2,414 research outputs found
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
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
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
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
Results from the first heavy ion run at the LHC
Early November 2010, the LHC collided for the first time heavy ions, Pb on
Pb, at a centre-of-mass energy of 2.76 TeV/nucleon. This date marked both the
end of almost 20 years of preparing for nuclear collisions at the LHC, as well
as the start of a new era in ultra-relativistic heavy ion physics at energies
exceeding previous machines by more than an order of magnitude. This
contribution summarizes some of the early results from all three experiments
participating in the LHC heavy ion program (ALICE, ATLAS, and CMS), which show
that the high density matter created at the LHC, while much hotter and larger,
still behaves like the very strongly interacting, almost perfect liquid
discovered at RHIC. Some surprising and even puzzling results are seen in
particle ratios, jet-quenching, and Quarkonia suppression observables. The
overall experimental conditions at the LHC, together with its set of powerful
and state-of-the-art detectors, should allow for precision measurements of
quark-gluon-plasma parameters like viscosity and opacity.Comment: Invited talk at the Rutherford Centennial Conference on Nuclear
Physics, July 25 - 29, 2011, Manchester, U
NA49/NA61: results and plans on beam energy and system size scan at the CERN SPS
This paper presents results and plans of the NA49 and NA61/SHINE experiments
at the CERN Super Proton Synchrotron concerning the study of relativistic
nucleus-nucleus interactions. First, the NA49 evidence for the energy threshold
of creating quark-gluon plasma, the onset of deconfinement, in central
lead-lead collisions around 30A GeV is reviewed. Then the status of the
NA61/SHINE systematic study of properties of the onset of deconfinement is
presented. Second, the search for the critical point of strongly interacting
matter undertaken by both experiments is discussed. NA49 measured large
fluctuations at the top SPS energy, 158A GeV, in collisions of light and medium
size nuclei. They seem to indicate that the critical point exists and is
located close to baryonic chemical potential of about 250 MeV. The NA61/SHINE
beam energy and system size scan started in 2009 will provide evidence for the
existence of the critical point or refute the interpretation of the NA49
fluctuation data in terms of the critical point.Comment: 11 pages, invited talk at Quark Matter 201
Medium information from anisotropic flow and jet quenching in relativistic heavy ion collisions
Within a multiphase transport (AMPT) model, where the initial conditions are
obtained from the recently updated HIJING 2.0 model, the recent anisotropic
flow and suppression data for charged hadrons in Pb+Pb collisions at the LHC
center of mass energy of 2.76 TeV are explored to constrain the properties of
the partonic medium formed. In contrast to RHIC, the measured centrality
dependence of charged hadron multiplicity dN_ch/deta at LHC provides severe
constraint to the largely uncertain gluon shadowing parameter s_g. We find
final-state parton scatterings reduce considerably hadron yield at midrapidity
and enforces a smaller s_g to be consistent with dN_ch/deta data at LHC. With
the parton shadowing so constrained, hadron production and flow over a wide
transverse momenta range are investigated in AMPT. The model calculations for
the elliptic and triangular flow are found to be in excellent agreement with
the RHIC data, and predictions for the flow coefficients v_n(p_T, cent) at LHC
are given. The magnitude and pattern of suppression of the hadrons in AMPT are
found consistent with the measurements at RHIC. However, the suppression is
distinctly overpredicted in Pb+Pb collisions at the LHC energy. Reduction of
the QCD coupling constant alpha_s by ~30% in the higher temperature plasma
formed at LHC reproduces the measured hadron suppression.Comment: Talk given by Subrata Pal at the 11th International Conference on
Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1,
2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference
Series (JPCS
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