with many twists, some dead ends, and a never-ending string of surprises. This $30^{th}$ anniversary of heavy ion physics, and the start of the 26$^{th}$ Quark Matter in Chicago, is a good opportunity to look back and mention a few of the major results from each of the three eras (fixed target/RHIC/LHC), along with some of the answers they have provided us and some of the key questions which remain to be solved.Comment: Opening Talk of the 'XXVIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2017

Hard Probes 2012: Experimental Summary

The 5th international Conference on Hard and Electromagnetic Probes in High-Energy Nuclear Collisions was held in May 2012 in Cagliari, Italy. This contribution summarises some of the experimental highlights presented at the meeting, concentrating on new results from LHC and RHIC on parton energy loss ('jet-quenching') and heavy quark meson production ('quarkonia suppression').Comment: Writeup of experimental summary talk of the 5th international Conference on Hard and Electromagnetic Probes in High-Energy Nuclear Collisions ('Hard Probes 2012'). Version 2: some minor typos corrected, references added, version as publishe

CERN, a working example of global scientific collaboration

The topic of this conference is 'South-South and North-South Collaboration in Science and Technology', which is addressed in this contribution in the context of basic research in high energy physics (HEP). The question whether developing countries can or should invest scarce resources in big science is not covered. HEP may be less expensive than one might fear, but cheap it is not, so priorities have to be set and these may indeed differ from country to country. The scope of this article is not to argue one way or another, but rather to give an indication and practical examples of both the requirements and the opportunities for scientific collaboration with CERN.Comment: Invited talk at the international meeting 'South-South and North-South Collaboration in Science and Technology', Islamabad, Pakistan, 12-13 March 2004; 3 pages, no figure

The Future of High Energy Nuclear Physics in Europe

In less than two years from now, the LHC at CERN will start operating with protons and later with heavy ions in the multi TeV energy range. With its unique physics potential and a strong, state-of-the complement of detectors, the LHC will provide the European, and in fact worldwide Nuclear Physics community, with a forefront facility to study nuclear matter under extreme conditions well into the next decade.Comment: Invited talk at the 'D. A. Bromley Memorial Symposium', Yale University, USA, 8-9 December 2005; to be published in the proceedings; 6 pages, 4 figure

ALICE results from the first Pb-Pb run at the CERN LHC

After 20 years of preparation, the dedicated heavy ion experiment ALICE took first data at the CERN LHC accelerator with proton collisions at the end of 2009 and with lead beams at the end of 2010. This article will give a brief overview of the main results presented at the Quark Matter 2011 conference.Comment: Inited talk at the 22nd International Conference on Ultra-relativistic Nucleus-Nucleus Collision (Quark Matter 2011), 23 - 28 May 2011, Annecy, Franc