Rivet analyses
Jet fragmentation using charged particles
Experiment: ATLAS (LHC)
Inspire ID: 1740909
Status: VALIDATED
Authors: - Ben Nachman - Deepak Kar
References: - Expt page: ATLAS-STDM-2017-16 - arXiv: 1906.09254 - Phys.Rev.D 100 (2019) 5, 052011
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - p + p -> jj
This paper presents a measurement of quantities related to the formation of jets from high-energy quarks and gluons (fragmentation). Jets with transverse momentum 100 GeV < pT< 2.5 TeV and pseudorapidity |η| < 2.1 from an integrated luminosity of 33 fb−1 of $=$13 TeV proton-proton collisions are reconstructed with the ATLAS detector at the Large Hadron Collider. Charged-particle tracks with pT> 500 MeV and |η| < 2.5 are used to probe the detailed structure of the jet. The fragmentation properties of the more forward and the more central of the two leading jets from each event are studied. The data are unfolded to correct for detector resolution and acceptance effects. Comparisons with parton shower Monte Carlo generators indicate that existing models provide a reasonable description of the data across a wide range of phase space, but there are also significant differences. Furthermore, the data are interpreted in the context of quark- and gluon-initiated jets by exploiting the rapidity dependence of the jet flavor fraction. A first measurement of the charged-particle multiplicity using model-independent jet labels (topic modeling) provides a promising alternative to traditional quark and gluon extractions using input from simulation. The simulations provide a reasonable description of the quark-like data across the jet pT range presented in this measurement, but the gluon-like data have systematically fewer charged particles than the simulations.
Source
code:ATLAS_2019_I1740909.cc
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/VetoedFinalState.hh"
#include "Rivet/Projections/InvisibleFinalState.hh"
#include "Rivet/Projections/PromptFinalState.hh"
#include "Rivet/Projections/FastJets.hh"
namespace Rivet {
/// @brief jet fragmentation at 13 TeV
class ATLAS_2019_I1740909: public Analysis {
public:
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1740909);
/// Book cuts and projections
void init() {
const FinalState bare_MU(Cuts::abspid == PID::MUON);
VetoedFinalState jetinput;
jetinput.addVetoOnThisFinalState(bare_MU);
jetinput.addVetoOnThisFinalState(InvisibleFinalState());
FastJets jetpro(jetinput, JetAlg::ANTIKT, 0.4);
declare(jetpro, "Jets");
book(_p["nch_jetpt_F"], 1, 1, 1);
book(_p["nch_jetpt_C"], 2, 1, 1);
book(_p["nch_jetpt_B"], 9, 1, 1);
vector<double> ptbins{100., 200., 300., 400., 500., 600., 700., 800.,
900., 1000., 1200., 1400., 1600., 2000., 2500.};
for (const string& suff : vector<string>{"B", "F", "C"}) {
book(_h["nch_"+suff], ptbins);
book(_h["r_"+suff], ptbins);
book(_h["zeta_"+suff], ptbins);
book(_h["pTrel_"+suff], ptbins);
}
for (size_t idx = 0; idx < ptbins.size()-1; ++idx) {
dualbook(_h["nch_B"]->bin(idx+1), 13 + idx, 1, 1);
dualbook(_h["r_B"]->bin(idx+1), 27 + idx, 1, 1);
dualbook(_h["zeta_B"]->bin(idx+1), 41 + idx, 1, 1);
dualbook(_h["pTrel_B"]->bin(idx+1), 55 + idx, 1, 1);
dualbook(_h["nch_F"]->bin(idx+1), 69 + idx, 1, 1);
dualbook(_h["r_F"]->bin(idx+1), 83 + idx, 1, 1);
dualbook(_h["zeta_F"]->bin(idx+1), 97 + idx, 1, 1);
dualbook(_h["pTrel_F"]->bin(idx+1), 111 + idx, 1, 1);
dualbook(_h["nch_C"]->bin(idx+1), 125 + idx, 1, 1);
dualbook(_h["r_C"]->bin(idx+1), 139 + idx, 1, 1);
dualbook(_h["zeta_C"]->bin(idx+1), 153 + idx, 1, 1);
dualbook(_h["pTrel_C"]->bin(idx+1), 167 + idx, 1, 1);
}
}
void dualbook(Histo1DPtr& hist, unsigned int d, unsigned int x, unsigned int y) {
const string hname = mkAxisCode(d, x, y);
book(hist, "_aux_"+hname, refData(hname));
book(_s[hist.get()->basePath()], hname);
}
void analyze(const Event& event) {
//Init
double fnch=0;
double cnch=0;
double fzval=0;
double czval=0;
double frval=0;
double crval=0;
double ftval=0;
double ctval=0;
// Event selection
Jets m_goodJets = apply<JetFinder>(event, "Jets").jetsByPt(Cuts::pT > 100*GeV && Cuts::abseta < 2.1);
if (m_goodJets.size() < 2) vetoEvent;
if (fabs(1.0 - m_goodJets[0].pT()/m_goodJets[1].pT()) > 0.5) vetoEvent;
// Decide forward or central
bool check = m_goodJets[0].abseta() < m_goodJets[1].abseta();
int pos_f = int(check);
int pos_c = int(!check);
// Calculate obs, separately for central and fwd, also get bin
double fpt = m_goodJets[pos_f].pT();
double cpt = m_goodJets[pos_c].pT();
for (const Particle& p : m_goodJets[pos_f].particles()) {
if (p.pT() < 0.5*GeV) continue;
if (p.charge() != 0) {
++fnch;
fzval = p.pT() / m_goodJets[pos_f].pt();
ftval = p.pT()*sin(p.phi()-m_goodJets[pos_f].phi());
frval = deltaR(m_goodJets[pos_f], p);
_h["r_F"]->fill(fpt, frval);
_h["r_B"]->fill(fpt, frval);
_h["zeta_F"]->fill(fpt, fzval);
_h["zeta_B"]->fill(fpt, fzval);
_h["pTrel_F"]->fill(fpt, ftval);
_h["pTrel_B"]->fill(fpt, ftval);
}
}
for (const Particle& p : m_goodJets[pos_c].particles()) {
if (p.pT() < 0.5*GeV) continue;
if (p.charge() != 0) {
++cnch;
czval = p.pT() / m_goodJets[pos_c].pt();
ctval = p.pT()*sin(p.phi()-m_goodJets[pos_c].phi());
crval = deltaR(m_goodJets[pos_c], p);
_h["r_C"]->fill(cpt, crval);
_h["r_B"]->fill(cpt, crval);
_h["zeta_C"]->fill(cpt, czval);
_h["zeta_B"]->fill(cpt, czval);
_h["pTrel_C"]->fill(cpt, ctval);
_h["pTrel_B"]->fill(cpt, ctval);
}
}
if (fnch > 63) fnch = 63;
if (cnch > 63) cnch = 63;
//Fill nchg histo
_p["nch_jetpt_F"]->fill(fpt,fnch);
_p["nch_jetpt_C"]->fill(cpt,cnch);
_p["nch_jetpt_B"]->fill(fpt,fnch);
_p["nch_jetpt_B"]->fill(cpt,cnch);
_h["nch_F"]->fill(fpt, fnch);
_h["nch_C"]->fill(cpt, cnch);
_h["nch_B"]->fill(fpt, fnch);
_h["nch_B"]->fill(cpt, cnch);
}
void finalize() {
for (const string& suff : vector<string>{"B", "F", "C"}) {
const double num = suff=="B"? 2.0 : 1.0;
vector<double> sf = _h["nch_"+suff]->sumWGroup();
for (double& f : sf) {
f = safediv(num, f, 0.0);
}
scale({_h["nch_"+suff], _h["zeta_"+suff], _h["pTrel_"+suff], _h["r_"+suff]}, sf);
for (auto& r : _h["r_"+suff]->bins()) {
for (auto& b : r->bins()) {
b.scaleW(1.0/(2*M_PI*b.xMid()));
}
}
}
for (auto& hist : _h) {
for (auto& b : hist.second->bins()) {
barchart(b, _s[b.get()->basePath()]);
}
}
}
private:
map<string, Histo1DGroupPtr> _h;
map<string, Estimate1DPtr> _s;
map<string, Profile1DPtr> _p;
};
RIVET_DECLARE_PLUGIN(ATLAS_2019_I1740909);
}