Les Houches
2021 Session
 Working Groups Pages
 Session 1
 Session 2

 Use of wiki. Wifi access/setup. Printing
 Important info about lodging. Bus. Facilites
 Bulletins.
Wikis of Previous sessions
Les Houches Themes
(Lyrics and Music)
(Lyrics and Music)
Aim
The aim of this project is to continue the series of projects on defining/assessing parton shower variations in Les Houches. This time, we hope to investigate some details of initialstate backward evolution.
In initialstate backward evolution, we rely on the fact that the parton shower “unfolds” the evolution of parton distribution functions. However, given that parton showers implement momentum conservation, use different ordering variables, and that PS evolotion kernels may differ from DGLAP away from the collinear limit, it is worth checking the quality of this “unfolding” by
* Checking how PDFindependent the ratio [NoEmission probability of (x,t0,t1)] / [ f(x,t1)/ f(x,t0) ] actually is in current parton showers.
* Checking how xindependent the ratio [NoEmission probability of (x,t0,t1)] / [ f(x,t1)/ f(x,t0) ]is in current parton showers (note: the xindependence is not exact, and e.g. spoiled by threshold logarithms and subleading pieces, so that it is a useful tool to profile the status)
Bins
x: log(x) \in [0,4] → bins of 0.1 x \in (0,1] → bins of 0.1
“dipole mass” mD: mD \in {1 TeV, 500 GeV, 100 GeV, 10 GeV, 5 GeV}
starting scale t0 (GeV^2) t0 \in {0.1 mD^2, 0.5 mD^2, 0.75 mD^2, mD^2}
stopping scale t1 (GeV^2) t1 \in {0.8 t0, 0.5 t0, 0.1 t0, 0.01 t0, 0.001 t0}
Interested people
Stefan Prestel, Davison Soper, Davide Napoletano, Leif Gellersen, Enrico Bothmann, Simone Amoroso, Helen Brooks, Joey Huston …