1 / 15

Studies of J et S hapes and S ubstructure with ATLAS Adam Davison University College London

Studies of J et S hapes and S ubstructure with ATLAS Adam Davison University College London. ATLAS. Recorded ~5 fb -1 of 7 TeV pp collisions from the LHC Highly granular calorimetry (down to 0.025x0.025 in η-φ ). Jets at ATLAS. At the LHC jets are everywhere

gabby
Download Presentation

Studies of J et S hapes and S ubstructure with ATLAS Adam Davison University College London

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Studies of Jet Shapes and Substructure with ATLASAdam DavisonUniversity College London

  2. ATLAS • Recorded ~5 fb-1 of 7 TeVpp collisions from the LHC • Highly granular calorimetry (down to 0.025x0.025 in η-φ)

  3. Jets at ATLAS • At the LHC jets are everywhere • ATLAS primarily uses anti-kt jets with R = 0.4 and 0.6 • Other algorithms available for specialised needs • Rich series of jet physics publications from ATLAS already • Inclusive jets, dijets, multijets, b-jets, azimuthal correlations etc…

  4. Inside a Jet • Jets can contain a lot of complex physics • Non-perturbative effects like fragmentation and hadronisation • Hard process, colour connections, UE, pile-up • Massive particle production (b, c, W, Z, top etc…) • Measurements of the internal structure of jets can help us test models and tunes for all of these • Good models of all of these a necessity for BSM searches

  5. Jet Shapes • Jet shapes are the classic test of the internals of jets • Measure the fraction of a jet’s pt which is within an annulus • Formally, measure the quantity: pT in annulus pT of jet

  6. Jet Shapes 2.4.2 • Results released 2010, now published: • Phys.Rev. D83 (2011) 052003 • More recently, newer tunes tested • ATL-PHYS-PUB-2011-010

  7. Fragmentation • Can also study the distribution of charged particles the jet (jet) a track (ch) • Distribution of energy parallel or transverse to jet axis:

  8. Eur. Phys. J. C 71 (2011) 1795 Fragmentation • Distributions are reasonably well modelled

  9. Jet Mass and Substructure • Jets are 4-vectors, for example (E/pT, η, φ, m) • Of these, mass is probably the least studied • At the LHC, lots of interest in jet mass and substructure • Especially large radius jets • Jets can contain boosted W, Z, top … • … and potentially new physics • Measurements targetted at this ATLAS-CONF-2011-103

  10. New Results! Jet Mass and Substructure • Looking at Cambridge-Aachen R=1.2 and anti-kt R=1.0 • Jet mass measured for jet pt of 200 – 600 GeV • Systematics determined in-situ using inner-detector track jets • Herwig++didn’t describe this terribly well in version 2.4.2 http://arxiv.org/abs/1203.4606

  11. Jet Mass and Substructure • Also look at application of a substructure procedure: Splitting and filtering a la PRL 100, 242001 (2008) Less sensitive to soft physics, observe better agreement than in plain jet mass http://arxiv.org/abs/1203.4606

  12. Jet Mass and Pile-up • Looking at mean mass vs. pile-up • Splitting/filtering reduces dependence significantly http://arxiv.org/abs/1203.4606

  13. Jet Mass and Substructure • Also look at kT splitting scales (aka y-scales, d12) • Measure of scale at which a jet breaks into two subjets

  14. Jet Mass and Substructure More like 3 subjets than 2 • n-subjettiness, new variable (arXiv:1011.2268 (2011) Thaler, Tilburg) Sum distances from constituents to 2 or 3 ktsubjet axes Take ratio of sums http://arxiv.org/abs/1203.4606

  15. Conclusions • ATLAS has made many measurements of internals of jets • Jet shapes (Phys.Rev. D83 (2011) 052003) • Jet fragmentation (Eur. Phys. J. C 71 (2011) 1795) • Jet mass and substructure variables (arxiv:1203.4606) • All available in HepData(in a week-ish for jet mass) • Variables designed for new physics searches appear to be well modelled generally by Monte Carlo • More to come with 8 and 14 TeV

More Related