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Super Symmetry and Higgs boson Search by an improved particle and energy flow reconstruction within the CMS detector at the LHC – SUSY-HIGGS

Submission summary

Scientific Context In 2008, the physics programme of the Large Hadron Collider (LHC) at CERN, Geneva, will start with its first collisions at the nominal energy of 14 TeV. In the first three years of its operation the experiment CMS will accumulate a total of 1 fb-1 in 2008 increasing to about 10 fb-1 by the end of 2010. For these luminosities fundamental new discoveries are expected in the scalar sector of the standard model (SM) of particle physics and in many of its extensions like supersymmetry (SUSY). Supersymmetry would manifest itself at LHC by large missing transverse energy together with multiple leptons and hard jets. For a large part of the allowed mass range the best discovery channel for the SM Higgs boson is the detection of two or four isolated leptons. In the case of a supersymmetric Higgs boson, the associated production bbA/H, followed by the decay A/H to tau-tau or bb, has the best discovery potential. Project Description and Methodology The aim of the SUSY-Higgs project is to merge the expertise of three French research groups in order to develop new tools for the best identification and reconstruction of isolated leptons (electron, muon and tau), photons, missing transverse energy and jets (including the identification of b quark jets, of utmost importance for the reconstruction of top quarks). The teams participating in this project have strongly contributed to the development and construction of the silicon detector tracking system and the electromagnetic crystal calorimeter, the two crucial detectors for discoveries at the LHC. The groups involved are known for their expertise in developing reconstruction algorithms for electrons, tau leptons, photons and the identification of b jets. The new method proposed here, 'particle flow', will make optimal use of these two most precise detectors of the CMS experiment in the off-line reconstruction of all physics objects. Their combined power can in many cases significantly compensate the marginal resolution of the hadronic calorimeter Indeed, while charged hadrons are traditionally reconstructed using the hadronic calorimeter, particle flow makes use of the tracker, and thus benefits of its superior angular and energy resolution. Preliminary studies have already demonstrated that the energy resolution of the reconstruction of hadronic tau jets is improved by a factor of 4. For a Higgs boson decaying to a pair of b quarks, a gain of 20% can be achieved on the invariant mass resolution. Expected Results Particle flow reconstruction will improve the signal over noise ratio of most Higgs channels in three different ways: first by improving the invariant mass resolution on resonances such as A/H to tau-tau; then by reducing the background coming from misidentifications, for example of tau leptons; finally by allowing the reconstruction of non isolated electrons and muons. Particle flow will provide a more robust understanding of missing transverse energy, which is particularly important to unveil supersymmetry. Together with the better tau lepton reconstruction this may well allow its discovery in the early years of LHC in a convincing way. Furthermore, even without new physics signal, the developed method will be of great benefit for the whole CMS collaboration in many other physics analyses, particularly for precision tests of the standard model which will help to constrain its possible extensions. International Context The French High Energy Physics community is involved in the CMS experiment since the beginning. IN2P3 represented by the three institutes (IPHC, LLR, IPNL) has contributed with important investments of manpower, scientific and technical know-how and financial support to the development and construction of the experiment over the last 15 years. The three laboratories are now active in the preparation of physics analysis possibly leading to new discoveries. The goal of this ANR project is to reinforce the cohesion of these teams by three post-doc positions, working together for the complicated physics analysis in the beginning of the LHC operation. This will assure that the scientific investments done in the past will be compensated by a prominent role and visibility of the French institutions and their physicists within the international competition, not only between the two large experiments at the LHC, but also within the CMS collaboration itself.

Project coordination

Ulrich GOERLACH (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 220,000 euros
Beginning and duration of the scientific project: - 36 Months

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