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--- 2015:groups:sm:qg [2015/06/04 14:40]
gregory.soyez [Original Notes from Gregory]
+++ 2015:groups:sm:qg [2015/06/04 17:06]
jesse.thaler [Basic Plan]
@@ Line 3: / Line 3: @@
 a.k.a. Hunting the White Whale of Jet Substructure
+  * Andy Buckley
   * Jon Butterworth
+  * Mario Campanelli
   * Marat Freytsis
   * Peter Loch <loch@physics.arizona.edu>
   * Deepak Kar
   * Andrzej Siodmok
-  * Peter Skands
+  * Peter Skands <peter.skands@monash.edu>
   * Dave Soper
   * Gregory Soyez
+  * Frank Tackmann
   * Jesse Thaler <jthaler@mit.edu>
-  * who did I forget?
+  * ...
-  * Remotely:  Andy Buckley, Mario Campanelli
 Link to GitHub repository:  https://github.com/gsoyez/lh2015-qg
@@ Line 78: / 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.
   * 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 =====
@@ Line 93: / Line 115: @@
   * Do we understand FSR modeling by workhorse parton showers?
+  * Start with the clean case of e+e-, move to pp later.
 ==== Basic Plan ===
@@ Line 102: / Line 125: @@
   * 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.
+    * Better answer:  Use separation (S-B)^2 / (2 (S + B)).
 ==== Core Jet Shapes ====
@@ Line 132: / Line 156: @@
   * Generalized angularities with soft-drop jets, varying beta_SD
   * Do sum over pairs version of angularities (i.e. ECF-style)
+==== Analysis Workflow ====
+  * 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?
+  *
 ===== Next Les Houches Study (for after LH) =====
@@ Line 144: / Line 177: @@
 {{:2015:groups:sm:ga_20_00.pdf|}}
-===== Original Notes from Gregory =====
+===== Notes from Tuesday Meeting =====
 <code>
@@ Line 274: / Line 307: @@
      above, +PU, VBF
      [Peter L.]
+</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)
+GeV/sqrt(S) < T < 0.1
+.1 < T < 0.2
+.2 < T
 </code>

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