Soft Collinear Effective Theory

Soft collinear effective theory (SCET) was developed by my collaborators and myself from 2000-2001. It describes the interactions of particles which have mass considerably smaller than their energy. SCET has many applications, and is by now a widely used by many groups. Its first applications have been in B physics, helping to describe B decays into either exclusive light mesons, or into narrow jets recoiling against weakly interacting particles.

Most applications of SCET nowadays are in the area of collider physics, where the presence of energetic, narrow jets make this effective theory ideally suited for this application. Most of the interest of the particle physics community is focused on the large hadron collider (LHC), which collides protons at a center of mass energy of initially 7 TeV, and at a later stage at 14 TeV. Since the initial colliding particles are strongly interacting, a factorization theorem is required to allow any theoretical insight into the measured data. While such factorization proofs have been developed since the early 1980’s, SCET has allowed to understand the factorization of more complicated processes. Another aspect where SCET is being used is to understand the structure of perturbation theory of the short distance physics.

Development of

The goal of high energy physics is to understand the universe at its most fundamental level, and experiments at the energy frontier collide particles at extremely high energy in a quest to directly produce elementary particles and study their interactions. The Large Hadron Collider (LHC), set to start taking data at the end of this year, will for the first time probe directly the physics responsible for the generation of mass of all elementary particles, and there is much reason to believe that new particles and laws of nature will be discovered. Our ability to interpret the vast data sets from the LHC critically depends on the availability of reliable predictions of the experimental signatures. The nature of the strong interactions makes such predictions difficult, since higher order corrections and logarithmic effects are often sizable, and long distance dynamics are crucial to describe the experimental data. So far, calculations that make accurate predictions of the underlying short distance physics neglect long distance effects, and event generators constructed to describe the long distance dynamics do not treat the short distance physics adequately. Theoretical tools combining both the short distance and long distance effects do exist, but none of them is universally applicable, and none of them incorporate the most accurate calculations available. It is the goal of this proposal to develop an event generator that combines higher order calculations and large logarithmic effects with existing parton shower algorithms into one consistent framework. The resulting program, which will be compatible with input and output used by familiar event generators today, will generate events based on the most accurate available calculations that can be compared directly with events produced at the LHC. Without such a high precision tool, many signals of new particles and new laws of nature may remain hidden in the vast data sets produced at the LHC. To succeed in this effort, I will have to hire highly capable theorists with strong computational backgrounds. The project will also benefit through personnel support from the High Performance Computing Research Department and from the presence of the strong experimental HEP group at LBNL.

Contact information:

Dr. Christian W Bauer, Lawrence Berkeley National Laboratory, M/S 50A5104, Berkeley, CA 94720

Email:, Phone: (510) 486-7773, Fax: (510) 486-4608

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