Some Remarks on Cone Jets

Cone jets are not simple circles:

• From Zdenek: How jet towers look in various algorithms (JCCB, JCCA, and two kT algos).

Example: Merge procedure ending up in a wide jet

• A study by Lars Sonnenschein, July 2008:
• Using D0 Run II mid-point algorithm with R=0.5.
• The black circles show the stable proto jets before looking at midpoints.
• Every merge step, where the algorithm did a merging, has been combined into the animated gif.
• The particles which are merged to the leading pT jet are indicated as yellow/green. Indeed the leading jet sucks in all the particles of lower pT proto jets, since they share at each step over 50% in pT.
• Rising the ratio threshold e.g. to 75% yields 2 splitted jets in this region. In conclusion, this is a feature of the algorithm.
• From Henrik Nilsen: It is amazing how large the effect can be: adding all stable hadrons in a dR<0.5 cone around the jet axis, for some jets the pT of the 4vec sum of the hadrons is less than 1/3 of the jet pT.
• From Mikko: The jet growing far beyond it's cone size is one of those not so well known aspects of the cone algorithms, and in the JetID group we were also a little worried about eventually getting "monster jets" that could span the whole calorimeter when the calorimeter gets very busy in high luminosity events.