Rivet analyses
Inclusive 4-lepton lineshape at 13 TeV
Experiment: ATLAS (LHC)
Inspire ID: 1720442
Status: VALIDATED
Authors: - Max Goblirsch - Jon Butterworth - Christian Gutschow
References: - Expt page: ATLAS-STDM-2017-09 - Submitted to JHEP - arXiv: 1902.05892
Beams: p+ p+
Beam energies: (6500.0, 6500.0)GeV
Run details: - pp → ℓℓℓℓ + X at 13 TeV
A measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb−1 of proton-proton collisions at $\sqrt{s} = 13$ TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single Z boson production, Higgs boson production, and Z boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of gg → ZZ → 4ℓ and Z → 4ℓ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model.
Source
code:ATLAS_2019_I1720442.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
#include "Rivet/Projections/LeptonFinder.hh"
#include "Rivet/Projections/PromptFinalState.hh"
namespace Rivet {
/// ATLAS 4-lepton lineshape at 13 TeV
class ATLAS_2019_I1720442 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(ATLAS_2019_I1720442);
void init() {
PromptFinalState photons(Cuts::abspid == PID::PHOTON);
PromptFinalState elecs(Cuts::abspid == PID::ELECTRON);
PromptFinalState muons(Cuts::abspid == PID::MUON);
// Selection
Cut el_fid_sel = (Cuts::abseta < 2.47) && (Cuts::pT > 7 * GeV);
Cut mu_fid_sel = (Cuts::abseta < 2.7) && (Cuts::pT > 5 * GeV);
LeptonFinder dressed_elecs(elecs, photons, 0.005, el_fid_sel);
declare(dressed_elecs, "elecs");
LeptonFinder dressed_muons(muons, photons, 0.005, mu_fid_sel);
declare(dressed_muons, "muons");
// Book histos
book(_h["m4l_inclusive"], 1, 1, 1);
book(_h["m4l_ptslice1"], 2, 1, 1);
book(_h["m4l_ptslice2"], 3, 1, 1);
book(_h["m4l_ptslice3"], 4, 1, 1);
book(_h["m4l_ptslice4"], 5, 1, 1);
book(_h["m4l_rapidityslice1"], 6, 1, 1);
book(_h["m4l_rapidityslice2"], 7, 1, 1);
book(_h["m4l_rapidityslice3"], 8, 1, 1);
book(_h["m4l_rapidityslice4"], 9, 1, 1);
book(_h["m4l_4mu"], 12, 1, 1);
book(_h["m4l_4e"], 13, 1, 1);
book(_h["m4l_2e2mu"], 14, 1, 1);
}
/// @brief Generic dilepton candidate
/// @todo Move into the Rivet core?
struct Dilepton : public ParticlePair {
Dilepton() { }
Dilepton(ParticlePair _particlepair)
: ParticlePair(_particlepair) {
assert(first.abspid() == second.abspid());
}
FourMomentum mom() const {
return first.momentum() + second.momentum();
}
operator FourMomentum() const {
return mom();
}
static bool cmppT(const Dilepton& lx, const Dilepton& rx) {
return lx.mom().pT() < rx.mom().pT();
}
int flavour() const {
return first.abspid();
}
double pTl1() const {
return first.pT();
}
double pTl2() const {
return second.pT();
}
};
struct Quadruplet {
Quadruplet(Dilepton z1, Dilepton z2)
: _z1(z1), _z2(z2) { }
enum class FlavCombi { mm = 0, ee, me, em, undefined };
FourMomentum mom() const {
return _z1.mom() + _z2.mom();
}
Dilepton getZ1() const {
return _z1;
}
Dilepton getZ2() const {
return _z2;
}
Dilepton _z1, _z2;
FlavCombi type() const {
if (_z1.flavour() == 13 && _z2.flavour() == 13) {
return FlavCombi::mm;
}
else if (_z1.flavour() == 11 && _z2.flavour() == 11) {
return FlavCombi::ee;
}
else if (_z1.flavour() == 13 && _z2.flavour() == 11) {
return FlavCombi::me;
}
else if (_z1.flavour() == 11 && _z2.flavour() == 13) {
return FlavCombi::em;
}
else
return FlavCombi::undefined;
}
};
vector<Quadruplet> getBestQuads(Particles& particles) {
// H->ZZ->4l pairing
// - Two same flavor opposite charged leptons
// - Ambiguities in pairing are resolved by choosing the combination
// that results in the smaller value of |mll - mZ| for each pair successively
vector<Quadruplet> quads{};
size_t n_parts = particles.size();
if (n_parts < 4) return quads;
// STEP 1: find SFOS pairs
vector<Dilepton> SFOS;
for (size_t i = 0; i < n_parts; ++i) {
for (size_t j = 0; j < i; ++j) {
if (particles[i].pid() == -particles[j].pid()) {
// sort such that the negative lepton is listed first
if (particles[i].pid() > 0)
SFOS.push_back(Dilepton(make_pair(particles[i], particles[j])));
else
SFOS.push_back(Dilepton(make_pair(particles[j], particles[i])));
}
}
}
if (SFOS.size() < 2) return quads;
// now we sort the SFOS pairs
std::sort(SFOS.begin(), SFOS.end(), [](const Dilepton& p1, const Dilepton& p2) {
return fabs(p1.mom().mass() - Z_mass) < fabs(p2.mom().mass() - Z_mass);
});
// Form all possible quadruplets passing the pT cuts
for (size_t k = 0; k < SFOS.size(); ++k) {
for (size_t l = k + 1; l < SFOS.size(); ++l) {
if (deltaR(SFOS[k].first.mom(), SFOS[l].first.mom()) < 1e-13) continue;
if (deltaR(SFOS[k].first.mom(), SFOS[l].second.mom()) < 1e-13) continue;
if (deltaR(SFOS[k].second.mom(), SFOS[l].first.mom()) < 1e-13) continue;
if (deltaR(SFOS[k].second.mom(), SFOS[l].second.mom()) < 1e-13) continue;
vector<double> lep_pt{SFOS[k].pTl1(), SFOS[k].pTl2(), SFOS[l].pTl1(), SFOS[l].pTl2()};
std::sort(lep_pt.begin(), lep_pt.end(), std::greater<double>());
if (!(lep_pt[0] > 20 * GeV && lep_pt[1] > 15 * GeV && lep_pt[2] > 10 * GeV)) continue;
quads.push_back(Quadruplet(SFOS[k], SFOS[l]));
}
}
return quads;
}
bool passMassCuts(const Quadruplet& theQuad) {
const vector<double> cuts_m34{5 * GeV, 5 * GeV, 12 * GeV, 12 * GeV, 50 * GeV};
const vector<double> cuts_m4l{0, 100 * GeV, 110 * GeV, 140 * GeV, 190 * GeV};
double m4l = theQuad.mom().mass();
double mZ1 = theQuad.getZ1().mom().mass();
double mZ2 = theQuad.getZ2().mom().mass();
// Invariant-mass requirements
double cutval = cuts_m34.back();
for (size_t k = 0; k < cuts_m34.size(); ++k) {
if (cuts_m4l[k] > m4l) {
cutval = cuts_m34[k - 1]
+ (cuts_m34[k] - cuts_m34[k - 1]) / (cuts_m4l[k] - cuts_m4l[k - 1]) * (m4l - cuts_m4l[k - 1]);
break;
}
}
return inRange(mZ1, 50 * GeV, 106 * GeV) && inRange(mZ2, cutval, 115 * GeV);
}
bool pass_dRll(const Quadruplet& theQuad) {
const double dR_min_same = 0.1;
const double dR_min_opp = 0.2;
double dr_min_cross = dR_min_opp;
if (theQuad.getZ1().flavour() == theQuad.getZ2().flavour()) {
dr_min_cross = dR_min_same;
}
return !((deltaR(theQuad.getZ1().first, theQuad.getZ1().second) < dR_min_same)
|| (deltaR(theQuad.getZ2().first, theQuad.getZ2().second) < dR_min_same)
|| (deltaR(theQuad.getZ1().first, theQuad.getZ2().first) < dr_min_cross)
|| (deltaR(theQuad.getZ1().first, theQuad.getZ2().second) < dr_min_cross)
|| (deltaR(theQuad.getZ1().second, theQuad.getZ2().first) < dr_min_cross)
|| (deltaR(theQuad.getZ1().second, theQuad.getZ2().second) < dr_min_cross));
}
bool pass_Jpsi(const Quadruplet& theQuad) {
Particles all_leps{theQuad.getZ1().first, theQuad.getZ1().second, theQuad.getZ2().first,
theQuad.getZ2().second};
for (const Particle& lep1 : all_leps) {
for (const Particle& lep2 : all_leps) {
if (lep1.pid() == -lep2.pid() && (lep1.mom() + lep2.mom()).mass() < 5 * GeV) return false;
}
}
return true;
}
// Handle 3 further CF stages - m12/34, dRmin, jpsi veto
bool passSelection(const Quadruplet& theQuad) {
return passMassCuts(theQuad) && pass_dRll(theQuad) && pass_Jpsi(theQuad);
}
// Do the analysis
void analyze(const Event& event) {
//preselection of leptons for ZZ-> llll final state
Particles dressed_leptons;
for (auto lep : apply<LeptonFinder>(event, "muons").dressedLeptons()) {
dressed_leptons.push_back(lep);
}
for (auto lep : apply<LeptonFinder>(event, "elecs").dressedLeptons()) {
dressed_leptons.push_back(lep);
}
auto foundDressed = getBestQuads(dressed_leptons);
// if we don't find any quad, we can stop here
if (foundDressed.empty()) vetoEvent;
bool pass = passSelection(foundDressed[0]);
if (pass) {
double m4l = foundDressed[0].mom().mass() / GeV;
double pt4l = foundDressed[0].mom().pT() / GeV;
double y4l = foundDressed[0].mom().absrap();
Quadruplet::FlavCombi flavour = foundDressed[0].type();
_h["m4l_inclusive"]->fill(m4l);
if (pt4l < 20.)
_h["m4l_ptslice1"]->fill(m4l);
else if (pt4l < 50.)
_h["m4l_ptslice2"]->fill(m4l);
else if (pt4l < 100.)
_h["m4l_ptslice3"]->fill(m4l);
else if (pt4l < 600.)
_h["m4l_ptslice4"]->fill(m4l);
if (y4l < 0.4)
_h["m4l_rapidityslice1"]->fill(m4l);
else if (y4l < 0.8)
_h["m4l_rapidityslice2"]->fill(m4l);
else if (y4l < 1.2)
_h["m4l_rapidityslice3"]->fill(m4l);
else if (y4l < 2.5)
_h["m4l_rapidityslice4"]->fill(m4l);
if (flavour == Quadruplet::FlavCombi::mm)
_h["m4l_4mu"]->fill(m4l);
else if (flavour == Quadruplet::FlavCombi::ee)
_h["m4l_4e"]->fill(m4l);
else if (flavour == Quadruplet::FlavCombi::me || flavour == Quadruplet::FlavCombi::em) {
_h["m4l_2e2mu"]->fill(m4l);
}
}
}
/// Finalize
void finalize() {
const double sf = crossSection() / femtobarn / sumOfWeights();
scale(_h, sf);
}
private:
map<string, Histo1DPtr> _h;
static constexpr double Z_mass = 91.1876;
};
RIVET_DECLARE_PLUGIN(ATLAS_2019_I1720442);
}