rmadar/go-simple-examples

First try of go language

Simple Go examples

This repository contains few examples in go, mostly connected to high energy physics (HEP). Mostly:

• CLs: computation of a stat-only CLs exclusion wikipedia
• plotting: very short example of plots produced in go
• lhe2root: example of how to convert a LHE file into a ROOT file
• reading-root-ttree: event loop based on a ROOT::TTree, the main HEP software.

CLs exclusion

LHE to ROOT - based on go-hep

LHE format is convention to store data from particle collision into an ASCI file. A LHE parser is available in go-hep and is used to create a TTree for a 10000 proton-proton collisions leading to a top-antitop quark pair production.

Reading a TTree - based on go-hep

In this example, the initial TTree - stored in ttbar_0j_parton.root - was produced from a LHE file [arXiv:0609.017] describing 10000 proton-proton collisions leading to a top-antitop quark pair production, as predicted by MadGraph tool [arXiv:1405.0301], ran at the leading order. These collisions are described at the parton level only and each event is described by

• partonic intial state: parton flavour and momentum
• partonic final state: 4-vectors for each particle in the decay t->Wb->lvb

The program reading-root-ttree/main.go loads some variables of the TTree, compute some angular variables probing the spin correlation between the top and the antitop quarks [e.g. arXiv:1612.07004]. These involves Lorentz transformation and simple geometrical calculations, and this progam relies then on the lorentzvector package. The commands

cd reading-root-ttree
go run ./main.go

will produce a ROOT file containing the new TTree with 10 variables:

• dphi_ll: lab-frame angle between the two leptons
• k, r, n: the three 3-vectors of the spin basis
• cos(Theta[axis, lepton]): 6 cosines for 3 axis and 2 leptons