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Introduction
The LHC is to see first beam in 2007. Sometime in 2008, the first data from proton-proton collissions at a center-of-mass energy of 14 TeV are expected. Soon after, the accelerator should ramp up to its initial luminosity of 2 times 10 to the 33 per cm squared and per second (the luminosity is a function of the beam intensity and size, it indicates how many collissions take place per unit time. At higher the luminosity we do not have to wait as long to gather sufficient statistics on our rare signal process.). Then, it's another year or two to reach the full design luminosity of 10 to the 34 cm-2s-1. Thus, the LHC - the most powerful and luminous accelerator of all times - will have an unprecedented reach for physics beyond the Standard Model.
This new physics may manifest itself in a number of ways. In many theoretical proposals new particles are predicted (the Higgs boson, supersymmetric partners). One approach is to try to reconstruct these new particles by combining their decay products. In some cases, i.e. for SUSY where the lightest superparticle isstable, the new particles may escape detection: their presence must be inferred
from an imbalance in the momentum of the remaining particles produced in the collission. More subtle and indirect methods exist as well: a precise measument ofsome key observables may reveal the existence of new physics through its impact
on the mass or production rate of a Standard Model particle.
Four experiments are being installed in interactions points along the LHC ring. Two of them - ATLAS and CMS - aim to provide a broad coverage for all possible signatures of new physics. Their detectors are designed for a complete and precise reconstruction of all the collission products. Charged particle trajectories are tracked by silicon pixel and strip detectors in the magnetic field in theinner volume of the detector. The energy of all particles is measured in the ca
lorimeters. Muons - that interact only weakly and sail through calorimeters leaving a minimal signal - are identified through their hits in the muon chambers.
My work is in the reconstruction and identification of highly energetic jets of particles stemming from a bottom quark. These jets may be identified (tagged) through the long lifetime of particles made up of bottom quarks: the B-hadron f lies a considerable distance before decaying. This displaced B-decay can be reconstructed by fitting the common origin (vertex) of the charged particles in the jet. Some recent results from this study can be found .
The relevance of high-transverse-momentum b-tagging is mostly in searches for heavy resonances with hadronic decays. An excellent example is the reconstruction of cascade decays of heavy W bosons in the twin Higgs model. On this page more information on this model can be found.
In the near future, the b-tagging
reconstructi on of top pairs at large invariant mass. There are two reasons why we believe th ese topologies may be more interesting than others:
- for Standard Model production, the high-mass region is especially sensitive to non-standard physics.
- the topology with two highly boosted top quarks may be produced by the deca y of heavy resonances.
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