This is a proposal for a Research Training Network (RTN) that will explore 
the fundamental question of the origin of mass, using the early data from 
the ATLAS detector at the Large Hadron Collider of CERN.

Our current understanding of elementary particles and their fundamental 
interactions is embodied in the Standard Model (SM) of Particle Physics, 
which was developed during the 1960s and 1970s. In the past three decades 
a large number of experiments have provided very stringent tests for the 
SM and in all cases the predictions of the theory were convincingly 
confirmed by the experimental results.

Despite its impressive success, the SM provides no explanation for some of 
the most fundamental questions in modern science. Indeed, one of the least 
satisfactory sectors of the theory is related to the origin of mass of the 
elementary particles. In order to accommodate the masses of elementary 
particles, the SM relies on the existence of a Higgs field and the 
mechanism of electroweak symmetry breaking. This leads to the prediction 
of a fundamental, massive particle, the Higgs boson. The Higgs has not 
been observed experimentally yet. Its discovery would be a triumph of the 
SM and would provide a great insight into the mass generation mechanism, 
while at the same time it will open up the way for probing the theory 
beyond the SM. 

The SM predicts all the properties of the Higgs boson except - ironically! 
- its mass. Direct experimental searches have so far produced negative 
results, concluding that the SM Higgs must be heavier than ~114GeV at 95% 
confidence level (CL). Although not directly observable, the Higgs has, 
according to the SM, an indirect influence on experimentally observable 
quantities. Combining very precise measurements of such quantities 
(electroweak observables), it has been inferred that the SM Higgs is 
lighter than ~250GeV at 95% CL, with the most likely mass value close to 
the limit from the direct searches. 

Independent of any experimental results, internal consistency of the SM 
requires that the mass of the Higgs boson is below 700GeV or so. This is 
one of the main reasons why the Particle Physics community is confident 
that the data taken with the Large Hadron Collider (LHC) at CERN will mark 
the beginning of a new era in our understanding of nature.
The LHC is expected to start operation in summer 2007 and will collide 
proton beams at a centre-of-mass energy of 14TeV, almost an order of 
magnitude higher than is currently achieved, at a design luminosity of 
1034cm-2s-1, more than one order of magnitude higher than ever before. 
With this performance, the LHC will provide within a few years a 
phenomenal amount of data that will allow the full exploration of the 
energy range up to a few TeV.

ATLAS is one of the two general purpose detectors that will record the 
data from the LHC collisions and is currently in the installation phase at 
CERN. Nearly 2,000 physicists and engineers from over 100 institutes are 
contributing to the project, which relies on numerous novel technologies 
to address the challenges posed by the unprecedented conditions at the 
LHC. In addition, state-of-the-art computing, network and software 
technologies are being put together to record and analyse a colossal 
volume of data. 

Given the complexity of the project, the expertise is spread among the 
various institutes of the ATLAS collaboration worldwide. The RTN proposed 
in this outline will draw together the expertise in certain key areas of 
ATLAS in order to achieve the optimal performance both of individual 
components and their combination, and hence to maximize the physics 
potential of the experiment. The expertise of the institutes participating 
in this proposal is particularly suited for the physics programme we 
intend to pursue, but much of the work that will be carried by the RTN 
will have a major positive impact on the overall performance and the 
physics reach of the ATLAS detector.

The main scientific objective of the proposed RTN is to investigate the 
nature of the electroweak symmetry breaking, by searching directly for the 
Higgs boson in a number of key topologies or indirectly, through the 
process of longitudinal vector boson fusion, which will provide valuable 
insight in the absence of a Higgs discovery. In order to maximize our 
chances of success, we will use the commissioning period and the first 
data of ATLAS to understand and optimise the performance of its 
subsystems. We will then concentrate on measuring some fundamental SM 
cross sections, which will be largely used as benchmark measurements to 
ensure that the ATLAS data are well understood. At the same time, some of 
these processes are often among the important backgrounds in the Higgs 
searches. Finally, while continuing to ensure the optimal quality of the 
recorded data, we will then move systematically to the investigation of 
the electroweak symmetry breaking as detailed above.

An important element of the proposed RTN is that it also brings together 
world experts from both the theoretical and the experimental Particle 
Physics communities, which often are fragmented and work independently. 
This is of particular importance as the LHC takes us into a completely 
unexplored energy regime and many theoretical projections and predictions 
will be seriously tested. The close interaction between theory experts and 
experimentalists will allow for swift, thorough and critical evaluation of 
the experimental results and will no doubt require revisions of 
theoretical models and new calculations.  

In the following sections of this outline proposal we present in more 
detail the work plan of the RTN, and describe the training programme, 
benefits and opportunities for the participating young researchers.