Using Fastjet in Pythia to plot distribution of particles

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Discussion Overview

The discussion revolves around using Fastjet in Pythia8 to analyze jet formation in proton-proton collisions, specifically focusing on plotting the distribution of transverse momentum of the fastest particle within the fastest jet formed from simulated events. Participants seek guidance on accessing particle properties post-jet formation and clarify definitions related to jets.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks to identify the fastest particle within a jet, expressing difficulty in accessing particle properties after jet formation.
  • Another participant questions the relevance of the "fastest particle" as a quantity, suggesting that the term may be unusual.
  • Clarification is provided that "fastest" refers to the particle with the highest transverse momentum (pt).
  • A participant inquires about accessing the lowest pt particle of the subleading jet, suggesting that the manual may cover this.
  • It is noted that the quickstart example functions are sufficient for accessing jet constituents.
  • A participant mentions encountering errors when fewer than two jets were formed in some events and imposes a condition to select events with more than one jet.
  • Another participant confirms that it is indeed possible for some events to not produce jets, depending on the simulated events.
  • There is a discussion about the definition of a jet, with one participant questioning whether a muon would qualify as a jet and emphasizing the need for certain quality criteria for jet formation.
  • Clarification is provided that the jets being referred to are those resulting from hard scattering processes after fragmentation and hadronization.

Areas of Agreement / Disagreement

Participants express varying definitions and understandings of what constitutes a jet, indicating a lack of consensus on this aspect. While some technical questions are resolved, others remain open for further clarification.

Contextual Notes

Participants highlight limitations in their understanding of jet formation, particularly regarding the conditions under which jets are produced and the criteria for defining jets in the context of their simulations.

Sandeep Hundal
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I am using fastjet in pythia8.I am studying jet formation in pp collisions.I need to plot distribution of transverse momentum of fastest particle in fastest jet formed in 1000 events simulated.But i don't know how to access particle properties after jet formation.Like if I want to know the fastest particle out of the particles which have formed that jet ,I am not able to access it.Can anybdy explain ?
Thanks
 
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The fastest particle? That is an unusual quantity.

The quickstart has an example how to access the jet constituents.
 
by fastest you mean the one with the highest pt? (would make more sense at least from my experience)
 
yes ,here fastest means with highest pt
 
mfb said:
The fastest particle? That is an unusual quantity.

The quickstart has an example how to access the jet constituents.
It worked
Thanks
 
How can we access lowest pt particle(constituent) of sub leading jet ?
 
Does Section 3.5 of the manual not cover that?
 
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The functions shown in the quickstart example are sufficient for this as well.
 
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yes,It worked now.Actually in some of the events,only less than 2 jets were formed.so It gave an error.Now I have imposed the condition to select only those events that have more than 1 jet.Now the question is -is that possible that in some events no jet formed even after clustering in pythia using fastjet?
Thanks .Your guidance is helping me a lot :)
 
  • #10
It depends on the events simulated, but in general: sure. Not every pp collision produces particles high-energetic enough to be included in jets. Some don't produce particles in the detector at all.
 
  • #11
Sandeep Hundal said:
Now the question is -is that possible that in some events no jet formed even after clustering in pythia using fastjet?
Hmmm, I would like to know what you define as a jet? Would a muon give you a jet?
As jets I was imagining objects of grouped clusters (which are grouped cells), that satisfy certain quality criteria (some energy thresholds and so on). Those are formed only for signals recorded in the calorimeter (so objects that are recoed from the calorimeter won't be called jets?).
Then are you referring to the jets that come from the hard scattering process?
 
  • #12
yes,I am referring to the jets that come from hard scattering processes after fragmentation and hadronization.
 
  • #13
So ignoring the pileup jets, the process: qq\to W \to \mu \nu wouldn't necessarily give you a "jet" in your event.
 

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