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2015:groups:sm:qg [2015/06/04 14:40] gregory.soyez [Original Notes from Gregory] |
2015:groups:sm:qg [2015/07/14 08:27] (current) philippe.gras Added instructions for CERN account |
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a.k.a. Hunting the White Whale of Jet Substructure | a.k.a. Hunting the White Whale of Jet Substructure | ||
- | * Jon Butterworth | + | //If you are interested in contributing please subscribe to the [[https://e-groups.cern.ch/e-groups/EgroupsSearch.do?searchValue=houches-2015-topics-sm-qg-separation|mailing list]]. You will be asked to log in with your CERN account. If you don't have a CERN account, please fill [[https://account.cern.ch/account/Externals/RegisterAccount.aspx|this form]] to create a lightweight account.// |
- | * Marat Freytsis | + | |
+ | * Andy Buckley <andy.buckley@cern.ch> | ||
+ | * Jon Butterworth <J.Butterworth@ucl.ac.uk> | ||
+ | * Mario Campanelli <mario.campanelli@cern.ch> | ||
+ | * Marat Freytsis <freytsis@physics.harvard.edu> | ||
* Peter Loch <loch@physics.arizona.edu> | * Peter Loch <loch@physics.arizona.edu> | ||
- | * Deepak Kar | + | * Philippe Gras <philippe.gras@cern.ch> |
- | * Andrzej Siodmok | + | * Sam Bein <samuel.bein@gmail.com> |
- | * Peter Skands | + | * Deepak Kar <deepak.kar@cern.ch> |
- | * Dave Soper | + | * Simon Plätzer <simon.plaetzer@desy.de> |
- | * Gregory Soyez | + | * Andrzej Siodmok <andrzej@cern.ch> |
+ | * Peter Skands <peter.skands@monash.edu> | ||
+ | * Dave Soper <soper@uoregon.edu> | ||
+ | * Gregory Soyez <Gregory.Soyez@cern.ch> | ||
+ | * Frank Tackmann <frank.tackmann@desy.de> | ||
* Jesse Thaler <jthaler@mit.edu> | * Jesse Thaler <jthaler@mit.edu> | ||
- | * who did I forget? | + | * ... |
- | + | ||
- | * Remotely: Andy Buckley, Mario Campanelli | + | |
Link to GitHub repository: https://github.com/gsoyez/lh2015-qg | Link to GitHub repository: https://github.com/gsoyez/lh2015-qg | ||
+ | ===== Slides from Saturday ===== | ||
+ | |||
+ | * {{:2015:groups:sm:qcdaware.pdf|Andy's upcoming paper on QCDAware jet algorithms}} | ||
+ | |||
+ | * {{|Peter's VBF Slides}} | ||
+ | |||
+ | * {{:2015:groups:sm:jetmass_ft.pdf|Frank's Hadronization Power Correction Slides}} | ||
+ | |||
+ | * {{:2015:groups:sm:jthaler_lh_saturday.pdf|Summary of MC Studies}} | ||
+ | |||
+ | * Quark as an noun vs. quark as an adjective (pseudo-quarks? uarks? quarky jets?) | ||
+ | |||
+ | ===== Plan of attack for Wednesday Les Houches Presentation ===== | ||
+ | |||
+ | * Write our quark/gluon manifesto/history. | ||
+ | * Catalog quark gluon discriminants and performance measures | ||
+ | * e+e- -> u uubar , gg | ||
+ | * Baseline: Q = 200 GeV, R = 0.6, all Monte Carlo programs optimal | ||
+ | * Quark distribution, gluon distribution, separation, integrated separation | ||
+ | * Pythia variations: noME, nogqq | ||
+ | * Herwig variations: ... | ||
+ | * Sherpa variations: ... | ||
+ | * Vincia variations: noME | ||
+ | * Q = 50, 100, 200, 400, 800 GeV (everything else baseline) | ||
+ | * R = 0.2, 0.4, 0.6, 0.8, 1.0 (everything else baseline) | ||
+ | * delta alphas / alphas = -0.2, -0.1, 0.0, +0.1, +0.2 (everything else baseline) | ||
+ | |||
===== Preliminaries ===== | ===== Preliminaries ===== | ||
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* ATLAS A14 tune already uses jet shapes, and finds that alpha_s has to be tuned downward in Pythia 8. This, however, has a detrimental effect on LEP measurements, so one has to be cautious about this. | * ATLAS A14 tune already uses jet shapes, and finds that alpha_s has to be tuned downward in Pythia 8. This, however, has a detrimental effect on LEP measurements, so one has to be cautious about this. | ||
* Is there a tuning flat direction? | * Is there a tuning flat direction? | ||
+ | |||
+ | |||
+ | ==== Hemisphere quark/gluon definitions in e+e- ==== | ||
+ | |||
+ | * Consider the case of e+ e- -> q qbar. Partition event into (thrust) hemisphere, define hemisphere flavor by summing over flavors of hemisphere constituents. | ||
+ | * At LO, we can unambiguously define hemisphere flavors. | ||
+ | * At NLO, we can also unambiguously define flavor via hemisphere, though there is now a small gluon fraction from gluon recoiling against q qbar pair. | ||
+ | * At NNLO, things are more complicated. | ||
+ | * Can have soft gluon splitting into q-qbar in different hemispheres, creates IRC safety issue. | ||
+ | * One can use a flavored algorithm (BSZ) to define the flavour of two flavor-kt jets | ||
+ | * Ultimately, want to give an operational definition of flavor based on the Born-level operator contributing to the process. | ||
+ | * Claim: all subtleties are formally power suppressed. | ||
+ | * Use case, VBF, two jets with a third jet veto, q/g well-defined in the exclusive limit. | ||
+ | |||
+ | ==== Flavored Jet Algorithms ==== | ||
+ | |||
+ | * This is a topic worthy of its own Les Houches study. | ||
+ | * For pp collisions, multiple possible uses of flavored jet algorithms. | ||
+ | * One can just run flavor-kT | ||
+ | * Or one can run flavor-kT to define flavor ghosts, and run standard anti-kT. | ||
+ | * Or one can run flavor-kT for deflavoring constituents, and then run standard anti-kT. | ||
===== Ultimate Goal for Les Houches Study ===== | ===== Ultimate Goal for Les Houches Study ===== | ||
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* Do we understand FSR modeling by workhorse parton showers? | * Do we understand FSR modeling by workhorse parton showers? | ||
+ | * Start with the clean case of e+e-, move to pp later. | ||
==== Basic Plan === | ==== Basic Plan === | ||
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* Question: use ROC curves or mutual information (I(T;A)) to quantify discrimination power? | * Question: use ROC curves or mutual information (I(T;A)) to quantify discrimination power? | ||
* Answer: doesn't really matter, probably I(T;A) is easier to begin with. | * Answer: doesn't really matter, probably I(T;A) is easier to begin with. | ||
+ | * Better answer: Use separation (S-B)^2 / (2 (S + B)). | ||
==== Core Jet Shapes ==== | ==== Core Jet Shapes ==== | ||
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* Question: Sum over particles (angularity-style) vs. sum over pairs (ECF-style) | * Question: Sum over particles (angularity-style) vs. sum over pairs (ECF-style) | ||
* Answer: Sum over particles (angularity-style) | * Answer: Sum over particles (angularity-style) | ||
+ | * Question: Plot linear or log scale? | ||
+ | * Answer: Do both if it makes sense, better for angularities to have log scale. | ||
==== Supplemental Jet Shapes ==== | ==== Supplemental Jet Shapes ==== | ||
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* Generalized angularities with soft-drop jets, varying beta_SD | * Generalized angularities with soft-drop jets, varying beta_SD | ||
* Do sum over pairs version of angularities (i.e. ECF-style) | * Do sum over pairs version of angularities (i.e. ECF-style) | ||
- | ===== Next Les Houches Study (for after LH) ===== | ||
- | * Above study at hadron colliders, using dijets, W/Z/gamma + j, and maybe t tbar samples | + | ==== Analysis Workflow ==== |
+ | |||
+ | * Rivet analysis in place which computes from a HepMC event sample the various generalised angularity distributions. | ||
+ | * Processes to consider: | ||
+ | * mu+mu- -> spin1 -> q qbar take photons | ||
+ | * mu+mu- -> spin0 -> g g take Higgs | ||
+ | * for tests of universality: mu+mu- -> spin0 -> q qbar | ||
+ | * Energies | ||
+ | * Q=sqrt{s} = 50, 200, 800 GeV | ||
+ | * Optionally: Q = 100, 400 GeV | ||
+ | * Jet definition: | ||
+ | * ee-antikt [genkt, p=-1], WTA_modp recomb scheme | ||
+ | * R = 0.3, 0.6, 0.9 | ||
+ | * Add thrust from thrust hemispheres for anticipated analytic comparisons | ||
+ | * Add multiplicity (event-wide) in bins of thrust: | ||
+ | * T < 5 GeV/sqrt(S) | ||
+ | * 5 GeV/sqrt(S) < T < 0.1 | ||
+ | * 0.1 < T < 0.2 | ||
+ | * 0.2 < T | ||
- | ===== Preliminary plots for meeting on Thursday ===== | + | ==== Preliminary plots for meeting on Thursday ==== |
{{:2015:groups:sm:ga_10_20.pdf|}} | {{:2015:groups:sm:ga_10_20.pdf|}} | ||
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{{:2015:groups:sm:ga_20_00.pdf|}} | {{:2015:groups:sm:ga_20_00.pdf|}} | ||
- | ===== Original Notes from Gregory ===== | + | ==== Questions ==== |
+ | |||
+ | * Is discrimination power (e.g. for width) coming from the hadronization regime? | ||
+ | * Possibility: Isolate hadronization regime (thrust ~ LambdaQCD/Q) and shower regime (thrust ~ 0.1-0.2) and optionally hard jet regime (thrust >~ 0.25). Study scaling of, e.g., multiplicity as a function of Q in each of these regimes. | ||
+ | * By testing pythia vs. herwig, can we test string vs. cluster hadronization? | ||
+ | * Is there jet radius dependence? | ||
+ | * Does matching help in controlling quark/gluon uncertainties? | ||
+ | * Universality/process dependence of conclusions? | ||
+ | * Related to whether the discrimination power comes from the core or the periphery of jet. | ||
+ | |||
+ | ===== Next Les Houches Study (for after LH) ===== | ||
+ | |||
+ | * Above study at hadron colliders, using dijets, W/Z/gamma + j, and maybe t tbar samples | ||
+ | |||
+ | ===== Analytic Les Houches Study? ===== | ||
+ | |||
+ | * Analytic predictions known/available/straightforward for: | ||
+ | * Quark thrust: N^3LL' + N^3L0 | ||
+ | * Gluon thrust: N^2LL' + N^2L0 | ||
+ | * ang (kappa =1): NLL' | ||
+ | * Can we do useful quark/gluon study from analytic results? | ||
+ | |||
+ | ===== Notes from Tuesday Meeting ===== | ||
<code> | <code> | ||
Line 276: | Line 373: | ||
</code> | </code> | ||
+ | |||
+ | ===== Notes from Thursday Meeting ===== | ||
+ | |||
+ | <code> | ||
+ | |||
+ | |||
+ | Meeting in Les-Houches | ||
+ | |||
+ | |||
+ | Presentation of the wiki notes: list of contributors, ... | ||
+ | |||
+ | Presentation of the status of the software: | ||
+ | start w e+e- and do pp later | ||
+ | Rivet analysis in place which computes from a HepMC event sample the various generalised angularity distributions | ||
+ | |||
+ | Reminder: what we mean by a q and a g is e+e-\to qq and e+e-\to gg | ||
+ | If we want to do something more refined: | ||
+ | - at LO we can unambiguously sum flavours in hemispheres defined by thrust | ||
+ | - at NLO we can unambiguously sum flavours in hemispheres defined by thrust | ||
+ | we get a quark and a small gluon fraction | ||
+ | - at NNLO things are more complicated. We can use a flavoured | ||
+ | algorithm (BSZ) to define the flavour of each hemisphere | ||
+ | - for pp collisions, we should use a flavoured algorithm to | ||
+ | determine flavour, and then find a way (e.g. using ghosts) to | ||
+ | run anti-kt jets. This would deserve a topic per se (a LH accord)? | ||
+ | |||
+ | - Question: can we match to the Born and find an operatiroal | ||
+ | definition up t power corrections? | ||
+ | Use case: VBF, two jets with a third jet veto. q/g well-defined | ||
+ | in the exclusive limit | ||
+ | |||
+ | Questions to look into: | ||
+ | - is the discrimination power (e.g. for width) coming from the hadronisation regime? | ||
+ | - plotting in log binninb? | ||
+ | - pythia v. herwig important to test string v. cluster hadronisation | ||
+ | - isolate hadronisation regime. Study the scaling in different bins | ||
+ | of one angularity (e.g. thrust). Take a hadronisation region | ||
+ | (T\propto LQCD/Q) and a shower region (T~0.1-0.2) plus optionally a | ||
+ | "hard jet region" (T >~ 0.25) | ||
+ | - does mathing help? | ||
+ | - jet radius dependence (edit analysis and recompile) | ||
+ | - analytic predictions? | ||
+ | for thrust: ee->qq known at N^3LL' + N^3LO | ||
+ | ee->qq known at N^2LL' + N^2LO | ||
+ | ang(bkappa=1): NLL' | ||
+ | - question of the universality/process dependence of the conclusions? | ||
+ | Related to whether the power comes from the core or the periphery? | ||
+ | |||
+ | - process to consider: | ||
+ | mu+mu- -> spin1 -> qq take photons | ||
+ | mu+mu- -> spin0 -> gg take Higgs | ||
+ | for tests of universality | ||
+ | mu+mu- -> spin0 -> qq | ||
+ | |||
+ | - Energies Q=sqrt = 50, 200, 800 GeV | ||
+ | jetdef: ee-antikt [genkt, p=-1], WTA_modp recomb scheme | ||
+ | radii: 0.3, 0.6, 0.9 | ||
+ | |||
+ | - add thrust from thrust hemispheres for analytic purpose | ||
+ | |||
+ | - add multiplicity (event-wide) in bins of thrust: | ||
+ | T < 5 GeV/sqrt(S) | ||
+ | 5 GeV/sqrt(S) < T < 0.1 | ||
+ | 0.1 < T < 0.2 | ||
+ | 0.2 < T | ||
+ | |||
+ | |||
+ | </code> | ||
+ | |||
+ | ===== Notes for Jesse for Preparing Summary Talk ===== | ||
+ | |||
+ | * Quark is more of an adjective than a noun. | ||
+ | * Pseudo-quark? (That language doesn't go over very well.) | ||
+ | |||
+ | ==== What is a Quark Jet? ==== | ||
+ | |||
+ | (From ill-defined to well-defined) | ||
+ | |||
+ | * A quark parton | ||
+ | * A Born-level quark parton | ||
+ | * The initiating quark parton in a final state shower | ||
+ | * An eikonal line with baryon number 1/3 and carrying triplet color charge | ||
+ | * A quark operator that appears in a hard matrix element in the context of a factorization theorem. | ||
+ | * A parton-level jet object that has been tagged as a quark using a soft-safe flavored jet algorithm (automatically collinear safe if you sum constituent flavors). | ||
+ | * A phase space region (as defined by an unambiguous hadronic fiducial cross section measurement) that yields an enriched sample of quarks (as interpreted by some suitable, though fundamentally ambiguous, criterion). | ||
+ | | ||
+ | (Sometimes people think we care about the top of the list while we are really focused entirely on the bottom.) |