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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 17:11] jesse.thaler [Questions] |
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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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* 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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* 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. | ||
+ | ==== 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) ===== | ===== Next Les Houches Study (for after LH) ===== | ||