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I'm new here so hopefully this is the right place for the question. I have tried to extend and label the variables available, and have a couple of questions to get started:
\n\nWhat is the meaning (or is there a quick reference) for the variable: VertexChi2 - χ2 of τ vertex.
What are the units for LifeTime - Life time of tau candidate (10^-12 seconds, 10^-18 seconds??)
What are the units FlightDistance - Distance between τ and PV (primary vertex, the orginal protons collision point).
Thanks and regards ..
\n\n
I'm new here so hopefully this is the right place for the question. I have tried to extend and label the variables available, and have a couple of questions to get started:
\n\nWhat is the meaning (or is there a quick reference) for the variable: VertexChi2 - χ2 of τ vertex.
What are the units for LifeTime - Life time of tau candidate (10^-12 seconds, 10^-18 seconds??)
What are the units FlightDistance - Distance between τ and PV (primary vertex, the orginal protons collision point).
Thanks and regards ..
\n\n
my two cents for your first question, please correct me if I got it wrong since I come from CMS.
\n\nVertexChi2 is a variable for measuring the tau vertex reconstruction quality. Each vertex can be considered as a tau decay point, and it is reconstructed/fitted from the decay muon traces, kind of like the picture in your post. This 'fit' or 'reconstruction' is not ideal or perfect, so LHCb uses chi2 to measure the quality of this fit. Usually the larger chi2, the worse fit. For more knowledge about this fitting method and details, we can go to https://twiki.cern.ch/twiki/bin/view/LHCb/VertexFitters
\n\nFor the unit question, I don't think it is so important for this competition, CMS uses ps (10^-15 second) and cm, but not sure about LHCb's, so let's wait for the admin :-)
", "rawMarkdown": "my two cents for your first question, please correct me if I got it wrong since I come from CMS.\r\n\r\nVertexChi2 is a variable for measuring the tau vertex reconstruction quality. Each vertex can be considered as a tau decay point, and it is reconstructed/fitted from the decay muon traces, kind of like the picture in your post. This 'fit' or 'reconstruction' is not ideal or perfect, so LHCb uses chi2 to measure the quality of this fit. Usually the larger chi2, the worse fit. For more knowledge about this fitting method and details, we can go to https://twiki.cern.ch/twiki/bin/view/LHCb/VertexFitters\r\n\r\nFor the unit question, I don't think it is so important for this competition, CMS uses ps (10^-15 second) and cm, but not sure about LHCb's, so let's wait for the admin :-)", "votes": null }, { "id": "88111", "postDate": "08/03/2015 16:30:11", "content": "Thanks, great resource, missed it somehow earlier. I've made a few changes/corrections to the diagram already, but would love to add in a grid and a timeframe.
", "rawMarkdown": "Thanks, great resource, missed it somehow earlier. I've made a few changes/corrections to the diagram already, but would love to add in a grid and a timeframe.", "votes": null }, { "id": "90382", "postDate": "08/25/2015 23:34:23", "content": "As a follow-up, what are Track Isolation Variables and Cone Isolation Variables?
\n\nI see "Quality of p0 muon track." What is a muon track and how does one measure its quality?
\n\nWhat is "Pseudorapidity of p2 muon. of p2 muon?"
\n\nWhat is the definition of "Signal?" Is this a strength, frequency, information index, unknown, ... ?
", "rawMarkdown": "As a follow-up, what are Track Isolation Variables and Cone Isolation Variables?\r\n\r\nI see \"Quality of p0 muon track.\" What is a muon track and how does one measure its quality?\r\n\r\nWhat is \"Pseudorapidity of p2 muon. of p2 muon?\"\r\n\r\nWhat is the definition of \"Signal?\" Is this a strength, frequency, information index, unknown, ... ?", "votes": null }, { "id": "90441", "postDate": "08/26/2015 15:53:32", "content": "[quote=Matthew Barrett;90382]
\n\nAs a follow-up, what are Track Isolation Variables and Cone Isolation Variables?
\n\nI see "Quality of p0 muon track." What is a muon track and how does one measure its quality?
\n\nWhat is "Pseudorapidity of p2 muon. of p2 muon?"
\n\nWhat is the definition of "Signal?" Is this a strength, frequency, information index, unknown, ... ?
\n\n[/quote]\n1. Muon track: it is the trace of a charged muon (https://en.wikipedia.org/wiki/Muon) flying through the detector. Since the detector can't see the full trace but the 'hit' on each layer of the detector, the detector software need to 'reconstruct' the trace from these 'hits', thus this reconstruction quality should be measured by the chi2 between these hits and the reconstructed traces. The larger Chi2, the worse (not reliable) reconstruction.
\n\nPseudorapidity is called eta, it is explained here https://en.wikipedia.org/wiki/Pseudorapidity P2 means the momentum of the second muon (tau can decay to 3 muons in the signal)
Signal and background are HEP jargons. You can think they are positive samples and negative samples (which are statistical learning jargons)
my two cents for your first question, please correct me if I got it wrong since I come from CMS.
\n\nVertexChi2 is a variable for measuring the tau vertex reconstruction quality. Each vertex can be considered as a tau decay point, and it is reconstructed/fitted from the decay muon traces, kind of like the picture in your post. This 'fit' or 'reconstruction' is not ideal or perfect, so LHCb uses chi2 to measure the quality of this fit. Usually the larger chi2, the worse fit. For more knowledge about this fitting method and details, we can go to https://twiki.cern.ch/twiki/bin/view/LHCb/VertexFitters
\n\nFor the unit question, I don't think it is so important for this competition, CMS uses ps (10^-15 second) and cm, but not sure about LHCb's, so let's wait for the admin :-)
", "votes": null, "replies": [] }, { "id": 88111, "author_name": "edguy99", "author_url": "", "post_date": "08/03/2015 16:30:11", "content": "Thanks, great resource, missed it somehow earlier. I've made a few changes/corrections to the diagram already, but would love to add in a grid and a timeframe.
", "votes": null, "replies": [] }, { "id": 90382, "author_name": "mrbarret", "author_url": "", "post_date": "08/25/2015 23:34:23", "content": "As a follow-up, what are Track Isolation Variables and Cone Isolation Variables?
\n\nI see "Quality of p0 muon track." What is a muon track and how does one measure its quality?
\n\nWhat is "Pseudorapidity of p2 muon. of p2 muon?"
\n\nWhat is the definition of "Signal?" Is this a strength, frequency, information index, unknown, ... ?
", "votes": null, "replies": [] }, { "id": 90441, "author_name": "phunter", "author_url": "", "post_date": "08/26/2015 15:53:32", "content": "[quote=Matthew Barrett;90382]
\n\nAs a follow-up, what are Track Isolation Variables and Cone Isolation Variables?
\n\nI see "Quality of p0 muon track." What is a muon track and how does one measure its quality?
\n\nWhat is "Pseudorapidity of p2 muon. of p2 muon?"
\n\nWhat is the definition of "Signal?" Is this a strength, frequency, information index, unknown, ... ?
\n\n[/quote]\n1. Muon track: it is the trace of a charged muon (https://en.wikipedia.org/wiki/Muon) flying through the detector. Since the detector can't see the full trace but the 'hit' on each layer of the detector, the detector software need to 'reconstruct' the trace from these 'hits', thus this reconstruction quality should be measured by the chi2 between these hits and the reconstructed traces. The larger Chi2, the worse (not reliable) reconstruction.
\n\nPseudorapidity is called eta, it is explained here https://en.wikipedia.org/wiki/Pseudorapidity P2 means the momentum of the second muon (tau can decay to 3 muons in the signal)
Signal and background are HEP jargons. You can think they are positive samples and negative samples (which are statistical learning jargons)