Rivet analyses
Track-based underlying event at 13 TeV in ATLAS
Experiment: ATLAS (LHC)
Inspire ID: 1509919
Status: VALIDATED
Authors: - Roman Lysak
References: - Expt page: ATLAS-STDM-2016-07 - arXiv: 1701.05390
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - pp QCD interactions at 13 TeV. Diffractive events should be included.
We present charged-particle distributions sensitive to the underlying event, measured by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV, in low-luminosity Large Hadron Collider fills corresponding to an integrated luminosity of 1.6 nb−1. The distributions were constructed using charged particles with absolute pseudorapidity less than 2.5 and with transverse momentum greater than 500 MeV, in events with at least one such charged particle with transverse momentum above 1 GeV. These distributions characterise the angular distribution of energy and particle flows with respect to the charged particle with highest transverse momentum, as a function of both that momentum and of charged-particle multiplicity. The results have been corrected for detector effects and are compared to the predictions of various Monte Carlo event generators, experimentally establishing the level of underlying-event activity at LHC Run 2 energies and providing inputs for the development of event generator modelling. The current models in use for UE modelling typically describe this data to 5% accuracy, compared with data uncertainties of less than 1%.
Source
code:ATLAS_2017_I1509919.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/ChargedFinalState.hh"
namespace Rivet {
/// Track-based underlying event at 13 TeV in ATLAS
class ATLAS_2017_I1509919 : public Analysis {
public:
// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2017_I1509919);
// Pre-run histogram and projection booking
void init() {
declare(ChargedFinalState(Cuts::abseta < 2.5 && Cuts::pT > 500*MeV), "CFS500");
// Nch profiles vs. pT_lead
book(_hist_nch[0], 22, 1, 1);
book(_hist_nch[1], 23, 1, 1);
book(_hist_nch[2], 21, 1, 1);
book(_hist_nch[3], 3, 1, 1);
book(_hist_nch[4], 2, 1, 1);
book(_hist_nch[5], 4, 1, 1);
// pTsum profiles vs. pT_lead
book(_hist_ptsum[0], 25, 1, 1);
book(_hist_ptsum[1], 26, 1, 1);
book(_hist_ptsum[2], 24, 1, 1);
book(_hist_ptsum[3], 6, 1, 1);
book(_hist_ptsum[4], 5, 1, 1);
book(_hist_ptsum[5], 7, 1, 1);
// <pT> profiles vs pT_lead (not measured for trans diff)
book(_hist_ptavg[0], 29, 1, 1);
book(_hist_ptavg[1], 30, 1, 1);
book(_hist_ptavg[2], 11, 1, 1);
book(_hist_ptavg[3], 13, 1, 1);
book(_hist_ptavg[4], 12, 1, 1);
// <pT> profiles vs. Nch (not measured for trans diff)
book(_hist_dn_dpt[0], 27, 1, 1);
book(_hist_dn_dpt[1], 28, 1, 1);
book(_hist_dn_dpt[2], 8, 1, 1);
book(_hist_dn_dpt[3], 10, 1, 1);
book(_hist_dn_dpt[4], 9, 1, 1);
// Only measured for trans max/min
book(_hist_dn_dpt2[3], 32, 1, 1);
book(_hist_dn_dpt2[4], 31, 1, 1);
// Nch vs. Delta(phi) profiles
book(_hist_N_vs_dPhi[0], 15, 1, 1);
book(_hist_N_vs_dPhi[1], 16, 1, 1);
book(_hist_N_vs_dPhi[2], 17, 1, 1);
// pT vs. Delta(phi) profiles
book(_hist_pT_vs_dPhi[0], 18, 1, 1);
book(_hist_pT_vs_dPhi[1], 19, 1, 1);
book(_hist_pT_vs_dPhi[2], 20, 1, 1);
//ptLead histos only for 1 and 5 GeV cuts
book(_hist_ptLead[0], 1, 1, 1);
book(_hist_ptLead[1], 14, 1, 1);
for (size_t iC = 0; iC < NCUTS; ++iC) {
book(_counters[iC], "Ctr_cut_" + toString(iC));
}
}
void analyze(const Event& event) {
// Get charged particles (tracks) with pT > 500 MeV
const ChargedFinalState& charged500 = apply<ChargedFinalState>(event, "CFS500");
const Particles& particlesAll = charged500.particlesByPt();
MSG_DEBUG("Num tracks: " << particlesAll.size());
const Cut& pcut = ( (Cuts::abspid != PID::SIGMAMINUS) && (Cuts::abspid != PID::SIGMAPLUS) &&
(Cuts::abspid != PID::XIMINUS) && (Cuts::abspid != PID::OMEGAMINUS) );
const Particles& particles = charged500.particlesByPt(pcut);
MSG_DEBUG("Num tracks without strange baryons: " << particles.size());
// Require at least one track in the event for pTlead histograms
if (particles.empty()) vetoEvent;
for (size_t iC = 0; iC < 2; ++iC) {
if (particles[0].pT() < PTCUTS[iC]*GeV) continue;
_counters[iC]->fill();
_hist_ptLead[iC]->fill( particles[0].pT()/GeV);
}
// Require at least one track in the event with pT >= 1 GeV for the rest
if (particles[0].pT() < 1*GeV) vetoEvent;
// Identify leading track and its phi and pT
const Particle& p_lead = particles[0];
const double philead = p_lead.phi();
const double etalead = p_lead.eta();
const double pTlead = p_lead.perp();
MSG_DEBUG("Leading track: pT = " << pTlead << ", eta = " << etalead << ", phi = " << philead);
// Iterate over all particles and count particles and scalar pTsum in three basic regions
vector<double> num(NREGIONS, 0), ptSum(NREGIONS, 0.0), avgpt(NREGIONS, 0.0);
// Temporary histos that bin Nch and pT in dPhi.
Histo1D hist_num_dphi(_hist_N_vs_dPhi[0]->binning());
hist_num_dphi.setPath("/hist_num_dphi");
Histo1D hist_pt_dphi(_hist_pT_vs_dPhi[0]->binning());
hist_pt_dphi.setPath("/hist_pt_dphi");
hist_num_dphi.reset();
hist_pt_dphi.reset();
int tmpnch[2] = {0,0};
double tmpptsum[2] = {0,0};
for (const Particle& p : particles) {
const double pT = p.pT()/GeV;
const double dPhi = deltaPhi(philead, p.phi()); // in range (0,pi)
const int ir = region_index(dPhi); // gives just toward/away/trans
// Toward/away/trans region: just count
num [ir] += 1;
ptSum[ir] += pT;
// Determine which transverse side
if (ir == kTrans) {
const size_t iside = (mapAngleMPiToPi(p.phi() - philead) > 0) ? 0 : 1;
tmpnch [iside] += 1;
tmpptsum[iside] += p.pT();
}
// Fill temp histos to bin Nch and pT in dPhi
if (p.genParticle() != p_lead.genParticle()) { // We don't want to fill all those zeros from the leading track...
hist_num_dphi.fill(dPhi/M_PI*180);
hist_pt_dphi .fill(dPhi/M_PI*180, pT/GeV);
}
}
// Construct max/min/diff regions
num[kTransMax ] = std::max(tmpnch[0], tmpnch[1]);
num[kTransMin ] = std::min(tmpnch[0], tmpnch[1]);
num[kTransDiff] = num[kTransMax ] - num[kTransMin ];
ptSum[kTransMax ] = std::max(tmpptsum[0], tmpptsum[1]);
ptSum[kTransMin ] = std::min(tmpptsum[0], tmpptsum[1]);
ptSum[kTransDiff] = ptSum[kTransMax ] - ptSum[kTransMin ];
avgpt[kToward] = (num[kToward] > 0 ) ? ptSum[kToward] / num[kToward] : 0. ;
avgpt[kAway] = (num[kAway ] > 0 ) ? ptSum[kAway] / num[kAway] : 0. ;
avgpt[kTrans] = (num[kTrans ] > 0 ) ? ptSum[kTrans] / num[kTrans] : 0. ;
// Avg pt max/min regions determined according sumpt max/min
int sumptMaxRegID = (tmpptsum[0] > tmpptsum[1]) ? 0 : 1 ;
int sumptMinRegID = (sumptMaxRegID == 0) ? 1 : 0;
avgpt[kTransMax ] = (tmpnch[sumptMaxRegID] > 0) ? tmpptsum[sumptMaxRegID] / tmpnch[sumptMaxRegID] : 0.;
avgpt[kTransMin ] = (tmpnch[sumptMinRegID] > 0) ? tmpptsum[sumptMinRegID] / tmpnch[sumptMinRegID] : 0.;
avgpt[kTransDiff] = ((tmpnch[sumptMaxRegID] > 0) && (tmpnch[sumptMinRegID] > 0)) ? avgpt[kTransMax ] - avgpt[kTransMin ] : 0.;
// Now fill underlying event histograms
// The densities are calculated by dividing the UE properties by dEta*dPhi
// -- each basic region has a dPhi of 2*PI/3 and dEta is two times 2.5
// min/max/diff regions are only half of that
const double dEtadPhi[NREGIONS] = { 2*2.5 * 2*PI/3.0, 2*2.5 * 2*PI/3.0, 2*2.5 * 2*PI/3.0,
2*2.5 * PI/3.0, 2*2.5 * PI/3.0, 2*2.5 * PI/3.0 };
for (size_t iR = 0; iR < NREGIONS; ++iR) {
_hist_nch [iR]->fill(pTlead/GeV, num[iR] /dEtadPhi[iR] );
_hist_ptsum[iR]->fill(pTlead/GeV, ptSum[iR] /GeV/dEtadPhi[iR] );
// <pT> profiles vs. pT_lead (first 3 are the same!)
switch (iR) {
case kToward :
case kAway :
case kTrans :
if (num[iR] > 0) _hist_ptavg[iR]->fill(pTlead/GeV, avgpt[iR]/GeV);
break;
case kTransMax :
if (tmpnch[sumptMaxRegID] > 0) _hist_ptavg[iR]->fill(pTlead/GeV, avgpt[iR]/GeV);
break;
case kTransMin :
if (tmpnch[sumptMinRegID] > 0) _hist_ptavg[iR]->fill(pTlead/GeV, avgpt[iR]/GeV);
break;
case kTransDiff :
break;
default: //should not get here!!!
MSG_WARNING("Unknown region in <pT> profiles vs.pt lead switch!!! : " << iR);
}
// <pT> profiles vs. Nch (first 3 are the same!)
switch (iR) {
case kToward :
case kAway :
case kTrans :
if (num[iR] > 0) _hist_dn_dpt[iR]->fill(num[iR] , avgpt[iR]/GeV);
break;
case kTransMax :
if (tmpnch[sumptMaxRegID] > 0) {
_hist_dn_dpt [iR]->fill(num[kTrans] , avgpt[iR]/GeV);
_hist_dn_dpt2[iR]->fill(tmpnch[sumptMaxRegID], avgpt[iR]/GeV);
}
break;
case kTransMin :
if (tmpnch[sumptMinRegID] > 0) {
_hist_dn_dpt [iR]->fill(num[kTrans] , avgpt[iR]/GeV);
_hist_dn_dpt2[iR]->fill(tmpnch[sumptMinRegID], avgpt[iR]/GeV);
}
break;
case kTransDiff :
break;
default : //should not get here!!!
MSG_INFO("unknown region in <pT> profiles vs. nch switch!!! : " << iR);
}
}
// Update the "proper" dphi profile histograms
// Note that we fill dN/dEtadPhi: dEta = 2*2.5, dPhi = 2*PI/nBins
const double dEtadPhi2 = (2*2.5 * 2) * M_PI/180.;
for (size_t i = 0; i < hist_num_dphi.numBins(); ++i) {
// First Nch
double mean = hist_num_dphi.bin(i).xMid() ;
double value = 0.;
if (hist_num_dphi.bin(i).numEntries() > 0) {
mean = hist_num_dphi.bin(i).xMean() ;
value = hist_num_dphi.bin(i).sumW()/hist_num_dphi.bin(i).xWidth()/dEtadPhi2;
}
for (size_t iC = 0; iC < NCUTS; ++iC) {
if (pTlead >= PTCUTS[iC]*GeV) _hist_N_vs_dPhi[iC] ->fill(mean, value);
}
// Then pT
mean = hist_pt_dphi.bin(i).xMid();
value = 0.;
if (hist_pt_dphi.bin(i).numEntries() > 0) {
mean = hist_pt_dphi.bin(i).xMean() ;
value = hist_pt_dphi.bin(i).sumW()/hist_pt_dphi.bin(i).xWidth()/dEtadPhi2;
}
for (size_t iC = 0; iC < NCUTS; ++iC) {
if (pTlead >= PTCUTS[iC]*GeV) _hist_pT_vs_dPhi[iC] ->fill(mean, value);
}
}
}
void finalize() {
for (size_t iC = 0; iC < NCUTS; ++iC) {
if (iC == 0 || iC == 1) scale(_hist_ptLead[iC], 1.0/_counters[iC]->sumW());
}
}
private:
enum regionID {
kToward = 0,
kAway,
kTrans,
kTransMax,
kTransMin,
kTransDiff,
NREGIONS
};
// Little helper function to identify basic Delta(phi) regions: toward/away/trans
int region_index(double dphi) {
assert(inRange(dphi, 0.0, PI, CLOSED, CLOSED));
if (dphi < PI/3.0) return kToward;
if (dphi < 2*PI/3.0) return kTrans;
return kAway;
}
const static size_t NCUTS = 3;
const vector<double> PTCUTS = { 1., 5., 10. };
/// @name Histograms
/// @{
// Nch, sumpT, avgpT profiles vs. pTlead
Profile1DPtr _hist_nch [NREGIONS]; //for regions: all 6 regions
Profile1DPtr _hist_ptsum [NREGIONS]; //for regions: all 6 regions
Profile1DPtr _hist_ptavg [NREGIONS]; //for regions: trans towards/away/all/min/max
// Nch, sumpT, avgpT profiles vs. Nch
Profile1DPtr _hist_dn_dpt [NREGIONS]; //regions: towards/away/ vs nch(region) & trans all/min/max vs nch(trans)
Profile1DPtr _hist_dn_dpt2[NREGIONS]; //regions: trans min/max vs. nch(region)
Profile1DPtr _hist_N_vs_dPhi [NCUTS];
Profile1DPtr _hist_pT_vs_dPhi[NCUTS];
Histo1DPtr _hist_ptLead[NCUTS]; //for 1,5 GeV cuts only
CounterPtr _counters[NCUTS];
/// @}
};
RIVET_DECLARE_PLUGIN(ATLAS_2017_I1509919);
}