2015:groups:sm:qg
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2015:groups:sm:qg [2015/06/04 16:41] jesse.thaler [Supplemental Jet Shapes] |
2015:groups:sm:qg [2015/06/04 17:29] andrzej.siodmok |
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| * Peter Loch <loch@physics.arizona.edu> | * Peter Loch <loch@physics.arizona.edu> | ||
| * Deepak Kar | * Deepak Kar | ||
| - | * Andrzej Siodmok | + | * Andrzej Siodmok <andrzej@cern.ch> |
| * Peter Skands <peter.skands@monash.edu> | * Peter Skands <peter.skands@monash.edu> | ||
| * Dave Soper | * Dave Soper | ||
| Line 79: | Line 79: | ||
| * 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 ===== | ||
| Line 104: | Line 125: | ||
| * 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 ==== | ||
| Line 119: | Line 141: | ||
| * 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 ==== | ||
| Line 138: | Line 162: | ||
| * Rivet analysis in place which computes from a HepMC event sample the various generalised angularity distributions. | * 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 ==== | |
| - | ===== Next Les Houches Study (for after LH) ===== | + | |
| - | + | ||
| - | * Above study at hadron colliders, using dijets, W/Z/gamma + j, and maybe t tbar samples | + | |
| - | + | ||
| - | ===== Preliminary plots for meeting on Thursday ===== | + | |
| {{:2015:groups:sm:ga_10_20.pdf|}} | {{:2015:groups:sm:ga_10_20.pdf|}} | ||
| Line 151: | Line 186: | ||
| {{:2015:groups:sm:ga_00_00.pdf|}} | {{:2015:groups:sm:ga_00_00.pdf|}} | ||
| {{:2015:groups:sm:ga_20_00.pdf|}} | {{:2015:groups:sm:ga_20_00.pdf|}} | ||
| + | |||
| + | ==== 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 ===== | ===== Notes from Tuesday Meeting ===== | ||
2015/groups/sm/qg.txt · Last modified: 2015/07/14 08:27 by philippe.gras
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