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 initial-state backward evolution.

In initial-state 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 PDF-independent the ratio [No-Emission probability of (x,t0,t1)] / [ f(x,t1)/ f(x,t0) ] actually is in current parton showers.

* Checking how x-independent the ratio [No-Emission probability of (x,t0,t1)] / [ f(x,t1)/ f(x,t0) ]is in current parton showers (note: the x-independence 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 …