Anti-kt algorithm

• Everything comes from,
• Kt algorithm : http://arxiv.org/pdf/hep-ph/9305266v1.pdf
• Anti-kt algorithm : http://arxiv.org/pdf/0802.1189v2.pdf
• To grab the jet made by hadronization of parton comes from particle collider (such as electron collider, LHC, Tevatrom), physicists have used many algorithms.
  In the CMS, many jet analysis are done with anti-kt algorithm. Let's briefly check what it is.
• As a first step, we tag every hadrons as proto-jet. After that, merging hadrons as components of the same jet should be done.
  The anti-kt algorithm is about the way to merge hadrons.

• The kt-algorithm uses this variable.

1. Now, find the minimum value among d_ij and d_i.
   If d_ij is the minimum value, merge i and j proto-jet and give
   Energy : E_k = E_i + E_j
   phi = (E_i * phi_i + E_j * phi_j ) / E_k
   and same way for eta.

• Anti-kt  algorithm.

1. If we let p = -1, this is anti-kt algorithm.

• Why we used anti-kt algorithm?